Study On Surface Modification Of Aramid Pulp And Properties Of Composite Materials

Aramid pulp（AP）with high strength,high modulus,excellent thermal stabilityand good friction behavior,is used in a wide range of applications,such as brakes,hoses,seals,sealants,adhesives,coatings,and filters.However,AP has high surface area because of its highly fibrillated fibrils,it is easy to be agglomerated,which limiting the application of this material.In this paper,the process of sol-gel and supercritical CO₂（Sc CO₂）were used to synthesize the SiO₂on the surface of aramid pulp to improve its distribution in the matrix.The effect of the TEOS（Tetraethyl orthosilicate）concentration,reaction temperature,reaction time on aramid pulp surface and properties of AP/Epoxy composites using sol-gel modification was investigated.The SiO₂ nanoparticles were successfully prepared on the aramid pulp surface from the results of the FTIR and XPS.And the thermal stability of the aramid pulp modified by SiO₂ was improved from results of TGA.Comparing to the pure epoxy,the tensile strength,tensile modulus of the modified SiO₂-AP/Epoxy composites were increased by 53.5%and 162.3%,and the elongation at break was decreased slightly.The flexural strength and flexural modulus were increased by 25.8%and 71.0%,respectively.Therefore,the optimum reaction conditions are that TEOS concentration is0.15 mol/L,reaction temperature is 90℃,reaction time is 4 h,and the content of aramid pulp is 0.5 phr.DMA results showed that the storage modulus of the composite was basically unchanged after aramid pulp modify by SiO₂,but the glass transition temperature was falled,and the loss factor was increased slightly,indicating that the toughness of the composite is increased,which is accdrding with the result of flexural strength.To improve the distribution of the AP in the matrix,SiO₂ was prepared on the surface of aramid pulp in Sc CO₂ modify.The influence of the temperature,pressure and reacton time of Sc CO₂ treatment on the surface morphology and the mechanical properties of AP/EPDM composites were studied.The optimum experimental conditions are:the temperature,pressure,time of supercritical reaction is 100℃,15 MPa and 3 h respectively,the content of aramid pulp is 10 phr.The fracture surfaces of AP/EPDM composites showed that dispersion of Sc CO₂-SiO₂-AP and interfacial bonding of AP and EPDM had improved.The mechanical properties,oil resistance and dynamic mechanical properties of the AP/EPDM were investgated.The tensile strength and tear strength of the Sc CO₂-SiO₂-AP/EPDM were increased by 121.1%and 134.9%respectively,while the elongation at break was decreased greatly than pure EPDM.The DMA results showed that the storage modulus of the composite was 56%higher than that of pure resin,and the loss factor is slightly decreased,which also verifies the above conclusion.Supercritical modification of AP also improves the oil resistance of the composites.ScCO₂-SiO₂-AP was further modified by silane coupling agent in Sc CO₂,which further improves the bonding strength between AP and EPDM.The result of SEM、XPS showed that the fiber surface further was modified by the silane coupling agent,we can be seen active epoxy groups were introduced on the surface of aramid pulp,which uusedful for improving the interfacial compatibility of aramid pulp and EPDM.Comparing to Sc CO₂-SiO₂-AP/EPDM,the tensile strength,tear strength and elongation at break of Sc CO₂-SiO₂-AP/EPDM composites in KH-560 were increased by 31.8%,43.1%and100.3%than ScCO₂ treatment AP/EPDM,respectly.