A review on conducting polymer reinforced polyurethane composites

Accepted Manuscript Title: A review on conducting polymer reinforced polyurethane composites Authors: Halima Khatoon, Sharif Ahmad PII: DOI: Reference:

S1226-086X(17)30153-3 http://dx.doi.org/doi:10.1016/j.jiec.2017.03.036 JIEC 3349

To appear in: Received date: Revised date: Accepted date:

23-1-2017 3-3-2017 18-3-2017

Please cite this article as: Halima Khatoon, Sharif Ahmad, A review on conducting polymer reinforced polyurethane composites, Journal of Industrial and Engineering Chemistryhttp://dx.doi.org/10.1016/j.jiec.2017.03.036 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

A Review on Conducting Polymer Reinforced Polyurethane Composites

Authors Detail 1

Halima Khatoon

Research Scholar Materials Research Laboratory Department of Chemistry, Jamia Millia Islamia (A Central University) New Delhi-110025, India Mobile: +918470065690 E.mail address: [email protected]

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Sharif Ahmad*

Prof Sharif Ahmad Materials Research Laboratory Department of Chemistry, Jamia Millia Islamia (A Central University) New Delhi-110025, India Tel no. +91 11 26827508 Fax: +91 11 26840229 E-mail address: [email protected] *Corresponding Author 1

Graphical abstract

Abstract With the endless efforts in the development of polymer composite materials, conducting polymer reinforced in polyurethane (CP/PU) composites are gaining tremendous attention of scientific community in the past few years. Conducting polymers as a reinforcement, offers exceptional properties when it combines with the thermoplastic polyurethane matrix. In view of this, we critically highlight the development of different types of conducting polymers reinforced in polyurethane composites, with a detailed discussion on their method of synthesis and various characterizations techniques. Furthermore, the promising applications of CP/PU composites have also been discussed. Finally, we attempted to assemble the existing challenges and the possible future perspectives.

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Keywords: Conducting Polymer, Polyurethane, Composites, Synthesis, Characterizations, Applications.

1 Introduction Since the discovery of Polyacetylene (1976), conducting polymers (CPs) due to their versatile electrical and optical properties, have become the main focus of interest for researchers, technologist and industrialist [1]. Generally, CPs constitute π conjugation in their backbone, responsible for the phenomena of delocalization. The delocalized π electrons generate conductivity throughout the polymer chain through the formation of polarons and bipolarons [2]. Their conductivity can be further increased by several orders by means of doping [3]. The high electrical conductivity, good thermal and environmental stability and ease of synthesis, are considered as the key features of CPs, which makes them superior in the queue of other conductive materials like graphene oxide (GO), carbon nanotubes (CNT) and their derivatives [4]. While the discovery of nanoconducting polymers, a subclass of CPs, have revolutionized the applications of CPs due to their unique characteristics such as high charge to surface ratio, high efficiency, light weight and low cost [5]. Further, they are dispersed in reasonably small quantity (0.5-5%) as a filler in the dielectric polymers based matrices resulting in the formation of their composites, which are used in the development of various electronic and optical devices like sensors [6], actuators [7], membranes [8], light emitting diodes [9], coatings and others [10]. However, literature survey reveals that some of the CPs and their derivatives such as Polyacetylene (PA), Polyaniline (PANI), Polypyrrole (PPy), Polythiophene (PTh) and Poly (ethylenedioxythiophene) (PEDOT) etc. have been extensively investigated [11–13]. The structure of these CPs are portrayed in Fig. 1. They have achieved their applications on 3

commercial scales. However, some of their drawbacks like poor processability, low solubility, low yield and poor mechanical properties have limited their direct applications in various fields, like coatings, optical and solar devices etc. [14]. In order to overcome these drawbacks researchers have suggested a number of strategies in the form of new methods of their synthesis, in which these polymers are added to conventional polymers to formulate their copolymer, blends, IPNs, composites and nanocomposites [15–18]. These studies suggest that there is a wide scope for the improvements in their properties and applications. For example, the reinforcement of CPs in insulating polymer matrices resulted in the processing of polymer composites seem to be an intelligent approach used to enhance the processability, solubility, stability and mechanical properties (flexibility, toughness) of conducting polymers [12]. However, for the dispersion of CPs, choice of an appropriate insulating polymer matrix is a prerequisite, as the matrix offers the processesability and stability to the CP nanoparticles dispersed composites [15]. A number of works have been reported on conducting polymers dispersed insulating polymer composites [19–23]. The properties of such composites mainly depend on the nature of dispersion of CPs within the insulating polymer matrices as well as the interactions between the CP fillers and insulating polymer matrices [24]. Among various insulating polymers matrices like those of epoxy, alkyd, polyacrylates, PU etc. PU is the most important one, widely used and are of versatile nature, comprises hard (isocyanate) and soft (polyols) segments [25]. For the very first time PU was synthesized by Otto Bayer in 1937 [26–28]. It has unique properties like good elasticity, elongation, high impact and tensile strength, high abrasion resistance, good weathering resistance, excellent gloss, colour retention and corrosion resistance properties [29–31]. These properties make them a potential candidate for several applications in the field of leather [32], foams [33,34], furniture [35], fibers [36], elastomers [37], adhesives [38], paints [39], and coatings [40–42]. However, under harsh conditions PU alone fails to give satisfactory thermal, mechanical and 4

corrosion resistance performance [43–45]. Thus, there is a need to induce such structural properties in PUs through their blending and composites formations, which make them able to provide good services even under harsh environmental conditions. It has been observed that the synergistic effect between CPs (filler) and insulating PUs (matrices) enhances their proccessability, stability, solubility, thermal, mechanical, electrical and optical properties [46]. These modified CP/PU composite materials are capable enough of having further enhanced service life in the above cited areas even under stringent conditions. Thus, there is a good scope of research and development for various types of CP/PU composites, which may also possess value added properties. It is interesting to note that only one review article has been published on the CP/PU composites by Njuguna et al. in 2004 [47]. Beyond this, no other review article is published till date. Although, revolutionary developments in this area have been reported that resulted in the increased application of these materials in the wide range of industries. Various new approaches have also been adopted for the processing of these materials, found to be significant from academic and research point of view. In this account, the present review article explores the year’s efforts in the development of CP/PU composites. The review starts with the latest scalable methods for the synthesis of CP/PU composite emphasising on melt mixing, solution blending and in situ polymerization. Additionally, we also discussed some other recently developed methods, followed by an extensive review of literature about some important conducting polymers fillers like PANI, PPy, and PTh dispersed in polyurethane composites. Besides this, the review also gives an insight to the various characterizations techniques which confirms the formation of composite. Furthermore, the promising applications of CP/PU composites in EMI shielding, sensors, biomedical, SMPs, membrane, anticorrosive coatings, films and foams have also been discussed. Finally, we have attempted to assemble the existing challenges and all the possible future perspectives. 5

2 Synthesis of CP/PU composites The CP/PU composites have gained much attention due to their versatile nature and scope of applications. Some of the widely used methods for the processing of CP/PU composites are melt mixing, solution blending and in situ polymerization (Fig. 2) [48–50]. However, Prior to the formation of composite of CP/PU, generally both the components (CP and PU) were synthesized or either one of these two components (CP or PU) was either purchased or synthesized and then dispersed together. It has been revealed that the polyurethane of different molecular weight i.e. from 23,000 g/mol to 108,430 g/mol have been used in the processing of CP/PU composites [20,51–53]. Nevertheless, very few authors have discussed the effects of molecular weight of polyurethane on the properties of CP/PU composites [20]. Thus, there is an opportunity for the researchers and scientists to study the effects of molecular weights on the properties of CP/PU composites. Among various conducting polymers, PANI, PPY, PTh and their derivatives, are the most commonly used as fillers to dispersed into polyurethane matrices [51,54,55]. The formulation of CP/PU composite reported by various workers are discussed in the proceeding units. 2.1 Melt mixing The melt mixing is a solvent free dispersion technique which involves the mixing of conducting polymer particles (fillers) in dried powder form with the melted polymer matrix under high shear mixing using twin screw extruder [56]. This allows easy dispersion by softening the polymer matrix [57]. A general reaction scheme for the synthesis of CP/PU composites by melt mixing is given in Fig. 3. The technique is economical and safer as it does not involve any volatile organic solvents (VOCs), and is mainly used for large scale industrial productions 6

[58,59]. Moreover, the theoretical and experimental studies have suggested that the process of melt mixing has resulted in the enhanced chemical or physical interactions between the fillers and the polymer matrices [60]. However, the melt mixing in comparison to solution blending is generally found to be less effective and is operative only for a lower concentrations of fillers, this may be attributed to the high viscosity of composites [56]. The approach has been used for the preparation of CP dispersed various polymer composites like those of nylon 6, polyolefines (Polyethylene or Polypropylene), polyamides, polyesters, polystyrene, polyurethane etc. [61]. Many other conductive PU composites and nanocomposites have been prepared using this technique such as clay/PU nanocomposite [62], polypropylene/MWCNT nanocomposte [63], graphite/PU nanocomposite [64], boron nitride/PU nanocomposite [65], SWCNT/PU nanocomposite [66], graphene/PU nanocomposite [67] and GO/PU nanocomposite [68]. However, a very scanty work on the advantages and preparation of CP/PU composites based on this techniques, have been reported [69,70]. To the best of our knowledge only few references are found on the said method used for the processing of CP/PU composites discussed here. Recently, Barra et al. described the melt mixing synthesis of conductive nanocomposites of thermoplastic polyurethane (TPU) and montmorillonite-dodecylbenzenesulfonic acid-doped polypyrrole (Mt-PPy.DBSA) [69]. Their electrical conductivity, morphology and rheological properties were evaluated and compared with those of other different TPU nanocomposite containing dodecylbenzenesulfonic acid-doped polypyrrole (PPy.DBSA), montmorillonitehydrochloric acid-doped polypyrrole (Mt-PPy.Cl) and hydrochloric acid-doped polypyrrole (PPy.Cl). Wen et al. have demonstrated the synthesis of PANI/PU modified epoxy composite using solventless method [70]. The powder of PANI was dispersed in PU modified epoxy resin and heated at 80 0C with vigorous stirring for 1h. Post curing was performed at 120 0C for 2h.

