First, "white pollution" has become a public hazard
At present, China has occupied the position of the largest plastics country in the world and has rapidly become a world leader in plastics. According to relevant data, in 2003, China produced more than 13 million tons of synthetic resin for its own plastics, and more than 13 million tons of imported synthetic resin was recorded by the customs, and more than 3 million tons of scrap were imported as raw materials and synthetic resins for plastics. The apparent consumption has exceeded 30 million tons. With the use of fillers and auxiliaries, the total output of plastic products is second only to the United States, far exceeding Germany, Japan, France, Italy and other countries. At present, "white pollution" caused by plastic packaging has brought adverse effects on China's economic development and ecological environment.
Because ordinary plastics and their additives and additives are polymer materials, chemical structures and performance are stable, they are generally not self-degradable, and they are not easily eroded by bacteria. Plastic packaging materials do not rot or decompose after being discarded and will not form rot for hundreds of years. Permanent trash. In particular, the waste of disposable plastic packaging materials is large, scattered, and messy, making it difficult to collect. Some of these wastes are discarded and scattered on the ground to pollute the urban appearance and environmental landscape. Some of them are buried in landfills and left in the soil, destroying the permeability of the soil, reducing the water storage capacity of the soil, and affecting the absorption of water and nutrients by crops. As a result, crop production is reduced; pours into rivers, lakes and seas will pollute water bodies and cause massive deaths of aquatic organisms. If not treated separately, some plastics will release toxic gases, destroy the ozone layer and form acid rain, and destroy ecological balance. .
In order to solve the "white pollution" problem, the government, enterprises, and science and technology workers have done a lot of work. Advocates the use of less, limited, prohibited it; advocate and formulate local laws and regulations to promote the implementation of degradable plastics; proposed the use of economic means (taxation, fees) to guide consumption also have, unfortunately, many measures have little effect. Restrictions and bans have made ordinary people feel inconvenience; fees have increased the burden on the public.
Facts have proved that modern society can not be separated from plastics. It is not as good as diverting, and the development of biodegradable plastics is carried out with materials with better performance and price ratio and with technologies and methods more consistent with the characteristics of the times, and the recycling of plastic waste is increased. Use is the solution to the "white pollution" way out.
Second, plastic waste recycling method
At present, there are many recycling methods for waste plastic packaging materials. The first is recycling and recycling, the second is regaining raw materials or incineration to obtain energy, and the third is implementing landfill.
1. Recycling of plastic packaging
Recycling of plastic packaging is the most active way to promote the recycling of materials, that is, there is no longer a process of processing, but it is reused directly after cleaning. This is a recycling and recycling technology, which is an important means to effectively save raw material resources and energy and reduce the amount of packaging waste generated.
Many plastic packaging containers, such as trays, turnover boxes, large packaging boxes, plastic buckets, etc., are large, smooth, clean and easy-to-clean containers for transport packaging. Trimming, cleaning and disinfection can be repeated. Its multiplexing technology processing process is generally:
Classification → Selection (discarded after use, basically no pollution, no scratches, transparent, smooth) → washing → pickling → caustic washing → disinfection → washing → sodium bisulfite soaking → washing → distilled water washing → 50 °C drying → reuse
In order to reuse bottled containers many times, we must pay attention to the development of sterilization and re-filling technologies. For example, in Sweden and other countries, thanks to the advanced sterilization and washing technology, PET bottles can be reused up to 20 times. One of the largest dairy plants can use polycarbonate resin plastic bottles for 75 times; Germany has paid attention to development in recent years. In addition to enzymatic washing technology, polycarbonate bottles can be reused and reused for up to 100 times. The United States is energetically developing concentrated cleaning products and heavy filling technology, and its heavy-duty fabric washing products can reach 40%.
2. Mechanical treatment and modified regeneration of plastic packaging materials
Mechanical treatment and reuse include direct regeneration and modified regeneration. As a direct regeneration, the process is relatively simple, easy to operate, easy to implement, so the application is more extensive. However, due to aging of products during use and aging during reprocessing, the mechanical properties of recycled products are lower than those of new resin products, so they are generally used for plastic products with low grades, such as agricultural, industrial, and construction industries.
(1) Direct recycling. Direct regeneration mainly refers to direct plasticization of waste plastics after pretreatment, followed by molding or granulation. In some cases, it is necessary to add a certain amount of new resins or suitable compounding agents (such as antioxidants, lubricants, stabilizers, and additives). Plasticizers, colorants, etc.) The process of making recycled plastic products. It can use existing technology, equipment, both economic and efficient. The general process of direct recycling is:
Pretreatment (sorting, cleaning, defoaming, etc.) → crushing → washing and stirring → mixing and homogenizing → plasticizing → granulation or remolding
(2) Modified regeneration. The purpose of the modified regeneration is to improve the basic mechanical properties of the recycled material to meet the needs of the quality of recycled special products. There are many ways to modify, can be divided into two categories:
1 physical modification. That is, a composite material and a multicomponent copolymer are prepared by a kneading process. It usually includes the process of filling and modifying activated inorganic particles, toughening modification of waste plastics, fiber reinforced modification of waste plastics, and alloying of recycled plastics. It mainly involves forcibly adding various activations during the process of blending and plasticizing. After the inorganic fillers, elastomers or reinforcing fibers to enhance the mechanical properties of plastics, toughness or made of thermoplastic fiberglass.
