2.2 Modified starch packaging materials

Starch is a natural polymer material that can be regenerated, completely degraded in the natural environment after being discarded, and can also be eaten or used as feed. The starch itself is very brittle and should not be used as a degradable material alone. It must be physically modified or chemically modified to change its molecular structure, making it disordered and having thermoplastic properties.

Novon is a new resin made entirely by starch developed by the United States Warnefiamber Pharmaceutical Company. Its composition is 70% amylopectin and 30% amylose, with a melting point of 175-200°C. It can be granulated and can be injected. , extrusion and other standard methods for forming. This research solves the problem that only the starch part can solve the problem that the bio-destructive plastics made of starch and synthetic polymers are blended. It can replace various kinds of biodegradable plastics that are being used in agriculture and medicine, and is considered to be material science. On the major progress. In addition, Nater-Bi produced by Italy's Novamont company has good molding processability, secondary processing properties, mechanical properties and excellent biodegradability of the material, has been used in the packaging industry. The National Food Processing and Packaging Science Center of Australia has successfully launched an all-starch packaging material with good flowability, mold release, and ductility. The product is soft, transparent, high-strength, and has a controlled degradation time. It has been used in foods. Packaging and agricultural film and other aspects. Modified Green Pea High Amylose Starch from Battelle Research Institute, Germany. It can be directly processed by conventional molding methods. Its film is transparent, soft, and its performance is similar to PVC film. It can be completely decomposed in biologically active environments. Four kinds of different technologies are applied to the disordered starch molecular structure in the Chemical Science Institute of Jiangxi Academy of Sciences in China. The prepared thermoplastic starch is processed into a film and can be used as a disposable packaging material. According to the Beijing Evening News, Beijing Light Industry Research has made cassava starch as a raw material and has produced disposable biodegradable fast food tableware, and has obtained a patent. According to another report, edible fast food bowls (boxes) made from corn residue (60%), dietary fiber (30%), and other grains (10%) can be eaten and recycled as high-grade feeds after use. After the fast food bowl is abandoned, it can basically achieve no garbage and no pollution.

2.3 Chitin Packaging Materials

Chitin, also known as chitin, is the main component of crustaceans such as shrimps and crabs, or the outer shell of insects and fungi, and is abundant in natural resources. The yield is second only to cellulose. Chitin is insoluble in water and common organic solvents. As a biodegradable material, chitin is mainly deacetylated under basic conditions to form chitosan. Chitosan is easily dissolved in organic acids such as formic acid and acetic acid, and is easily modified and processed. Chitosan can be blended with other polymer materials to make biodegradable materials. For example, an aqueous acetic acid solution of chitosan, an aqueous polyvinyl alcohol solution, and glycerin are mixed at a certain ratio, cast on a flat plate mold, and the solvent is removed by drying to obtain a biodegradable film, which is expected to be used in food packaging and the like.

2.4 Microbial fermentation material packaging materials

Many microorganisms have the ability to synthesize aliphatic polyesters when they use organic compounds as a carbon source. Microorganism-synthesized polymers are mainly polyhydroxyalkanoates (PHAs) and more than 40 species have been discovered, the most common of which are polyhydroxybutyrate (PHB) and polyhydroxyvalerate (PHV). Among them, PHB is a naturally degradable thermoplastic polymer with physical and chemical properties similar to polypropylene. The representative products of this type of synthetic material include 3-hydroxybutyric acid (trade name "Biopol") and 3-hydroxyvaleric acid copolymer (P3HB/3HV) developed by British ICI. Bipol has good mechanical properties, excellent heat resistance, and good oil resistance and gas barrier properties. Its field test results show that it is safe and stable in air and purified water, and it is widely used in various fields. Packaging Materials. However, under anaerobic conditions, Biopol showed good biodegradability and eventually decomposed into carbon dioxide and water. Poly-L-lactide (PLA) is a kind of good biodegradable packaging material. It is produced by chemical synthesis method after some bacteria obtain L-lactic acid from carbohydrates such as starch and molasses. PLA plasticity is similar to that of polystyrene, and can be produced by conventional molding processing methods. It has good biodegradability. Generally, the soil is crushed within 3 to 6 months after burying, and it turns into lactic acid within 6 to 12 months. The final conversion to CO2 and H20 will not cause environmental pollution. Can be used for food packaging, agricultural film and medical materials and other fields.

Although breakthroughs have been made in the research and development of biodegradable packaging materials using microbial fermentation, the following problems still exist: low production efficiency, low melting temperature and initial temperature difference between degradation, slow crystallization rate, difficult processing, and high prices. Practical applications are limited. Therefore, the cultivation of transgenic plants to produce PHAs such as PBH has become a hot area for the research and development of biodegradable plastics.

2.5 Transgenic plant packaging materials

With the rapid development of plant genetic engineering, the production of PHBs for microbial fermentation is expensive, and some large companies have successively developed the use of transgenic plants as reactors to produce PHB and other packaging materials. The long-term goal set by the UK's ICI/Zeneca Seed Company is to introduce the pathway for bacterial biosynthesis of PHB into suitable crops to produce large-scale production of PHB/V packaging materials using transgenic plants; the Monsanto Company in the United States launched a major project in 1996 with the aim of establishing Technology system for producing packaging materials using genetically modified rapeseed.

Monsanto company Houmilel et al. reported that they used a key enzyme gene involved in the biosynthesis of PHB isolated from microorganisms such as Alacaligenes eutrophus to construct a gene containing four genes (IlvA4461BktB/ph-bA, phbBtphbC). A plant expression vector, each of which is fused with a chloroplast-transmitting peptide (ctp) and a Lesguerella carboxylase promoter (P-Lhr), and a terminator of the E93′ sequence of the pea bcSE9 gene fused to the tail of the gene (E93′). The target gene phbB was used to transmit peptides on the small subunit of PeaBubisco. This multi-gene expression vector was introduced into Brassica napus by Agrobacterium-mediated method, and the transgenic plant seeds contained 7.7% of fresh PHB. Further changing the flow of intermediates in the biosynthesis of fatty acids and amino acids, the team obtained genetically modified rapeseed that can accumulate PHB/V copolymers and demonstrated that the accumulation of the copolymer does not affect the synthesis and production of oil in rape seeds.

According to reports, two key enzyme genes (phbB and phbC) synthesized by PHB have been cloned from Alcaligenes eutropha in China, and prokaryotic vectors have been constructed and introduced into E. coli for expression. This gene was also successfully introduced into potatoes. In order to increase the production of PHB, they completed the cloning of the phbA gene and constructed a seed-specific expression vector for transformation into rapeseed. The gene product will be located in rapeseed on-demand plastids.

3. Conclusion

The development and development of green packaging materials has greatly reduced the use of non-degradable packaging materials, relieved the pressure on the ecological environment to a certain extent, reduced the depletion of increasingly exhausted petroleum resources, reduced environmental pollution, and also solved the international prohibition. The use of non-degradable packaging materials and restrictions on China's export commodities. The extensive application of green packaging materials, whether from the perspective of the protection of the earth from a practical point of view, or from the overall perspective of the sustained and healthy development of the national economy, or from the academic point of view of high-tech packaging materials technology, has an important significance and broad prospects. Although there are still some problems with green packaging materials, such as poor material thermoplasticity, high cost, complicated production process, unstable products, narrow application scope, and potential hazards associated with food contact packaging materials. However, there are reasons to believe that with the cross-infiltration of disciplines such as environmental science, biochemistry, and polymer chemistry, with the application of high-tech, these problems will be gradually resolved.



Source: China Packaging Industry

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