Nano CaCO3 imprinted starch hybrid polyethylhexylacrylate\polyvinylalcohol nanocomposite thin films

Carbohydrate Polymers 139 (2016) 90–98

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Nano CaCO3 imprinted starch hybrid polyethylhexylacrylate\polyvinylalcohol nanocomposite thin films Kalyani Prusty, Sarat K Swain ∗ Department of Chemistry, Veer Surendra Sai University of Technology, Sambalpur 768018, Odisha, India

a r t i c l e

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Article history: Received 16 September 2015 Received in revised form 13 November 2015 Accepted 4 December 2015 Available online 12 December 2015 Keywords: Nano composite film Topology Thermal conductivity Antimicrobial properties Tensile strength

a b s t r a c t Starch hybrid polyethylhexylacrylate (PEHA)/polyvinylalcohol (PVA) nanocomposite thin films are prepared by different composition of nano CaCO3 in aqueous medium. The chemical interaction of nano CaCO3 with PEHA in presence of starch and PVA is investigated by Fourier transforms infrared spectroscopy (FTIR). X-ray diffraction (XRD) is used in order to study the change in crystallite size and d-spacing during the formation of nanocomposite thin film. The surface morphology of nanofilms is studied by scanning electron microscope (SEM). The topology and surface roughness of the films is noticed by atomic force microscope (AFM). The tensile strength, thermal stability and thermal conductivity of films are increased with increase in concentrations of CaCO3 nanopowder. The chemical resistance and biodegradable properties of the nanocomposite thin films are also investigated. The growth of bacteria and fungi in starch hybrid PEHA film is reduced substantially with imprint of nano CaCO3 . © 2015 Elsevier Ltd. All rights reserved.

1. Introduction Polymer nanocomposites are involved in a great attention during last two decades for their academic importance and industrial applications. Nanocomposite thin films (NCTF) consist of an ultrathin barrier layer of a polymer chain with reinforcement of nanoparticles. The incorporation of nanostructured material would be eventually affects the physicochemical properties of NCTF. NCTF with nanofillers have attracted wide scientific and industry report due to the superior properties contributed by the nanofillers. In present study, starch is used as a binder and an active agent for making the material biodegradable in nature. Starch is consists of two anhydroglucoses, amylose and amylopectin where, anhydroglucose polymers are arranged into a semi crystalline granular structure (Warren, Royall, Gaisford, Butterworth, & Ellis, 2011). The presence of pores in the granule surface and its interaction with amylase is a factor affecting the binding nature of starch. The binding property of starch with substrate is due to the loss of crystalline structure inside the starch granules. Hence binding of starch with substrate increases the biodegradability of the material, when it is hydrolyzed due to carboxymethylation mechanism. However, the limitation of using starch alone is due to its slow compatibility with hydrophobic polymers and having flammability properties. PVA is chosen as one of the component in present study due to its

∗ Corresponding author. Tel.: +91 9937082348; fax: +91 6632430204. E-mail address: [email protected] (S.K. Swain). http://dx.doi.org/10.1016/j.carbpol.2015.12.009 0144-8617/© 2015 Elsevier Ltd. All rights reserved.

excellent film forming properties along with emulsifying surfactant and adhesive behaviors. PVA has the properties of non-toxic, odorless having high flexibility and tensile strength (Gokmen et al., 2015). Therefore, PVA is used as an additive in present investigation in order to improve the compatibility of PEHA matrix. In literature PVA has been used as an additive in order to study heat sealing property of the materials (Su et al., 2010). Out of different acrylic polymers, polyethylhexylacrylate (PEHA) is important which is used in differential industrial applications. But its application becomes limited because of its non-biodegradable nature. Polysaccharide polymers like starch, chitosan and alginate are commonly used as host matrices (Brayner, Vaulay, Fievet, & Coradin, 2007; Djokovic et al., 2009; Vigneshwaran, Nachane, Balasubramanya, & Varadarajan, 2006; Vimala et al., 2010; Wei, Sun, Qian, Ye, & Ma, 2009) for degradation of polymers. Starch is one of the promising and popular biodegradable polymers obtained as granule sheet plant. However, there are several strong limitations to develop a starch-based film as it has poor tensile properties due to their hydrophilic nature and sensitivity to moisture content. One of the methods to overcome this limitation is to improve the strength of starch matrixes with organic or mineral fillers (Cyras, Manfredi, Ton-That, & Vazquez, 2008). Nanoparticles are novel type of filler materials that displays a higher level of efficiency and improved the physicochemical, mechanical properties of starch-based films. CaCO3 is one of the important nanoparticles which show unique properties like thermal conductivity, high melting decomposition temperature, high thermal stability, and oxidation resistance and in lubricating

