Biocomposites with increased dielectric constant based on chitosan and nitrile-modified cellulose nanocrystals

Accepted Manuscript Title: Biocomposites with increased dielectric constant based on Chitosan and nitrile-modified cellulose nanocrystals Authors: Sebasti´an Bonardd, Eduardo Robles, Irati ´ Barandiaran, Cesar Sald´ıas, Angel Leiva, Galder Kortaberria PII: DOI: Reference:

S0144-8617(18)30743-4 https://doi.org/10.1016/j.carbpol.2018.06.088 CARP 13762

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

17-4-2018 1-6-2018 20-6-2018

Please cite this article as: Bonardd S, Robles E, Barandiaran I, Sald´ıas C, Leiva ´ Kortaberria G, Biocomposites with increased dielectric constant based on A, Chitosan and nitrile-modified cellulose nanocrystals, Carbohydrate Polymers (2018), https://doi.org/10.1016/j.carbpol.2018.06.088 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.

Biocomposites with increased dielectric constant based on Chitosan and nitrile-modified cellulose nanocrystals

Sebastián Bonardd1,2, Eduardo Robles3, Irati Barandiaran2, Cesar Saldías1, Ángel Leiva1, and

SC RI PT

Galder Kortaberria2*

1

Departamento de Química Física, Facultad de Química, Pontificia Universidad Católica de Chile, Casilla 302, Correo 22, Santiago, Chile 2

´Materials + Technologies´´ Group, Chemical & Environmental Engineering Department, Basque Country University, Plaza Europa 1, 20018 Donostia (Spain) 3

N

corresponding author: [email protected]

A

*

U

Biorefinery Processes Research Group, Chemical & Environmental Engineering Department, University of the Basque Country UPV/EHU, Plaza Europa 1. 20018. Donostia (Spain)

CC

EP

TE

D

M

Graphical abstract

A

Highlights

 

First cyanoethylation over cellulose nanocrystals obtained from blue agave waste was achieved Flexible bio-based thin films nanocomposites were obtained by mixing cyanoethylated nanocrystals with chitosan

 

Thermal characterization results indicate the use of these compounds in hightemperature applications Bio-Based nanocomposites show an improvement in their dielectric properties compared to pure chitosan and nanocomposites with unmodified cellulose nanocrystals

SC RI PT

Abstract

The motivation of the present work was the preparation of bio-based thin film nanocomposites with improved dielectric properties using modified nanocellulose and chitosan, both materials

known to derive from industrial waste. Cyanoethylation of cellulose nanocrystals (CNC) was

achieved through a “green” method for the first time. Then, modified CNCs were incorporated

U

into a chitosan (Chi) matrix, obtaining a homogeneous and flexible material with higher

dielectric constant due to the high dipole moment of the nitrile functional group. The value of

N

dielectric constant rises with the content of modified CNCs, from a value of 5.5 for pure chitosan

A

at 25 ºC and 1 kHz up to a value of 8.5 for the nanocomposite with 50 wt% at the same conditions. These bio-based nanocomposites show an improvement in their dielectric properties

M

compared to pure chitosan and chitosan/unmodified CNC nanocomposites (for which dielectric constant decreases up to 4.5 at 25 ºC and 1 kHz) and can be considered for high-temperature

D

applications. Characterization of cyanoethylated cellulose nanocrystals (CN-CNC) and

TE

nanocomposites was carried out by infrared spectroscopy (FT-IR), attenuated total reflectance spectroscopy (ATR), atomic force microscopy (AFM), thermogravimetric analysis (TGA), Xray diffraction (XRD), and solid-state NMR and broad band dielectric spectroscopy (BDS).

EP

Tensile tests were developed for mechanical characterization.

A

CC

Keywords: chitosan; cellulose; dielectric properties; cyanoethylated

1. Introduction

Due to the importance of energy resources, electrical energy storage through capacitor devices is nowadays an area of great industrial interest with different potential applications like batteries, hybrid electric vehicles, advanced propulsion systems, aircraft industries, etc. (Q. Wang & Zhu, 2011) (Q. Li et al., 2018) (Zhu, 2014). The main component of a capacitor is the dielectric

material, which in addition to complying with insulating properties, it is polarized when exposed to an electric field increasing the capacitance, that is, the amount of charge that the device manages to store at a given voltage. The most representative parameter of this type of material is the dielectric constant (ε’), which is directly related to the efficiency of the device: higher values of ε’, lead to higher charge and stored electrical energy values(Nasreen et al., n.d.). Due

SC RI PT

to the latter, in recent years there has been an increase in the development of new materials with adequate dielectric properties (Baer & Zhu, 2017) (Zhu, 2014).

In the last years, “all-polymer” dielectrics have turned out more attractive materials than ceramic ones or electrolytes, mainly due to their inherent insulator nature, excellent mechanical

properties, lightweight, easy processing, low-cost production and higher dielectric breakdown

values (Zhu, 2014) (Qiao, Yin, Zhu, Li, & Tang, 2018). The only disadvantage of those materials would be the low values of ε’, usually ranging around 2-4 (Zhu, 2014) (Qiao et al.,

U

2013) (P. Barber et al., 2009). This issue can be counteracted by increasing the polarization of

N

the material when it is exposed to an electric field, which would result in higher ε’ values. It is

A

well understood that matter, depending on its atomic structure, can present different polarization mechanisms (electronic, atomic, orientational or dipolar, ionic and interfacial), the orientational

M

one promising to the best candidate for achieving high ε’ values (Chi, 2004) (Baer & Zhu, 2017) (Solymar & Walsh, 1993) (Zhu, 2014). To afford this mechanism, molecular groups with high

D

dipole moment and reduced size must be present in the polymer structure so that, under an electric field, they can move and orient themselves, contributing to the polarization. Examples

TE

of these molecular groups are sulfone (-SO2R), fluorine (-F), nitro (-NO2) and nitrile (-CN) ones. Recently, polymers that achieve higher ε’ values than the average, due to the orientational

EP

mechanism, have been reported in the literature(Wei et al., 2015) (Zhang, Wang, Litt, Tan, & Zhu, 2018) (Treufeld, Wang, Kurish, Tan, & Zhu, 2014) (D. H. Wang, Kurish, Treufeld, Zhu,

CC

& Tan, 2015) (Dünki, Cuervo-Reyes, & Opris, 2017). Besides the energetic problem, another topic of great relevance for the scientific community is

A

the care of the environment. Regarding polymer science, the so called “green chemistry” is not only based on the development of clean synthetic routes or the production of biodegradable materials, but also involves the extraction and use of materials provided either by nature or as a side-stream generated from an established industry (Anastas & Warner, 1998) (Gonzalez & Smith, 2003), thus giving them value-added applications in topics of current interest (e.g energy, catalysis, etc). The use of cellulose and chitin constitutes an example (first and second most abundant polysaccharides on earth, respectively). Both are biocompatible, non-toxic and

biodegradable biopolymers (Avérous & Pollet, 2012), being an important part of domestic and industrial biowaste (Nisticò & Roberto, 2017). They can be recycled or composted reducing environmental pollution and therefore, their use in new applications can be an attractive approach to the efficient use of natural resources, minimizing the harm to the environment and reducing industrial waste and byproducts (M. N. V. R. Kumar, 2000) (Prashanth & Tharanathan,

SC RI PT

2007) (Rebouillat & Pla, 2013) (P. S. Barber, Shamshina, & Rogers, 2013). Traditionally, the applications of cellulose and chitin recovered from industrial side-streams have faced difficulties because of their low processability, mainly due to the low solubility in

common solvents (Rinaudo, 2006). However, several strategies can be found to overcome this situation. On one hand, chitin can be chemically transformed through an alkaline hydrolysis

treatment into chitosan, which is a polyelectrolyte that maintains the "green" properties of chitin but being soluble in acid aqueous media (Barber et al., 2013). So, through solvent evaporation

U

method of chitosan solutions, flexible thin films with good mechanical properties can be

N

obtained (Yoshida, Oliveira Junior, & Franco, 2009) (Croisier & Jérôme, 2013) (Srinivasa,

A

Ramesh, & Tharanathan, 2007). On the other hand, cellulose can be subjected to an acid hydrolysis, which allows the obtention of disperse aqueous systems in which the disperse phase

M

corresponds to cellulose crystals with nano or micro dimensions (Bondeson, Mathew, & Oksman, 2006) (Kargarzadeh et al., 2012) (Kumar, Negi, Choudhary, & Bhardwaj, 2014).

