Preparation Of Comb-like Copolymer Grafted Carbon Fiber Multi-scale Reinforcement And Its Composite Properties

Carbon fiber reinforced polymer composites (CFRP) have many advantages, suchas high strength, high modulus, low density, devisable and good dimensional stability.Therefore, they have been widely used in aerospace, military industry, sports equipmentand building materials fields. However, bonding interface between carbon fibers andmatrix materials has many defects because carbon fibers surfaces are large inertia andless reactive functional groups. It severely limites the overall applications of CFRPperformance. In this paper, the multi-scale reinforcement was prepared by graftingcomb-like copolymers onto carbon fibers surface, which could significantly improve themechanical and interfacial properties of CFRP. The main research content is as follows:Firstly, the chain transfer agents, S-1-dodecyl-S′-(,′-dimethyl-′′-aceticacid)trithiocarbonate(DDACT), were synthesized and grafted onto the carbon fibers surfaces via couplingagents. Poly(chloride methyl styrene)(PCMS) was then grafted onto the carbon fiberssurfaces via the reversible addition-fragmentation chain transfer polymerization (RAFT).The infrared spectrum, hermal gravimetric analysis, X-ray photoelectron spectroscopyand nuclear magnetic analysis results showed that PCMS were grafted onto the carbonfibers surfaces successfully, and the grafting ratio of PCMS was8.75%. The scanningelectron microscopy results indicated that PCMS were distributed on the carbon fiberssurfaces in the form of fringed shape.Secondly, the PCMS grafted onto carbon fibers surfaces were used as themacromolecular initiator, the poly(glycidyl methacrylate)(PGMA) was grafted ontoPCMS main chain of carbon fibers surfaces via the atom transfer radical polymerization(ATRP). The multi-scale reinforcement was prepared by comb-like copolymers（P(CMS-g-GMA)）grafted carbon fibers. The infrared spectrum, thermal gravimetricanalysis, X-ray photoelectron spectroscopy and nuclear magnetic analysis resultsindicated that P(CMS-g-GMA) were grafted onto the carbon fibers surfacessuccessfully, and the grafting ratio of（P(CMS-g-GMA)）was10.75%. The surface freeenergy test results showed that the polar components of carbon fibers surfaces graftedwith PCMS and P(CMS-g-GMA) were increased, compared with the raw carbon fibers.The multi-scale reinforcement surface free energy was improved by22.08%. The scanning electron microscopy results indicated that the comb-like copolymers wereevenly distributed on carbon fibers surfaces.Finally, the multi-scale reinforcement reinforced epoxy resin composites wereprepared by using hot pressing molding process. And the effect of P(CMS-g-GMA) onthe mechanical properties of composites was studied. The results showed that themonofilament tensile strength and multifilament tensile strength of the multi-scalereinforcement were increased by18.53%and46.95%, respectively, compared to theraw carbon fibers. The interlaminar shear strength (ILSS) and bending strength of themulti-scale reinforcement composites were increased by84.99%and78.12%,respectively, compared to the raw carbon fibers composites. Furthermore, the effect ofP(CMS-g-GMA) on the interfacial properties of monofilament resin droplets compositeswas studied via droplets debonding method. The results indicated that the interface shearstrength (IFSS) of composites prepared by P(CMS-g-GMA) grafting onto carbon fiberswas improved by143.62%compared to the raw carbon fibers composites. The scanningelectron microscopy of composites fracture morphology results showed that themulti-scale reinforcement composites occurring shear failure were ductile fracture, andcarbon fibers rarely pulled out from the resin matrix. This indicated that the interfacebetween carbon fibers and resin matrix had good bonding performance. In a word, thereasons that interfacial properties of the multi-scale reinforcement composites wereimproved are due to:(1) the grafting P(CMS-g-GMA) improved the infiltratingperformance between carbon fibers and resin. At the same time, a large number ofreactive functional groups of comb-like copolymers could participate in the curingreaction of resin, which formed chemical bonding between carbon fibers and resin.(2)P(CMS-g-GMA) made carbon fibers surfaces possessing the multi-scale branchedstructure, increased the specific surface area of carbon fibers, and improved the van derWaals force and mechanical joggling force combined with resin.