Starch Polymer Bionanocomposite

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Graphene Oxide Filled Lignin/Starch Polymer bionanocomposite: Structural, Physical and Mechanical studies. Meryem Aqlil, Annie Moussemba Nzenguet, Younes Essamlali, Asmae Snik, Mohamed Larzek, and Mohamed Zahouily J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.7b04155 • Publication Date (Web): 07 Nov 2017 Downloaded from http://pubs.acs.org on November 9, 2017

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Journal of Agricultural and Food Chemistry

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Graphene Oxide Filled Lignin/Starch Polymer bio-

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nanocomposite: Structural, Physical and

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Mechanical studies

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Meryem Aqlil1, Annie Moussemba Nzenguet1, Younes Essamlali1,2, Asmae Snik1,

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Mohamed Larzek3 and Mohamed Zahouily1,2*

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Laboratoire de Matériaux, Catalyse et Valorisation des Ressources Naturelles (MaCaVa), URAC 24, FST Mohammedia B. P. 146, 20650, Université Hassan II Casablanca Morocco. 2 MAScIRFoundation, Nanotechnologie, VARENA Center, Rabat Design, Rue Mohamed El Jazouli, Madinat El Irfane 10100-Rabat, Morocco ; 3 OLAC : Omnium de l’anti corrosion, ZI Tit Melil Casablanca-Morocco. * Correspondence: [email protected] ; Tel. +212661416359

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1 ACS Paragon Plus Environment


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Abstract

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In this study, graphene oxide(GO)was investigated as a potential nano-reinforcing agent in

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starch/lignin (ST/L) biopolymer matrix. Bio-nanocomposite films based on ST/L blend matrix

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and GO were prepared by solution casting technique of the corresponding film forming

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solution. The structure, morphologies and properties of bio-nanocomposite films were

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characterized by FTIR, thermal gravimetric analysis (TGA), Ultraviolet-visible (UV-Vis),

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SEM and tensile tests. The experimental results showed that contents of GO have a significant

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influence on the mechanical properties of the produced films. The results revealed that the

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interfacial interaction formed in the bio-nanocomposite films improved the compatibility

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between GO fillers and ST/L matrix. The addition of GO also reduced moisture uptake (Mu)

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and water vapor permeability of ST/L blend films. In addition, TGA showed that the thermal

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stability of bio-nanocomposite films was better than that of neat starch film. These findings

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confirmed the effectiveness of the proposed approach to produce biodegradable films with

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enhanced properties, which may be used in packaging applications.

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Starch;

Lignin;

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Keywords:

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Physicochemical properties.

Graphene

oxide;

Bio-nanocomposite;

32 33 34 35


Interaction;

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1. Introduction

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Due to the environmental impact caused by petrochemical-based synthetic polymers, natural

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polymers have received tremendous attention in the last few decades because of their

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potential to substitute the current synthetic polymers1 owing to their non-toxicity,

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biodegradability and biocompatibility.2 Apart from their environmental benefits, bio-based

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polymers exhibit other advantages such as low cost, non-dependence on petroleum sources

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and availability from renewable resources. Moreover, natural bio-based polymers are easily

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biodegradable within a short period of time and solve the waste disposal problems generated

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by using non-biodegradable polymers.3,4 Among the many candidates of natural

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biodegradable polymers, starch and lignin have been widely studied for the fabrication of

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biodegradable films owing to their renewability, biodegradability and availability at low cost.

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Starch is one of the most commonly available natural polysaccharides obtained from a great

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variety of crops.5 It has been accepted as a good alternative for the production of

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biodegradable plastics and has high potential for replacing current synthetic polymers.6-8

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Starch has been widely used in several food and non-food applications, particularly in

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agriculture, alimentary, medicine, and packaging industries.9-12 Unfortunately, thermoplastic

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starch suffers from many drawbacks related to its water sensitivity and poor mechanical

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properties.13,14 To overcome these limitations, many approaches were suggested in literature.

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One of the most effective methods for the development of new and inexpensive biodegradable

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materials with improved properties is to blend starch with either synthetic or natural

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polymers15-18 or to incorporate a nanoscale reinforcing materials into the starch based

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polymeric matrix.19-22 Another, approach that has been widely studied consists of the use a

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chemically modified starch by either oxidation or carboxymethylation methods.23-25

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Lignin, a natural biopolymer extracted from sugarcane bagasse, is the second most abundant

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natural polymer after cellulose, it has been widely used in biodegradable polymers



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manufacturing owing to its intrinsic properties such as high degree of crosslinking between

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the units, hydrophobic nature, amorphous structure and three-dimensional structure.26,27 The

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abundance of carbonyl and carboxylic groups, phenolic and aliphatic hydroxyl groups confer

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to lignin a good ability to establish a strong interfacial interaction with other polymers making

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this natural biopolymer a suitable candidate for blending polymers. Many researchers put

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forward the use of lignin to blend with various synthetic polymers, either in their native state

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or after compatibilization, such as poly(vinyl alcohol), poly(ethylene oxide) and poly(lactic

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acid).28,29 Blending starch with lignin is an appealing approach since no compatibilization is

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required. It is well known that the addition of lignin within starch matrix significantly

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improves the physical and the chemical properties of starch.30-33 Baumberger et al.34-36

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reported that blending lignin extracted either from traditional or novel pulping processes

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within starch matrix resulted in an important improvement of the performances of starch

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films. Besides, a significant reduction of the water solubility and water content of

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starch/lignin film has been observed.36 Moreover, it has been previously shown that the

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incorporation of lignin into starch can also reduce the water permeability and increases the

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thermal stability and tensile strength of the resulted ST/L blend film.37-40 However, the

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properties of the resulting ST/L film are highly dependent on the origin of the lignin and also

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on the adopted extraction process. Most of the interest in developing low cost biodegradable

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plastics is due to their wide spectrum of application which includes packaging and consumer

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products. The major applications for starch-lignin bio-nanocomposites would be packaging

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containers for single or short-term use, as naturally biodegradable alternatives to conventional

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synthetic polymers, so they have great potential to be used as fresh food packaging.

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Recently, much more attentions have been paid to the development of the new materials with

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specific properties by incorporation of nanometric reinforcements in polymeric matrix.41,42

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This method has been considered as an effective strategy to improve the physicochemical


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properties of the polymeric matrix.43,44 The synergic effect between the nanosized filler and

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polymer resulted in a significant improvement of properties of obtained nanocomposites.

