Biodegradable plastic film: a new environmental protection garment for farmland

Recently, Dr. Yan Yan, associate researcher of the Facility Cultivation Research Group of the Vegetable and Flower Research Institute of the Chinese Academy of Agricultural Sciences, and his team published relevant research results in the General Environmental Science, providing a new formula of PBAT/PLA humic acid biodegradable mulch film for tomato planting in solar greenhouse.

In agricultural production activities, plastic film mulching plays an important role in restraining weeds, preserving water and moisture, and reducing nutrient losses. However, the residue of ordinary polyethylene (PE) film in the use process will damage the soil structure, which will not only lead to the decline of soil fertility, but also cause a series of problems such as crop root development, yield reduction and environmental pollution. How to ensure food security while giving consideration to ecological benefits? How to deal with the problem of residual film pollution in the use of traditional plastic film? Biodegradable mulching film may provide a new way to solve these problems.

(Data pictures are for reference only)

Degradation is realized through the joint action of water, light, heat and microorganism

Biodegradable mulching film is made of materials that can be completely degraded by microorganisms in the natural environment as the main component, and is blown with environment-friendly additives that are harmless to the environment. In agricultural production, it not only has the functions of the traditional PE film, such as moisture conservation, warming and weed control, but also does not need manual recovery after use. It can be directly ploughed into the soil and degraded in the soil, which is efficient and environmentally friendly.

The main raw materials of biodegradable mulching films are biodegradable resins, including PBAT, PLA, PPC and PHAs.

"Biodegradable mulching film is degraded through the combined action of water, light, heat and microorganisms in the nature." Yan Yan explained that the principle is that when bacteria, fungi, actinomycetes and other microorganisms erode the plastic film, due to the growth of cells, the polymer components are hydrolyzed, ionized or protonated, mechanically damaged, and split into oligomer fragments. Enzymes secreted by fungi or bacteria can decompose or oxidize water-soluble polymers into water-soluble fragments, generating new small molecular compounds, until they are finally decomposed into water and carbon dioxide.

In terms of specific evaluation of the performance of biodegradable mulch film, China adopts the product standard of fully biodegradable agricultural ground covering film, and comprehensively considers the impact of soil, climate, regional environment, etc. on the mechanical performance, natural degradation, weather resistance, crop growth period matching and other indicators of biodegradable mulch film. "According to relevant regulations, the biodegradable film used in China must meet the relevant requirements of the national standard GB/T 35795-2017," Yan Yan said.

At present, the requirements of sustainable agricultural development have accelerated the pace of research and development of biodegradable mulch film, which has also promoted the promotion and application of biodegradable mulch film in many provinces, autonomous regions and cities, including Hainan, Xinjiang, Inner Mongolia, Shandong, etc., covering more than 20 economic crops, such as peanuts and potatoes. While many places throughout the country are carrying out the recycling of waste agricultural film, they are also actively promoting the demonstration of biodegradable film, promoting the green development of agriculture and reducing rural environmental pollution.

Biodegradable plastic film with PBAT and PLA as the main components has also been widely used in more than 10 fields, cash crops and vegetables in more than 20 provinces and cities across the country.

Scientific and technological innovation helps the continuous progress of biodegradable plastic film

As early as 1973, British scientist Griffin took the lead in proposing the concept of biodegradable plastics. By adding natural starch as filler in inert polyolefin, Griffin has made biodegradable starch PE, a significant breakthrough 50 years ago.

In the early 1980s, British researchers invented the extraction and purification method of polybeta hydroxybutyrate (PHB) and made it into a film. PHB is a kind of PHAs, and PHAs is a kind of bio polyester synthesized by microorganisms using renewable raw materials (such as polysaccharides, alcohols and low molecular weight fatty acids).

In the early 1990s, China began to invest in the research of PHAs biodegradable plastics. At present, many colleges and universities are engaged in the research of biodegradable plastic film materials, and some scientific research institutions and production enterprises have made many achievements in the research and development of biodegradable materials such as PBAT and PHAs.

