秸秆纤维基棕榈蜡/明胶双涂层抑菌地膜药物释放性能

    Drug release performance of straw-fiber-based carnauba wax/gelatin double-coated antibacterial mulch film

    • 摘要: 根据环境条件实现农药控制释放是当前作物病害绿色防控的重要发展趋势,以秸秆纤维基地膜为载体的农药控释技术是当前研究热点。该研究针对温湿度这两种病害发生的关键气象因子,以湿度敏感性的秸秆纤维基地膜为基体,温度响应材料明胶为缓释载体,多菌灵为模型农药,疏水材料棕榈蜡为阻隔层,通过双层涂布制备秸秆纤维基棕榈蜡/明胶双涂层抑菌地膜(straw-fiber-based carnauba wax/gelatin double-coatedantibacterial mulch film,CW-C-Gel-WFM)。通过改变棕榈蜡阻隔层厚度,探究其对CW-C-Gel-WFM性能的影响。结果显示,随着阻隔层厚度增加,地膜力学性能略有下降,透气度明显下降,但其性能仍满足使用需求。经棕榈蜡涂覆后,CW-C-Gel-WFM含水率低于秸秆纤维基明胶涂层抑菌地膜(carbendazim gelatin straw-fiber-based mulch film,C-Gel-WFM)。药物缓释动力学表明,30 μm阻隔层使缓释时间长达96~168 h,较C-Gel-WFM延长48~60 h;40 ℃以上药物释放遵循Fickian扩散机制,40 ℃以下则遵循非Fickian扩散机制。盆栽试验和土壤微生物分析证实,CW-C-Gel-WFM具有持续抑菌效果,且能促进植物生长。该研究可为农业废弃物资源化利用和农药减施增效提供技术参考。

       

      Abstract: An antibacterial mulch film is required for the rapid response to two key meteorological factors (temperature and humidity) in crop diseases during agricultural production. Conventional disease prevention and control measures respond to the dynamic meteorological conditions—for instance, when a sudden rise in field temperature or a surge in humidity can trigger an outbreak of diseases, often fail to adjust prevention and control strategies in a timely manner; Prevention and control can rely mainly on the large-scale pesticide spraying. This "flood-irrigation" style of pesticide application can easily result in low pesticide utilization efficiency, i.e., substantial pesticide loss. In turn, a series of environmental issues can also cause problems, such as soil pollution and water eutrophication. Meanwhile, excessive pesticide residues in agricultural products can also pose a dual threat to the ecological environment and human health. In this study, an antibacterial mulch film with temperature and humidity responsiveness (CW-C-Gel-WFM) was successfully developed using carnauba wax, gelatin, and temperature-sensitive straw fibers as core raw materials. Each component of mulch film also shares the structural functions. Among them, carnauba wax and gelatin acted as temperature-controlled release materials. Their own structural states were adjusted at the environmental temperature, thereby regulating the pesticide release rate; While temperature-sensitive straw fibers served as carriers, due to their unique porous fiber structure. The active ingredients of pesticides were stably loaded in environmental humidity, thus synergistically achieving precise regulation of "on-demand release". The mulch film was synergistically adjusted as the timing of pesticide release using the physical barrier of carnauba wax and the temperature-sensitive responsiveness of gelatin. As such, the pesticide-controlled release was realized with the changes in field temperature and humidity. Pesticide loss caused by blind release was effectively reduced to dynamically optimize the field pesticide concentration, according to the disease risk at different stages of crop growth, significantly enhancing the controllability of the crop growth environment. Furthermore, the thickness of the mulch film's barrier layer had a significant impact on the mechanical properties (e.g., tensile strength and elongation at break) of CW-C-Gel-WFM. The tensile strength of the mulch film showed a trend of firstly decreasing, then increasing, and finally decreasing again, as the thickness of the barrier layer increased. While the elongation at break decreased slightly. The performance of the straw-fiber-based mulch film was attributed to the repeated coating with a coater and the interaction arising from carnauba wax molecules filling the gaps between gelatin molecules. The tests further indicated that the air permeability rate of the mulch film decreased significantly with the increasing thickness of the barrier layer—when the thickness of the barrier layer reached 30 μm, the air permeability rate dropped to 12.03 μm/(Pa·s). The water evaporation was effectively reduced in the area covered by the mulch film. At the same time, the stable soil humidity was maintained to avoid the excessive volatilization of pesticides caused by overly strong air permeability. In addition, the moisture absorption performance of CW-C-Gel-WFM was significantly superior to that of the control mulch film without carnauba wax (C-Gel-WFM), due to the hydrophobicity of the carnauba wax coating. The mulch film from structural collapse was also prevented under excessive moisture absorption, in order to avoid the premature degradation of pesticides caused by excessive contact with water. Pesticide release kinetics analysis was carried out to evaluate the performance of controlled-release mulch films. The results showed that the pesticide release rate slowed down significantly at constant temperature, with the increasing thickness of the carnauba wax barrier layer, and the controlled release time was extended accordingly. When the thickness of the barrier layer reached 30 μm, the maximum controlled release time reached 96, 120, and 168 h, respectively, which was 48-60 h longer than that of C-Gel-WFM. More importantly, the temperature dominated the pesticide release, with 40 ℃ as a critical threshold: Once the environmental temperature was higher than 40 ℃, pesticide release mainly followed the Fickian diffusion—at this time, the high temperature intensified the molecular movement of the carnauba wax barrier layer for the more internal pores. As such, the pesticides were mainly released from the polymer matrix through molecular diffusion; Once the temperature was lower than 40 °C, the pesticide release shifted to the non-Fickian diffusion. The release was controlled by the swelling of gelatin, the relaxation of polymer chains, and the physical diffusion of carbendazim. The mulch film can be expected to flexibly adjust the release mode according to different temperature environments, further improving the precision of pesticide use. The pot experiments and soil microbial analysis also demonstrated that CW-C-Gel-WFM shared a controlled bacteriostatic behavior to promote plant growth.

       

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