Preparation And Properties Of Phenolic Molding Compounds Reinforced With Sisal Fiber

In this paper, the preparation, structures and properties of phenolic molding compounds reinforced with sisal fiber (SF) and sisal-glass (GF) hybrid fibers were studied systematically. The influence of different surface treatments, length and content of SF, and blend resin matrix on the properties of phenolic molding compounds were investegated, also the fracture mechanism of fibers was analyzed. The research work is useful to develop new phenolic molding compounds and optimize their properties.Surface treatment had great influence on the properties of phenolic molding compounds reinforced with fibers. Alkali-thermal, silane coupling agent KH-550 and plasma treatments were used to treat the surface of SF, silane coupling agent KH-550 and plasma treatments were used to treat the surface of GF. The results showed that all these treatments could improve the reinforcement of SF and GF to phenolic molding compounds. The properties of phenolic molding compounds could be improved significantly by incorporation of SF compared with wood powder, and exhibited larger impact strength than GF.Length of SF had great influence on the properties of phenolic molding compounds. Longer SF had more advantages to improve the mechanical and thermal properties of phenolic molding compounds than shorter SF, but it would cause lower electricity and water resistivity. Furthermore, using longer SF to reinforce phenolic molding compounds would cause complication in preparation processes, resulting roughness of molding composites and puffing of product by injecting molding.Substituting part of wood powder, SF (alkali-thermal treated) was used to reinforce phenolic molding compounds. The results showed that with the increasing of SF contents, flexural strength and notched impact strength of composites increased at first and then dropped; heat distortion temperature and water absorption increased; electric strength presented slightly raising trend.Blend resin matrix of novolac and resole was used to substitute the traditional novolac matrix to prepared composite reinforced with SF. It was found that curing system had great influence on the properties of composite. When no curing agent was used, the flexural strength and heat distortion temperature of composite changed slightly with blend ratio of phenolic resin, but it was opposite to the impact strength, volume resistivity and water absorption of composite. All properties were improved when curing agent was used. With the dosage of resole increased in blend system, the mechanical and thermal properties increased first and then dropped, reached their maximum at about 1:1 blend ratio; volume resistivity presented an increasing trend as a whole; water absorption dropped first but raised later, reached its minimum at 1:1 blend ratio. The observation of SEM showed that there had better adhesion effect in resole and blend system than novolac system.Hybrid fibers of SF and GF were treated with silane to reinforce phenolic molding compounds. The results showed that as the hybrid ratio of SF-GF increased, notched impact strength and percentage of water absorption of phenolic molding compounds increased, flexural strength, heat distortion temperature and volume resistivity decreased. In rheology test, a positive hybrid effect was observed. The micrographs of SEM revealed that the fracture mechanism of composites reinforced with GF was typical rigid fracture, and the fracture mechanism of composites reinforced with SF was typical toughness fracture. It was observed that SF-GF hybrid fibers dispersed homogeneously and arranged alternatively on the fracture surface.For the blend resin system reinforced with SF, GF was used to substitute part of SF to reinforce phenolic molding compounds. With the increasing content of GF, the flexural strength, heat distortion temperature and volume resistivity of composite presented an increasing trend, but the impact strength and water absorption of composite presented a decreasing trend.