Why Plastic Mulch Is Hard to Recycle: The Problem Lies in the Mulch Itself
After more than 30 years of development and application, plastic mulch coverage has become one of the most important agronomic techniques in our country, and in the northwest region it has even created a situation in which agricultural production cannot be carried out without plastic mulch coverage. At present, on the one hand, plastic mulch coverage has been incorporated into major national and local agricultural production extension and application techniques; on the other hand, residual plastic mulch pollution is also a key part of the national “one control, two reductions, three basics” prevention and control of agricultural non-point source pollution. Therefore, on the basis of continuing to expand the area under plastic mulch coverage, achieving a substantial increase in the plastic mulch recovery rate is an extremely arduous task, and it is necessary to adopt a prevention and control strategy of walking on two legs: source control and efficient recovery, to ensure the goal recently proposed by the Ministry of Agriculture of achieving a recovery rate of more than 80% for agricultural film in the current season by 2020.
Plastic mulch recycling is an extremely difficult task, and it includes two processes: plastic mulch recovery and regeneration and reuse. In view of the realities of agricultural production and the characteristics of residual plastic mulch, the residual film recovery machines developed in our country, such as spring-tooth type, drum type, pneumatic type, roller-winding type and toothed-chain type, have already reached the world's advanced level, but there is still a gap compared with the realities of agricultural production in our country. Improving and simplifying the machine structure, reducing operating costs and increasing work efficiency are the biggest challenges currently faced, and are also the key to moving plastic mulch from the field to the field edge.
The recovered waste plastic mulch is mainly handled in the following ways. The first is landfill, but because residual film is not easy to rot, it will eventually cause pollution to the environment, so this method is used less and less. The second is incineration, which uses the heat energy generated by burning plastic mulch for power generation or other purposes. The third is recycling and reuse, by decomposing waste plastic mulch, recovering ethylene or refining petroleum products for reuse, or subjecting it to regeneration treatment to make plastic products.
More and more countries have tended to realize the circulation and utilization of waste film through various technical means. According to different mechanisms, the recycling and utilization of waste plastic mulch can be divided into physical recycling, chemical recycling and energy recycling. Waste agricultural film has an extremely high calorific value, so recovery through thermal energy has great potential; Japan and Germany, among others, have already established specialized waste plastic processing plants, showing good economic benefits.
⟦NL> Replacing PE plastic mulch with degradable plastic mulch is the best way to solve residual film pollution in farmland, and it can solve the problem of residual plastic mulch from the source. According to the degradation mechanism, it can be divided into two products: photo-oxidative degradation and full biodegradation. In China, after research in recent years, a systematic integrated technology system for polyester material engineering equipment has been formed, a relatively large-scale degradation material synthesis workshop has been established, and good application prospects have emerged. Using degradation-promoting agents to degrade ordinary PE plastic is also a research hotspot; by adding degradation-promoting agents that catalyze the photo/thermal degradation of polyethylene into PE in a special way, degradable PE materials can be produced. In recent years, our country has made great progress in research and application in this area, but related research needs to be strengthened to achieve breakthroughs in mechanisms and controllability of degradation, thereby ensuring the safe application of this type of plastic mulch product.
Overall, due to the complexity of the degradation and application of degradable plastic mulch, degradable plastic mulch of the same formula has different degradation performance in different places and for different crops, and it must be promoted and used through application research. Compared with ordinary polyethylene plastic mulch, the high cost of degradable film is a fatal problem. With the future development of materials science and the improvement of process levels, biodegradable plastic mulch using biomass as the main raw material will replace traditional polyethylene plastic mulch and become the ultimate way to solve “white pollution.”