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To the best of our knowledge only these references are found on the said method used for the processing of CP/PU composites discussed here. Thus, there is wide scope of research on the application of this technique in the development of these materials. 2.2 Solution blending The solution blending technique consists of three different stages [71], i.e. (i) initially the CP fillers are dispersed in a solvent via ultrasonication technique. (ii) the well dispersed solution of CP fillers is then mixed into PU matrix under continuously stirred conditions for several hours till a homogenous mixture of CP filler and PU matrix was obtained (iii) followed by the removal of solvents through distillation or evaporation using rotatory vacuum evaporator as per the scheme illustrated in Fig. 4. Several conducting polymer blends and composites have been synthesized using this technique [72,73,74]. Sharif et al. have reported the synthesis of polyorthotoulidine (POT) dispersed castor oil Polyurethane (COPU) nanocomposite using solution blending method [75]. The synthesis was carried out by mixing different amounts of POT (0.25 wt %, 0.5 wt%, 1.0 wt %) in 10 wt% solution of COPU in ethyl methyl ketone. Because of low volume and higher surface area ratio of the POT nanoparticles, the homogeneous dispersion of POT in a COPU was not gained beyond 1 wt %. Later on, Putson et al. have prepared PANI/PU polymer composite using the same technique [76]. During the preparation of PANI/PU composite, the polymer was dissolved in N, N-dimethylformamide (DMF). The different wt % PANI nanofillers were ultrasonicated in DMF for 20 min and then the PU and PANI nanofillers solutions in DMF were mixed and stirred for 2h at 60 0C to obtain the homogeneous mixture of PANI/PU nanocomposite. After this, the solvent was evaporated by pouring the composite onto a glass plate and dried in an oven at 60 0C for 24h. Ghosh et al. described the formulation of poly(otoludine)/poly(ester)urethane (POT/PU) blends by solution blending method [77]. In their preparation, two separate solutions of PU/THF and POT/THF with different wt % were

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prepared and the later were added dropwise into the PU/THF solutions and stirred continuously. Recently, Sobha et al. have reported the preparation of PANI functionalized MWCNT (FMWCNT-PANI) based thermoplastic polyurethane conductive composite (FMWCNT-PANI/TPU) via solution casting method [79]. They have synthesized FMWCNTPANI through in situ and ex situ polymerization of aniline in the presence and absence of FMWCNT, which was further used to process the FMWCNT-PANI/TPU(I) and FMWCNTPANI/TPU(E) composites respectively. For the preparation of FMWCNT-PANI/TPU (I) composite, fixed amount of TPU and different wt % of FMWCNT-PANI filler was dissolved in 100 ml THF separately and was stirred vigorously. After 1 h of continuous stirring these two solutions were mixed and ultrasonicated for another 1 h. At the end solvent was removed by keeping the solution in an oven at 60 0C for 10 h. The FMWCNT-PANI/TPU (E) composites were prepared through the same procedure as was used in FMWCNT-PANI/TPU (I), difference occurs only in the synthesis of FWCNT-PANI (i.e. ex situ). The fixed amount of PANI was mixed with FMWCNT and then the different wt % of FWCNT-PANI was dissolved in 100 ml THF solution. The remaining procedure was the same as followed in the preparation of FMWCNT-PANI/TPU (I) composite. Auad et al. have reported the reinforcement of polyurethane with the cellulose nanofibrils modified PANI (PANI-CNF) [80]. Firstly they have synthesized PANI-CNF via in situ polymerization of aniline on the surface of CNF and then the PANI-CNF obtained was dried and dispersed in DMF solution through ultrasonication. Finally, the composite was obtained by mixing this solution with the PU-DMF solution. 2.3 In situ polymerization It is a single stage process in which conducting monomers are polymerized in the presence of insulating polymer matrices or vice versa. The preparation was carried out either by the addition of conducting monomer and an oxidant in polyol then cured with isocyanate or by

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adding the CP powder to the polyol followed by its polymerization with isocyanate [81]. The general schematic representation of in situ polymerization is demonstrated in Fig. 5. A number of reports on the synthesis of CP/PU composites have been reported in the literature based on in situ polymerization technique [82-84]. An in situ chemical polymerization was used by Wen et al. in the synthesis of PPy/TPU composite film. During their preparation, the synthesized TPU film of 75000 g/mol molecular weight was immersed in FeCl3/Polypropylene carbonate (FeCl3/PC) solution for about 1h [53]. After that, the film were taken out and then poured into the Py/PC solution for 6 h at 25 0C. Thus, the conductive film was obtained after washing with water and drying in oven for 1 weak at 70 0C. In another report, Fan et al. used an in situ polymerization method to formulate the conductive PANI/PU composite fibers [85]. The preparation involved the polymerization of aniline on the surface of commercially obtained PU fibers. The PU fibers were immersed in various concentration of aniline/HCl solutions (Ani) for 2 h. Due to the strong interaction between the aniline/HCl solution and PU fiber the resultant Ani-PU composite fibers were swelled. These swelled Ani-PU composite fiber were then placed in ammonium persulphate (APS)/HCl solution for 6 h at 0 0C for complete polymerization. Finally, the resulted PANI/PU fiber was removed and washed with distilled water and dried in air at room temperature. Spirkova et al. have synthesized electrically anisotropic PANI/PU composite through in situ polymerization [86]. In the procedure, different wt % (1, 5, 10) of PANI powder, trihydroxypoly (oxypropylene) (PPT) and DBTDL were ultrasonicated and then stirred at 50 0C. In the end, the MDI was added to form the PANI/PU composite. A conductive composite of polydiphenylamine (PDPA) entrapped TPU was prepared and characterized by Santhosh et al. [87]. The composite was prepared by in situ polymerization of diphenylamine (DPA) within the TPU matrix. For this synthesis, two separate solutions of oxidant, potassium peroxydisulphate (PDS) with polycarbonate (PC) i.e. PDS/PC solution and monomer DPA with PC i.e. DPA/PC solutions were prepared. The TPU

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was first immersed in PDS/PC solution for 2 h and then immersed in DPA/PC solution for 5 h at room temperature. The composite obtained was washed with water and then dried in oven at 85 0C. In addition to these three synthesis methods, some more recent and advanced methods have also used to synthesize the CP/PU composites that are discussed in proceeding units. 2.4 Other Synthesis Methods Apart from these chemical synthesis, some electrochemical techniques have also been used to synthesize the CP/PU composite. The technique is considered to be a better process in terms of cleanliness. The composites during this synthesis get deposited on the surface of the electrode, involving the use of cyclic voltammetry, potentiostatic and galvanostatic polymerization [88]. Generally, this method is used for the synthesis of free standing films but the formation of these standing films are restricted to the area of electrode [89]. Zinger et al. have used chemical-electrochemical process to insert the PPy into PU/Polyacrylamide (PAAm) to develop the PU/PAAm/PPy conductive composite films [90]. Further, they have compared its properties with that of PU/PPy films. Pei and Bi used potentiostatic polymerisation technique to prepare the PANI/PU composite films with high flexibilities and good mechanical strengths [91]. The composite was formed by electropolymerization of aniline on a PU-coated platinum electrode in a water/acetonitrile/ethylene glycol electrolyte solution at a constant potential of 2.0 V. Daroux et al. reported the preparation of PPy/PU composite using electropolymerization technique in different electrolyte viz. tetrabutylammonium floroborate, tetramethylammonium floroborate and perchloric acid [92]. The solution of Py monomer with different

solvents

mixture

(acetonitrile/water,

acetonitrile/polyethylene

glycol

and

polyethylene glycol/water) were electropolymerized onto PU coated electrode. Grafting is another method used for the synthesis of CP/PU composites and blends. The method is relatively recent and attractive. In this method the polyurethane backbone is functionalized 11

by conducting polymer chains. Here, the NCO terminated pre-polymer reacts with the amine capped CPs [93]. The general graft structure of CP/PU composite is demonstrated in Fig. 6. Carone et al. have reported that when elastomeric conducting copolymers prepared by grafted polyaniline (EB) or sulfonated polyaniline (SPAN) chains on the backbone of a carboxylated segmented PU, their electrical conductivity was found to be increased by many orders of magnitude, reaching the values of about 10−3 S/cm [94]. Later on, they have synthesized the PU/PANI Conducting graft copolymer and investigated the effects of crosslinking on the mechanical and electrical properties of the conducting copolymer obtained by grafting of PANI on a carboxylated polyurethane composites [95]. Son et al. have prepared the conducting PANI grafted waterborne PU-urea via using oxidative graft polymerization of aniline on the surface of WBPU [96]. In this preparation the carboxylic salt groups of WBPU was converted into the carboxylic acid groups by treating with aqeous HCl and with aniline. The reacion scheme for the preparation of PANI grafted WBPU is given in Scheme 1. The effect of reaction conditions e.g. reaction times/temperatures/ concentrations of aniline, and APS content on the % grafting, conductivity, and mechanical properties of PANI-grafted-WBPU films were analysed, and it was observed that the maximum % grafting was attained at 0.35M/10 min/25 0C and 0.2M/10 min/00C for aniline and APS. The thermal and mechanical properties of pristine WBPU and PANI-graft-WBPU films were compared. The sensor performance of PANI-graft-WBPU film for aqueous phenol was also studied. 2.5 Comparison of Various Methods of Synthesis CP/PU composites have been prepared by various methods, exhibiting changes in their properties [97,98]. Thus, a comparative study of properties of such composites processed by different routes are reported in the proceeding unit.

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Shriwastava et al. reported the synthesis of electrically conductive and thermally stable nanoblends of thermoplastic polyurethane (TPU)/dodecylsulphonic acid (DBSA) doped PPy (TPU/DBSA-PPy) using in situ polymerization and solvent blending methods [99]. They have explored the effect of these two preparative methods (i.e. solution blending and in situ polymerization) on the morphology, electrical conductivity and thermal stability. It was evident from their SEM and TEM studies that the nanoblends prepared by solution blending method resulted in the formation of more homogeneous and more conductive nanoblends due to the formation of hexagonal intercalated network. The electrical conductivity of TPU/DBSA-PPy nanoblends was found to be 0.07 S/cm for in situ polymerization and 0.26 S/cm for solution blending method. Similarly, Denice et al. prepared the DBSA doped PANI dispersed TPU blends (PANI/DBSA/TPU) using two different methods viz. solution blending and in situ polymerization [14]. In case of solution blending, the PANI/DBSA and the TPU were mixed in a common solvent THF and stirred for 3 h. After the completion of reaction the solvent was evaporated at room temperature. While in in situ polymerization, the DBSA, aniline salt and TPU were dissolved in THF. This solution was then added into an aqueous solution of APS and stirred for 6 h at 5 0C. They observed that the percolation limit for the dispersion of PANI//DBSA into TPU is higher in solution blending (2.7 wt %) as compared to in situ polymerization (2 wt %). Chwang et al. have fabricated a high performance dielectric PANI-DBSA/PU blends via in situ polymerization [100]. Aniline-DBSA was mixed with well dispersed aqueous solution of PU and stirred for 2 h. The solution was cooled to 0-5 0C, the polymerization was carried out by the addition of APS with continuous stirring for 12 h. The solution blending method was also used to fabricate the PANI-DBSA/PU blends. These were then compared with that prepared by in situ polymerization. The dielectric property, conductivity and thermal behavior was found 13

to be higher for the PANI-DBSA/PU blends prepared through in situ polymerization. The improved properties of the said blend can be attributed to the electrode polarization effect generated by the PANI present within the blend. In an another study, Wang et al. have synthesized a novel PANI/TPU composites doped with compound acid (composed of PTSA and phosphoric acid) by using in situ polymerization and solution blending methods [101]. Further, they have added lithium bis-oxalato borate to the PANI/TPU prepared by in situ polymerization. The conductivity of PANI/TPU composite synthesized by in situ was two orders of magnitude higher than that of the composites prepared from solution blending. Therefore, on the basis of above comparison and literature survey, Table-1 discusses the advantages and disadvantages of CP/PU composites prepared by different methods [89,90,102–107]. 3

