Photobiodegradable starch-based plastics
Biodegradable plastics are difficult to degrade in special environments such as drought or lack of soil, and photodegradable plastics cannot be effectively degraded when they are buried in the soil, so the materials are combined with photo-oxidation and bio-comprehensive decomposition to obtain plastics that can be degraded in different environments.
For this reason, the United States, Japan and other developing countries have taken the lead in developing a class of photo-biodegradable plastics that are both biodegradable and photo-degradable. Photo-biodegradable plastics are made of starch, photosensitizer, synthetic resin and a small amount of additives, among which photosensitizer is mainly organic compounds or salts of periphyton genus.
The degradation mechanism is that the starch is biodegraded, which makes the polymer matrix of degradable plastic raw materials become loose and increase the specific surface area: at the same time, sunlight, heat and oxygen trigger the photosensitizer, which causes the polymer to break the chain and the molecular weight to decrease.
China has listed the research of photomatter mulch as a national key science and technology research program for starch-based photo – matter degradable mulch. We have made significant technical breakthroughs in starch microfabrication, starch derivatives and masterbatch water absorption, starch and its derivatives and technical difficulties.
Through the modification treatment of starch, the surface of starch is loosened and its compatibility with polymer is increased, and the degradation rate of its degradation products in biological environment is more than 100 times than that of ordinary plastics.
Co-blended bio-starch-based plastics
Starch blended plastic is starch and synthetic resins or other natural polymers blended starch plastic, the main components are starch (30% ~ 60%), a small amount of PE synthetic resin, ethylene – acrylic acid (EAA) copolymer, ethylene – vinyl alcohol (V) copolymer polyvinyl alcohol (PVA), cellulose, lignin, etc., which is characterized by high starch content, some products can be completely degradable.
Japan has developed a modified starch-EVOH copolymer and low density polyethylene (LDPE) blend, dimethylsiloxane epoxy modified treatment of starch, and then blended with LDPE, Italy’s Novamont Mater-Bi plastic and the United States Warner-Lambert’s “Novon Mater-Bi plastics from Novamont (Italy) and “Novon” series from Warner-Lambert (USA) are also in this category.
Mater-B plastic is a polymer alloy formed by the physical cross-linking network of continuous EVOH and starch phases. Since both components contain a large number of hydroxyl groups, the product is hydrophilic and its mechanical properties will be reduced after absorbing water, but it is insoluble in water.
At present, the starch blended biodegradable plastics developed in Japan, the continuous phase are used with biodegradable plastic, and the starch is disordered to form thermoplastic starch, which greatly improves the degree of starch dispersion and interfacial state, and can increase the component of starch to more than 67%.
All-biological starch plastics
After the 1990s, plastics based on starch as the main raw material have made important research progress in the field of total biodegradation. By changing the molecular structure of starch to make it disordered, and then adding a very small amount of plasticizers and other additives, a fully starchy resin with thermoplasticity is formed. The starch content can be more than 90%, and the small amount of other substances added is also non-toxic and completely degradable, so all-starch is truly a completely degradable plastic.
Plastic processing methods can be applied to process all-starch plastics, but traditional plastic processing requires almost no water, while the processing of all-starch plastics requires a certain amount of water to play a plasticizing role, and the water content during processing should be 8% to 15%, and the temperature should not be too high to avoid scorching.
Sumitomo Corporation (Japan), Warner-Lambert Corporation (USA) and Ferrizz Corporation (Italy) claim to have successfully developed full starch plastics with 90% to 100% starch content, which can be completely biodegraded within 3 months to 1 year without residue and pollution, and can be used for manufacturing various containers, films and garbage bags, etc. The Battelle Institute in the United States has developed biodegradable plastics with modified green pea starch with super high straight chain starch content, which can be processed and molded by traditional methods as a substitute for PVC and can be completely degraded in a humid natural environment.
At present, there is no production process of all-starch plastics in China. The mechanical properties of all-starch plastics made by mixing corn starch and cellulose can basically reach the performance standards of traditional plastics, and the degradation performance is very good.
