Blog | Yeh Her Yow : Plasticdecomposablematerial-Biodegradablematerial
Plastic decomposable material / Biodegradable material
Due to the complex external factors encountered in the actual industrial production and use of polymer materials, the forms of polymer cracking are various, such as thermal cracking, mechanical cracking, photolysis, radiation cracking, oxidative cracking, biological cracking , chemical cracking, etc. Different types of cleavage can occur simultaneously. In the production, processing and use of polymer materials in the natural environment, the air will inevitably come into contact, and the problem of oxidative cracking is the most common problem. How to control these factors to prolong the structural strength and service life of the product has always been an important task in dealing with the polymer process and the use of the product. In recent years, with the diversified development and research of synthetic materials, especially the rapid development of the plastics industry, the application and development of plastic polymer materials has been advancing in two distinct directions. Cleavage, the other is to accelerate the degradation and cracking of polymer materials under certain conditions.
The way of strengthening and strengthening to avoid degradation and cracking is the research and development of the molecular chain of the material to strengthen its performance and efficiency. Longevity may enhance the physical properties of polymer materials to delay degradation or cracking time,
Second, in order to solve the environmental pollution problem of solid waste, as most countries in the world have issued various levels of plastic restriction orders, the research and development of degradable materials/decomposable materials has become an important direction for the long-term sustainable development of the polymer materials industry. Nowadays, people have developed biodegradable, photodegradable, thermally degradable and chemically degradable polymer materials.
Under the issue of environmental protection, plastic products have completely entered our lives after a hundred years, and the waste plastics in the garbage are also accumulating more and more, and the proportion of plastics in the waste is also increasing year by year. Due to the high chemical stability of synthetic plastics, plastic products are not only resistant to acid and alkali, but also non-mite, mildew, and corrosion. If it is buried in the ground, it will not rot after hundreds of years, so it has become a very serious public hazard. Human beings urgently need to eliminate these pollution or reduce this type of garbage. Plastic lunch boxes, etc., these disposable packaging materials and daily necessities are replaced by degradable decomposed plastics, which can be alleviated and reduced to a certain extent within a certain period of time, environmental conditions and processes. The so-called degradable plastic refers to the plastic that will decompose on its own under certain conditions. The chemical properties of plastic polymers are very stable, and they will not rot for decades or even centuries buried underground, which is mainly related to their molecular structure. Plastic macromolecules are formed by many small molecules linked in various ways to form macromolecules. For example, polyethylene is polymerized from many ethylene monomers. Polymer compounds have a common feature, that is, the carbon atoms in the molecule are connected with carbon atoms by carbon-carbon chemical bonds to form a carbon chain.
The arrangement of carbon atoms in the carbon chain is mainly divided into three types:
- The first is a line between carbon atoms, showing a linear structure without side branches
- The second type is a line between carbon atoms, but there are some branches, showing a linear structure with branched side chains
- The third is that the arrangement of carbon atoms is intertwined to form an interlinked network structure.
However, the main chain of the polymer is not only carbon-carbon bonds, but also different chemical molecular bonds such as carbon-sulfur bonds, carbon-oxygen bonds, and carbon-nitrogen bonds.
Due to the special structure and huge molecular weight, the polymer has excellent physical, chemical and mechanical properties that small molecular compounds do not have, such as a high-strength structure physically, a material with a high melting point, and high corrosion resistance. Wait. Plastic is a type of polymer compound. The carbon chain in the molecule is very strong. It is very difficult to weaken or break this molecular chain into small molecules, that is, the process of degradation. There are currently three effective degradation methods, namely biodegradation, chemical degradation and photodegradation. According to these three degradation methods, many scientists have successfully synthesized "biodegradable plastic/biodegradable plastic", "chemically degraded plastic/chemically decomposed plastic" ” and “Light-degrading plastics/light-degrading plastics”. These degradable plastics/decomposable plastics have made great contributions to solving the problem of "white pollution".
Biodegradable Plastic / Biodegradable Plastic
Biodegradable plastic The so-called "biodegradable plastic" is a kind of plastic that can be decomposed by microorganisms and enzymes in the soil. Just like organic plants, it is a type of material that can decay in the soil. It is degraded by the action of microorganisms existing in nature under the conditions of nature such as soil and/or sandy soil, and or under specific conditions such as composting conditions or anaerobic digestion conditions or aqueous medium, and finally completely degraded into carbon dioxide (CO2) or/and methane (CH4), water (H2O) and mineralized inorganic salts of the elements it contains, as well as new biomass (such as dead microorganisms, etc.). For example, in many advanced countries, "biodegradable plastic" is used for the sapling protective cover during the sapling cultivation process. When transplanting seedlings, the sapling plastic cover is buried in the soil together with the sapling. When the sapling roots start to grow in the next year, the plastic cover will be early. It has decomposed in the soil and disappeared. In addition, a degradable surgical thread produced in the United States is also made of degradable plastic, which disappears after 3 months in the human body. However, there are still some difficulties to overcome in the production of degradable plastics. One of them is that the price is too expensive, which is several times or even ten times that of ordinary plastics.
