بهبود عملکرد پلیمرهای استحصالی ازآگار استخراجی از جلبک گراسیلاریا Persica) Gracilaria) از طریق کربوکسی‌متیلاسیون‌آگار

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The environmental impact of plastic and non-degradable materials, particularly polymers used in food packaging, has become a significant global concern. Recycling plastic waste has proven insufficient because conventional plastics can release hazardous chemicals during degradation and often exhibit poor mechanical properties, which limit their reuse and applications. In recent years, the food industry has increasingly explored biodegradable alternatives to synthetic polymers, with polysaccharides emerging as a promising category. Bioplastics are sustainable and eco-friendly alternatives to petro plastics, which are non-renewable and non-biodegradable. While a number of bioplastics have been synthesized, large-scale applicability of many of them is restricted by their low strength and high water absorption, especially in comparison to petro-plastics. Improvement in the above properties are desired to make them more suitable for packaging applications. When some types of plastics are burnt, they can release dangerous gases to theatmosphere while burying plastics in soil cannot destroy plastics. These naturally abundant polymers offer diverse functional properties and environmental compatibility. One of the main advantages of polysaccharides as natural biomaterials is their availability in natural resources and low- costprocessing. Furthermore, polysaccharides possess several favorable characteristics incluing biocompatibility, biodegradability, highly stable, safe, Non-toxic and abundance of functional grops for modification or functionalization. Agar, one of the oldest known polysaccharides, is extracted from red seaweed and is commonly used to develop biofilms. Agar is widely used for medical, pharmaceutical, and electronic and experimental purposes due to its combination of renewability, biological activities, biocompatibility, biodegradability and nontoxicity. Agar-based biopolymers are considered suitable candidates for edible films and coatings because of their high gel strength and biodegradability. However, native agar films typically lack the mechanical and physical robustness of synthetic films, limiting their suitability for food packaging applications. Therefore, modification methods are required to improve the physical and chemical properties of agar and broaden its applications. To overcome these limitations, researchers have developed carboxymethylated agar films. CMA is one of the water-soluble polysaccharide derivatives obtained from agar. Alkalization and carboxymethylation process will influence the quality of the CMA. Synthesis of CMA is affected by several factors, including alkalization and carboxymethylation. The alkalization stage was carried out using reaction media (solvents) and NaOH with the aim of activating hydroxyl groups of the agar. The physicochemical and functional properties, as well as the stability of agar, can be improved by replacing the hydroxyl groups with other functional groups, thus decreasing the dissolution temperature, improving the gel strength and transparency, and yielding gels tailored for particular industries. The solvent mixture will affect the number of dissolved monochloroacetic salt so that in large amounts it will facilitate and accelerate the diffusion of monochloroacetic salts to react with the hydroxyl group of agar. CMA synthesis is simple, efficient and low cost. It includes alkalization and carboxymethylation reactions. One of the main factors in CMA synthesis is the alkalization process. Alkalization is carried out using NaOH to activate OH groups on agar molecules and function as developers, while carboxymethylation is accomplished by adding monochloroacetate. carboxymethylation modification significantly improves the solubility, transparency, and colloidal system stability of polysaccharides, particularly their solubility. Modified agar through carboxymethylation significantly increased.the transparency of agar. This chemical modification addresses the inherent weaknesses of unmodified biopolymers and provides a cost-effective alternative to more expensive biodegradable materials. Previous studies have demonstrated that carboxymethylation enhances the functional properties of agar, including improved water resistance and mechanical strength, making it more viable for industrial use. Additionally, the incorporation of additives such as polyethylene glycol (PEG) and citric acid (CA) has been shown to significantly enhance the performance of agar-based biofilms. This study aims to modify agar via carboxymethylation to improve its functional properties and enhance its applicability in industrial food packaging. The resulting biofilms, characterized by high performance and environmental safety, can significantly reduce plastic pollution and improve packaging quality. Specifically, this research focuses on synthesizing carboxymethyl agar (CMA), reducing water vapor permeability (WVP), and enhancing mechanical properties. The use of marine algae, such as Gracilaria spp., as a raw material for bioplastic production is considered a sustainable and viable approach for achieving these objectives. Agar was extracted from Gracilaria algae using an alkaline extraction method. The process began with washing and drying the algal samples, followed by bleaching and alkaline treatment