Accepted Manuscript Title: Synthesis, characterization and antibacterial activity of biodegradable Starch/PVA composite films reinforced with cellulosic fibre Author: Vinod Kumar Gupta Bhanu Priya Deepak Pathania Amar Singh Singh PII: DOI: Reference:
S0144-8617(14)00276-8 http://dx.doi.org/doi:10.1016/j.carbpol.2014.03.044 CARP 8706
To appear in: Received date: Revised date: Accepted date:
14-2-2014 4-3-2014 7-3-2014
Please cite this article as: Gupta, V. K., Priya, B., Pathania, D., & Singh, A. S.,Synthesis, characterization and antibacterial activity of biodegradable Starch/PVA composite films reinforced with cellulosic fibre, Carbohydrate Polymers (2014), http://dx.doi.org/10.1016/j.carbpol.2014.03.044 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.
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Synthesis, characterization and antibacterial activity of biodegradable Starch/ PVA
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composite films reinforced with cellulosic fibre
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Vinod Kumar Gupta1*, Bhanu Priya2, Deepak Pathania2, Amar Singh Singh3 Department of Chemistry, Indian Institute of Technology Rookree, Roorkee- 247667, India
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Department of Chemistry, Shoolini University, Solan -173212, Himachal Pradesh, India
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Department of Applied Chemistry, National Institute of Technology Hamirpur, 177005, Himachal Pradesh, India
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*Corresponding author: E-mail: [email protected]; [email protected]
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Fax: 00911332273560; Tel: 00911332285801,
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Abstract
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Cellulosic fibres reinforced composite blend films of Starch/poly(vinyl alcohol) (PVA) were
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prepared by using citric acid as plasticizer and glutaraldehyde as the cross-linker. The
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mechanical properties of cellulosic fibres reinforced composite blend were compared with
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starch/PVA crossed lined blend films. The increase in the tensile strength, elongation
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percentage, degree of swelling and biodegradability of blend films was evaluated as
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compared to starch/PVA cross linked blend films. The value of different evaluated
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parameters such as citric acid, glutaraldehyde and reinforced fibre to Starch/PVA (5:5) were
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found to be 25wt.%, 0.100 wt.% and 20wt.%, respectively. The blend films were
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characterized using Fourier transform-infrared spectrophotometry (FTIR), scanning electron
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microscopy (SEM) and thermogravimetric analysis (TGA/DTA/DTG). Scanning electron
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microscopy illustrated a good adhesion between Starch/PVA blend and fibres. The blend
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films were also explored for antimicrobial activities against pathogenic bacteria like
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Staphylococcus aureus and Escherichia coli. The results confirmed that the blended films
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may be used as exceptional material for food packaging.
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Keywords: Starch/PVA blend film; Mechanical properties; Degree of swelling; Thermal
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analysis; Antibacterial activity
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1. Introduction In the latest years, industries have been working to decrease the dependence on petroleum
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based fuels and products due to the increase in environmental consciousness. This leads to
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investigate the environmentally friendly sustainable materials to replace the existing ones.
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The tremendous increase in production and use of plastics in our life resulted in generation of
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huge plastic wastes. Due to disposal problems, as well as strong regulations and criteria for
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cleaner and safer environment, have directed great part of the scientific research toward eco-
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composite materials (Bledzki & Gassan, 1999). In order to solve the problems generated by
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plastic waste, many efforts have been made to obtain the environmental friendly materials.
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Many researchers are working on the substitution of the petro-based plastics by
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biodegradable materials with similar properties and low in cost. Several studies have been
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reported the use of biodegradable starches from different sources to prepare films and
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coatings with different properties (Bertuzzi, Armada & Gottifredi, 2007; Larotonda, Matsui,
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Sobral & Laurindo, 2005; Mali, Grossmann, Garcia, Martino &
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Sakanaka, Yamashita, & Grossmann, 2005). Starch is the most important polysaccharide
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polymer used to develop biodegradable films, as it has potential to form a continuous matrix.
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Starch exhibits some disadvantages such as a strong hydrophilic character and poor
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mechanical properties as compared to conventional synthetic polymers, which make it
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inadequate for some packaging purposes (Alves, Costa, Hilliou, Larotonda, Goncalves &
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Sereno, 2006; John & Thomas, 2008).Poly(vinyl alcohol) is an important synthetic
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biodegradable polymer having excellent gas barrier properties, high strength, tear and
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flexibility. However, it has poor dimensional stability due to high moisture absorption.
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Moreover, it has relatively high price compared to other commercial polymers. Therefore,
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blended with renewable and abundant agro-resource based such as polysaccharides,
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particularly starch can be utilized to reduce the manufacturing cost. Blending with starch
Zaritzky, 2005; Mali,
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resulted in improved moisture resistance and accelerated degradation (Russo, O'Sullivan,
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Rounsefell, Halley, Truss & Clarke, 2009; Han, Chen & Hu, 2009). However, the properties
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of the blends deteriorated as starch content in the blend formulation increased, owing to poor
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compatibility between the two components and phase separation during blend preparation.
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Many techniques have been reported to improve the compatibility between PVA and starch
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such as addition of suitable plasticizers, cross-linking agents, fillers and compatibilizers
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(Siddaramaiah & Somashekar, 2004; Sreedhar, Sairam, Chattopadhyay, Rathnam & Mohan,
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2005; Sin, Rahman, Rahmat & Samad, 2010; Yoon, Chough & Park, 2006; Krumova, Lopez,
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Benavente, Mijangus & Perena, 2000; Jia, Cheng, Zhang & Zhang, 2007; Dean & Petinakis,
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2008; Peng, Kaishuen, Wei & Lui, 2005; Zhu, Zhang, Lai & Zhang, 2007; Nath, Gupta, Yu,
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Blackburn & White, 2010; Sanghavi, Sitaula, Griep, Karna, Ali & Swami, 2013; Sanghavi,
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Mobin, Mathur, Lahiri, & Srivastava, 2013; Sanghavi & Srivastava, 2013). However, some
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of these cross-linking agents always display toxicity and thus their potential applications as
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biomaterials have been limited. To overcome these disadvantages, certain nontoxic functional
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additives and simple modification techniques are required to improve the mechanical
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properties and water resistibility of the St/PVA films. Citric acid (CA) with one hydroxyl and
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three carboxyl groups exists widely in citrus fruits as main organic acid. Due to its multi-
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carboxylic structure, interaction could take place between the carboxyl groups of CA and the
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hydroxyl groups on the starch. It resulted in improved water resistibility (Borredon, Bikiaris,
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Prinos & Panayiotou, 1997), prevent recrystallization and retrogradation and enhance the
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mechanical properties (Yoon, Chough, & Park, 2006; Shi, Zhang, Liu, Han, Zhang & Chen,
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2007; Raddy & Yang 2010; Park, Choughy, Yun & Yoon, 2005; Imam Cinelli, Gordon &
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Chiejjini, 2005; Shi et al 2008; Park, Choughy, Yun & Yoon, 2005; Yoon, Chough & Park
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2006). CA is nontoxic metabolic product of the body (Krebs or citric acid cycle) and has been
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approved by FDA for using in food formulations (Ghanbarzadeh, Almasi & Entezami, 2011).
