Preparation And Characterization Of Bamboo Fiber Reinforced Polyethylene Composite

In recent years,with the increasing shortage of forest resources in China,the research and development of wood substitutes has become the current research focus.China is rich in bamboo resources,the growth cycle of bamboo is short and the timber is fast.In order to improve the utilization rate of bamboo and reduce the white pollution caused by plastic use,bamboo fiber（BF）reinforced polyethylene（PE）composites which can replace wood,bamboo and plastic products were developed.Phyllostachys heterocycla（CARR.）Mitford cv Pubescens)was used as raw material,Na OH and Na₂SO₃ were used as cooking reagents,and the dual dissolution of Na OH and Na₂SO₃ on lignin was used.Through cooking,extrusion,opening,carding and other processing technologies,bamboo fiber was prepared by chemical mechanical method.The effects of cooking parameters on bamboo yield,sulfonic acid content and crystallinity were studied by orthogonal experiment.The effects of hot pressing temperature,paving method,plastic type and fiber content on the mechanical properties and water absorption properties of BF/PE composite were discussed.The mechanical properties,dynamic thermodynamic properties,thermal stability,interfacial morphology,and chemical structure of the composites were studied by universal mechanical testing machine,DMA,SEM,FTIR,XRD and other equipments.The main conclusions were as followed:（1）When cooking temperature was 100℃,cooking time was 2 h,Na OH content was 16%,and Na₂SO₃ content was 10%,the crystallinity of bamboo was 62.48%,the yield of bamboo was 92.23%,and the content of sulfonic acid group was 43.11mmol/kg.The results showed that the cellulose content increased from 44.80%to 52.68%,the hemicellulose content and lignin content decreased from 15.10%and 30.84%to 12.68%and 21.74%,respectively.The removal of hemicellulose and lignin is conducive to the separation of fiber in bamboo,and the hardness of bamboo decreases after cooking,which is more conducive to the extrusion carding of bamboo and improves the preparation efficiency of bamboo fiber.The average length,width,elastic modulus and tensile strength of the fiber were20 mm,0.07 mm,32.76 GPa,and 564.94 MPa,respectively.（2）The mechanical properties of BF/PE composites increased with the increase of pressing temperature.When the pressing temperature increased from 150℃to 180℃,the tensile,bending,and impact strength of the composite increased by 34.11%,73.55%,and 34.94%,respectively.Through the analysis of mechanical properties,the preparation process of BF/PE composite was determined.The pressing temperature was 180℃,paving method was three layers of fiber and two layers of plastic,and the plastic type was 5000S.（3）With the increased of fiber content,the tensile strength and flexural strength of BF/PE composite first increased and then decreased,and the impact strength decreased continuously.When the fiber content was 30%,the comprehensive mechanical properties of the composite were better.The tensile strength,bending strength and bending modulus were18.57 MPa,27.17 MPa,and 2238.22 MPa,respectively,and the impact strength was 33.17 k J/m².The water absorption of BF/PE composite with0%,15%,30%,45%,60%fiber content was 0.79%,6.07%,9.29%,10.00%,11.83%,respectively,and the thickness swelling was 3.13%,6.87%,9.58%,13.71%and 16.08%,respectively.（4）DSC results showed that with the increased of fiber content,the initial thermal decomposition temperature（T_i）of the composite decreased and the carbon residue rate increased.When the fiber content were 0%and30%,T_i were 425.84℃and 255.41℃,and the residue weight rate were1.86%and 10.85%respectively.DMA test results showed that with the increased of fiber content,the storage modulus and loss modulus of the composite increased,the rigidity increased,and the glass transition temperature（T_g）increased.When the fiber content were 0%,and 30%,T_gincreased from 151.1℃to 153.6℃.（5）Bamboo fiber were modified by KH550 and DN-302 coupling agents respectively.The effect of coupling agent on mechanical properties and thermal stability of the composites was studied.The results showed that the mechanical properties of BF/PE composites can be effectively improved by KH550 and DN-302 modified bamboo fibers.The tensile strength,flexural strength and impact strength of the composites reached the maximum value when the content of KH550 was 1%,which was increased by 21.92%,26.39%,and 23.42%,respectively.When the dosage of DN-302 was 1%,the tensile strength and impact strength of the composite increased by 11.42%and 33.76%,respectively.（6）The DSC test results of BF/PE composite before and after the modification showed that the first-order weight loss rate and initial thermal decomposition temperature of the modified BF/PE composite were reduced.The results showed that the first-order weight loss rate of the material were 21.80%,18.67%,17.52%and 15.66%,respectively,when the dosage of KH550 were 0%,1%,2%and 3%,respectively,and the T_iwere 255.41℃,235.5℃,254.4℃,and 249.7℃,respectively.When the dosage of DN-302 were 0%,1%,2%and 3%,respectively,the first-order weight loss rate of the material were 21.80%,15.49%,12.68%,14.18%,and the initial thermal decomposition temperature were 255.41℃,248.7℃,244.9℃,and 250.6℃,respectively.（7）SEM analysis showed that KH550 and DN-302 coupling agent can significantly reduce the interface gap between bamboo fiber and PE matrix,and improved the interface bonding ability between them.FTIR and XRD results showed that KH550 and DN-302 coupling agents can reduced the activity of hydroxyl groups on the surface of bamboo fiber and improved the crystallinity of BF/PE composite.When the dosage of KH550 and DN-302 was 1%,the diffraction intensity and crystallinity of BF/PE composite were the highest.