Preparation And Properties Of Bidirectional Warp Knitted Glass Fiber/Nylon 6 Composites

The braided fiber-reinforced thermoplastic composites present high strength,high stiffness,short molding cycle,and recyclable utilization.It is an important material to realize lightweight in the fields of automotive,construction,aerospace,and so on.However,during the preparation of the knitting fiber reinforced thermoplastic composites,the high viscosity of the thermoplastic resin leads to the problem of interface bonding between resin and fiber.In this work,bidirectional warp knitted glass-fiber(BWKGF)was used as reinforcement which possessed high strength and high specific modulus and nylon 6(PA6)as matrix.The BWKGF/PA6 composites were fabricated by thermoplastic resin transfer molding(T-RTM)process with self-made low-pressure casting and pressing mold.First,a low-pressure casting and pressing mold for T-RTM process was designed,and the molding process and optimal process parameters based on low-pressure casting and pressing were determined,followed by the preparation of BWKGF/PA6 composites with good infiltration via in situ polymerization.Secondly,3-aminopropyltriethoxysilane(KH550)and toluene diisocyanate(TDI)were used to modify BWKGF.The modified k-BWKGF/PA6 composite and t-BWKGF/PA6 composite were prepared by the improved T-RTM process,and their structure,morphology and mechanical properties were analyzed.The results show that the surface of BWKGF modified by KH550 and TDI was grafted with active groups,and the interfacial bonding between glass fiber and PA6 was improved.Besides,the mechanical properties of the composites were promoted.Compared with the tensile strength of the unmodified BWKGF/PA6 composite,the tensile strength of t-BWKGF/PA6 composite was increased by 44.5%,reaching 130 MPa.The tensile strength of k-BWKGF/PA6 composites increased firstly and then decreased with the increase of the dosage of KH550.When the dosage of KH550 was 0.5% of GF mass,it reached the optimal value of 140 MPa,which increased by 55.5%.Finally,polyethylene glycol(PEG)was introduced into the polymer matrix,and BWKGF/nylon elastomer(PATE)composites were prepared by improved T-RTM process,and their structure,morphology and mechanical properties were analyzed.The results show that compared with BWKGF/PA6 composite,the interface bonding between resin and fiber in BWKGF/PATE composite is better,and the tensile strength of the composite was increased by 225% to 231 MPa.In addition,PEG was introduced into the polymer matrix,which made the composite exhibit excellent shape memory effect.The mold and the composites of BWKGF/PA6 and BWKGF/PATE developed in this work provide a strategy for preparing high-performance thermoplastic composites by RTM process,which is expected to be applied in the field of automotive lightweight.