The application and development of fully biodegradable materials

Abstract: Completely biodegradable materials can be completely decomposed by microorganisms and have a positive effect on the environment. This article describes the definition, classification, evaluation of degradation performance and development trends of fully biodegradable materials.

Keywords: Biodegradation, Testing, Application

While creating modern civilization, human beings also have a negative impact - white pollution. Disposable cutlery, disposable plastic products, and agricultural mulch are difficult to recycle, and their disposal is mainly incineration and burial. Incineration generates a large amount of harmful gases and pollutes the environment; burying the polymer in it cannot be decomposed by microorganisms for a short time, and it also pollutes the environment. Abandoned plastic film exists in the soil, impedes the development of crop roots and the absorption of water and nutrients, so that the permeability of the soil is reduced, resulting in reduced yield of crops; after eating the plastic film, it will cause intestinal obstruction and death; Synthetic fiber fishing nets and fishing lines to the sea or abandoned in the ocean have caused considerable damage to marine life. Therefore, it is imperative to promote green consumption and strengthen environmental protection. In the face of increasingly depleted oil resources, trend-compliant biodegradable materials are emerging as a hot spot for research and development as high-tech products and environmentally friendly products.

1, biodegradable materials

Biodegradable materials are materials that can be completely decomposed by microorganisms (such as bacteria, fungi, algae, etc.) into low-molecular compounds under natural and appropriate environmental conditions.

1.1. Classification of Biodegradable Materials

Biodegradable materials can be roughly divided into two categories according to their biodegradation process. One is a completely biodegradable material, such as natural polymer cellulose, synthetic polycaprolactone, etc. The decomposition mainly comes from: 1 due to the rapid growth of microorganisms leading to the physical collapse of the plastic structure; 2 due to the biochemical effects of microorganisms , Enzymatic or acid-base catalysis of various hydrolysis; 3 other factors caused by free radical chain degradation. The other are biodegradable materials, such as blends of starch and polyethylene, whose decomposition is mainly due to the destruction of the additives and weakening of the polymer chain, which causes the molecular weight of the polymer to be degraded to the extent that the microorganism can digest, and finally decomposes into Carbon dioxide (CO2) and water.

Biodegradable materials are mostly made by adding starch and photosensitizers, and are blended with polyethylene and polystyrene. Studies have shown that [2], starch-based biodegradable plastic bags will eventually enter the garbage site, not exposed to sunlight, even if there is a double degradation of the resulting material, the degradation occurs mainly in the main biodegradation. Experiments for a certain period of time showed that there was no obvious degradation of the garbage bag, and the garbage bag was not damaged naturally, and even had a certain “preservation” effect on the garbage in the bag.

In order to solve the environmental pollution, although starch-based plastics are more effective than disposable plastic products, since non-biodegradable polyethylene or polyester materials are still used as raw materials, in addition to the added starch being able to degrade, the remaining large amount of polyethylene or Polyester will still remain and not be fully biodegradable, but it will be broken down into pieces and cannot be recovered. After entering the soil, the situation will be even worse. It will cause confusion in the disposal of wastes. Therefore, biodegradable materials will become the focus of research on degradable materials.

1.2. The variety and performance of completely biodegradable materials

Safe biodegradable materials include natural polymer cellulose, synthetic polycaprolactone, polyvinyl alcohol, and the like. Nature itself has the ability to decompose, absorb, and metabolize 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 a carbon source.

Polycaprolactone is a low-cost, fully microbially degradable synthetic polymer. The polycaprolactone used is a cyclic monomer, caprolactone. Caprolactone is obtained by ring-opening polymerization of organometallic compounds. The aliphatic polyester. The main properties are: lower melting point and glass transition temperature, respectively, only 60 °C -60 °C, crystallization temperature of 22 °C; its fiber strength and polyamide 6 fiber is almost equivalent, the tensile strength can reach 70.56cN / tex or more, nodules The strength is also above 44.1cN/tex, and the strength loss in the wet state is very small; the biodegradability is similar to that of the artificial fiber, and the product degrades to a sheet that cannot be tested within about one week.