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Scheme 1. Scheme for the synthesis of starch hybrid PEHA/PVA–CaCO3 nanocomposite thin films.

materials as compared to other nano particles (Hosoda & Kato, 2001). Further, CaCO3 nanoparticles are used as fillers in making of composite materials like plastics and paper industry (Kim, Douglas, & Gower, 2007). In present study, CaCO3 is used as reinforcing agent in order to improve the properties of starch hybrid PEHA/PVA composite thin films. Now a day composite based on polymers and inorganic nanoparticles have focused a lot of attention and interest because of their academic and industrial applications. Nanocomposites synthesized from polymers, biopolymers and copolymers with reinforcement of inorganic nanoparticles are of great interest for packaging material with enhanced physical, thermal (Swain, Dash, & Pradhan, 2014a), mechanical (Kisku, Das, & Swain, 2014), gas barrier properties (Pradhan, Behera, & Swain, 2014), chemical resistance, fire retardant (Swain et al., 2014a; Swain, Patra, & Kisku 2014b) and processing characteristics (Li, Chen, Li, & Sun, 2011b). Although preparation, characterization and study of different properties of inorganic nanopowder incorporated polymer and copolymer thin films are not rare, however the preparation of CaCO3 dispersed starch hybrid PEHA/PVA composite thin films are new in the literature. In present study, we have synthesized starch hybrid PEHA/PVA–CaCO3 thin film is a low cost in situ green polymerization technique. The chemical interaction, morphology, topology and surface roughness of synthesized nanocomposite films are studied. The influence of CaCO3 nanopowder on the chemical–physical properties of the polymeric matrix is studied for structural, thermal conducting and tensile properties. In present investigation, the study of antibacterial properties in combination with chemical resistance, biodegradability, tensile strength, thermal conductivity and thermal stability shows the possibility for packaging applications.

2. Experimental 2.1. Materials The monomer, 2-ethyl hexyl acrylate (EHA) is purchased from Sisco Research Laboratory (SRL) Mumbai; India. It is washed

with 3% ortho phosphoric acid and with 5% sodium hydroxide to remove inhibitor followed by washing with distilled water. The washed monomer EHA is dried over calcium chloride and stored in refrigerator before use. The polyvinyl alcohol (PVA) is purchased from Loba Chemi (India). The surface active radical initiator ␣,␣ -Azoisobutylronitrile (AIBN) (Spectrochem, 99.9%) is used as received. Potato starch is purchased from Fischer Scientific Pvt. Ltd, Mumbai, India. Calcium carbonate (CaCO3 ) nano powder is obtained from Sisco Research laboratories Pvt. Ltd, India with average diameter of 50 nm. The water used for the experiment is distilled two times over alkaline permanganate solution. 2.2. Methods 2.2.1. Preparation of thin film The starch hybrid PEHA/PVA composite thin film with reinforcement of CaCO3 can be prepared by in situ polymerization method using aqueous solution. EHA (4.2 × 10−3 ), AIBN (4 × 10−3 ), PVA and starch in the ratio of 20:80, 40:60, 60:40, 50:50 and 80:20 are prepared in a conical flask under 60 ◦ C temperatures and stirred for 40 minute. Then calculated amount of CaCO3 (1 wt%, 3 wt%, 5 wt% and 8 wt%) is added to starch hybrid PEHA/PVA solution under same temperatures and stirred for 20 min. Then the CaCo3 reinforced starch hybrid PEHA/PVA nanocomposites gel is poured in to a petridishes to make the films. A round, transparent, thin and flexible nanocomposites film is obtained after drying in a hot air oven at 70 ◦ C. The structural representation of synthesis process is represented as Scheme 1. 2.3. Characterization techniques FTIR spectra of nanofilms (in the form of KBr pellets) are recorded by using a shimadzu IR affinity-I Fourier transform infrared spectrophotometer in the range of 4000 cm−1 to 400 cm−1 . X-ray diffraction patterns are obtained using a Rigaku X-ray machine operating of 40 kV and 15 MA. The morphology and dispersion of nano CaCO3 in starch hybrid PEHA/PVA thin films are

