Application of Talc and Calcium Carbonate in Degradable Plastics
In recent years, China’s packaging plastics are about 4 million tons, of which disposable plastic packaging that is difficult to recycle accounts for about 30%, and the annual plastic packaging waste is about 1.2 million tons; plastic film is more than 400,000 tons, due to its thinness ( 8μm or less), after use, it is broken in the farmland and mixed with a large amount of sand, which is difficult to recycle; the disposable daily sundries that are difficult to recycle and the medical supplies that are not suitable for recycling are about 400,000 tons.
In recent years, biodegradable plastics have been the most popular. According to the source of raw materials, biodegradable plastics can be divided into petroleum-based and bio-based plastics. Petroleum-based degradable plastics mainly include: polybutylene succinate (PBS), polyadipate/butylene terephthalate (PBAT), polyglycolic acid (PGA), polycaprolactone (PCL), etc. ; Bio-based degradable plastics mainly include: polylactic acid (PLA), starch, cellulose, etc.
Taking into account factors such as material degradability and cost, the current biodegradable plastics on the market generally choose starch, cellulose, etc. as fillers. The composite of starch and polymer materials can be made into degradable materials. Generally, starch or its derivatives are added as additives to synthetic polymers to improve the biodegradability of synthetic polymers. When the material is degraded, the porous polymer remaining due to the degradation of starch is prone to further degradation reactions such as oxidation. However, starch, cellulose and resin have poor compatibility, insufficient temperature resistance, and high cost, so they are not suitable for large-scale filling.
Non-metallic mineral powders such as talcum powder and calcium carbonate, low price, environmentally friendly, sufficient raw materials, high fineness, good whiteness, easy color matching, can improve the dimensional stability, temperature resistance, rigidity of plastic products, and improve plastics Processing performance, etc.
Talcum powder
The addition of talc powder to biodegradable plastics can increase the rigidity, heat distortion temperature, dimensional stability, surface hardness, etc.; at the same time, ultrafine talc powder can also be used as an inorganic nucleating agent for polylactic acid (PLA), adding an appropriate amount of super Fine talc powder can increase the crystallinity and crystallization rate of polylactic acid, and greatly improve its mechanical properties.
Talc has three functions in the modification of polylactic acid:
- Reduce cost: The preparation method of talc-filled polylactic acid composite material provides a heat-resistant polylactic acid composite material preparation technology and method with beautiful appearance, good rigidity, short product molding cycle, light weight and low price.
- Improve strength: the natural talc powder is melt blended, and the composite material is a completely biodegradable material; it has excellent mechanical properties, and the tensile strength can reach 50~70MPa.
- Improve heat resistance: Polylactic acid has better heat resistance due to its own crystallization and the promotion of crystallization of nucleating agent talc.
Calcium carbonate
Calcium carbonate is filled with biodegradable plastics, which can accelerate the degradation of biodegradable plastics. At the same time, calcium carbonate can be directly used by some inorganic nutrient microorganisms as a carbon source. The organic acids and nitrifying bacteria and sulfides produced by microorganisms in the soil Both nitric acid and sulfuric acid produced by bacteria can further improve the solubility of calcium carbonate.
The role of calcium carbonate in biodegradable plastics:
- Promote degradation: Calcium carbonate particles increase the distance between resin molecules, reduce the force of polymer chains, hinder the re-crosslinking of macromolecular free radicals, promote free radical chain scission caused by photodegradation, and accelerate biodegradation of plastics的degradation.
- Easy to decompose: When buried in a humid environment, calcium carbonate can chemically dissolve, and it is directly used by some inorganic nutrient microorganisms as a carbon source.
- Reduce viscosity and improve fluidity: The calcium carbonate after surface treatment increases the viscosity of the degraded plastic, improves the fluidity of the material, and reduces energy consumption.
Traditional disposable non-degradable plastic products have been widely used in food delivery, e-commerce and other industries, but the subsequent processing is more complicated, which limits their development. Therefore, higher requirements are put forward for the development and innovation of biodegradable plastic production and processing technology. In future research, according to the needs of the biodegradable market, we will in-depth study the application of suitable inorganic non-metal powders to achieve the purpose of improving the degradability of biodegradable plastics and make a contribution to the realization of a green and sustainable development of a friendly environment.