Preparation And Properties Of Flame-retardant Ramie Reinforced Epoxy Resin Composites

Ramie fabric reinforced epoxy resin composites（EP/RF）have shown great potential in civil construction,aerospace,automotive machinery and other fields due to their low price,low density,light weight,high specific strength,low energy consumption,wide range of sources,sound insulation,vibration damping and noise reduction,etc.However,ramie fabrics（RF）and epoxy resin（EP）are both flammable substances,which lead to the limitation of EP/RF in high-tech applications.Therefore,it is of great practical importance to improve the flame retardancy of EP/RF while ensuring its mechanical properties as much as possible.The phosphorus-based flame retardant ammonium polyphosphate（APP）has the advantages of high flame retardancy,little impact on mechanical properties,making it the perfect choice for achieving EP/RF with both flame retardancy and mechanical properties.On this basis,in this thesis,flame retardants such as APP were first compounded and coated onto the RF surface.The flame-retardant EP/RF was then produced by hand lay-up method.Finally,the flame retardancy,thermal stability,burning behavior,flame retardant mechanism and mechanical properties of the flame-retardant RF and flame-retardant EP/RF were investigated in detail.The main research results of this work are as follows:（1）The flame-retardant RF was prepared by the dip-pad-bake method using APP as the flame retardant and named RF-APPn,where n is the weight gain rate,and then m-phenylenedimethylamine（m-XDA）was selected as the curing agent and the composite was prepared by the hand lay-up method and named EP/RF-APPn.Thermogravimetric analysis（TGA）,cone calorimetry test（CCT）,thermogravimetric-fourier transform infrared spectroscopy（TG-FTIR）,X-ray photoelectron spectroscopy（XPS）and universal material testing machine were used to investigate the surface morphology,flame retardancy,thermal stability,burning behavior,flame retardant mechanism and mechanical properties of RF-APP.Vertical flame test（VFT）,limiting oxygen index（LOI）,TGA,CCT,TG-FTIR,universal material testing machine,impact testing machine and dynamic mechanical analysis（DMA）were used to investigate the flame retardancy,thermal stability,burning behavior,flame retardant mechanism,mechanical properties and thermo-mechanical properties of EP/RF-APP.The results of the fabrics showed that the presence of APP effectively improved the flame retardancy of the fabrics.Taking RF-APP5 as an example,its LOI value reached 28.6%,while it passed VFT,the afterflame time and afterglow time were 0 s,the damaged length was only about 80 mm,and the pictures taken by a scanning electron microscope（SEM）showed that the fibre structure of the fabrics was preserved intactly.The TGA results showed that the thermal degradation rate of RF-APP was significantly lower and the amount of char residues at 700℃ was much higher than that of RF,demonstrating that the thermal stability of RF-APP was significantly improved in the high temperature range.The peak heat release rate（PHRR）and total smoke production（TSP）were much lower than those of RF,and the fire growth rate index（FGIRA）was also much lower,proving that the fire safety of RF-APP was guaranteed.In terms of flame-retardant mechanism,the analysis of TG-FTIR and XPS results shows that the presence of APP promotes the production of more dense and stable char residues during the burning process of RF-APP,which in turn inhibits the production of flammable volatiles and thus fulfils the purpose of flame retardancy.In addition,the tensile strength of RF-APP remains largely unchanged.The above facts demonstrate that RF-APP has both flame retardancy and mechanical properties and meets the basic requirements for flame-retardant composites.The results of the composite showed that RF-APP improved the flame retardancy of the composites,while 20%of weight gain was required to meet the requirements.CCT results showed that the PHRR and TSP of EP/RF-APP20 were reduced by 26%and 41%,respectively,compared with those of EP/RF.In terms of flame-retardant mechanism,the condensed phase products were observed by SEM leads to the conclusion that APP promotes the carbonization of EP and RF to form dense char layers,protecting the integrity of the fiber structure and the substrate.The gas phase products were studied by TG-FTIR showed that APP inhibited the production of flammable volatiles during burning to improve the flame retardancy of the composites.As for the mechanical properties,DMA results showed that the presence of APP did not affect the movement of EP chain segments,but had a negative impact on the internal compatibility of the composites,which in turn affected its overall mechanical properties.In conclusion,APP imparts excellent flame retardancy to fabrics and composites,but the weight gain is still too high for composites,and it is hoped that this will be reduced.（2）APP was selected as the main body of the flame retardant system,four metal oxides（nickel oxide,iron oxide,zinc oxide,manganese oxide）were selected as the flame-retardant synergist,and sodium alginate（SA）aqueous solution was selected as the dispersant of the metal oxides.The flame-retardant RF was prepared by dip-pad-bake method on the basis of a controlled weight gain of about 15%,and was named as RF-a APP-MO,where MO was metal oxide.The flame-retardant composites were named as EP/RF-a APP-MO by hand lay-up method with m-XDA as curing agent.VFT,TGA,CCT,TG-FTIR and universal materials testing machine were used to investigate the flame retardancy,thermal stability,burning behavior,flame retardant mechanism and mechanical properties of RF-a APP-MO.VFT,LOI,TGA,CCT,TG-FTIR,universal material testing machine,impact tester and DMA were used to investigate the flame retardancy,thermal stability,burning behavior,flame retardant mechanism,mechanical properties and thermo-mechanical properties of EP/RF-a APP-MO.The results of the fabrics showed that the introduction of MO did not further improve the flame retardancy of the flame-retardant fabrics at the same weight gain rate,however,the thermal stability in the high temperature range under air conditions was improved.The results of TG-FTIR analysis showed that the flame retardant mechanism of RF-a APP-MO was the same as that of RF-APP,both reducing the formation of flammable volatiles to impart flame retardancy to the fabric.In terms of tensile properties,the presence of MO reduces the tensile strength of the fabric in the warp direction and increases the tensile strength in the weft direction,but in general the mechanical properties were still guaranteed.The introduction of MO improved the flame retardancy of the flame-retardant composite at a reduced weight gain rate,from UL-94 V-1 rating to UL-94 V-0 rating,but had little effect on the thermal stability.TG-FTIR showed that MO did not affect the flame retardant mechanism of the flame-retardant composites and that the flame retardancy was still achieved by significantly reducing the amount of gas phase products generated.In terms of mechanical properties,DMA results showed that the presence of MO and SA did not affect the movement of the EP chain segments,however,as the polarity of SA was similar to that of EP,the compatibility of the composites was improved.Some of the mechanical properties of EP/RF-APP-MO were slightly improved and the impact strength was significantly increased.In conclusion,the presence of MO had little effect on flame-retardant fabrics,while the flame retardancy and mechanical properties of flame-retardant composites can still be marginally improved even if the weight gain rate of the flame retardant system was reduced.Among the four specific MOs,ZnO showed the most outstanding effect,followed by Fe₂O₃ and MnO,while the effect of NiO was not so satisfactory.