Interfacial Properties And Sizing Agent Study Of Sulfur For Carbon Fiber Reinforced Poly(Polyphenylene Sulfide) Composites

Carbon fiber(CF)reinforced thermoplastic composites have received much attention for their short molding cycle,high toughness,high recyclability and their unique welded connections.Among them,carbon fiber(CF)reinforced poly(polyphenylene sulfide)(PPS)composites are widely used in the aerospace,marine and automotive industries for their excellent high temperature resistance,corrosion resistance and superior mechanical strength.However,unlike the typical thermosetting epoxy resin,PPS processing temperature is high,the general commercial epoxy sizing agent is difficult to tolerate,thus prone to decomposition and resulting in interface failure.In addition,the interaction force between CF surface and PPS resin molecular chain is weak and the reactivity is low,which cannot achieve a good interfacial effect between fiber and resin,thus affecting the overall mechanical properties of the composite.In order to explore an effective and industrializing method to improve the interface strength of carbon fiber reinforced polyphenylene sulfide(PPS)composites,the effects of sulfur treatment of carbon fiber surface on the interface strength of PPS resin were studied according to the characteristics of carbon fiber and PPS resin.Firstly,the molding temperature and pressure conditions of carbon fiber-reinforced PPS composites were determined by thermal analysis of PPS resins.Then,the surface impregnation and heat treatment of carbon fiber were performed by emulsion prepared with different concentrations of sulfur.The effects of sulfur modification on the surface of carbon fiber and the interface properties of carbon fiber reinforced polyphenylene sulfide composites(CF/PPS)were compared and analyzed by means of interlaminar shear strength test,scanning electron microscopy and X-ray photoelectron spectroscopy Then,the sulfur and watersoluble monomers were prepared into an emulsion sizing agent,and the effect of the sizing agent on the interfacial enhancement and on the processable properties of carbon fibers was analyzed by relevant testing means.The obtained research results are as follows:(1)The DSC and TGA results showed that the PPS melting point was 285°C and the decomposition temperature was 430°C.Combined with previous studies and many trial production,the pressing temperature of CF/PPS unidirectional fiber composite sheet was determined to be310°C and the molding pressure is 0.75-1.0-2.0 MPa in three stages.At this time,the ILSS of untreated CF/PPS composites is 58.56 MPa.After sulfur treatment of CF,the oxygen-to-carbon ratio on the fiber surface was increased and the grooves on the surface of CF were extended,the monofilament strength did not change significantly.The interfacial effect of CF/PPS composites was improved after sulfur treatment,and the ILSS was up to 79.7 MPa at a sulfur concentration of0.05 wt.%,which was 36.1% higher than that of untreated carbon fibers.However,when the sulfur concentration is too high,the residual sulfur will react with the PPS resin,reducing its fluidity and affecting the resin’s wettability to the fiber,resulting in a decrease in the interlaminar shear strength;when the sulfur concentration is low,the etching effect on the fiber surface is small,and the interlaminar shear strength is correspondingly low because the sulfonic acid functional groups generated by the reaction of sulfur-containing functional groups are not conducive to interfacial bonding.(2)Sulfur-containing sizing agent emulsions were produced by blending sulfur as the active components with PEG 600 and phthalic anhydride.Compared with pure sulfur emulsion,the stability of the sizing agent was improved by the dispersing effect of PEG 600.In addition,the workability of the carbon fiber bundles is improved,the amount of filaments is significantly reduced compared with the untreated carbon fiber,and the overhang is reduced from 90% to 20% of the untreated carbon fiber,indicating that the polymer generated by the water-based monomer plays a bunching role.After the CF surface was sized by sizing agent,the grooves on the fiber surface were uniformly covered,and the oxygen-containing functional groups on the fiber surface increased significantly,and the oxygen-carbon ratio increased with the increase of sulfur content.Regarding the interfacial properties of the composite,the ILSS of the CF/PPS composite reached a maximum of 69.67 MPa after the CFs were treated with a sizing agent emulsion with a sulfur content of 0.05 wt.%,which was 19% higher than that of the unsized carbon fibers and 25.8% higher than that of the carbon fibers treated with the sizing agent without sulfur.However,when the sulfur content was increased,the sulfur-containing functional groups generated by the reaction of sulfur in carbon fibers would interact with the sizing agent layer,and the interlaminar shear strength began to decrease.In summary,the appropriate amount of sulfur treatment of carbon fibers is beneficial to the interfacial bonding between CF and PPS resin,and by blending sulfur into sizing agent,it is expected to replace the anodizing and sizing method,thus reducing the manufacturing cost of special carbon fiber.