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investigated using scanning electron microscopy (SEM) utilizing JEOL-JSM-5800 model. The topology of thin film is investigated using atomic force microscope (AFM) utilizing VEECO DICP II auto probe (model AP 0100). The mechanical properties are measured by using an Instron machine (canton, MA, USA) of room temperature with crossed-head speed of 1.5 mm\min. The biodegradability properties are investigated by activated sludge H2 O. The activated sludge H2 O is collected from tank areas receiving toilet and domestic waste water. The sludge water contains many microorganisms (bacteria, fungi, yeast, etc.) responsible for the biodegradation of waste materials. Starch hybrid PEHA\PVA–CaCO3 thin film is investigated for 90 days using sludge water. Further, chemical resistance of the synthesized thin films toward chemicals is investigated for 90 days according to ASTM D 543-87. Thermal coefficient (K) of the nanocomposites thin film is measured by Disc apparatus, NV 6044 as per ASTM D 5930. Thermal conductivity of the nanocomposite thin films is calculated by the equation, K = [Msd (d/dt)]/A( 1 −  2 ), where  1 is the boiling point of water and  2 is the steady temperature. The thermo gravimetric analysis (TGA) of the prepared samples is achieved by using a TGA apparatus model DTG-60 by shimadzu corporation, Japan. The prepared samples are heated under nitrogen purge with heating rate of 10 ◦ C/min. Antibacterial activity of starch hybrid PEHA/PVA–CaCO3 thin film composite is determined by the agar cup diffusion method against four bacteria (Escherichia coli (ATCC® 25922TM ), Bacillus subtilis (ATCC® 23857D-5), Staphylococcus aureus (ATCC® 25923TM ), and Pseudomonas aeruginosa (ATCC® 27853D-5TM )) and three fungi (Candida krusei (ATCC® 14243TM ), Candida viswanathii (ATCC® 38835TM ) and Candida albicans (ATCC® MYA-2876TM )) as test pathogens. All the test microorganisms are obtained from the Institute of Microbial Technology (IMTECH), Chandigarh, India. Agar cups are prepared by scooping out the media with a sterile corn borer (7 mm in diameter). The cups are then filled with of 0.0167 g of the prepared sample dissolved in 3 ml dimethylsulphoxide (DMSO). The plates are then incubated at 36 + 1 ◦ C for 24 and 48 h, respectively, for bacterial and fungal pathogens. After the specified incubation period, the zone of inhibition was recorded and compare with the control (i.e. a cup fill with just DMSO solution). Three replicates are maintained in each case. It is noticed that starch hybrid PEHA/PVA–CaCO3 nanocomposite thin films has antibacterial properties unlike the starch matrix. The activities of different bacteria and fungi are leveled.

Fig. 1. FTIR spectra of Starch, PVA and CaCO3 , PEHA, starch hybrid PEHA/PVA and starch hybrid PEHA/PVA composite thin films with 5 wt% of CaCO3 .

also present in FTIR of starch hybrid PEHA\PVA and starch hybrid PEHA\PVA–CaCO3 . Presence of both carbonyl peak of PEHA and hydroxyl peak of PVA and starch confirmed the formation of starch hybrid PEHA\PVA grafting. In FTIR of starch hybrid PEHA\PVA–CaCO3 , it is noticed that the peak at 713 cm−1 of calcite and 1750 cm−1 peak of carbonyl stretching along with the hydrogen bonded hydroxyl stretching at 3300 cm−1 are appeared. The right shifting of OH stretching to lower wave number is due to intermolecular hydrogen bonding and interaction of nano CaCO3 with starch hybrid PEHA\PVA matrix. Therefore the chemical interaction of nano CaCO3 with starch hybrid PEHA\PVA matrix is evidenced by the FTIR study. The present results are in accordance with the results reported elsewhere (Priya, Gupta, Pathania, & Singha, 2014). 3.2. X-ray diffraction (XRD)

