Fabrication and mechanism analysis of degradable fiber membrane by in situ polymerization

Plastic films have been widely adopted to improve plant growth in agriculture, covering soil temperature, evaporation reduction, and water conservation in the soil. The most extensively-used materials are polyethylenes (PEs) for agricultural mulching applications, due to their excellent tensile strength and resistance to degradation, such as the low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and copolymer poly (ethylene-vinyl acetate) (EVA). However, conventional film is made of polyethylene, leading to serious "White Pollution". Therefore, degradable materials can be expected to improve the polluted environment. Among them, crop straw can serve as the biggest renewable material with a variety of sources on the earth. Particularly, film mulching can be one of the most important approaches for the growth of crops. Normally, the degradable mulch film is commonly composed of biobased materials that rely on the biodegradable effects of sunlight (ultraviolet rays) and soil microorganisms. Furthermore, the biodegradable mulch film can be decomposed into carbon dioxide, water, and minerals, indicating a friendly environment. Moreover, the degradation rate of biodegradable films is influenced by the chemical components of the polymers. Crop straw can be obtained from corn, rice, wheat, sorghum, soybean, or sugar cane, indicating an abundant source of biomaterials. For instance, 700 million tons of various types of crop straw have been generated each year in China. Many attempts have been made to manufacture wood-based composites with agricultural residues, such as straw. Crop straw is an abundant agricultural residue with higher ash content, leading to the potential additional application as fodder. This study aims to improve the comprehensive utilization rate of crop straw. The straw film was made of rice straw by the in-situ polymerization, and tested as the ridge mulch for the crops. The results demonstrate that the mechanical properties of the straw fiber film were significantly enhanced by the modification. XRD results show that the crystallinity index of the modified film increased to 64.42% (raw film=38.11%). The enhancement in the crystallinity of the straw fiber film can be attributed to the functional additives, which penetrated into the amorphous region of cellulose. Microfibriles were obtained in the amorphous region, particularly close to the crystalline region, resulting in an increase in the width of the crystalline region of cell wall cellulose microfibril. The contact angle of the modified mulching film increased from 95.35° to 118.43°. Thermogravimetric (TG) analysis results indicated that the thermal stability of the modified film was improved after treatment. Moreover, the different chemical bonds in the unmodified and modified films revealed the chemical cross-linking between the film fibers and modifier after FTIR analysis. XPS analysis showed that there was an increase in the atomic concentration ratio of oxygen and carbon in the straw fiber base membrane after modification, indicating that the chemical cross-linking reaction between the modifier and the mulch fiber resulted in the increase of oxygen-containing functional groups. SEM-EDXA indicated that the modifier was uniformly dispersed in the fiber film, indicating an improvement in the mechanical properties. The experiment of tobacco mulch showed that the straw fiber base membrane improved the overall level of tobacco planting. Overall, the superior properties of the modified straw fiber film can make great potential for agricultural application.