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Various types of nanofillers organic or inorganic are used as an effective nano-reinforcements

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for many biopolymer matrix, like carbon nanotubes and nanofibers,45 GO,46 nanoclay47 and

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cellulose nanocrystals,48 etc. Among the family of nanofillers, GO has attracted a great deal of

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interest and has been widely used as a nano-reinforcement in polymer composite materials.

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GO has been widely used in combination with different biopolymers to design new bio-

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nanocomposites with improved mechanical, thermal, electrical, as well as, gas-, and water

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vapor-barrier properties. In addition, high surface area, high aspect ratio, large number of

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functional groups, and high strength of GO allow it to establish strong interfacial interactions

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between the filler and the polymeric matrix. Moreover, the functional groups, such as

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carboxyl, amino, or hydroxyl groups, contained in biopolymers matrix leads to a very

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efficient interaction with the functional groups on GO.49,50 GO has the ability to form a strong

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physical interaction within the polymeric matrix since it contains several oxygen-containing

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functional groups, such as hydroxyl (OH) and carbonyl groups (-C=O).51,52 It has been widely

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used to improve the thermal stability, electrical and mechanical properties of several

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polymers.53The aim of the present work was to study the preparation of graphene oxide (GO)

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reinforced ST/L based polymer blends. GO nanosheets were characterized using X ray

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diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM),

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high resolution-transmission electron microscopy (HR-TEM) and atomic force microscopy

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(AFM). The influence of incorporation of increasing amount of GO on the structural,

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morphological and mechanical properties as well as thermal stability of the ST/L based bio-

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nanocomposite films was studied. Furthermore, the water swelling, hydrolytic degradation

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and moisture absorption of the prepared bio-nanocomposites were also investigated. The



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fundamental structure-property relationship of GO-based starch/lignin bio-nanocomposites

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was also investigated and discussed.

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2. Materials and methods

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2.1. Materials

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The sugarcane bagasse (SCB) was provided from COSUMAR Group, company in south

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Morocco. The moisture content of the sugarcane bagasse fibers was about 7%. Wheat starch

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and graphite powder (≤ 20 µm, 99.99%)were purchased from VWR International and Sigma-

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Aldrich, respectively. Analytical grade chemicals used for lignin extraction and graphite

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oxidation were purchased from Sigma-Aldrich and were used as received.

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2.2. Lignin Extraction

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Lignin was extracted from sugarcane bagasse by alkaline hydrolysis. Firstly, the SCB fibers

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were ground and sieved (150 µm) to remove the fine powder and the small particles. The

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ground fibers were repeatedly washed with hot water for 2 hours at 60°C and then filtered.

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After complete washing, the obtained residue was digested with alkali solution (15wt%

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NaOH). The solution was then filtered and the filtrate, lignin solution, was acidified with 5N

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H2SO4 until pH = 2 was reached. The obtained precipitate was recovered by centrifugation,

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washed with distilled water, dried in a hot desiccator at 60°C for a complete removal of water

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and finally ground into a uniform powder.

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2.3. Synthesis of graphene oxide

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Graphene oxide was prepared from natural graphite according to the Hummers method.54 In a

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typical procedure, 1 g of graphite powder and 1g of sodium nitrate were firstly mixed together

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until complete homogenization. Afterward, 30 ml of sulfuric acid (98%) was added and the

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mixture was stirred for 30 minutes in an ice-bath. Next, 3 g of KMnO4 (99%) was slowly

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added in a controlled manner to avoid the increase of the temperature (˂20°C). The flask was

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then removed and heated in an oil bath at 40°C under constant magnetic stirring for 2hours.


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Afterward, 50 ml of distilled water was slowly added, which generate an increase in the

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temperature to 98°C. The mixture was maintained at this temperature under continuous

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stirring for 15 minutes. Subsequently, 12 ml of H2O2 solution (30% v/v) was added to the

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reaction mixture under vigorous stirring for 10 min. Finally, the resulting yellow cake was

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cooled until room temperature diluted with 260 mL of distilled water and centrifuged. The

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obtained precipitate was washed several times with distilled water and dried at 60°C during

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72 hours. Appropriate amounts of the as-prepared graphite oxide (0.3, 0.5 and 0.7wt% with

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respect to ST/L weight) were dispersed in 20 mL of distilled water and sonicated for

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to make a homogeneous brown dispersion of graphene oxide nanosheets.

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2.4. Bio-nanocomposite film processing

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The preparation ST/L-GO bio-nanocomposites films were carried out in two consecutive

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steps. Firstly, 0.5 g of lignin was dissolved in 50 mL of distilled water with constant stirring

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within 12 hours at 25°C followed by sonication for 1 hour until complete dissolution.

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Separately,

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2.5 g of wheat starch and 0.75 g of glycerol, as a plasticizer, were dissolved in 46.25 mL of

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distilled water at 95°C during 90 min under vigorous stirring. The starch solution was cooled

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until room temperature while keeping a constant stirring, and then it was sonicated for

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15 minutes to ensure the complete homogenization. The ST/L film-forming solution was

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prepared by mixing the starch and lignin solutions under vigorous magnetic stirring for 1 h at

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25°C until the formation of a homogeneous solution (Fig. 1). In the second step, a

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predetermined amount of GO suspension was slowly added to the ST/L blend and the mixture

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was sonicated during 30 minutes followed by vigorous magnetic stirring for 6 hours until the

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formation of a homogeneous dispersion. The GO loading levels were 0.3, 0.5 and 0.7wt%

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based on dry ST/L blend. Subsequently, the ST/L-GO film-forming solutions (Figure 1) were

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cast onto plastic disk and left to cure at room temperature for complete water evaporation.


3 hours


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After that, the ST/L-GO bio-nanocomposites were dried at 60°C for 6 hours to obtain dry

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films. Pure ST/L blend and neat starch films were prepared according to the same procedure.

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The films were coded as ST, ST/L, ST/L-0.3, ST/L-0.5 and ST/L-0.7, where the number

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stands for the GO loadings.

