Use of gamma irradiation technology for modification of bacterial cellulose nanocrystals/chitosan nanocomposite film
Introduction
The environmental impact of non-biodegradable plastic material wastes is a major global concern. Biodegradable polymers made of polysaccharides, proteins and lipids are considered as the good alternative to common synthetic polymers owing to its biodegradability, biocompatibility, edibility and non-petroleum based source (Sarwar, Niazi, Jahan, Ahmad, & Hussain, 2018).
Chitosan, a natural polymer obtained by deacetylation of chitin, is a linear binary heteropolysaccharide composed of β-1,4-linked glucosamine and N-acetylglucosamine (Nasef, Khozemy, Kamoun, & El-Gendi, 2019). When chitosan is compared with other polysaccharides, it has several advantages such as non-toxicity, biodegradability, biocompatibility, excellent film-forming properties and strong bacteriostatic and fungistatic activity (Ojagh, Rezaei, Razavi, & Hosseini, 2010). Films prepared from chitosan are reasonably tough, long-lasting and flexible with good oxygen barrier but they exhibit poor water vapor barrier and relatively low mechanical properties; therefore, they need some modifications (Azeredo et al., 2010). For example, film performances can be significantly improved by the use of reinforcing nanofillers to create nanocomposite films.
Cellulose, the most abundant biopolymer, is a natural linear organic compound consisting of D-glucopyranose units connected by β-1,4-glycosidic bonds (Dehnad, Mirzaei, Emam-Djomeh, Jafari, & Dadashi, 2014). Apart from plants, various algae (Valonia, Oocystis apiculata), marine tunicates, and bacteria (Gluconacetobacter xylinus) are also known to produce cellulose (Abdul Khalil, Bhat, & Ireana Yusra, 2012). However, for packaging applications, bacterial cellulose (BC) is more preferred over plant cellulose since it exhibits higher crystallinity, purity, mechanical strength, and water holding capacity (George & Siddaramaiah, 2012). Bacterial cellulose nanocrystal, which is derived from BC by mechanical shearing and controlled acid hydrolysis, can be applied as nano-reinforcer material for the production of cheap, lightweight, and very strong nanocomposite films, and they are more effective than their microsized counterparts to reinforce polymers (Sun et al., 2018).
Gamma irradiation is an ionic and no-heat process that is widely used as the cold sterilization method for foods, food packaging and medical products (Jipa et al., 2012). To avoid microbial recontamination, sometimes foods are prepackaged with polymers and then are irradiated. Radiation of polymers can cause an increase (cross-linking) or decrease (degradation, chain scission) of molecular weight (Nabiyev et al., 2020). Although in many polymers, both processes take place simultaneously. Thus, gamma irradiation as a general sterilization method for biomaterial possesses might have some side effects on packaging materials i.e. discoloration, permeability and mechanical properties (Khan et al., 2012). However, these effects depend on several factors, including the chemical structure of the polymer, the amount of dosage, the rate of dosage, the testing conditions (atmosphere and temperature) and the presence of additives (García et al., 2015). For this reason, the effect of ionizing radiation on the functional properties of biopolymers is still an interesting subject of scientific investigation.
The modification of functional properties of Ch/BCNC nanocomposite films using gamma irradiation was not reported before. Therefore, the objectives of this research are (1) to demonstrate the effect of different gamma irradiation dose (5, 10 and 15 kGy) on the physical and mechanical properties of Ch/BCNC nanocomposite film; (2) to evaluate the proper irradiation dose.
Section snippets
Materials and microbial strain
Chitosan powder (medium molecular weight, degree of deacetylation: 75–85 %) was provided from Sigma Aldrich Chemical Co., Germany. Liquid glycerol was bought from Sigma Chemical Co., USA. For BC production, Gluconacetobacter xylinus was purchased from the Persian Type Culture Collection (PTCC 1734), Iran. All chemicals were analytical grade and were purchased from Merck Co., (Germany).
Preparation of BCNC
BCNC was prepared according to our previous study (Salari, Sowti Khiabani, Rezaei Mokarram, Ghanbarzadeh, &
Moisture content and Solubility in water
The MC and SW of non-irradiated and irradiated films are shown in Table 1. The moisture content of pure chitosan and Ch/BCNC films was dramatically decreased after gamma irradiation. Although the lowest moisture content was obtained for 10 kGy-irradiated films, there was no significant difference among the data. This is due to the improved hydrophobic properties in polysaccharide-based polymer using gamma irradiation (Kyung Kim, Jo, Jin Park, & Woo Byun, 2008).
The solubility in water of the
Conclusions
Chitosan-based nanocomposite films were prepared by incorporating BCNC at a concentration of 4 wt% (based on dry chitosan). Nanocrystals of cellulose were isolated from bacterial cellulose pellicles by acid hydrolysis under controlled conditions. Chitosan and Ch/BCNC films were gamma irradiated at 0, 5, 10 and 15 kGy in order to display the effect of irradiation on functional properties of them. Barrier and thermal properties enhancement, as well as the increase in TS and EM and decrease in %EB
CRediT authorship contribution statement
Mahdieh Salari: Investigation, Methodology. Mahmoud Sowti Khiabani: Software. Reza Rezaei Mokarram: Resources. Babak Ghanbarzadeh: Supervision. Hossein Samadi Kafil: Visualization.
Acknowledgment
The authors would like to thank for the support provided by the University of Tabriz and Drug Applied Research Center of Tabriz University of Medical Science.
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