Study On Preparation,Properties And Mechanisms Of Flame Retardant Modified Ramie Fabric-reinforced Unsaturated Polyester Resin

On the basis of research progress on flame retardant modification of unsaturated polyester resin?UPR?and ramie fiber,and considering potential severe fire risks of ramie/UPR composite,the research of my dissertation is to focus on the flame retardant modification of ramie/UPR composite.It takes two aspects to prepare halogen-free flame retardant ramie/UPR composite:on one hand,the addition of nanofillers or the phosphorous-containing flame retardant into UPR to reduce the fire hazard of composite.On the other hand,ramie fabrics are modified by sol-gel or layer-by-layer assembly technique.The flame retardant modified fabric can play a role of condense phase fire retardation to promote the char formation and reduce heat release rate of the whole composite due to the interface flame retardant effect.Besides,The thermal stability,pyrolysis and flame retandancy mechanisms of ramie/UPR composite have been intensively developed.The main research work is as follow:1.Multi-walled carbon nanotubes?MWCNTs?have been decorated with NiFe₂O₄ by chemical co-deposition method and the synthetized MWCNT@NiFe₂O₄ are incorporated into UPR and ramie/UPR composite to investigate the effect on the thermal stability,combustion behavior and mechanical properties.The test results indicate that NiFe₂O₄ decorating on the surface of MWCNT may act as barriers and wedges to improve the dispersion of MWCNT in the UPR matrix.The protective network structure of well-dispersed MWCNTs and the catalytic charring effect of NiFe₂O₄ nanoparticles will lead to the increased char residue and effectively decrease peak heat release rate?PHRR?by 69.49%.Meanwhile,the release of the combustible organic volatiles and toxic gases are also greatly reduced.In addition,MWCNT@NiFe₂O₄ also dramatically improve the storge modulus and glass transition temperature of UPR.Furthermore,the incorporation of MWCNT@NiFe₂O₄ also increases the thermal stability of ramie/UPR composite.The reduced PHRR value and organic volatiles indicates that MWCNT@NiFe₂O₄ endow the ramie/UPR composite with the improved flame retardancy.2.Flame-retarding ramie/UPR composites are fabricated by two ways,that is the addition of flame retardant into UPR and flame retardant modification on ramie fabric.Different kinds of phosphorus containing flame retardants are employed for preparing flame retardant ramie/UPR composite and the flame retardant mechanisms have been investigated.Firstly,each different contents of aluminum hypophosphite?AHP?,aluminum diethylphosphinate?ADP?and ammonium polyphosphate?APP?are added into UPR to enhance fire safety of ramie/UPR composite.Through comparison and analysis,APP20/UPR sample has the best excellent flame retardancy with a high limiting oxygen index?LOI?value of 38%and V-0 rating in UL-94.The results of tests indicate that hypophosphite salts can play a role in gas phase flame retardant to inhibit combustion in gas phase and also promote the pyrolysis for char formation in condense phase to a certain extent.APP play an condense phase flame retardation,explained by that poly phosphoric acid derived from the decomposition of APP at lower temperature can catalyze pyrolysis of the composite to promote the char formation.The condensed char layer will act as physical barrier to keep from the exchange of heat and air,and then prevent material from further burning.Secondly,ramie fabrics are modified by grafting the synthesized flame retardant,TMSAP,via sol-gel method.After TMSAP modification,the PHRR and total heat release?THR?of ramie/UPR composite are obviously decreased and LOI value is raised from 26%to 30.5%.However,it has no rating in UL-94.With the addition of 10 wt%APP into UPR matrix and the TMSAP-coated fabric as reinforcement,APP10/Coated/UPR successfully reach the UL-94 V-0 rating due to the compact and continuous char layer.3.Ramie fabrics are modified with biobased electrolytes by layer-by-layer?LbL?assembly method,using chitosan?CH?and melamine?ME?as cationic electrolyte and phytic acid?PA?as anionic electrolyte.The effect of LbL-modified ramie fabrics as reinforcement on the thermal stability,flame retardancy,combustion and mechanical behavior of ramie/UPR composite are discussed.The PHRR and THR of ramie/UPR composite are greatly reduced with the LOI value of 34.5%.From TG-IR and char residue of scanning electron microscopy tests,CH/ME and PA on ramie can catalyze decomposing ramie/UPR composite in advance and the compact char residues will benefit for suppress the combustible organic volatiles during thermal decomposition process.However,the tensile and flexural strength of LbL-modified ramie fabric-reinforced UPR composite are reduced,owing to the hydrolysis of linkages between cellulose and hemicellulose and the slightly decrement for cross-linking density of UPR by PA.The excess PA chelated with Fe³⁺ can maintain a certain mechanical performance.