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3. Characterization techniques

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3.1. Characterization of graphene oxide

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X-ray diffraction (XRD) patterns were recorded at room temperature on a Bruker D8

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Discover diffractometer using Cu-Kα radiation (λ = 1.5438 Å). The samples were finely

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grounded before being analyzed. Fourier transform infrared spectroscopy (FTIR)

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measurements were performed on anAffinity-1S SHIMADZU spectrometer fitted with a

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Golden Gate single reflection ATR accessory in the range of 4000 to 400 cm−1 with a

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resolution of 16 cm-1and an accumulation of 42 scans. Thermogravimetric analyses (TGA)

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were conducted under air gas using a TGA-Q500 (TA Instruments) apparatus at a heating rate

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of 10 °C/min-1 from 25 and 800°C. The Ultraviolet-visible (UV-vis) spectra were recorded on

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the LAMBDA 1050 UV/Vis/NIR instrument in the range of 200-800 nm. Scanning electron

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microscopy (SEM)analyses were recorded using a FEI Quanta 200 field emission. The

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transmission electron microscopy (TEM) micrographs were obtained on a Tecnai G2

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microscope at 120 kV. The sample used for TEM characterization were dispersed in a mixture

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of water/ethanol (10% v/v) and then deposited on the TEM grid. The solvent was left to

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evaporate for few minutes before analysis. High resolution transmission electron microscopy

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(HR-TEM) analysis was carried out by a Jeol 2100F microscope, equipped with ultra-high-

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resolution pole piece, field emission Schottky electron source and operating at 200 kV with a

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resolution point of 0.235 nm. Atomic Force Microscopy (AFM) measurements were obtained

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using a Veeco Dimension ICON. Before being analyzed, the samples used for AFM

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characterizations were deposited on mica sheets.


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3.2. Characterization of nanocomposite films

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Mechanical tensile properties of the prepared bio-nanocomposite films were measured on the

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LUDWIG mpk tensiometer upon samples with dimensions of 80 mm × 10 mm

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(width × length), at tensile rate of 10 mm/min. Five tests were performed and the obtained

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values are the averages of the five measurements. All film samples were preconditioned for

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24h in a constant-temperature humidity chamber set at 40°C before testing.

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Film thickness was measured to the nearest 0.01 mm using a hand-held micrometer (digital

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GALIPER). Three thickness measurements were taken on each tensile testing specimen along

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the length of the rectangular specimen, and the mean value was used in thickness calculation.

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In order to avoid the influence of the thickness of specimens, all the samples used for the

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measurement have a same thickness of 130 µm.

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The moisture uptake (Mu) of the ST/L-GO bio-nanocomposites was determined according to

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the ASTM E104 standard with slight modifications.55 Typically, rectangular specimens of the

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prepared bio-nanocomposites (20 mm × 20 mm) were firstly dried at 105°C for 2 hours in a

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hot desiccator and then weighted and incubated in a climatic chamber at 25°C with controlled

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relative humidity (RH) of 75 ± 0.5%. At different intervals of time (each hour) over duration

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of 6 hours, the films were then removed and weighted. The moisture uptake of the as-

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prepared films was calculated according to the following equation:

Mu% =

Mf − Mi × 100 Mi

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Where Mf and Mi are the weights of the sample after 6 hours exposure to 75 % RH and of the

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dried sample before being incubated in the climatic chamber, respectively.

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The water swelling capacity (SW) was determined as following: rectangular specimens

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(20 mm × 20 mm) of neat ST, ST/L blend and ST/L-GO bio-nanocomposite films were firstly

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dried in an oven at 100°C for 24h until constant weight (Wi) taken. Then, the films were



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immersed in a glass bottle containing 20 mL of distilled water during 24 hours. After

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immersion in water, samples were removed and weighted (Wf). The water swelling capacity

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(SW) was calculated according to the following equation: SW % =

Wf − Wi × 100 Wi

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The hydrolytic degradation of the prepared bio-nanocomposites was also investigated.

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Previously dried and weighed films specimens (20 mm × 30 mm) were immersed in a glass

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bottles containing 25 mL of distilled water and stored at room temperature. After 30 days of

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incubation, the rectangular specimens were removed from the solution and dried at 80°C for

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2 days. The hydrolytic degradation was estimated by weighing the films before and after

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immersion in water.

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The water vapor permeability (WVP) of the prepared bio-nanocomposite films was

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determined according to the standard method E96-90 with some modifications.56 Glass bottles

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with 20 mm diameter and of 40 mm depth were charged with 10g of distilled water and were

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covered with the prepared bio-nanocomposite. The charged bottles were then weighted and

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incubated in a climatic chamber at 25°C at a relative humidity of 50%. Successive weightings

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were carried out every hour for duration of 7 hours and the changes in the bottles weight were

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recorded function of time. The relationship between weight change and time should be

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represented by a linear plot; the slope of this plot divided by the area of the glass bottle (m2)

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represents the water vapor transmission rat (WVTR). The WVP (gm/m2 h Pa) was calculated

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as follows: WVP=

WVTR WVTR X= X ΔP SR1-R2

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Where X is the thickness of the film (m), S is the saturation vapor pressure (Pa) at the test

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temperature (25°C), R1 and R2 are the relative humidity in the glass bottle and climatic

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chamber, respectively.

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4. Results and discussions

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4.1. Characterization of GO

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Before proceeding to the incorporation of the GO into the ST/L blend, the successfully

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oxidation and exfoliation of GO into multilayer nanosheets was investigated by means of

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X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force

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microscopy (AFM) techniques. The GO nanosheets dispersion was achieved by alternating

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vigorous magnetic stirring and intense sonication of the oxidized natural graphite. This

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dispersion of GO was stable even after 4 weeks storage at room temperature.

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The FTIR spectrum of GO showed many characteristics bands (Fig. 2b; right). The broad

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band located at 3373 cm-1 was attributed to the stretching vibration of the hydroxyl groups

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(O-H), and those observed at around 1714 and 1612 cm-1were attributed to the stretching

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vibration of carboxylic groups and the skeletal vibrations of unoxidized graphitic domains,

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respectively.57 In addition, other oxygen-containing functional groups such as C-OH, C-O-C

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and C-O were clearly observed at 1363, 1148 and 1036 cm-1, respectively.58 The appearance

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of these bands revealed the presence of numerous oxygen-containing functional groups thus

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indicating that the graphite has been successfully oxidized into the GO nanosheets.

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The XRD patterns of graphite and graphite oxide prepared according to the Hummer’s

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method are shown in Figure 2 (left). The XRD pattern of the graphites how done single sharp

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peak at 26.5° assigned to the highly organized layer structure of graphite. The interlayer

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distance corresponding to the 002 reflections was 0.34 nm, which is in good agreement with

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the JCPDS data N°75-2078. After oxidation of graphite, the diffraction peak observed at 2Ɵ =

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26.5° was shifted to 2Ɵ = 10° and the d-spacing was increased from 0.34 nm to 0.88 nm (Fig. 11 ACS Paragon Plus Environment


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2b; left). This shifting was mainly due to the formation of oxygen-containing functional

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groups between the layers of the graphite.59 The obtained results confirmed the successful

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oxidation of graphite into graphite oxide.