2 chemical modification. That is, the properties of the material are changed by means of chemical crosslinking, graft blocks, and the like. In recent years, a new method has been developed that combines both chemical and physical modifications. Its technological process and characteristics are that in the specific screw extruder, the materials of various components are physically blended and modified while chemical grafting is performed, and after the modification of both components is further strengthened. Blend, then granulate or shape directly at a specific temperature. This is an integrated system that integrates grafting, cross-linking and blending. This technology approach can shorten the time and production cycle of the improvement process, produce continuous production, and can obtain more effective modification effects.
It should be noted that the current inorganic powder-modified plastic materials have emerged as new environmentally friendly materials and become new materials that can effectively control white pollution and can be accepted by producers, consumers and regulators.
Inorganic powder-modified plastic materials have significant economic, functional, and environmental benefits.
The huge difference in the price of inorganic powder materials and synthetic resins leads to a significant drop in the cost of raw materials for modified plastics, and the rational use of inorganic powders can improve the performance of certain aspects of matrix plastics or be given new functions. Inorganic powder-filled plastics are easily absorbed by the environment after use. Less use of synthetic resins is a saving of petroleum resources. The use of 20-30% of inorganic minerals in plastic materials is a major contribution to society. According to actual calculations, if inorganic powders are used in packaging plastic bags of around 3 million tons produced nationwide, at least 700,000 tons of synthetic resin can be saved, which means less investment in a large-scale petrochemical company that invests over 10 billion yuan. It also meets the principle of reducing "white pollution". On the other hand, the use of inorganic minerals derived from nature and harmlessly returning to nature instead of synthetic resins based on petroleum is itself a contribution to environmental protection.
In terms of waste and recycling, water and carbon dioxide in the soil have little effect on the buried polymer materials, but they rapidly erode the inorganic mineral powder in the plastic products. The resulting products have a certain degree of water solubility and are not detached from the plastic products. After leaving micropores, the area of ​​oxygen exposure of plastic products can be greatly increased, which is beneficial to the aging and disintegration of products. After the plastics are landfilled, inorganic minerals such as calcium carbonate, dolomite and talcum powder will not cause harm to the ecological environment when they return to nature.
It is understood that some companies have made remarkable achievements in the production of inorganic powder-modified plastic environmentally friendly materials. For example, Linda (LD) brand photodegradable polyethylene film products (bags) produced by Shanghai Linda Plastics & Chemicals Co., Ltd. have been awarded the China Environmental Labeling Product Certification for compliance with the environmental labeling product technical requirements issued by the State Environmental Protection Administration; Environmental Protection Plastics Co., Ltd. has also taken a solid step in the industrialization of inorganic powder modified plastics and entering the market.
3. Chemical degradation of plastic packaging materials
The basic principle of chemical degradation regeneration is to perform a thorough macromolecular chain decomposition of the original resin polymer in the waste plastic products to return it to a low molecular state. Some components are its monomers, and other components are basic organic materials. High-value chemical products such as small molecules, compounds, and fuels with different degrees of polymerization. This recycling method can be said to make the use of natural resources really form a closed circle of circulation.
Regeneration of this method has the following advantages: First, the chemical raw materials produced by decomposition are separated from the new raw materials in terms of quality, and can be used in the same way as new materials to achieve recycling; Second, it has considerable processing potential. It can achieve the true pollution of white pollution caused by plastics. Therefore, this method has higher economic and social benefits and is an inevitable development trend. It can be divided into depolymerization, hydrolysis and alcoholysis, thermal cracking, hydrogenolysis, and gasification. Among them, hydrolysis is a convenient and economical means of plastic recycling; thermal cracking is also a relatively promising technology, both at home and abroad. Thermal cracking can be divided into oiling process, gasification process and carbonization process according to the different products obtained.
4. Incineration heat recovery and landfill treatment
(1) Incineration method. The incineration method uses a mixture of miscellaneous plastics and other waste that cannot be used for recycling, and burns it in an incinerator, and then fully utilizes the heat generated by combustion. The most important feature of this method is that it converts what really becomes waste into energy.
Source, at the same time, has a significant reduction in volume. The residue after combustion has a small volume and high density, and it occupies a very small area when it is buried. It is also convenient and stable at the same time. It is easy to dissolve in the soil.
However, the incineration method has the following deficiencies: The incineration equipment construction has a large one-time investment and high cost; if the incineration processing is not differentiated, some plastics inevitably generate secondary pollution harmful substances in the incineration process, such as SO2, HC1 , HCN, etc. There are heavy metals and harmful substances remaining in the remaining ash, which will cause harm to the ecological environment and human health.
(2) landfill method. The landfill method is a negative and simple method of disposal. It is the landfilling of waste packaging plastics in the wasteland or crater of the suburbs to make it self-destruct. However, ordinary plastics will not decompose and disappear for hundreds of years. Therefore, this kind of treatment is economically simple, but it is the most unsatisfactory for reducing the environmental load.
In short, a variety of processing methods for plastic packaging materials should be applied in accordance with different packaging forms and qualities, as well as the nature of plastic packaging materials. The general principle is that secondary pollution cannot be caused during recycling and the most efficient recycling of resources and energy is beneficial. For example, for PVC, it can be re-formulated into plastic, or modified into bituminous or plastic grease; for polystyrene foam, it can be directly re-expanded and used, or modified. Into anti-rust paint or furniture paint and construction cement. For polyolefins and polyesters, they can be directly recharged, crushed and reused, or made into calcium plastics. Therefore, a complete set of comprehensive recovery and treatment model for waste plastic packaging materials should be formed.