with sodium hydroxide. After treatment, the samples were thoroughly rinsed with distilled water. During the extraction phase, the dried algae were soaked in beakers, heated, filtered, and allowed to gel. The resulting gels were dehydrated, washed, and compressed. The agar was then ground and dried at 60°C. The yield was calculated using a predetermined formula. Carboxymethylation of agar was carried out by dispersing agar powder in isopropanol, followed by the addition of a sodium hydroxide solution and chloroacetic acid. Ethanol was then added to precipitate the product. The resulting solid material was dried in an oven at 50°C for 24 hours and stored at 25°C for further use. CMA films were prepared with five different treatment formulations, incorporating polyethylene glycol (PEG), citric acid (CA), and beta-cyclodextrin (β-CD). The films were cast in Petri dishes and dried under controlled conditions in a desiccator before testing. Water vapor permeability (WVP) was measured according to the ASTM E96 standard method. Water absorption was determined by calculating the weight difference using a digital balance. Mechanical properties, including tensile strength and elongation at break, were evaluated using a tensile testing machine. Film transparency was assessed by measuring light absorption at 600 nm using a UV-visible spectrophotometer. All experiments were conducted in triplicate. Statistical analysis was performed using SPSS software. One-way analysis software. One-way ANOVA followed by Duncan’s multiple range test was used to show significant differences among treatment groups. The extraction of agar from Gracilaria species yielded relatively high amounts, consistent with prior findings indicating that yield is closely linked to the extraction methodology. Moisture absorption rates of CMA films were found to be lowest in the treatment containing citric acid, beta-cyclodextrin, and polyethylene glycol. This reduction is attributed to the formation of hydrogen bonds and intermolecular interactions between functional groups introduced by these additives. CMA was synthesized via a reaction involving agar, sodium hydroxide, and chloroacetic acid, resulting in a transparent polymer with surface activity, thermoplastic behavior, and thickening capabilities. Chemical crosslinking of a number of bioplastics using various crosslinkers has been employed to increase tensile strength, and reduce water uptake. During crosslinking two or more polymeric chains/molecules are bonded chemically. The addition of a plasticizer (PEG) that can reduce the attraction among polymer chains can make the polymer properties more flexible. Chemical crosslinking of agarose to increase the tensile strength of the bioplastic films. During crosslinking two or more polymeric chains/molecules are bonded chemically. Citric acid is chosen as the crosslinker because it is biocompatible water soluble and a mild organic acid. Citric acid is a non-toxic crosslinking agent which has been used for grafting β-cyclodextrin (B-CD) onto agar fibres. The observed reduction in moisture absorption and enhanced cross-linking—especially between citric acid and beta-cyclodextrin—is consistent with findings reported by Gurpad et al. (2016) in hydroxypropyl methylcellulose (HPMC) hydrogel films. The lowest WVP value was observed in the treatment containing CMA, PEG, CA, and β-CD (CMA+P+A+B), with a result of 0/0072 g/m·s·Pa. This significant decrease is likely due to reduced hydrophilicity and increased structural compactness of the treated films, which, in turn, increased the tortuosity of water molecule pathways through the matrix, thereby enhancing the moisture barrier properties. The cross-linking occurred by reaction between the carboxyl groups in CA and the hydroxyl group in ethylene glycol present in the agarose. Transparency measurements revealed that the CMA+P+A+B films allowed more light to pass through compared to the control (transmittance values of 3/4 and 2/39, respectively). This suggests that the inclusion of additives not only enhances functional performance but also improves visual clarity, an important factor in consumer acceptance of food packaging. Mechanical testing showed a substantial increase in tensile strength for the films treated with PEG, CA, β-CD, and CMC. These enhancements are attributed to the strong intermolecular interactions and partial cross-linking within the polymer matrix. Improved tensile strength and flexibility are vital for food packaging films, as they enhance the ability to withstand mechanical stress and protect food from physical damage and contamination. This study demonstrates the potential of carboxymethylated agar (CMA) films, enhanced with beta-cyclodextrin, citric acid, and polyethylene glycol, as viable biodegradable materials for food packaging applications. The modifications resulted in films with reduced water vapor permeability, improved mechanical strength, and increased hydrophobicity. These functional improvements render CMA films competitive with conventional synthetic packaging materials while offering significant environmental benefits. The use of marine algae as a raw material for CMA production provides a sustainable and renewable resource base. The findings suggest that the strategic modification of agar and incorporation of targeted additives can overcome the limitations of native polysaccharide films, paving the way for broader industrial adoption of eco-friendly packaging solutions.