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The scanning electron microscopy provides significant morphological information especially

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those ascribed to the morphology and the size of the as-prepared GO. Typical SEM and TEM

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micrographs are shown in Figure 3. SEM image in Fig. 3a showed that the as-prepared GO

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was mainly consisting of multilayer agglomerate, which formed a three-dimensional porous

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network. The surface morphology of GO was characterized by the presence of distinct

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wrinkles and folding. TEM image of GO nanosheets (Fig. 3b) revealed that this sample is

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mainly composed of assembled thin layers nanosheets with wrinkled and folded morphology.

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These observations indicate that a high degree of exfoliation was achieved during the

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oxidation and exfoliation processes. According to the HR-TEM micrograph of GO (Fig. 3c),

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the value of the inter-planar distance d002 was found to be 0.75 nm. The selected area electron

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diffraction (SAED)pattern (Fig. 3d) showed a two clear diffraction spots characteristic of

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crystalline order, suggesting the presence of unoxidized graphitic regions within the graphene

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oxide. This pattern is consistent with a hexagonal lattice of GO nanosheet.

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The exfoliation level of the GO nanosheets was further investigated by AFM. As shown in

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Fig. 3e the GO sample is mainly consisting of thin sheets irregular in sharp and adopting a

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uniform thickness. The mean thickness of the obtained sheets was approximately 1 nm while

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the other lateral dimensions varied from 100 to 800 nm. This relatively higher thickness,

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which is relatively higher than that expected one for a single sheet of graphene oxide (0.34

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nm), might be due to the presence of oxygen-containing functional groups to the surface of

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GO nanosheets or to the existence of space between the nanosheets and the substrate due to

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the wrinkled and folded structure of GO nanosheets that arises during solvent evaporation.60

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4.2. Characterization of bio-nanocomposites

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4.2.1. Fourier transform infrared spectroscopy

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FTIR measurements provide significant information about the possible interfacial interactions

281

among starch, lignin and GO nanosheets in bio-nanocomposite films. Fig. 4 shows the typical

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FTIR spectra of GO, neat starch and ST/L-GO bio-nanocomposite films loaded with various

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GO amounts. It should be noted that all films were dried under vacuum at 40°C overnight

284

before being analyzed. As shown in Figure 4, neat starch exhibits typical stretching and

285

bending vibration of OH groups at 3229 and 1420 cm-1, respectively. The band observed at

286

2929 cm-1 was assigned to the C-H stretching. Besides, the bands located at 1152 cm-1 and

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those observed at approximately 1077 and 1008 cm-1 were assigned to the stretching vibration

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of C-O group in C-O-H and C-O-C groups of the anhydro-glucose ring of starch molecule,

289

respectively.61 The FTIR spectra of pristine lignin showed a broad peak between 3600 and

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3200 cm-1 assigned to the alcoholic and phenolic -OH absorptions. The broad peaks at around

291

1600 and 1400 cm-1 are attributed to the aromatic structures (Fig. 4). After addition of lignin

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biopolymer, a strong interfacial interaction between functional groups of lignin and starch

293

was occurred resulting in a better compatibility between these two biopolymers, thus

294

suggesting the formation of strong hydrogen bond between lignin and starch molecules.62,63

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This indicated that starch and lignin achieved a high degree of compatibility. This finding was

296

further confirmed by the displacement of the carbonyl band located at around 1008 cm-1

297

towards lower wavelength numbers as shown in Fig. 4b. Compared the spectrum of ST/L

298

film to those of starch and lignin, it can be found that the spectrum of ST/L film is similar to

299

that of neat starch because the blend matrix composition is mainly based on starch

300

biopolymer.

301

The FTIR spectras of ST/L-0.3,ST/L-0.5 and ST/L-0.7 offer some important information

302

related to the interactions between oxygenated groups in GO and ST/L blend. Indeed, when



303

GO was added, the characteristic bands at 1152, 1077, 1002 cm-1 of ST/L blend shifted to

304

lower wave-numbers 1134, 1062, 999 cm-1, respectively, in ST/L blend filled by 0.7wt% of

305

GO, suggesting the occurrence of strong crosslinking reaction between the oxygen-containing

306

surface functional groups of GO (-OH, -COOH and -O-) and fuctional groups of ST/L matrix

307

(C-O and OH groups). The occurence of this interaction was further confirmed by the

308

increase in the intensity of the OH groups which indicate that additional hydrogen bondings

309

were formed (Fig. 4a). Based on the latter explanations, it seems that the ST/L-GO bio-

310

nanocomposites exhibitedan interconnected network structure linked by strong hydrogen

311

bonds either between starch and lignin biopolymers and also between ST/L blend and GO

312

nanosheets (Scheme 1).

313

4.2.2. Thermogravimetric analysis

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The thermal stability of the ST and ST/L blend films as well as the bio-nanocomposites films

315

was evaluated in order to determine if the addition of lignin and GO could produce any

316

improvement in the thermal behavior of starch. The thermogravimetric (TG)and derivative

317

thermogravimetric (DTG) curves of the starch, crosslinked ST/L and ST/L-GO bio-

318

nanocomposite are shown in Fig. 5a and Fig. 5b, respectively. Starch film exhibited tree

319

major weight losses (Fig. 5a). The first weight loss before 120°C was attributed to the

320

evaporation of water, the second one within a range of 120-330°C was due to the removal of

321

glycerol added as a plasticizer, whereas the third weight loss around 330-500°C was assigned

322

to the thermal degradation of starch. The ST/L blend showed similar thermal degradation

323

behavior as starch film (Fig. 5a). The weight losses observed at 25-150°C, 150-330°C and

324

330-490°C were due to the removal of water, thermal degradation of plasticizer and the

325

decomposition of starch and lignin, respectively. Moreover, the thermal stability of the ST/L

326

film was found to be improved after the lignin addition, since the degradation rate in the range

327

of 150-330°C was found to be decreased. This improvement in thermal stability of ST/L film


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could be assigned to the high thermal stability of the lignin molecule and the formation of a

329

crosslinked ST/L network.64 For ST/L-GO bio-nanocomposites, the weight loss occurred at

330

below 100°C was related to the evaporation of the absorbed water. The water absorbency of

331

ST/L-GO bio-nanocomposites was lower than ST/L blend, suggesting that the addition of GO

332

nanosheets prevents the prepared films from the absorption of water when exposed to the

333

moisture.65 The incorporation of GO in the crosslinked ST/L matrix resulted in a slight

334

improvement of thermal stability at a loading amount of 0.3 to 0.5wt% of GO since the

335

residue increases with increasing amounts of GO. According to the DTG curve of ST/L-GO

336

films (Fig. 5b), it can be observed that the maximum degradation temperature of the ST/L-

337

0.7GO film (482°C), in the third degradation step, is slightly higher than that corresponding to

338

the ST/L blend (472°C), thus indicating that when additional amount of GO was added (up to

339

0.7wt%), the thermal stability of the resultant bio-nanocomposite was further improved.