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It has been reported that sorbitol, glycerol, urea are used as the plasicizer blend films but
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citric acid showed improved properties (Imam, Cinelli, Gordon & Chiellini 2005; Park,
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Chough, Yun & Yoon 2005). Several studies has been reported on the development of
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composite blends of starch with polyethylene of low and high density (LDPE, HDPE), starch
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and poly(vinyl alcohol) (PVA), poly(3-hydroxybutyrate co-3-hydroxyvalerate) (PHBV) and
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poly(lactic acid) (PLA), poly (butylene succinate) (PBS) with cellulosic fibres such as
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banana, pineapple leaf, sisal, jute, ramie and bamboo fibres (Avella, Martuscelli & Raimo,
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2000; Averous & Boquillon, 2004; Cao, Shibata & Fukumoto, 2006; Carvalho, Curvelo &
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Agnelli, 2001; Chen, Qiu, Xi, Hong, Sun & Chen, 2006; Choi, Lim, Choi, Mohanty, DrzaL &
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Misra, 2004; Cunha, Liu, Feng, Yi & Bernardo, 2001; Fang & Fowler, 2003; Godbole, Gote,
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Latkar & Chakrabarti, 2003; Misra, Misra, Tripathy, Nayak & Mohanty, 2002; Zobel, 1988;
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Luo & Netravali, 1999; Kunanopparat, Menut, Morel & Guilbert, 2008; Digabel, Boquillon,
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Dole, Monties & Averous, 2004; Rodriguez, Ramsay & Favis, 2003; Ma, Yu & Kennedy,
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2005; Guimaraes, Wypych, Saul & Ramos, 2010; Lee & Wang, 2006; Pinto, Carbajal,
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Satyanarayana, Fernando & Ramos, 2009; Tripathi, Mehrotra & Dutta, 2009; Sanghavi &
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Srivastava, 2010; Gadhari, Sanghavi & Srivastava, 2011; Sanghavi, Kalambate, Karna &
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Srivastava, 2014). Globally, efforts have been made to develop bioplastics from renewable
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polymers for use as mulch film, materials for green-house construction, packaging, and aids
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for transporting and transplanting plants/seedlings and antimicrobial properties which
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improve the food safety and shelf-life. Antimicrobial packaging has one of the most
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promising active packaging systems. Antimicrobial packaging has been used for the
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inhibition of certain bacteria in foods, but barriers to their commercial implementation
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continue to exist (Tripathi, Mehrotra & Dutta, 2009).
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This paper describes the preparation of cellulosic Grewia optiva fibre reinforced
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composite cast films from blends of corn starch and PVA. Citric acid and glutaraldehyde
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have been used as plasticizer and crosslinker, respectively. The effect of citric acid and
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gluteraldehyde on mechanical properties and degree of swelling were also attempted. Further,
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the composite blend films were characterized with Fourier transform infrared
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spectrophotometer (FTIR), Scanning electron microscopy (SEM) and Thermogravimertic
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analysis (TGA). The antibacterial activity of St/PVA crosslinked blend films and composite
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blend films were explored on food pathogenic bacteria such as Escherichia coli and
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Staphylococcus aureus.
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2. Experimental
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2.1 Materials and methods
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Starch (corn starch) (St), Gluteraldehyde (GLU) and polyvinyl alcohol (PVA) were
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obtained from CDH India and used without any further purification. Citric acid (CA) was
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obtained from Aldrich Company India. PVA was 99% hydrolyzed with average molecular
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weight of 99,000-10,00,000. The weighing of the samples has been done on Libror AEG-220
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(Shimadzu, Japan) electronic balance. Bacterial strain, S. aureus ATCC 43300 and E. coli
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MTCC 739 were used by Bio Tech. Research Laboratory Shoolini University, Solan,
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Himachal Pradesh, India. Antibiotic discs (Amoxicillin 25µg/disc) and Nutrient agar were
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obtained from Himedia Laboratories Limited.
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2.2 Preparation of St/PVA blend films
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St/PVA blend films were prepared by casting method. In this method, 5 g of PVA was
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dissolved in hot water (90°C). The gelatinized starch was mixed to form homogeneously gel
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solution. The mixture was continuous stirring for 5 min on a mechanical stirrer (1500 rpm) at
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room temperature. CA (5-30%) and GLU (0.05-0.250%) were added to above mixture with
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continuous stirring. The total amount of polymeric mixture was 100 g. The mixing
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compositions of different additives were shown in Table 1. The reaction parameters such as
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mixing time, CA and GLU concentration were optimized. Bubbles formed during the
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preparation of blend films were removed by using an aspirator. The suspension so formed
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was poured onto teflon plate to prepare blend film. The blend films were dried at room
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temperature for 72 h.
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2.3 Reinforcing material
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In this study Grewia optiva fibres collected from local resources were used as
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reinforcing material. The fibres were washed with mild detergent to remove the impurities
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involved during extraction of fibres. The fibres were dried at hot air oven maintained at 80°C
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for 12 h. After drying the fibres were converted into fine particle using ball mill (FRITCH
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Pulbersette-5) of dimension 15-20µm.
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2.4 Synthesis of lignocellulosic fibre reinforced St/PVA blend films
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Grewia optiva fibres of dimension 15-20µm were mixed thoroughly with St/PVA
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blend using a mechanical stirrer, at different loadings (5-30% in terms of weight). This
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mixture was poured into teflon plate and allowed to dry at room temperature. The mixing
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composition of raw Grewia optiva fibre was shown in Table 1.
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2.5 Mechanical properties of St/PVA blend films and fibre reinforced St/PVA blend films
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Tensile strength (TS) and elongation percentage (%E) of St/PVA blend films and
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fibre reinforced St/PVA blend films were performed on a computerized Universal Testing
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Machine (Hounsfield H25KS). The tensile test was conducted in accordance with the ASTM
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D 638 method. The specimen average thickness was about 1mm and operated at a cross-head
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speed of 20mm/min at 30°C.
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2.6 Degree of swelling (DS) of St/PVA blend films
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In this, dried St/PVA blend films were immersed in distilled water at room
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temperature (35°C) and kept for 24 h, moisture on the surface of the film was removed, and
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the weight of the films was measured. The degree of swelling (DS) of St/PVA blend films
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were calculated as (Ghanbarzadeh, Almasi & Entezami, 2011):
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Where, Wi is the initial weight of St/PVA blend films and Wf is the final weight of St/PVA
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blend films.
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2.7 Fourier transforms infrared (FTIR) spectroscopy
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FTIR spectra of St/PVA blend films were recorded on a Perkin Elmer
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spectrophotometer using KBr pellets. The spectrum was recorded in the range from 4000 to
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400 cm-1 with a resolution of 2 cm-1.
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2.8 Scanning electron microscopy (SEM)
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The scanning electron microscopic analysis of different samples was performed on a
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Leo Electron Microscopy Machine (No. 435-25-20).
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2.9 Thermogravimetric analysis
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Thermogravimetric analysis of starch/PVA blend film was performed using EXSTAR
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TG/DTA 6300 at a heating rate of 10 °C/min under nitrogen atmosphere.
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2.10 Antibacterial activity
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Antibacterial activities of Starch/PVA blend films were measured against Gram
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negative (E. coli) and positive bacteria (S. aureus) with disc diffusion method (Vimala et al.,
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2007).
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2.11 Biodegradability in Soil
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In this method, samples of Starch/PVA films, 20×20×1mm small pieces were
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weighted and placed for 120 days into the agricultural soil in a pot. The pot was covered with
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a plastic net and exposed to atmospheric conditions for 120 days. Variations in film
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morphology, the time of films disintegrated and weight loss were recorded. To determine the
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weight loss the specimen of each sample was quickly washed with cold water and dried in an
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oven at 70°C to constant weight. The weights of the sample, before and after washing were
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recorded (Imam, Cinelli, Gordon & Chiejjini, 2005).
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3. Results and discussion
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3.1 Optimization of different parameters on mechanical properties
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3.1.1 Effect of mixing time Fig. 1a shows Tensile strength (TS) and elongation (%E) of St/PVA blend film
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without additives for 40 min at 90°C. At the mixing time of 10 min, TS and %E were found
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to be 16.4 MPa and 68.74% respectively. Further, increase in time resulted in change in
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colour and decrease in TS and %E of blend films.
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3.1.2 Effect of citric acid (CA)
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Effect of CA on TS and %E of St/PVA blend film was shown in Fig. 1 b. The CA as
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the crosslinker and the plasticizer in the St/PVA blend films. With the initial increase in CA
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value from 5-30 wt.%, value of TS and %E increases. It has been evident that with increase in
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CA wt.%, the decrease in TS (17.11-11.35 MPa) and increase of the %E (70.65-198.59%)
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was observed. The residual CA in the blends acted as the plasticizer, which reduced the
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interactions among the macromolecules. The decrease in the interactions may be due to the
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presence of hydroxyl group and carboxyl groups present on CA, which form hydrogen bonds
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between St/PVA and additive molecules (Yoon, Chough & Park 2006; Ghanbarzadeh,
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Almasi & Entezami, 2011). It has been extensively used to improve the flexibility due to its
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diplex function (Avella, Martuscelli & Raimo, 2000).
