Carbon fibre-reinforced polypropylene composite filaments were fabricated via the extrusion–pultrusion method. One of the important factors influencing composites’ filament processability and structural properties is the impregnation quality, which can be represented by interfacial adhesion between the matrix and fibre. To improve the interfacial shear strength (IFSS) of the filament, four processing variables—melt temperature, pulling speed, number of pins in the impregnation die and fibre treatment—have been optimised using the Box–Behnken response surface methodology (RSM). Analysis of variance (ANOVA) was conducted to evaluate the linearity of the response surface models. Three levels were set for each independent variable. The melt temperature was varied at levels 190, 210 and 230 °C, while the pulling speed was set at three levels, namely, 40, 47 and 50 cm/min. The number of spreader pins was varied at 1, 2 and 3 pins, and there were three variations of the fibre treatment, namely, vinyltrimethoxysilane (VTMS), γ-aminopropyltriethoxy silane (APTS) and liquid nitrogen. Twenty-seven experimental runs were conducted, and a significant regression for the coefficient between the variables was obtained. The filament IFSS was measured by a customised pull-out test, and its surface morphology was characterised using a scanning electron microscope. ANOVA showed that fibre treatment significantly affected the IFSS due to their surface roughness, followed by pulling speed and melt temperature in quadratic order. Liquid nitrogen is recommended for carbon fibre treatment because of the high surface roughness, thereby providing a better matrix–fibre bonding effect. The results demonstrated that a melt temperature of 190 °C, pulling speed of 40 cm/min, three spreader pins and treatment of the fibre with liquid nitrogen afforded the optimum impregnation quality. It is important to keep a reasonable low processing temperature to obtain the geometrical stability of the product.

Fiber factor strongly influences the flexural properties of fiber-reinforced composites. Theoretically, strong fiber-matrix bonds combined with long fibers can produce high composite strength, while short fibers influence the ductility of the composite. Both conditions are obtained by aligning the fiber with the loading direction. In this study, an experimental study was conducted on the effect of fiber factors on the flexural strength and modulus of carbon fiber reinforced polypropylene. The fiber factors included in this study were: cryogenic fiber surface treatment, fiber length, and fiber orientation; each factor was divided into three levels. The relationship between the fiber factors and the responses was analyzed using the Response Surface Method (RSM) and Analysis of Variance (ANOVA). The results indicate that there is a good correlation between the predicted response values of the model and the results of the confirmation test. The fiber orientation has the most significant effect on the flexural strength of the composite. All fiber factors significantly affected flexural modulus, with fiber orientation as the most significant factor.

Currently, fiber-reinforced thermoplastic composites are widely applied in structural applications. It has great potential to replace metal structures and provides advantages in weight reduction. In this study, the pretensioned unidirectional carbon fiber was overmolded by Polyamide 6 contained 30%wt of glass fibers (PA 6-30GF). Process parameters such as injection pressure, melting temperature, duration of carbon fiber cryogenic treatment, and fiber pretension were optimized to maximize the flexural strength, impact strength, and interlaminar properties of the hybrid composite. The relationship between factors and responses was analyzed using Box–Behnken design (BBD) from response surface methodology (RSM) and analysis of variance (ANOVA). Three levels were assigned for each factor. There were 27 experimental trials carried out, and a significant regression for the coefficient between the factors was derived. The BBD and ANOVA analysis demonstrate that the predicted values from the model are in satisfactory correlation with the experimental results. The optimum responses found were achieved by setting the following injection molding parameters: melting temperature of 278 °C and injection pressure of 122 bar. Carbon fiber, as a unidirectional reinforcement, should be immersed in liquid nitrogen for 10 min and mounted on the mold in a pretensioned state with a force of 100 N. The combination of these parameters can produce an optimum flexural strength of 248.6 Mpa, impact strength of 173.4 kJ/m² and an ILSS of 30.4 Mpa.

Peningkatan jumlah sampah plastik di Indonesia disebabkan oleh meningkatnya penggunaan produk plastik. Menurut data, pada tahun 2018 sampah plastik akan diperkirakan 24.500 ton per hari. Daur ulang sampah plastik adalah salah satu cara untuk mengurangi jumlah sampah plastik di Indonesia. Pembuatan filamen 3D Printing berbahan plastik bekas daur ulang tidak hanya untuk mengurangi limbah sampah plastik, tetapi juga untuk memenuhi kebutuhan filamen untuk mesin 3D Printing tipe FDM (Fused Deposition Modeling). Dalam proses pembuatan produk, keakuratan dimensi menjadi faktor penting dalam mempengaruhi kualitas dan bentuk produk. Pada penelitian terkait keakuratan dimensi dilakukan dengan menggunakan metode Taguchi, dengan pengoptimalan parameter terukur seperti temperature printing, layer height and print speed. Penggunaan Signal to Noise Ratio (SNR) dengan tipe Smaller is Better untuk analisa hasil eksperimen yang memiliki tingkat perbedaan yang sedikit, dan untuk mengetahui parameter terukur yang berpengaruh dalam proses 3D Printing. Berdasarkan hasil analisa didapatkan parameter optimum untuk mencetak produk dengan dimensi 20x20x20 mm, berbahan dasar material plastik daur ulang PP adalah untuk parameter printing temperature adalah 260 ^oC, layer height 0,16 mm dan print speed 20 mm/s. The increase in the amount of plastic waste in Indonesia is due to the increasing use of plastic products. According to data, in 2018 plastic waste will be estimated at 24,500 tons per day. Recycling plastic waste is one way to reduce the amount of plastic waste in Indonesia. Making 3D Printing filament from recycled used plastic material is one of the applications of how to reduce plastic waste, but also to fulfill the needs of filament for 3D printing with FDM type printing. In the 3D printing process with the FDM technique, dimensional accuracy is an important factor in influencing the quality and shape of the product. Research related to the accuracy of these dimensions is carried out using the Taguchi method, by optimizing measured parameters such as temperature printing, layer height and print speed. Smaller is Better type Signal to Noise Ratio (SNR) is used to analyze the results of experiments that have the least difference, and to find out the measured parameters that affect the 3D printing process Based on the analysis results, the optimum parameters for printing products with dimensions of 20x20x20 mm, based on PP recycled plastic material are the printing temperature parameters 260 oC, layer height 0.16 mm and print speed 20 mm / s.

This study aimed to develop an extrusion and pultrusion system for producing carbon fiber-filled thermoplastic pellets. The extruder delivers a plastic melt to an impregnation die in sufficient volume and is pulled out along with the fibers. The fibers pass in a sideways stretched condition through spreader pins attached in the melt pool, which can then be wetted optimally. The wetting effect was also improved by immersing fiber in a coupling agent solution at an elevated temperature before feeding to the extruder die. For machine performance testing, polypropylene was used as a matrix resin with the following parameters: a screw speed of 5 rpm, a die temperature of 210 °C, and a pulling speed of 56 mm/s. The pull-out test was conducted to assess the interfacial shear strength (IFSS) between fibers and matrix. Scanning electron microscopy (SEM) was applied to characterize the quality of fiber impregnation. SEM characterized a good bonding performance between carbon fiber and the matrix. The average IFSS of the results indicated a good resistance of fiber–matrix bonding against a pulling force. It proved that the combination of the extrusion–pultrusion system can produce high-quality filaments as a raw material of composite pellets.