Up to now, starch-based degradable plastics are mainly filled, light/biodegradable, * * mixed and all-starch plastics.
1973, filled with starch plastics made Griffin obtain the patent of starch surface modified filled plastics for the first time. In 1980s, some countries developed starch-filled biodegradable plastics based on Griffin's patent. Starch-filled plastics, also known as biodegradable plastics, are made by adding a certain amount of starch and other small additives to general plastics, and then processing and molding them. The starch content does not exceed 30%. Starch-filled plastics have mature technology and simple production process, and can be produced with a little modification of existing processing equipment. Therefore, at present, most degradable starch plastic products in China are of this type.
Natural starch contains a large number of hydroxyl groups, which makes it form strong hydrogen bonds within and between molecules, and the molecular polarity is large, while synthetic resin is hydrophobic and polar. Therefore, natural starch must be surface treated to improve its hydrophobicity and compatibility with polymers. At present, physical modification and chemical modification are mainly used.
Photodegradation/biodegradation type. Biodegradable plastics are difficult to degrade in some special areas such as drought or lack of soil, and photodegradable plastics cannot be degraded when buried in soil. For this reason, the United States, Japan and other countries took the lead in developing a class of photodegradable and biodegradable optical/biodegradable plastics. Photodegradable plastics are made of photosensitizer, starch, synthetic resin and a small amount of additives (solubilizer, plasticizer, crosslinking agent, etc.). ), wherein the photosensitizer is an organic compound or salt of a transition metal. Its degradation mechanism is that starch is biodegraded, which makes the polymer matrix loose and increases the specific surface area. At the same time, sunlight, heat, oxygen and so on trigger photosensitizers, which leads to polymer chain breakage and molecular weight decline.
* * * hybrid. Starch * * * mixed plastic is a kind of plastic made by mixing starch plastic with synthetic resin or other natural polymers. Its main components are starch (30% ~ 60%), a small amount of PE synthetic resin, ethylene/acrylic acid (EAA)*** polymer, ethylene/vinyl alcohol (EVOH)*** polymer, polyvinyl alcohol (PVA) and cellulose.
Japan has developed modified starch /EVOH * * * polymer mixed with LDPE***, dimethylsiloxane epoxy modified starch, and then mixed with LDPE***. Mster-Bi Plastics of Novamont Company in Italy and NoVon series products of Warner-Lambert Company in America also belong to this kind of products. MSTER-BI plastic is a polymer alloy formed by a continuous physical cross-linking network of EVOH phase and starch phase. Because both components contain a lot of hydroxyl groups, the product is hydrophilic, and its mechanical properties will decrease after water absorption, but it is insoluble in water.
Full starch type. Starch molecules are deformed out of order to form thermoplastic starch resin, and a very small amount of plasticizer and other additives are added, which is the so-called full starch plastic. Among them, the starch content is above 90%, and a small amount of other substances added are non-toxic and can be completely degraded, so the whole starch is a truly completely degradable plastic. Almost all plastic processing methods can be applied to the processing of all starch plastics, but the traditional plastic processing hardly needs water, and the processing of all starch plastics needs a certain amount of water to play a plasticizing role. The water content during processing should be 8% ~ 15%, and the temperature should not be too high to avoid scalding. Sumitomo Corporation of Japan, Wanlerlambert Company of the United States and Ferruzzi Company of Italy claim to have successfully developed all-starch plastics with starch content of 90% ~ 100%. The product can be completely biodegradable within one year, leaving no trace and pollution, and can be used to make various containers, films and garbage bags. Germany's Battelle Institute developed a degradable plastic from improved green pea starch with high linear content, which can be processed and molded by traditional methods. As a substitute for PVC, it can be completely degraded in humid natural environment.
Oxidative degradation plastic
Degradable plastic self-sealing bag
This is a technology that has not been understood by most people in China. Adding additives to traditional plastic raw materials is the same as adding general masterbatch. After plastic products are discarded, there are two substances in the additives: ① pre-oxidant (mainly some nontoxic metal ions) and ② biodegradable promoting substances (mainly some natural plant cellulose). Pre-oxidant controls the life and function of plastics when they are not discarded, and reduces the molecular weight through peroxide reaction after being discarded, making the polymer brittle and easy to be decomposed by microorganisms. Biodegradation promoting substances mainly promote the growth of microorganisms. Compared with starch-based plastic technology, this technology is simple and feasible, with lower cost, and can be produced by general equipment. According to the relevant verification, the properties of plastics have also been well maintained, saving food. This method was adopted by WELLS Company in Britain.