Do you know these commonly used biodegradable plastics?
Introduction: With the increasing favor of environmentally friendly packaging, the demand for degradable materials has gradually increased. People began to look for and develop some environmentally friendly materials that are sustainable or eco-cyclable. Biodegradable plastics are one of the most environmentally friendly and promising green materials. This article briefly describes several common plastics for biodegradable plastics. Friends reference:
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Degradable plastic
Under specified environmental conditions, after a period of time and including one or more steps, resulting in a significant change in the chemical structure of the material and loss of certain properties (such as integrity, molecular weight, structure or mechanical strength) and / or broken plastic. Standard test methods that reflect changes in performance should be used for testing, and the type should be determined according to the degradation method and service life. Degradable plastics are classified into biodegradable plastics, compostable plastics, photodegradable plastics, and thermal oxygen degradable plastics according to the final degradation pathways designed.
Biodegradable plastic
Under natural conditions such as soil and / or sandy soil, and / or specific conditions such as composting conditions or anaerobic digestion conditions or in aqueous culture fluids, degradation is caused by the action of microorganisms such as bacteria, molds and seaweeds present in nature, And eventually completely degraded into carbon dioxide (CO2) or / and methane (CH4), water (H2O) and mineralized inorganic salts of the elements and new biomass plastic. Also known as biodegradable plastics.
Classification of biodegradable plastics: According to the different raw material composition and manufacturing process, it can be divided into the following three types: natural polymers and their modified materials, microbial synthetic polymer materials and chemically synthesized polymer materials.
The commonly used biodegradable plastics are: poly 3-hydroxyalkanoate (PHA), polylactic acid (PLA), polyε-caprolactone (PCL) and polybutylene succinate (PBS).
Poly 3-hydroxyalkanoate (PHA)
Polyhydroxy fatty acid esters are aliphatic copolyesters of different structures synthesized by microorganisms through various carbon source fermentations. Among the most common are poly 3-hydroxybutyrate (PHB), polyhydroxyvalerate (PHV) and copolymers of PHB and PHV (PHBV). PHB is a thermoplastic polyester widely found in nature, especially found among bacterial cells. Many physical and mechanical properties of PHB are close to polypropylene plastics, but it has biodegradability and biocompatibility, and can be completely degraded into β-hydroxybutyric acid, carbon dioxide and water in the living body. The material made of this bioplastic can be used in drug release systems, implants and some devices that harmlessly decompose in the human body after healing, but compared to polypropylene, PHB is harder and more brittle. PHB and PHV copolymerization (PHBV) can improve PHB's high crystallinity, brittle weakness, improve its mechanical properties, heat resistance and water resistance. PHB / PHV copolymers are already available for sale under the trade name Biopol. Biopol is composed of a series of different materials. When the content of PHV is not more than 30%, and the PHB / PHV is 89/11, the copolymer has the best strength and toughness. Such products can be used in food packaging, cosmetics, medicine , Health and agriculture industries.
Polylactic acid (PLA)
Polylactic acid (PLA) is a polyester chemically synthesized from microbial fermentation product-lactic acid.
Polylactic acid production is based on lactic acid. Traditional lactic acid fermentation mostly uses starchy raw materials. At present, the United States, France, Japan and other countries have developed and used agricultural, sideline products such as corn, sugar cane, sugar beet, potatoes as raw materials to ferment to produce lactic acid, and then produce polylactic acid. Corn is the preferred raw material for biodegradable plastic polylactic acid. The process of manufacturing biodegradable plastic polylactic acid is as follows: firstly, the corn is pulverized, the starch is separated, the original glucose is extracted from the starch, and finally the beer-like fermentation process is used to convert the glucose into lactic acid, and then the extracted Lactic acid is made into the final polymer-polylactic acid.
Polylactic acid is a biodegradable polymer produced from renewable resources such as cereals. In the production route of polylactic acid, the lactic acid monomer is firstly hydrolyzed to glucose through the grain sediment, and glucose is converted into sodium lactate by the fermentation process, thus prepared. The lactic acid is further concentrated and then polymerized in the order of polycondensation (forming a prepolymer), thermal depolymerization (forming dilactide), ring-opening polymerization and depolymerization. The molecular weight of the obtained polylactic acid is as high as 75,000 g / mol.
