Starch-based plastics
Starch-based plastics use chemical reactions to chemically modify starch to reduce the hydroxyl groups of starch and change its original structure, thereby changing the corresponding properties of starch and turning native starch into thermoplastic starch.
R & D background
Starch is a natural polymer whose output is second only to cellulose on the earth. It is rich in source, renewable, and low in price. It can be used to produce starch-based plastics through modification and plasticization. As an important category of bio-based materials, starch-based plastics have successfully realized industrialized production and application. Starch-based plastic is a kind of plastic product made from starch as the main raw material, modified and plasticized and then blended with other polymers. It is a kind of bioplastic. Starch-based bioplastics can be divided into two categories: bio-based plastics and biodegradable plastics.
Starch-based biodegradable plastic is generally a blend of modified starch and biodegradable polyester (such as PLA/PBAT/PBS/PHA/PPC, etc.). It can be completely biodegradable, compostable, environmentally friendly, and suitable for waste Compost, landfill and other treatment methods. Bio-based plastics based on starch are generally a mixture of modified starch and polyolefins (such as PP/PE/PS, etc.). Its environmental protection significance lies in reducing the use of petrochemical resources and reducing carbon dioxide emissions, and waste is suitable for incineration. Both of these materials can replace traditional petroleum-based plastics and are widely used in plastic packaging materials, shock-proof materials, plastic films and plastic bags, disposable tableware, food containers, toys, etc.
Process principle
Starch is a kind of natural high molecular polymer. Its molecule contains a lot of hydroxyl groups (molecular structure is II and III). Therefore, the interaction between starch macromolecules is very strong, which makes it difficult for the original starch to melt processing, and it is in co-polymerization with other polymers. The compatibility with other polymers during mixing is also poor. However, these hydroxyl groups can undergo chemical reactions such as esterification, etherification, grafting, and crosslinking. These chemical reactions are used to chemically modify starch, reduce the hydroxyl groups of the starch, change its original structure, thereby changing the corresponding properties of the starch, and turning the original starch into a thermoplastic starch.
1. Esterification, transesterification or etherification reaction
In order to change the hydrophilicity of starch to hydrophobicity, the hydroxyl groups on the starch molecule are esterified and transesterified with fatty acids, fatty acid esters, etc., to form starch esters.
2. Cross-linking reaction
In order to improve the strength and heat resistance of starch materials, the starch is cross-linked with compounds with two or more functional groups (such as polybasic acids, etc.), so that the starch is appropriately cross-linked.
3. Independent innovation of blending and co-gathering
Most starch plastics are prepared by filling and blending starch with other polymer materials. The products obtained in this way have poor compatibility and low strength, and their application range is limited. In the starch-based plastic, the starch is copolymerized in the starch modification process to obtain graft copolymers of starch and other polymers, thereby improving the compatibility of starch with other polymer materials. Through chemical modification, three modifications of starch have been realized: hydrophilicity changed to hydrophobicity; heat sensitivity changed to temperature resistance; hardness and brittleness changed to plasticity. This modification solves the worldwide problem of starch modification and lays a good foundation for subsequent processing.
process status
Starch-based bioplastics have a 30-year research and development history. It is a biodegradable plastic with the longest research and development history, the most mature technology, the largest industrialization scale, and the highest market share. In the early 1980s, the research and development of modified starch and degradable plastic alloy master batches that can be completely biodegradable or soluble plastics, and the blending of starch and biodegradable resins received attention. Among them, the most successful is "MaterBi" from Novamont, Italy. It is an interpenetrating network structure polymer plastic alloy composed of modified starch and modified polyvinyl alcohol. It has good processing properties, secondary processing properties, and mechanical properties. Performance and excellent biodegradability. In addition, the "Vinex" developed by Air Product & Chemical in the United States is a resin based on polyvinyl alcohol with a low degree of polymerization. It has water solubility, thermoplastic processability and biodegradability, and has received great attention in recent years.
In recent years, various countries have generally shifted their research focus to plastics with as much starch content as possible, and developed some completely degradable materials with excellent performance, and even obtained pure starch products without synthetic polymers, namely thermoplastic starch. The "Novon" biodegradable material produced by the Warner-Lambert Company of the United States has a starch content of more than 90%; the Japanese Corn Company and the Michigan Production Technology Research Institute jointly developed a high starch content material, which has the advantages of strong water resistance In addition, Japan's Sumitomo Corporation, Italy's Ferrizz Corporation, etc. also announced that they have successfully studied all-starch plastics with 90% starch content. Research institutions such as the German Batekke Research Institute, the Warner-Lambert Company of the United States, and the Swiss universities have all made great progress in converting starch into thermoplastic starch for the production of biodegradable plastics. The Australian National Food Processing and Packaging Science Center has launched a full starch thermoplastic, which has good fluidity, ductility, mold release, soft, transparent, high strength, and controllable degradation rate. It can be used to make agricultural films and food. Packaging film and other products.
