The Studies On The Preparation, Structure And Physical Properties Of Rubber Composites Filled With Hemp Hurd Powder

In recent years, natural fibers as the fillers of polymer have been paid more attention. With the application of hemp fiber in the textile industries, hemp plantation has been focused on in some areas of China. Traditionally, the utilization of hemp fiber focuses on the bast, on the contrary, the hemp hurd accounting for 70-80wt% of hemp stem was disposed by combustion or landfill. Therefore, in this paper, the hemp hurd powder (HP) as rubber filler was studied in order to investigate its effect on the structure and performances of the rubber. At the same time, the mixed use of HP and silica, the mixed use of HP and nylon, as well as the mixed use of HP and aramid were also filled in the rubber and the effect on the structure and physical properties of filled rubber composites was also investigated. It is beneficial to realize the comprehensive utilization of hemp resource, reduce the agro-waste accumulation and environmental pollution. It would play a positive role in the construction of resource society and low carbon economic development. Firstly, the comparations and effects of different treatment methods containing phenol formaldehyde-hexamethylene tetramine bonding system, RFL bonding system, and the coupling agent treatment on the properties of HP filled styrene-butadiene rubber (SBR) were researched. Among these methods, coupling agent modification appeared as a quick and effective method to provide good interfacial adhesion and HP dispersion in the rubber matrix. Bis-(3-triethoxysilylpropyl) tetrasulfide (Si69) with bi-functional groups could produce chemical bonding between SBR and the hemp fiber, and improved effectively HP-SBR interfacial interaction. Therefore, Si69 treatment is superior to that of the y-aminopropyl triethoxysilane (KH550) in terms of the properties of SBR/HP composites. With the optimum Si69 dosage of 3 wt% of HP through the modification in the mixer, the curing characteristics, the proccessability, mechanical properties, and dynamical mechanical properties of HP filled SBR were systematically investigated. When the loading is no more than 60phr, the addition of HP would improve the hardness, modulus, and tensile properties of SBR composites. Si69 treatment could shorten the curing process and improve the proccessability. Moreover, the mechanical properties such as hardness, modulus, tensile and tear strengths, dynamical mechanical properties, and water resistance of SBR composites also considerably increased.Secondly, the combination effects of HP and silica on the proccessability, microstructure, mechanical properties, and dynamic mechanical properties of SBR and ethylene-propylene-diene rubber (EPDM) composites were investigated. At 20phr silica, when the loading of HP was no more than 30phr, the rubber composites showed the better combination of stiffness and toughness. The addition of HP obviously improved the modulus, hardness, and tear strength of rubber composites filled with silica, simultaneously had a positive impact on tensile mechanical properties. The excessive HP content was helpful to the improvement of modulus and hardness of rubber composites, however, and led to the sharp decrease of elongation at break and tensile strength due to the deterioration of silica-matrix interfacial interaction.Based on traditional latex coagulation treatment, SBR/HP composite was successfully prepared. The addition of small portion of KH550 modified clay and styrene-butadiene-vinyl pyridine latex in suspension could obviously decrease the HP agglomeration during coagulation and improve the HP-SBR matrix interfacial bonding. The effects of microstructure and physical properties of HP/clay/SBR composites on different modified methods such as latex coagulation and Si69 melt organic modification were systematically studied. After the latex coagulation treatment, due to the synergistic reinforcement of HP and clay, the composites showed better fillers dispersion in matrix and stronger filler-matrix interfacial bonding, more superior mechanical properties, dynamic mechanical properties and fatigue resistance. At the same time, the combination effects of latex coagulation modified HP and silica on the structure and properties of SBR composites were investigated. When HP loading was no more than 20phr, the filled rubber composites showed superior physical properties.The effects of mixed use of small portion of nylon, aramid and HP on the structure and properties of SBR composites were explored. The effects of length, feature, and loading of synthetic fibers, as well as different HP modifications on the structure and properties of SBR composites were studied. The composites filled with short fibers with 1mm length and latex coagulation treated HP showed the optimal physical properties.In order to improve the proccessability and mechanical properties of SBR, the related performance of filled SBR/NR blends was investigated. The introduction of NR could obviously improve the proccessability, curing process, and tensile properties of SBR composites, and resulted in the decrease of hardness and modulus. Comparing the structure and properties of SBR/NR composites filled with different pretreatment HP, the results revealed latex coagulation treatment was superior to the coupling agent treatment during the mixer. Under this circumstance, the composites with 30phr HP content showed the optimal physical properties.