Biodegradable plastic
Degradable plastics, also known as environmentally degradable plastics, refer to plastics that are easily degraded in the natural environment by adding a certain amount of additives during the production process to reduce their stability.
The main application areas of biodegradable plastics are agricultural mulch, various plastic packaging bags, garbage bags, shopping bags in shopping malls, and disposable tableware.
table of Contents
1 Introduction
2 classification
Photodegradable plastic
Biodegradable plastic
Light/biodegradable plastic
Water-degradable plastic
3 Entry Atlas
1 Introduction
Tests have shown that most degradable plastics begin to become thinner, lose weight, and lose strength after being exposed to the general environment for 3 months, and gradually break into pieces. If these fragments are buried in garbage or soil, the degradation effect is not obvious.
2 classification
Biodegradable plastic
Biodegradable plastic
Degradable plastics are generally divided into four categories:
Photodegradable plastic
The photosensitizer is mixed into the plastic to gradually decompose the plastic under sunlight. It belongs to an earlier generation of degradable plastics. Its disadvantage is that the degradation time is difficult to predict due to sunlight and climate changes, so the degradation time cannot be controlled.
Biodegradable plastic
Under the action of microorganisms, plastics can be completely decomposed into low molecular compounds. It is characterized by convenient storage and transportation, as long as it is kept dry, does not need to be protected from light, and has a wide range of applications. It can not only be used for agricultural mulch film and packaging bags, but also widely used in the field of medicine. With the development of modern biotechnology, more and more attention has been paid to biodegradable plastics and has become a new generation of research and development hotspots.
PHA degradable plastic has the best performance among biodegradable plastics. At the same time, due to its high cost and complicated production process, it is still in the initial stage of the market. In 2010, the global PHA production capacity was less than 80,000 tons, of which Metabolix in the United States had a production capacity of about 50,000 tons, accounting for more than 60% of the market. Chinese companies are also leading the way in the production process and R&D of PHA. Tianjin Guoyun Biomaterials Co., Ltd. has a PHA production capacity of 10,000 tons, Ningbo Tianan has a production capacity of 2,000 tons, and Shenzhen Ekman Biotechnology Co., Ltd. has 5,000 tons. Tons of production capacity. Kaneka in Japan and PHBIndustrial in Brazil are also typical representatives of the PHA industry. These companies are the promoters of the PHA industry. Although the application of PHA is relatively limited, the actual sales volume of Metabolix per year is not more than 100 tons, but with With the gradual expansion of downstream applications in the future, especially the further maturity of applications in film packaging, agricultural film, edible tableware, non-woven fabrics and other industries, the market potential of PHA is huge. [1]
Light/biodegradable plastic
A type of plastic that combines photodegradation and microorganisms. It has the characteristics of photodegradation and microorganism degradation.
Water-degradable plastic
Water-absorbent substances are added to plastics, which can be dissolved in the water after use. They are mainly used for medical and sanitary appliances (such as medical gloves) for easy destruction and disinfection.
Starch-based plastics
So far, starch-based degradable plastics mainly include four types: filling type, light/bio-degradable type, blending type and full starch plastics.
1. Filled starch plastics. In 1973, Griffin obtained the patent for starch surface modification filled plastics for the first time. By the 1980s, some countries developed starch-filled biodegradable plastics based on Griffin's patents. Filled starch plastic is also called biodestructive plastic. Its manufacturing process is to add a certain amount of starch and other small amounts of additives to general-purpose plastics, and then process them into a shape with a starch content of no more than 30%. Filled starch plastic has mature technology, simple production process, and can be produced by slightly improving existing processing equipment. Therefore, most of the domestic degradable starch plastic products are of this type.
Natural starch molecules contain a large number of hydroxyl groups to form extremely strong hydrogen bonds within and between molecules. The molecules are more polar, while synthetic resins are less polar and are hydrophobic substances. Therefore, natural starch must be surface-treated to improve its hydrophobicity and its compatibility with polymers. Two methods of physical modification and chemical modification are mainly used.
Biodegradable plastic raw materials
2. Photo/biodegradable 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 have taken the lead in developing a A kind of photodegradable and biodegradable photo/biodegradable plastics. Light/biodegradable plastics are made of photosensitizers, starch, synthetic resins and a small amount of auxiliary agents (solubilizers, plasticizers, crosslinkers, coupling agents, etc.). The photosensitizers are organic compounds or salts of transition metals. The degradation mechanism is that starch is biodegraded, making the polymer matrix looser and increasing the specific surface area. At the same time, sunlight, heat, oxygen, etc. trigger the photosensitizer, which leads to polymer chain scission and molecular weight drop.