D

These entities, called cellulose nanocrystals (CNC), are used as organic fillers to improve, among others, mechanical properties of different matrices with outstanding results (El Miri et

TE

al., 2015) (Khan et al., 2012) (Celebi & Kurt, 2015). In recent years, several authors have prepared green nanocomposites based on chitosan and vegetal or bacterial nanocellulose for

EP

different potential applications such as electroactive papers (Jang, Kim, Zhijiang & Kim, 2009), packaging membranes (Sundaram et al., 2016), antimicrobial membranes (Bansal, Chauhan,

CC

Kaushik, & Sharma, 2016) or wound dressing applications (Ardila et al., 2016), among others. Taking all this into account, the development of “green polymer dielectrics” based on

A

biodegradable polymers or composites presenting increased dielectric properties constitutes an interesting and challenging goal. In the present work, the preparation and characterization of flexible thin films composed by chitosan and different amounts of CNC obtained from industrial biowaste are presented. CNCs have been chemically modified with CN groups (CN-CNC) in order to increase the dielectric constant of nanocomposites for their potential application in energy storage devices. Structural characteristics of components and nanocomposites have been analyzed in terms of X ray difraction (XRD) and nuclear magnetic resonance (NMR), while

thermal properties have been studied by thermogravimetric analysis (TGA), morphology of thin films by atomic force microscopy (AFM), while mechanical characterization was performed in terms of tensile tests. Finally, the improvement of dielectric properties has been followed by dielectric relaxation spectroscopy (DRS), with promising results. For the best or our knowledge, it is the first time in which the modification of CNC with CN groups is reported in the literature.

SC RI PT

The hypothesis for the present paper was the increase of dielectric constant of chitosan/CNC composites by modifying nanocrystals with highly polarizable –CN group.

2. Experimental 2.1. Materials

U

CNCs were obtained from blue agave waste provided by Finca Noctitlan, Jalisco, Mexico. Their characteristics can be found in a previous paper (Robles et al., 2018). Chitosan (low molecular

N

weight, with a deacetylation degree of 75%), acrylonitrile (99%), tetrabutylammonium bromide

A

(TBAB) and sodium hydroxide (99%) were purchased from Sigma-Aldrich. Chitosan was purified by dissolution-precipitation method using HCl 0.5M aqueous solution and methanol.

2.2. Techniques

D

M

All solvents were purchased from Merck and used without further purification.

TE

Fourier Transformed Infrared Spectroscopy (FT-IR) Spectra for CNC and CN-CNC were obtained using a Nicolet Nexus 600 FTIR spectrometer,

EP

performing 32 scans with a resolution of 2 cm-1 in the range between 4000 and 600 cm-1. Pellets of milled samples and KBr were used.

CC

Attenuated Total Reflectance spectroscopy (ATR) Polymer blends spectra were obtained in a Perkin Elmer Spectrum Two equipped with a

A

Universal ATR accessory with internal reflection diamond crystal lens, in the range between 4000 and 500 cm-1 with an accumulation of 50 scans and a resolution of 4 cm-1. Nanocomposite films were characterized by ATR without any further preparation. Atomic force microscopy (AFM) Atomic force microscopy images were obtained with a NanoScope IIIa Multimode TM-AFM (Digital Instruments-Veeco) operating in tapping mode. The equipment contains an integrated

silicon tip cantilever with a resonance frequency of 300 kHz. Sample films were placed on AFM metallic support for measurement. X-ray powder diffraction (XRD) Characterization of CNC and CN-CNC powder was performed with a Panalytical Phillips

SC RI PT

X’Pert PRO multipurpose diffractometer. Sample films were mounted on a zero background silicon wafer fixed in a generic sample holder, using monochromatic CuKα radiation (λ = 1.5418 Å) in a 2θ range from 5 to 70 with step size of 0.026 and 80 s per step. Solid-state 13C-NMR

Solid-state NMR spectra were recorded on a Bruker AVANCE III, 9.4 T (Larmor frecuency 100.64 MHz for

13

C) equipped with MAS/DVT BL4 X/Y/H probe head. The samples were

U

insert in rotor of 4 mm at a spinning rate of 12 kHz. The 13C CP-MAS spectra were recorded

Termogravimetric analysis (TGA)

A

of scans 6024 and the spectral width 30 kHz.

N

with a p90º pulse of 3.5 μs and a contact time of 2 ms. The recycling delay was of 5 s, the number

M

Thermal behavior was studied using a TGA/SDTA851 Mettler–Toledo thermobalance (TGA). TGA thermograms were carried out between 25ºC and 900 ºC at a heating rate of 20 ºC/min

D

under air and nitrogen atmosphere. Thermal degradation onset temperature (T5%) corresponds to the temperature at which the material losses the 5% of its weight without considering the loss

TE

of adsorbed water. Besides, the maximum weight loss rate temperatures (TMD) were detected as peaks in the differential thermogravimetric analysis curves. A piece of each film was put in the

EP

capsules for this analysis. Dielectric properties

CC

Dielectric relaxation spectroscopy (DRS) measurements were carried out by a Novocontrol Alpha high-resolution analyzer over a frequency range between 10-1 Hz and 106 Hz, in which

A

the AC voltage applied was Vrms = 1.0 V at room temperature. Thin films were placed between gold platted electrodes in a sandwich configuration. Mechanical characterization Tensile tests of nanocomposite films were carried out using an Insight 10 (MTS Company, Eden Prairie, Minnesot a, USA) equipment, following ASTM D1708-93 standard, with a rate of deformation of 5 mm/min. The thickness of the samples was determined using a micrometer,

while the length and the width were the same in all cases (16 mm and 4.9 mm, respectively). Tensile strength, Young’s modulus and elongation at break were measured. For each test, a minimum of six samples were tested.

2.3. Sample preparation

SC RI PT

Preparation of Cyanoethylated cellulose nanocrystals (CN-CNC)

CNCs were obtained from blue agave waste as reported in a previous work (Robles et al., 2018), after which they were freeze-dried to eliminate the water contribution to the mass of the product.

The cyanoethylation of CNCs was performed following a protocol proposed by Li et al. with minor variations (Li, Goh, Lai, & Deng, 1999). In a first step, 50 mL of a 1% w/v CNC aqueous dispersion was prepared in a round bottom glass, alternating 15 min of sonication with 5 min of

U

magnetic stirring three times. A NaOH aqueous solution (0.124 mg in 2 mL of water) was added

to this dispersion at room temperature, and stirred for 10 min. Finally, a solution conformed by

N

0.81 mL of acrylonitrile and 52 mg of TBAB in 5 mL of acetone was added dropwise and stirred

A

24 h at room temperature. Purification process was achieved through dialysis against distilled

giving a pale-yellow powder.

M

water during 48 h (changing water three times a day), after which CN-CNC were freeze-drying

D

Preparation of Chitosan /CN-CNC composites

TE

Firstly, a 1% w/v chitosan solution was prepared dissolving the polymer in an aqueous acetic acid solution (1% v/v) at room temperature and filtering to eliminate insoluble residues. On the other hand, following the above mentioned sonication-stirring procedure, a 1% w/v aqueous

EP

dispersion of CN-CNC was prepared. Blends containing 10, 30 and 50 wt% of CN-CNC were prepared mixing dropwise the chitosan

CC

solution over the modified nanocrystal dispersion in the desire proportions and kept under vigorous stirring during 24 h. Blend solutions were placed over plastic petri dishes and dried at

A

45°C for 24 h and then neutralized by immersion in a 0.5M NaOH aqueous solution overnight. Finally, the blends were dialyzed against distilled water during 48 h (changing water three times a day) and dried at 80ºC for 72 h allowing the obtainment of flexible thin films.

