The development of lightweight automotive parts is an important issue for improving the efficiency of vehicles. Polymer composites have been widely applied to reduce weight and improve mechanical properties by mixing polymers with carbon fibers, glass fibers, and carbon nanotubes. Polypropylene (PP) has been added to carbon fiber-reinforced nylon-6 (CF/PA6) composite to achieve further weight reduction and water resistance. However, the mechanical properties were reduced by the addition of PP. In this research, multiwalled carbon nanotubes (CNTs) were added to compensate for the reduced mechanical properties experienced when adding PP. Tensile testing and bending tests were carried out to evaluate the mechanical properties. A small amount of CNTs improved the mechanical properties of carbon fiber-reinforced PA6/PP composites. For example, the density of CF/PA6 was reduced from 1.214 to 1.131 g/cm3 (6.8%) by adding 30 wt % PP, and the tensile strength of 30 wt % PP composite was improved from 168 to 173 MPa (3.0%) by adding 0.5 wt % CNTs with small increase of density (1.135 g/cm3). The developed composite will be widely used for lightweight automotive parts with improved mechanical properties.

Promising carbon fiber-reinforced thermoplastic (CF/polyetherketoneketone (PEKK)) composites were fabricated by the state-of-the-art technology known as “Automated Fiber Placement.” The mechanical properties of CF/PEKK were evaluated for four different postprocessing methods: in situ consolidation, annealing, vacuum bag only (VBO), and hot press (HP). The evaluation was performed by narrowing down the relevant processing parameters (temperature and layup speed). Furthermore, the void content and crystallinity of CF/PEKK were measured to determine the effect of these postprocessing processes. The HP process resulted in the best quality with the highest interlaminar shear strength, highest crystallinity degree, and lowest void content. The second most effective method was VBO, and annealing also realized an improvement compared with in situ consolidation. The correlation between the postprocessing method and the void content and crystallinity degree was also discussed.

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Conventional glass fiber/unsaturated polyester resin (UPR) composites were fabricated by four layers to verify the optimum fabrication conditions such as the initial curing temperature, fiber changes and vacuum. Before that another optimum condition for stir mixing multi-walled carbon nanotubes (MWCNTs) into UPR was further investigated based on the initial curing temperature. Exothermic temperature measurements, density measurements, thermo-gravimetric analysis and tensile testing were utilized to identify the effects of these factors on the UPR and composite laminates. Consequently, an initial curing temperature range of 25°C–35°C was recommended to start the polymerization. In addition, the fiber combination and applying vacuum were also represented as the other optimum conditions in composite fabrication. The optimum initial curing temperature was applied for modifying UPR with 0.1 wt.% MWCNTs. Then, all of optimum conditions were used to fabricate glass fibers/modified UPR composites. The higher tensile strength and modulus of fiber combination with the adding of MWCNTs were obtained at 25.29 MPa and 1.39 GPa, respectively. The results indicate that simple MWCNT mixing can be used in industry due to the reduction of the fabrication time and better tensile properties.

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