3. Results and discussion 3.1. Fourier transform infrared spectroscopy (FTIR) The FTIR spectra of nano CaCO3 , starch, and PVA, PEHA, starch hybrid PEHA/PVA and starch hybrid PEHA\PVA–CaCO3 nanocomposite films are compared in Fig. 1. From both FTIR spectra of CaCO3 and starch hybrid PEHA\PVA–CaCO3 nanocomposite films, the sharp peak of 713 cm−1 is due to the presence of calcite peaks. The peak of 1750 cm−1 is appeared for C O stretching in the FTIR spectra of PEHA, starch hybrid PEHA/PVA and starch hybrid PEHA\PVA–CaCO3 nanocomposite films. The FTIR results of CaCO3 are similar to the reported results (Vagenas, Gatsouli, & Kontoyannis, 2003). The strong peak of 3350 cm−1 is due to OH group of PVA, whereas the peak of 1020 cm−1 is due to C O bending vibration. In FTIR of starch, the C O stretching is appeared at 1057 cm−1 in addition to the OH group of 3350 cm−1 . The strong sharp peak of 1750 cm−1 of PEHA is due to carbonyl peak which confirms the presence of PEHA in FTIR of starch hybrid PEHA/PVA. Further, the hydroxyl peak of both PVA and starch at 3350 cm−1 is

The structural properties of nano CaCO3 , starch, PVA, Starch hybrid PEHA/PVA and starch hybrid PEHA\PVA–CaCO3 are studied by XRD are shown in Fig. 2. The nano CaCO3 shows the crystalline peaks at 2 values of 23.10◦ , 29.75◦ , 36.17◦ , 39.20◦ , 43.22◦ , 47.65◦ and 48.86◦ due to the different phase of CaCO3 . However, the distinct peak at 2 values of 29.75◦ in XRD plot of CaCO3 is due to the calcite peak. The peaks at 2 values of 16.65◦ and 20.09◦ , respectively in the starch and PVA are due to corresponding crystalline peaks. In case of nano thin films, peaks of CaCO3 are appeared at same position with less intensity. The crystallinity of thin films is reduced by the addition of nano CaCO3 with copolymer matrix. The sizes measured from XRD by using Scherer’s formula are crystallite size of CaCO3 . The crystallite sizes of CaCO3 are increased slightly due to interaction of CaCO3 with that of in starch hybrid PEHA/PVA matrix. The enhancement in crystallite size is due to slight growth of grain. The present results are in accordance with the results reported earlier (Xu, Han, & Cho, 2004). Further, XRD is used to characterize the physical structure of CaCO3 and starch hybrid PEHA/PVA nanocomposite film. The average crystallite size of crystallinity is determined by using Scherrer equation,  = K/ˇcos; where  is crystalline size; K is dimensional shape factor with a

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Fig. 2. XRD Pattern of PVA (a), nano CaCO3 (b), starch (c) and Starch hybrid PEHA/PVA (d) composite thin film with 5 wt% of CaCO3 (d-spacing of crystalline size ()).

typical value of 0.89;  is the wavelength of the X-ray of Cu K␣ radiation and ˇ is the full width half of the maximum intensity (FWHM). The d-spacing is calculated using the Bragg’s equation, n = 2dsin; where d is the space between one consecutive layer. The crystallite size and d-spacing of different 2 value are summarized as the inset tables of Fig. 2. XRD pattern of starch hybrid PEHA/PVA nanocomposite films with nano CaCO3 (Fig. 3d, inset table) is explaining that an increase of nano CaCO3 loading correspond to an enhancement in average crystallite size from 0.79 nm to 1.17 nm. That means average crystallite size of nano CaCO3 is increased in composite due to interaction of CaCO3 with starch hybrid PEHA/PVA matrix. This positive effect is due to different factors including the important role of patterned of starch hybrid nanocomposite film in the formation of nanostructures through hydrogen bonding, interfacial interaction of CaCO3 with polymer matrix along with the ability to control and enhance the surface tension of liquids in solution techniques. In literature the average crystallite size of sodium montomorillonitrile is increased when it is forming composite with