3. Results and discussion

The presence of nitrile groups in chemical structures has been of great importance in different applications such as adhesives, intermediates for further chemical modifications, host-guest drug interaction, hydrophilic-hydrophobic balance and, due to its high dipolar moment (4.0 D), in the manufacture of dielectric materials with high dielectric constant (Castelvetro, Capaccioli, Raihane, & Atlas, 2016) (Sanchez-Chaves, & Arranz, 1996) (Fiege, Lünsdorf, Atarijabarzadeh,

SC RI PT

& Mischnick, 2012) (He, Wang, Zhong, Ding, & Zhang, 2015) (Schmidt et al., 2018) (Gonzalo et al., 2009) [REF]. There are several reaction paths to add nitrile groups to molecular structures

(amine oxidations, halogen exchange using cyanide salts, etc.), among which the cyanoethylation reaction is one of the most common methods due to its tolerance to different solvents and reaction conditions.

Li et al. (X. Li et al., 1999) developed a cyanoethylation process for modifying poly(vinylalcohol) using a mixture of water and acetone as mixed solvent, in which acrylonitrile

U

and (ACN) a quaternary ammonium halide were solubilized in a basic medium, allowing the

N

addition of nitrile groups over the hydroxyl ones present at the polymer backbone. A similar

A

procedure was employed for CNC modification, in which a value of 4 for [ACN]/[OH] ratio of 4 and an amount of TBAB corresponding to 5 mol % with respect to the total hydroxyl groups

M

present, were used. Taking into account the insolubility of CNC in water, the [ACN]/[OH] ratio was even higher due to the fraction of hydroxyl groups forming part of the inner crystalline and

D

amorphous phases, that are not exposed to the reaction medium (Scheme 1). Different [ACN]/[OH] ratios were used in order to check its effect on CNCs modification (data not shown

TE

here). For a ratio of 8, any appreciable differences were obtained, probably due to the fact that the excess provided by a [ACN]/[OH] ratio of 4 was enough to reach a plateau. When a ratio of

EP

2 was used, a low degree of modification was achieved, that could be attributed to the heterogeneous nature of the reaction system. For all the above mentioned, authors believe that

CC

the modification could mainly occur at the surface of the CNCs. From elemental analysis (corresponding results and procedure included in Supplemental Data) a degree of substitution

A

of around 15% was obtained. The success of chemical modification of CNC with –CN groups was probed in terms of FTIR and solid-state

13

C-NMR. Figure 1 shows the FTIR spectra for both unmodified and CN-

modified CNCs. The characteristic bands related with cellulose can be clearly seen in both spectra: band related to O-H stretching at around 3350 cm-1, the band at 2870 cm-1 related to – C-H stretching, those in the range 1649–1634 cm−1 due to the O–H bending of adsorbed water, the band corresponding to –CH2 scissoring at 1430-1420 cm-1, that of C-H bending at around

1380 cm-1, -CH2 wagging at around 1317 cm-1, C-C ring stretching band at 1155 cm-1, the band corresponding to C-O-C pyranose ring stretching vibration at 1054 cm-1, and bands associated with cellulosic β-glycosidic linkages at 900-890 cm-1 (Le Troedec et al., 2008) (Mandal & Chakrabarty, 2011) (Garside & Wyeth, 2003) (A. Kumar et al., 2014). The main difference among both spectra is the presence of the band corresponding to the C≡N

SC RI PT

stretching located at around 2250 cm-1, indicated by an arrow in the Figure 1 (Fiege et al., 2012)

(X. Li et al., 1999) (Raskó & Kiss, 2006). The presence of this band and the diminishing in the value of the ratio among the -OH and -C-H signals transmittance after modification probes the success of chemical modification of CNCs.

Figure 2 shows solid-state 13C-CP MAS and 13C-MAS NMR results obtained for unmodified and cyanoethylated CNC.

13

C-CP MAS analysis (Figure 2A) allows a better resolution for

U

carbon signals, which are bonded directly to hydrogen atoms. Non-modified CNC spectrum shows the typical signals for pyranose ring carbon atoms present in cellulose backbone,

N

demonstrating the correct structure and the purity of the nanocrystals obtained. After the

A

modification, a new signal (labelled as β) appeared at 18.5 ppm and could be related to the

M

presence of cyanoethyl moieties. Due to the chemical structure of nitrile group, in which the carbon atom does not have any hydrogen atoms bonded, this functional group can not be detected by 13C-CP MAS. So, to demonstrate the presence of the nitrile group, 13C-MAS analysis

D

was used. 13C MAS spectra (Figure 2B) clearly shows the presence of previously detected β

TE

signal and the appearance of a new signal centered at 118 ppm (labelled as α), which is characteristic for nitrile group (Gunstone, 1993) (Zhou, Li, Song, Zhang, & Lin, 2010). In addition, for CN-CNC spectra an overlapping in the range between 80 and 50 ppm can be

EP

observed, which is probably attributed to the appearance of a new carbon signal (assigned as γ in Figure 2B) due the chemical modification. So, considering the 13C-NMR and FTIR results, it

CC

seems that the cyanoethylation reaction over CNC was achieved successfully. In order to check the crystalline structure and crystallization degree of CNC and the effect of

A

chemical modification on it, XRD measurements were carried out. Figure 3 shows XRD spectra of both CNC and CN-CNC with normalizes intensities. Both spectra are quite similar, with the presence of several peaks that are related to the presence of type I and II structures of cellulose. Peaks appearing at 2θ = 12.5º and 2θ = 20.5º are due to 101 side, indicating the presence of the typical type II cellulose structure(Yan et al., 2013). On the other hand, peaks at 2θ = 14-16º, 2θ = 22.5º and 2θ = 35º are related to 110, 200 and 004 crystalline planes of type I cellulose (Horikawa & Sugiyama, 2009)(Cho & Park, 2011)(Robles

et al., 2018). From those results, it seems that, as it was found by other authors, both samples present a mixture of polymorphs of cellulose I and cellulose II (Orue, Santamaria‐ Echart, Eceiza, Peña‐ Rodriguez, & Arbelaiz, 2017). In addition, diffraction planes corresponding to cellulose I crystalline allomorphs (α and ) can be observed, in which cellulose I diffractions (planes 110, 1-10, 102 and 200) are more intense (Focher et al., 2001). This fact is common in

SC RI PT

cellulose from higher plants. Crystallinity of CNC before and after modification was calculated with the Peak Fitting method

(Park, Baker, Himmel, Parilla, & Johnson, 2010) using Origin software assuming pseudo-Voigt

signals (Lorentzian and Gaussian) for the crystalline peaks and a Gaussian peak corresponding to the amorphous contribution. Iterations were made until fit converged with the scatter (R2>0.975). Crystallinity index was calculated as the sum of the integrated areas of the curves

simulated for crystalline planes, divided by the integrated area of the whole simulated pattern.

U

Crystallinity index for CNC was 52.25 while for CN-CNC it was 48.98, which implies a slight

N

decrease in the crystalline order of the CNC after modification. Moreover, to promote comparison with works that prefer this index, the Segal index was also calculated, being of

A

76.24 for CNC and 75.49 for CN-CNC, respectively (Segal, Creely, Martin Jr, & Conrad, 1959).

M

Both indexes show a similar correlation between neat and modified CNC which involves a slight reduction of the crystalline contributions to the diffractogram. In any case, although there is a decrease in the crystallinity after modification, this change can be considered as small. This

D

allow us to state that the modification did not affect in great manner to the polymorphism and

TE

crystallinity degree, supporting the hypothesis that the modification is mainly achieved at the surface of the CNC.

EP

Once the successful modification of CNCs has been probed, prepared nanocomposites have been characterized. Figure 4 shows ATR spectra for pure chitosan and nanocomposites with 10,

CC

30 and 50 wt% of CN-CNC.