Formation of different types of CP/PU composite

A number of conductive polyurethane composites have been reported by many researchers. The conductive nanofillers like conducting polymers, graphene, CNT, MWCNTs, Clay, gold and silver etc. are also being used to prepare the CP/PU composites by many researchers [29,65,67,108,109]. However, the present review solely highlights the use of various types of conducting polymer nanoparticles such as PANI, PPy, PTh etc. and their derivatives as a filler in PU matrices (shown in Fig. 7). An exhaustive literature survey on PANI/PU, PPY/PU, PTh/PU and their derivatives based PU composites are discussed below, covering various aspects of these materials. 3.1 PANI/PU composite

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Literature survey reveals that PANI based polyurethane composites are found to be more stable and easily processible amongst different conducting polymers based polyurethane composites. This can be attributed to the formation of H-bonding between the -NH group of PANI and – NHCOO group of PU, which leads to their better miscibility, higher conductivity and tensile strength [110]. Siddaramaiah and co-workers showed the effect of H-bonding between -NH of PANI and -NHCOO of PU/PMMA on the physico-mechanical, electrical and thermal properties of IPN [49]. The probable molecular structure of PANI/PU composite network is given in Scheme 2 [111]. In view of this, number of scientists are working on the synthesis of PANI/PU composites. Jaaoh et al. have prepared a conductive blends of PANI/PU in two different solvents (DMF and NMP) and showed the effect of solvent on the electrostrictive behaviour of these blends [112]. The PANI/PU blend prepared in NMP solvent showed the enhanced electrostrictive behavior. In another study, they have synthesized PANI/PU composite with different content of PANI (0-2 wt %). Their dielectric and mechanical properties were determined to illustrate the electrostriction and energy conversion behavior [113]. The experimental results showed that the 2 wt % PANI dispersed in PU provide high power density and high efficiency of electromechanical conversion. Wang et al. reported the synthesis of series of PANI/PU/Silica organic inorganic hybrids [20]. Initially, they synthesized low molecular weight (144 x 10-3 g/mol) amine capped PANI with high solubility, which was then used along with nano silica as a chain extender to prepare conductive polyurethane hybrids. The SEM images of the same has revealed that the PANI was found to be homogeneously dispersed and continuously interconnected with insulating PU-silica matrix. It was also observed that the addition of conducting PANI and inorganic silica nanoparticle enhanced the thermal stability, glass transition temperature and polydispersity index (3.5). Biscaro et al. have investigated the effect of dopants [dodecylbenzene sulphonic acid (DBSA) and camphor sulphonic acid (CSA)] on

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the microwave absorption properties of PANI/DBSA/PU and PANI/CSA/PU blends using rheological analysis [114]. The rheological analysis showed that the addition of PANI/DBSA and PANI/CSA into PU causes a significant variation in viscosity. Additionally, DBSA exhibits larger influence on the interaction between PANI and PU than the CSA. This behavior can be attributed to the aliphatic and long nonpolar dodecyl chain of DBSA, which interacts with the aliphatic polyester polymer chain of PU matrix. Sanjai et al. have reported the charge transport and magnetic properties of methane sulphonic acid doped PANI (PANI-MSA) and their blend with polyurethane [115]. The properties of PANI-MSA and PANI-MSA/PU blend were investigated through temperature measurements (T) and electric field (E) dependence conductivity, temperature dependence thermoelectric power, magnetic susceptibility and electron spin resonance at room temperature. All these properties of the two systems were also compared. From these measurements it was confirmed that the PANI-MSA and PANIMSA/PU blend follow a 3D and 1D variable range hopping type of conduction respectively. In PANI-MSA/PU blend, the value of conductivity is found to be decreased in comparison to that of PANI-MSA by 2 orders of magnitude. The larger ESR line width was also observed for PANI-MSA/PU blend attributed to the greater localization of charge carriers in blended polymer. Rodrigues et al. reported the synthesis of PANI/PU blends via condensation of NCO terminated PU prepolymer and amine group of PANI [116]. They have maintained the constant length of high molecular weight (23000 g/mol) of PU segment and set the degree of crosslinking by an optimum distance through each point of interconnection between PANI and PU. For the first time they have reported this type of molecular model of PANI/PU. Merlini et al. have used the PANI coated coconut fiber (CF-PANI) as conductive additive into the COPU matrix [117]. The CF-PANI was synthesized by in situ polymerization of aniline in the presence of CF using APS and FeCl3 as an oxidant. The electrical conductivity of CF-PANI with FeCl3 was found higher than that with APS. Thus, the CF-PANI.FeCl3 and pure PANI

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was chosen as a filler for their comparison. The structure and properties of CF-PANI.FeCl3/PU, PANI/PU and pure PU was compared and found that the CF-PANI.FeCl3/PU exhibit higher electrical conductivity.

3.2 PPy/PU composites PPy has extensively been studied because of its high conductivity in their doped state and easy chemical or electrochemical polymerization, which makes them a good candidate for many applications. However, PPy has poor mechanical properties and poor stability under ambient conditions, which restricts its applications at commercial scale. A considerable research has been undertaken on PPy with a view to improve its stability and mechanical properties as well as its processability through the formulation of its nanocomposites [118,119]. Robila et al. reported the synthesis of conductive composite of PPy with sulphonated PU anionomers (PUAPPy) [120]. The structure, properties and concentration of ionomer as well as effect of synthesis process on the performance were studied in detail. Thermogravimetric study suggests that the PU anionomer with PPy has better thermal stability than that of pure PU anionomer. In their further study, they have synthesized carboxylated PU anionomer/PPy composite by immersing the PU in an aqueous solution of Py monomer and FeCl3 [121]. Here the mechanical and electrical properties of the composite were compared with that of PU anionomer and observed that the addition of PPy increases the electrical conductivity but reduces the mechanical properties. Yalinmaz et al. have fabricated the PU-PPy nanofiber composite using cerric ammoniumnitrate [52]. The dielectric, electrical, mechanical and thermal properties of the composite enhances with the introduction of PPy in PU matrix (molecular weight=93000 g/mol). The interaction of PPy and cerium (Ce) with PU matrix is shown in Scheme 3. Wang et al. have prepared a series of waterborne cationic PPy/PU composites by the addition of oxidant and Py to the cationic PU dispersion [122]. The effects of Py content, reaction time, 17

temperature and molar ratio of oxidant to Py on the surface resistivity of conductive films were systematically investigated. In parallel to this, they have also synthesized the waterborne PU/PPy dispersion to further improve the compatibility between PPy and PU [123]. They have introduced Py into the NCO terminated PU prepolymer and then the water was added to form the waterborne PPy/PU dispersion. They have developed PPy/PU conductive coatings for cellulose fiber paper with good conductivity and high mechanical strength. Wen et al. investigated the morphological and electrical changes in thermoplastic PU doped LiClO 4 through the introduction of PPy [53]. The surface morphology of pure TPU and composite was found to change from smooth to cauliflower like surfaces. They observed that the interaction of NH groups of PPy with ether or carbonyl groups of TPU caused the decrease in Tg value, which was further confirmed by DSC technique. The conductivity of composite, was found to be one order higher than that of pure TPU, due to the increased mobility of ClO 4 - ions which was promoted via the coordination of Li+ ions with nitrogen atoms of PPy. Buruiana et al. have reported the synthesis and characterization of PU cationomer containing PPy [124]. PU cationomer were synthesized using poly (oxytetramethylene), 4,4'-bibenzyldiisocyanate, N methyldiethanolamine as chain extender, and acrylic acid poly(acrylic acid) as quaternizating agent. Pyrrole was polymerized into the PU cationomer in presence of CuCl2 used as an oxidant. On 15 wt % loading of Py in PU, the composite showed an increase in conductivity by two order as compared to that of pure PU. The conductive composite of PPy/PU was prepared by Ruckenstein et al. via three step process [125]. Initially, (i) the concentrated emulsion of PU-sodium dodecylsulphate was prepared then (ii) PPy was synthesized by chemical oxidative process, (iii) followed by the formation of the composite of PPy/PU by blending the PU emulsion with an aqueous suspension of PPy powder. The effect of PPy content on the conductivity of composite was also investigated and it was observed that the optimum condition for the processing of the same was found at 68 wt % loading of PPy. Further

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the mechanical strength was reinforced by infiltrating and polymerizing the acrylamide into the composite. The reinforcement of polyacrylamide not only enhance the mechanical strength but also provides better stability towards the action of the environment. Wallace et al. reported the synthesis of nitrate (NO3) and Tiron (3,4 dihydroxy 1,3 disulphonic acid) doped PPy coated PU colloids (PPy/NO3/PU and PPy/Tiron/PU respectively) using electrohydrodynamic process [126]. They have also investigated the effect of these dopants and reaction conditions on the conductivity, as well as that of electroactivity and particle size distribution. From their investigations, it was concluded that the reaction proceeds faster with Tiron and gives the same yield in half of the reaction time as compared for PPy/NO3/PU colloidal system. This can be attributed to the effective electrocatalytic property of Tiron, which resulted in the formation of a large number of oxidized species at the electrode surface. These oxidized species are responsible for the transport of monomer at higher electrode rotation speed. Thus, a greater amount of polymer was formed in a shorter period of time, and was not transported away from the electrode before depositing. In another study, reported by Merlini et al. a conductive composite of PPy coated banana fibers (PPy-BF) incorporated PU (PU/PPyBF) was synthesized [127]. The influence of PPy-BF on the mechanical and electrical properties of PU/PPy-BF composite has also been investigated. They have also synthesized PPy, PPy-BF, PPy/PU and PU/PPy-BF to compare their properties and found that the PU/PPyBF exhibit best properties than that of pure PU and PPy-BF. The study further revealed that the composite containing 25 wt % PPy-BF exhibits good tensile strength and electrical resistivity of around 108 fold lower than that of pure PU. 3.3

PTh/PU composite

Among the various conducting polymers PTh, due to its environmental stability in oxidized form, high conductivity, interesting electrochemical behavior, and its capability to form a

