Biodegradable materials refer to materials that can be completely decomposed into low molecular weight compounds by microorganisms (such as bacteria, fungi and algae) under appropriate and predictable natural environmental conditions.
Chinese name
Completely biodegradable material
nature
Transforming low molecular compounds
trait
Environmental protection and degradation
applied range
Degradation of bacteria, fungi and algae
quick
navigate by water/air
1. 1, classification of biodegradable materials 1.2, varieties and properties of completely biodegradable materials, degradation performance and evaluation of biodegradable materials 2. 1, soil burial method 2.2, quantitative method of Petri dish incubator 2.3, enzyme analysis method 2.4, and application of radioactivity c/kloc-0.
Application and development trend of completely biodegradable materials
Abstract: Completely biodegradable materials can be completely decomposed by microorganisms, which has a positive effect on the environment. The definition, classification, degradation performance evaluation and development trend of completely biodegradable materials are introduced.
Keywords: biodegradation, testing, application
While creating modern civilization, human beings have also brought negative effects-white pollution. It is difficult to recycle disposable tableware, disposable plastic products and agricultural plastic films, and the disposal methods are mainly incineration and burial. Incineration will produce a lot of harmful gases and pollute the environment; When buried, the polymer in it cannot be decomposed by microorganisms in a short time, which also pollutes the environment. Waste plastic film exists in soil, which hinders the development of crop roots and the absorption of water and nutrients, reduces soil permeability and leads to crop yield reduction; After eating discarded plastic film, it will cause intestinal obstruction and die; Synthetic fiber fishing nets and fishing lines lost or abandoned in the ocean have caused considerable harm to marine life, so it is imperative to advocate green consumption and strengthen environmental protection. Facing the increasingly exhausted petroleum resources, biodegradable materials conform to the trend, and as high-tech products and environmental protection products, they are becoming the focus of research and development.
1. 1, classification of biodegradable materials
Biodegradable materials can be roughly divided into two categories according to their biodegradation process. One is completely biodegradable materials, such as natural polymer cellulose and synthetic polycaprolactone, whose decomposition mainly comes from: ① the physical collapse of plastic structure caused by the rapid growth of microorganisms; (2) Enzymatic hydrolysis or acid-base hydrolysis due to the biochemical action of microorganisms; ③ Degradation of free radical chain caused by other factors. The other is biodegradable materials, such as the mixture of starch and polyethylene. Its decomposition is mainly due to the destruction of additives and the weakening of polymer chains, which makes the molecular weight of polymers degrade to the extent that microorganisms can digest them, and finally decompose into carbon dioxide (CO2) and water.
Most biodegradable materials are mixed with polyethylene and polystyrene by adding starch and photosensitizer. The research shows that [2], starch-based biodegradable plastic bags will eventually enter the garbage dump without contact with sunlight, and even if there is biodegradation, it is mainly biodegradation. After a certain period of testing, the garbage bag has no obvious degradation, no natural damage, and even has a certain "preservation" effect on the garbage in the bag.
For solving environmental pollution, although plastics containing starch are more effective than disposable plastic products, because non-biodegradable polyethylene or polyester materials are still used as raw materials, in addition to the added starch, a large amount of residual polyethylene or polyester will remain, which cannot be completely biodegradable, and will only be broken down into pieces and cannot be recycled. After entering the soil, the situation will become worse, resulting in confusion in waste treatment. Therefore, completely biodegradable materials have become the research focus of degradable materials.
1.2, varieties and properties of completely biodegradable materials
Safe biodegradable materials include natural polymer cellulose, synthetic polycaprolactone, polyvinyl alcohol and so on. Nature itself has the self-purification ability of decomposing, absorbing and metabolizing natural polymer cellulose. After being used and discarded, the material can be degraded by enzymes of natural microorganisms, and the degradation products can be absorbed and metabolized by microorganisms as carbon sources.