PVA matrix. The explanation related to the reason for increase of crystallite size is similar to the present explanation (Gokmen et al., 2015). In Fig. 2b and d (inset table), XRD peaks of nano CaCO3 are shifted to lower 2 value in composite. As a result at which dspacing is due to each peaks increases in composite as compared to pure nano CaCO3 . Hence starch hybrid PEHA/PVA nanocomposite film with dispersion of nano CaCO3 are form due to intercalation and partial exfoliation. 3.3. Microscopic analysis of thin film 3.3.1. Explanation of scanning electron microscope (SEM) The nanostructure analysis of thin films along with crystalline pattern is established in Fig. 3. The SEM micrographs of the fractured surfaces of the nanocomposites thin films containing 5 wt% of the calcium carbonate nanoparticles are shown as example. It is observed that starch flakes are noticed in the SEM images of starch hybrid PEHA/PVA composites (Fig. 3). Further, it is observed

Fig. 3. SEM of starch hybrid PEHA/PVA (PVA/starch: 60/40) and nano CaCO3 imprinted starch hybrid PEHA/PVA (PVA/starch: 60/40) composite thin films as a function of CaCO3 concentration of 5 wt%.

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Fig. 4. AFM images of starch hybrid PEHA/PVA nanocomposite thin films (5 wt% of nano CaCO3 ) at different phases (a and b), Fig. 2d pictures of AFM (c and d).

that the porosity of copolymer is decreased due to incorporation of nano CaCO3 . The nano CaCO3 occupied the position in the micro void of starch hybrid PEHA/PVA matrix. Moreover, the mobility of copolymer chain is slightly restricted due to creation of hindrance by distribution of nano CaCO3 which is the reason for decrease the porosity of nanocomposites films. Nano CaCO3 permeated into the molecular chains of starch and PVA, the gel network structure is formed through the hydrogen bonding occurred by combining the OH of nano CaCO3 with that of starch\PVA as shown in Fig. 3b. This result is in agreement with the results of H-bonding obtained in the explanation of FTIR. The gel network structure is formed by combining nano CaCO3 with starch hybrid PEHA/PVA due to plenty of OH on the nano CaCO3 (Fig. 3b). This represents a porous morphology with pore sizes varying in the range 25–50 ␮m. Similar information is also in agreement with the earlier report (Cook, Chen, & Beall, 2015). From the images, the fine nanoparticle into the starch hybrid PEHA\PVA polymeric matrix is also evident, and with slight agglomeration. This result shows that the current method of preparation is suitable to obtain a good dispersion of the nanoparticles into the starch hybrid PEHA\PVA polymeric matrix. 3.3.2. Explanation of atomic force microscope (AFM) The atomic force microscopic analysis is an ideal technique for quantitative measurement of the nanomatric dimensional surface roughness and for visualizing the surface nano texture of the nanocomposites. The surface roughness and topology are studied by AFM as shown in Fig. 4. The quantitative calculation of surface roughness is done by measuring the height of the peaks observed in the out of plane direction. Fig. 4 shows the three dimensional AFM picture of the surface and images are captured with a scan size between two 0.5 to 5 ␮m with a scan speed of 0.5 line cm. It is found that the surface of the film shows elevated peaks which are evidence of the rough surface of films. The roughness parameters are estimated by analyzing the topography scans of the sample surface. The average roughness of starch hybrid PEHA/PVA composite thin film is found to be 0.345 nm with accuracy of 0.05 nm. The quantitative calculation of the roughness are processed by flatten using picovio 1.12 version software which has been manipulated through picovio image through advance image software (Agilent technologies, USA). The two dimensional picture of the AFM is represented