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3.1.3 Effect of glutaraldehyde as crosslinking agent
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Fig. 1c shows the effect of GLU (0.05-0.250%) on TS and %E of St/PVA/CA blend
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film. The effect of crossslinking of GLU on St/PVA films has been reported (Yoon, Chough
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& Park, 2006). It has been found that TS (43.4 MPa) increases and %E (204.23%) decreases
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with the increased in wt.% of GLU from 0.05-0.150%. The blend film so formed was referred
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as St/PVA crosslinked blend film with remarkable TS and %E.
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3.1.4 Effect of fibre loading on St/PVA crosslinked blend films
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TS and %E of Grewia optiva fibre loading onto St/PVA crosslinked blend films was
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shown in Fig. 1d. Fibres were added to crosslinked blend from 5-30 wt.%. The result
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indicated that TS increased on reinforcement with cellulosic fibres. It has been observed that
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at 20% loading, TS and %E were found to be 38.53 MPa and 182.1%, respectively. The film
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so formed was referred as fibre reinforced St/PVA composite blend film.
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3.2 Degree of swelling
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The swelling behaviour of St/PVA, St/PVA/CA, St/PVA/CA/GLU and fibre
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reinforced St/PVA composite blend films were shown in Table 2. It was observed that degree
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of swelling decreased with increase in time. The addition of CA and GLU in St/PVA blend
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films decreased the DS value which confirmed the superior reactivity of CA and GLU
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(Krumova, Lopez, Benavente, Mijangus & Perena, 2000). The slight increase in DS value
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was recorded in fibre reinforced St/PVA composite blend films, which may be due to the
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greater affinity of water for OH groups present in the fibre reinforced St/PVA blend films.
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3.3 FTIR analysis
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FTIR spectra of raw Grewia optiva fibre, St/PVA crosslinked blend films and fibre
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reinforced St/PVA composite blend films were shown in Fig. 2 a-c. FTIR spectra of raw
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Grewia optiva fibre (Fig. 2a) showed a broad peak at 3431.39 cm-1 due to bonded OH groups.
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The absorption peak at 2922.31, 1431.01, and 1021.93 cm-1 were due to -CH2, C–C, and C–
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O stretching, respectively(Singha & Rana, 2012; Singha, Rana & Guleria, 2012). Fig. 2b
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showed the IR spectra of St/PVA crosslinked blend films. The peak at 3434 cm-1 was
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assigned to the stretching vibration of the hydroxyl groups. Broad peak at 1717 cm-1 may be
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due to the C=O stretching vibration and it was probably caused by the ester bond and
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carboxyl C=O groups in CA (Shi et al., 2008). The peak at 2858.10 cm-1 and 2925 cm-1
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corresponds to C-H stretching of aldehydic group of gluteraldehyde cross linked to blend
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(Tudorachi, Cascaval, Rusu & Pruteanu, 2000). The change in peak intensity at 3434 cm-1 in
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Fig. 2c confirmed the number of the hydroxyl groups rises due the interaction of fibre with
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St/PVA crosslinked blend.
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3.3 Surface morphology Scanning electron micrographs of corn starch, PVA, St/PVA crosslinked blend film
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and fibre reinforced St/PVA composite blend film were shown in Fig. 3 a-e. The corn starch
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(Fig. 3a) showed polyhedra or polygon shape granules. Fig. 3b confirmed the smooth surface
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of PVA film. The St/PVA crosslinked blend film (Fig. 3c) was found to be smooth without
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any cracks and pores. The SEM images of Grewia optiva fibre confirmed the rough surface
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(Fig. 3d). Morphological investigations of fibre reinforced St/PVA composite blend film (Fig.
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3e) clearly indicate the proper mixing of fibre particles with the St/PVA crosslinked blend.
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3.4 Biodegradability in Soil
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The crosslinked and fibres reinforced St/PVA composite blend films were exposed to
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soil for 120 days under prevailing environmental conditions. After 120 days of exposure in
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soil, films eventually diminished in size and appeared hard and fragile. Film deterioration
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was also accompanied by loss in their total weight after soil exposure (Table 2). The weight
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loss may be due to adhering of soil and debris partial to the film surface (Imam, Cinelli,
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Gordon & Chiejjini, 2005). The decay of 34.54% and 45.65% weight loss were recorded for
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St/PVA crosslinked film and fibres reinforced St/PVA composite blend films, respectively.
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Thus, crosslinking results in slow rate of film deterioration in soil.
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3.5 TGA analysis
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Thermogravimetric analysis of Grewia optiva fibre, St/PVA crosslinked blend films
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and fibres reinforced St/PVA composite blend films were studied as a function of percentage
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weight loss with temperature and shown in Fig. 4 a-c and Table 3. In case of fibre,
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depolymerization, dehydration and glucosan formation took place between the temperature
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range of 26.0ºC to 190.0ºC followed by the cleavage of C-H, C-C and C-O bonds (Maiti,
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Kaith, Jindal & Jana, 2011; Thakur, Singha & Thakur, 2013). The initial decomposition
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temperature (IDT) and final decomposition temperature (FDT) were found to be 241.18ºC
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(8.04% weight loss) and 356.38ºC (77.11% weight loss). On the other hand, in case of
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St/PVA crosskinked blend films, two stage decomposition was observed. The IDT and FDT
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have been found to be 156.06ºC (7.29% weight loss) and 490.29ºC (79.03% weight loss),
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respectively. The degradation temperatures for fibres reinforced St/PVA composite blend
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films fall between the degradation temperatures for the blend films and the fibres. It has been
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observed that for fibres reinforced composite blend films, IDT and FDT was 210.40ºC
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(13.85% weight loss) and 450.99ºC (82.26 % weight loss), respectively. It indicated that the
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presence of cellulose fibres affect the degradation process. TGA studies were further
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supported by DTA curve as shown in Fig. 4 a-c. Two peaks were observed in the DTA curve
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of Grewia optiva fibre and St/PVA crosslinked blend films. Fibre reinforced St/PVA
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composite blend films shows three DTA peaks. The TGA and DTA curves revealed that the
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Grewia optiva fibre, St/PVA blend films and fibres reinforced St/PVA composite blend films
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decompose in different stages in the temperature range of 199-500ºC, 150-600ºC and 190-
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600ºC, respectively. The magnitude and location of peaks found in the derivative
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thermogravimetric (DTG) curve also provide similar information (Tudorachi, Cascaval, Rusu
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& Pruteanu, 2000; Jiang, Qiao & Sun, 2006).
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3.6 Antibacterial activity
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St/PVA crosslinked blend film and fibres reinforced St/PVA composite blend film
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were screened for their antibacterial activity against Gram-positive (S. aureus) and Gram
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negative (E.coli) bacteria as shown in Fig. 5 a-b. Antibiotic amoxicillin (25µg/disc) was used
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as a standard (+ control). The inhibitory effect was measured based on clear zone surrounding
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circular film disc. Measurement of clear zone diameter included diameter of film disc,
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therefore, the values were always higher than the diameter of film disc whenever clearing
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zone was present. If there is no clear zone surrounding, it suggests that there is no inhibitory
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zone, and furthermore, the diameter was valued as zero. Films showed fair antibacterial
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activity against Gram-positive (S. aureus) and Gram negative (E.coli) bacteria. Inhibitory
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zone against S. aureus and E. coli was measured to be 1.5 and 1.2 cm, 1.7 and 1.5 cm for
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St/PVA crosslinked blend film and fibre reinforced St/PVA composite blend films,
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respectively (Tripathi, Mehrotra & Dutta 2009; Arora, Lala, Sharma &Aneja, 2011;
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Abdelgawada, Hudsona & Rojas, 2014).
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Conclusion
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St/PVA blend films were prepared by a casting method using citric acid as the plasticizer and
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glutaraldehyde as crosslinker. Addition of GLU increases the tensile strength and degree of
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swelling of St/PVA blend films. The mechanical properties of fibre reinforced St/PVA
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composite blend films were found to be higher than those of the St/PVA crosslinked blend
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films with 20% of Grewia optiva fibre loading. These properties can make Grewia optiva
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fibres a potential material for the synthesis of a new class of bio-composites. The composite
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films were characterized using Fourier transform-infrared spectrophotometry (FTIR),
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scanning electron microscopy (SEM) and thermogravimetric analysis (TGA/DTA/DTG).
