Preparation And Properties Of Continuous Glass Fiber Reinforced Polyolefin Composites

Continuous fiber reinforced thermoplastic composites(CFRTP)have been widely used in aerospace,construction,automotive and other fields due to the advantages of high strength,strong design,good chemical resistance,and environmental protection,etc.With the further expansion of the application field,the market's demand for CFRTP has also grown rapidly.In this paper,continuous glass fiber-reinforced polyolefin prepreg tapes were prepared by melting-impregnation method,and composite laminates were prepared by compression molding and roll forming.The best molding process was determined by studying the effects of temperature,traction speed,different molds,number of layers,and fiber arrangement angles on the mechanical properties and structure of the composites,the dynamic mechanical properties and non-isothermal crystallization kinetics of polyethylene(PE)and GF/PE composites were studied.In view of the weak interlaminar mechanical properties,the impact response and damage mechanisms of polypropylene(PP)and GF/PP(GF/PP)composites by drop hammer impact were further investigated.It provides performance parameters and theoretical guidance for the research and production of composite materials.The main research contents of the dissertation are as follows:(1)The tensile strength of GF/PE prepreg tapes firstly increased and then decreased with the increase of mold temperature.The impregnation effect and mechanical properties of the GF/PE prepreg tapes were best when the traction speed was 10r/min and the mold temperature was 240°C.When the fiber content is 40%,the tensile strengths of GF/PP prepreg tapes and GF/PE prepreg tapes are 491 MPa and 435 MPa,respectively.Through the SEM image,the interfacial bonding effect of GF/PP prepreg tape is better than GF/PE prepreg tape.When the mold temperature is 200°C,the GF/PE composite laminates have the best mechanical properties,tensile strength and flexible strength are 336 MPa and 286 MPa,respectively.The porosity and mechanical properties of the composites prepared by the mold(a)are better than those of the composites prepared by the mold(b);with the increase of the number of prepreg tape layers,the mechanical properties of the composite laminates decrease due to the weakening of interlaminar shear strength;with the increase of the angle of fiber arrangement,the component of the fiber in the force direction is getting larger and larger,which improves the mechanical properties of the composite laminates.The mechanical properties and impregnation effect of the composite laminates were best when the mold temperature was 230°C and the pulling speed was 2r/min.(2)Dynamic mechanical analysis(DMA)was used to study the effect of fiber content and fiber length on GF/PE composites.The results show that the storage modulus of GF/PE composites gradually decreases with increasing temperature,and the effect of fibers on the storage modulus at high temperatures is more pronounced.The storage modulus of GF/PE composites gradually increased with the increase of fiber content.The ? relaxation peak shifts to high temperature and the ? relaxation peak shifts to low temperature.As the fiber content increases,the loss factor decreases.The mechanical properties and storage modulus of continuous fiber-reinforced composites are significantly better than those of long fibers.The storage modulus and loss factor of the 5mm and 50 mm long fiber reinforced composites are almost the same,indicating that the 5mm and 50 mm long fiber reinforced composites have similar resistance to external force deformation.(3)The non-isothermal crystallization and melting behavior of pure PE and GF/PE composites were analyzed by differential scanning calorimetry(DSC).The crystallization curves of pure PE and GF/PE composites were analyzed.It was found that with the increase of cooling rate,crystalline peak broadened,the crystallization peak and the crystallization starting temperature shift to low temperature.The heterogeneous nucleation of fibers improved the initial crystallization temperature and crystallization peak temperature of the GF/PE composites,but the crystallization enthalpy decreased.The melting curves of pure PE and GF/PE composites were analyzed.It was found that the cooling rate and fiber addition have little effect on the melting temperature and melting peak temperature of pure PE and GF/PE composites.Non-isothermal crystallization kinetics of PE and GF/PE composites were simulated by using Ozawa and Mo equations.The Mo method was suitable for describing the non-isothermal crystallization kinetics.(4)Instron 9250 HV drop hammer was used to perform low-velocity impact tests on PP and GF/PP composites,the effects of impact energy,width of weaving prepreg tapes,angle of fiber arrangement,and number of prepreg tape layers on impact history and damage were investigated.The results show that the addition of fibers improves the carrying capacity of GF/PP composites and reduces the damage area.With the increase of impact energy,the peak load gradually increase,and the damage pattern of the specimens change from matrix cracking and debonding to delamination and fiber breakage,etc.Knitted prepreg tape width has little effect on impact load and energy absorption of GF/PP composites.Due to the uniformity of the load distribution,[-45o/45o] sample's carrying capacity is obviously better than that of [-30o/30o],[-60o/60o] Specimens.With the same impact energy,the peak load gradually increases with the increase of the number of layers,and the damage area gradually decreases,indicating that the material's rigidity and bearing capacity increase.The critical value of thickness of the "damage mechanism" changing is at the 6~8 layers under the 10 J impact energy.