as Fig. 4c and d. The surface roughness is increased by incorporation of nano CaCO3 in starch hybrid polymer matrix. The increase roughness is due to interfacial chemical adhesion of CaCO3 with starch hybrid PEHA/PVA chain. It is noticed that, the surface roughness is increased with decrease in porosity of the starch hybrid PEHA/PVA nanocomposites films with incorporation of CaCO3 . As per earlier report, (Haafiz et al., 2013) the result obtained from the AFM topographic image of polylactic acid composite reinforced with oil biomass, are similar to present investigation. Further the dispersion of graphene oxide (GO) in starch biocomposites is also investigated (Li, Liu, & Ma, 2011a) in similar way for study. 3.4. Antibacterial properties From Fig. 5, the antibacterial activities of synthesized nanocomposites film is measured by agar cup diffusion method against bacteria such as E. Coli, B. subtilis, S. aureus, and P. aeruginosa and fungi such as C. krusei, C. Viswanathii and C. albicans as test pathogens. The bacterial growth is different for thin film composite with and without CaCO3 nanopowder. The antibacterial activity is measured based on clear zone surrounding, circular disc. When clear zone is present, the diameters of film disc are higher. Similarly, when there is no clear zone surrounding then there is no inhibitory zone. This mechanism is also explained in the earlier report in the literature (Chatzistavrou et al., 2014). This result is similar to the result obtained from the study of antimicrobial composite coatings of silver deposited 3-amino propyltriethoxy silane in an earlier publication (Guo, Yin, Sha, Wei, & Zhao, 2015). Similarly, starch/PVA composite film is behaved as antibacterial materials with reinforcement of cellulosic fiber (Priya et al., 2014). In present study, the CaCO3 is behaving as an antibacterial agent in presence of starch hybrid PEHA/PVA composites film. Further, nanocomposites film reinforced by CaCO3 nanopowder has better antibacterial activities as compared to untreated films. Among bacterial the growth of P. aeruginosa and E. Coli are more effective to different extend in the film without CaCO3 than with CaCO3 . Moreover, among fungi, the growth of C. krusei is less. The interaction between micro organisms and the surface of materials may be a key mechanism for their growths. The starch hybrid PEHA/PVA inhibits the growth of micro organisms

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Fig. 5. Antibacterial activity of nanoCaCO3 imprinted starch hybrid PEHA/PVA composite thin film.

in direct contact with the active sites. However, the inhibition zone increased significantly when CaCO3 nanopowder is incorporated within starch hybrid PEHA/PVA matrix and it is increased as compared to the nanocomposites thin film without CaCO3 nanopowder. It has been found that CaCO3 nanopowder can produce the “reactive oxygen species”, which is resulted an increased antimicrobial activity of the nanocomposites thin film. Due to this antimicrobial behavior the nano CaCO3 reinforced composite films can be used in clinical requirement. 3.5. Tensile properties The tensile strength of starch hybrid PEHA/PVA nanocomposite thin film with reinforcement of various nano CaCO3 contents are shown in Fig. 6a. The micro structural and mechanical behavior of multiwalled carbon nanotubes reinforced Al Mg Si alloy composite are also studied (Kondoh, Fukuda, Umeda, Imai, & Fugetsu, 2014), which has similar trend of increment of mechanical strength with present study. The tensile strength of starch hybrid PEHA/PVA

composite thin films is 8 MPa, when nano CaCO3 are added in to starch hybrid PEHA/PVA solution, & it increases with an increase in nano CaCO3 . The tensile strength of the resulting composite thin film is approximately two times higher as compared to that of the virgin starch hybrid PEHA/PVA thin film. It is due to uniform distribution of nano CaCO3 with copolymer matrix. Further, the remarkable increase in the tensile strength of the thin film indicates the presence of strong inter molecular adhesion between nano CaCO3 and starch hybrid PEHA/PVA. The results are also reported in the literature is like to the present study which is related to the improvement of tensile properties of polymers due to dispersion of CaCO3 (Sharma et al., 2015). 3.6. Thermal conductivity Thermal conductivity of nanocomposite thin films having matrix of starch hybrid PEHA/PVA containing nano CaCO3 is investigated in Fig. 6b. The thermal conductivity of nanocomposite thin films increases monotonically with increase in concentration of

Fig. 6. Tensile strength (a), thermal conductivity (b) of starch hybrid PEHA/PVA composite thin film with different wt% of CaCO3 .

