# Optimization of Processing Parameters to Increase Thermal Conductivity of Rice Straw Fiber Film
## 1 Introduction  
Plastic mulching film (PMF) has been widely used in modern intensive farming in order to inhibit weed growth, increase soil temperature, reduce water evaporation, control the leaching of crop nutrients, and increase the yield [1; 2]. About one million tons of petroleum-based PMF is consumed annually in the farmlands of China [3; 4]. However, petroleum-based PMF is not easily degraded in farmland, and its bio-degradation rate is very low even after years of exposure to soil microbial communities [5; 6; 7]. Furthermore, wind and rain erosion often cause the entire film to break into small pieces, thus making the recycling very difficult and time-consuming [8; 9]. Ultimately, most plastic residues are commonly left in the field or burned by farmers, which leads to serious environmental pollution. Biodegradable materials mainly include biodegradable ceramics and biodegradable plastics [10; 11]. To address this issue, the development of a biodegradable film with desired properties for both plant growth and environmental impact has become a research focus [12; 13; 14]. Biodegradable mulching film (BMF) is a promising alternative to petroleum-based PMF. At present, the degradable film can be mainly divided into photo-degradable, biodegradable, photo-biodegradable mulching, and plant fiber films [15; 16; 17]. Although some progress has been made in the first three degradable films, they are mainly synthesized by the co-polymerization of starch and other nutrients with degradable organic compounds. The adoption of these films is always favorable due to high costs, incomplete degradation, etc. To overcome this issue, researchers have developed plant fiber films derived from plant raw materials, such as softwood, hardwood, hemp, reed, waste cotton,straw, etc. Plant fiber film has great potential to replace petroleum-based PMF, due to its green, environmentally-friendly, biodegradable, and renewable properties [18; 19; 20; 21; 22]. In addition to plant fiber film, rice wastes like straw, husk, etc. have many applications [23; 24; 25]. Most previous studies related to plant fiber films have been focused on improving the mechanical strength, light transmittance, water vapor permeability, heat preservation, soil moisture conservation, and other functions of the films [26; 27; 28]. However, studies regarding the thermal conductivity of plant fiber film mulching are quite limited. In view of the positive effects of temperature on plant morphological attributions, physiological growth, photosynthetic characteristics, physiological chemistry, and crop growth and development [29; 30], increasing the ambient temperature of crop growth is necessary. One solution to improve the ambient temperature of crop growth is to improve the thermal conductivity of plant fiber film, which will accelerate the heat exchange inside and outside the greenhouse. In the daytime, high thermal-conductivity film allows the rapid input of external heat into the greenhouse in order to improve the ambient temperature of plant growth, thus enhancing the plant photosynthesis and formation of nutrient components. At night, high thermal-conductivity film allows the rapid output of internal heat into the atmosphere in order to lower the ambient temperature of plant growth, thus weakening the plant respiration and reducing the loss of daytime-photosynthesized nutrition components [31; 32]. However, the thermal conductivity of the currently reported fiber film itself is very low [33]. Thus, developing plant fiber film with high thermal-conductivity is highly desirable. Charcoal as an environmental-friendly additive has high thermal-conductivity and is, therefore, a great warming agent to improve the thermal conductivity of plant fiber film [34]. In this work, charcoal was used to enhance the thermal conductivity of fiber film. Furthermore, to avoid the addition of charcoal on the fiber film strength, wet strength agent and neutral sizing agent were used to enhance the dry and wet strengths of the film.