Ramie (Boehmeria nivea) is one of the strongest natural cellulose fibers. Optimizing abundant resources ramie as a candidate materials used for reinforcing in polymeric composite material is a must to obtained high-performance natural fibers reinforced polymer especially for bulletproof panel or high-impact flexibility safer structures. Ramie woven was treated using common chemical solvents that were ethanol, methyl ethyl ketone, acetone, and silane as coupling agent. Composite panels were made by hand lay-up process with epoxy as a matrix. These prototype bulletproof panels were to be believed lighter in weight and much lower economic cost than conventional bulletproof panels made from ceramic plate, Kevlar/aramid composite, and steel-based material as a popular today in military standard antiballistic equipments. From the bullet testing result, it showed that panel could be able to resist the penetration of high-impact projectile for level II with some fractures phenomenon. Level IV ballistic testing showed that all prototype panel could not resist the high-impact velocity of the projectile yet. It was found that ramie fibers have sufficient breaking strength and toughness for level II bullet testing, although still needs improvements to optimize process parameters to meet a very high military standard and application

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.

Phenolic resin is the most common resin binder used in brake pad materials. Selection of the relative amount of phenolic resin is an important to maintain structurally intact with the other ingredients of brake pad composite. In this experimental study, the effects of phenolic resin as a binder in non-asbestos organic brake pad was investigated. The brake pad composite was made using a powder metallurgy technique. Four formulations with different volume fractions 10, 15, 20, and 25 were selected. Parameters applied were 47 MPa compaction pressure, 150 °C molding temperature, and 130 °C post curing temperature with 6 hours holding time. The properties of brake pad composite were examined density, porosity, hardness, thermal stability, and friction performance (refers to SNI 09-0143-1987). The results show the increase of phenolic resin content can decrease the density, porosity, thermal stability, friction coefficient, and volume wear rate by 1%, 16.79%, 2.39%, 42.5%, 24.16%, respectively. However, the hardness increases by 19.29 %. This investigation also recommends not to select 10 and 15 volume fraction of phenolic resin due to lower resistance to mechanical stresses although the thermal stability is better than the other studied composites.

The effects of alcohol, acetone, and methyl ethyl ketone solvent-based treatment on surface topography of ramie single fiber are investigated. In this study, the average of specific porous volume and specific surface area of ramie single fiber are determined to interpret the effects of the treatment quantitatively using Brunauer-Emmet-Teller surface area method. Fourier Transform Infrared Spectroscopy is applied directly to the fiber to detect the differences of molecular group function in the fiber surface. Qualitatively, scanning electron microscopy was also provided. The result shows that the solvent treatment could improve surface topography to gain matrix penetration when utilizing the fiber into polymeric composite material.

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.