Surface Modification And Mechanism Of Thermotropic Liquid Crystal Polyarylate Fiber

Thermotropic liquid crystal polyarylate?TLCP?fiber has excellent mechanical properties and can be widely used as reinforcing materials for composites.However,TLCP fiber lacks reactive groups and has poor bonding with matrix,so that its excellent performance cannot be exerted in the composite material.In order to improve the interfacial adhesion between the TLCP fiber and the substrate,it is necessary to modify the surface of TLCP fibers.At present,the research on surface modification of TLCP fiber at home and abroad is still in its infancy,and the application of industrialization is progressing slowly.Therefore,it is of great practical significance and research value to modify the surface of TLCP fibers and to study its modification mechanism.In this paper,TLCP fibers were modified with DMAc/CaCl₂ system,2-phenoxyethanol system and NaOH/urea system,respectively.The samples before and after modification were characterized by FTIR,SEM and optical microscope.The results showed that the molecular structure of TLCP fibers remained unchanged after modification with DMAc/CaCl2,and a large number of longitudinal grooves were generated on the surface of TLCP fibers.Hydrogen bonds might be formed after modification with 2-phenoxyethanol,and the fibril structures arranged along the axis were found on the surface.The fibers were hydrolyzed locally after modification with NaOH/urea,and a large number of irregular pits appeared on the surface of the fibers.After modification with DMAc/CaCl2 and NaOH/urea,the breaking strength of the TLCP fibers decreased from 27.82 cN/dtex to 26.72 cN/dtex and 23.56cN/dtex,while 2-phenoxyethanol had no significant effect on the breaking properties of the fibers.The interfacial properties of TLCP fabrics were improved after modification.The peeling strength of fabrics modified with 2-phenoxyethanol increased from 0.47 N/mm to1.20 N/mm,which was more significant than that of DMAc/CaCl₂ and NaOH/urea systems.Therefore,2-phenoxyethanol was determined as the optimum modification system.Secondly,the mechanism of TLCP fiber modified by 2-phenoxyethanol was studied.The surface elements,crystalline structure,cross-sectional morphology and thermal properties of TLCP fibers after modification with 2-phenoxyethanol were analyzed by XPS,XRD,TEM,DSC and TG.The results showed that the content of O element on the surface of modified TLCP fibers increased from 14.38%to 18.22%.The crystallinity TLCP fibers decreased from69.0%to 66.6%.The surface of the fibers swelled moderately and the boundary thickness increased from 135 to 200 nm.The K/S value of TLCP fabrics dyed with disperse red AM-SLR increased from 0.55 to 2.31 after modification,which proved that 2-phenoxyethanol was effective in surface modification of TLCP fibers.The effect of controlling the surface structure of TLCP fibers was determined by colored macromolecule tracer method,which realized the macro-evaluation of the control effect of nano-structure of fibers.Finally,the TLCP fabric was modified via ultraviolet-induced grafting of acrylic acid.Moreover,ultraviolet modification was combined with DMAc/CaCl2,2-phenoxyethanol and NaOH/urea systems,respectively.Then the effects of these modification treatments on the interface properties of TLCP fabrics were compared and analyzed.The results showed that acrylic could be grafted onto the surface of TLCP fabric after ultraviolet modification.The content of-OH group on the surface of fibers increased significantly,and the content of O element increased from 14.38%to 21.90%.A large number of uneven pits appeared on the surface of fibers.After dyeing with cationic red FBL,the K/S value of ultraviolet modified fabrics increased from 0.32 to 4.66,which macroscopically proved that acrylic acid was grafted onto the surface of TLCP fabrics.The shear strength of TLCP fabric/polyurethane composites increased by 20%³0%,and the peeling strength increased by 17%compared with that before modification.In addition,In addition,the peeling strength of TLCP fabrics could be improved to a greater extent by combining DMAc/CaCl₂ system,ethylene glycol phenyl ether system and NaOH/urea system with ultraviolet modification respectively.In this paper,by coordinating the effect of polar molecule on the dynamic regulation of nano-scale surface macromolecular chains and polar small molecule grafting,the target control effect of the surface structure of fibers has been achieved,which provides basic theoretical research for the realization of industrial application.