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highly conjugated networks, have gained much attention in the past few years [128,129]. In some cases, it exhibits similar or superior properties than PPy and PANI due to its higher electrical conductivity and chemical stability [130]. PTh and their derivatives such as PEDOT and P(3HT) have gained enormous devotion of researchers and scientist. Additionally, they delivered the best properties with insulating polyurethane matrix when they have been used for certain applications [131]. Up to now several authors have worked on the synthesis of PTh/PU composite. Sari et al. synthesized PU/PTh conducting copolymer by electrochemical polymerization [132]. Two different approaches (Dropping–coating (D–C) method and Suspension (S) method) have been adopted by the authors. In both cases, the PTh/LiClO4 and PTh/Et4NBF4 were used to synthesize the PU/PTh composite using different solvents (acetonitrile and benzonitrile). The authors have also reported that the synthesized copolymer exhibit enhanced thermal stability in comparison to that of virgin PTh. The synthesis of regioregular poly (3-hexyl thiophene) (P3HT) wrapped multi walled carbon nanotubes (MWCNTs) dispersed thermoplastic PU was reported by Goswami et al. The different concentration of P3HT and MWCNTs were used to prepare the stable self-sustained homogeneous composites [133]. It has been observed that the best property is achieved for 2.5 wt % P3HT with 0.5 wt % of MWNTs. Furthermore, Siddiqui et al. have reported the synthesis of blend and nanocomposite of PU/PTh and PU/PTh/NH2-MWCNTs respectively and investigated their mechanical, thermal and electrical properties and reported that these properties was increased with the increasing concentration of PTh [46]. The interaction of modified MWCNTs with PU/PTh composite is shown in Scheme 4. Razal et al. have reported the preparation of homogeneous PU/PEDOT:PSS composite fiber via wet-spinning method [134]. It was found that with increased loading of PEDOT: PSS in the PU fiber composites, the Young’s modulus increased exponentially and the yield stress increased linearly. Cho et al. have prepared conducting core sheath of PEDOT/PU nanofibers 20

with and without incorporating graphene nanoplatelets (GNP) by vapour phase polymerization [135]. The morphology, mechanical properties, electrical conductivity, and electroactive actuation of the core-sheath nanofibres were investigated. It was found that the core-sheath of PU-PEDOT nanofibre webs were the most effective for enhancing the displacement of a CP actuator, whereas the incorporation of GNP in PU-PEDOT Nanofiber webs showed reduced actuator displacement because of a high modulus. Schematic representation core-sheath of PUPEDOT nanofiber is given in Fig. 8. 4. Effects of conducting polymers on the properties of CP/PU Composite In addition to different methods of synthesis, various types of conducting polymers and their concentrations affects the properties of the CP/PU composites [84]. A number of researchers and scientists have reported that the overall properties of CP/PU composite enhances at very low concentration of CPs in the PU matrix [113,141]. However, in case of PANI and their derivatives, higher concentration (75-90 wt %) can be dispersed within the PU matrix [144, 155]. On the other hand, PTh filler in PTh/PU have not been used to higher concentration beyond 8 wt % [139]. The higher concentration of PANI in PANI/PU composites can be attributed to the strong hydrogen bonding between the –NH- group of PANI with urethane group of PU, which is in case of PTh/PU composites are found to be least that may be due to the presence of relatively less electronegative sulphur group. Most of the authors have evaluated the effect of CPs on the thermal, mechanical and electrical properties [136,137]. Lakshmi et al. have studied the electrical properties like dielectric and conductivity of some of the selected conducting composites [84]. They have selected polyparaphenylene diazomethine (PPDA), polythiophene (PTH), poly-3, 4-Ethylenedioxythiophene (PEDOT), and polyaniline (PANI) as a conducting filler for PVC and PU matrices. From their studies, it was observed that the PANI-PU composite has highest conductivity and dielectric loss while PPDA-PVC composite showed the lowest. The thermal, mechanical and electrical properties of novel 21

PANI/PU blends were investigated by sattar et al. [136]. The blends were prepared with different loading of PANI (0.1 wt% - 1 wt%) and it was inferred that the glass transition temperature (Tg) and melting temperature (Tm) was found to increase with increasing content of PANI content which may be further assigned due to the presence of strong hydrogen bonding and high cross linking. The mechanical properties such as tensile strength and Young’s modulus was found to be 24.50 MPa and 427.87 MPa respectively, which are higher than that of pure PU. On the other hand, the elongation at break point was found to decrease with the increasing content of PANI. This can be attributed to the higher cross linked density which induces rigidity in blends. Additionally the formation of conductive phase was observed on the addition of PANI in the PU matrix that leads to the increase in electrical conductivity (1.296.94 × 10−6 Scm−1). Auad et al. have studied the possible changes in physical properties with the addition of 1-10 wt % of PANI coated cellulose nanofibrils (PANI-CNF) [80]. It was noticed that the percolation threshold for unmodified and modified CNF coated PANI was recorded to be 1 wt% and 4 wt % respectively. It has been determined that the young’s modulus and yield stress is increasing with the increase loading of PANI-CNF while elongation at break decreases. Wen et al. have explored the effect of PPy on thermal and electrical properties of thermoplastic polyurethane (TPU) [53]. It has been observed that the composite with 4.24% loading of PPy showed far better thermal and chemical stability than that of pure PU. The conductivity was examined by AC impedance measurements and was found to be increased by one order of magnitude. A detailed study on the effect of PPy concentration and polymerization conditions on the mechanical and electrical properties has been explored by Chiu et al. [139]. It was observed that as the concentration of Py monomer increases from 0 - 1.5%, the tensile strength of the composite decreases while the elongation at break and modulus increases. The electrical conductivity of composites was found to increase from 10 -4 to 1 Scm-1.

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Likewise, several other authors have examined the effects of these CP on thermal, mechanical and electrical properties of CP/PU composites. However, it has been noticed that most of the literature is devoted on PANI and PPy containing PU composite. PTh based PU composites have paid less attention, although the composite with low concentration of PTh have exhibited superior properties. In view of this, we separately discuss the effect of PTh, PPy and PANI on the physical properties of PANI/PU, PPy/PU and PTh/PU composites given in Table 2 (a), 2(b) and 2 (c) respectively. On comparing the properties of PANI/PU, PPy/PU and PTh/PU composites given in table 2(a), 2(b), 2(c), it has been observed that PANI/PU exhibit excellent thermal stability up to 680 0C at only 12.5 wt % loading [49]. However, PPy/PU attains the best electrical properties like conductivity (100 Scm-1) and dielectric constant (7000) with 20 wt% loading [90,140]. Moreover, in terms of mechanical properties, it is inferred from the literature [92 and 127] that the PPy/PU composite possess high tensile strength (i.e. 592 psi), while PANI/PU shows the highest modulus and impact strength (4875 KJ/m2) at 15 wt% loading [151]. On the other hand, PTh/PU composite have also exhibited the superior properties with small loading. However, not much work has been reported on PTh/PU in comparison to PANI/PU and PPy/PU as to the best of our knowledge very few references are available in literature. 5 Techniques for the Characterization of CP/PU composites It is important to discuss various characterization techniques used to investigate the spectral, structural and morphological aspects of CP/PU composites, especially, in order to establish the relation between structure and properties of these materials, such studies provide significant information that help in the development of new materials with controlled and value added properties [158–163]. Thus, the application of some of these characterization techniques are discussed in the proceeding unit.

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5.1 Fourier Transform Infrared (FTIR) Spectroscopy It is primarily used to detect the presence of various functional groups in polymers and various interactions of the fillers with that of matrices. The shift in IR absorbance peaks clearly describes the interaction of filler with the matrix. The infrared absorbance peak of the polyurethane conductive composite shows the significant shift in the urethane stretching as well as the carbonyl absorbance band due to the interaction between the urethane groups of PU with the functional group of the CP. For example the FTIR values and their shifting for various functional groups for MO–PANI/COPU composites is given in Table 3 [78]. The -NH peak in MO–PANI shifted from 3432 cm−1 to lower frequencies. This can be attributed to the strong interaction between the urethane groups of PU and the -NH groups of MO-PANI. The carbonyl absorption peaks is also found to shift from 1744 cm-1 to lower frequency 1630cm-1, due to the strong hydrogen bonding between -NH of PANI and -NHCOO of COPU. 5.2 Nuclear Magnetic Resonance (NMR) Spectroscopy The technique is used to establish the structural behavior of materials that gives great insight about the structure of the material. Figure 9 (a) and (b) shows the solid state 13C NMR spectra of pure PANI and PANI/PU copolymer [20]. It is evident from the figure 9b that the spectra of PANI and PU were superimposed. Two strong and sharp peaks centered at 27.2 ppm and 71.1 ppm are ascribed for the PTMG soft-segment carbons. The peak at 154 ppm is attributed to the resonance of urethane carbonyl. The resonance at 40 ppm is for –CH2– groups of MDI. This is due to –CH2– in MDI, restricted by the neighboring PANI oligomers. In addition, the aromatic region ranging from 115 to 140 ppm is due to the contributions of PANI carbons and aromatic rings of the PU prepolymer. The peaks at 119 and 129 ppm are assigned to the benzenoid protonated ring carbons of PANI and the protonated aromatic MDI carbons, while the peak at

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136 ppm is associated with the quinoid protonated ring carbons of PANI and quaternary MDI ring carbons. 5.3 X-ray diffraction XRD is commonly used to understand the amorphous and crystalline nature of CP/PU composite. The XRD spectra of the PU was found to change from amorphous to crystalline or semicrystalline on increasing the loading of conducting polymer or vice versa. The dispersion of CP filler in PU is confirmed by the change in intensity of peaks from virgin PU to that of conductive PU composite. Fig. 10. shows that the crystallinity increases with the increase in concentration of MO-PANI into the PU matrix [78]. In an another report, the crystalline behavior of PANI-PTSA and PANI-PTSA/PU composites were characterized by XRD. The XRD patterns of pure aliphatic PU and PANI-PTSA/PU composites with different amount of PANI [164] depicting that the amorphous phase of aliphatic PU is localized by the small peak observed at 2ϴ = 20.6 0 while the peaks at 2ϴ = 250, 31.30 and 33.30 observed in the composite indicates the crystalline structure of the composite. 5.4 Scanning Electron Microscopy (SEM) The SEM describes the surface morphology associated with a sample under investigation. The difference in surface morphology of pure TPU and PPy/TPU composite have been shown in Fig. 11. [53]. It is clearly visible that the globular structure of PPy was polymerized on to the surface of TPU. Another author has reported the morphological change with the increased content of PANI.DBSA into the PU matrix [165]. They have performed the SEM of PU and PANI-DBSA/PU composite nanofibers with different PANI-DBSA concentrations (0, 10, 20, and 30 wt %) to observe the morphological changes in the PANI-DBSA/PU composite. It was observed that the diameter of nanofibers gradually decreased with increasing PANI-DBSA content in the blend, and more beads were recorded on the surface of composite. 25

5.5 Transmission Electron Microscopy (TEM) TEM allows a qualitative understanding of the spatial distribution of particles, internal structure of the various phases, direct visualization of defects in the structure and a detailed topography. It also gives information about the homogenous dispersion of nanoparticles into the polymer matrix. Fig.12.1 (a) and (b) shows the TEM images of methyl orange doped PANI (MO-PANI) nanoparticles and MO-PANI dispersed in castor oil based polyurethane (COPU). No aggregation or cluster formation of the nanoparticles was noticed in the TEM images, and the discrete particles of uniform size were found to be dispersed homogeneously in the COPU matrix [166]. In Fig. 12.2, the dark region corresponds to spherical particles of PPy.DBSA dispersed in the white matrix of TPU. It also shows that the domain size is nearly 10 nm for 2.5 wt %, whereas it increases up to 100 nm with 30 wt % of PPy.DBSA which can be attributed to the formation of well dispersed PPy.DBSA/TPU nanoblends [99]. 6 Applications Excellent work has been reported on the dispersion of conducting polymer in the polyurethane matrix, used for the processing of CP/PU composites, which finds versatile applications in the field of electromagnetic interference (EMI) shielding, sensors, biomedical, shape memory polymers (SMP), membranes, anticorrosive coatings, films and foams [54,74,166–170] (Fig. 13). A detailed discussion on these applications is elaborated in the given below sections. 6.1 EMI Shielding There is a growing interest of electronic industry and its widespread application in communication, computations, automation, biomedical, space and other areas. However, it has been observed that their applications have created a pollution known as electromagnetic interferences (EMI) [171]. These EMI consists of many unwanted radiated signals, which may cause severe damage to communication system and safety operation of many electronic devices

