Polypropylene will age during use, and the molecular structure will change during processing. High temperature oxidation, mechanical shearing, etc. all cause chain shear reaction, leading to cross-linking reaction and degradation reaction, molecular weight increase or decrease; also greatly affect molecular weight distribution, thereby changing the rheological properties and mechanical properties of polypropylene materials. Different applications of polypropylene, the mechanical properties of the waste are also different; the used polymer materials will degrade faster due to the presence of initiators, defects and the like. Therefore, to adjust the stability of the recycled material system, the stability of the recycled material can be greatly improved or improved by adding a stabilizer. Physical processing is the primary method of recycling for waste plastics with little change in performance during use. Like polyethylene, the use of waste polypropylene also includes direct use, modification and utilization, chemical recycling, and the like.
Direct use of waste polypropylene:
The most promising recycled polypropylene material is currently from the battery box. It is estimated that 45kt of PP can be recycled every year in the United States, about 18kt is used to make new battery boxes, and other recycled PP materials can be used as solid wheels, decorative blinds and other injection molded crystals.
In the UK, the largest recycler of hard polyolefins is Cookson lndustrialMaterials Ltd., which recycles PP battery cases. The company processes and processes 10kt of used polyolefin articles annually to make horticultural molded items such as altars and plates. According to statistics, 42 companies in the UK are recycling PP, such as MawrCohen Industries Ltd. to recover PP film and make pellets. The amount of PP waste recovered in the UK is 25kt per year.
In Germany, Herbold developed a recycling system for PP battery cases, in which the battery box was first wet pulverized, and the dirt was separated by a two-stage wet separation process, and the PP pellets were used as a battery jacket. Hoechst established a $7.3X106 polyolefin recovery unit at the Kna~ack plant. It started construction in 1992. The plant processes 5kt of waste per year. The main raw materials are PP waste from automobiles and daily use.
In the process of producing polypropylene from a chemical plant, 5% to 10% of amorphous polypropylene (APP) by-products are produced, and APP can be added to asphalt or concrete as a filler. APP has good adhesion and is suitable for binders of various materials. For example, APP is mixed with PP and ash to make concrete, and aluminum slag is added to make bricks. APP and asphalt can also be mixed and melted and coated. Paper or cloth for roofing materials, etc.
The amount of waste plastics from supermarkets is large, relatively clean and easy to recycle. The mixture can greatly improve the properties of the material by adding a phase diffusing agent (mixing agent). By adding stabilizers (antioxidants, light stabilizers), the performance of the mixture, one-component polymer material can be improved to a large extent. For PP, nickel or zinc dinonyl dithiocarbamate is used (nickel or Zinc dinonyldithiocarbamate) works well. The stabilizer attached to the polymer also stabilizes the polymer mixture well.
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