Polyvinyl alcohol is a biodegradable resin, so starch-based polyvinyl alcohol plastic can be completely biodegradable. The copolymers of ethylene and modified starch based products have good molding processability, secondary processing properties, mechanical properties and excellent biodegradability. Nippon Synthetic Chemical Industry Co., Ltd. has developed a thermoplastic, water-soluble, biodegradable polyvinyl alcohol resin that can be melt-molded, has a melting point of 199°C, and can be extruded, blown, injection molded, etc. at 214°C to 230°C. forming. The transparency, water-solubility, and chemical resistance of the product are all excellent. It can be used to coat composite molded containers and packaging materials.

Polylactic acid was first developed by Shimadzu Corporation and Bell Spinning Co., Ltd. and it uses lactic acid as the main raw material to polymerize the resulting polymer. Lactic acid is a natural compound commonly found in animals, plants and microorganisms. It is naturally degradable. Its fibers have excellent properties, between synthetic fibers and natural fibers. Hydrophilicity is superior to polyester fiber, its specific gravity is lower than that of polyester fiber, it has excellent feel, drape and appearance, good resilience, excellent curl and curl retention, controllable shrinkage, strength up to 62cN / tex, not affected by ultraviolet light, can be dyed with a variety of dyes, outstanding processability, thermal bonding temperature can be controlled, crystal melting temperature up to 120 °C -230 °C, low flammability.

The main characteristic of lactic acid monomer is that it exists in two optically active forms. The polylactic acid technology utilizes this unique polymer property to control the crystallization of the product by controlling the ratio of the D and L isomers on the polymer chain and its distribution. Melting point.

Poly-L-lactic acid (PLLC) is a high-molecular material synthesized by a chemical method in which L-lactic acid is obtained by fermentation of biological resources such as starch and molasses. PLLC is a thermoplastic material, its plasticity is similar to polystyrene and polyester, its crystallinity and rigidity are relatively high, and its tensile strength is excellent.

2. Biodegradable material degradation performance and evaluation

The testing of the degradability of biodegradable materials has not yet established a uniform standard, and can adopt a method that includes or is to be adopted by the American Materials Testing Standard (ASTM) as a standard method, and is evaluated through biochemical and microbiological experimental means. The main methods are the following.

2.1, soil buried method

There are two kinds of soil burial method: outdoor soil burial method and indoor soil burial method. The microbial source is mainly the microbial population in the soil. After a certain period of time, the sample is taken out to measure its weight loss, mechanical properties, or determined by electron microscopy. The status of microbial invasion in the soil. The advantage is that it can reflect the biodegradation performance under natural environmental conditions; the disadvantage is that the test period is long, the test results are different due to different soil quality, and the repeatability is poor.

2.2. Petri dish quantification

The test sample and nutrient agar were added to the container and inoculated with microorganisms for cultivation. After a certain period of time, the sample was analyzed for weightlessness and certain physical or chemical changes. The advantage is that it can be quickly degraded, the test results can be obtained in a short time, the repeatability is good, and the quantification is good; the disadvantage is that it cannot reflect the actual situation in the natural world.

2.3, enzyme analysis

The buffer and the test sample were added to the container to allow the enzyme to act for a certain period of time. The weight loss of the sample was analyzed, and the growth of the mold was measured visually. The physical or chemical properties of the sample were analyzed microscopically. The advantages are short test cycle, good repeatability, and good quantification; the disadvantage is that it does not reflect the actual situation in nature.

2.4. Radioactive C14 tracer method

C14 is used to mark the polymer product, CO2 is produced under the action of microorganisms, absorbed by alkaline solution, the total amount of CO2 is measured by titration, and the CO2 amount of C14 is measured by the radioactive decay rate method. The CO2 produced by C14 is used as the CO2. The percentage indicates the degree of microbial attack. The advantage is that the experimental results are reliable and clear. The biodegradability test can test the biodegradability of the sample.