As it can be seen, nanocomposites do not show significant variations in their spectrums when

A

compared with a pure chitosan spectrum, except the band at 2255 cm-1 present in nanocomposites, due to the modification of CNC with –CN groups. This is due to the similarity between cellulose and chitosan in terms of their chemical structure. For that reason, the bands for both polysaccharides are mainly the same. Morphological characterization of nanocomposite thin films was carried out by AFM. Figure 5 shows AFM images for chitosan and nanocomposites with 10, 30 and 50 wt% of CN-CNC.

AFM images show the good dispersion of cyanoethylated CNCs through the film for all compositions. The presence of a higher amount of CN-CNCs is clearly seen for the nanocomposites with 30 and 50 wt%, with a proper dispersion of the filler even at the highest concentration and without the presence of remarkable agglomerations. For all the nanocomposites, CN-CNCs present a nanometric size. Size distribution obtained from AFM

SC RI PT

images analysis is summarized for all systems in Table 1, together with the surface average roughness obtained for each film. As it can be seen, size distribution is very similar for all the composites prepared. Moreover, obtained average size is in agreement with size distribution

found when CNCs were obtained from blue agave waste (Robles et al., 2018), that seems to be constant during modification and nanocomposite preparation. The film roughness increased

U

with the incorporation and amount of CN-CNCs.

Thermal stability of CNCs before and after modification was studied under air and nitrogen

N

atmosphere. The main advantage of the use of nitrogen is to avoid the occurrence of side reactions

A

due to oxidation promoted by heat. These reactions induce chemical changes (functional group oxidation, cross-linking process, etc.) in the structure of the material, modifying its thermal behavior

M

(Bengisu & Yilmaz, 2002) (Zawadzki & Kaczmarek, 2010). Figure 6 shows the degradation profiles and their derivatives for CNC and CN-CNC in both atmospheres. A first inspection of the

D

thermograms indicates that CN-CNC begin to degrade at lower temperatures than CNC. Figure 6B shows an initial degradation stage (pointed by blue arrow) that overlaps the main degradation step

TE

and is not present in the CNC thermogram. In order to clarify if this initial degradation is related to the presence of cyanoethyl residues, the CN-CNC sample was heated up to 300°C and then a FTIR

EP

spectrum was recorded, which revealed the total disappearance of the nitrile signal. Under air atmosphere this initial degradation stage cannot be visualized (Figure 6D). A possible explanation

CC

could be that at this temperature the oxygen present begins to promote the oxidation of the nitrile group, changing its chemical structure and therefore its thermal behavior. Comparing Figure 6A and 6C it seems evident that, depending on the atmosphere applied, the

A

thermal degradation process is different. Both CNC and CN-CNC, under oxygen exposure, showed a degradation step between 410°C-550°C, not observed when the experiment was carried out under nitrogen. This loss of weight is related to the chain scission and subsequently volatilization of oxidized species formed in-situ during the heating of the sample. In addition, it is important to note that the single degradation step in nitrogen atmosphere can be related with the loss of similar volatile compounds to those in the first degradation observed under air. In any case, the maximum decomposition rate temperatures (TMD) obtained in air for CNC and

CN-CNC are lower in comparison to those calculated under nitrogen atmosphere (see values in Figure 6B and 6C). This result could be explained through the in-situ formation of thermally labile oxidized compounds during the heating process. As most applications are carried out in the presence of oxygen, thermogravimetric analysis for chitosan, CN-CNC and nanocomposites was carried out under air, being the results exposed in

SC RI PT

Figure 7 (measurements under nitrogen can be seen in the supporting information). Degradation profiles observed in Figure 7A showed three weight loss steps for all samples, being CN-CNC

the exception in which the first stage is negligible. The first degradation stage takes place from 50°C to 160°C and is associate with the loss of water content. Weight loss below 100°C is related to the evaporation of water physically adsorbed (moisture), while above 100°C until

160°C it could be due to strongly hydrogen-bonded water (Zawadzki & Kaczmarek, 2010). It is important to note that at higher content of CN-CNC, the amount of water in the material is

U

lower.

N

The second stage between 250°C and 400°C is relate to chitosan and CN-CNC backbones

A

degradations which are clearly distinguished by two degradation peaks in Figure 7B. The weight loss associated to this stage is caused mainly by depolymerization of polymer chains,

M

decomposition of pyranose structure through dehydration and subsequently ring-opening reactions (Bengisu & Yilmaz, 2002) (de Britto & Campana-Filho, 2007). Comparing the

D

thermal stability of chitosan and CN-CNC fractions in the nanocomposites, TMD values are not greatly affected by the composition (Figure 7C). This could be attributed to the low density of

TE

interaction of both polymers through hydrogen bonds, since only the hydroxyl groups on the CN-CNC surface can interact with chitosan, leaving the internal structure of the nanocrystals

EP

intact and maintaining almost unaltered the thermal stability of chitosan bonds. In any case, in the nanocomposites there is a slight tendency to increase the thermal stability of the chitosan

CC

fraction when the amount of CN-CNC increases and, in the same way, when the chitosan content increases, the thermal resistance of the CNC-CN rises. Moreover, probably due to its semi-

A

crystalline inner structure, CN-CNC has higher thermal stability respect to chitosan. The third stage would be associate to an oxidative degradation process because it is not detected when the experiments are carried out under nitrogen atmosphere (see supporting information). Similarly, as it was explained previously, the oxidative degradation corresponds to the volatilization of oxidized products formed during the heating. Due to the presence of oxygen and heat, the polymer structure can be exposed to chemical reaction that involve the oxidation of functional groups or even the crosslinking between chains promoted by radical

formation(Zawadzki & Kaczmarek, 2010), resulting in a material with new chemical structure and therefore with a different thermal stability which degrades in a new stage. Finally, is important to note that for all the nanocomposites the initial degradation temperature (T 5%) are above 280°C, so these materials would be considered as high-temperature stable materials (Q. Li et al., 2018).

SC RI PT

A basic mechancial characterization of films was carried out by tensile tests. Figure 8 shows the

evolution of tensile strength, Young’s modulus and elongation at break with the amount of CNCNC. For the sample with 50 wt% of CN-CNC it has not been possible to obtain reproducible

and feasible data. As it can be seen from the figures, the addition of nanocrystals produces an increment of 11 % and 80 % for the nanocomposites containing 10 and 30 % of nanocrystals, respectively. It seems the hydroxyl groups remaining at the surface (as indicated by the degree

of modification) could be able to interact with the chitosan matrix through hydrogen bonds and

U

therefore, the increment in tensile strength would be attributed to an efficient stress transference

N

through the interface between chitosan and nanocrystals (Khan et al, 2012) (Fernandes et al,

D

M

A

2010).

TE

Regarding Young’s modulus, the addition of 10 and 30 wt% of CN-CNC produced an increment of 27 and 84 %, respectively, confirming that the entities act as good reinforcing agents. A good

EP

correlation with others works can be found in relation to the magnitude and tendency of the obtained values (Khan et al, 2012) (Fernandes et al, 2009). Filler-reinforced films usually tend to become more brittle as the concentration of the reinforcing particles increases (Rhim et al,

CC

2011). This behavior is also common for nanocomposite films. The increased Young’s modulus values of reinforced chitosan films may be attributed to the increased stiffness of the films by

A

the addition of nanocrystals. The increase in brittleness can be seen with the values of elongation at break. Several authors have found a decrease in elongation at break values with the incorporation of cellulose nanocrystals, indicating strong interactions between filler and matrix, which could restrict the motion of the matrix, hence decreasing deformation (Li et al, 2009) (Azeredo et al, 2010) (Samir, Alloin, Sanchez, & Dufresne, 2004). Regarding the dielectric characterization of films, the frequency dependencies of dielectric constant and loss for chitosan, for the nanocomposite with unmodified CNC and for those with

different amounts of CN-CNC, at room temperature, are shown in Figure 8, together with the evolution of dielectric constant at selected frequencies for all the systems. All films present a significant increase of the dielectric constant at low frequencies, due to strong interfacial polarization and electrode effects (Agrebi, Ghorbel, Ladhar, Bresson, & Kallel, 2017) (Ladhar, Ben Mabrouk, Arous, Boufi, & Kallel, 2017). The intrinsic dielectric properties of the material

SC RI PT

are revealed only for frequencies above 1 kHz. The continuous decrease of dielectric constant with an increase in frequency is quite common

for all dielectric substances. It is well known that, when frequency of electric field is increased the mechanism of polarization cannot be able to follow the change in the electric field and therefore, the contribution of polarization to the dielectric constant will be lowered.