340 341

4.2.3. Scanning electron microscopy

342

The surface morphology of the different films was examined by SEM to verify the

343

compatibility between both starch and lignin and also ST/L blend and GO. Fig.5 shows

344

typical SEM images of ST (Fig. 6a), ST/L (Fig. 6b) blend, ST/L-0.3(Fig. 6c) and ST/L-0.7

345

(Fig. 6d) films. It can be observed that all the produced films exhibited a compact and non-

346

porous structure. The ST film showed granular particles (zone marked by a yellow circle, Fig.

347

6a), which may be associated to retrograde starch. Furthermore, the ST/L blend (Fig. 6b)

348

display rod-like lignin particles embedded within the starch matrix. The presence of these

349

fiber-like lignin particles indicates that lignin acts as filler and has been successfully blended

350

within the starch matrix, which might be the reason for the strong interaction between these

351

two biopolymers. Interestingly, SEM image of ST/L blend and ST/L-GO bio-nanocomposites

352

(Fig. 6) showed that many small fibers align inside a larger single fiber of lignin.

353

Additionally,

SEM

images

of


the

ST/L-GO


354

(Fig. 6c,d) revealed that the produced films exhibited a more compact and closed

355

microstructures.

356

4.2.4. Mechanical Properties Measurement

357

The mechanical properties of polymers are of great importance especially for a versatile

358

application in food packaging. Mechanical testing provides significant information about the

359

stiffness or brittleness of the prepared bio-nanocomposites. Tensile tests were carried out to

360

investigate the effect of the addition of lignin and incorporation of GO nanosheets on the

361

mechanical properties of the resulting ST/L-GO bio-nanocomposite films. The ST/L weight

362

ratio was fixed at 50wt%. The mechanical properties of the neat starch, ST/L blend and

363

ST/L-GO bio-nanocomposites at different GO loading were measured from the stress-strain

364

curves of the corresponding bio-nanocomposites film. The tensile properties, namely Young’s

365

modulus (E, MPa), tensile strength (σ, MPa) and elongation at break (ε, %) of neat starch,

366

ST/L blend and ST/L-GO bio-nanocomposites are shown in Fig. 7. It was difficult to obtain

367

film from lignin so its mechanical properties were not mentioned. As can be seen from Fig. 7,

368

both Young’s modulus (Fig. 7a) and tensile strength (Fig. 7b) of the ST/L biofilms increased

369

and the elongation at break values decreased owing to the occurrence of strong interaction

370

between the functional groups of starch and lignin. This improvement may arise from the

371

good compatibility between the hydrophobic lignin and the hydrophilic starch moieties in the

372

presence of glycerol, which acts as a compatibilization agent and contributes to the miscibility

373

of the twophases.66 Similarly, Ҫalgeris et al.64 reported that the addition of lignin extracted

374

from hazelnut shells to plasticized starch matrix greatly improves the mechanical strength of

375

the ST/L biofilms. The evidence of the occurrence of strong interfacial interactions between

376

starch and lignin was confirmed by the FTIR spectra of the ST/L film (Fig.4). As expected,

377

both Young’s modulus and tensile strength were significantly improved after incorporation of

378

increasing amount of GO (Fig. 7a,b). The E and σ increased from 32 and 3.37 MPa to 60.23


Page 16 of 40

Page 17 of 40


379

and 5 MPa when the GO loading increased from 0 to 0.7wt%, respectively. The mechanical

380

properties enhancement was probably due to the interfacial interactions between the

381

biopolymer matrices and exfoliated GO nanosheets. These results are in good agreement with

382

the previous studies, indicating that the addition of well-dispersed GO as a reinforcement can

383

significantly enhance the resultant mechanical properties of several biopolymeric matrices

384

such as starch,67 alginate,68 polylactic acid69 and carboxymethyl cellulose.70 The elongation at

385

break (ε) does not follows the same tendency as E and σ, and decreased from 13,68 to 9.07%

386

after incorporation of increasing amount of GO from 0.3 to 0.7wt% (Fig. 7c). The significant

387

improvement in mechanical properties of ST/L-GO bio-nanocomposite films, mainly E and σ,

388

was due to the strong interaction between GO and ST/L matrix and the good dispersion of GO

389

within the ST/L matrix. The GO nanofiller, with their abundant oxygen-containing functional

390

groups, formed an interconnected network linked by strong hydrogen-bonding interaction and

391

becomes difficult to disconnect from the ST/L matrix. Moreover, the substantial enhancement

392

of the Young’s modulus (E) and tensile strength (σ) could also be due to the resistance of GO

393

to the imposed force and the applied stress. Similar results were also reported when the starch

394

was reinforced by nanofiller.71,72

395

4.2.5. UV-Vis Absorbance of the films

396

The UV-Vis spectra of pure ST, ST/L blend and ST/L-GO bio-nanocomposites films are

397

depicted in Fig. 8a. Since the ST film is transparent in the UV-Vis region, a very low

398

absorption level was obtained. Once blended with lignin, the absorption of the ST/L blend

399

was found to increase, suggesting that the transparence of the prepared film was reduced. The

400

lignin containing film was brown in color as shown in Figure 1. Additionally, when

401

increasing the amounts of GO were added to the ST/L blend, the absorption level was

402

increased gradually and follow the subsequent order: ST/L-0.3< ST/L-0.5< ST/L-0.7 (Fig.

403

8a). These results revealed that the transparency of ST/L was affected by the incorporation of



404

GO nanosheets. This behavior is expected since the color of the ST/L-GO bio-

405

nanocomposites was found to darken as the GO amount was increased (Fig.1).

406

4.2.6. Moisture uptake of the films

407

The moisture uptake (Mu) of neat ST, ST/L blend and ST/L-GO bio-nanocomposites films

408

are depicted in Fig.8b. Pure starch is well known to be sensitive to water and moisture due to

409

its hydrophilic character. As shown in Fig. 8b, the Mu value of the neat ST film, after

410

exposition to an environmental relative humidity of 70% for 6h, was approximately 12.36%.

