Research On Preparation And Mechanical Properties Of Kenaf Powders/PP Composites

In recent years,with the public awareness of environmental protection,using plant fiber as a reinforcing material to develop environment friendly composites has attracted more and more attention around the world.Kenaf is a crop,with high fiber content,barren resistance,drought-enduring,toughness and low density.In order to improve the comprehensive utilization market of kenaf and make full use of abundant kenaf resources in China,we researched and developed the application of kenaf powders/polypropylene(PP)composites.In this paper,kenaf bast and stalk were grinded by mechanical method to obtain kenaf bast powders(KB)and kenaf stalk powders(KS)respectively.After different surface treatments of kenaf powders,it were blended and granulated with PP and the kenaf powders/PP composites were prepared by hot-pressing.The parameters of granulation and hot-pressing process were determined,and we analyzed the effects of KB and KS,different kenaf powders content and kenaf powders particle size on the mechanical properties,crystallization,water absorption and thermal stability of the composites.The effects of alkali treatment and maleic anhydride compatibilizer(PP-g-MAH)on properties of kenaf powders/PP composites were investigated.Results were illustrated as follows:(1)KB and KS were grinded by mechanical method.The kenaf powders was modified by alkali and silane coupling agent.The modification results and thermostability of kenaf powders were characterized by Fourier transform infrared spectroscopy and thermogravimetric analyzer respectively.The results showed that the kenaf powders could be successfully grafted with vinyltrimethoxysilane(A-171).The thermal stability of kenaf powders in 220℃ was not obvious decline.(2)In the prepared process,the process parameters of blending granulation and hot pressing were adjusted to determine the optimal processing parameters.Results showed that the optimum parameters of extrusion granulation process are extrusion temperature 195℃ and rotational speed 100 rpm.The optimum process parameters are pressing temperature 195℃,pressing time 10 min and heating pressure 3 MPa.(3)The mechanical properties,crystallinity and water absorption of kenaf powders/PP composites were tested and analyzed.The results showed that the tensile strength,impact strength and elongation at break of kenaf powders/PP composites decreased with the increase of kenaf powders content,but the bending strength,flexural and tensile modulus are increasing,the mechanical properties of KB/PP composites are better than that of KS/PP composites.With the increase of the content of kenaf powders,the water absorption of kenaf powders/PP composites gradually increases;KS/PP composites’ water absorption was slightly higher than KB/PP composites.The water absorption of the composites immersed in boiling water for 2 h was higher than it in cold water for 24 h.The kenaf powders could induce the PP’s heterogeneous nucleation,and increased the crystallization temperature.When the particle size of kenaf powders was 120 mesh,the mechanical properties of the composites were the best.(4)The interfacial properties of kenaf powders/PP composites were improved by alkali treatment and PP-g-MAH,and the mechanical properties of the composites were improved.The results showed that the tensile strength,flexural strength and impact strength of the KS/PP and KB/PP composites increased after alkali treatment,and the water absorption capacity of the composites increased.PP-g-MAH can improve the mechanical properties,thermal stability and crystallization temperature of kenaf powders/PP composites.When the content of PP-g-MAH is 2%,the tensile strength of the composites is the highest.PP-g-MAH decreased the water absorption of the composites,and with the content of PP-g-MAH increased,water absorption decreased gradually.