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TGA analysis confirmed the good thermal properties of blend films. The antibacterial
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experiment indicated that St/PVA blends had good activity against the Gram-negative (E.
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coli) and Gram- positive (S. aureus) bacteria. Thermal and antibacterial study reveals that the
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synthesized blend films might be used as potential materials in food packaging.
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Acknowledgements
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The authors are thankful to Shoolini University of Biotechnology and Management Sciences,
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Solan and Director, National Institute of Technology Hamirpur (H.P.) for providing
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necessary laboratory facilities to complete this work.
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507
d
506
M
503
508
Ac ce p
509 510 511 512 513 514 515 516 517 518
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Figure captions
521
Fig. 1. Tensile Strength (TS) and % Elngation (%E) of (a) St/PVA (b) St/PVA/CA (c)
522
St/PVA/CA/GLU (d) St/PVA/CA/GLU/Grewia optiva fiber.
523
Fig. 2. FT-IR of (a) raw Grewia optiva fibre, (b) St/PVA crosslinked blend film and (c) fibres
524
reinforced St/PVA composite blend film.
525
Fig. 3. SEM images of (a) Starch, (b) PVA film, (c) St/PVA crosslinked blend film, (d) raw
526
Grewia optiva fibre and (e) fibres reinforced St/PVA composite blend film.
527
Fig. 4. TGA/DTA of (a) raw Grewia optiva fibre, (b) St/PVA crosslinked blend films and (c)
528
fibres reinforced St/PVA composite blend film.
529
Fig. 5. Inhibitory effect of St/PVA crosslinked blend film and fibres reinforced St/PVA
530
composite blend film against (a) S. aureus and (b) E. coli.
M
an
us
cr
ip t
520
Ac ce p
te
d
531
22
Page 22 of 30
531
Table caption
532 533 534 535 536 537 538 539 540 541 542
Table 1 Composition of St/PVA blend films and fibres reinforced St/PVA composite blend films.
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Table 2 Degrees of swelling of St/PVA blend films and Weight loss in St/PVA crosslinked blend film and fibre reinforced St/PVA composite blend film exposed to soil for 120 days.
us
cr
Table 3 Thermogravimetric analysis of Grewia optiva fibre, St/PVA crosslinked blend film and fibres reinforced St/PVA composite blend film.
543
an
544 545
M
546 547
d
548
te
549 550
Ac ce p
551 552 553 554 555 556 557 558 559 560
23
Page 23 of 30
Table 1 Composition of St/PVA blend films and fibres reinforced St/PVA composite blend films. Sample Starch PVA CA GLU Fibre loading (%) (%) (wt.%) (wt.%) (wt.%) St/PVA 5 5 5
5
-
St/PVA/CA
5
5
10
-
St/PVA/CA
5
5
15
-
St/PVA/CA
5
5
20
St/PVA/CA
5
5
St/PVA/CA
5
5
St/PVA/CA/GLU
5
St/PVA/CA/GLU
5
St/PVA/CA/GLU
5
St/PVA/CA/GLU
5
-
ip t
5
cr
St/PVA/CA
us
-
-
-
-
30
-
-
25
0.050
-
5
25
0.100
-
5
25
0.150
-
5
25
0.250
-
5
25
0.300
-
5
5
25
0.100
5
5
5
25
0.100
10
St/PVA/CA/GLU/fibre
5
5
25
0.100
15
St/PVA/CA/GLU/fibre
5
5
25
0.100
20
St/PVA/CA/GLU/fibre
5
5
25
0.100
25
St/PVA/CA/GLU/fibre
5
5
25
0.100
30
St/PVA/CA/GLU/fibre
5
Ac ce p
St/PVA/CA/GLU/fibre
d
St/PVA/CA/GLU
563
M
an
25
5
te
561 562
564 565 566 567
24
Page 24 of 30
-
St/PVA/CA
1.72
-
St/PVA/CA/GLU
0.53
35.54
Fibre reinforced St/PVA blend film
0.74
45.65
ip t
2.8
an
us
cr
St/PVA
Table 3 Thermogravimetric analysis of Grewia optiva fibre, St/PVA crosslinked blend film and fibres reinforced St/PVA composite blend film. Sample IDT FDT DT (˚C) at DT(˚C)at DT(˚C)at Residual 60%wt. left (%)at 40%wt. (˚C) (˚C) 20%wt. 800˚C loss loss loss 356.38 287.74 326.35 348.77 18.93 Grewia optiva 241.18 Fibre St/PVA/CA/ 156.6 490.23 224.93 296.00 371.64 GLU 210.43 450.43 240.74 310.17 367.66 9.82 fibres reinforced St/PVA composite blend film
Ac ce p
te
d
572 573 574 575 576
Table 2 Degree of swelling of St/PVA blend films and Weight loss in St/PVA crosslinked blend film and fibre reinforced St/PVA composite blend film exposed to soil for 120 days. Sample Degree of Swelling % wt.571 (DS) loss
M
568 569 570
577 578
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Highlights •
579
Starch/PVA blend films were prepared using citric acid (CA) and glutarldehyde (GLU) as plasticizer and crosslinker, respectively.
580
•
Blend film shows increased tensile strength and degree of swelling.
582
•
The mechanical properties of Grewia optiva fibre reinforced composite blend films
TGA showed the good thermal properties of blend films.
us
•
584
cr
have been found to be higher than those of the Starch/PVA cross-linked blend films.
583
585
ip t
581
Ac ce p
te
d
M
an
586
26
Page 26 of 30
Figure(s)
17
18
130
a
120
16
200
Tensile Strength % Elongation
180 16
100 90
14
80 13 70
160 15 140 14 120 13
% Elongation
Tensile Strength % Elongation
15
Tensile Strength(MPa)
110
% Elongation
Tensile Strength(MPa)
b 17
100 12 80
ip t
60
12
11
50 0
5
10
15
20
25
30
35
40
60
45
5
10
Mixing time(min)
44
40 35
25
140
20 120 15 100
5 0.20
0.25
Glutardehyde content(wt.%)
160 150 140 130
34
120
32
80 0.15
170
36
M
10
38
180
an
160
% Elongation
30
40
190
% Elongation
Tensile Strength(MPa)
180
200
us
42
0.10
30
Tensile Strength % Elongation
d
200
0.05
25
cr
220
Tensile Strength % Elongation
c 45
20
Citric acid content(wt.%)
50
Tensile Strength(MPa)
15
110
30
100 5
10
15
20
25
30
Fiber reonforcement(wt.%)
ed
Fig. 1. Tensile Strength (TS) and % Elngation (%E) of (a) St/PVA (b) St/PVA/CA (c)
ce pt
St/PVA/CA/GLU (d) St/PVA/CA/GLU/Grewia optiva fiber.
Ac
c
b
%T
a
4000
3500
3000
2500
2000
Wavelength cm
1500
1000
500
-1
Fig. 2. FT-IR of (a) raw Grewia optiva fibre, (b) St/PVA crosslinked blend film and (c) fibres reinforced St/PVA composite blend film. 1 Page 27 of 30
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Ac
Fig. 3. SEM images of (a) Starch, (b) PVA film, (c) St/PVA crosslinked blend film, (d) raw Grewia optiva fibre and (e) fibres reinforced St/PVA composite blend film.
2 Page 28 of 30
ip t cr
ed
M
an
us
(a)
Ac
ce pt
(b)
(c) Fig. 4. TGA/DTA of (a) raw Grewia optiva fibre, (b) St/PVA crosslinked blend films and (c) fibres reinforced St/PVA composite blend film.
3 Page 29 of 30
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Ac
ce pt
ed
M
an
composite blend film against (a) S. aureus and (b) E. coli.
us
Fig. 5. Inhibitory effect of St/PVA crosslinked blend film and fibres reinforced St/PVA
4 Page 30 of 30
S0144-8617(14)00276-8 http://dx.doi.org/doi:10.1016/j.carbpol.2014.03.044 CARP 8706
To appear in: Received date: Revised date: Accepted date:
14-2-2014 4-3-2014 7-3-2014
Please cite this article as: Gupta, V. K., Priya, B., Pathania, D., & Singh, A. S.,Synthesis, characterization and antibacterial activity of biodegradable Starch/PVA composite films reinforced with cellulosic fibre, Carbohydrate Polymers (2014), http://dx.doi.org/10.1016/j.carbpol.2014.03.044 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.