411

Moreover, it can be clearly seen that blending lignin within the starch matrix significantly

412

reduced the moisture uptake percentage of the resulting ST/L blend to 9.2%. This decrease in

413

water uptake at equilibrium can be ascribed to the partial miscibility of hydrophobic phenolic

414

compounds of lignin with the starch matrix and also to the reduction of the free hydrophilic

415

functional groups of starch witch form strong interactions within the oxygen containing

416

groups of lignin.73After the addition of an increasing amount of GO as a nanofiller, the

417

moisture uptake values were further reduced to 5.71, 5.16 and 5.15% for ST/L-GO-0.3, ST/L-

418

GO-0.5 and ST/L-GO-0.7, respectively. This decrease in the moisture uptake could be

419

assigned to the improvement of the hydrophobic nature of the ST/L-GO bio-nanocomposites

420

films and the possible occurrence of stronginterfacial interaction between the oxygen-

421

containing groups of GO and those of ST/L biopolymeric matrix, which reduce the water

422

accessibility and therfore the ability of the prepared bio-nanocomposites to absorb moisture.

423

4.2.7. Water swelling capacity of the films

424

The water swelling is one of the most significant disadvantages of a biopolymer especially for

425

packaging application. The water swelling capacity of the ST, ST/L blend and ST/L-GO bio-

426

nanocomposite films loaded with different GO contents is shown in Fig. 8c. The examination

427

of this figure revealed that the water swelling (SW) of the starch film was slightly decreased

428

after addition of lignin owing to the hydrophobic nature of lignin molecule. The SW values of


Page 18 of 40

Page 19 of 40


429

starch and lignin, after immersion in water for 24h, were 50.06 and 47.82%, respectively. At

430

GO loading of 0.3 and 0.5wt%, no significant improvement of the water uptake was observed,

431

whereas when increasing the amout of GO was used (0.7wt%) the water swelling was found

432

to decrease to 35.07%in comparison to 50 and 48% for neat ST and ST/L blend film,

433

respectively (Fig. 8c). These results suggest that theincoporation of an increasing amount of

434

GO could significantly improve the hydrophobicity of the ST/L blend films and therfore limit

435

the absorption of water by the ST/L-GO bio-nanocomposites films. Indeed, the presence of a

436

well dispersed GO nanosheets resulted in the occurence of a strong interfacial interaction

437

between the biopolymeric ST/L matrix and GO nanofiller, which resulted in the formation of

438

an interconnected network and water molecules cannot diffuse inside the bio-nanocomposite

439

film, thus preventing the absoprtion of water of the films when immersed in water and

440

decreasing the water swelling ability.72The obtained results are in good agreement with those

441

of TGA curve (Fig. 5a) since the water content, which is absorbed from the moisiture, of the

442

prepared bio-nanocomposites films decreased with an increasing amount of GO from 0.3 to

443

0.7wt%. These findings are in good argeement with those reported by Khan et al.70when

444

using GO as a nanofiller in polymeric blends.

445 446

4.2.8. Water vapor permeability of the films

447

Water vapor permeability of ST/L-GO bio-nanocomposite is one of the most important

448

features for the substitution of traditional polymers, particularly, for packaging applications.

449

Conventionally, films must limit or at least reduce moisture transfer between food and the

450

external environment. The WVP of neat ST and ST/L-GO bio-nanocomposite films at

451

different GO loading are given in Figure 8d. It was clearly observed that the values of WVP

452

for

453

ST/L-GO bio-nanocomposite were lower than that of neat ST. The WVP of the neat starch

454

was around 11.43 g m/m2 h Pa. This value was found to decrease when ST was blended with 19 ACS Paragon Plus Environment


455

lignin and filled with 0.3wt% of GO to reach 3.86 g m/m2 h Pa (Fig. 8d). After addition of

456

increasing amount of GO, the WVP of the prepared ST/L-GO films was found to decrease

457

following the loading level of GO. When GO loading was increased from 0.3 to 0.7wt%, the

458

WVP was found to decrease from 3.86 to 3.74 g m/m2 h Pa, respectively. These results could

459

be explained by the formation of a strong hydrogen bonding between GO and the blend

460

matrix which reduce the diffusion of water in the films and produce a tortuous pathway for

461

the water molecules.74,75

462

4.2.9. Hydrolytic degradation of the films

463

The hydrolytic degradation experiments were performed in water-based environment during

464

30 days in order to study the effect of blending starch with lignin biopolymer on the

465

hydrolytic degradation of ST/L blend film and also to investigate the effect of the

466

incorporation of GO as a nano-reinforcement on the long-term hydrolytic degradation of

467

ST/L-GO films. Fig.8a shows the photographs of pure ST, ST/L blend and ST/L-GO films

468

immersed in water. The digital images are taken at t = 5 min and t = 30 days in order to

469

monitor their state and check the possible visual degradation of the films.

470

It is prominent that starch is highly sensitive to water. After immersion in water for 30 days,

471

the starch film seems to keep rather good morphological dimensions, but it becomes brittle

472

and easy to break. The residual mass measured for this sample after the removal of water and

473

drying (Fig. 8b) was found to be 40.43% indicating that the major part of ST is hydrolyzed in

474

water media. This is mainly due to the presence of free hydroxyl groups, which have a high

475

affinity to water. When lignin was blended within ST matrix, the hydrolytic degradation of

476

the resulting ST/L blend was slightly reduced when compared to neat ST owing to the

477

reduction of the free hydroxyl groups of ST, which interact with those of hydrophobic lignin.

478

As shown in Fig.8b, a slight increase of the residual mass to 41.02% was observed,

479

suggesting that the starch was well blended with the lignin, which reduces the ability of water


Page 20 of 40

Page 21 of 40


480

for degradation mechanism. However, the partial degradation of ST/L blend could be ascribed

481

to the existence of free oxygen-containing functional groups remaining in the ST/L blend,

482

which favorably interact with water thus resulting in hydrolysis mechanism. In the case of

483

ST/L-GO, no visual degradation was detected since the bio-nanocomposite films still

484

maintain a good morphological aspect (Fig.8a). The remaining weight increases by increasing

485

the amount of GO (Fig. 8b). Indeed, the residual mass increased from 45.35 to 65.21wt%

486

when the GO loading was increased from 0.3 to 0.7wt%, respectively. This resistance to the

487

hydrolytic degradation might be due to the occurrence of additional interaction between the

488

free oxygen-containing functional groups of ST/L blend and the oxygenated groups of GO as

489

established by FTIR analysis (Fig. 4). Furthermore, the highly dispersed GO nanofiller in the

490

polymeric matrix resulted in the formation of a tortuous path, which limits the penetration of

491

water and therefore reduces the hydrolytic degradation of the produced bio-nanocomposites.76

492

These results are in good agreement with those reported by El achaby et al.77 when using

493

2wt% of GO filled chitosan/poly(vinylpyrrolidone) blend.

