Effect Of Sizing Agent On The Mechanical Properties Of Carbon Fiber/Polypropylene Composites Moled By Direct-Fiber Feeding Injection Molding

Carbon fiber thermoplastic composites are widely used in the automotive industry.The interface between carbon fiber and matrix is still a hot topic worth exploring.This paper selects high-performance carbon fiber to reinforce polypropylene composite materials,of which carbon fiber comes from three famous companies at home and abroad named as J company,D company and Z company.The carbon fibers are treated by hot water to desize the original sizing on the surface of carbon fibers.The original carbon fiber and the treated carbon fiber are respectively molded into 20wt% CFRP in all 6 types through DFFIM process with PP pellets.By measuring the tensile properties at different temperatures and speeds,and observing the cross-section morphology of tensile fracture by scanning electron microscopy,the effect of desizing process on the interface property between carbon fiber by and PP.Carbon fiber suppliers,tensile speed and temperature gradient on the tensile properties were also discussed.Then the bending properties by three-point bending test and impact performance with cantilever notch of carbon fiber composites were evaluated.The applicability of time-temperature equivalence principle to the mechanical test was discussed..Finally,the fatigue life of the tensile strength of the material under the mechanical test and the rate of decline of the storage modulus were simulated.The rough conclusions were drawn as followings: 1.For tensile strength of carbon fiber reinforced PP composites by DFFIM process,the ranking is Z company,D company,J company in the order.Carbon fiber composite material of Z company tensile strength is about 20% higher than that the lowest one i.e.J company’s.The strength of carbon fiber composites after desizing by hot water increased about 10% for most of the specimens.2.For Young’s modulus,the D company’s are similar as J company’s while better than Z company’s.D company and J company Young’s modulus both consistently are 3.5 GPa,far higher than that of Z company(2.5GPa).3.For tensile strength fatigue life after simulating of Carbon fiber reinforced PP composite,the ranking is D company,Z company,J company in the order.The fatigue life of tensile strength about original carbon fiber composite material from D company is nearly 24 years.The tensile fatigue life of specimens after desizing decreases,indicating that the original sizing agent has good adhension with PP resin.4.Due to the inconsistent initial modulus of different types of carbon fiber composites,time comsumption of the storage modulus which is reduced to 60% of the initial one was used as a standard.The time consumption ranking is D company,J company,Z company in order.In detailed,for D company’s,the time is twice than that of other companies when the modulus reduced by 40%.Therefore,the stiffness of D company’s modulus changes more slowly and the service life of the material is longer than the other two companies.5.It can be seen from the SEM electron micrograph that large amount of slurry are existing the surface of primitive carbon fiber,which affects the uniform distribution of carbon fiber in the matrix.The gap between carbon fiber and PP matrix is too large.And carbon fiber is easy to be pulled out structure which lead to the reduce of the mechanics performance.After dehydrating by hot water,the sizing on the surface of carbon fiber was washed out even there is still a small amount remained.And the fluidity of the carbon fiber is enhanced and uniformly distributed in the PP matrix,and the gap between the carbon fiber and the PP matrix is also reduced,which is greatly improve the mechanical properties.6.Bending strength of carbon fiber reinforced PP composite material by long-fiber direct injection molding ranking is as “D company>J company>Z company”.Specifically,D company’s is 12.6% higher than J company’s and 16.8% higher than Z company’s.And impact strength ranking is as “Z company>D company>J company”.Specifically,Z company’s is 69% higher than D company’s and 114% higher than J company’s.7.Overall,J company’s carbon fiber quality is not good and sizing agent for PP matrix might not match.D company carbon fiber quality is good and sizing agent seems compatible with thermoplastic resin matrix.Z company carbon fiber quality is good while sizing agent and thermoplastic resin matrix may not match.The comprehensive mechanical properties of D company are outstanding.The desizing process by hot water is obviously helpfulfor the material system with lower mechanical properties such as J、Z company.It shows that the original sizing of company D has considerable compatibility with PP,which can effectively improve the interface bonding performance,while the original sizing of Z and J company needs to be improved.