The general degradable plastic bag is made of polyethylene and starch, but this kind of degradable plastic can only degrade large pieces of plastic into smaller pieces. The components of the plastic molecules have not completely disappeared, so its degradation is Limited. At present, experts have developed a new type of degradable plastic, which is composed of polyvinyl alcohol, starch, and photosensitizer. Polyvinyl alcohol is easier to degrade than polyethylene. Adding photosensitizer can accelerate the plastic by absorbing sunlight. Degradation, starch can promote the rate of biodegradation of plastics in the soil. Therefore, this new type of degradable plastic is easier to degrade than the previous one, and after it is degraded, the plastic components are decomposed into simple molecular structures such as carbon and water, which is more environmentally friendly.
Biodegradable plastics are articles made from plant straws that are friendly to the human body and the environment. They are different from the three synthetic plastics. After being discarded, they can be decomposed by themselves under the action of the biological environment, and they are harmless to humans or the environment. , Belongs to the green packaging.
The degradable plastic bag is a kind of disposable shopping bag that is “degradable and easily degradable”. Biodegradable plastic bags can be divided into two types according to their raw materials and decomposition factors:
• One is a plastic bag made of polyethylene plastic as the main ingredient and blended with biodegradable agents such as starch. It is also called a biodegradable plastic bag. This kind of plastic bag is decomposed mainly by the action of microorganisms.
• The other is a plastic bag made of polyethylene plastic as the main component, mixed with a photodegradation agent and mineral powder such as calcium carbonate, also called a photodegradable plastic bag. This kind of plastic bag is decomposed under the action of sunlight.
Biodegradable plastic bag
- Bioplastics can be used in the production of plastics to reduce oil consumption;
- Biodegradable plastics can promote slow-moving plastic recycling in the United States. According to the U.S. Environmental Protection Agency
(theU. S· Environmental Protection Agency) data show that in 2005 only about 6% of plastics in the United States were recycled. - Bioplastics do not contain toxic substances such as polyvinyl chloride and phthalate. The health effects of these toxins have received widespread attention, and some countries and regions have banned the addition of phthalates in toys and baby products.
The remaining problems of bioplastics entering the WTO:
- Price issue. At this stage, the price of bioplastics is two or three times higher than that of ordinary plastics, which hinders the rapid popularization of such materials. Some Japanese companies use bioplastics in their products, mainly to establish an environmental image of the company. However, once bioplastics enter the mass production stage, the cost can be greatly reduced.
- Bioplastics, like biofuels, may compete with people for food. Biofuels come from food crops such as corn and wheat, which will drive world food prices up. Bioplastics made from corn and other raw materials may also cause the same problem. At present, scientists in Japan, the United States and other countries have begun to use waste wood and weeds to make bioplastics.
- The supply of bioplastics is still relatively limited. To a certain extent, product prices are still driven by oil prices.
Fourth, the end-of-life management of bioplastics. The focus is on the pollution of the PLA bottle to the regeneration stream. Although the current PLA level does not pose a serious pollution threat, a large number of PLA bottles will be harmful to the recycling economy of PET bottles. - Lack of a unified bioplastic labeling method.
- Consumer awareness of bioplastics is increasing, but most consumers do not know how to distinguish these materials, such as biomaterials and biodegradable materials, or renewable materials and recycled content, and how to balance different attributes. Therefore, it is important to strengthen the promotion of consumers, such as accurately explaining the definition of related terms. In addition, consumers know little about the best disposal route for biodegradable materials. It is also very important for the bioplastics industry to strengthen marketing to eliminate the distrust of some consumers.
- The issue of global warming. Bioplastics can be biodegraded to varying degrees. It points out a way for the world to no longer rely on petroleum to produce plastics. However, the manufacturer’s “green argument” is very complicated, and environmentalists also have reservations about it. The production of bioplastics will produce carbon dioxide, leading to global warming.
- Doubts about the safety of genetically modified materials. The willow branches, sugar cane, and even sweet potatoes used in bioplastics-these require land and water to grow. In order to promote fermentation, manufacturers often use genetically modified organisms, and recycling of this plastic also has some drawbacks.
Light-degradable plastic bag
Definition of photodegradable plastics: Plastics that can only degrade after backlighting become photodegradable plastics. Once the photodegradable plastic product is buried in the soil and loses light, the degradation process stops. The production process of photodegradable plastics is simple, low cost, and the disadvantage is that the degradation process is greatly affected by environmental conditions.
