The process includes cleaning, crushing, and granulation. Because physical recycling cannot remove additives such as colorants, antioxidants, and other components, and it is easy to cause plastic deterioration after repeated processing and recycling, recycled plastic can usually only be used in reduced order. As a result, major global manufacturers began to invest in the development of chemical recycling technology, so that recycled plastics can be transformed into more valuable products. This article will be divided into upper and lower episodes to share the development of chemical recycling technologies such as polyester, polyurethane, and polyimide at home and abroad.
According to the British news channel Sky News, about 300 million tons of plastic waste is generated every year; only 12% of them are recycled. The average annual amount of plastic waste in the world's oceans is about 12.7 million tons, which poses a serious threat to marine life, including suffocated turtles and poisoned whales. The United Nations also pointed out that if the current rate of plastic waste is generated, by 2050, the total weight of plastic waste in the ocean will be greater than the weight of all fish. According to the statistics published by the Environmental Protection Agency's Environmental Resource Database and the Watchdog Taiwan Association, in 2018 Taiwan produced 9.74 million tons of general waste (aqueous), and plastics accounted for approximately 1.66 to 2.05 million tons (about 17 to 21%), of which The total amount of recycling is less than 30%, and the ratio of effective reuse is even lower. More than 70% of the waste plastic is incinerated.
Because of this, countries around the world (including Taiwan) have regulated the timetable for the establishment and implementation of the plastic restriction law since 2010. The United Nations Environment Programme and the Allen MacArthur Foundation signed a new plastic economic global commitment with more than 350 manufacturers in various countries in March (2019), which requires 100% of plastic packaging materials to be reusable, recyclable or Compostable. The EU also issued a global plastic strategy declaration in May this year, which stipulates that member states must achieve the above goals by 2030.
Faced with the rapidly growing plastic usage, researchers around the world have also begun to provide solutions to issues such as recyclability, such as the use of chemical reactions to crack plastic polymer structures into monomeric raw materials or even light oil fuel. This article takes four common plastic materials as examples to share the current status of waste chemical recycling and reuse, as well as the research and development progress of plastic chemical recycling in the Institute of Materials Science and Technology.
Polyethylene terephthalate (PET) chemical recycling technology
PET chemical recovery technology is to use a melting agent to break the bond of PET ester group to degrade into monomers such as glycol, dibasic acid and diamine, which can be recycled as the raw material for PET polymerization. At present, chemical melting processes mainly include hydrolysis, alcoholysis, mono alcohol, methanolysis, and aminolysis.
The gr3n company in Switzerland mainly focuses on the economical process design in the development of PET unlinking technology. Compared with the traditional alcoholysis, hydrolysis and acidolysis process that takes several hours and high energy consumption disadvantages, gr3n company integrates alkaline hydrolysis and microwave processes, the processing time can be greatly reduced to about 10 minutes. Besides, since microwave radiation can be regarded as a catalyst system during PET depolymerization, and because depolymerization is an exothermic reaction, no additional energy is required to maintain a high-temperature state. The magnetic catalyst material developed by Ioniqa Technologies in the Netherlands can recover the catalyst and at the same time separate the colorants and contaminants in the PET plastic recovery product.