U

The enhancement of dielectric properties of composite films usually is related to different types of polarizations. The interfaces of composite materials contain large numbers of defects, which

N

results in unequal charge distributions paving the way to space charge polarizations under an

A

electric field. However, as it can be seen in Figure 9 for frequencies higher than 1 kHz (range

M

at which the intrinsic dielectric properties are revealed), the composite film containing unmodified CNCs, shows a lower dielectric constant than pure chitosan. For the rest of composites (prepared with CN-modified CNCs), the increase in dielectric constant with CN-

D

CNC content can be clearly seen. As it was previously pointed out, one of the procedures to

TE

increase ε’, would be to increase the polarization of the material when exposed to an electric field, the orientational or dipolar mechanism being the best candidate for this purpose. For this reason, CN groups with high dipole moment and reduced size have been included in CNCs so

EP

that, under an electric field, they can move and orient themselves, contributing to the polarization and increasing dielectric constant values (from values around 6 and 5.5 for pure

CC

chitosan at 1 kHz and 1 MHz, respectively, to values of 8.5 and 8 for the composite with 50 wt% of CN-CNC at the same frequencies). The composite with unmodified CNC, not presenting

A

the polarizable CN group, obtained values have been lower. Those values found for ε’of chitosan are in the same order than those reported by other authors in similar frequencies, but presenting sligthly higher values (Lima et al., 2006) (Rahman, Mujeeb, Muraleedharan, & Thomas, 2018). As it was previously pointed out, the main disadvantage of “all polymer” dielectrics would be the low values of ε’, so it seems that this issue has been counteracted. One of the disadvantages of classic synthetic polymeric materials would be their low dielectric constant values, usually ranging between 2 and 4 (Ahmad, 2012) (Khutia, Joshi, Deshmukh, & Pandey, 2015) (Li et al,

2018) (Martin et al, 2000) while for their use as dielectrics high ε’and low ε’’ values are strongly requiered, for potential advanced electrical applications. Analyzed chitosan /nanocellulose nanocomposites, besides their renewable “green” origin, showed improved dielectric constant with respect to the most of conventional synthetic polymers. Regarding obtained dielectric loss values, they increase with the addition of CNC up to frequencies higher than 10 kHz, but with

SC RI PT

quite low values below 0.6 in the range at which the intrinsic dielectric properties are revealed. Moreover, for frequencies higher than 30 kHz, the ε’’ values of nanocomposites (below 0.2) are

lower than that of pure chitosan, thus obtaining “green” nanocomposites with increased dielectric constant and decreased dielectric losses, which would lead to higher charge and stored electrical energy values, adequate for their potential application as capacitor devices.

N

U

Conclusions

A

Biodegradable chitosan/CNC composites with increased dielectric constant have been successfully obtained by modification of CNCs with –CN groups. Chemical modification has

M

been probed in terms of FTIR and NMR, checking by XRD spectroscopy the presence of type I and II structures for cellulose and the small effect of chemical modification in the degree of

D

crystallinity, as it probably occurred only at the surface of CNCs.

TE

AFM characterization revealed a good dispersion of CNCs without the presence of any remarkable agglomerations, all CNCs presenting similar nanometric size at all samples

EP

prepared. In addition, the results obtained from thermogravimetric analysis show that for all nanocomposites the decomposition onset temperatures are above 280°C, allowing to consider

CC

them as high-temperature stable materials. Mechanical characterization in terms of tensile tests showed the increase in tensile strength and Young’s modulus with the incorporation of CN-CNC, while elongation at break decreased as

A

the brittleness increased, indicating strong interactions between filler and matrix, which could restrict the motion of the matrix, hence decreasing deformation. The aim of increasing dielectric constant values with the chemical modification of CNCs with a polarizable group has been achieved, as composites with CN-CNCs present the highest values when compared with pure chitosan or composites with unmodified CNCs. The improvement of dielectric constant values without remarkably increasing dielectric loss values or even

decreasing them at high frequencies, seems to present Chi/CN-CNC composites as candidates for potential application in capacitor devices, as higher charge and stored electrical energy values would be obtained for those biobased nanocomposites, being the first time to the best of

Acknowledgements

SC RI PT

our acknowledge that cellulose nanocrystals have been modified with –CN groups.

S. Bonardd thanks CONICYT for Doctoral Fellowship Grant 21150512. A. Leiva thanks

Fondecyt 1161159 project for partial financiation. Financial support from the Basque Country

Government (Grupos Consolidados, IT-776-13) and the Ministry of Economy and Competitiveness (MAT 2015) is gratefully acknowledged. The technical and human support

A

CC

EP

TE

D

M

A

N

U

provided by SGIker of UPV/EHU is also acknowledged.

References

Agrebi, F., Ghorbel, N., Ladhar, A., Bresson, S., & Kallel, A. (2017). Enhanced dielectric properties induced by loading cellulosic nanowhiskers in natural rubber: Modeling and analysis of polarization.

Materials

Chemistry

and

Physics,

200,

155–163.

SC RI PT

electrode

https://doi.org/10.1016/j.matchemphys.2017.06.058

Ahmad, Z. 2012. Dielectric Materials. London, United Kingdom: Intech Open Inc., 1-24. http://dx.doi.org/10.5772/50638

Anastas, P. T., & Warner, J. C. (1998). Green chemistry: theory and practice. Oxford, United Kingdom: Oxford university press, 1-30.

U

Ardila, N., Medina, M., Arkoun, M., Heuzey, M. C., Ajji, A., & Panchal, C. J. (2016). Chitosan

N

bacterial nanocellulose nanofibrous structures for potential wound dressing applications.

A

Cellulose, 23, 3089-3104. https://doi.org/10.1007/s10570-016-1022-y Avérous, L., & Pollet, E. (2012). Biodegradable polymers. In Environmental silicate nano-

M

biocomposites (pp. 13–39). Springer.

Azeredo, H. M., Mattoso, L. H., Avena-Bustillos, R. J. A., Filho, G. C., Munford, M. L., Wood, D.,

D

et al. (2010). Nanocellulose reinforced chitosan composite films as affected by nanofiller

TE

loading & plasticizer content. Journal of Food Science, 75, 19–28. DOI: 10.1111/j.17503841.2009.01386.x

EP

Azizi Samir, M. A. S., Alloin, F., & Dufresne, A. (2005). Review of recent research into cellulosic whiskers, their properties and their application in nanocomposite field. Biomacromolecules, 6,

CC

612–626. DOI: 10.1021/bm0493685 Baer, E., & Zhu, L. (2017). 50th Anniversary Perspective: Dielectric Phenomena in Polymers and

A

Multilayered

Dielectric

Films.

Macromolecules,

50(6),

2239–2256.

https://doi.org/10.1021/acs.macromol.6b02669

Barber, P., Balasubramanian, S., Anguchamy, Y., Gong, S., Wibowo, A., Gao, H., & Zur Loye, H.C. (2009). Polymer composite and nanocomposite dielectric materials for pulse power energy storage. Materials, 2(4), 1697–1733. https://doi.org/10.3390/ma2041697 Barber, P. S., Shamshina, J. L., & Rogers, R. D. (2013). A “green” industrial revolution: using chitin

towards transformative technologies. Pure and Applied Chemistry, 85(8), 1693–1701. http://dx.doi.org/10.1351/PAC-CON-12-10-14 Bansal, M., Chauhan, G. S., Kaushik, A., & Sharma, A. 2016. Extraction and functionalization of bagasse cellulose nanofibres to Shciff-base based antimicrobial membranes. International Journal

of

Biological

Macromolecules,

887-894.