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Table 1 Glass transition temperature (Tg ), wt% loss due to thermal degradation (Td ) at different temperature of neat PEHA, PVA, starch hybrid/PEHA-PVA nano composite thin films with and without CaCO3 nanoparticles. Materials

PEHA PVA Starch Starch hybrid PEHA/PVA (0 wt% CaCO3 ) Starch hybrid PEHA/PVA (1 wt% CaCO3 ) Starch hybrid PEHA/PVA (2 wt% CaCO3 ) Starch hybrid PEHA/PVA (3 wt% CaCO3 ) Starch hybrid PEHA/PVA (5 wt% CaCO3 ) Starch hybrid PEHA/PVA (8 wt% CaCO3 )

Tg (◦ C)

55 85 25 92 125 132 138 144 148

CaCO3 nanopowder. It is interesting to notice that thermal conductivity is enhanced by about 16 times due to incorporation of 8% CaCO3 as compared to the film without CaCO3 . Present result is superior as compared to the earlier reported result where thermal conductivity of polystyrene is increased by 5 times by incorporation of 20% of aluminum nitride (Yu, Hing, & Hu, 2002). Similar result is also described in the earlier study during the enhancement of thermal conductivity of polymers due to dispersion of CaCO3 (Kharitonov et al., 2015). The increase in thermal conductivity of nanocomposite thin film with increasing CaCO3 loading could be due to higher stability of thermal conductivity path for more distribution of CaCO3 particles. Thus thermal conductive path can be considered as more stable for higher concentration of CaCO3 nanopowder because thicker conducting path may have less possibility of been disrupted by nano CaCO3 . Therefore, thermal transport properties of starch hybrid PEHA/PVA matrix are substantially improved with dispersion of CaCO3 nanopowder. 3.7. Thermal stability From TGA, the glass transition temperature (Tg ) and weight loss due to thermal degradation of different temperature of PEHA, PVA, Starch and starch hybrid PEHA/PVA composite film with and without nano CaCO3 are summarized in Table 1. The thermal stability of material at temperature 150 ◦ C, 250 ◦ C, 350 ◦ C and 450 ◦ C is predicted. The glass transition temperature of nanocomposite film of starch hybrid PEHA/PVA is increased due to imprintment of nano CaCO3 . Further, Tg increases with increase in concentration of CaCO3 . The weight loss due to thermal degradation at different temperature is decreased with increase in CaCO3 contents. It is interesting to see that 45% residue is remaining at 450 ◦ C of nanocomposite films is enhanced due to incorporation of CaCO3 . In literature CaCO3 is dispersed in PVC matrix for improvement of

Wt %loss due to degradation (Td ) 150 ◦ C

250 ◦ C

350 ◦ C

450 ◦ C

12 7 9 6 1.2 0.8 0.2 0 0

21 11 25 15 10 8 7.2 5 3

35 80.5 60 42.5 33 30.2 27.5 18.4 15

74 95 90.3 70.4 64.5 62.3 60 58.5 55

thermal properties which is accordance with the present investigation (Xie et al., 2004). In this study glass transition temperature of composite with 5% CaCO3 is increased slightly (less than 5%) compared to pure polymer (PVC) matrix, whereas; in present study Tg of nanocomposite film is enhanced by 50% with incorporation of the 5% CaCO3 . In another study (Ye, Zhang, Feng, Ye, & Li, 2015) the thermal stability of methyl methacrylate has been increased due to dispersion of CaCO3 nanoparticles. 3.8. Biodegradable properties The biodegradable properties of Starch hybrid PEHA/PVA– CaCO3 composite thin films are compared with virgin starch hybrid PEHA/PVA studied for 90 days in an interval of 15 days (Fig. 7a). The degradation is studied in order to calculate percentage of weight loss of materials in activated sludge water. In Fig. 7a the biodegradability of synthesize nanocomposite thin film is checked to monitor the progress of the biodegradable nature of the film by taking the weight of sample after every 15 days of the biodegradation. It is interesting to notice that the nanocomposite film of 8 wt% of CaCO3 is degraded by 65% after 15 days, as compared to the earlier publication regarding the composite of polyacrylamide-co-acrylic acid where it is reported the degradation of 20% after 15 days by compost method (Mittal, Maity, & Ray, 2015). The present results are similar to the earlier reported findings regarding biodegradable study of starch based composites with reinforcement date palm & flax fibers (Ibrahim, Farag, Megahed, & Mehanny, 2014). It is observed that the rate of degradation is much fast in starting but it becomes slower after a certain period of time. The slower degradation rate in the latter stage of the biodegradation is due to fact that the films are inert and restrict the action of microorganisms. The faster rate of degradation of the initial stage is due to the fact that sample achieved maximum swelling and softening by which the