3. Blended starch blend plastics are starch plastics made by blending starch with synthetic resins or other natural polymers. The main components are 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., which are characterized by high starch content, and some products can be completely degraded.
Japan has developed a modified starch/EVOH copolymer blended with LDPE, dimethylsiloxane epoxy modified starch, and then blended with LDPE. Mster-Bi plastics of Italy's Novamont company and NoVon series products of American Warner-lambert company also belong to this kind of products. Mster-Bi plastic is a polymer alloy formed by a physical cross-linked network of continuous EVOH phase and starch phase. Since both components contain a large amount of hydroxyl groups, the product is hydrophilic and its mechanical properties will decrease after absorbing water, but it is insoluble in water.
4. The whole starch type transforms starch molecules into disorder and forms a starch resin with thermoplasticity, and then adds a very small amount of plasticizers and other additives, which is the so-called whole starch plastic. The starch content is above 90%, and a small amount of other substances added are also non-toxic and can be completely degraded, so whole starch is a truly completely degradable plastic. Almost all plastic processing methods can be used to process full starch plastics, but traditional plastic processing requires almost no water, while the processing of full starch plastics requires a certain amount of water for plasticization. The water content during processing is 8% to 15%. % Is appropriate, and the temperature cannot be too high to avoid burning. Sumitomo Corporation of Japan, Wanlerlambert Corporation of the United States, and Ferruzzi Corporation of Italy have claimed to have successfully developed all-starch plastics with a starch mass fraction of 90% to 100%. The products can be completely biodegraded within one year without leaving any traces, no pollution, and can be used Manufacturing various containers, films, garbage bags, etc. The German Battelle Research Institute has developed a biodegradable plastic with a high linear content of modified green pea starch, which can be processed and shaped by traditional methods. As a substitute for PVC, it can be completely degraded in a humid natural environment.
Oxidative degradation
This is a technology that has not been understood by most people in China. Adding additives to traditional plastic production raw materials is the same as the general method of adding color masterbatch. After the plastic products are abandoned, two substances in the additives play a role: one is a pre-oxidant (mainly some non-toxic metal ions), and the other is a biodegradation promoting substance (mainly some natural plant cellulose). The pre-oxidant controls the plastic to maintain its proper life and function when it is not abandoned. After being abandoned, the molecular weight is reduced through the peroxide reaction, which makes 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 easy to implement, with lower cost, and can be produced with general equipment. According to related verification, the performance of the plastic is also well maintained. Saved food. British WELLS company adopts this method.
Simple identification method for common plastics. Before using various plastic recycling methods to recycle waste plastics, most of the plastics need to be sorted. Due to the many and complicated plastic consumption channels, some post-consumed plastics are difficult to distinguish by simple appearance. Therefore, it is best to indicate the material variety on the plastic products. China has formulated GB/T16288-1996 "Plastic Packaging Product Recycling Mark" with reference to the material variety marking proposed and implemented by the American Plastics Association (SPE). Although the above marking method can be used to facilitate sorting, there are still many unmarked labels in China. The plastic products of different kinds bring difficulties to sorting. In order to separate different types of plastics for sorting and recycling, we must first master the knowledge of identifying different plastics.
Appearance identification
By observing the appearance of plastics, it is possible to initially identify the major categories of plastic products: thermoplastics, thermosetting plastics or elastomers. Generally, thermoplastics are crystalline and amorphous. The appearance of crystalline plastic is translucent, milky or opaque, and it is transparent only in the film state, and its hardness ranges from soft to horny. Amorphous is generally colorless, fully transparent when no additives are added, and its hardness is from harder than horny rubber (additives such as plasticizers are often added at this time). Thermosetting plastics usually contain fillers and are opaque, such as transparent without fillers. The elastomer has a rubber-like feel and has a certain stretch rate.
Biodegradable plastic
Biodegradable Plastic (3)
Heating identification
The heating characteristics of the above three types of plastics are also different, which can be identified by heating methods. Thermoplastics soften when heated, are easy to melt, and become transparent when they are melted, and can often draw filaments from the melt, and are usually easy to heat seal. The thermosetting plastic is heated until the material is chemically decomposed, and its original hardness is not softened, and the size is relatively stable, until it is carbonized at the decomposition temperature. When the elastomer is heated, it does not flow until the chemical decomposition temperature, and the material is decomposed and carbonized at the decomposition temperature.
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