Mechanical Activation-assisted Coupling Modification Of Cassava Less And The Preparation Of Wood Plastic Composites

Wood plastic composites(WPC)are a kind of composites which are prepared with using nonpolar or less polar thermoplastics as matrix and strong polarity of plant fiber as filling or reinforcing material.Due to the incompatibility between the polar and hydrophilic plant fiber and non-polar and hydrophobic thermoplastics,the interface of WPC becomes the region of stress concentration,which leads to poor physical and mechanical properties of WPC.In order to solve this problem,cassava lees,a kind of plant fibers,was treated by mechanical activation(MA)-assisted coupling modification for the purpose of enhancing the interfacial compatibility between thermoplastics and cassava lees,and thus improved the mechanical properties of WPC.(1)The pretreated cassava lees,PVC and additives were mixed in a high-speed mixing machine,and then cassava lees/PVC composites were prepared by compression-molded in a plate vulcanizing press.Firstly,the effects of cassava lees content,and species and dosage of coupling agent on the mechanical properties of WPC were investigated.On this basis,MA-assisted coupling modification was used for the surface modification of cassava lees,and then the effects of MA time and temperature on the mechanical properties of cassava lees/PVC composites were investigated with using flexural strength and tensile strength as evaluation indexes.In addition,original and MA-assisted coupling modified cassava lees were characterized by Fourier transform infrared spectroscopy(FT-IR),X-ray diffraction(XRD),and scanning electron microscope(SEM),respectively,illustrating the effect of MA on surface modification of cassava lees.The results showed that under the conditions of cassava lees content 50%,aluminate coupling agent(ACA)dosage 1%,MA temperature 80 0C,MA time 25min,molding temperature 170 0C,molding pressure 5MPa,and molding time 12min,the flexural strength and tensile strength of the cassava lees/PVC composite were 39.51 and 15.24MPa,respectively.FT-IR analysis showed that the mechanical force led to the weakening of intermolecular hydrogen bonding and the increase of free hydroxyl content in cassava lees fiber.XRD analysis showed that the mechanical force reduced crystalline region of cassava lees fiber and increased the amorphous area.SEM analysis showed that the mechanical force increased the specific surface area of cassava lees,and the surface had concave convex groove and loose pore structure.When the pores or concave of the cassava lees surface was fully or partly filled with matrix,molecular interaction and irregular infiltration took place.Then various forms of mesh structure were formed by solidify at the interface,which resulted in high interface strength.(2)Under the conditions of cassava lees content 50%,aluminate coupling agent(ACA)dosage 1%,MA temperature 80 0C,MA time 25min,for the preparation of the composites,the effects of molding temperature,molding pressure and molding time on the mechanical properties of cassava lees/PVC composites were investigated with using flexural strength and tensile strength as evaluation indexes,and the molding process conditions of the composites were optimized by using orthogonal experiments.The order of the factors for influencing the flexural strength and tensile strength of the composites in molding process was molding temperature>pressure>forming time.The molding process conditions optimized by orthogonal experiments were as follows:molding temperature 195 0C,molding pressure 6MPa,and molding time 12min,and the flexural strength and tensile strength of the cassava lees/PVC composite were 49.59 and 21.84MPa,respectively.(3)The effects of different surface treatment methods of cassava lees on mechanical strength,24h water absorption,and average change rate of each direction size of cassava lees/PVC composites were investigated,respectively,and SEM was used to observe microstructure of fracture section of the composites.The results indicated that MA-assisted coupling modification had best effect on the mechanical properties of the composites.ACA could effectively reduce the water absorption of cassava lees.MA made the surface of cassava lees coated by ACA evenly,and the interface of composites was fuzzy,showing that MA-assisted coupling modified cassava lees uniformly distributed in the PVC matrix,and thus improved the interfacial compatibility between cassava lees and PVC matrix.Under the conditions of cassava lees content 50%,the flexural strength,flexural modulus,tensile strength,24h water absorption,24h thickness swelling of the MA-assisted coupling modified cassava lees/PVC composite reached the physical and chemical performance standards of the ordinary,furniture and decoration WPC.