Biodegradation and swelling behaviour of cellulose-based plastic incorporation of pennisetum purpureum, chitosan and gelatine

This paper reports on the biodegradation and swelling behaviour of cellulose-based plastic incorporation of Pennisetum purpureum (PS), chitosan and gelatine. Cellulose-based plastic (CP) was obtained from chitosan and gelatin; and from the cortex (CPS), pith (PPS), and whole (WPS) of Pennisetum purpureum (PS). The films were prepared by solution casting with untreated, 4, 8, 12, 16, and 20% alkali-treated cellulose of CPS, PPS, and WPS. The ASTM D5988-method was used to conduct the CP biodegradation tests. The swelling behaviour test was performed to measure the swelling percentage for each CP samples in aqueous solution with different pH values. The results reveal that the biodegradation of untreated CPS (60.30%), untreated WPS (49.74%), and untreated PPS (CP) showed the biggest relative weight reduction. CP added with the 8, and 16% alkali-treated cellulose of CPS, and PPS continues swelling in the solution of pH 7 throughout 24 hours of analysis. Increasing the cellulose loading accelerated the biodegradation rate of the bioplastic films. The results also suggest that the CP with the incorporated cortex (CPS) of Pennisetum purpureum (PS), is the most water-resistant in neutral followed by acid and alkali.


Introduction
There are numerous things that are used on a daily basis that are made of plastic, including water bottles, toothbrushes, and other items.There are a few examples of plastic being used in the medical industry, including sutures, syringes, blood bags, and pharmaceutical containers.Plastics combine a great strength-to-weight ratio, durability, and adaptability.Due to these qualities, the need for plastic has increased, particularly during the COVID-19 pandemic, in the healthcare industry and for public health safety, with major uses in packaging, single-use medical tools and equipment, and transplants [1].
According to Wróblewska-Krepsztul et al. (2019), medical packaging is a technique that enables the end of a pharmaceutical product from the beginning and end of its life cycle [2].Notably, petroleumbased plastic is required as a lifesaver for protection against the COVID-19 virus infection among people, including PPEs, face masks, and face shields.Additionally, the demand for plastics has significantly increased as a result of consumer behavior shifts and a reliance on online shopping and takeaway services for home delivery of crucial commodities during the pandemic.The use of plastic made from petroleum has substantially increased as a result, both for medical and non-medical uses.To address the demands of the existing ecological system, researchers have been developing easily recyclable biodegradable plastic.
In previous researches, many research studies have been conducted to design both medical and non-medical applications [3], such as biosensors, drug delivery, vehicles parts, hydrogel, scaffolds, and composite for commercial hemostasis and wound dressing.Remarkably, Revati et al. (2017) had demonstrated the potential application of pith of PS in PLA based scaffolds [4].Besides, the research introduced by Dey et al. (2019) revealed a good miscibility between gelatine and chitosan for the hydrogel applications [5].Thus, this shows high demand and potential of CP in the industrial applications.Hence, it also would be interesting if the interaction between cellulose, chitosan and gelatine material can used in the many applications including the medical and non-medical industrial applications.

Materials
This research utilized material from Pennisetum Purpureum stem (PS), sodium hydroxide (NaOH), sodium chlorite (NaClO 2 ) , chitosan, gelatine, acetic acid, and glycerol for CP fabrication.The untreated and different cellulose extracted from the cortex, pith and whole of PS were used as base materials in the cellulose based-plastic (CP) preparation.The alkali and bleaching procedures utilized NaOH and NaClO2, respectively to remove non-cellulosic materials from the cortex, pith and whole of PS have been use for extraction of cellulose.The PS commonly named as Napier grass, was collected from a local farm near Bukit Kayu Hitam in Malaysia.Meanwhile, NaOH was obtained from Fisher Chemical Co. and supplied by A.R. Alatan (K) Sdn.Bhd.It is in pallet form with white colour.NaClO2 with the CAS number 7758-19-2 manufactured by R&M chemicals, which was supplied by A.R. Alatan (K) Sdn.Bhd.NaClO2 is a white flaky salt prepared at a concentration of 80%.
Furthermore, the gelatin from cold water fish skin and chitosan with CAS number 9000-70-8 and 9012-76-4, respectively were obtained from Sigma Aldrich and supplied by A.R. Alatan (K) Sdn.Bhd.The gelatin from cold water fish skin and chitosan are in powder form.Moreover, acetic acid glacial (Ethanoic acid) with 99% purity manufactured by R&M chemicals with the CAS number 64-19-7, which was supplied by A.R. Alatan (K) Sdn.Bhd.The acetic acid glacial of 2wt% was utilised for CP fabrication.Preparation of 2wt% acetic acid glacial was prepared by adding an amount of water that has been mixed into 99% of acetic acid glacial.Besides, the glycerol manufactured by HmbG reagent chemical also was supplied by A.R. Alatan (K) Sdn.