Polycaprolactone is a cheap biodegradable synthetic polymer. Polycaprolactone used is a cyclic monomer-caprolactone, which is an aliphatic polyester prepared by ring-opening polymerization of organometallic compounds. The main properties are: the melting point and glass transition temperature are low, only 60℃-60℃ respectively, and the crystallization temperature is 22℃; Its fiber strength is almost the same as that of polyamide 6 fiber, the tensile strength can reach above 70.56cN/tex, and the node strength is also above 44. 1cN/tex, and the wet strength loss is very small. Biodegradability is similar to that of man-made fiber, and its products degrade into untestable sheets in a week or so.
Polyvinyl alcohol is a biodegradable resin, so starch-based polyvinyl alcohol plastics can be completely biodegradable. The products of ethylene and modified starch-based poly have good formability, secondary processability, mechanical properties and excellent biodegradability. Japan Synthetic Chemical Industry Co., Ltd. has developed a thermoplastic, water-soluble and biodegradable polyvinyl alcohol resin, which can be melt molded with a melting point of 199℃ and can be extruded, blow molded and injection molded at 2 14℃-230℃. The product has excellent transparency, water solubility and drug resistance, and can be used to coat composite molding containers and packaging materials.
Poly (lactic acid) was first developed by Shimadzu Company of Japan and China Textile Corporation, and polymerized with lactic acid as the main raw material. Lactic acid is a common natural compound in animals, plants and microorganisms, which is easy to decompose naturally, and its fiber performance is excellent, which is between synthetic fiber and natural fiber. Hydrophilicity is better than polyester fiber, specific gravity is lower than polyester fiber, and it has excellent hand feeling, drape and appearance, good resilience, excellent curl and curl retention, controllable shrinkage, strength up to 62cN/tex, no influence of ultraviolet rays, excellent processability, controllable thermal bonding temperature, and low crystallization melting point as high as 120℃-230℃.
The main feature of lactic acid monomer is that it exists in two optical forms. Polylactic acid technology is to use this unique polymer property to control the crystallization melting point of products by controlling the proportion and distribution of D and L isomers in the polymer chain.
Poly (L- lactic acid) (PLLC) is a polymer material synthesized by fermentation and chemical method with biological resources such as starch and molasses as raw materials. PLLC is a kind of thermoplastic material, with plasticity similar to polystyrene and polyester, relatively high crystallinity and rigidity, and excellent tensile strength.
Degradation performance of biodegradable materials and its evaluation
At present, there is no uniform standard for testing the degradation performance of biodegradable materials, and methods that have been adopted or will be adopted by American Material Testing Standard (ASTM) can be adopted as the standard. The main methods to evaluate the degradation performance through biochemical and microbial experiments are as follows.
2. 1, burial method
There are two methods of burying soil: outdoor burying method and indoor burying method. The source of microorganisms is mainly the microbial community in the soil. After a certain period of time, the samples were taken out and their weight loss and mechanical properties were measured, or the microbial invasion in the soil was measured by electron microscope. The advantages are that it can reflect the biodegradability under natural environmental conditions; The disadvantage is that the test period is long, the test results vary with the soil properties, and the repeatability is poor.
2.2. Quantitative method of Petit incubator
Add the test sample and nutrient agar into the container, inoculate microorganisms for culture, and analyze the weightlessness and some physical or chemical changes of the sample after a certain period of time. The advantages are high degradation speed, good repeatability and good quantification, and the test results can be obtained in a short time. The disadvantage is that it can't reflect the actual situation of nature.
2.3, enzyme analysis method
Add buffer solution and test sample into the container, let the enzyme act for a certain time, analyze the weightlessness of the sample, visually observe the growth of mold, and analyze the changes of physical or chemical properties of the sample with a microscope. The advantages are short test period, good repeatability and good quantification; The disadvantage is that it can't reflect the actual situation of nature.
2.4, radioactive C 14 tracer method
The polymer products labeled with C 14 produce CO2 under the action of microorganisms, and CO2 is absorbed by alkaline solution. The total amount of CO2 was determined by titration, and then the amount of CO2 in C 14 was determined by radioactive decay rate method. The CO2 percentage of C 14 in the generated CO2 indicates the degree of microbial erosion. The advantage is that the experimental results are reliable and clear. Biodegradability test can test the biodegradability of samples.