Long fiber reinforced thermoplastics (LFT) have been used in the automotive industry for semi-structural applications. Their main advantages are attractive cost/performance ratios and relatively low density. The European ELV (end of life vehicle) legislation promotes the development of this material, which promotes recycling and thus promotes the replacement of thermoset materials by thermoplastic materials.
In the automotive industry, LFT is primarily used to make structural and semi-structural components such as front end modules, bumper girders, dashboard skeletons, battery bays, spare tire compartments, seat frames, foot pedals and integral floor panels. Long-fiber reinforced polypropylene is used in car hoods, dashboard skeletons, battery brackets, seat frames, car front-end modules, bumpers, luggage racks, spare placents, fenders, fan blades, engine chassis, roof sheds Lining, etc.; long fiber reinforced PA, is further extended into the hood, because LFT-PA not only has high hardness, low weight, but also high glass fiber content, its thermal expansion coefficient is almost the same as that of metal, can withstand the high temperature brought by the engine .
The two main materials of the LFT are described below. LFT-G is the result of technological innovations in short glass fiber thermoplastic particulate materials (FRTP). Although the length of the early FRTP pellets can reach 5-6mm, after the process of mixing, pelletizing, plasticizing, injection molding, etc., the final length of the fibers in the product is often less than 1mm, which can only be used as a filler to increase the rigidity of the product. However, the improvement in tensile strength and impact resistance is very limited. Therefore, at the time FRTP was not the mainstream composite material. In order to give full play to the advantages of high productivity and low cost of injection molding, efforts were made to minimize the degree of fiber breakage. LFT-G was born in the early 1980s. LFT-G products are produced in a process similar to GMT and require two mature processes, namely long-particle molding and injection molding or compression molding of the product.
The LFT-G pellets have a diameter of about 3 mm and a length of 12 mm and 25 mm. Among them, pellets of about 12 mm length are mainly used for injection molding, while pellets of about 25 mm length are mainly used for compression molding. In the LFT-G pellet injection molding process, although the injection molding machine has undergone many improvements, it is limited to the injection molding process, and the fiber can only reach 3.2 to 6.4 mm in the final finished product.