Film preparation
Solution casting method was used to fabricate the CP from the CPS, PPS, and WPS by combining the first and second solutions as depicted in Figure 3.4.For the first solution, 100mL of 2% (v/v) acetic acid was combined with 2g of chitosan powder for 12 hours.The second solution contained 2g of gelatine that had been dissolved in 100mL of room temperature water.40 mL of the second solution was then added to 1% untreated, 4, 8, 12, 16, and 20% alkali-treated cellulose of CPS, PPS, and WPS before the CP solution was prepared.The mixture was then mixed once more for a further twelve hours without heating.The combination was then given 60 mL of the initial solution, and it was stirred for 30 minutes after that.The next stage involved adding 1mL of glycerol to the mixture and stirring it for 2 hours.So, from the untreated and 4, 8, 12, 16, and 20% alkali-treated cellulose of CPS, PPS, and WPS, 18 different types of CP solutions were produced.To fabricate the CPs, 30mL of the CP solution was poured onto a glass petri dish with a 120mm diameter and allowed to evaporate for 24 hours at room temperature.The CPs were finally removed from the petri dishes.

Biodegradation test
The ASTM D5988-method was used to conduct the CP biodegradation tests.12.500g of soil from around the roots of plants with a high concentration of nitrogenous bacteria was gathered and kept in a container.The soil was then put into a container with a 4 cm thickness.The CP samples with a 4cm 2 dimension area were dried in an oven at 80°C until the samples reached a constant dry weight.The CP samples were consequently buried 2 cm into the ground.To maintain humidity, water was sprayed twice daily onto the soil.Up until day 28, samples were taken out of the ground, cleaned, and dried in an oven at 80 degrees Celsius to obtain a uniform dry weight.The weight loss was determined for each CP sample using the formula [6]: where   and   are the weights of the CP samples before and after the burial, respectively.

Swelling test
The swelling behaviour was performed to measure the swelling percentage for each CP samples in aqueous solution with different pH values, namely 0.5M NaOH (pH 13.5), distilled water (pH 7), and 0.1M HCl (pH 1.2).The used method was ISO 62.In an oven at 80°C, the CP samples with a 4cm 2 dimension area were dried until the samples achieved a consistent dry weight.Subsequently, the dried CP samples were drowned into aqueous solution and withdrawn after 2, 4, and 24 hours.Prior to measure the wet weights of the CP samples, the surplus water was removed by using a filter paper.The swelling percentage was calculated as follows [7]: where   and   are the weights of the CP samples in the wet and dry states, respectively.

Biodegradation
Figure 1 illustrates the weight loss dynamics that correspond to the CP for the untreated and 4, 8, 12, 16, and 20% alkali-treated cellulose of CPS, PPS, and WPS.The study's CP samples can be inferred to be biodegradable based on the results in Figure 1.Untreated CPS (60.30%), untreated WPS (49.74%), and untreated PPS (CP) showed the biggest relative weight reduction.This illustrates how soil microorganisms' steady biodegradation of the CP for untreated PPS, CPS, and WPS was demonstrated [8].Untreated CPS, PPS, and WPS surfaces have small holes that made it easier for bacteria to interact with them, which increased the risk of contamination.Small pores that were found on the untreated surfaces of CPS, PPS, and WPS made it easier for microorganisms to interact with them, speeding up deterioration and lowering structural integrity [8,9].
Moreover, the CP for untreated CPS exhibited a rapid weight loss (49.37%), following its burial in soil for 14 days.Meanwhile, the CP for untreated PPS demonstrated a rapid weight loss after 21 days.This good biodegradability may be caused by the low tensile strength of these CP which leads to being easily ruptured [8].However, Figure 1 also shows the increase of alkali treatment concentration in the cellulose extracted which was used in the CP had reduced the CPs' biodegradability.Nevertheless, the weight loss of CP progressively increased by increasing the time of being buried in soil, improving the biodegradability of CP [10].According to Jahit et al. (2016), the crystallinity of cellulose contributes to the biodegradability of CP.Therefore, owing to the higher crystallinity for the cellulose of CPS, PPS and WPS had become more resistant to microbial activity [11].Overall, the CP for cellulose CPS, PPS

