Preparation And Performance Of Liquid Crystal Polyarylate Fiber/Unsaturated Polyester Resin Composite

Liquid crystal polyarylate(LCPAR)fiber is a high-performance fiber with excellent properties such as high strength and modulus,chemical and heat resistance.As a reinforcement of resin-based composite,it has broad applied in aerospace,military,sports and other fields.Unsaturated polyester resin(UPR)is one of the most widely used thermosetting resins with outstanding mechanical properties.The surface polarity and active groups of LCPAR fiber is poor,resulting in the low interfacial adhesion with the resin matrix,which makes its reinforcing effect in the composite unable to play fully.So it must be modified.Plasma modification can increase the surface roughness of the fiber and introduce active groups.The silane coupling agent can not only react with the hydroxyl groups on the fiber,but also form Si-O bonds with the resin.In this paper,we designed an orthogonal experiment of plasma-assisted graft modification of silane coupling agent to study the interface properties between LCPAR fiber and UPR before and after modification.Based on this,the liquid crystal polyarylate fiber/unsaturated polyester resin composite was prepared by heat-curing and UV-curing.The curing behavior and mechanical properties of UPR and its composite were systematically studied.At first,LCPAR fiber was modified by oxygen plasma and silane coupling agent G570individually.The plasma discharge power,discharge time and the concentration of silane coupling agent G570 were analyzed by contact angle and filament tensile strength.Based on the influence of the sexual effect,an appropriate level range was chosen to design an orthogonal experiment with three factors and three levels,and the LCPAR fiber was modified by plasma-assisted silane coupling agent G570.The interface shear strength between LCPAR fiber and UPR was used as an index to determine the best modification condition.The results show that when the discharge power of oxygen plasma is 250 W,the discharge time is 12 minutes and the concentration of silane coupling agent G570 is 45%,the effect of modification is the best.In this condition,the LCPAR fiber/unsaturated polyester resin interface shear strength is the highest,which is 16.0 MPa,compared with the unmodified LCPAR fiber/unsaturated polyester resin,the interfacial shear strength is increased by 73%.Compared with the LCPAR fiber modified by single factor,the fiber surface damage after plasma-assisted silane coupling agent modification is less obvious,and the fiber strength retention rate can reach 90%.The silane coupling agent G570 is more uniformly grafted on the surface of the LCPAR fiber,and the Si element content on the fiber surface rises to3.2%.The surface wettability of LCPAR fibers has also been greatly improved,and the contact angle has reduced from 93.2°to 45.9°.The heat-curing process of UPR and its composite was explored.The effects of heat-curing temperature,heat-curing time and heat initiator AIBN concentration on curing behavior and effect were studied.The cured gel rate and Barcol hardness were used to reflect the degree of curing,and the structure and performance of UPR and its composites were characterized by FTIR,TG and mechanical property tests.The results show that if the curing temperature is too low or too high,the cross-linking and curing of the unsaturated polyester would be incomplete,and the curing gel rate is about 90%when the temperature is 90?.When the AIBN content is 0.75%,there are excellent mechanical properties of the cured product,and its tensile strength and bending strength are equivalent to about 3.3 times than when the AIBN concentration is 0.25%.The comprehensive analysis of the curing degree and mechanical properties of UPR and its composite was carried out.It is confirmed that the heat-curing temperature of 90?,the thermal curing time of 3 h and the AIBN concentration of 0.75%as the best heat-curing process.In this condition,the curing gel rate can reach 99%and the Barcol hardness is about 11 HBa.The UV-curing process of UPR and its composite was discussed.The influence of light intensity,light irradiating time and photoinitiator TPO concentration on curing behavior and effect was considered.The results of DSC and cured gel rate show when the UV irradiating time exceeds30 s,the cross-linking and curing of UPR can be fully initiated,but if the irradiating time is too long,the mechanical properties of the cured product would decrease.The curing effect is better when the light intensity is 600 m W/cm~2,the curing gel rate can reach 99%,and the Barcol hardness is about 26 HBa.If the concentration of photoinitiator is too high,the mechanical properties of UPR and its composites would be affected.The TPO concentration is 0.75%,the mechanical properties performed best,but when it increases to 1.5%,the tensile strength and bending strength decrease by about 30%.Based on the comprehensive analysis of the UV-curing process,it is determined that the light intensity of 600 m W/cm~2,the light irradiating time of 90 s and the TPO concentration of 0.75%is the best UV-curing process.In addition,it is shown that not only the time of UV-curing is shorter,but the glass transition temperature of the cured product is increased by 18.2?.The tensile strength and bending strength of UPR and its composites by UV-curing are 1.6-2.6 times of those by heat-curing.In this paper,the best surface modification method of LCPAR fiber was obtained through orthogonal experiments.The greatest heat-curing and UV-curing schemes were concluded by comparing and analyzing the curing gel rate and mechanical properties of UPR and its composite.The paper provided a technological basis for preparing liquid crystal polyarylate fiber/unsaturated polyester resin composite.