The Preparation And Properties Of Wood Fiber/polyolefin Blends Composites

To produce wood plastic composites(WPC) is the major path for the effective utilization of waste plastic,however,the waste plastics are usually the mixtures of nonpolar polymers with different properties.The compatibility between the polymers composing waste plastic and the compatibility between plastics,which may undergo degradation,and wood fiber are poor, resulting in the poor mechanical properties of WPC.Therefore the effective modification of waste plastics is a key factor for WPC industry.In this paper,the melt grafting of MAH onto PP-PE blends was performed in a twin screw extruder in the presence of dicumyl peroxide (DCP) as initiator.The wood plastic composites were prepared by modified PP-PE blends and wood fiber.Experiments were carried out using pure polymers for influencing factor investigation,and the waste plastics were further studied.The grafted polyolefin blends were characterized by Fourier Transform Infrared(FTIR) spectroscopy.The mechanical properties of the polyolefin blends and their composites with wood fiber were evaluated respectively,and the rheological properties of the blends and composites were studied.By comparing the FTIR spectra of the grafted PP-PE with that of the unmodified PP-PE blend,it proved that MAH was grafted onto PP-PE.The tensile strength of the grafted blends was enhanced,however,the impact strength decreased.The MAH dosage and grafting conditions had great impact on the grafting results,which would in turn affect the mechanical properties of the grafted PP-PE blends.By using grafted PP-PE blends as the matrix of the wood plastic composites,no matter virgin plastics or waste plastics,the interracial bonding between wood fiber and PP-PE blends were improved,and it would enhance the mechanical properties of the composites accordingly.When MAH dosage is 1.0%,the flexural strength and unnotched impact strength of the wood-fiber/virgin PP-PE blend composites increased by 50.4%and 90.8%respectively,and which of the wood-fiber/waste PP-PE blend composites increased by 40.2%and 53.4%.The results of SEM also indicated that both the compatibility between PP and PE in PP-PE blends and that between wood fiber and PP-PE blends were improved.Using a rotational rheometer,the linear viscoelastic regions(LVR) of PP-PE blends and the corresponding WPC composites were determined according to dynamic strain sweep.The results showed that MAH dosage had minor influence on the LVR range of PP-PE blends,and the LVR of the WPC appeared at much lower strain range in the presence of wood fiber.The dynamic frequency sweep results revealed that all the samples exhibited similar rheological behaviors at high frequency region,however,the rheological parameters showed much more significant differences at low frequency region relative to that high frequency region.The low frequency region also indicated the influences of MAH dosage and screw rotating speed on the rheological properties during grafting process.The differences between rheological parameters before and after grafting implied that the structure of the polyolefins changed,which indicated that the degradation reaction of the polyolefin occurred during the grafting,and the somewhat crosslinking between polyolefin molecules may also possible.The presence of wood fiber caused the rheological behavior of the composites to deviate from the polymer matrix,and it exhibited obvious shear thinning behavior.The emergence of "the second plateau" of the storage modulus and tand peak reflected the "solid-like behavior",which offered important information related to the morphology and structure of the macromolecule system.The rheology results could be a key scientific basis of the extruding process control and die design of WPC.