Swelling behaviour
In Figure 2 the swelling behavior of the CP for the untreated and 4, 8, 12, 16, and 20% alkalitreated cellulose of CPS, PPS, and WPS in pH 7, pH 1.2, and pH 13.5 is provided.As a whole, the swelling ratios of the CP samples at pH 7, pH 13.5, and pH 1.2 were, respectively, between 24 and 77, 40 and 143, and 48 and 146% during a 24-hour examination.Interestingly, Figure 2 illustrates the variations in water uptake rates for the untreated, 8 and 16% alkali-treated, and CPS, PPS, and WPS cellulose at pH 7, pH 1.2, and pH 13.5.According to Figure 4.13, the CP's water intake is substantial.Based on Figure 2, it can be seen that when exposed to pH 7 for two hours as opposed to pH 1.2 and pH 13.5, CP samples absorbed less water.This suggests that there is less water soaking into the CP bulk and that there are fewer free -OH groups available to interact with water molecules [12].This is also due to the interactions among the cellulose, chitosan, and gelatine in the CP [7]. Figure 2 (a) shows that the CP added with the 8, and 16% alkali-treated cellulose of CPS, and PPS continues swelling in the solution of pH 7 throughout 24 hours analysis.Meanwhile, for WPS filler, only the CP added with the 16% alkali-treated cellulose of WPS continues swelling in the solution of pH 7 throughout 24 hours analysis.Figure 2 (b) shows that only the CP added with the untreated WPS, and 16% alkali-treated cellulose of CPS were beginning to dissolve in the solution of pH 1.2 after 2 hours while other CP began to dissolve after 4 hours analysis.Meanwhile, Figure 2 (c) shows that only the CP for the 8 and 16% alkali-treated cellulose of WPS were not dissolved and continue to swell in the solution of pH 13.5 throughout 24 hours analysis.
This further proves that the solubility of CP in pH 7 was reduced by the up to 8% alkali concentration treatment [13].This is due to the fact that, according to Figure 2, after 2 or 4 hours of analysis, the CP for the untreated CPS, PPS, and WPS was starting to dissolve in the solution of pH 7, pH 13.5, and pH 1.2.However, because CP is water resistant, its solubility depends on the application and intended use [13].Overall, the CP showed promise for usage in a variety of applications by offering the option of tailoring for a particular use that calls for either high or low solubility [14].As a result, measuring the total soluble matter in various pH environments is a crucial component of guaranteeing applicability [15].

Conclusion
The results show that the addition of different cellulose of CPS, PPS, and WPS in CP can enhance the biodegradability and swelling behaviour of CP.The results reveal that the biodegration of untreated CPS (60.30%), untreated WPS (49.74%), and untreated PPS (CP) showed the biggest relative weight reduction.CP added with the 8, and 16% alkali-treated cellulose of CPS, and PPS continues swelling in the solution of pH 7 throughout 24 hours analysis.CP showed promise for usage in a variety of applications by offering the option of tailoring for a particular use that calls for either high or low solubility.Overall, the CP for cellulose CPS, PPS and WPS were considered as promising sustainable packaging, owing to their biodegradability, excellent tensile properties, and good appearance.
ICADME-2023 Journal of Physics: Conference Series 2643 (2023) 012010 IOP Publishing doi:10.1088/1742-6596/2643/1/0120103 a) CP for untreated and cellulose of CPS b) CP for untreated and cellulose of PPS c) CP for untreated and cellulose of WPS

Figure 1 .
Figure 1.Weight loss dynamics of the CP for untreated and cellulose of CPS, PPS and WPS.

Figure 2 .
Figure 2. Swelling behaviour for the CP using untreated, 8 and 16% alkali-treated cellulose of CPS, PPS and WPS