SC RI PT

https://doi.org/10.1016/j.ijbiomac.2016.06.045

91,

Bengisu, M., & Yilmaz, E. (2002). Oxidation and pyrolysis of chitosan as a route for carbon fiber derivation.

Carbohydrate

Polymers,

50(2),

165–175.

8617(02)00018-8

https://doi.org/10.1016/S0144-

Bondeson, D., Mathew, A., & Oksman, K. (2006). Optimization of the isolation of nanocrystals from microcrystalline

cellulose

by

acid

hydrolysis.

13(2),

171.

U

https://doi.org/10.1007/s10570-006-9061-4

Cellulose,

N

Castelvetro, V., Capaccioli, S., Raihane, M., & Atlas, S. (2016). Complex Dynamics of a Fluorinated

A

Vinylidene Cyanide Copolymer Highlighted by Dielectric Relaxation Spectroscopy.

M

Macromolecules, 49(14), 5104–5114. https://doi.org/10.1021/acs.macromol.6b00683 Celebi, H., & Kurt, A. (2015). Effects of processing on the properties of chitosan/cellulose nanocrystal

films.

Carbohydrate

Polymers,

133,

284–293.

D

https://doi.org/10.1016/j.carbpol.2015.07.007

TE

Chi, K. K. (2004). Dielectric phenomena in solids: with emphasis on physical concepts of electronic processes. Boston, USA: Elsevier Academic Press, 94-97

EP

Cho, M.-J., & Park, B.-D. (2011). Tensile and thermal properties of nanocellulose-reinforced poly (vinyl alcohol) nanocomposites. Journal of Industrial and Engineering Chemistry, 17(1), 36–

CC

40. https://doi.org/10.1016/j.jiec.2010.10.006

Croisier, F., & Jérôme, C. (2013). Chitosan-based biomaterials for tissue engineering. European

A

Polymer Journal, 49(4), 780–792. https://doi.org/10.1016/j.eurpolymj.2012.12.009

de Britto, D., & Campana-Filho, S. P. (2007). Kinetics of the thermal degradation of chitosan. Thermochimica Acta, 465(1–2), 73–82. https://doi.org/10.1016/j.tca.2007.09.008 Dünki, S. J., Cuervo-Reyes, E., & Opris, D. M. (2017). A facile synthetic strategy to polysiloxanes containing sulfonyl side groups with high dielectric permittivity. Polymer Chemistry, 8(4), 715– 724. http://dx.doi.org/10.1039/C6PY01917J

El Miri, N., Abdelouahdi, K., Zahouily, M., Fihri, A., Barakat, A., Solhy, A., & El Achaby, M. (2015). Bio-nanocomposite films based on cellulose nanocrystals filled polyvinyl alcohol/chitosan polymer

blend.

Journal

of

Applied

Polymer

Science,

132(22),

1–13.

https://doi.org/10.1002/app.42004 Fernandes, S. C., Oliveira, L., Freire, C. S., Silvestre, A. J., Neto, C. P., Gandini, A., & Desbrieres,

Green Chemistry, 11, 2023-2029. DOI: 10.1039/B919112G

SC RI PT

J. (2009). Novel transparent nanocomposite films based on chitosan and bacterial cellulose.

Fernandes, S. C., Freire, C. S., Silvestre, A. J., Neto, C. P., Gandini, A., Berglund, L. A., & Salmen,

L. (2010). Transparent chitosan films reinforced with a high content of nanofibrillated cellulose. Carbohydrate Polymers, 81, 394-401. https://doi.org/10.1016/j.carbpol.2010.02.037

Fiege, K., Lünsdorf, H., Atarijabarzadeh, S., & Mischnick, P. (2012). Cyanoethylation of the glucans

nanoparticles.

Beilstein

Journal

of

Organic

Chemistry,

8,

551–566.

N

magnetic

U

dextran and pullulan: Substitution pattern and formation of nanostructures and entrapment of

A

https://doi.org/10.3762/bjoc.8.63

Focher, B., Palma, M. T., Canetti, M., Torri, G., Cosentino, C., & Gastaldi, G. (2001). Structural

M

differences between non-wood plant celluloses: evidence from solid state NMR, vibrational spectroscopy and X-ray diffractometry. Industrial Crops and Products, 13(3), 193–208.

D

https://doi.org/10.1016/S0926-6690(00)00077-7

TE

Garside, P., & Wyeth, P. (2003). Identification of cellulosic fibres by FTIR spectroscopy-thread and single fibre analysis by attenuated total reflectance. Studies in Conservation, 48(4), 269–275.

EP

https://doi.org/10.1179/sic.2003.48.4.269 Gonzalez, M. A., & Smith, R. L. (2003). A methodology to evaluate process sustainability. Progress

&

Sustainable

Energy,

22(4),

269–276.

CC

Environmental

https://doi.org/10.1002/ep.670220415

A

Gonzalo, B., Vilas, J. L., Breczewski, T., Pérez‐Jubindo, M. A., De La Fuente, M. R., Rodriguez, M., & León, L. M. (2009). Synthesis, characterization, and thermal properties of piezoelectric polyimides. Journal of Polymer Science Part A: Polymer Chemistry, 47(3), 722–730. https://doi.org/10.1002/pola.23183 Gunstone, F. D. (1993). High-resolution 13C NMR spectra of long-chain acids, methyl esters, glycerol esters, wax esters, nitriles, amides, alcohols and acetates. Chemistry and Physics of Lipids, 66(3), 189–193. https://doi.org/10.1016/0009-3084(93)90004-M

He, J., Wang, J., Zhong, H., Ding, J., & Zhang, L. (2015). Cyanoethylated Carboxymethyl Chitosan as Water Soluble Binder with Enhanced Adhesion Capability and electrochemical performances for

LiFePO4Cathode.

Electrochimica

Acta,

182,

900–907.

https://doi.org/10.1016/j.electacta.2015.10.006 Horikawa, Y., & Sugiyama, J. (2009). Localization of crystalline allomorphs in cellulose microfibril.

SC RI PT

Biomacromolecules, 10(8), 2235–2239. DOI: 10.1021/bm900413k

Jang, S. D., Kim, J. H., Zhijang, C., & Kim, J. (2009). The effect of chitosan concentration on the

electrical property of chitosan-blended cellulose electroactive paper. Smart Materials and Structures, 18, 015003 (5 pp). https://doi.org/10.1088/0964-1726/18/1/015003

Kargarzadeh, H., Ahmad, I., Abdullah, I., Dufresne, A., Zainudin, S. Y., & Sheltami, R. M. (2012). Effects of hydrolysis conditions on the morphology, crystallinity, and thermal stability of

U

cellulose nanocrystals extracted from kenaf bast fibers. Cellulose, 19(3), 855–866. DOI:

N

10.1007/s10570-012-9684-6

A

Khan, A., Khan, R. A., Salmieri, S., Le Tien, C., Riedl, B., Bouchard, J., … Lacroix, M. (2012). Mechanical and barrier properties of nanocrystalline cellulose reinforced chitosan based films.

Carbohydrate

M

nanocomposite

Polymers,

90(4),

1601–1608.

https://doi.org/10.1016/j.carbpol.2012.07.037

D

Kumar, A., Negi, Y. S., Choudhary, V., & Bhardwaj, N. K. (2014). Characterization of cellulose

TE

nanocrystals produced by acid-hydrolysis from sugarcane bagasse as agro-waste. Journal of Materials Physics and Chemistry, 2(1), 1–8. DOI: 10.12691/jmpc-2-1-1

EP

Kumar, M. N. V. R. (2000). A review of chitin and chitosan applications. Reactive and Functional Polymers, 46(1), 1–27. https://doi.org/10.1016/S1381-5148(00)00038-9

CC

Khutia, M., Joshi, G. M., Deshmukh, K., & Pandey, M. 2015. Polycarbonate/Polystyrene modified blend by ceramic metal oxide. Polymers-plastics Technology and Engineering, 54, 383-389.

