Preparation And Properties Of Polyester Sizing Agent For Carbon Fiber

Carbon fiber reinforced unsaturated polyester resin?CF/UPR?composites have been widely used in rail transit,wind power generation,construction materials,and septic tank owing to their many outstanding advantages including lightweight,excellent thermostability,and high specific strength.At present,however,most domestic carbon fibers generally use epoxy resin sizing agent to sizing carbon fibers.Due to the different curing mechanism,effective cross-linking between the sized carbon fiber and the unsaturated polyester resin cannot be formed,which makes the interface bonding strength of CF/UPR composite is poor.Therefore,a novel polyester carbon fiber sizing agent is prepared to improve the interface bonding ability of CF/UPR composite.Firstly,carboxyl-terminated linear unsaturated polyester was synthesized through polycondensation,subsequently,epoxy resin and catalyst were added to synthesize polyhydroxy linear unsaturated polyester.Next,methyl tetrahydrophthalic anhydride was added which aims to introduce a hydrophilic carboxyl group into the molecular chain.Finally,triethylamine and deionized water were added to neutralize the carboxyl group and a polyester carbon fiber sizing agent can be prepared.The influence of different chain structure of the sizing agent was analyzed.The test results showed that the sizing agent synthesized by adipic acid,neopentyl glycol,and maleic anhydride was the most stable.At this time,the particle size of the emulsion was about 152 nm,the particle size distribution PDI was 0.157,the Zeta potential is-52.88mV and the surface tension were 33.1 mN/m.In addition,ethyl orthosilicate?TEOS?was added into the molecular chain of carboxylic,and TEOS was hydrolyzed in the presence of the carboxyl group,which nano-SiO₂ reinforced polyester sizing agent was synthesized.The effect of TEOS content on sizing agent performance was studied,and results showed that when the TEOS content was 5 wt.%,the sizing agent emulsion has good stability.The synthetic sizing agent was diluted and the carbon fiber was sized with it.The surface morphology,element analysis,and surface energy of carbon fiber before and after sizing were measured by SEM,EDS,and video dynamic contact angle meter.The results showed that after sizing,the surface groove of carbon fiber was filled effectively,and the content of the element of O on carbon fiber was increased significantly,besides the content of the element of Si on the surface of carbon fiber was also increased after sizing with the nano-SiO₂ reinforced polyester sizing agent.Through SEM,it can be observed that SiO₂ protrusions on the surface of carbon fibers.The interlaminar shear strength?ILSS?of unidirectional CF/UPR composite was tested by a universal tensile testing machine.The results showed that the ILSS of the sizing agent CF/UPR composite with adipic acid,neopentyl glycol,and maleic anhydride was the highest,which was 42%higher than that of the epoxy resin sizing agent.When the TEOS addition amount was 5 wt.%,the ILSS of the CF/UPR composite was the highest,which was 91%higher than that of the CF/UPR composite which CF sized by commercially epoxy resin sizing agent.