Study On Manufacture And Properties Of Fire-retardant Wood Fiber-polypropylene Composites

Research on wood-plastic composites is one of important part in the filed of biomaterials science.As flammability character of wood-plastic composites,fire hazard exists for its indoor usage.The main objective of this study is to find out new flame-retardant wood-plastic composites that can be used indoors and collect technical data for study in its further indoor application.In the experiment,wood fiber-polypropylene (PP) composites were made by manufacturing process of wood-based board.The main experimental factors that influence physical-mechanical properties and combustion properties of wood fiber-PP composites was analyzed first,then proper fire retardants were chosen for wood fiber-PP composites by utilizing these data from TG-DTA analysis,cone calorimeter and FTIR analysis.Finally orthogonal experimental design method was used to analyze the relations among key factors and properties of fire retardant composites.By the experiment result,a kind of flame-retardant wood fiber-PP composites with excellent physical-mechanical properties was produced.In this paper,the main research conclusions are as follows.1.PP content,reinforcement species,density of products and fiber size were considered as experimental factors and their influence on physical-mechanical properties of wood fiber-PP composites was analyzed.The results showed that the four factors had different effect on physical-mechanical properties.More PP content caused significant enhancement of physical-mechanical properties;reinforcement can increase the properties very well,especially when adding 2％PAPI in the composites;When the designed density increased,it caused the most significant improvement on properties of modulus of rupture (MOR) and modulus of elasticity (MOE);Influence of fiber size on properties is not significant,but middle-size fiber had relatively better performance.As a result,to produce excellent wood fiber-PP composites,the levels of factors should be:40％PP content,2％PAPI,1.05g/cm~3 density and middle size fiber.Test results showed that composites made under the chosen factors had super properties and could meet requirement of national standard GB/T11718-1999 for exterior fiberboard. 2.The crucial factor dominating combustion properties of composites was combustion heat of PP material.Combustion heat of PP was much higher than wood and it badly decreased fire endurance of composites. With the increase of PP,the oxygen index (OI) fell down,heat release rate (HRR) and effective heat of combustion (EHC) increased rapidly.Reinforcement kept dimensional stability in fire but accelerated burring behavior of composites;other variables,such as density of product and fiber size had some effect on fire behavior,but their influence was not significant.The calculated apparent activation energy showed that in the pyrolysis process of wood and PP composites,the materials showed co-decomposition behavior.3.TG and DTA analysis results showed that SA changed thermal pyrolysis characteristics of wood.Flame-retardance resulted from SA catalyzing decomposition of wood to charcoal at lower temperature to slower combustion process.The test results of physical-mechanical properties showed that differ from regular fire-retardant wood-based panels,the SA fire retardant enhanced physical-mechanical properties of wood fiber-PP composites.It can be explained like that SA enhanced surface activation of wood fiber and that could make activated bonding at interface of wood and PP and was identified in mechanism analysis.Different ratio of plastic fire retardant led to different OI of PP.Following three kind of compound have good performance on flame retardance:DBT compound by 3 parts of decabromodiphenyl ethane (DBDPE) and 1 part of antimony trioxide (ST);DBZ compound by 2.7 parts of DBDPE and 1 part of zinc borate (ZB),APM made from 100％ammonium polyphosphate (APP).Because of different fire retarding mechanism,using wood fiber fire retardant or plastic fire retardant alone can not meet fire retardant objective of wood fiber-PP composites.4.Six experimental variables,such as SA content,reinforcement species,reinforcement content,plastic fire retardant species (PFRS, plastic fire retardant content (PFRC) and ratio between wood fiber and PP (WPR) were tested in manufacturing fire-retardant wood-plastic composites.The results showed that the SA content,PFRC and WPR were significant factors for fire retardant effect (OI) and other factors were not very important.Increase of SA content not only improved OI of composites,but also improved some physical-mechanical properties greatly;cooperation of APP in APM prescription and SA fire retardant made flameproof property improved significantly;adding PP can increase physical-mechanical properties at large scale but decrease OI rapidly.Reinforcement can increase the properties greatly,but reinforcement species and PWFS were not significant compared with other factors.Properties of SA had some bad effect on cure degree of reinforcement;their interaction had some influence on physical-mechanical properties of composites.Compared with normal wood fiber-PP composites,fire-retardant wood fiber-PP composites had much higher OI,and heat release rate (HRR),mean mass loss rate (MMLR) and mean effective heat of combustion (MEHC) was slow down greatly.Using the optimized factors the properties of fire-retardant wood fiber-PP composites were excellent.OI was 39.6％,which meet requirements of OI≥35％in standard GA87-94;thickness swelling after 24hour water absorption (24hTS) was 10.18％,internal bond (IB) was 0.966MPa,modulus of rupture (MOR) was 35.45MPa, modulus of elasticity (MOE) was 4031MPa and boiling test of internal bond (BTIB) was 0.272MPa. The test result surpassed national requirements of GB/Tl1718-1999 of humid resistant fiberboard, and it even meet requirement for outdoor usage.Objectives of the research had been met.