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[172]. It is a common phenomenon seen that when a light is switched on, some form of flashes on the distorted television screen are produced, causing hazardous sounds in the form of electromagnetic (EM) waves [173]. By the exposure to these EM waves various health hazards have been reported like insomnia; nervousness and headache [174]. Thus to overcome all these problems, it is advised to shield the electronic devices in such a way that both incoming and outgoing interferences may get filtered. Among various polymer composites, conducting polymer based polyurethane composites are found to be the best candidate to meet the requirement of EMI shielding properties of electronic devices. In view of this, several workers have designed conductive polyurethane composites and studied their EMI shielding effects [175]. Mathew et al. have studied the EMI shielding properties of PANI-PU composite at Sband and X-band frequencies. The composite have found to be a potential candidate for EMI applications, and their shielding efficiency was increased with an increase in thickness of the sample [176]. In addition to this, electrically conductive composites of castor oil polyurethane with polypyrrole coated peach palm fiber (PPY-PPF) was fabricated by dispersing different amounts of PPY-PPF in PU matrix [177]. They found that the composite containing 25 wt % of PPY-PPF showed good EMI shielding effects. Gunjan Gupta and his group have developed PANI/PPY based polyurethane composite coatings for EMI shielding. Various concentration of PANI/PPY were incorporated in the polyurethane matrix [178]. It was observed that the coatings with 6 wt % PANI and 6 wt % PPY, showed appreciable EMI shielding properties. A composite of polyurethane reinforced with PEDOT coated multiwalled carbon nanotubes (MWCNT) was synthesized exhibiting exceptionally good EMI shielding properties [138]. The PEDOT coated MWCNT composite (PCNT) was synthesized and used as a filler for the processing of PU sandwiched composite. It was found that the EMI shielding effectiveness increases with the increased loading of PCNT filler. The maximum effectiveness was found with 30 wt % loading of PCNT filler. The synergistic effects of PCNT in PU matrix enhanced

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the EMI shielding properties. Primarily, the shielding mechanism of EMI depends upon the absorption and reflection of the electromagnetic radiations [179]. The basic mechanism of EMI shielding is presented in Fig. 14. The delocalized electrons of conducting PCNT provides a tortuous path to the EM waves, which reflect these waves at the surface of the shield. 6.2. Sensors During the past few decades, conductive polyurethane based sensors have become a subject of extensive research and development. The application of these sensors ranged from human physiology monitoring sensor to chemical monitoring sensor [180–182]. A number of publications have been reported on sensor application. Wang et al. have successfully designed wearable electronics that can monitor human physiology, which shows excellent stretchability and electrical conductivity [183]. The PPy/PU elastomers were prepared by in situ polymerization of Py in and on sides of porous PU substrates. The prepared elastomers were allowed to form a netlike microcracks, under stretching, which causes variations in morphology, structures, stretchability, conductivity and sensitivity. They have used these properties to construct a waistband for human breath detection. In another report, S. Brady and B. Carson et al. successfully developed wearable and wirelessly integrated body monitoring system of PPy/PU composite [180]. In this study, five breathing patterns were selected to represent a variety of breathing styles that a person may perform during daily activities. A novel flexible sensing fibers were fabricated by introducing the coating of nanostructured PANI on the surface of PU via in situ chemical oxidative polymerization [168]. The conductive composite exhibited remarkable chemoresistive properties for chloroform vapour detection, which were found to show superior sensing properties than that of neat PANI. This was attributed to a change in the conducting pathway of PANI layers induced by remarkable and reversible solvent-swelling properties of PU fiber matrix. Fig. 15 shows the schematic diagram for conformational change of PANI/PU composite induced by chloroform. They investigated 28

the high sensitivity (4x10 -4ppm), fast response time (>30 s), and low detection limit (30 ppm), for this sensor, which can be achieved with the composite fibers of 55 um diameter of PU and 550 nm thickness of PANI layer for chloroform gas detection. Kim et al. have synthesized PANI-grafted-WBPU composite film and studied its phenol sensing properties by exposing to different concentrations of various aqueous phenol solutions (0 ppm–10,000 ppm) [96]. The changes in normalized electrical resistance was monitored at different concentrations. It was observed that with the increased concentration of phenol solution the normalized electrical resistance was found to decrease and then levelled off. 6.3 Biomedical Conductive polyurethane composites have received much attention of researchers to explore their applications in biomedical sources due to their excellent physico-mechanical properties and good cytocompatibility [184]. The smart and new generation conductive composite material has been investigated for its applications in the field of drug delivery and tissue engineering [185]. On this account, Prabhakar et al. have reported the modification of medical grade PU with PANI (PU+PA) and PANI-silver nanoparticles (PU+PA+Np) [186]. They have performed the biocompatibility test of modified and unmodified surfaces to investigate the response for adipose muscle cell line and bacteria (P. aeruginosa and B. subtilis). Toxicity test of these polymers subjected to 3T3 L1 adipocytes (extracted from mouse) cell lines, after 48 h of incubation, showed that the percentage of dead cells drastically reduced on PU + PA (23 %) and PU + PA + NP (18 %) surfaces when compared to the virgin PU (41%) surface. The less cytotoxicity was observed for the modified polyurethane as compared to that of unmodified polyurethane (shown in Fig. 16). The adhesion of P. aeruginosa and B. subtilis to these surfaces was assessed. The presence of P. aeruginosa was found to be decreased by 63.5 % and that of B. subtilis by 25.8 % on the surface of PU+PA, while the concentration of these bacterias was further decreased by 90.6 % and 50.5 % on PU+PA+NP surface, respectively in comparison to 29

that of unmodified PU surface. The decrease in bacterial attachment can be attributed to the anti-adhesion and antibacterial nature of PANI and silver nanoparticles respectively. In another report, Broda et al. have synthesized PPy/PU composite for biomedical tissue engineering applications [187]. The composite with 1:5 ratio of PPy and PU was found to have the highest conductivity (2.3 x 10 -6 S cm-1) while the composite with ratio 1:100 showed least conductivity (1.0 x 10-10 S cm-1). They have performed cytocompatibility test by culturing human dermal cells (C2C12 myoblast cells) and found no signs of cytotoxicity. Madrigal et al. have prepared nanomembranes by spin coating, using the mixture of polythiophene derivative (P3TMA) and thermoplastic polyurethane (TPU) in different weight ratios [188]. They have investigated the biomedical applications of the TPU:P3TMA nanomembranes and observed that the swelling and enzymetic degradation of membrane was increased by increasing the concentration of P3TMA. TPU:P3TMA nanomembranes behaves as biodegradable and bioactive material for stimulating the cell viability. Matrix assisted pulse laser evaporation (MAPLE) technique was used by Paun et al. to fabricate the biocompatible electrically conductive composites of PPy with two insulating matrices i.e. poly(lactic-co-glycolic)acid (PLGA) and polyurethane (PU) for bone regeneration [189]. They proposed the MAPLE technique to promote the compact spatial arrangement of PPy nanograins embedded in PLGA and PU matrix. The PPy/PU layer showed the highest degree of biocompatibility and provides the strongest mineralization support for the cultured cells. A conductive composite film of aniline trimer based polyurethane (CPU) doped and undoped with CSA were synthesized for biomedical applications [190]. The CPU film was characterized by their mechanical, electrical and biodegradable properties. The enzymatic degradation rate was investigated by immersing the CPU film in phosphate buffer solution (PBS) and lipase/PBS solution. The film was kept for 7 days for enzymatic degradation and it was found that the electrical conductivity of CSA doped CPU film decreased and become equal to the undoped CPU. Mouse 3T3 fibroblast and 30

control tissue culture polystyrene (TCPS) was used to perform the cytocompatibility test of the CPU film. After 5 days of incubation, no significant difference was observed for CPU film. This suggested that the CPU film had good cytocompatibility to support the cell growth on their surfaces and hence can be applied for tissue engineering, smart drug delivery, and electronics. 6.4 Shape Memory Polymer Shape-memory polymers (SMPs) have the ability to regain their lost property to some extent on their deformation and try to recover their original shape following the application of various external stimuli like heat, light, electricity, voltage and magnetic field. High electrical conductivity and high mechanical impact are the two key factors, which largely affect the properties of shape memory polymers. In account of this, researchers have prepared conductive shape memory polyurethane through the incorporation of conducting polymers. Sahoo et al. prepared an electroactive shape memory PU/PPy conductive composite via chemical oxidation method [137]. A good shape recovery of 85–90% was obtained within 25 sec by the shape recovery test with bending mode on applying an electric field of 40 V. Fig. 17. Shows the prototype of electroactive shape recovery behavior of PU/PPy composite. The same group has also shown the electroactive effect of shape memory polyurethane composites by incorporating the multiwalled carbon nanotubes and PPy [191]. From their study, they have inferred that when 2.5% PPy and 2.5% MWNTs was fused with the PU matrix, the obtained composite shows good electroactive shape recovery and almost 96% of the original shape was recovered in 20 sec with the applied voltage of 25V. A novel shape memory polymer blends of PU/PANI was prepared and characterized by FTIR and SEM analysis [136]. Their thermal, mechanical, electrical and shape memory properties were explored and observed that the overall properties significantly increases with the increase in concentration of PANI

