Assessing Biodegradability of PVA/Starch Based Composite Films Reinforced With Long Chain Fatty Acid Grafted Barley Husk

7 The main objective of this study is the preparation of poly (vinyl alcohol) PVA/starch based composite films 8 reinforced with barley husk and grafted barley husk (prepared using lauric acid, palmitic acid and arachidic 9 acid) for packaging applications and assessment of their biodegradability. The biodegradability test of the films 10 was performed by measuring weight loss of the films after degradation in soil under natural environmental 11 conditions and by measuring evolved carbon dioxide (CO 2 ) during degradation under aqueous aerobic 12 environment containing activated sludge. Physico-chemical variation in the films after degradation were 13 observed using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The 14 composite films containing barley husk showed highest degradation in soil (70 % after 180 days) as well as in 15 aqueous aerobic medium (58.83 % after 30 days). The results of scanning electron microscopy showed the 16 formation of cracks and holes over the surface of the composite films after degradation. The degradation of the 17 films occurred inside the composite films, not only on their surface. The incorporation of starch and barley husk 18 in PVA matrix enhanced the degradation rate of films.


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There has been introduction of new regulations considering the processing and manufacturing of the plastic products using modified natural polymers or synthetic raw materials in the European Union (Directive EU 23 2019/904) (Borowski et al. 2020). The marketing of single use plastic products will be prohibited from 2021 24 onwards. There is also possibility that the composites made from non-degradable and synthetic polymers may 25 be replaced with biocomposites containing natural fillers in the near future (Ibrahim et al. 2020). Therefore, the 26 research is more focused towards replacement of non-degradable synthetic plastic with environment friendly The biodegradation of complex biomaterials results into small and environmentally acceptable products such as 36 CO 2 , water and biomass by naturally available microorganisms (bacteria and fungi) and other biological activity 37 under natural environmental conditions. However, now-a-days there have been an increased demand for 38 biodegradability and more reliable biodegradation data of the packaging films due to raised concerns about the 39 environment quality. Therefore, many researchers have made efforts towards establishment of different methods 40 for biodegradation of packaging films by observing change in physical and chemical properties of films (Garg 41 and Jana, 2011;Mittal et al. 2020b;Hoffman et al. 2003;Tripathy et al. 2018;Kaith et al. 2009;Negim et al. 42 2014;Abdullah et al. 2017;Castro-Aguirre et al. 2018, Borowski et al. 2020. Soil burial degradation method is 43 the most common method based on the direct measurement of weight loss of the film after biodegradation under 44 natural environmental condition (Mittal et al. 2016, Garg andJana, 2011). Another indirect method for 45 evaluation of biodegradability is based on the measurement of evolved CO 2 during the biodegradation of film in 46 aqueous aerobic medium (Strotmannet al. 2004;Hoffamann et al. 2003). The biodegradability of the PVA/corn 47 starch based composite films reinforced with orange fiber was measured using soil burial degradation method 48 and by measuring evolved CO 2 during degradation (Imam et al. 2005). The addition of orange fiber and starch 49 in the blend also stimulated the degradation of PVA as starch and lignocellulosic fiber are easily degraded by 50 microbes. In literature, neither PVA/starch based composite films reinforced with BH and grafted BH (prepared 51 using lauric acid, palmitic acid and arachidic acid) were synthesized nor the effect of their reinforcement on the 52 biodegradability of composite film by measuring evolved CO 2 during degradation of films was studied.

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Therefore, present work deals with the biodegradation study of the PVA/starch based composite films 54 containing BH and grafted BH (prepared using lauric acid, palmitic acid and arachidic acid) by soil burial 55 degradation test in natural environmental conditions and by CO 2 evolution method in aqueous medium. The 56 composite films were characterized by using scanning electron microscopy (SEM) and Fourier transform 57 infrared spectroscopy (FT-IR) before and after biodegradation test. PVA/St blend films were prepared by casting method as reported in our earlier studies (Mittal et al. 2016;Mittal et al. 2020a, b). Starch (5g) was gelatinized in hot water and mixed with PVA solution. The mixture of PVA and onto the glass petri dish (dia. 14 cm), dried in hot air oven (24h at 45 o C) and the dried film was peeled off from 75 the dish. Cross linked films were prepared using urea formaldehyde as crosslinking agent in PVA/St matrix 76 (Mittal et al. 2016). Urea formaldehyde prepolymer was prepared by refluxing of formalin solution with urea 77 (molar ratio 1:1.5) for 15 min. The crosslinker was added slowly in PVA/St suspension in acidic condition (pH 78 3.0) and the mixture was continuously stirred. The crosslinked films were prepared by solvent casting method 79 with urea/starch ratio 0.5(w/w).

