——Material innovation, performance optimization and ecological value
Abstract
In the context of global agricultural sustainable development, agricultural degradable mulch film, as an alternative to traditional polyethylene (PE) mulch film, is accelerating the process of agricultural white pollution control. Based on the cross-perspective of materials science, agronomy and environmental engineering, this report systematically analyzes the technical principles, production practices and ecological benefits of degradable mulch film, and provides scientific decision-making basis for all links in the industrial chain.
Chapter 1 Technical principles and material evolution
1.1 Scientific basis of degradation mechanism
The core function of degradable mulch film lies in its controllable environmental responsive degradation ability. According to the difference in the mechanism of action, it is mainly divided into three categories:
Photodegradation type: by adding photosensitizers (such as ferrocene derivatives), the polymer chain breaks under ultraviolet irradiation, but there are problems such as uneven degradation and residual fragments.
Biodegradation type: relying on enzymes secreted by microorganisms to decompose polymer chains, represented by polylactic acid (PLA) and polybutylene adipate/terephthalate (PBAT), it is necessary to meet composting conditions (temperature ≥50℃, humidity ＞60%).
Oxidation-biological dual degradation type: combining transition metal salt catalytic oxidation and microbial degradation, suitable for non-ideal composting environments, but may produce microplastic intermediates.
The International Organization for Standardization (ISO) clearly stipulates in the “ISO 17088” revised in 2021 that truly biodegradable mulch must have a decomposition rate of more than 90% within 180 days under industrial composting conditions, and the ecotoxicity test must meet the standard.
1.2 Innovative breakthroughs in material systems
The current mainstream material systems show a diversified development trend:
Starch-based composite materials: corn starch (accounting for 30%-50%) is blended with PLA, which is low in cost but poor in water resistance and suitable for arid areas.
PBAT/PLA blending system: compatibility is improved through ester exchange reaction, and the mechanical properties (tensile strength ≥18MPa) are close to PE mulch, with a market share of over 60%.
Polyhydroxyalkanoate (PHA): synthesized by microorganisms, it can be completely degraded in the ocean and soil, but the production cost is as high as 40,000-60,000 yuan/ton, and it has not yet been commercialized on a large scale.
Nanocellulose reinforced materials: Using cellulose nanocrystals (CNC) extracted from agricultural and forestry waste as the reinforcing phase, the puncture resistance of the mulch is increased by 40%, and the moisture permeability exceeds 1000g/m²·24h.
Chapter 2 Production Process and Quality Control
2.1 Industrial Production Process
The manufacture of degradable mulch film needs to solve the contradiction between material thermal sensitivity and processing stability. The typical process flow includes:
1.Raw material pretreatment: PLA needs to be vacuum dried at 80℃ for 4 hours, and the moisture content is controlled to be less than 200ppm.
2.Twin-screw blending modification: adopt segmented temperature control (160-185℃) and high shear screw combination to ensure uniform distribution of PBAT and PLA phases.
3.Three-layer co-extrusion blown film: ABC structure design (outer layer PLA anti-ultraviolet, middle PBAT toughness, inner layer starch base to promote degradation), film thickness fluctuation ≤±0.002mm.
4.Corona treatment: surface tension is increased to 50-52dyn/cm to ensure printing and soil adhesion.
2.2 Demonstration of key process parameters
Screw speed: Too high speed will lead to thermal degradation of PLA (molecular weight decrease>15%), it is recommended to control it at 120-150rpm.
Cooling efficiency: The double-inlet air ring is used to make the film bubble cooling rate reach 30℃/s, and the crystallinity is reduced to <30%, ensuring flexibility.
Traction ratio: When the longitudinal stretching ratio is 3.5-4.0:1, the right-angle tear strength is optimal (≥60kN/m).
Chapter 3 Field Application and Data Verification
3.1 Analysis of Crop Yield Increase Mechanism
Comparative tests show that degradable mulch can achieve yield increase through the following ways:
Ground temperature regulation: black mulch can increase the accumulated temperature of the 5cm soil layer by 120-150℃·d, and potato seedlings emerge 5-7 days earlier.
Water retention: the soil moisture content under the film increased by 18%-25%, and the cotton bud and boll shedding rate decreased by 9.3%.
Microbial activation: degradation products stimulate the proliferation of actinomycetes, and the soil organic matter increases by 0.2-0.5% per year.
3.2 Typical regional application cases
Arid areas:
Using 12μm thick PBAT/PLA mulch film and furrow sowing technology, the cotton yield per mu reaches 450kg (the control PE film is 420kg), and the residual film detected after harvest is less than 3kg/mu (traditional mulch film>35kg/mu).
Rainy areas:
High moisture permeability (WVTR≥800g/m²·24h) mulch film reduces the incidence of root rot, and the survival rate of tobacco transplanting is increased from 78% to 93%.
Cold areas:
PLA mulch film with low-temperature degradation inhibitors has an induction period of 200 days in an environment of <10℃, and covers the entire growth period of corn.
Chapter 4 Environmental Benefits
Carbon Footprint Life Cycle Assessment (LCA)
Production stage: The carbon emission of degradable mulch is 2.8kg CO₂/kg, which is 47% higher than that of PE mulch (1.9kg CO₂/kg).
Use stage: No recycling saves labor energy consumption, and the carbon compensation reaches 0.6kg CO₂/kg.
Degradation stage: Biocarbon release offsets the carbon emission of fossil raw materials, and the net emission reduction in the whole life cycle is 62%.
Chapter 5 Technical Challenges and Future Trends
1. Existing Technical Bottlenecks
Cost issues: The price of PBAT raw material BDO fluctuates greatly, and the cost per ton is 2-3 times higher than that of PE.
Performance balance: It is difficult to achieve both degradation controllability and mechanical strength, and the field verification period requires 3-5 years.
Lack of standards: The current national standard does not cover scenarios such as seawater degradation and low-temperature degradation.
2. Frontier research directions
Intelligent response materials:
Thermosensitive type: Degradation is triggered after the set accumulated temperature value (such as 40℃ for 10 days).
pH responsive type: Root secretions change the pH value of the microenvironment to start degradation.
Functional composite:
Water-retaining and slow-release fertilizer integrated mulch: The membrane material loaded with attapulgite can absorb precipitation and release it slowly.
Insect-proof mulch: Adding azadirachtin microcapsules can reduce insect pests by 40%-60%.
Biosynthesis technology:
Using synthetic biology to transform Alcaligenes, directly ferment and prepare PHA, and reduce the target cost by 20%.
Conclusion
The technological breakthrough and large-scale application of agricultural degradable mulch marks that agricultural green inputs have entered a new stage of development. With the continuous iteration of material modification technology, the improvement of policy support system and the implementation of extended producer responsibility system, the global market size is expected to exceed US$5 billion in 2025.