PET bottles are widely used in water and beverage packaging due to their multiple advantages such as light weight, high strength, sanitation, barrier preservation, weather resistance, aging resistance, convenient use, safety, and high recycling value after use. At present, the domestic annual consumption has reached Millions of tons, with an annual growth rate of nearly 20%. From a global perspective, its consumption is even greater, and a considerable part of it enters my country in the form of waste plastic after use.
The molecular formula of PET is shown in the figure below. Its glass transition temperature Tg is 80°C, and its melting point Tm is 265°C.
An indisputable fact is that my country has achieved 100% recycling of PET bottles after use, and every year a large number of PET bottles or bottle flakes are imported from abroad in the form of waste plastic.
In theory, there are two major ways of recycling PET bottles, chemical and physical. Physical recycling accounts for the vast majority. The physical recycling steps of PET bottles include: after removing the caps (HDPE materials) and labels (PVC, BOPP, EVA and other materials), crushing and cleaning the PET bottles to remove dust and residues in the bottles. And the adhesive attached to the outer surface of the bottle when labeling. The cleaned bottle flakes are dehydrated by a centrifugal dehydrator, the water content can be reduced to 2.0%, and then dried by a belt or tube dryer, the water content can be reduced to less than 0.5%. At this time, the bottle flakes can be processed into various products after subsequent processing or modification treatment according to the purpose.
After the PET bottle is used, its material properties remain good. It is ideal if it can be used as a bottle raw material after washing and drying, because the intrinsic viscosity of the PET resin for the bottle is much higher than that of the fiber-grade resin. Not ordinary PET resin can be used Bottled.
Under the condition of ensuring that the impurities and moisture are qualified, the intrinsic viscosity of the bottle flakes is still maintained above 0.75, making plastic bottles that can replace fragile glass bottles for packaging liquid pesticides, motor oil, chemical reagents, etc. If the chain extension or bulk viscosity-increasing technology is introduced during the processing, the bottle-to-bottle technology is even more advantageous.
The key to this technical route is the limited market capacity for such uses. For most markets used for water and beverage packaging, in view of the seriousness of food safety, my country does not yet have the option of using recycled PET as raw material to make packaging bottles. There is a social consensus that even more than a dozen countries in the world have allowed refillable water and beverages made from PET bottles.