A

https://doi.org/10.1080/03602559.2014.961082

Ladhar, A., Ben Mabrouk, A., Arous, M., Boufi, S., & Kallel, A. (2017). Dielectric properties of nanocomposites based on cellulose nanocrystals (CNCs) and poly(styrene-co-2-ethyl hexylacrylate)

copolymer.

Polymer

(United

Kingdom),

125,

76–89.

https://doi.org/10.1016/j.polymer.2017.07.090 Le Troedec, M., Sedan, D., Peyratout, C., Bonnet, J. P., Smith, A., Guinebretiere, R., … Krausz, P.

(2008). Influence of various chemical treatments on the composition and structure of hemp fibres. Composites Part A: Applied Science and Manufacturing, 39(3), 514–522. https://doi.org/10.1016/j.compositesa.2007.12.001 Li, Q., Yao, F.-Z., Liu, Y., Zhang, G., Wang, H., & Wang, Q. (2018). High-Temperature Dielectric

https://doi.org/10.1146/annurev-matsci-070317-124435

SC RI PT

Materials for Electrical Energy Storage. Annual Review of Materials Research, 48, 1-3.

Li, X., Goh, S. H., Lai, Y. H., & Deng, S. M. (1999). Synthesis and hydrolysis of β-cyanoethyl ether

of poly(vinyl alcohol). Journal of Applied Polymer Science, 73(13), 2771–2777. https://doi.org/10.1002/(SICI)1097-4628(19990923)73:13<2771::AID-APP26>3.0.CO;2-#

Li, Q., Zhou, J., & Zhang, L. (2009). Structure and properties of the nanocomposite films of chitosan

reinforced with cellulose whiskers. Journal of Polymer Science Part B: Polymer Physics, 47,

U

1069–1077. https://doi.org/10.1002/polb.21711

N

Lima, C. G. A., de Oliveira, R. S., Figueiredo, S. D., Wehmann, C. F., Gomes, J. C., & Sombra, A.

A

S. 2006. DC conductivity and dielectric permittivity of collagen-chitosan films. Materials

M

Chemistry and Physics, 99, 284-288. DOI:10.1016/j.matchemphys.2005.10.027 Mandal, A., & Chakrabarty, D. (2011). Isolation of nanocellulose from waste sugarcane bagasse (SCB)

and

its

characterization.

Carbohydrate

Polymers,

86(3),

1291–1299.

D

https://doi.org/10.1016/j.carbpol.2011.06.030

TE

Martin, S. J., Godschalx, J. P., Mills, M. E., Shaffer II, E. O., & Townsend, P. H. (2000). Development of a low-dielectric constant polymer for the fabrication of integrated circuit interconnect. Materials,

EP

Advanced

12,

1769-1778.

https://doi.org/10.1002/1521-

4095(200012)12:23<1769::AID-ADMA1769>3.0.CO;2-5

CC

Nasreen, S., Treich, G. M., Baczkowski, M. L., Mannodi‐ Kanakkithodi, A. K., Cao, Y., Ramprasad, R., & Sotzing, G. (n.d.). Polymer Dielectrics for Capacitor Application. Kirk-Othmer

A

Encyclopedia of Chemical Technology.

Nisticò, R., & Roberto. (2017). Aquatic-Derived Biomaterials for a Sustainable Future: A European Opportunity. Resources, 6(4), 65. https://doi.org/10.3390/resources6040065

Orue, A., Santamaria‐Echart, A., Eceiza, A., Peña‐Rodriguez, C., & Arbelaiz, A. (2017). Office waste paper as cellulose nanocrystal source. Journal of Applied Polymer Science, 134(35). https://doi.org/10.1002/app.45257

Park, S., Baker, J. O., Himmel, M. E., Parilla, P. A., & Johnson, D. K. (2010). Cellulose crystallinity index: measurement techniques and their impact on interpreting cellulase performance. Biotechnology for Biofuels, 3(1), 10. https://doi.org/10.1186/1754-6834-3-10 Prashanth, K. V. H., & Tharanathan, R. N. (2007). Chitin/chitosan: modifications and their unlimited application potential—an overview. Trends in Food Science & Technology, 18(3), 117–131.

SC RI PT

https://doi.org/10.1016/j.tifs.2006.10.022

Qiao, Y., Islam, M. S., Han, K., Leonhardt, E., Zhang, J., Wang, Q., … Tang, C. (2013). Polymers

Containing Highly Polarizable Conjugated Side Chains as High‐ Performance All‐ Organic Nanodielectric

Materials.

Advanced

Functional

Materials,

https://doi.org/10.1002/adfm.201300736

23(45),

5638–5646.

Qiao, Y., Yin, X., Zhu, T., Li, H., & Tang, C. (2018). Dielectric polymers with novel chemistry, and

architectures.

Progress

in

Science,

80,

153-162.

N

https://doi.org/10.1016/j.progpolymsci.2018.01.003

Polymer

U

compositions

A

Rahman, P. M., Abdul Mujeeb, V., Muraleedharan, K., & Thomas, S. K. (2018). Chitosan/nano ZnO composite films: Enhanced mechanical, antimicrobial and dielectric properties. Arabian

M

Journal of Chemistry, 11, 120-127. http://dx.doi.org/10.1016/j.arabjc.2016.09.008 Raskó, J., & Kiss, J. (2006). Adsorption and surface reactions of acetonitrile on Al 2O3-supported metal

catalysts.

Applied

D

noble

Catalysis

A:

General,

298,

115–126.

TE

https://doi.org/10.1016/j.apcata.2005.09.028 Rebouillat, S., & Pla, F. (2013). State of the art manufacturing and engineering of nanocellulose: a

EP

review of available data and industrial applications. Journal of Biomaterials and Nanobiotechnology, 4(02), 29869 (24 pp). 10.4236/jbnb.2013.42022

CC

Rinaudo, M. (2006). Chitin and chitosan: properties and applications. Progress in Polymer Science, 31(7), 603–632. https://doi.org/10.1016/j.progpolymsci.2006.06.001

A

Robles, E., Fernández-Rodríguez, J., Barbosa, A. M., Gordobil, O., Carreño, N. L. V, & Labidi, J. (2018). Production of cellulose nanoparticles from blue agave waste treated with environmentally

friendly

processes.

Carbohydrate

Polymers,

183,

294-302.

https://doi.org/10.1016/j.carbpol.2018.01.015 Sanchez-Chaves, M., & Arranz, F. (1996). Synthesis of amidoxime-containing modified dextran. Polymer, 37(19), 4403–4407. https://doi.org/10.1016/0032-3861(96)00269-8

Schmidt, M., Saavedra, M., Alegría, L., Alvarado, N., Fuentes, I., Menares, P., Kortaberria, G., & Leiva, A. (2018). Host-guest interactions of non-steroidal anti-inflammatory drugs on the functionalized dendronized polymeric nanocomposite, Poly (N-tris [((cyano-ethoxy) methyl] methylacrylamide). Journal of Macromolecular Science, Part A, 55(3), 296–309. https://doi.org/10.1080/10601325.2018.1426389

SC RI PT

Segal, L., Creely, J. J., Martin Jr, A. E., & Conrad, C. M. (1959). An empirical method for estimating the degree of crystallinity of native cellulose using the X-ray diffractometer. Textile Research Journal, 29(10), 786–794. https://doi.org/10.1177/004051755902901003

Solymar, L., & Walsh, D. (1993). Lectures on the electrical properties of materials. Oxford, Great Britain: Oxford University Press

Srinivasa, P. C., Ramesh, M. N., & Tharanathan, R. N. (2007). Effect of plasticizers and fatty acids

U

on mechanical and permeability characteristics of chitosan films. Food Hydrocolloids, 21(7),