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(0.1% to 1%). An extent of 96% recovery was obtained with 1wt% loading of PANI. Sattar et al. have deduced the influence of PTh and NH2 functionalized MWCNTs (NH2-MWCNTs) on the mechanical, thermal and shape memory properties of PU [46]. They have prepared PU/PTh blend and PU/PTh/NH2-MWCNTs composites and compared their mechanical and shape memory properties. The obtained result revealed that the composite containing 1 wt% PTh and 3 wt% NH2-MWCNTs have high mechanical strength and maximum shape recovery of 92%. This was attributed to the high degree of crystallinity due to the encapsulation of MWCNT caused by the adsorption of PTh chains. 6.5 Membrane Membranes are mainly used to perform various processes like microfiltration, ultrafiltration, reverse osmosis, eletrodialysis, and others [8]. M.A. Shehzad and colleagues synthesized cation-exchange membranes of thermoplastic polyurethane (TPU) and polyaniline (PAni) doped with camphor sulphonic acid (CSA) by solution casting method [169]. Ion-exchange capacity and electrical conductivity was increased by increasing the PANI content in the TPU membranes whereas the mechanical properties showed a significant decrease confirming that PANI was incorporated as non-reinforcing filler in these blends. A comparative study of castor oil polyurethane (CAPU) and TPU modified membranes with PANI has been presented by Almeida et al. [152]. These membranes were used in the electrodialysis tests and it was found that the membrane exhibited higher mechanical property. It has been concluded from TGA and DMA analysis, that the CAPU/PANI membrane presented better thermal and mechanical performance compared to other membranes. The conducting PANI/COPU membrane with variable conductivities in the range 1.7 x 10-5 S/cm to 2.5 x 10-5 S/cm was synthesized for the purpose of fuel cells and electro dialysis [193]. These membranes were prepared by mixing sulfonated PANI (SPANI) and PANI doped with p-toluene sulfonic acid (PANI-PTSA) with castor oil and further cured with HMDI. The membrane showed high mechanical resistance 32

and was thermally stable up to 220 0C. A cation exchange conductive membrane of PU/PANI were designed by Amado et al. [192]. The membrane were produced by mixing PU with PTSA and CSA doped PANI. Further, they have also investigated the effect of dopant and PANI content on the swelling and electrical conductivity of the prepared membrane. The membrane was used for zinc recovery and were compared to that of commercial membrane Nafion 450, and it was found that the synthesized membrane has better absorbing property. The swelling and zinc transport properties were found to increase with increase in concentration of PANI, which was attributed to the presence of SO3 group and hydrophilic character of dopant. Based on these studies, they have suggested that the PU/PANI membrane can be the good alternative to commercial membrane used in metal finishing industry. Lim et al. have successfully developed a superhydrophobic nanostructured fibrous membrane of PEDOT/PU using electrospining and dilute polymerization techniques [193]. First the backbone of membrane was fabricated using PU polymer via electrospining and then the PU membrane was coated with the nanostructured PANI using dilute polymerization technique. The membrane showed rubberlike stretchability and gas breathability. They have also expected that the membrane will provide new insight to the development of functional clothes, packaging of stretchable electronics, and gas–liquid exchange applications. 6.6 Anticorrosive Coatings Corrosion may be defined as the degradation of materials by chemical or electrochemical reactions with their environment. These metallic corrosion results in massive economic losses per year worldwide [194]. Thus, there is an urgent need to protect the metallic surfaces from their surroundings and enhance their life. Literature reveals that the use of conductive organic coatings is the most intelligent and simplest approach to minimize these economic losses [195]. A large number of articles have been published, on the protection of the metal surfaces under the harsh environmental conditions by using various types of conductive protective coatings

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[196–199]. Among these, the CP/PU based coatings have shown promising protection ability, providing double protection to the coating materials through redox and barrier mechanism [75,170]. PU acts as a barrier coating and prevents the penetration of corrosive ions. On the other hand, CP forms the passive oxide layer between the metal and coating interface and acts as a protective layer until the CP has the ability to continuously undergo for charge transfer at the metal-coating interface [200]. In addition, the strong interaction of CP/PU with the metal surface is another important factor for improving adhesion to metal.

Ahmad et al. have

synthesized polyorthotoulidine (POT) dispersed COPU (i.e. POT/COPU) nanocomposite and studied its corrosion protection performance in acid and saline media [75]. It was found that the POT/COPU nanocomposite showed enhanced corrosion protective performance as compared to that of pristine COPU. Diniz et al. have represented the comparative study of epoxy and polyurethane based conductive composite coatings containing PANI-DBSA as a filler [201]. The corrosion protection ability of these coatings were evaluated by immersing these coatings into salt mist chamber for 30 days of exposure. The results were different for epoxy/PANI-DBSA and PU/PANI-DBSA coated samples. The epoxy/PANI-DBSA exhibited better corrosion protection ability as compared to PU/PANI-DBSA. Reza et al. have provided an ingenious method for the preparation of poly (urethane-co-pyrrole)s CPUPYs [202]. The CPUPYs were prepared by oxidative polymerization of pyrrole with a hydroxyl-terminated polyurethane prepolymer (HPU) in the presence of varying moles of ceric (IV) ammonium nitrate (CAN). They have assessed the corrosion protective performance of poly (urethane-copyrrole)s CPUPYs anticorrosive coatings using tafel polarization and electrochemical impedance spectroscopy. The anticorrosive performance of these coatings was compared with the bare steel, parent PU and neat PPy coated stainless steel and found that CPUPYs coating, prepared using 0.0023 mole of pyrrole and 0.0050 mole of CAN, showed highest conductivity and Rct values. These findings were indicated the good corrosion protection ability of their

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coatings by forming passive metal oxide layer at metal-coating interface. Riaz et al. have reported the comparative study of corrosion protective and corrosion sensing performance of nanostructured methyl orange (MO) doped PANI and camphorsulphonic acid (CSA) doped poly(1- naphthylamine) (PNA) dispersed PU composite coatings [170]. Castor oil and linseed oil were used for the formulation of polyurethane. Nanostructured MO doped PANI was dispersed in castor oil polyurethane (COPU) while nanostructured CSA doped PNA was dispersed in linseed oil polyurethane (LOPU) to obtain the conducting composite coatings. It was found that the CSA acts as a better dopant than MO and CSA-PNA/LOPU nanocomposite exhibits promising corrosion protective performance than MO-PNA/COPU. Alam et al. used a nanotechnological approach to design nanostructured PANI reinforced COPU nanocomposites [203]. The improvement in overall properties of the nanocomposite was observed at lower loading of nanostructured PANI due to the formation of hydrogen bonding with COPU. The conductivity of pristine MO–PANI was found to be 2.1 9 x 10-3 S/cm while that of 0.5-MO– PANI/COPU, 1.0-MO–PANI/COPU, and 2.0-MO–PANI/COPU were found to be 5.79 x10-4, 4.39 x 10-4, and 3.59 x 10-4 S/cm, respectively. Moreover, the author showed that the synthesized nanocomposite exhibits a superior corrosion protective performance. Iribarrein et al. have examined the corrosion resistant property of five commercial paints, four of them were based on polyurethane resin, two organic (PUR-1 and PUR-3) and two aqueous based (PUR-2 and PUR-4) [204]. These four polyurethane resins were modified with the incorporation of 1w % PPy and poly(3-decylthiophene-2,5-diyl) and were compared with those of unmodified polyurethane resins. Poly(3-decylthiophene-2,5-diyl) was used for the organic base polyurethanes i.e. PUR-1 and PUR-3, while polypyrrol was mixed with the aqueous based paints (PUR-2 and PUR-4). They have developed a home-made equipment for performing the corrosion test of these coatings in 3.5% aqueous NaCl solution and 3.0 % H 2SO4 acidulated NaHSO3 aqueous solution. The PPy modified PUR-2 coating showed the best corrosion

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resistance performance as compared to Poly(3-decylthiophene-2,5-diyl) modified PUR-1 and PUR-3. However, PPy modified PUR-4 exhibit the same anticorrosive property as that of unmodified PUR-4. Thus, they concluded that the polyurethane coating without conducting polymers showed fast degradation, while the polyurethane coating with PPy offered high resistance. Rao et al. have reported the anticorrosive properties of novel conductive polyurethanes (CPUs) coatings containing tetra-aniline (TAni) and trianiline (TriAni) oligomers [205]. The corrosion protection efficiency was evaluated by using potentiodynamic polarization in 3.5 % aqueous NaCl solution using I corr and Ecorr value. They observed that the corrosion protective performance of PU containing TAni is better than that of PU containg TriAni. This can be attributed to the presence of higher concentration of TAni in polyurethane. In their further investigation, they have prepared and characterized the conductive composite of polyurethane using p-toluene sulphonic acid doped tetra aniline (TANi-PTSA) as a conductive filler [206]. The conductive composite of TANi-PTSA /PU was prepared with three different composition of TANi-PTSA (i.e. 4.75, 9.0, 13.0). The corrosion resistance performance was evaluated by tafel polarization curve. The I corr and Ecorr value was found to increase with increased concentration of TANi-PTSA. They have also suggested that the prepared composite can be used as anti-corrosive coatings, conductivity-based sensors, antistatic coatings and EMI shielding materials. 6.7 Films The organic molecular and polymeric composite conductors in the form of films ranging thin to thick, find wide industrial applications. Among these, CP/PU composites films have significantly been used in electronic industries. Malmonge et al. have developed PANI dispersed castor oil polyurethane (PANI/COPU) flexible and free standing films in different medium (DMF and aqueous) [89]. The film, synthesized in DMF exhibited higher conductivity (10-2 S/cm) in comparison to that synthesized in aqueous medium (10-4 S/cm). In another study

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they have also reported the synthesis of Castor oil Polyurethane/Poly(o-methoxyaniline) blend films, based on casting method [207]. The synthesized films were characterized by FTIR, UVVis-NIR spectroscopy, and electrical conductivity measurements. Wen et al. have prepared TPU–PPy composites using in situ chemical polymerization of pyrrole inside TPU films. The effect of conducting PPy on the morphology and ionic conductivity of thermoplastic polyurethane (TPU) doped with LiClO4 have also been studied and compared with those of pure TPU system [53]. It was further noticed that only 4.24 % of PPy were able to enhance the thermal and chemical stability of the composite. Pei and Bi used potentiostatic polymerization technique to prepare the highly flexible and mechanically strong PANI-PU composite films [88]. The thermal, mechanical, dielectric and morphological properties of these films were characterized using DMA, UV-Visible spectroscopy and SEM techniques. A PANI/PU concave lense array film was prepared by Xioming et al. [208]. The resultant PANI/PU film exhibits high sensitivity and high stability. The sensitive electrical response is attributed to the rearranged molecular chain of redox PANI powder while the PU doping provide the stability to the film, which enhances the mechanical strength and chemical solubility of the film. Gurunathan et al. have synthesized castor oil-based waterborne polyurethane/polyaniline (COWPU/PANI) conducting films by mixing 2, 4 and 6 wt % of commercially available PANI [209]. Further, they have reported that the synthesized new COWPU/PANI coatings have encouraging antistatic and corrosion protective properties. A light weight film based on pTSA and HCl doped PANI/PU composite was fabricated by Zeghina et al. [164]. The effect of type of dopant, content of PANI and thickness of the film on morphology, dielectric and microwave absorption properties were investigated. The PANI-PTSA/PU films show higher permittivity and better microwave absorbing properties than PANI-HCl/PU for the same weight fraction of PANI. A highly stretchable and elastic PEDOT/PU conductive composite film has been prepared by Hansen and groups [210]. The composite film has high conductivity (120 Scm-1)