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Synthesis, characterization and antibacterial activity of biodegradable Starch/ PVA
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composite films reinforced with cellulosic fibre
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Vinod Kumar Gupta1*, Bhanu Priya2, Deepak Pathania2, Amar Singh Singh3 Department of Chemistry, Indian Institute of Technology Rookree, Roorkee- 247667, India
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Department of Chemistry, Shoolini University, Solan -173212, Himachal Pradesh, India
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3
Department of Applied Chemistry, National Institute of Technology Hamirpur, 177005, Himachal Pradesh, India
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*Corresponding author: E-mail: [email protected]; [email protected]
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Fax: 00911332273560; Tel: 00911332285801,
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Page 1 of 30
Abstract
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Cellulosic fibres reinforced composite blend films of Starch/poly(vinyl alcohol) (PVA) were
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prepared by using citric acid as plasticizer and glutaraldehyde as the cross-linker. The
29
mechanical properties of cellulosic fibres reinforced composite blend were compared with
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starch/PVA crossed lined blend films. The increase in the tensile strength, elongation
31
percentage, degree of swelling and biodegradability of blend films was evaluated as
32
compared to starch/PVA cross linked blend films. The value of different evaluated
33
parameters such as citric acid, glutaraldehyde and reinforced fibre to Starch/PVA (5:5) were
34
found to be 25wt.%, 0.100 wt.% and 20wt.%, respectively. The blend films were
35
characterized using Fourier transform-infrared spectrophotometry (FTIR), scanning electron
36
microscopy (SEM) and thermogravimetric analysis (TGA/DTA/DTG). Scanning electron
37
microscopy illustrated a good adhesion between Starch/PVA blend and fibres. The blend
38
films were also explored for antimicrobial activities against pathogenic bacteria like
39
Staphylococcus aureus and Escherichia coli. The results confirmed that the blended films
40
may be used as exceptional material for food packaging.
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Keywords: Starch/PVA blend film; Mechanical properties; Degree of swelling; Thermal
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analysis; Antibacterial activity
44 45 46 47 48 49 50
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1. Introduction In the latest years, industries have been working to decrease the dependence on petroleum
53
based fuels and products due to the increase in environmental consciousness. This leads to
54
investigate the environmentally friendly sustainable materials to replace the existing ones.
55
The tremendous increase in production and use of plastics in our life resulted in generation of
56
huge plastic wastes. Due to disposal problems, as well as strong regulations and criteria for
57
cleaner and safer environment, have directed great part of the scientific research toward eco-
58
composite materials (Bledzki & Gassan, 1999). In order to solve the problems generated by
59
plastic waste, many efforts have been made to obtain the environmental friendly materials.
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Many researchers are working on the substitution of the petro-based plastics by
61
biodegradable materials with similar properties and low in cost. Several studies have been
62
reported the use of biodegradable starches from different sources to prepare films and
63
coatings with different properties (Bertuzzi, Armada & Gottifredi, 2007; Larotonda, Matsui,
64
Sobral & Laurindo, 2005; Mali, Grossmann, Garcia, Martino &
65
Sakanaka, Yamashita, & Grossmann, 2005). Starch is the most important polysaccharide
66
polymer used to develop biodegradable films, as it has potential to form a continuous matrix.
67
Starch exhibits some disadvantages such as a strong hydrophilic character and poor
68
mechanical properties as compared to conventional synthetic polymers, which make it
69
inadequate for some packaging purposes (Alves, Costa, Hilliou, Larotonda, Goncalves &
70
Sereno, 2006; John & Thomas, 2008).Poly(vinyl alcohol) is an important synthetic
71
biodegradable polymer having excellent gas barrier properties, high strength, tear and
72
flexibility. However, it has poor dimensional stability due to high moisture absorption.
73
Moreover, it has relatively high price compared to other commercial polymers. Therefore,
74
blended with renewable and abundant agro-resource based such as polysaccharides,
75
particularly starch can be utilized to reduce the manufacturing cost. Blending with starch
Zaritzky, 2005; Mali,
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resulted in improved moisture resistance and accelerated degradation (Russo, O'Sullivan,
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Rounsefell, Halley, Truss & Clarke, 2009; Han, Chen & Hu, 2009). However, the properties
78
of the blends deteriorated as starch content in the blend formulation increased, owing to poor
79
compatibility between the two components and phase separation during blend preparation.
80
Many techniques have been reported to improve the compatibility between PVA and starch
81
such as addition of suitable plasticizers, cross-linking agents, fillers and compatibilizers
82
(Siddaramaiah & Somashekar, 2004; Sreedhar, Sairam, Chattopadhyay, Rathnam & Mohan,
83
2005; Sin, Rahman, Rahmat & Samad, 2010; Yoon, Chough & Park, 2006; Krumova, Lopez,
84
Benavente, Mijangus & Perena, 2000; Jia, Cheng, Zhang & Zhang, 2007; Dean & Petinakis,
85
2008; Peng, Kaishuen, Wei & Lui, 2005; Zhu, Zhang, Lai & Zhang, 2007; Nath, Gupta, Yu,
86
Blackburn & White, 2010; Sanghavi, Sitaula, Griep, Karna, Ali & Swami, 2013; Sanghavi,
87
Mobin, Mathur, Lahiri, & Srivastava, 2013; Sanghavi & Srivastava, 2013). However, some
88
of these cross-linking agents always display toxicity and thus their potential applications as
89
biomaterials have been limited. To overcome these disadvantages, certain nontoxic functional
90
additives and simple modification techniques are required to improve the mechanical
91
properties and water resistibility of the St/PVA films. Citric acid (CA) with one hydroxyl and
92
three carboxyl groups exists widely in citrus fruits as main organic acid. Due to its multi-
93
carboxylic structure, interaction could take place between the carboxyl groups of CA and the
94
hydroxyl groups on the starch. It resulted in improved water resistibility (Borredon, Bikiaris,
95
Prinos & Panayiotou, 1997), prevent recrystallization and retrogradation and enhance the
96
mechanical properties (Yoon, Chough, & Park, 2006; Shi, Zhang, Liu, Han, Zhang & Chen,
97
2007; Raddy & Yang 2010; Park, Choughy, Yun & Yoon, 2005; Imam Cinelli, Gordon &
98
Chiejjini, 2005; Shi et al 2008; Park, Choughy, Yun & Yoon, 2005; Yoon, Chough & Park
99
2006). CA is nontoxic metabolic product of the body (Krebs or citric acid cycle) and has been
100
approved by FDA for using in food formulations (Ghanbarzadeh, Almasi & Entezami, 2011).
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It has been reported that sorbitol, glycerol, urea are used as the plasicizer blend films but
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citric acid showed improved properties (Imam, Cinelli, Gordon & Chiellini 2005; Park,
103
Chough, Yun & Yoon 2005). Several studies has been reported on the development of
104
composite blends of starch with polyethylene of low and high density (LDPE, HDPE), starch
105
and poly(vinyl alcohol) (PVA), poly(3-hydroxybutyrate co-3-hydroxyvalerate) (PHBV) and
106
poly(lactic acid) (PLA), poly (butylene succinate) (PBS) with cellulosic fibres such as
107
banana, pineapple leaf, sisal, jute, ramie and bamboo fibres (Avella, Martuscelli & Raimo,
108
2000; Averous & Boquillon, 2004; Cao, Shibata & Fukumoto, 2006; Carvalho, Curvelo &
109
Agnelli, 2001; Chen, Qiu, Xi, Hong, Sun & Chen, 2006; Choi, Lim, Choi, Mohanty, DrzaL &
110
Misra, 2004; Cunha, Liu, Feng, Yi & Bernardo, 2001; Fang & Fowler, 2003; Godbole, Gote,
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Latkar & Chakrabarti, 2003; Misra, Misra, Tripathy, Nayak & Mohanty, 2002; Zobel, 1988;
112
Luo & Netravali, 1999; Kunanopparat, Menut, Morel & Guilbert, 2008; Digabel, Boquillon,
113
Dole, Monties & Averous, 2004; Rodriguez, Ramsay & Favis, 2003; Ma, Yu & Kennedy,
114
2005; Guimaraes, Wypych, Saul & Ramos, 2010; Lee & Wang, 2006; Pinto, Carbajal,
115
Satyanarayana, Fernando & Ramos, 2009; Tripathi, Mehrotra & Dutta, 2009; Sanghavi &
116
Srivastava, 2010; Gadhari, Sanghavi & Srivastava, 2011; Sanghavi, Kalambate, Karna &
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Srivastava, 2014). Globally, efforts have been made to develop bioplastics from renewable
118
polymers for use as mulch film, materials for green-house construction, packaging, and aids
119
for transporting and transplanting plants/seedlings and antimicrobial properties which
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improve the food safety and shelf-life. Antimicrobial packaging has one of the most
121
promising active packaging systems. Antimicrobial packaging has been used for the
122
inhibition of certain bacteria in foods, but barriers to their commercial implementation
123
continue to exist (Tripathi, Mehrotra & Dutta, 2009).