By carrying out the lactic acid polycondensation reaction by a general method, only lactic acid oligomers can be obtained. At present, the most studied method for preparing high molecular weight PLA is through ring-opening polymerization of lactide, and lactide is synthesized from lactic acid oligomers through high temperature cracking. There are detailed research reports on the ring-opening polymerization mechanism and reaction conditions of lactide. Recently, Japan's Mitsui Chemicals Co., Ltd. proposed a new technology for preparing polylactic acid directly by polycondensation of lactic acid without passing through lactide. This technology uses a highly active catalyst through solution polycondensation to obtain high molecular weight polylactic acid. Since lactic acid and lactide contain asymmetric carbon atoms, PLA with different stereoregularity can be obtained by polymerization, such as L-PLA, D-PLA and DL-PLA.
Polylactic acid has good moisture resistance, grease resistance and airtightness, and its performance is stable at room temperature, but it will degrade automatically when the temperature is higher than 55 ℃ or under the action of oxygen enrichment and microorganisms. After use, it can be completely degraded by microorganisms in nature, and eventually generate carbon dioxide and water without polluting the environment, which is very beneficial for protecting the environment.
The degradation of polylactic acid is divided into two stages: 1) First, it is hydrolyzed into lactic acid monomers; 2) The lactic acid monomers are degraded into carbon dioxide and water under the action of microorganisms. The food cup made of polylactic acid can be completely degraded in only 60 days, truly achieving the dual effects of ecology and economy.
Polyε-caprolactone (PCL)
Polyε-caprolactone (PCL) is a low-melting polymer obtained by ring-opening polymerization of ε-caprolactone. Its melting point is only 62 ° C. The research on the degradability of PCL has been started since 1976. In both anaerobic and aerobic environments, PCL can be completely decomposed by microorganisms. Compared with PLA, PCL has better hydrophobicity, but the degradation rate is slower; at the same time, its synthesis process is simple and the cost is lower. PCL has excellent processing performance, and can be made into films and other products with ordinary plastic processing equipment. At the same time, PCL and many polymers have good compatibility, such as PE, PP, PVA, ABS, rubber, cellulose and starch, etc., through blending, and copolymerization can obtain materials with excellent performance. Especially its blending or copolymerization with starch can not only maintain its biodegradability, but also reduce costs, so it has attracted much attention. PCL and starch can be blended to obtain degradable plastic with good water resistance, and its price is similar to that of paper. Using in-situ polymerization method, ε-caprolactone can be grafted with starch to obtain thermoplastic polymer with excellent performance.
Polyester--PBS / PBSA
Compared with similar products, the advantages of polyester biological sub-plastics:
1) One of the fatal weaknesses of the above bio-decreasing plastics (polylactic acid, polyε-caprolactone, polyhydroxyalkyl ester) is poor heat resistance, which affects its application and promotion in the field of catering.
2) The processing conditions of the above biological sub-plastics (polylactic acid, polyε-caprolactone, polyhydroxyalkyl ester) are severe, and there are some difficulties in industrialization.
3) Polylactic acid is a water-degradable bioplastic. It cannot accept water molecules during storage, and its performance cannot be guaranteed during normal storage and normal use.
Polybutylene succinate (PBS) is a typical polyester biodegradable plastic. It is because of overcoming the above weaknesses that it has become a leader in biodegradable plastic materials. It is extremely versatile and can be used in packaging, tableware, cosmetics Bottles and medicine bottles, disposable medical supplies, agricultural films, pesticide and fertilizer slow-release materials, biomedical polymer materials and other fields. PBS has excellent comprehensive performance, reasonable cost performance, and has good application and promotion prospects. Compared with PCL, PHB, PHA and other degradable plastics, the price of PBS is basically the same, there is no advantage; compared with other biodegradable plastics, PBS has excellent mechanical properties, close to PP and ABS plastics; good heat resistance, thermal deformation temperature close to 100 ℃, the use temperature after modification can exceed 100 ℃, can be used to prepare hot and cold beverage packaging and lunch boxes, overcome the shortcomings of other biodegradable plastics with low heat resistance temperature; the processing performance is very good, can be used on existing plastic processing general equipment Carrying out various molding processes is currently the best in the processing performance of degradable plastics. At the same time, a large amount of fillers such as calcium carbonate and starch can be blended to obtain low-cost products; PBS production can be slightly modified by existing general polyester production equipment Ongoing, the current domestic polyester equipment has a serious overcapacity, and the transformation and production of PBS provides new opportunities for excess polyester equipment.
In addition, PBS only degrades when exposed to specific microorganisms, such as compost, and its performance is very stable during normal storage and use.
PBS uses aliphatic succinic acid and butylene glycol as the main raw materials for production.It can meet the demand through petrochemical products, or it can be produced through bio-fermentation through natural, renewable crop products such as starch, cellulose, glucose, etc. Green circular production from nature and return to nature. Moreover, the raw materials produced by the biological fermentation process can also greatly reduce the cost of raw materials, thereby further reducing the cost of PBS.
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