Preparation And Characterization Of Vinyl Ester Resin Emulsion Type Sizing Agent For Carbon Fiber

Through phase inversion emulsification method emulsion type vinyl ester resin sizingagent (VESA) for carbon fiber was prepared by using vinyl ester resin (VE) and epoxyterminated butadiene-acrylonitrile oligomer (ETBN). Effects of emulsifiers, emulsificationtemperature, shear rate and dripping speed of water on properties of emulsion wereinvestigated by centrifuge, laser particle size analyzer, electrophoresis apparatus, rotationalviscometer and interfacial tension meter. Results showed that the optimal emulsion wasobtained when the mass ratio of polyoxyethylene nonylphenol phosphoric ammonium(NP-10A) and polyoxyethylene castor oil (EL-40) was3:1, mass ratio of emulsifiers was10%,weight ratio of VE and ETBN was60:40, emulsification temperature was50℃, shear ratewas10000r/min and dripping speed of water was2ml/min before phase inversion and7ml/min after that. The average particle size of the emulsion was0.068μm. The sedimentweight fraction and viscosity were8.67%and13mPa·s, respectively. Zeta potential andsurface tension of the emulsion were53.24mV and32mN·m-1, respectively. Fourier transforminfrared spectroscopy and gel permeation chromatography were used to represent themolecule structure and molecule weight of sizing agents, which indicated that Japanese sizingagent SA-1and Chinese sizing agent SA-2were both epoxy resin emulsion type sizing agents.Compared with SA-1and SA-2, the performance of VESA was better than SA-2and as goodas SA-1.The desized T700SC carbon fibers were sized with three sizing agents SA-1, SA-2andVESA. Wearable instrument, contact angle analyzer and universal testing machine were usedto characterize the effects of the sizing agent on carbon fiber and carbon fiber reinforced vinylester resin composites. Carbon fibers with1.5%sizing percentage were of proper surfacebrightness, collection property, smoothness and cross-linking property. The fluffs andbreakage of sized carbon fibers were greatly reduced and wear resistance was significantlyimproved. VESA sized carbon fibers were of lower stiffness and better flexibility. The contactangle measurement results showed that the wettability of sized carbon fibers to matrix resinwas improved, which reflected by the increased surface energy and decreased contact angleagainst deionized water, diiodomethane and vinyl ester resin. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to represent theelement component and morphology of carbon fibers. The XPS results demonstrated that theproportion of oxygen to carbon of VESA sized carbon fibers increased, which indicatedsurface activity of carbon fiber improved. The SEM results indicated that the surface ofcarbon fibers became smooth and the longitudinal streaks became shallower due to streaksand flaws filled with sizing agents during sizing process.Interlaminar shear strength (ILSS) tests demonstrated ILSS of sized CF/VE compositeincreased, compared to desized carbon fiber/vinyl ester resin (CF/VE) composite with ILSSof38.09MPa. ILSS of VESA sized CF/VE composite reached the maximum value of45.96MPa, increasing by20.7%. This result may be attributed to the good compatibility ofVESA sizing agent and vinyl ester resin matrix. SEM images of the fracture surfaces ofdesized CF/VE composite indicated that many carbon fibers were pulled out from vinyl esterresin matrix and the surfaces of fibers were smooth, which illustrated the weak layers in thefiber/resin interface region. While the largest amount of resin matrix was covered on thesurface of VESA sized carbon fibers, which indicated the strongest interfacial adhesion. Thewater absorption of CF/VE composite decreased, compared with desized CF/VE composite.The water absorption of VESA sized CF/VE composite was0.73%.