Study On Modification Of Natural Hemp Fiber And Its Reinforced Rubber Composites

Natural plant fiber is derived from renewable resources,which possesses the advantages of light weight and low price,abundant sources,degradation and recoverability.It has become a research hotspot in recent years.Hemp fiber(HF)is a natural plant fiber with high strength and modulus.Using HF fiber instead of traditional synthetic fiber as the reinforcement of natural rubber(NR)is one of the effective ways to obtain natural environment-friendly rubber composites.In this paper,different chemical modification methods were used to modify the surface of HF fiber,and the interface adhesive of hyperbranched polyester polyol(P500)was added into the system to strengthen the interfacial bonding between HF fiber and NR matrix.The effects on the properties of fiber / rubber composites were investigated.The main contents are as follows:(1)The effects of HF fiber fraction and surface modification on the properties of natural rubber composites were investigated first.Scanning electron microscopy(SEM),rubber processing analyzer(RPA),static mechanical properties test,dynamic mechanical property analysis(DMA)were performed to research the composites and results found that the composite material possessed the best comprehensive performance when the amount of HF fiber was 4 phr,furthermore,the modulus at100% and 300% were increased by 33.18% and 20.29%,respectively,which better reflected the reinforced effect of HF fiber on NR rubber.The rolling resistance of the composite decreased after the addition of the HF fiber with the increasing content.Fourier transform infrared spectroscopy(FTIR)result showed that C=C double bond was successfully introduced on the surface of HF fiber with the reaction between maleic anhydride(MAH)and HF.The mechanical properties of the composite were improved.The number of voids left by the extraction was reduced,and the interfacial porosity between fiber and rubber matrix was reduced,indicating that the bonding force between the HF fiber and the NR matrix was enhanced,and the interfacial adhesion was improved meanwhile;the reduction of tan ? also indicated theenhancement of bonding ability with the interface between the NR and HF.(2)The effect of hyperbranched polyester polyol(P500)on the properties of HF/NR composites was discussed.It was found that the positive vulcanization time Tc90 of the HF/NR composites after the addition of hyperbranched P500 gradually shortened with the increase of the amount,indicating that the addition of P500 promoted the vulcanization of NR.When 2 g hyperbranched polymer P500 was added,the ML of composite increased by 42.10%,indicating the increase in the degree of filler network.Moreover,the interaction between the fillers were increased,and the mechanical properties of the material improved significantly.The modulus at 100%and 300% increased by 53.92% and 21.09%,respectively.When 2 g hyperbranched P500 was added,the relative interfacial slip energy(RISE)of the composite was the largest,which also indicated that the interface between the HF and NR was better.(3)By controlling the presence or absence of HF fibers in the system,the mechanism of action between hyperbranched P500,HF and NR matrix in composites was investigated.It was found that the interaction between hyperbranched P500 and NR matrix was weak,mainly via molecular chain entanglement.There is a synergistic effect between P500 and HF fibers.The treatment of HF fiber by NaOH could increase the surface polarity(-OH),and the mechanism of action between the hyperbranched P500 and HF fiber was verified.It was found that the performance of the composite material was further improved,the loss factor of the material was lowered,the movement of the rubber molecular chain was more difficult,and the interfacial bond between the HF fiber and the NR matrix was enhanced,indicating that the interaction between P500 and HF was enhanced.The main mechanism including two side: First,P500 contained a large number of polar groups,which can form hydrogen bonding with the polar HF fibers,improving the dispersion of fibers in rubber matrix;In addition,the hyperbranched P500 had a cavity structure and a large number of branched structures,which can also entangle with the NR rubber molecular chains to further enhance the interaction between HF and NR,thereby improving the interfacial bonding of the composite and the properties of the material.(4)The HF fiber modified by MAH and the hyperbranched P500 can worksynergistically to obtain an environmentally friendly fiber/rubber composite with better performance.In the composite material,the interface between HF fiber and NR matrix was better,thus the comprehensive properties of the material were better than the untreated one.The modulus at 100% was 4.27 MPa,and the tear strength as well as tensile strength were also improved to some extent.At the same time,the cutting resistance of the material and the heat situation had also improved.