On natural polymer film for packaging (2)

1.2.2 Mixed Degradation Film of Starch and Cellulose

Bio/photo-degradable I s (pre-gelatinized) starch plastics foaming fast food appliance J, which promotes multi-component cross-linking by blending plant fibers into PS starch resin, making the molecular chain from the original linear or slightly branched chain structure It is converted into a three-dimensional network structure to form a fiber-reinforced starch plastic foam, thereby effectively improving the degradation performance, mechanical properties, processing performance, and cost of fast food products.

The biodegradable tableware can be made by using the molding powder of a biodegradable molding powder system using straw powder (mainly composed of plant fibers) and light calcium carbonate as the main body and PVA and starch as the adhesive. Egg packaging trays, etc., meet environmental requirements.

The Wageningen Agricultural University in the Netherlands developed biodegradable bioplastics that are free of petrochemicals. These materials are made from wheat, corn, and potato starch and are blended with hemp fiber to increase strength. Can be used as packaging coatings, food storage boxes, litter liners, shopping bags and agricultural films. U.S. scientists use fast-food packaging made from wheat straw fiber and starch from wheat kernels, which is a new type of fast food packaging material that is inexpensive and environmentally friendly.

1.3 Chitin

The main use of chitin is to deacetylate chitin under alkaline conditions to produce chitosan. Chitosan is a kind of positively charged barite substance, has good biological activity, and is compatible with biological energy and affinity, and can exhibit antibacterial properties to a variety of fungi. And easy to dissolve in some organic solvents and film, easy to modify and process, cross-linked acid and heat resistance is better than cellulose acetate film, tensile strength, good toughness, alkali-resistant and resistant to organic solvents. At the same time non-toxic, hydrophilic. The chitin and chitosan molecules contain highly reactive hydroxyl and amino groups, and are easily derivatized with chitins of different properties and uses through chemical reactions such as acylation, sulfation and hydroxyethylation, and carboxymethylation. Film.

Based on the considerations of human safety and ecological environment, more toxic antibacterial agents have been phased out. Chitosan has received great attention due to its good biosafety and broad-spectrum antibacterial properties. High-molecular-weight chitosan binds microorganisms through the attracting action of an NH and anions such as sialic acid phospholipids in the cell walls of microorganisms, thereby impeding microbial metabolism and reproduction. Chemical modification of chitosan to increase the density of structural unit antibacterial factor-NH" can synthesize chitosan derivatives with good human safety and antibacterial properties. The chitosan edible packaging film successfully developed by the United States is The combination of chitosan and lauric acid produces a uniform edible film with a thickness of only 0.2-0.3 mm and good transparency. It is mainly used for fresh packaging of fruits (peeled) and vegetables.

Chitosan can also be blended with other polymer materials to make biodegradable materials. Chitosan has a similar structure to cellulose fiber and can be regarded as a product in which the hydroxyl group (0H) on the carbon atom of cellulose macromolecule is substituted by an amino group (NH,), and the blending of the two is expected to be developed. Biodegradable plastics with high dry and wet strength. Liux et al. used a mixture of viscose and chitosan to prepare biodegradable membranes. The study of the preparation of blend membranes using chitosan acetic acid solution blended with cellulose has some Japanese patents. Liu Weijin and Lin Zhihao used cellulose powders. Chitosan acetic acid solution was blended to make biodegradable films, and related factors affecting the mechanical properties of the blended films were studied. Zhao Tie et al. introduced salicylic acid with antibacterial effect into chitosan-gelatin blend membrane, and successfully prepared chitosan salicylate-gelatin blend membrane by solution blending method in order to achieve the synergistic physiological function of the two materials. Synergies and improvements in the properties of the material itself. At the same time, the structure and properties of chitosan salicylate-gelatin blends were studied. And tested its antibacterial properties.

Zheng Hua et al. performed a carboxymethylation modification of chitosan to synthesize carboxymethyl chitosan to increase the density of the chitosan structural unit antibacterial agent-NH, through the blending of carboxymethyl chitosan and cellulose. In order to prepare a functional polymer warm with good antibacterial properties, the compatibility, mechanical properties and antibacterial properties of the blend membrane were studied.

2 Conclusion

The development and development of green biodegradable packaging materials has greatly reduced the use of plastics that use petroleum as raw materials, eliminated “white pollution” to a certain extent, and eased the pressure on the ecological environment. The organic combination and comprehensive utilization of natural polymer materials in biodegradable materials has been paid more and more attention by people. Through the reasonable modification of molecular structure and the improvement of process conditions, it is a development trend in the field of technology. It is believed that their rational use will promote the continuous improvement and improvement of the performance and degradation performance of biodegradable packaging materials, and make greater contribution to solving environmental pollution and saving energy.

Xu Xiaofeng, Zhang Guanghua, Shaanxi University of Science and Technology, Information Source: Packaging Engineering