Study On Thermal Oxygen Aging And Flame Retardancy Of Para-aramid/Polyphenylene Sulfide Composite Paper

Para-aramid paper is a kind of advanced material with excellent performance which has the advantages of high strength and high modulus,high breakdown strength,acid and alkali resistance,good thermal stability and so on,and it has been widely used in aerospace,high-temperature filtration,insulation materials,auto parts and other fields.At present,aramid chopped fibers(ACFs)and fibrid or pulp fiber are through the wet papermaking process and hot pressing.Using polyphenylene sulfide(PPS)melt-blown ultrafine fiber pulp as a binder to produce ACFs/PPS composite paper through wet papermaking technology has attracted great interest.This kind of composite paper has the advantages of high mechanical strength,good stiffness,hydrophobic,high flame retardant,etc.At the same time,the preparation process is relatively simplified and the cost can be significantly reduced.The application environment of ACFs/PPS composite paper is harsh,and long-term high temperatures can cause material aging and safety hazards.Therefore,the application conditions need to be systematically verified.Studying the thermal oxidation aging mechanism of ACFs/PPS composite paper,as well as the physical and chemical structure changes of para-aramid and polyphenylene sulfide during thermal oxidation aging,is of great significance for guiding the actual use of ACFs/PPS composite paper.In addition,polyphenylene sulfide and aramid fibers have a synergistic flame-retardant effect.Studying the flame-retardant properties of ACFs/PPS composite paper and understanding its flame-retardant mechanism is necessary.This project mainly explores the thermal-oxidative aging properties of polyphenylene sulfide and aramid fiber composite paper,as well as the flame-retardant properties of polyphenylene sulfide and aramid fibers.The specific content is as follows:(1)Study on thermal and oxygen aging characteristics and mechanism of ACFs/PPS composite paper.The ACFs/PPS composite paper was prepared uniformly by modern wet papermaking and rolling process.The mass ratio of ACFs/PPS was 7:3 and the gram weight of the composite paper was 120 g/m~2.The prepared composite paper is pretreated to eliminate the influence of thermal history,and then subjected to heat treatment at different temperatures(150℃,180℃,200℃,230℃)for different times(up to 720 h)to investigate the effects of thermal-oxidative aging time and temperature on the mechanical properties,microstructure,apparent color,and molecular structural changes of the composite paper,and to explore the thermal-oxidative aging mechanism of the composite paper.The retention rates of mechanical strength of the composite paper after thermal-oxidative aging were determined under different temperatures and durations to provide reliable data support for the practical use of the composite paper.The experimental results showed that the color of the composite paper deepened with increasing aging temperature and time,and aramid fibers and PPS underwent oxidation during thermal-oxidative aging,producing chromophores and auxochromes.There was a correlation between the color difference of the composite paper and the retention rates of tensile strength,elongation at break,and tear strength,and a correlation model was derived to predict the aging behavior of the composite paper based on color difference.When the thermal oxygen aging temperature is 230℃ for 720 h,the retention rates of tensile strength,elongation at break,and tear strength of the composite paper were 60.68%,43.65%,and 1.46%,respectively.The study of the fracture behavior of the aged composite paper found that the aramid fiber fracture mechanism changed from fiber splitting to fiber breakage,and the interface between fiber and resin cracks with the aging time and temperature increase.(2)Study on flame-retardant properties and mechanism of ACFs/PPS composite paper.The combustion experiment of ACFs/PPS composite paper with different ratio and gram weight of 120 g/m~2was conducted to study the effect of the ratio of ACFs and PPS on the flame retardant property of the composite paper.The thermal stability and flame retardant mechanism of the composite paper were investigated by infrared(FT-IR),thermogravimetric analysis(TG),X-ray photoelectron spectroscopy(XPS),scanning electron microscopy(SEM),micro calorimetry(MCC)and Raman spectroscopy.The results show that the ACFs/PPS composite paper has good thermal stability,PPS improves the carbon formation rate of aramid paper,and the carbon residue of the composite paper increases with the increase of PPS content.The combustion experiments show that the carbon residue of ACFs/PPS 70composite paper can withstand the weight of 50 g,which indicates that the carbon residue has mechanical properties.The vertical combustion results show that ACFs/PPS composite paper has a shorter carbonization length.The MCC results show that the ACFs/PPS composite paper has a smaller total heat release than neat aramid paper.SEM results show that ACFs/PPS composite paper forms a core-shell structure after combustion,which PPS form a continuous carbon structure to protect the aramid fiber,so that the carbon structure is complete.Raman results show that the graphitization degree of carbon residue of ACFs/PPS composite paper is higher than that of neat aramid paper.