There are many ways to turn ordinary plastic into "biodegradable plastic":
Method 1:
Add starch to the plastic, because the addition of starch can easily destroy the carbon chain in the plastic, and the chemical molecular chain is weakened enough to meet the requirements of microbial digestion and decomposition, and finally the plastic is decomposed into water and carbon dioxide.
2nd method:
Add 40∼50% gelatinous starch to plastic, or add starch treated with organosilicon coupling agent and a small amount of unsaturated fatty acid of corn oil. However, the degraded plastic obtained by this method has high cost and a long degradation time. For example, under composting conditions, it will take 3 to 5 years to fully decompose.
3rd method:
Make the plastic ingredients contain starch and polycaprolactam. The degradable plastic made by this method has a short degradation time and can be used to make degradable surgical sutures. However, the disadvantage is that the cost is too high. Reducing production costs is an important factor in the promotion and application of biodegradable plastics. At present, scientists are actively trying to use natural wastes such as rice husks and wood pulp to make "biodegradable plastics" to reduce costs.
Chemically Degradable Plastics / Chemically Degradable Plastics
Chemically degradable plastics are plastics that contain a special packaging. This packaging is wrapped in starch with oxidizing agents, which can promote the degradation of macromolecules, such as corn oil. When this plastic is buried in the soil, the starch is first eaten by bacteria, leaving behind a reticulated shell full of holes. The oxidant hidden in the shell chemically reacts with the salt and water in the soil to form oxide, which begins Destroy the carbon-carbon bonds in plastic molecules to achieve the purpose of degradation. This kind of degradable plastic is not only low in cost, but also has a good degradation effect. In an ideal situation, generally speaking, the plastic can be turned into a powder in about 6 months, and it can be completely degraded in a few years.
Photodegradable plastic / Photodegradable plastic
Light-degradable plastic, as the name suggests, is a plastic that can be degraded under light. From the perspective of molecular chain composition, plastics contain hydroxyl groups, which will undergo chemical changes under the action of solar ultraviolet light, resulting in the destruction of carbon-carbon bonds, which in turn results in chain scission of the molecular chain. The degradation effect of "photodegradable plastic" is similar to that of "chemically degraded plastic". During the degradation process, a pile of residues and debris will be left first, and it will take several years to fully degrade. The difference between the two is that the former must be exposed to sunlight containing ultraviolet light for a longer time to degrade, while the latter must be buried in soil or submerged in seawater to ensure that bacteria can survive in the surrounding environment to produce bacteria. Play the process of digestion and decomposition. At present, the use of "photodegradable plastic" is mainly to make some food packaging bags.
Biodegradable Materials / Biodegradable Materials
Four types and their advantages and disadvantages
- PLA type (polylactic acid)
- PBS type (polyester type)
- PBAT type (polyester type)
- PHAs (polyhydroxyalkanoates)
PLA (polylactic acid)
These are the most common degradable plastics, which are polymers obtained by polymerizing lactic acid as the main raw material. The production process of PLA is pollution-free, and the product is biodegradable. The used PLA can be degraded into carbon dioxide and water by composting at a temperature higher than 55°C, enriched by oxygen and microorganisms, and realize the natural circulation of substances in nature. No impact on the environment. PLA has reliable biosafety, biodegradability, good mechanical properties and easy processability, and is widely used in packaging, textile industry, agricultural mulching film and biomedical polymers. The disadvantage of PLA is that the degradation conditions are relatively harsh, but due to the relatively low cost of PLA in biodegradable plastics, the consumption and use of PLA ranks first.
PBS type (polyester type)
This type of degradable plastic is formed by the condensation polymerization of succinic acid and butanediol, and the raw material source is the fermentation of petroleum or biological resources. PBS is easily decomposed into carbon dioxide and water by various microorganisms or enzymes in nature, and has good biocompatibility and bioabsorbability, as well as good heat resistance. PBS can be used in packaging films, tableware, foam packaging materials, daily necessities bottles, medicine bottles, agricultural films, pesticides and chemical fertilizer slow-release materials and other fields. Due to the limited availability of succinic acid raw materials in some areas, other different types of PBS have been derived, such as PBAT and PBSA, which are basically similar in performance to PBS, but their processing performance is not as good as PBS.
PBAT type (polyester type)
These are thermoplastic degradable plastics. Generally, aliphatic acids and butanediol are used as raw materials. They are produced by petrochemical or biological fermentation. They have good ductility and elongation at break, as well as good heat resistance and impact performance. . Due to its good film-forming properties and easy film blowing, PBAT is widely used in the field of disposable packaging films and agricultural films. In addition, PBAT also has excellent biodegradability, and is one of the most widely used and well-applied degradable materials in the research of degradable plastics.
PHAs (polyhydroxyalkanoates)
PHAs degradable plastics include polyhydroxyalkanoate (PHA), polyhydroxybutyrate (PHB), etc. PHA has a very special degradation method. After use, PHA can be completely degraded into β-hydroxybutyric acid in vivo , carbon dioxide and water. PHAs degradable plastics have high heat distortion temperature and good biocompatibility, but have a relatively narrow processing temperature range, poor thermal stability, high brittleness, and unstable production quality. They are often used in disposable products, medical equipment surgery Clothing, packaging bags and compost bags, medical sutures, repair devices, bandages, bone pins, non-stick continuous films and stents.