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This paper describes the preparation of cellulosic Grewia optiva fibre reinforced
125
composite cast films from blends of corn starch and PVA. Citric acid and glutaraldehyde
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have been used as plasticizer and crosslinker, respectively. The effect of citric acid and
127
gluteraldehyde on mechanical properties and degree of swelling were also attempted. Further,
128
the composite blend films were characterized with Fourier transform infrared
129
spectrophotometer (FTIR), Scanning electron microscopy (SEM) and Thermogravimertic
130
analysis (TGA). The antibacterial activity of St/PVA crosslinked blend films and composite
131
blend films were explored on food pathogenic bacteria such as Escherichia coli and
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Staphylococcus aureus.
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2. Experimental
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2.1 Materials and methods
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Starch (corn starch) (St), Gluteraldehyde (GLU) and polyvinyl alcohol (PVA) were
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obtained from CDH India and used without any further purification. Citric acid (CA) was
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obtained from Aldrich Company India. PVA was 99% hydrolyzed with average molecular
138
weight of 99,000-10,00,000. The weighing of the samples has been done on Libror AEG-220
139
(Shimadzu, Japan) electronic balance. Bacterial strain, S. aureus ATCC 43300 and E. coli
140
MTCC 739 were used by Bio Tech. Research Laboratory Shoolini University, Solan,
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Himachal Pradesh, India. Antibiotic discs (Amoxicillin 25µg/disc) and Nutrient agar were
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obtained from Himedia Laboratories Limited.
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2.2 Preparation of St/PVA blend films
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St/PVA blend films were prepared by casting method. In this method, 5 g of PVA was
144 145
dissolved in hot water (90°C). The gelatinized starch was mixed to form homogeneously gel
146
solution. The mixture was continuous stirring for 5 min on a mechanical stirrer (1500 rpm) at
147
room temperature. CA (5-30%) and GLU (0.05-0.250%) were added to above mixture with
148
continuous stirring. The total amount of polymeric mixture was 100 g. The mixing
149
compositions of different additives were shown in Table 1. The reaction parameters such as
150
mixing time, CA and GLU concentration were optimized. Bubbles formed during the
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preparation of blend films were removed by using an aspirator. The suspension so formed
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was poured onto teflon plate to prepare blend film. The blend films were dried at room
153
temperature for 72 h.
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2.3 Reinforcing material
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In this study Grewia optiva fibres collected from local resources were used as
156
reinforcing material. The fibres were washed with mild detergent to remove the impurities
157
involved during extraction of fibres. The fibres were dried at hot air oven maintained at 80°C
158
for 12 h. After drying the fibres were converted into fine particle using ball mill (FRITCH
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Pulbersette-5) of dimension 15-20µm.
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2.4 Synthesis of lignocellulosic fibre reinforced St/PVA blend films
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Grewia optiva fibres of dimension 15-20µm were mixed thoroughly with St/PVA
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blend using a mechanical stirrer, at different loadings (5-30% in terms of weight). This
163
mixture was poured into teflon plate and allowed to dry at room temperature. The mixing
164
composition of raw Grewia optiva fibre was shown in Table 1.
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2.5 Mechanical properties of St/PVA blend films and fibre reinforced St/PVA blend films
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Tensile strength (TS) and elongation percentage (%E) of St/PVA blend films and
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fibre reinforced St/PVA blend films were performed on a computerized Universal Testing
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Machine (Hounsfield H25KS). The tensile test was conducted in accordance with the ASTM
169
D 638 method. The specimen average thickness was about 1mm and operated at a cross-head
170
speed of 20mm/min at 30°C.
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2.6 Degree of swelling (DS) of St/PVA blend films
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In this, dried St/PVA blend films were immersed in distilled water at room
173
temperature (35°C) and kept for 24 h, moisture on the surface of the film was removed, and
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the weight of the films was measured. The degree of swelling (DS) of St/PVA blend films
175
were calculated as (Ghanbarzadeh, Almasi & Entezami, 2011):
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Where, Wi is the initial weight of St/PVA blend films and Wf is the final weight of St/PVA
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blend films.
179
2.7 Fourier transforms infrared (FTIR) spectroscopy
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FTIR spectra of St/PVA blend films were recorded on a Perkin Elmer
181
spectrophotometer using KBr pellets. The spectrum was recorded in the range from 4000 to
182
400 cm-1 with a resolution of 2 cm-1.
183
2.8 Scanning electron microscopy (SEM)
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The scanning electron microscopic analysis of different samples was performed on a
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Leo Electron Microscopy Machine (No. 435-25-20).
186
2.9 Thermogravimetric analysis
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Thermogravimetric analysis of starch/PVA blend film was performed using EXSTAR
187
TG/DTA 6300 at a heating rate of 10 °C/min under nitrogen atmosphere.
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2.10 Antibacterial activity
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Antibacterial activities of Starch/PVA blend films were measured against Gram
191
negative (E. coli) and positive bacteria (S. aureus) with disc diffusion method (Vimala et al.,
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2007).
193
2.11 Biodegradability in Soil
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In this method, samples of Starch/PVA films, 20×20×1mm small pieces were
194 195
weighted and placed for 120 days into the agricultural soil in a pot. The pot was covered with
196
a plastic net and exposed to atmospheric conditions for 120 days. Variations in film
197
morphology, the time of films disintegrated and weight loss were recorded. To determine the
198
weight loss the specimen of each sample was quickly washed with cold water and dried in an
199
oven at 70°C to constant weight. The weights of the sample, before and after washing were
200
recorded (Imam, Cinelli, Gordon & Chiejjini, 2005).
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201
3. Results and discussion
202
3.1 Optimization of different parameters on mechanical properties
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3.1.1 Effect of mixing time Fig. 1a shows Tensile strength (TS) and elongation (%E) of St/PVA blend film
205
without additives for 40 min at 90°C. At the mixing time of 10 min, TS and %E were found
206
to be 16.4 MPa and 68.74% respectively. Further, increase in time resulted in change in
207
colour and decrease in TS and %E of blend films.
208
3.1.2 Effect of citric acid (CA)
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Effect of CA on TS and %E of St/PVA blend film was shown in Fig. 1 b. The CA as
210
the crosslinker and the plasticizer in the St/PVA blend films. With the initial increase in CA
211
value from 5-30 wt.%, value of TS and %E increases. It has been evident that with increase in
212
CA wt.%, the decrease in TS (17.11-11.35 MPa) and increase of the %E (70.65-198.59%)
213
was observed. The residual CA in the blends acted as the plasticizer, which reduced the
214
interactions among the macromolecules. The decrease in the interactions may be due to the
215
presence of hydroxyl group and carboxyl groups present on CA, which form hydrogen bonds
216
between St/PVA and additive molecules (Yoon, Chough & Park 2006; Ghanbarzadeh,
217
Almasi & Entezami, 2011). It has been extensively used to improve the flexibility due to its
218
diplex function (Avella, Martuscelli & Raimo, 2000).