Li Chengtao, associate professor of Shaanxi University of Science and Technology, has successfully developed a biodegradable film with controllable degradation rate after nearly 10 years of technical research and development and tackling key problems. The film can be fully biodegradable under natural conditions after crop harvesting. At the same time, according to the needs of agricultural production, the products developed by the team are divided into white and black. The white plastic film can achieve heat preservation and moisture preservation, while the black plastic film can also inhibit the growth of weeds on the basis of heat preservation and moisture preservation; In the mulching film, they also added the bio based fully biodegradable material - plant cellulose, which not only regulates the biodegradation speed of the biodegradable mulching film, but also improves the comprehensive utilization value of plant derived cellulose, and realizes the high value resource utilization of agricultural and forestry wastes.

On the other hand, the PBAT/PLA humic acid biodegradable mulching film produced by Yan Yan's team, on the basis of ensuring rapid degradation and meeting the growth needs of tomatoes, has ideal water and heat retention and regulation performance at the initial stage of coverage. Compared with PE film and PBAT/PLA lignin biodegradable film, PBAT/PLA humic acid biodegradable film can significantly improve soil conductivity and organic matter content, and the relative abundance of soil fungi Chaetomium also increased, which are more conducive to crop growth. In addition, the yield, soluble solids, vitamin C, soluble sugar and lycopene of tomato covered with PBAT/PLA humic acid biodegradable film were significantly higher than those covered with PE film, while the total acid and hardness were significantly reduced.

After observation, the research team found that the PBAT/PLA humic acid biodegradable mulch film covered in the experiment had reached level 2 degradation at the end of planting. Through SEM scanning, the research team found that the surface of PBAT/PLA humic acid biodegradable mulching film showed obvious porous structure after use.

"Covering PBAT/PLA humic acid biodegradable film in tomato cultivation in solar greenhouse in autumn and winter can not only improve quality and increase production, but also effectively reduce the problem of 'white pollution'." Yan Yan told reporters that in addition to being used in the production of tomato in solar greenhouse, the scientific research team is also actively carrying out relevant tests. According to the different characteristics of crop growth period, cultivation needs, etc, Timely adjust the thickness and color of the new film, hoping that the PBAT/PLA humic acid biodegradable film can also be widely used in the production of cabbage, radish, strawberry and other crops.

Reduce cost and refine technology to expand the scale of promotion and use

"Although the performance of biodegradable mulch film is outstanding, its production cost is still relatively high at this stage, which is more than twice that of traditional PE mulch film." Yan Yan said that the production cost cannot be reduced, which is a major limiting factor in the practical promotion and use of biodegradable mulch film.

In addition, the biodegradable plastic film with PBAT also has problems such as poor water vapor barrier, poor rupture time and poor degradation controllability. In terms of production function, biodegradable plastic film also needs to be strengthened. "For example, the deviation of physical and mechanical properties and the insufficient mechanical strength may cause the film to be punctured during the laying process, affecting agricultural operations; the ability to increase temperature and preserve moisture is also relatively weak compared with the traditional film, which is not conducive to the growth and development of crops," Yan Yan said.

How to preserve soil moisture and reduce cost with biodegradable plastic film has always been a hot issue for researchers. In the future, the further optimization of biodegradable mulch film by researchers will also focus on reducing costs, improving mechanical properties, and enhancing the controllability of degradation.

With the continuous improvement of the performance of biodegradable mulching film and the maturity of the modification mechanism, new opportunities will be ushered in in the research, development, production and application of this field. Biodegradable plastic film has great potential for application and development.

Yan Yan believes that although there are still some shortcomings in biodegradable mulching film, it is still expected to achieve low production cost, high degradation efficiency and good mechanical properties through improving production and processing technology, and to promote green and sustainable agricultural development.

key word: