Study Of Low Foaming Wood-flour/Poly (Vinyl Chloride) Composites

Low Foaming wood-flour/PVC composites(WF-PVC) was prepared by crust foaming extrusion of the mixture of wood-flour as filler,poly(vinyl chloride)(PVC) as matrix, modified AC as foaming agent and rare-earth stabilizer using a SJSZ50/105 conical twin screw extruder.The study was carried out in the aspects as follows:(1) The modification of AC foaming agent(2) The interracial modification of foaming wood-flour/PVC composites and the effect of interracial modification on properties of composites(3) The influence of the additives on micro-morphology and properties of foaming wood-flour /PVC composites.The effects of foaming control agent ZB-530 and impact modifier ACR and CPE on rheological properties of the low foaming wood-flour/PVC composites as well as the relationship between rheological properties,processing and mechanical properties of foaming wood-flour/PVC composites were studied.(4) The relationship between the processing and properties of foaming wood-flour/PVC composites.(5) Composite lead-free rare-earth stabilizer was prepared and its influence on thermal stability of PVC and WF-PVC composites was studied.(6) The properties of fire-retardancy and smoke-suppression of WF-PVC composites were studied and a new fire retardant for WF-PVC was synthesized.Main research results of this study are as follows:(1) AC foaming agent was modified to apply to WF-PVC composites.The results showed that the induction time of modified AC foaming agent was shortened to 10min and the decomposition temperature can be controlled in the range from 165℃to 180℃,which is consistent with the processing temperature of foaming wood-flour/PVC composites.Improved properties were obtained when added this modified AC foaming agent 1.2phr to the formulation of foaming wood-flour/PVC composites.(2) The effects of interfacial modification on the properties of low foaming wood-flour /PVC composites were studied using coupling agents(tetrabutyl titanate,ND 1010 titanate coupling agent,silane coupling agent,isocyanate) and sodium hydroxide solution and interracial compatibillizer MAPP.The results are as follows:â‘ There is difference between foaming and non-foaming wood-flour/PVC composites in flexural modulus.Flexural modulus of foaming wood-flour/PVC composites was decreased 40%compare with that of non-foaming composites when using the same treating agent to modify wood-flour.Flexural modulus have little changed when treated wood-flour with different treating agent for the same type of composites.Impact strength of foaming wood-flour /PVC composites was not only related to the treating agent but also affected by the cell morphology.Compare with non-foaming wood-flour/PVC composites,the impact strength of foaming wood-flour/PVC composite was enhanced and the change range was related to the interfacial modification of foaming wood-flour/PVC composites.Meanwhile,the impact strength was also affected by the melt strength and cell morphology.â‘¡Apparent density of low foaming wood-flour/PVC composites was decreased when using treated wood-flour in composites.The lowest apparent density among all samples was obtained when wood-flour was treated using tetrabutyl titanate and particle size is 80～100 mesh in formula.â‘¢Wood-flour with different treatment has influence on the melt viscosity of low foaming wood-flour/PVC composites.In the study,compare with the system of no-treated wood-flour,the melt viscosity of samples with treated wood-flour decreased.Besides the sample,in which wood-flour was treated with titanate coupling agent ND1010,the melt viscosity was increased.Melt viscosity of the sample was decreased most significantly in all samples when treated wood-flour with MAPP(3) The processing technology of low foaming wood-flour/PVC composites has its own characteristics.Compared with non-foaming wood-flour/PVC composites,the technique of the raw materials and formulation design,technology and equipment in the process of foaming wood-flour/PVC composites extrusion has special technology requirement.More factors affect the foaming process and the properties the product.In this research,the extrusion equipment SJSZ50/105 conical twin screw extruder was designed and assembly by our laboratory. Because of high temperature sensitivity of PVC,wood-flour and foaming agent decomposition temperature,all which made the producing technology of low foaming wood-flour/PVC composites becoming more difficult.Some deficiencies and questions such as the carbonization phenomenon when the equipment operating continuous has no avoided,that require further study.(4) Lead-free rare-earth thermal stabilizer was prepared which are suitable for foaming wood-flour/PVC composites.The orthogonal test design was adopted to study the optimal formula of composite lead-free rare-earth stabilizer based on rare earth stearate.Results showed that synergistic effect occurred between composite stabilizer and pentaerythritol or organotin stabilizer.Composite rare-earth stabilizer LS was prepared which is nontoxic, excellent in transparency and good thermal stability was obtained when used this stabilizer about 10phr in foaming wood-flour/PVC composites formula.Meanwhile,mechanical properties of low foaming wood-flour/PVC composites,especially in impact properties,were improved obviously when LS was used. (5) Fire-retardancy and smoke-suppression of wood-flour/PVC composites was investigated.The results revealed that there occurs the relationship between wood-flour and PVC in composites using cone calorimeter testing,TGA and Py-GC-MS analysis.The effects of different metal oxides CuO and La₂O₃ on the properties of combustion and degradation of wood-flour/PVC composites were investigated.High effective fire retardant AMPC was synthesized and applied to the formula of wood-flour/PVC composites.The results are listed in following:â‘ The process of combustion and degradation of wood-flour/PVC composites is complicated.During the combustion and degradation of wood-flour/PVC composites the interaction occurred between wood-flour and PVC,in which decomposition of wood-flour was accelerated and the degradation of PVC was delayed.Meanwhile,residues of wood-flour/PVC composites were improved and the release rate of hydrogen chloride was decreased because of the addition wood-flour to PVC.Thermal degradation of wood-flour/PVC composites has more characteristics of PVC.During combustion of wood-flour/PVC composites average heat release rate(av-HRR),total heat release(THR),total smoke production(TSP) and average specific extinction area(av-SEA) was decreased 44%,9.2%,25.8%and 29.9%,respectively, compare to the burning of PVC.Therefore,the addition of wood-flour to PVC could obviously inhibit the heat release and smoke release.â‘¡The results of Py-GC-MS analysis at 500℃showed that the thermal degradation products of wood-flour/PVC composites were different from that of PVC.The yields of HCl and aromatic compounds decreased 59.7%and 96.5%,and aliphatic compounds increased from 2.49%to 38.58%.This further explained the reason that smoke release decreased obviously during the combustion of wood-flour/PVC composites.It was found that the degradation process of PVC was delayed by the addition of wood-flour and the path of PVC degradation was in the direction of forming cross-linked intermediates,promoting charring.â‘¢Metal oxides CuO and La₂O₃ play the role of flame-retardant in wood-flour/PVC composites and promote charring during combustion and degradation.Parameters,heat release rate(HRR),total heat release(THR),smoke production rate(SPR) and total smoke production (TSP),obtained from cone calorimeter testing were decreased obviously by the addition of CuO to wood-flour/PVC composites.CuO is an effective fire-retardant which is effective in smoke suppression.â‘£A novel fire retardant AMPC was synthesized which significantly promotes the complete combustion of the volatile components of the pyrolysis products of the wood-flour /PVC composites and made smoke release decreased obviously.The results showed AMPC is functioned in the condensed phase.When 5 phr AMPC was added to the formula of wood-flour/PVC composites with wood-flour content of 30%and 70%,total smoke production was decreased 39.1%and 57.4%respectively compare with the control(no AMPC).