219
3.1.3 Effect of glutaraldehyde as crosslinking agent
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Fig. 1c shows the effect of GLU (0.05-0.250%) on TS and %E of St/PVA/CA blend
221
film. The effect of crossslinking of GLU on St/PVA films has been reported (Yoon, Chough
222
& Park, 2006). It has been found that TS (43.4 MPa) increases and %E (204.23%) decreases
223
with the increased in wt.% of GLU from 0.05-0.150%. The blend film so formed was referred
224
as St/PVA crosslinked blend film with remarkable TS and %E.
225
3.1.4 Effect of fibre loading on St/PVA crosslinked blend films
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TS and %E of Grewia optiva fibre loading onto St/PVA crosslinked blend films was
227
shown in Fig. 1d. Fibres were added to crosslinked blend from 5-30 wt.%. The result
228
indicated that TS increased on reinforcement with cellulosic fibres. It has been observed that
229
at 20% loading, TS and %E were found to be 38.53 MPa and 182.1%, respectively. The film
230
so formed was referred as fibre reinforced St/PVA composite blend film.
231
3.2 Degree of swelling
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The swelling behaviour of St/PVA, St/PVA/CA, St/PVA/CA/GLU and fibre
233
reinforced St/PVA composite blend films were shown in Table 2. It was observed that degree
234
of swelling decreased with increase in time. The addition of CA and GLU in St/PVA blend
235
films decreased the DS value which confirmed the superior reactivity of CA and GLU
236
(Krumova, Lopez, Benavente, Mijangus & Perena, 2000). The slight increase in DS value
237
was recorded in fibre reinforced St/PVA composite blend films, which may be due to the
238
greater affinity of water for OH groups present in the fibre reinforced St/PVA blend films.
239
3.3 FTIR analysis
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FTIR spectra of raw Grewia optiva fibre, St/PVA crosslinked blend films and fibre
241
reinforced St/PVA composite blend films were shown in Fig. 2 a-c. FTIR spectra of raw
242
Grewia optiva fibre (Fig. 2a) showed a broad peak at 3431.39 cm-1 due to bonded OH groups.
243
The absorption peak at 2922.31, 1431.01, and 1021.93 cm-1 were due to -CH2, C–C, and C–
244
O stretching, respectively(Singha & Rana, 2012; Singha, Rana & Guleria, 2012). Fig. 2b
245
showed the IR spectra of St/PVA crosslinked blend films. The peak at 3434 cm-1 was
246
assigned to the stretching vibration of the hydroxyl groups. Broad peak at 1717 cm-1 may be
247
due to the C=O stretching vibration and it was probably caused by the ester bond and
248
carboxyl C=O groups in CA (Shi et al., 2008). The peak at 2858.10 cm-1 and 2925 cm-1
249
corresponds to C-H stretching of aldehydic group of gluteraldehyde cross linked to blend
250
(Tudorachi, Cascaval, Rusu & Pruteanu, 2000). The change in peak intensity at 3434 cm-1 in
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251
Fig. 2c confirmed the number of the hydroxyl groups rises due the interaction of fibre with
252
St/PVA crosslinked blend.
253
3.3 Surface morphology Scanning electron micrographs of corn starch, PVA, St/PVA crosslinked blend film
255
and fibre reinforced St/PVA composite blend film were shown in Fig. 3 a-e. The corn starch
256
(Fig. 3a) showed polyhedra or polygon shape granules. Fig. 3b confirmed the smooth surface
257
of PVA film. The St/PVA crosslinked blend film (Fig. 3c) was found to be smooth without
258
any cracks and pores. The SEM images of Grewia optiva fibre confirmed the rough surface
259
(Fig. 3d). Morphological investigations of fibre reinforced St/PVA composite blend film (Fig.
260
3e) clearly indicate the proper mixing of fibre particles with the St/PVA crosslinked blend.
261
3.4 Biodegradability in Soil
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The crosslinked and fibres reinforced St/PVA composite blend films were exposed to
263
soil for 120 days under prevailing environmental conditions. After 120 days of exposure in
264
soil, films eventually diminished in size and appeared hard and fragile. Film deterioration
265
was also accompanied by loss in their total weight after soil exposure (Table 2). The weight
266
loss may be due to adhering of soil and debris partial to the film surface (Imam, Cinelli,
267
Gordon & Chiejjini, 2005). The decay of 34.54% and 45.65% weight loss were recorded for
268
St/PVA crosslinked film and fibres reinforced St/PVA composite blend films, respectively.
269
Thus, crosslinking results in slow rate of film deterioration in soil.
270
3.5 TGA analysis
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Thermogravimetric analysis of Grewia optiva fibre, St/PVA crosslinked blend films
271 272
and fibres reinforced St/PVA composite blend films were studied as a function of percentage
273
weight loss with temperature and shown in Fig. 4 a-c and Table 3. In case of fibre,
274
depolymerization, dehydration and glucosan formation took place between the temperature
275
range of 26.0ºC to 190.0ºC followed by the cleavage of C-H, C-C and C-O bonds (Maiti,
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Page 11 of 30
Kaith, Jindal & Jana, 2011; Thakur, Singha & Thakur, 2013). The initial decomposition
277
temperature (IDT) and final decomposition temperature (FDT) were found to be 241.18ºC
278
(8.04% weight loss) and 356.38ºC (77.11% weight loss). On the other hand, in case of
279
St/PVA crosskinked blend films, two stage decomposition was observed. The IDT and FDT
280
have been found to be 156.06ºC (7.29% weight loss) and 490.29ºC (79.03% weight loss),
281
respectively. The degradation temperatures for fibres reinforced St/PVA composite blend
282
films fall between the degradation temperatures for the blend films and the fibres. It has been
283
observed that for fibres reinforced composite blend films, IDT and FDT was 210.40ºC
284
(13.85% weight loss) and 450.99ºC (82.26 % weight loss), respectively. It indicated that the
285
presence of cellulose fibres affect the degradation process. TGA studies were further
286
supported by DTA curve as shown in Fig. 4 a-c. Two peaks were observed in the DTA curve
287
of Grewia optiva fibre and St/PVA crosslinked blend films. Fibre reinforced St/PVA
288
composite blend films shows three DTA peaks. The TGA and DTA curves revealed that the
289
Grewia optiva fibre, St/PVA blend films and fibres reinforced St/PVA composite blend films
290
decompose in different stages in the temperature range of 199-500ºC, 150-600ºC and 190-
291
600ºC, respectively. The magnitude and location of peaks found in the derivative
292
thermogravimetric (DTG) curve also provide similar information (Tudorachi, Cascaval, Rusu
293
& Pruteanu, 2000; Jiang, Qiao & Sun, 2006).
294
3.6 Antibacterial activity
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St/PVA crosslinked blend film and fibres reinforced St/PVA composite blend film
296
were screened for their antibacterial activity against Gram-positive (S. aureus) and Gram
297
negative (E.coli) bacteria as shown in Fig. 5 a-b. Antibiotic amoxicillin (25µg/disc) was used
298
as a standard (+ control). The inhibitory effect was measured based on clear zone surrounding
299
circular film disc. Measurement of clear zone diameter included diameter of film disc,
300
therefore, the values were always higher than the diameter of film disc whenever clearing
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Page 12 of 30
zone was present. If there is no clear zone surrounding, it suggests that there is no inhibitory
302
zone, and furthermore, the diameter was valued as zero. Films showed fair antibacterial
303
activity against Gram-positive (S. aureus) and Gram negative (E.coli) bacteria. Inhibitory
304
zone against S. aureus and E. coli was measured to be 1.5 and 1.2 cm, 1.7 and 1.5 cm for
305
St/PVA crosslinked blend film and fibre reinforced St/PVA composite blend films,
306
respectively (Tripathi, Mehrotra & Dutta 2009; Arora, Lala, Sharma &Aneja, 2011;
307
Abdelgawada, Hudsona & Rojas, 2014).
308
Conclusion
309
St/PVA blend films were prepared by a casting method using citric acid as the plasticizer and
310
glutaraldehyde as crosslinker. Addition of GLU increases the tensile strength and degree of
311
swelling of St/PVA blend films. The mechanical properties of fibre reinforced St/PVA
312
composite blend films were found to be higher than those of the St/PVA crosslinked blend
313
films with 20% of Grewia optiva fibre loading. These properties can make Grewia optiva
314
fibres a potential material for the synthesis of a new class of bio-composites. The composite
315
films were characterized using Fourier transform-infrared spectrophotometry (FTIR),
316
scanning electron microscopy (SEM) and thermogravimetric analysis (TGA/DTA/DTG).