494 495

5. Conclusion

496

In this study, films based on ST/L biopolymer blend reinforced by GO were successfully

497

prepared via casting/solvent evaporation process. FTIR measurements revealed that the lignin

498

was successfully blended within the starch matrix via the occurrence of hydrogen bond

499

interactions, which resulted in the formation of a homogenous biocompatible blend matrix.

500

After the addition of GO, additional interactions were found to occur between the non-

501

interaction hydroxyls groups of starch and lignin and the oxygen containing groups of GO,

502

resulting in the formation of an interconnected network. Owing to these interactions, the

503

resulting properties of the prepared bio-nanocomposites such as water swelling, moisture

504

uptake, hydrolytic degradation, water vapor permeability, thermal stability and mechanical



Page 22 of 40

505

properties were significantly improved. As a conclusion, our findings confirmed the

506

effectiveness of the proposed approach to produce biodegradable films with enhanced

507

properties, which may be a suitable candidate for food packaging applications.

508 509

Acknowledgements

510

The financial assistance of the MAScIR Foundation, towards this research is hereby

511

acknowledged. We acknowledge also the financial assistance of the CNRST (Grant PPR2

512

Project, Category B).

513 514 515

6. Reference

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58. Chandra, S.; Sahu, S.; Pramanik, P.A novel synthesis of graphene by dichromate oxidation. Materials Science and Engineering B 2010, 167, 133-136.

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59. Paredes, J.I.; Villar-Rodil, S.; Martínez-Alonso, A.; Tascón, J.M.D. Graphene oxide

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dispersions in organic solvents. Langmuir ACS J. Surf. Colloids 2008, 24, 10560-

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10564.

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60. Stankovich, S.; Dikin, D.A.; Piner, R.D.; Kohlhaas, K.A.; Kleinhammes, A.; Jia, Y.;

673

Wu, Y.; Nguyen, S.T.; Ruoff, R.S. Synthesis of graphene-based nanosheets via

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chemical reduction of exfoliated graphite oxide. Carbon 2007, 45, 1558-1565.

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61. Prachayawarakorn, J.; Sangnitidej, P.; Boonpasith, P. Properties of thermoplastic rice

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starch composites reinforced by cotton fiber or low-density polyethylene. Carbohydr.

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Polym. 2010, 81, 425-433.

678 679

62. Kaewtatip, K.; Thongmee, J. Studies on the structure and properties of thermoplastic starch/luffa fiber composites. Mater. Des. 2012, 40, 314-318.

680

63. Prachayawarakorn, J.; Ruttanabus, P.; Boonsom, P. Effect of Cotton Fiber Contents

681

and Lengths on Properties of Thermoplastic Starch Composites Prepared from Rice

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and Waxy Rice Starches. J. Polym. Environ. 2011, 19, 274-282.

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64. Çalgeris, Đ.; Çakmakçı, E.; Ogan, A.; Kahraman, M.V.; Kayaman-Apohan, N.

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Preparation and drug release properties of lignin–starch biodegradable films. Starch-

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Stärke 2012, 64, 399-407.

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65. El Achaby, M.; El Miri, N.; Snik, A.; Zahouily, M.; Abdelouahdi, K.; Fihri, A.;

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Barakat, A.; Solhy, A. Mechanically strong nanocomposite films based on highly

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filled carboxymethyl cellulose with graphene oxide. J. Appl. Polym. Sci. 2016, 133,

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42356.

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66. Vengal, J. C.; Srikumar, M. Processing and study of novel lignin-starch and lignin-

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gelatin biodegradable polymeric films. Trends Biomater. Artif. Organs. 2005, 18, 237-

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241.

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67. Li, R.; Liu, C.; Ma, J. Studies on the properties of graphene oxide-reinforced starch biocomposites. Carbohydr. Polym. 2011, 84, 631-637.

695

68. Ionita, M.; Pandele, M.A.; Iovu, H. Sodium alginate/graphene oxide composite films

696

with enhanced thermal and mechanical properties. Carbohydr. Polym. 2013, 94, 339-

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344.

698

69. Li, W.; Xu, Z.; Chen, L.; Shan, M.; Tian, X.; Yang, C.; Lv, H.; Qian, X. A facile

699

method to produce graphene oxide-g-poly(L-lactic acid) as an promising

700

reinforcement for PLLA nanocomposites. Chem. Eng. J. 2014, 237, 291-299. 27 ACS Paragon Plus Environment


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70. Wang, J.; Feng, M.; Zhan, H. Preparation, characterization, and nonlinear optical

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properties of graphene oxide-carboxymethyl cellulose composite films. Opt. Laser

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Technol. 2014, 57, 84-89.

704 705 706 707

71. Ma, X.; Yu, J.; Wang, N. Glycerol plasticized-starch/multiwall carbon nanotube composites for electroactive polymers. Compos. Sci. Technol. 2008, 68, 268-273. 72. Li, R.; Liu, C.; Ma, J. Studies on the properties of graphene oxide-reinforced starch biocomposites. Carbohydr. Polym. 2011, 84, 631-637.

708

73. Lepifre, S.; Baumberger, S.; Pollet, B.; Cazaux, F.; Coqueret, X.; Lapierre, C.

709

Reactivity of sulphur-free alkali lignins within starch films. Ind. Crops Prod., 6th

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International Lignin Institute conference 2004, 20, 219-230.

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74. Bai, H.; Sun, Y.; Xu, J.; Dong, W.; Liu, X. Rheological and structural characterization

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of HA/PVA-SbQ composites film-forming solutions and resulting films as affected by

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UV irradiation time. Carbohydrate Polymers 2015, 115, 422-431.

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75. Yadollahi, M.; Namazi, H.; Barkhordari, S. Preparation and properties of

715

carboxymethyl

cellulose/layered

double

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Carbohydrate Polymers 2014, 108, 83-90.

hydroxide

bionanocomposite

films.

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76. Han, D.; Yan, L.; Chen, W.; Li, W. Preparation of chitosan/graphene oxide composite

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film with enhanced mechanical strength in the wet state. Carbohydr. Polym. 2011, 83,

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653-658.