N

1113–1122. https://doi.org/10.1016/j.foodhyd.2006.08.005

physicochemical

characterization

A

Sundaram, J., Pant, J., Goudie, M. J., Mani, S., & Handa, H. (2016). Antimicrobial and of

biodegradable,

nitric

oxide-releasing

M

nanocellulose−chitosan packaging membranes. Journal of Agricultural and Food Chemistry, 64, 5260-5266. DOI: 10.1021/acs.jafc.6b01936

D

Treufeld, I., Wang, D. H., Kurish, B. A., Tan, L.-S., & Zhu, L. (2014). Enhancing electrical energy

TE

storage using polar polyimides with nitrile groups directly attached to the main chain. Journal of Materials Chemistry A, 2(48), 20683–20696. DOI: 10.1039/C4TA03260H

EP

Wang, D. H., Kurish, B. A., Treufeld, I., Zhu, L., & Tan, L. (2015). Synthesis and characterization of high nitrile content polyimides as dielectric films for electrical energy storage. Journal of

CC

Polymer

Science

Part

A:

Polymer

Chemistry,

53(3),

422–436.

https://doi.org/10.1002/pola.27445

A

Wang, Q., & Zhu, L. (2011). Polymer nanocomposites for electrical energy storage. Journal of Polymer

Science

Part

B:

Polymer

Physics,

49(20),

1421–1429.

https://doi.org/10.1002/polb.22337

Wei, J., Zhang, Z., Tseng, J.-K., Treufeld, I., Liu, X., Litt, M. H., & Zhu, L. (2015). Achieving High Dielectric Constant and Low Loss Property in a Dipolar Glass Polymer Containing Strongly Dipolar and Small-Sized Sulfone Groups. ACS Applied Materials & Interfaces, 7(9), 5248– 5257. https://doi.org/10.1021/am508488w

Yan, M., Li, S., Zhang, M., Li, C., Dong, F., & Li, W. (2013). Characterization of surface acetylated nanocrystalline cellulose by single-step method. BioResources, 8(4), 6330–6341. DOI: 10.15376/biores.8.4.6330-6341 Yoshida, C. M. P., Oliveira Junior, E. N., & Franco, T. T. (2009). Chitosan tailor‐made films: the effects of additives on barrier and mechanical properties. Packaging Technology and Science,

SC RI PT

22(3), 161–170. https://doi.org/10.1002/pts.839

Zawadzki, J., & Kaczmarek, H. (2010). Thermal treatment of chitosan in various conditions. Carbohydrate Polymers, 80(2), 395–401. https://doi.org/10.1016/j.carbpol.2009.11.037

Zhang, Z., Wang, D. H., Litt, M. H., Tan, L., & Zhu, L. (2018). High‐Temperature and High‐Energy‐

Density Dipolar Glass Polymers Based on Sulfonylated Poly (2, 6‐dimethyl‐1, 4‐phenylene

U

oxide). Angewandte Chemie, 130(6), 1544–1547. https://doi.org/10.1002/ange.201710474

Zhou, J., Li, Q., Song, Y., Zhang, L., & Lin, X. (2010). A facile method for the homogeneous

N

synthesis of cyanoethyl cellulose in NaOH/urea aqueous solutions. Polymer Chemistry, 1(10),

A

1662–1668. http://dx.doi.org/10.1039/C0PY00163E

The

Journal

of

M

Zhu, L. (2014). Exploring Strategies for High Dielectric Constant and Low Loss Polymer Dielectrics. Physical

A

CC

EP

TE

D

https://doi.org/10.1021/jz501831q

Chemistry

Letters,

5(21),

3677–3687.

Figures Captions

Figure 1. FTIR spectra of both unmodified and CN-CNC Figure 2. 13C NMR spectra (A) and 13C NMR CP-MAS spectra (B) for both unmodified and CN-

SC RI PT

CNC

Figure 3. Normalized powder XRD scatters with fitted curves for the main crystalline planes for both unmodified and CN-CNC

Figure 4. ATR spectra for pure chitosan and nanocomposites with 10, 30 and 50 wt% of CN-CNC, at different regions

U

Figure 5. Height and phase AFM images of chitosan and nanocomposites with 10, 30 and 50 wt% of

N

CN-CNC

Figure 6. Weight loss (left) and differential thermogravimetric analysis (DTGA, right) curves for

A

CNC and CN-CNC under nitrogen (A, B) and air (C, D) atmospheres.

M

Figure 7. Weigtht loss (A) and differential thermogravimetric analysis (DTGA, B) curves for pure Chitosan, pure CN-CNC and all nanocomposites under air atmosphere. Evolution of T5% and TMRD

D

for chitosan and CN-CNC in all the samples (C).

TE

Figure 8. Evolution of tensile strength (A), Young’s modulus and elongation at break (B) with CNCNC amount. Solid lines are guides for the eye.

EP

Figure 9. Evolution of (a) dielectric constant, (b) dielectric loss factor and (c) tanδ with frequency for pure chitosan, for the nanocomposite with unmodified CNC and for those with different CN-CNC

A

CC

amounts. (d) Dielectric constant values at different frequencies for all samples analyzed.

SC RI PT

A

CC

EP

TE

D

M

A

N

U

Figure 1. FTIR spectra of both unmodified and CN-CNC

Figure 2. 13C NMR spectra (A) and 13C NMR CP-MAS spectra (B) for both unmodified and CN-CNC

SC RI PT U N A M

Figure 3. Normalized powder XRD scatters with fitted curves for the main crystalline planes

A

CC

EP

Chitosan Chi/CN-CNC (10%) Chi/CN-CNC (30%) Chi/CN-CNC (50%)

TE

D

for both unmodified and CN-CNC

A

B

C

Chi/CN-CNC (50%)

Chi/CN-CNC (50%)

Chi/CN-CNC (30%)

Chi/CN-CNC (30%)

Chi/CN-CNC (10%)

Chi/CN-CNC (10%)

Chitosan

Chitosan

Figure 4. ATR spectra for pure chitosan and nanocomposites with 10, 30 and 50 wt% of CN-

N

U

SC RI PT

CNC, at different regions

A

Figure 5. Height and phase AFM images of chitosan and nanocomposites with 10, 30 and 50

A

CC

EP

TE

D

M

wt% of CN-CNC

SC RI PT U N A M

Figure 6. Weight loss (left) and differential thermogravimetric analysis (DTGA, right) curves

A

CC

EP

TE

D

for CNC and CN-CNC under nitrogen (A, B) and air (C, D) atmospheres.

SC RI PT U N A M D

Figure 7. Weigtht loss (A) and differential thermogravimetric analysis (DTGA, B) curves for

TE

pure Chitosan, pure CN-CNC and all nanocomposites under air atmosphere. Evolution of T5%

A

CC

EP

and TMRD for chitosan and CN-CNC in all the samples (C).

SC RI PT U N A M D TE EP

A

CC

Figure 8. Evolution of Young’s modulus (A), tensile strength and elongation at break (B) with CN-CNC amount. Solid lines are guides for the eye.

SC RI PT U N

Figure 9. Evolution of (a) dielectric constant, (b) dielectric loss factor and (c) tanδ with

A

frequency for pure chitosan, for the nanocomposite with unmodified CNC and for those with

M

different CN-CNC amounts. (d) Dielectric constant values at different frequencies for all

A

CC

EP

TE

D

samples analyzed.

Scheme captions

A

CC

EP

TE

D

M

A

N

U

SC RI PT

Scheme 1. Cyanoethylation of cellulose nanocrystals

Table

Table 1. CN-CNC size distribution and average roughness for all nanocomposites as calculated from AFM images analysis. Size (nm) Roughness (nm) 0.75

10 wt% CN-CNC

35.29 ± 9.16

30 wt% CN-CNC

36.82 ± 7.63

50 wt% CN-CNC

38.65 ± 9.36

SC RI PT

-

7.19 17.4 24.8

A

CC

EP

TE

D

M

A

N

U

Chitosan