317
TGA analysis confirmed the good thermal properties of blend films. The antibacterial
318
experiment indicated that St/PVA blends had good activity against the Gram-negative (E.
319
coli) and Gram- positive (S. aureus) bacteria. Thermal and antibacterial study reveals that the
320
synthesized blend films might be used as potential materials in food packaging.
321
Acknowledgements
322
The authors are thankful to Shoolini University of Biotechnology and Management Sciences,
323
Solan and Director, National Institute of Technology Hamirpur (H.P.) for providing
324
necessary laboratory facilities to complete this work.
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507
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506
M
503
508
Ac ce p
509 510 511 512 513 514 515 516 517 518
21
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519
Figure captions
521
Fig. 1. Tensile Strength (TS) and % Elngation (%E) of (a) St/PVA (b) St/PVA/CA (c)
522
St/PVA/CA/GLU (d) St/PVA/CA/GLU/Grewia optiva fiber.
523
Fig. 2. FT-IR of (a) raw Grewia optiva fibre, (b) St/PVA crosslinked blend film and (c) fibres
524
reinforced St/PVA composite blend film.
525
Fig. 3. SEM images of (a) Starch, (b) PVA film, (c) St/PVA crosslinked blend film, (d) raw
526
Grewia optiva fibre and (e) fibres reinforced St/PVA composite blend film.
527
Fig. 4. TGA/DTA of (a) raw Grewia optiva fibre, (b) St/PVA crosslinked blend films and (c)
528
fibres reinforced St/PVA composite blend film.
529
Fig. 5. Inhibitory effect of St/PVA crosslinked blend film and fibres reinforced St/PVA
530
composite blend film against (a) S. aureus and (b) E. coli.
M
an
us
cr
ip t
520
Ac ce p
te
d
531
22
Page 22 of 30
531
Table caption
532 533 534 535 536 537 538 539 540 541 542
Table 1 Composition of St/PVA blend films and fibres reinforced St/PVA composite blend films.
ip t
Table 2 Degrees of swelling of St/PVA blend films and Weight loss in St/PVA crosslinked blend film and fibre reinforced St/PVA composite blend film exposed to soil for 120 days.
us
cr
Table 3 Thermogravimetric analysis of Grewia optiva fibre, St/PVA crosslinked blend film and fibres reinforced St/PVA composite blend film.
543
an
544 545
M
546 547
d
548
te
549 550
Ac ce p
551 552 553 554 555 556 557 558 559 560
23
Page 23 of 30
Table 1 Composition of St/PVA blend films and fibres reinforced St/PVA composite blend films. Sample Starch PVA CA GLU Fibre loading (%) (%) (wt.%) (wt.%) (wt.%) St/PVA 5 5 5
5
-
St/PVA/CA
5
5
10
-
St/PVA/CA
5
5
15
-
St/PVA/CA
5
5
20
St/PVA/CA
5
5
St/PVA/CA
5
5
St/PVA/CA/GLU
5
St/PVA/CA/GLU
5
St/PVA/CA/GLU
5
St/PVA/CA/GLU
5
-
ip t
5
cr
St/PVA/CA
us
-
-
-
-
30
-
-
25
0.050
-
5
25
0.100
-
5
25
0.150
-
5
25
0.250
-
5
25
0.300
-
5
5
25
0.100
5
5
5
25
0.100
10
St/PVA/CA/GLU/fibre
5
5
25
0.100
15
St/PVA/CA/GLU/fibre
5
5
25
0.100
20
St/PVA/CA/GLU/fibre
5
5
25
0.100
25
St/PVA/CA/GLU/fibre
5
5
25
0.100
30
St/PVA/CA/GLU/fibre
5
Ac ce p
St/PVA/CA/GLU/fibre
d
St/PVA/CA/GLU
563
M
an
25
5
te
561 562
564 565 566 567
24
Page 24 of 30
-
St/PVA/CA
1.72
-
St/PVA/CA/GLU
0.53
35.54
Fibre reinforced St/PVA blend film
0.74
45.65
ip t
2.8
an
us
cr
St/PVA
Table 3 Thermogravimetric analysis of Grewia optiva fibre, St/PVA crosslinked blend film and fibres reinforced St/PVA composite blend film. Sample IDT FDT DT (˚C) at DT(˚C)at DT(˚C)at Residual 60%wt. left (%)at 40%wt. (˚C) (˚C) 20%wt. 800˚C loss loss loss 356.38 287.74 326.35 348.77 18.93 Grewia optiva 241.18 Fibre St/PVA/CA/ 156.6 490.23 224.93 296.00 371.64 GLU 210.43 450.43 240.74 310.17 367.66 9.82 fibres reinforced St/PVA composite blend film
Ac ce p
te
d
572 573 574 575 576
Table 2 Degree of swelling of St/PVA blend films and Weight loss in St/PVA crosslinked blend film and fibre reinforced St/PVA composite blend film exposed to soil for 120 days. Sample Degree of Swelling % wt.571 (DS) loss
M
568 569 570
577 578
25
Page 25 of 30
578
Highlights •
579
Starch/PVA blend films were prepared using citric acid (CA) and glutarldehyde (GLU) as plasticizer and crosslinker, respectively.
580
•
Blend film shows increased tensile strength and degree of swelling.
582
•
The mechanical properties of Grewia optiva fibre reinforced composite blend films
TGA showed the good thermal properties of blend films.
us
•
584
cr
have been found to be higher than those of the Starch/PVA cross-linked blend films.
583
585
ip t
581
Ac ce p
te
d
M
an
586
26
Page 26 of 30
Figure(s)
17
18
130
a
120
16
200
Tensile Strength % Elongation
180 16
100 90
14
80 13 70
160 15 140 14 120 13
% Elongation
Tensile Strength % Elongation
15
Tensile Strength(MPa)
110
% Elongation
Tensile Strength(MPa)
b 17
100 12 80
ip t
60
12
11
50 0
5
10
15
20
25
30
35
40
60
45
5
10
Mixing time(min)
44
40 35
25
140
20 120 15 100
5 0.20
0.25
Glutardehyde content(wt.%)
160 150 140 130
34
120
32
80 0.15
170
36
M
10
38
180
an
160
% Elongation
30
40
190
% Elongation
Tensile Strength(MPa)
180
200
us
42
0.10
30
Tensile Strength % Elongation
d
200
0.05
25
cr
220
Tensile Strength % Elongation
c 45
20
Citric acid content(wt.%)
50
Tensile Strength(MPa)
15
110
30
100 5
10
15
20
25
30
Fiber reonforcement(wt.%)
ed
Fig. 1. Tensile Strength (TS) and % Elngation (%E) of (a) St/PVA (b) St/PVA/CA (c)
ce pt
St/PVA/CA/GLU (d) St/PVA/CA/GLU/Grewia optiva fiber.
Ac
c
b
%T
a
4000
3500
3000
2500
2000
Wavelength cm
1500
1000
500
-1
Fig. 2. FT-IR of (a) raw Grewia optiva fibre, (b) St/PVA crosslinked blend film and (c) fibres reinforced St/PVA composite blend film. 1 Page 27 of 30
ip t cr us an M ed ce pt
Ac
Fig. 3. SEM images of (a) Starch, (b) PVA film, (c) St/PVA crosslinked blend film, (d) raw Grewia optiva fibre and (e) fibres reinforced St/PVA composite blend film.
2 Page 28 of 30
ip t cr
ed
M
an
us
(a)
Ac
ce pt
(b)
(c) Fig. 4. TGA/DTA of (a) raw Grewia optiva fibre, (b) St/PVA crosslinked blend films and (c) fibres reinforced St/PVA composite blend film.
3 Page 29 of 30
ip t cr
Ac
ce pt
ed
M
an
composite blend film against (a) S. aureus and (b) E. coli.
us
Fig. 5. Inhibitory effect of St/PVA crosslinked blend film and fibres reinforced St/PVA
4 Page 30 of 30