3, the application of biodegradable materials

Biodegradable materials are widely used in various industries and can partially replace general plastics. The largest use of environmental protection materials, packaging materials and medical materials.

3.1. Agricultural Use

The ideal agricultural material is a material that can be converted into soil-enhancing properties by synergistic action with other biodegradable materials. The biodegradable material is mainly used as an agricultural mulch and crop growth container in agriculture.

3.1.1, agricultural mulch

Traditional films have played a major role in helping crop growth and increasing crop yields, but the resulting drawback is that handling after use is very difficult. After the whole crop grows in the sun, the strength of the film is reduced and split into small pieces that remain in the soil. Small pieces can cause soil compaction, impede the development of the crop roots and absorption of water, and can also cause wind drift. Environmental pollution. Apart from the advantages of traditional plastic film, biodegradable agricultural plastic film can be automatically degraded after use, and does not have to be collected. At the same time, the demand for agricultural fertilizer and water is reduced correspondingly, and the next season of farming can be carried out, thus reducing white pollution. It can also reduce production costs.

3.1.2, crop growth containers

Crop growth containers are used for sowing and transplanting seedlings, flowers, vegetables, and bonsai. If the container is not biodegradable, the container must be removed before transplanting to enable the root system to grow rapidly, and the bare root is easily damaged, it is difficult to use mechanical planting, and the biodegradable plastic container protects the root system when planted, and the survival rate is high. Planting and transplanting in this way can reduce the cost of many plants, extend the season of transplanting, and increase the survival rate.

Studies have found that crop growth devices based on polycaprolactone are significantly biodegraded in soil, lose weight 48% after 6 months and lose about 95% after one year.

Other applications of biodegradable materials in agriculture include turfgrass cultivation tablets, composting bags, and agricultural drug release materials.

3.2. Packing purposes

Biodegradable plastic food bags, bags, and garbage bags are popular because of their biodegradability. The biodegradable packaging material is generally a biodegradable polymer added to a laminated film or a film directly blended with a laminated material. Food packaging materials and containers generally require that the food is not rotted, oxygen is isolated, and the material is non-toxic. The most representative of these are polyhydroxybutyrate (PHB), polyhydroxyvalerate (PHV) and its copolymer (trade name Biopol). Its physical properties are similar to those of polyethylene and polypropylene, and its heat sealability is good. Biopol can be biodegraded or burned after use. The oxygen consumption of both is only equivalent to the photosynthesis of oxygen into the atmosphere. The CO2 produced after treatment is the total amount of CO2 ingested by photosynthesis and therefore can be considered as fully entering the organism. cycle.

Biodegradable plastics can also be used as disposable cushioning materials. According to reports, the polyvinyl alcohol starch-based biodegradable plastics developed by Koki Japan Co., Ltd. are excellent buffer materials with a slightly higher apparent density than conventional polystyrene cushion materials.

3.3, medical biodegradable materials

Medical materials not only need to be medically effective, but also safe, non-toxic, non-irritating, and have good biocompatibility with the human body. The medical biodegradable material is a biodegradable material that can be decomposed and absorbed by a lytic enzyme in a living body after the medical function is completed. The biodegradable plastic has been widely used in surgical sutures, artificial skin, orthopedic surgery, in vivo drug release agents and absorbent sutures. And other fields.

3.3.1, surgical sutures

The ideal suture should have good adaptability in vivo, non-toxic and non-irritating, and can be absorbed by the tissue after being maintained in the body for a certain period of time. Its suture, knotting performance and flexibility should meet the operational requirements. The previously used gut gizzards are prone to produce antigenic reactions. Their adaptability in the human body is not ideal and their preservation is inconvenient. Studies show that medical suture made from chitin and chitosan can be lysozyme in vivo