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with elastomeric mechanical properties. The film possess high stretching property and found stretchable up to 200%. 6.8 Foams The PU foams are versatile in nature, providing comfort and serves everyone’s daily life in the society. They have been used in the formation of mattresses, furniture, car seats, sponges in kitchen, medical dressing, buildings and many more [211–213]. The conductive polyurethane are found to be the leading member of the various forms of foams, in wide ranging and highly diverse family of polymeric foams. Thus, due to these diverse utility of conductive polyurethane foams, many researchers and industrialists have fabricated the conductive polyurethane foam by incorporating the CPs into PU foams. Fu et al. reported the formation of conductive PPy/PU foams using supercritical carbon dioxide (ScCO 2) to determine the feasibility of replacing the volatile organic content producing organic solvents with that of ScCO2 for impregnating the oxidant into the foam and for removing the byproducts of the pyrrole polymerization reaction from the foams [23]. Conductive composite of PPy/PU Foam was prepared by Vapor Phase Oxidative Polymerization [214]. In this fabrication, PU foam containing FeCl2 and FeCl3 as an oxidant was exposed to the Py vapour. In this fabrication, PU foam containing FeCl2 and FeCl3 as an oxidant was exposed to the Py vapour. The effect of iron chloride on the conductivity of the composite was further studied by varying the ratio of FeCl2-FeCl3. An electrically conductive PANI/PU foams were prepared by Harry et al. [212]. The DC conductivity of PANI in the open cell PU foams were also measured. They suggested that the prepared PANI/PU foams can be used as a packaging materials for electronic components. Some of the important conducting polymers based polyurethane composites along with their synthesis methodology, conductivity and applications are listed in Table 4. 7 Challenges and future perspectives

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The processing and development of various new grade of CP/PU composites with required characteristics and value added properties have attained a very prominent positions in every walk of life. Further, they have achieved a potential scope for their applications at commercial scale in various fields ranging from domestic to industries. However, the processing of CP/PU composites is mainly involved the applications of PANI, PPy, PTh and their derivatives, while the variety of other conducting polymers like polycarbazole, polydiphenylamine, polynaphthylamine etc. have paid less interest. The application of CP/PU composite in many areas (like membrane, films and foams) are also limited. So, this will be an emerging and focus area for future developments. Further, the precursors for PU are mainly based on fossil fuels, which are expected to deplete by near future. Thus, sustainable and renewable moieties like cellulose, bagasse, vegetable oils etc. may act as promising precursors for the development of nontoxic bio-compatible PU. Among these, vegetable oils based polyurethanes can be considered as a potential candidate for the replacement of petro-based PU and may find their commercial applications. It is important to record that the vegetable seeds and their oils are still underutilized. Further, the approach for production of polyurethane via non-isocyanate will provide a greener route for the processing of eco-friendly biocompatible PU. The processing of CP dispersed oil based PU composites are still at laboratory scale. The discussions in the review article revealed that there is a wide scope for research on the development of new CP (modified) dispersed sustainable resource based PU via modern methods. The application of biomaterials in the synthesis of CP dispersed high molecular weight sustainable PU composites, may open the emerging area for future developments. This may also provide a way to use the underutilized precursors in the production of PU and their composite with value added physico-mechanical and chemical resistance properties.

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8. Conclusions Overall, the proposed review article provided an overview on the development of different CP/PU composites by chemical and electrochemical approaches. Various integrated characterization techniques such as FTIR, NMR, XRD, SEM and TEM were also discussed in detail to give an insight to the dispersion and formation of CP/PU composites. The application of CP/PU composites in different fields like EMI shieling, sensors, biomedical, SMP, anticorrosive coatings, membranes, films and foams have also been presented. Additionally, we have discussed the existing challenges and future prospects related to the processing of CP/PU composite.

Acknowledgment: One of the authors acknowledges University Grants Commission, for providing financial assistance through Maulana Azad National Fellowship under award letter no. F1-17.12014-15 MANF. The author further wishes to express her thanks to Prof. Jawaid Ahmad Khan, Department of biosciences, Jamia Millia Islamia, for his kind suggestions and encouragements.

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51

Figure captions Fig. 1. Structures of some important conducting polymers.

52

Fig. 2. Different methods for the synthesis of CP/PU composites.

53

Fig. 3. General reaction scheme for the synthesis of CP/PU composite by melt mixing.

54

Fig. 4. Schematic illustration of solution blending method.

55

Fig. 5. The general schematic representation of in situ polymerization.

56

Fig. 6. General structure of CP/PU nanocomposite by grafting technique. Adapted from ref. [96].

57

Fig. 7. Different types of CP/PU composites.

58

Fig. 8. Schematic representation of core-sheath PU-PEDOT nanofibre. Adapted from ref. [135].

59

Fig. 9.

13

C NMR spectra of (a) PANI and (b) PANI/PU. Reproduced with permission [20].

Copyright 2009, Elsevier.

60

Fig. 10. XRD of (a) Pure COPU (b) 0.5-MO-PANI/COPU (c) 1-MO-PANI/COPU (d) 2-MOPANI/COPU (e) Pure MO-PANI. Reproduced with permission [78]. Copyright 2009, John Wiley and Sons.

61

Fig. 11. SEM images of (a) TPU and (b) PPy/TPU composite. Reproduced with permission [53]. Copyright 2001, Elsevier.

62

Fig. 12.1. TEM images of (a) MO-PANI and (b) MO-PANI/PU nanocomposite. Reproduced with permission [166]. Copyright 2008, John Wiley and Sons.

Fig. 12.2. TEM Images of (a) TPU/2.5 wt % PPy.DBSA (b) TPU/30 wt % PPy.DBSA. Reproduced with permission [99]. Copyright 2011, American Chemical Society

.

63

Fig.13. Applications of CP/PU composites.

64

Fig. 14. EMI shielding mechanism of PUPCNT composite. Reproduced with permission [138]. Copyright 2015, Royal Society of Chemistry.

65

Fig. 15. Schematic representation of conformational change of PANI/PU composite induced by chloroform. Reproduced with permission [168]. Copyright 2013, Royal society of Chemistry.

66

Fig. 16. Micrographs of 3T3-L1 adipocytes cells grown on (a) control (b) PU (c) PU + PA and (d) PU + PA + NP. Reproduced with permission [186]. Copyright 2011, Elsevier.

67

Fig. 17. Electroactive shape recovery behavior of PU/PPy composite. (Adapted from ref. 137).

68

_

+ COONH(CH2CH3)3

_ + COOH

1.5 HCl Surface modification _

+ COOH3N NH2

/H2O

(NH4)2S2O8+HCl+H2O Oxidative Polymerization

_

+ * COOH3N

H

H

H

H

N .+ _ Cl

N

N .+ _ Cl

N

*

Scheme 1 The preparation process of PANI graft WBPU (adapted from ref. [96])

69

N

N

H

C

N

N

n NH

m

O

NH CH3

O

C O (CH2)6 C

O

NH

O C

H

N

N

NH CH3

N

N

n

Scheme 2 The probable molecular structure of PANI/PU composite (adapted from ref. [111])

70

O

O O-CH2-CH2

O

C

CH2

N

N

C

H

H

n

N N N

m

m

Ce(III)

Ce(III) PU-PPy interaction

PU-PPy interaction

O-CH2-CH2

m

O

O

H

C

N

O CH2

N

C

H n

Scheme 3 Interaction of PPy and Ce with PU matrix (adapted from ref. [52])

71

CH 3

NH

O CH 3

C

O

NH C

O

S

O

S

C

NH

O NH

NH

NH

C

S

S

3

S

NH

Urethane linkage

CH

O

CH 3

C

S

O

O

C O

NH

O

S

NH

S S S

O

S

C

O

NH

C

O NH

S

O

S

C O

N

S

N H

H

O C

S

MWCNT s/PPy

3

S

S

C H

O

S

NH2 m odified

S

O

S S

C

S

O

N H

N H

S

C

NH

O

S

CH 3

Scheme 4 The interaction of modified MWCNTs with PU/PTh composite [46].

72

Table 1. Advantages and disadvantages of CP/PU composite prepared by different methods.

Synthesis Methods

Descriptions

Advantages

Disadvantages

Ref

Melt Mixing

This method involves the mixing (i) More economical and of CP particles (fillers) in dried ecofriendly as it does not powder form with the melted require any volatile organic polymer matrix under high shear solvents. mixing using twin screw (ii)Mainly used for large scale extruder. productions.

Solution Blending

Dissolution of CP and PU in a (i)Better particle dispersion than (i)Limited solubility of CPs and PU 104,106 common solvent followed by melt mixing. in organic solvents restricts its solvent evaporation. commercialization. (ii)Solvent removal is another major issue. (iii) Emission of toxic VOCs during solvent removal causes various health hazards. It involves the mixing of (i) Single step reaction. (i)It reduces the physical property as 102 monomer with PU matrix or CP (ii)Cost effective as there is no compared to that of solution with polyol followed by their need of additional processing step blending, due to weak hydrogen polymerization. for composite formation. bonding between PU and CPs.

In situ polymerization

73

(i) Fail to achieve the homogeneous 102-105 dispersion of high content of filler due to heavy viscosity of melt PU. (ii) Suitable only for the matrix that are prone to thermal degradation.

Electrochemical polymerization

The composites during this (i)The process is cleaner and helps (i)This Process is expensive. 89,90 synthesis get deposited on the to form free standing film easily. (ii) Here the yields are restricted by surface of the electrode. the area of the electrode.

Grafting

PU backbone is functionalized (i) The reaction setup is simple, (i)This process needs a strict control 102,107 by CP chains. The NCO various substrates for different of the amounts of initiator and terminated pre-polymer is applications can possible. substrate. reacted with the amine capped CPs.

74

Table 2(a) Effects of PANI and their derivatives on the mechanical, thermal and electrical properties of PANI/PU composites

S. No.

PANI/PU

CP loading (wt %)

Synthesis Method

1.

PANI/PU/PMMA

12.5

Sequential polymerization

2.

POT/PU

40

3.

PANI-CNF/PU

10

Mechanical properties

Thermal Properties

Electrical Properties

Ref

Tensile strength Thermally stable increases up to 1.38 increases up to 680 0C MPa while elongation at break decreases

Conductivity of the composite increases to 3.78 x 10-2 S/cm, dielectric constant increases up to 6.35

[49]

Solution blending

Modulus, % elongation and tensile strength, was maximum at 2.5%, 5% and 10% respectively

Thermal stability increases with increasing POT concentration

Conductivity increases (3.7x 10-3 Scm-1) with increase in POT concentration

[77]

Solution blending

Young’s and elastic modulus increases while elongation at break decreases

Overall thermal properties were found to be increased

Composite at 4% loading shows the minimum electrical resistivity 2.7x1010 after that it starts increasing

[80]

75

4.

PANI/PU

12

In situ polymerization

Tensile strength and elongation at break increases with PANI content due to increasing interaction of PANI and PU

5.

PANI/PU

10

In situ polymerization

Stress-strain reduces whereas shear modulus was 2.5 times higher than pure PU

--------------

Conductivity was found to be less than 0 – 7 Scm-1, electrical anisotropy decreases with increase in PANI content

[86]

6.

PANI/PU

-----

Electrochemical polymerization

Tensile strength, stress-strain and % elongation of PANI/PU composite are very close to PU

----------------

Composite attains maximum conductivity up to 1 Scm-1

[91]

7.

PANI/PU

30

Grafting

Young’s modulus increased by 9 times, while tensile strength and elongation at break was decreased

Conductivity increases from 10-14 to 10-3 Scm-1

[95]

76

-------------

Tg value and heat capacity changes. This is due to that PANI grafted on PU backbone make composite harder and less deformable

[82] Surface resistivity first increases for 10 wt % and then decreases for 12 wt % of PANI.

