Four categories of the hottest starch based degrad

Four categories of starch based degradable plastics and their research progress

plastic products are widely used in various fields of people's production and life. Plastics are favored by people for their excellent properties such as light weight, waterproof, corrosion resistance, high strength and so on

however, a large number of discarded plastic products have brought about "white pollution" because of their non degradability. Therefore, since the 1970s, people have begun to research and develop degradable plastics

as a natural polymer compound, starch has a wide range of sources, a wide variety, low cost, and can be completely degraded in various natural environments, and finally decomposed into CO2 and H2O, which will not cause any pollution to the environment. Therefore, starch based degradable plastics have become a kind of biodegradable plastics with the most research and development at home and abroad

so far, starch based degradable plastics are mainly divided into four categories: filled, photo/biological degradable, blended and all starch plastics

structure and properties of starch

natural starch exists in the state of small particles with crystal structure inside, and its molecular structure has two kinds of straight chain and branched chain. For different plant varieties, the morphology, size h and the proportion of amylose and amylopectin content of starch granules are different. The particle size of starch granules is mostly 15 ~ 100 μ m。 Amylose glucose α－ D-1.4-glycosidic bond linked chain compound, with a relative molecular weight of (20 ~ 200) × 104。 The connection mode of glucose units in amylopectin α－ In addition to D-1, 4-glycosidic bonds, there are also α－ D-1, 6-glycosidic bond, relative molecular weight (100 ~ 400) × 106。 The properties of starch are related to the relative molecular weight of starch, the length of amylopectin and the ratio of amylose to amylopectin. Experiments show that starch with high amylose content is more suitable for the preparation of plastics, and the products have better mechanical properties

there are hydrogen chains between natural starch molecules, which have poor solubility. The hydrophilic nose is sensitive but not easily soluble in water. There is no melting process when heating, and it decomposes above 300 ℃. However, under certain conditions, starch can break hydrogen bonds through physical processes and become gel starch or destructured starch. The crystalline structure of starch in this state is destroyed and the molecules become disordered

there are two ways to make starch lose its crystallinity: one is to heat the starch under the condition of water content greater than 90%. When it reaches 60 ℃ ~ 70 ℃, the starch particles first swell, and then when it reaches more than 90 ℃, the starch particles disappear and gel. Second, when the water content is less than 28%, the starch is heated in a sealed state, plasticized and extruded, and then the starch undergoes real melting. The starch under this condition is called disintegrating starch and gel starch. This kind of starch is different from natural granular starch, which is plastic when heated, so it is called thermoplasticstarch

filled starch plastic

in 1973, Griffin obtained the patent of starch surface modified filled plastic for the first time. In the 1980s, some countries developed starch filled biodegradable plastics against the background of Griffin's patents. Filled starch plastic is also known as biodestructive plastic. Its manufacturing process is to add a certain amount of starch and a small amount of other additives into general plastic, and then process it into shape. The starch content is no more than 30%. The technology of filled starch plastic is mature, the production process is simple, and the existing processing equipment can be slightly improved. Therefore, at present, most domestic degradable starch plastic products are of this type

natural starch molecules contain a large number of hydroxyl groups, which form strong hydrogen bonds within and between molecules. The molecular polarity is large, while the polarity of synthetic resin is small, which is a hydrophobic substance. Therefore, natural starch must be treated to improve its hydrophobicity and compatibility with polymers. At present, physical modification and chemical modification are mainly used

(I) physical modification

physical modification refers to the refinement of starch, the destruction of starch structure by extruder, or the addition of coupling agents, plasticizers and other additives to increase the compatibility between starch and general-purpose plastics. Yu Jiugao of Tianjin University refined the starch particles, and then selected a coupling agent to form a single molecule coating on the surface of the starch particles to cover the hydroxyl groups on the surface, that is, the lipophilic modification of the starch particles is an important market concerned by the development of plastic utilization, which greatly increases the oil absorption of the starch particles and significantly reduces the water absorption. The compatibility between starch and synthetic resin was obviously improved by this process. G. Griffin et al. Mixed siloxane with starch and water for drying, and then blended and extruded with self oxidant and ordinary plastics to make degradable plastic masterbatches. St.lawarnce starch company in Canada used this technology to industrialized produce ecostar degradable plastic masterbatch

greizersteinh B et al. Conducted composting experiments on plastic bags made of pe/ecostarplus blends, and found that the starch degradation agent used in this study could not effectively promote the degradation of PE in the compost

