First, photo degradable plastics (Photo degradable plastics) China from the 80's began to develop photodegradable plastics. Photodegradable plastics are basically divided into two categories: one is a copolymerized photodegradable plastic, and the other is an additive-based photodegradable plastic. The former is usually copolymerized with polyethylene (PE) and carbon monoxide or vinyl ketone, so that it has carbonyl or other "chromophore" or "weak bond", under the effect of sunlight (or ultraviolet light), such functional groups Appears, that is, the long chain of the polymer is oxidized and carbonized, thereby breaking the bond, resulting in photodegradability; the latter is added in the polymer with a small amount of photosensitizer, such as Scott photosensitizer, is a photooxidation degradation catalyst at low concentrations Sunlight (ultraviolet light) irradiation reacts to break the polyolefin polymer.
Adding photosensitizers such as ketones, amines and ferrocene derivatives to polymers such as PE, PP and PS can achieve good photodegradability.
The additive-type photodegradable plastic has low cost, simple production process and more scientific research results. It has also been used in large-scale application testing and promotion of Datian, and the effect of the use of the cover film is good. However, the degradation characteristics of the degradation of the exposed surface are relatively thorough, and the part buried in the soil is poorly degraded. The degradation induction period of such photodegradable plastics can be controlled for more than two months. However, the degradation time is less controllable.
2. Biodegradable plastics Most biodegradable plastics are starch-filled biodegradable plastics with modified colloidal starch or granular starch as additives. Among them, starch biodegradable degradable plastic is a research hotspot. The organisms that can degrade biodegradable plastics are mainly microorganisms in the soil such as fungi, bacteria and actinomycetes. The biophysical, biochemical and direct enzymatic action of the microorganisms during biodegradation results in biodegradable plastic biodegradation, which is incomplete biodegradation (so-called disintegration). Biodegradable plastics cannot be recycled and reused. The relative cost is relatively high, and the impact of disintegrated plastic debris on the soil is also more controversial.
At present, there are researches on biodegradable plastics, such as plant straws and bagasse, which are raw materials. However, there are still some technical difficulties that need to be overcome and there is still some distance from practical application.
The advantage of biodegradable collapsing degradable plastics is that they can be extended using general-purpose plastic processing technology and equipment.
Third, light - bio-degradable plastics (Photo-Bio degradable plastics) light - bio-degradable plastics is the combination of light and biological double degradation to achieve the goal of complete degradation, it is currently the main research and development direction of biodegradable plastics one. "Light-Study of Biodegradable PE Plastic Film" was included in the national "Eighth Five-Year Plan" technology research project.
Light-biologically degradable plastics are biodegradable agents such as starch that are first biodegraded. The weak polymer matrix weakens the polymer matrix and increases the surface/volume ratio. At the same time, sunlight, heat, oxygen and other photosensitizers, prooxidants and biodegradation sensitizer photooxidation and auto-oxidation, resulting in polymer oxidation, fracture. The molecular weight of the polymer is reduced so that it can be digested by microorganisms and eventually becomes carbon dioxide and water, which is absorbed by agricultural crops.
The production of light-biologically degradable plastics and its biodegradation pretreatment processes and equipment are relatively complex, including the refinement of starch and the removal of structural water. Temperature control is the key, and product quality control is difficult. Because of its large investment in equipment and complicated process, promotion of marketization and industrialization is not easy, thus limiting its development. Because the refined starch cost is difficult to reduce, the price of starch, especially modified starch, remains high. The price per ton is more than 2,000 yuan, which makes the production cost relatively high and also reduces the market competitiveness.
Decomosable plastics Composite degradable plastics are new types of environmentally degradable plastics that integrate photodegradation, biodegradation, and chemical degradation-induced degradation. Instead of starch, it uses inexpensive inorganic binders, together with polyolefins and various additives, and is manufactured using advanced production technology and equipment.
The price of calcium carbonate is far lower than that of starch, and the added usage accounts for 60-70%, which greatly reduces the production cost. According to the 2000t production scale, the annual production cost can be saved by more than RMB 1 million. The use of calcium carbonate as a base material brings many advantages, such as good processability of the product, excellent heat sealing property and opening property, and greatly improved tear strength. For example, a 10 kg load vest bag can hold 25 pounds of heavy materials. These excellent features are widely accepted by manufacturers and users.
The production of composite degradable plastics adopts advanced technology. First, the inorganic matrix is ​​treated and then crosslinked with polyalkylene. The chemical, physical reaction process of the production is completed once in a high aspect ratio twin screw extruder. The production cost is low, the product physical and chemical properties are good, and the degradation induction period is controllable.
Degradation of composite degradable plastics is primarily through induced photodegradation, which reduces macromolecules of polymers to below the molecular weight that can be eroded by microorganisms and phagocytose, and finally achieves complete degradation through bio-erosive degradation. Bring nature-derived substances back to nature.
From the perspective of the main uses of degradable plastics, the main purpose of degradable plastics in the world is to make plastic bags. (For example, 75% of U.S. degradable plastics are used to make garbage bags that are closely related to environmental protection.) If it includes food bags, shopping bags, etc., it will account for degradation. 83.7% of total plastic consumption. The degradable plastic film accounts for only 0.9-2%. Composite degradable plastics will be welcomed by the market because of their excellent quality, good quality and low price.
The production technology of composite degradable plastics is simple, the equipment cost is low, and the composite degradable plastics can be recycled and reused. The conditions for industrialized production and large-scale delivery to the market are already available.
Source: Sinochem