The starch is modified and plasticized by chemical methods, and the obtained modified starch has three characteristics: 1. Hydrophobicity. The starch is completely hydrophobic after chemical modification, and the moisture content is <1%, which has good compatibility with other synthetic polymer materials. 2. Temperature resistance. Modified starch can withstand a high temperature of 230 ℃ during the thermoplastic processing without turning yellow or decomposing. 3. Thermoplasticity. Modified starch can be thermoplastic processed on plastic processing equipment. The starch-based plastics produced by the company are divided into two series: bio-based and biodegradable. According to different processing techniques, they are divided into blown film materials, injection molding materials, sheet materials and foam materials. They can replace ordinary petrochemical plastics and are widely used in industry, medicine, Packaging of food, electrical appliances and other products, tableware, kitchenware, toys, and flower planting. In this way, a large amount of oil resources are saved, carbon dioxide emissions are reduced, and the harmless treatment of garbage is realized. It is also conducive to promoting agricultural development and farmers' income, and promoting the vigorous development of circular economy.
It was reported on July 12, 2018 that Yu Long successfully developed and industrialized the whole starch biodegradable material for the first time in the world.
Product advantages
Compared with traditional plastic products, the advantages of starch-based materials and products are shown in the following aspects:
⑴Similar performance: It has the same and similar performance as traditional plastic products of the same kind;
⑵Environmental protection: Starch-based bio-based plastics and products have the advantages of saving petroleum resources and reducing carbon dioxide emissions; starch-based bio-degradable plastics and products have the advantages of being completely biodegradable, compostable, and realizing the harmless treatment of garbage;
⑶ Safety: Starch-based materials and products do not contain plasticizers, bisphenol A, heavy metals and other toxic and harmful substances. Food-grade materials meet the requirements of relevant domestic and foreign food-grade plastic standards;
⑷Production process: No three wastes are discharged during the production process, and no new pollution will be caused to the environment;
⑸Cost: Starch-based bio-based plastic materials and products are the same as ordinary petroleum plastic products, and the cost of starch-based biodegradable materials and products is about twice that of ordinary petroleum plastics.
Application prospects
With the gradual shift in consumer preference for plastic products, renewable environmentally friendly materials have become increasingly popular in the market. Affected by this, the demand for bio-based plastics has increased. With the emphasis on bioplastics by governments, the total value of global bioplastics demand is expected to increase to US$5.9 billion in 2020, which is equivalent to an average annual growth rate of 20%.
Recently, the French Parliament passed laws on energy transition and green growth. In addition to reducing the proportion of nuclear energy in France's energy structure, the new law also contains legislative proposals related to renewable energy and plastic packaging. For example, renewable energy will increase by 40% by 2030 and carbon dioxide emissions will be reduced by 40% by 2030; lightweight packaging bags used for packaging fruits and vegetables will have to be made of bio-based materials from January 1, 2017; In addition, plastic packaging used for commercial mail will also be implemented with the same standards at the same time. The latest legislation of the French government requires that disposable tableware such as dishes, cups and forks must be made of bio-based raw materials instead of petroleum-based raw materials.
Market analysts at RnR Market Research have recently predicted that the global demand for bio-based plastics will increase at an annual growth rate of 19% in the next four years, and its market demand will reach 950,000 tons in 2017. Europe is the world's largest consumer market for bio-based plastics. In 2012, the use of bio-based plastics in this region accounted for more than half of the global total. The survey report shows that compared with traditional plastics, consumers in European countries are more inclined to choose new bio-based plastic products. Therefore, the region is expected to continue to lead the bio-based plastic consumption rankings. In terms of types, starch-based plastics and polylactic acid will still be the most demanded bio-based plastics in the next few years, and their market consumption will account for more than 60% of the total. RnR Market Research said that in recent years, various countries have successively issued plastic restrictions and continuously increased the supervision of the use of traditional plastics, which is conducive to further boosting the demand for bio-based plastics, especially starch-based plastics.
In 2013, the State Council issued the "Bio-industry Development Plan" (hereinafter referred to as the "Plan"). The "Plan" pointed out that the industrialization, promotion and application of bio-based materials, bio-based chemicals, and new fermentation products will be accelerated, and bio-based products will also be established. Certification mechanism, research and develop bio-based product consumption
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