Fig. 7. (a) Biodegradability of starch hybrid PEHA\PVA composite thin films as a function of CaCO3 concentration at different interval of time (b) chemical resistance (NaOH) starch hybrid PEHA/PVA composite thin films as a function of CaCO3 concentration.

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microorganisms attacked more effective. It is noticed that the percentage weight loss in thin films is decreased with increase in percentage of CaCO3 loading. However biodegradation of nano thin film as well as virgin starch hybrid PEHA\PVA are increased with increase in time duration with activated sludge water. The decrease in biodegradation of nanocomposite thin film as compared to virgin starch hybrid PEHA\PVA is due to active participation and well dispersion of CaCO3 with starch matrix. Further it is noticed that nano CaCO3 is contributing its effect during biodegradation process. Again the contribution of CaCO3 toward biodegradation is increased with increase in time interval. 3.9. Chemical resistance properties In order to study the effect of acid and base on the synthesized composite thin film, the synthesized materials are treated with dilute HCl (1N) and dilute NaOH (1N) for 90 days. The percentage weight loss of the nanocomposite thin film is measured in an interval of 15 days. The virgin starch hybrid PEHA/PVA is resistant to these chemicals but the resistance is more in case of starch hybrid PEHA\PVA–CaCO3 nanocomposite thin film. Further, the resistance is remarkably increased by increasing the CaCO3 nano filler loading (Fig. 7b). The higher resistance of the synthesized composite thin film may be due to superior properties and inertness of CaCO3 . These calcium compounds reacted with alkali solutions resulted to Ca(OH)2 compound. Ca(OH)2 continued to react with the surface of the films which contributed the strength of nanocomposite thin films. Unlike the alkali, the synthesized nanocomposite films have no resistance to acid. It is because the calcium carbonate is easily dissolved in HCl remaining the pores and cracks in the nanocomposites films with formation of calcium chloride which adversely affected the strength of composites. The result is in agreement with the earlier publication (Jawaid, Khalil, Bakar, & Khanam, 2011) during the investigation of chemical resistance of oil palm/jute fiber polymer hybrid composites. 4. Conclusion The starch hybrid PEHA/PVA composite thin films are prepared by aqueous medium with incorporation of nano CaCO3 . The uniform dispersion of nano CaCO3 is achieved with local agglomeration. AFM is used to monitor the surface morphologies of nano CaCO3 reinforced composites. The nanocomposite films are antimicrobial material after dispersion of CaCO3 nanoparticle. The nanocomposites films are resistance to alkali and not to mineral acid. The biodegradable properties of the starch hybrid PEHA/PVA composite thin films are investigated it is concluded that this property is much faster after 15 days and became slow with increase in time periods. The thermal conductivity of the nanocomposite films is enhanced by five folds at 10 wt% loading of nano CaCO3 as compared to without fillers. The thermal stability of nanocomposite films are measured, it is found that the Tg and residual weight of the material are increased due to incorporation of nano CaCO3 . The increase in wt% of nano CaCO3 particles improves the mechanical properties of the composites. The antibacterial properties of starch hybrid PEHA/PVA nanocomposite film along with enhancement of tensile and thermal conductivity may enable the material for packaging applications. Acknowledgements Authors express their thanks to Department of Science and Technology, Government of India for awarding Inspired Fellowship to Kalyani Prusty to pursue doctoral degree. Authors also express their thanks to Department of Science and Technology

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