Various methods for the recycling of used polypropylene

Polypropylene will age during use, and the molecular structure will change during processing. High-temperature oxidation, mechanical shearing and the like can all cause chain shear reaction, resulting in cross-linking reaction and degradation reaction, and the molecular weight can be increased or decreased. It also greatly affects the molecular weight distribution, thereby changing the rheological and mechanical properties of the polypropylene material. Different polypropylene applications, the mechanical properties of the waste is not the same; used polymer materials due to the presence of initiators, defects and other degradation will be faster. 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. For waste plastics with little change in performance during use, physical processing is the main method for recycling. Similar to polyethylene, the use of waste polypropylene also includes direct use, modification and utilization, and chemical recycling.

The direct use of waste polypropylene:
Currently the most promising recycled polypropylene material comes from the battery box. It is estimated that 45 kt of PP can be recycled every year in the United States. About 18 kt is used to make new battery boxes. Other recycled PP materials can be used as solid wheels, decorative shutters and other injection molding dies.
In the United Kingdom, the largest recycler of rigid polyolefin goods is Cookson Industries Materials Limited, which recycles PP battery boxes. The company processes and processes 10kt of used polyolefin products every year to make gardening molded objects such as altars and plates. According to statistics, 42 companies in the United Kingdom carry out PP recycling. For example, Mawr Cohen Lndustries Co., Ltd. recycles PP film and makes pellets. Recycling of PP scraps up to 25kt per year in the UK.
In Germany, Herbold has developed a recycling system for PP battery boxes. In this system, the battery box is first wet crushed and the dirt is separated by a two-stage wet separation process. The PP pellets are used as a battery jacket. Hoechst established a 7.3X106 US dollar polyolefin recovery unit at the Knaack plant, which began operations in 1992. The plant will process 5kt of waste annually. The main raw materials are PP and automotive waste from daily use.
During the production of polypropylene from chemical plants, 5% to 10% of non-crystalline atactic polypropylene (APP) by-products are produced, and APP can be added to asphalt or concrete as a filler material. APP has good adhesion and is suitable for binders of various substances. For example, APP is mixed with PP and ash to make concrete, aluminum slag is added to make bricks, and APP and asphalt can also be mixed and melted. Paper or cloth for roof materials.
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 spreader (mixer). By adding stabilizers (antioxidants, light stabilizers), the performance of the mixture and single-component polymer materials can be greatly improved. For PP, nickel or zinc dithiocarbodiimide is used (nickel or Zinc dinonyldithiocarbamate) works well. The stabilizer attached to the polymer also stabilizes the polymer mixture.

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