8.

PANI/PU

40

In situ polymerization

9.

PANI/PU

2

Solution blending

10.

PANI/PU

15

11.

PANI/PU

12.

PANI/PU-NC (NC=cellulose nanofibers)

-------------------

---------------

PANI/PU has 2 orders higher conductivity than pure PU

[101]

Young’s modulus increases on the addition of PANI

Thermal stability, melting temperature Tm and enthalpy change increases with increasing PANI content

Permittivity, conductivity and dielectric constant increases with increase in PANI content

[113]

Solution blending

---------------

Composite possess high thermal stability

Conductivity increased to 8.4 x10-8 Scm-1

[114]

30

Solution blending

Possess good mechanical properties

Glass transition temperature increases with increase in PANI content

Conductivity of composite increases to 10-4 Scm-1

[116]

5

Solution blending

Elastic and storage modulus of the composite increases with increased loading of PANI

Glass transition temperature of composite increases slightly

77

---------------

[143]

13.

PANI/PU

90

Solution blending

Tensile strength first increases due to interpenetrating effect then decreases due to rigidity and brittleness

Glass transition temperature increases with the increased concentration of PANI content

Conductivity increased up to 31.2 Scm-1

[144]

14.

PANI/PU

----

In situ polymerization

The value of average tensile strength and % elasticity of composite was 93 MPa and 14 respectively

------------------

Conductivity reaches up to 0.43 Scm-1

[145]

15.

PANI/SiO2/PU

0.9

------

Stress-strain curves showed elastomeric behaviour, tensile strength also increases due to the presence of urea group in the composite

Composite having higher concentration of PANI/SiO2 Exhibit high Tg values

Surface resistivity of composite reached to 1012 Ω/Sq

[146]

16.

PANI/PU

10

In situ polymerization

-------------------

Electrical resistivity reduces to 106 Ω/Sq, thus, conductivity reaches to 2.99x10-5 Scm-1

[147]

--------------

78

17.

PANI/PU

30

In situ polymerization

18.

PEG/PANI/PU

2

-----------

19.

PANI/PU

2

Grafting

--------------

Thermal stability increases with the addition of PANI

Composite showed the conductivity up to 5x10-5 Ω-1 cm-1

[148]

Young’s modulus and tensile strength increases while elongation at break decreases due to the increase in rigidity at higher concentration of PANI

Tg and Tm values decreases

-------------------

[149]

--------------------------

Thermally stable increases up to 300 0C

Conductivity increased to 10-1

[150]

Scm-1 20.

PANI/PU-Fe3O4

15

-----------

Possess high modulus and high impact strength of 4875 KJ/m2.

79

-----------------------

--------------------

[151]

21.

PANI/PU

10

Solution blending

Storage and loss modulus increases

Stable until 220 0C

5 x10-5 Scm-1 of conductivity was obtained

[152]

22.

PANI/PU

30

Solution blending

Overall mechanical properties were increased

Tg values shifted towards lower values than that of PU

--------------------

[153]

23.

PANI/PU

5

Solution blending

Tensile and impact strength decreases with PANI content

Thermal stability Conductivity increases with increase Increases with PANI in PANI content content (10-9 to 10-3 Scm-1)

[154]

24.

PANI/WPU

75

Solution blending

Tensile strength and hardness first increases from 0.1 to 1% addition of PANI then decreases. This may be due to the defective structure of PANI/WPU

Tg value shifted to a bit lower temperature, which indicates that the WPU is slightly compatible with PANI

0.33 Scm-1 of conductivity was shown by the composite containing 75% PANI

[155]

25.

PANI-DC/WBPU

34

Solution blending

Tensile strength, % elongation and hardness decreases with increase in PANI content

Tg value almost same, (not changes with PANI)

Conductivity reaches to 8.3x10-2 Scm-1

[156]

80

26.

PDPA/PU

------------

In situ polymerization

----------------

81

Tg values increases from -42.7 to -21.8 oC due to hydrogen bonding interactions

Composite showed 1 [157] fold increase in conductivity due to the hydrogen bonding interactions between the groups of PU and PDPA

Table 2(b) Effects of PPy and their derivatives on the mechanical, thermal and electrical properties of PPy/PU composites

S. No.

PPY/PU

CP loading (wt %)

3.

Properties

50

In situ polymerization

PPy.TPU/

4.24

In situ polymerization

-----------------

Melt blending

Electrochemical polymerization

LiClO4/PC

Mt.PPy.DBSA/ TPU

30

PPy/PU/PAAm 4.

Mechanical

PPy/PU 1.

2.

Synthesis Methods

-------

Thermal properties

Electrical Properties

Ref

AC conductivity and dielectric constant increases with increasing the loading of Py

[52]

Composite has better thermal stability than PPy but comparable to TPU

Temperature dependent conductivity increases with increasing the quantity of conducting polymers

[53]

Storage and loss modulus increases with the loading of Mt.PPy.DBSA

-------------------

Conductivity reaches to 1.5x10-2 Scm-1

[69]

Young’s modulus is similar to PU/PAAm, elongation at break decreases while

No effect of PPy on the thermal decomposition of the composite

Conductivity of the composite obtained up to 100 Scm-1

[90]

Stress-strain value The value of Glass increases with transition increase in Py temperature of concentration composites are increased

82

tensile increases PPy/PU

-------

Electrochemical polymerization

PPy/CWPU

20

In situ polymerization

-----------------

Composite showed better thermal stability than the pristine one

Resistivity decreases from 1700 Ω.cm to 180 Ω.cm

PPy-BF/PU

30

In situ polymerization

Composite possess 268% higher tensile strength value than that of pure PU at 25% PPy-BF after that it was decreased

----------------------

[127] Electrical resistivity was -5 found to be 1.8x10 Ω.cm, which was 108 fold lower than that of PU

5.

6.

7.

strength

Tensile strength -------------------increases from 44 to 592 psi while elongation increases from 3 to 70%

83

[92] Conductivity of composite reaches up to 8 Scm-1

[122]

PPy/PU

----

Electrochemical polymerization

Tensile strength, -------------------elongation at break and modulus at 4% decreases on the addition of PPy

Conductivity of the composite ranges from 10-4 to 1 Scm-1

PPy/PU

20

In situ polymerization

Young’s modulus increases up to 60% by increasing the concentration of PPy

Tg and Tm values are shifted to higher and lower values with increased concentration of PPy

Dielectric constant of composite, at 20 % loading of PPy reaches to 7000

8.

9.

[140]

PPy/PUA

0.04

Electrochemical polymerization

------------------

Composite shows better thermal stability

Composite showed 4.5x10-6 Scm-1 conductivity

PPy/PU

------

In situ polymerization

------------------

Composite exhibit enhanced thermal stability

Possess high value of [142] conductivity(10-1Ω-1cm-1)

10.

11.

[139]

84

[141]

Table 2(c) Effects of PTh and their derivatives on the mechanical, thermal and electrical properties of PTh/PU composites

S. No.

PTh/PU

CP loading (wt %)

Synthesis methods

Mechanical property

Thermal property

1.

PDPA/PU,PEDOT/ PU, PTh/PU and PANI/PU

-------

In situ polymerization

----------------------

---------------------

2.

P3HT/PU

2.5

3.

PEDOT/PU-GNP and PEDOT/PU

2.5

4.

PCNT/PU

------

-------------

Composite shows high tensile strength (13.4 MPa) and high modulus (15.3 MPa)

Reduces the thermal stability of the composite

Electro spinning and vapours phase polymerization

Incorporation of GNP into PEDOT/PU enhanced the breaking stress and modulus value

In situ polymerization

----------------------------

85

Electrical property

PANI/PU has highest conductivity and dielectric constant

Ref

[84]

--------------

[133]

PEDOT/PU has lower thermal stability than Pure PU, while PEDOT/PU-GNP has high thermal stability

Electrical conductivity of PEDOT/PU-GNP is higher than PEDOT/PU, while PEDOT/PU shows better actuation behavior than PEDOT/PU-GNP

[135]

Thermal stability increases on adding PCNT into PU

Conductivity of composite reaches up to 5.3x10-1 Scm-1

[138]

Table 3. Infrared spectra of MO-PANI/COPU Functional

COPU

MO–

0.5-MO–

1.0-MO–

2.0-MO–

PANI

PANI/COPU

PANI/COPU

PANI/COPU

3432

3350

3255

3130

3462

3333

3233

3130

3080

1744

----------

1740

1731

1721

Group NH-

stretching ---------

(cm-1 ) OH-

stretching

(cm-1 ) NHCOO vibration(cm-1 )

86

Table 4 Synthesis, conductivity and applications of CP/PU composites. S. No.

CP/PU composites

1.

PANI/PU

2.

Conductivity

Synthesis Methods

Applications

Ref

0.023Ω-1 cm-1

in situ polymerization

Gas sensors

[168]

PANI-PPY/PU

8 x 10-5 S cm-1

__________

EMI

[178]

3.

PANI/PU

__________

Resistivity assessment technique

Gas sensors

[215]

4.

PANI/PU

0.43 S cm-1

In situ polymerization

Sensors

[145]

5.

PANI/PU

1.65x10-2 S cm-1

Solution casting

Membranes

[169]

6.

PANI/PU

10-2 Scm-1

Casting

Films

[89]

7.

PANI/PU

1.296.94x10−6 Scm−1

In situ polymerization

Shape memory polymer

[136]

8.

MO-PANI/PU

3.59 x 10-4 Scm-1

Solution blending

Corrosion Protection

[78]

9.

PANI-CNF/PU

3.7 x 10-11 Scm-1

Solution blending

Shape memory polymer

[80]

9.

POT/PU

5.7x10-4Scm-1

Solution blending

Corrosion Protection

[75]

10.

PPy/PU

2.3 x 10-6 S cm-1

In situ polymerization

Tissue engineering

[187]

87

11.

MWCNT-PPy/PU

0.098 S/cm

In situ polymerization

Shape memory polymer

[216]

12.

PPy/MWCNT/Gl uox/PU

-------------

------------

Biosensor

[181]

13.

PPy/PU

__________

In situ polymerization

Pressure and chemical sensors

[217]

14.

PPy/PU

7.29x10 -2 Scm-1

Electrochemical Polymerization

Films

[139]

15.

PPy/PU

10-5 Scm-1

__________

Films

[218]

16.

PPy/PU

1.41x10-3 Scm-1

Chemical polymerization

Pressure sensor

[219]

17.

PPy/PU

1x10-7 Scm-1

In situ polymerization

Foams

[220]

18.

PEDOT-CNT/PU

2.7 Scm-1

Solution Casting

EMI

[138]

19.

PTh/PU

__________

Spin Coating

Membrane

[221]

20.

PTh/PU

5.19x10-6 Scm-1

Spin Coating

Membrane

[222]

21.

PEDOT:PSS/PU

30 Scm-1

Wet Spinning Technique

Strain Sensor

[134]

88