720

77. El Achaby, M.; Essamlali, Y.; El Miri, N.; Snik, A.; Abdelouahdi, K.; Fihri, A.;

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Zahouily, M.; Solhy, A. Graphene oxide reinforced chitosan/polyvinylpyrrolidone

722

polymer bio-nanocomposites. J. Appl. Polym. Sci. 2014, 41042, 1-11.


Page 29 of 40


723

Figure captions:

724

Figure 1. Digital images of ST, ST/L blend and ST/L-GO films forming solutions and the

725

corresponding isolated solid films.

726

Figure 2. XRD patterns (left)and FTIR spectra (right) of (a) graphite and (b)graphite oxide

727

Figure 3. (a) SEM micrograph of graphene oxide nanosheets, (b) TEM micrograph of

728

graphene oxide nanosheets, (c) HR-TEM image of graphene oxide, (d) Electron diffraction

729

pattern from SAED measurements for graphene oxide sample and (e) AFM image and the

730

corresponding line profiles of the GO nanosheets.

731

Figure 4. FTIR spectra of ST, lignin, ST/L blend, ST/L-0.3, ST/L-0.5and ST/L-0.7 bio-

732

nanocomposites films and GO powder in the region of (a) 600-4000 cm-1 and (b)

733

1600-600 cm-1.

734

Figure 5. (a) TGA and (b) DTG curves of neat ST, ST/L blend, ST/L-0.3, ST/L-0.5 and

735

ST/L-0.7 bio-nanocomposite films. Inset in figure 5a TGA curve in temperature range of 250-

736

500°C.

737

Figure 6. SEM micrographs of (a) neat starch, (b) ST/L blend, (c) ST/L-0.3 and (d) ST/L-0.7

738

films. Regions surrounded by yellow circle indicate granular particles.

739

Figure 7. Mechanical properties of ST, ST/L blend and ST/L-0.3, ST/L-0.5 and ST/L-0.7: (a)

740

Young’s modulus, (b) Tensile strength hand (c)Elongation at break.

741

Figure 8. (a)UV-Vis spectra, (b) Moisture uptake, (c) Water swelling and (d) Water vapor

742

permeability of neat ST, ST/L blend and ST/L-GO bio-nanocomposite films loaded with

743

different GO loading (0.3, 0.5 and 0.7wt%).

744

Figure 9. (a)Photographs of neat ST, ST/L blend and ST/L-GO bio-nanocomposites

745

immersed in water for 5 min and 30 days, (b) Residual mass of neat ST, ST/L blend and

746

ST/L-GO bio-nanocomposite loaded with different GO amount after a degradation period of

747

30 days 29 ACS Paragon Plus Environment


748

Figure graphics:

749

Figure 1.

750 751


Page 30 of 40

Page 31 of 40

752


Figure 2.

Transmittance (%)

Intensity (a.u)

d002 = 0.336 nm d002 = 0.88 nm

(b)

(b) C-O-C

(a)

(a) C-C

OH

5

10

15

20

25

30

35

40

C-O

4000 3500 3000 2500 2000 1500 1000 -1

2θ (°)

Wavenumber (cm )

753



754

Figure 3.

755 756


Page 32 of 40

Page 33 of 40

757


Figure 4. (a)

ST

(b) ST -1

1152 cm

% Transmitance (a.u)

% Transmitance (a.u)

Lignin ST/L ST/L-0.3 ST/L-0.5 ST/L-0.7 C-H

GO

C-H

1159 cm

4000

1714 cm -1 1612 cm

OH

3500

3000

2500

2000

1500

1152 cm

ST/L-0.3

-1

1002 cm

-1

1152 cm

ST/L-0.5

-1

1002 cm

-1

1148 cm

ST/L-0.7

-1

999 cm -1

1134 cm C-O

-1

989 cm

1000

1500

-1

758

ST/L

-1

1036 cm -1

-1

OH

Lignin

-1

1008 cm -1

1250

1000

750 -1

Wavenumbers (cm )

Wavenumbers (cm )

759



Figure 5.

Weight (%)

Weight loss (%)

80

2 1,6

60

40

1,4

5

20

60

1 0 250

300

350

400

450

500

Temperature (°C)

40

1: ST 2: ST/L 3: ST/L-0.3 4: ST/L-0.5 5: ST/L-0.7

20

0

(b) (b)

1,8

(a)

80

100

Deriv. Weight (%/°C)

760

Page 34 of 40

5 1

1,2 1,0

3

0,8 0,6 0,4

3

5

100

200

0,2 0,0

-20

-0,2 0

100

200

300

400

500

600

700

800

0

Temperature (°C)

300

400

500

Temperature (°C)

761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 34 ACS Paragon Plus Environment

600

700

800

Page 35 of 40

784


Figure 6.

785

786 787 788



789

Figure 7. 70

Young's modulus (MPa)

(a) 60 50 40 30 ST

Tensile strength (MPa)

5,4 4,8

ST/L

ST/L-0.3 ST/L-0.5 ST/L-0.7

ST/L

ST/L-0.3 ST/L-0.5 ST/L-0.7

ST/L

ST/L-0.3 ST/L-0.5 ST/L-0.7

(b)

4,2 3,6 3,0 2,4 1,8 1,2 ST

Elongation at break (%)

24

790 791

(c)

20 16 12 8 ST


Page 36 of 40

Page 37 of 40

Figure 8. 3,0

14

5

1. ST 2. ST/L blend 3. ST/L-0.3 4. ST/L-0.5 5. ST/L-0.7 6. GO

Absorbance (a.u)

2,5 2,0 1,5 1,0

4 3

(a)

6 2

0,5

1

(b)

12

Moisiture uptake (%)

792 793


0,0

10 8 6 4 2 0

400

500

600

700

800

ST

ST/L

ST/L-0.3 ST/L-0.5 ST/L-0.7

Wavelenght (nm) 60

12 10

WVP (g m/m h Pa)

40

8

2

Swelling (%)

50

30 20 10 0

6 4 2 0

ST

794 795

(d)

(c)

ST/L

ST/L-0.3 ST/L-0.5 ST/L-0.7

ST

A

796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 37 ACS Paragon Plus Environment

ST/L-0.3

ST/L-0.5

ST/L-0.7


817 818

Figure 9.

819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 38 ACS Paragon Plus Environment

Page 38 of 40

Page 39 of 40


843

Scheme

844

Scheme 1. Schematic representation of the structure of the ST/L-GO bio-nanocomposite film

845

and the possible interactions between starch, lignin and GO nanosheets.

846

847 848



849

TOC Graphic:

850 851

852 853


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Starch Polymer Bionanocomposite

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