Photodegradable plastics: Photodegradable plastics are divided into two types: copolymerization type and additive type. The former is a plastic composed of a copolymer composed of carbon monoxide or carbon-containing monomers and ethylene or other olefinic smoke monomers. Since the polymer chain contains carbon-based and other chromophoric groups and weak bonds, it is prone to photodegradation. The latter is prepared by adding photosensitizers such as benzophenone and p-phenylene to a general-purpose plastic substrate, and the manufacturing technology is simple. The photosensitizer can absorb light with a wavelength of 300nm, undergo a dehydrogenation reaction with adjacent molecules, transfer energy to the polymer molecule, initiate a photodegradation reaction, and reduce the molecular weight.
Degradation example of photodegradable plastic: The photodegradable polyethylene film can be decomposed into 4X4 square centimeters of fragments under light. Even if it does not decompose and exists in the soil for a long time, it will not affect the physical and chemical properties of the soil and affect the nutrients of the soil. Cause damage.
The main components of the photodegradable plastic formula
The components contained in the formulation of photodegradable plastics are mainly photodegradants and photodegradable resins. Photodegradation agent-photosensitizer A photosensitizer is a class of substances that can promote or induce a photodegradation reaction of a polymer. Commonly used photodegradants are group-based compounds and organometallic compounds. Among them, for organometallic compound photosensitizers, the photodegradation effect of this type of photosensitizer is better than that of carbon-based compounds. The photodegradation effect of transition metals is in order: Co>Mo>Cu>Fe>Vo.
Photodegradable polymers are mainly polymers with energy groups or double bonds in the macromolecular chain. The main purpose of the Fanglongjie regulator is to adjust the length of the induction period of the photodegradable plastic, which seems to be adapted to the needs of different occasions. The mechanism of action of photodegradation modifiers is to decompose hydroperoxides to prevent degradation. When it is used up, degradation begins to occur. Commonly used photodegradation regulators are antioxidants, such as antioxidant 1010, Manufacture 0 264 and so on.
Photodegradable plastics: Add photosensitizers to the plastics to gradually decompose the plastics 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 plastics: Plastics that can be completely decomposed into low-molecular compounds under the action of microorganisms. 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 in agricultural mulch film and packaging bags, but also widely used in the field of medicine.
Photo/biodegradation: A type of plastic that combines photodegradation and microbes. It has the characteristics of both photodegradation and microbiological degradation of plastics.
Water-degradable plastics: Water-absorbing substances are added to plastics, which can be dissolved in water after use. They are mainly used for medical and sanitary appliances (such as medical gloves) to facilitate destruction and disinfection. With the development of modern biotechnology, more and more attention has been paid to biodegradable plastics, and they have become a new generation of research and development hotspots.
All kinds of plastic products have greatly enriched people’s lives, but waste plastics decompose very slowly in nature, and it takes decades or even hundreds of years to completely decompose. Therefore, the degradation and reuse of plastics is a problem for all environmental chemists today before. However, it is interesting that biodegradable plastics are not the original intention of scientists to develop plastics. At present, the application scope of biodegradable plastics that scientists are developing or have successfully developed is still relatively narrow and still cannot replace popular plastics.
The harm of non-degradable mass plastics to the earth
It takes two hundred years to rot. It takes about two hundred years for plastic bags to decay when buried underground, which will seriously pollute the soil; if incineration is adopted, harmful smoke and toxic gases will be produced, which will pollute the environment for a long time.
Degradable plastics are difficult to degrade. The common “degradable plastic bags” in the market actually only add starch to the plastic raw materials. After the landfill, due to the fermentation of starch and the decomposition of bacteria, large plastic bags will be broken down into small pieces that are even invisible to the naked eye. This is a physical degradation and does not fundamentally change the chemical properties of plastic products.
Affect the normal respiration of the soil. The plastic bag itself is not one of the basic substances of soil and water. After being forced into the soil, due to its own air impermeability, it will affect the heat transfer and the growth of microorganisms in the soil, thereby changing the characteristics of the soil. The accumulation of these plastic bags over a long period of time will also affect the absorption of nutrients and water by crops, resulting in reduced crop yields. It is easy to cause animals to eat by mistake. Plastic bags discarded on the ground and on the water are swallowed by animals as food. Plastic bags cannot be digested in the animal’s stomach and can easily cause damage to the animal’s body and death.
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