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The composite films were prepared by reinforcing BH and fatty acid grafted BH within crosslinked PVA/St

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IR spectra of the films before and after degradation was recorded in order to study the chemical changes 88 occurred in the films after degradation. The film samples were equilibrated at 50°C and analyzed by FT-IR 89 instrument (Perkin Elmer, Model RX -1) at a resolution of 4 cm -1 within range 4000-400 cm -1 using KBr pellets 90 obtained from Sigma Aldrich. The surface morphology of the films before and after degradation was studied 91 using a scanning electron microscope (JEOL JSM-6100, JEOL, Tokyo, Japan) at a magnification up to 2000X.

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To avoid the charging under electron beam, the film samples were coated with gold in argon.

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The soil burial degradation test of the films (3cm×10 cm) was performed by burying all the samples in soil at 96 10cm depth under natural environmental conditions. The moisture and microbial concentration was maintained 97 by sprinkling sewage water over the soil. The samples were taken out after every 15 days and washed with 98 distilled water. The samples were dried in hot air oven and the weight loss (%) was calculated as (Mittal et al.
Where W i is initial weight of the sample and W d is final weight of the sample after degradation.
The test was done by determining the evolved carbon dioxide during degradation of films by ISO 9439:2000 103 procedure. The produced CO 2 during the degradation of sample was dissolved in the solution of hydroxide and 104 the subsequent amount of produced CO 2 was determined by titration. The percentage of degradation of the 105 sample was further calculated by knowing the amount of produced CO 2 during the degradation test.

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The experimental setup used is shown in Fig 1. The set up consists of three parts: common cleaning part, two 107 reactors and absorbers. The cleaning part consists of two gas washing vessels containing 500 mL of NaOH 108 solution (10 mol/L) and 100 mL of Ba(OH) 2 solution (0.0125 mol/L)., respectively. CO 2 free air from cleaning 109 part was then supplied to two reactors (Erlenmeyer flask) which were continuously stirred. First reactor contains 110 inorganic medium, inoculum and test sample while second reactor contained inorganic medium and inoculum.

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The sample was the nominal sole source of organic carbon and energy in the cultivating aqueous medium.

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The abiotic test was also performed with mercuric chloride (10 g/L) by similar method. Aniline was used a 119 reference compound for the degradation test with same concentration as test sample.

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Produced CO 2 reacted with Ba(OH) 2 to form precipitation of BaCO 3 as shown in the following reactions. 125 The mass of CO 2 dissolved in the absorber vessel was calculated using Eq. 1.
Where is the mass of CO 2 trapped in the absorber of vessel (mg), is the concentration of the HCl 127 solution (mol/L), is the concentration of the Ba(OH) 2 solution (mol/L), 0 is the volume of the Ba(OH) 2 128 solution (mL) at the beginning of the test, is the volume of the Ba(OH) 2 solution (mL) at time t; is the 129 volume of the aliquots of the Ba(OH) 2 solution (mL) used for titration; is the volume of the HCl solution The theoretical amount of CO2 produced in the test vessel is given by Where is the concentration of organic carbon of the test compound in the test vessel (mg/L), V L is the volume 136 of test solution in the reactor (L)

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The percentage of biodegradation D (%) can be calculated as Where ∑ is the mass of CO 2 released (mg) between the start of the test and time t and ∑ is the amount 139 of CO 2 released (mg) in blank control between the start of the test and time t. The results of soil burial degradation test of grafted BH composite films are shown in Fig. 2  in very low CO 2 production (approx. 5% of total production). The blank tests containing inoculum and inorganic 181 medium were run in parallel with all the test samples. The CO 2 production in all the blank tests was low and 182 contributed to approximately 33% of total CO 2 produced in the degradation test. Aniline was taken as reference 183 compound and showed highest CO 2 production (331.7 mg) as it is highly degradable in the given test conditions.

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The CO 2 production during degradation of PVA film was 161.37 mg after 30 days of test. However, composite 185 film (PVA-0.5C St-1BH) containing 1% BH showed 315 mg of CO 2 production after 30 days and was much 186 higher than blank test.

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There was not much significant variation in the amount of CO 2 produced during degradation of composite films