| With the wide application of carbon fiber composite materials,the recycling of their waste has become an increasingly hot research topic.Carbon fiber has secondary utilization value after reasonable recycling process,such as in injection molding for short fiber reinforced thermoplastic composite materials.However,the recycled carbon fibers are damaged at some degree.Therefore,at current study the improving the fiber-resin interface was focused in order to improve the performance of the composite material.This research is divided into two parts.In the first part,the research objects include recycled carbon fiber(RCF)prepared by thermal cracking,chopped recycled carbon fiber(SRCF)obtained by cutting process,and chopped recycled carbon fiber reinforced PP composite material(SRCF/PP)molded by injection molding process.The sizing method of SRCF was optimized through experiments,and its mechanical properties were compared with virgin carbon fiber.In addition,the effect of a sizing agent and MAPP additives on the mechanical properties of SRCF/PP was investigated based on tensile,three-point bending and cantilever impact tests.On the other hand,in the second part,in order to optimize the injection molding process of recycled carbon fiber in the future,Moldex3 D software was used to simulate the effect of fiber mass fraction on the fiber orientation,distribution and residual fiber length,distribution of short fiber reinforced composites.In addition,the simulation results are discussed under the comparison with experimental results.The following conclusions are obtained from the first part: 1)The funnel dipping method is found suitable for short fiber sizing.This method can control the sizing ratio by adjusting the immersion time,and it is considered helpful for continuous batch sizing.Regarding to the different size agents,it is found that Xc/Xy and Hc/He slurry show better well-distributed effect on SRCF surface than FY slurry.In addition,the results of infrared spectroscopy showed that new active groups were added to the fiber surface after sizing,which is considered helpful to improve the bond between the fiber and the resin.2)RCF tensile strength is reduced by 24.6% compared with virgin T300,and tensile modulus is reduced by 17.4%.It is observed that there are a large number of grooves on the RCF surface,which is the main reason for the decrease of the RCF tensile strength.3)After different treatments,the tensile strength and modulus of SRCF/PP increased by 44%-72%,16%-27%,and the bending strength and modulus increased by 35%-68%,13%-18%,The range of notched impact strength is the largest,increasing by 59%-182%.The bond between the fiber and the resin is significantly improved after treatment,in details,the bonding between the fiber resin is tighter,the hole in the fracture surface is significantly reduced,the number of quenched fibers is increased,and the surface of the fiber is coated with a large amount of resin.From the second part,the following conclusions are drawn: 1)The distribution of fiber orientation in the cross section of the rectangular plate has a "sandwich" structure,and the surface fiber orientation is more oriented in the injection direction than the core layer.2)When the fiber mass fraction is 25%,35%,and 50%,showing that the fiber orientation slightly increases with the increase of the mass fraction.3)When the fiber length-diameter ratio is 20,35,the change in fiber mass fraction has little effect on the remaining average fiber length;when the fiber length-diameter ratio arranged from 50 to 90,with the fiber content increasing from 25% to 35% or from 35% to50%,the remaining length of the fiber showed a decreasing trend.In details,when the lengthdiameter ratio is 50,it decreases by 29% and 8.7%,and when the ratio is 71,it decreases by 25.4%and 5.6%,respectively.In addition,by comparing the simulation results with the experimental results in the literature,the trend of the effect of fiber mass fraction on the fiber orientation and fiber length remains consistent. |
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