(II) chemical modification

chemical modification usually introduces hydrophobic groups into starch molecules to enhance the compatibility between starch and synthetic resin. The modification methods include esterification, hydroxyalkylation or graft copolymerization, etherification, cross-linking modification, etc. At present, the varieties of starch plastics produced by chemical modification methods include starch ethylene dienoic acid copolymer, pe9321 of Cabot plastic company in Germany, starch polypropylene plastic of Monte Edison Company in Italy, esterified starch/PE, etherified starch/PE and graft copolymer/starch/resin of colon company in the United States, gelatinized starch/polyester (or polyethylene, polypropylene ester) of agral tech company in the United States

photodegradable

biodegradable plastics are difficult to degrade in some special areas such as drought or lack of soil, and photodegradable plastics cannot degrade when buried in soil. Therefore, the United States, Japan and other countries took the lead in developing a kind of photodegradable and biodegradable photodegradable plastics. Photo/biodegradable plastics are made of photosensitizers, starch, synthetic resins and a small amount of additives (solvents, plasticizers, crosslinkers, etc.), in which photosensitizers are organic compounds or salts of transition metals. Its degradation mechanism is that starch is biodegradable, which makes the matrix of polymer loose and increases the specific surface area. At the same time, sunlight, heat, oxygen and other photosensitizers cause the chain breaking and molecular weight reduction of polymer

China once listed the research of photo/biodegradable mulching film as the key scientific and technological research plan of the national "Eighth Five Year Plan". In the research of starch based photo/biodegradable film, breakthroughs have been made in the technical problems such as the micronization of starch, the water absorption of starch derivatives and masterbatch, the compatibility of starch and its derivatives with PE, and the controllable induction period. Its representative products include "PE + Fe (I) x · Fe (f) X-ray sensitizer + modified starch" of Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, and "PE + ferrocene derivative photosensitizer + modified starch" of Shanghai Institute of organic sciences. Huang Xiangqi et al. [16] studied and developed "PE + fedbc/fedec photosensitizer + photosensitizer nidbc + aluminate modified starch CaCO3" and "PE + recoor3 photosensitizer + aluminate modified starch CaCO3", which improved the accurate time control and degradability of plastic degradation and reduced the cost. The products developed abroad include "polygrade III" of American ampact company, "polyclean" of ADM company and "ecostarplus" of Canadian St.Lawrence company. Ecostar Corporation of the United States developed "ecostar PlusTM". Through the modification of starch, the surface of starch is hydrophobic, which increases its compatibility with polymers. The degradation rate of its degradation products in the biological environment is more than 100 times that of ordinary plastics

blend type

starch blend plastic is a starch plastic made by blending starch with synthetic resin or other natural macromolecules. The main component is starch (30% - 60%), a small amount of PE synthetic resin, ethylene/acrylic acid (EAA) copolymer, ethylene/vinyl alcohol (EVOH) copolymer, polyvinyl alcohol (PVA), cellulose, lignin, etc. it is characterized by high starch content and complete degradation of some products

Japan has developed modified starch/EVOH copolymer blended with LDPE, dimethylsiloxane epoxy modified starch, and then blended with LDPE. Mster Bi plastic of novamont in Italy [4] and novon series products of Warner Lambert in the United States also belong to this kind of products. Mster Bi plastic is a polymer alloy formed by the physical interaction of continuous EVOH phase and starch phase. Because both components contain a large amount of hydroxyl, the product is hydrophilic, and its mechanical properties will be reduced after water absorption, but it is insoluble in water

the above plastics are not fully biodegradable in essence. Starch and PVA are blended plastics, and starch and aliphatic polyester or other natural polymers can be blended to make real biodegradable plastics. However, due to its high sensitivity to humidity, its application is very narrow. For example, Hosokawa and others blend the mechanically crushed fine starch particles with chitosan solution, and add a small amount of plasticizer, reinforcing agent, foaming agent, etc. into the blend solution. The film and sheet can be used as packaging materials by tape casting. Fu Xiujuan et al. Blended modified starch with a small amount of PVA to produce fully degradable plastic, which has high transparency and good mechanical properties. In the soil with a moisture content of 30%, the weight loss in one month is 25%

all starch type

deforms and disorder starch molecules to form thermoplastic starch resin, and then adds a very small amount of plasticizers and other additives, which is the so-called all starch plastic. Among them, the movement direction of starch 10 prefix is opposite to that in the tensile test, and the content is more than 90%, while a small amount of other substances added are also non-toxic and can be completely degraded, so full starch is a truly fully degradable plastic. Almost all plastic processing methods can be applied to the processing of all starch plastics, but the traditional plastic processing requires almost no water, and the processing of all starch plastics requires a certain amount of water to plasticize. The water content during processing is 8% - 15%, and the temperature cannot be too high to avoid burning. All starch plastic is considered the most promising starch plastic at home and abroad. Sumitomo Corporation of Japan, wanlerlambert Corporation of the United States and ferrazzi Corporation of Italy claim to have successfully developed all starch plastics with a starch mass fraction of 90% - 100%. The products can be completely biodegradable within one year without leaving any traces and pollution, and can be used to manufacture all kinds of containers, films and garbage bags. Germany Battelle Research Institute developed degradable plastics from improved green pea starch with high amylose content, which can be processed and molded by traditional methods. As a substitute for PVC, it can be completely degraded in humid natural environment

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source: China Starch Trading