Polylactic acid (PLA) is widely used in 3D printing for its biodegradability and ease of processing, but its brittleness and low impact strength often restrict its suitability for more demanding applications. The novelty of this work lies in its direct comparative approach: we systematically reinforce PLA with two distinct agricultural residues—rice husk and rice straw—under identical conditions to clarify how particle size (100 vs. 200 mesh) and NaOH surface treatment affect mechanical performance. Composite filaments containing 5–20 wt% of each fiber were produced and 3D-printed into standard tensile and flexural specimens. The results show that, although tensile strength declines at higher fiber loadings, tensile modulus, flexural strength, and impact resistance can improve significantly—particularly with 200-mesh and NaOH-treated fibers. Fourier transform infrared (FTIR) spectroscopy confirms partial lignin removal and enhanced cellulose exposure, improving fiber–matrix adhesion, which is corroborated by scanning electron microscopy (SEM) observations of reduced voids. This comparative study demonstrates that surface-treated, finely milled rice husk and rice straw significantly enhance PLA’s stiffness and toughness, offering a sustainable alternative to conventional polymeric additives. The insights gained here on fiber content, chemical treatment, and 3D printing parameters can guide the broader industrial adoption of these natural fiber-reinforced PLA composites, particularly in automotive and construction applications that require lightweight, durable materials.

Thermoplastic pultrusion is a suitable process for fabricating continuous unidirectional thermoplastics with a uniform cross-section, high mechanical properties due to continuous fiber reinforcement, low cost, and suitability for mass production. In this paper, jute and glass fibers were reinforced with a polypropylene matrix and fabricated using the thermoplastic pultrusion process. The volumetric fraction of the composite was designed by controlling the filling ratio of the reinforcing fiber and matrix. The effects of molding parameters were investigated, such as pulling speed and molding temperature, on the mechanical properties and microstructure of the final rectangular profile composite. The pulling speed and molding temperature varied from 40 to 140 mm/min and 190 to 220 °C, respectively. The results showed that an increase in molding temperature initially led to an increase in mechanical properties, up to a certain point. Beyond that point, they started to decrease. The resin can be easily impregnated into the fiber due to the low viscosity of thermoplastic at high temperatures, resulting in increased mechanical properties. However, the increase in molding temperature also led to a rise in void content due to moisture in jute fiber, resulting in decreased mechanical properties at 210 °C. Meanwhile, un-impregnation decreased with the increase in molding temperature, and the jute fiber began to degrade at high temperatures. In the next step, with varying pulling speed, the mechanical properties decreased as the pulling speed increased, with a corresponding increase in void content and un-impregnation. This effect occurred because the resin had a shorter time to impregnate the fiber at a higher pulling speed. The decrease in mechanical properties was influenced by the increase in void content and un-impregnation, as the jute fiber degraded at higher temperatures.

Thermoplastic pultrusion is a suitable process for fabricating continuous unidirectional thermoplastics with a uniform cross-section, high mechanical properties due to continuous fiber reinforcement, low cost, and suitability for mass production. In this paper, jute and glass fibers were reinforced with a polypropylene matrix and fabricated using the thermoplastic pultrusion process. The volumetric fraction of the composite was designed by controlling the filling ratio of the reinforcing fiber and matrix. The effects of molding parameters were investigated, such as pulling speed and molding temperature, on the mechanical properties and microstructure of the final rectangular profile composite. The pulling speed and molding temperature were varied from 40 to 140 mm/min and 190 to 220°C, respectively. The results show that an increase in molding temperature initially led to an increase in mechanical properties, up to a certain point. Beyond that point, they started to decrease. The increase in molding temperature also led to an increase in void content. Meanwhile, un-impregnation decreased with the increase in molding temperature, and the jute fiber began to degrade at high temperatures. In the next step, with varying pulling speed, the mechanical properties decreased as the pulling speed increased, with a corresponding increase in void content and un-impregnation. The decrease in mechanical properties was influenced by the increase in void content and un-impregnation, as the jute fiber degraded at higher temperatures.

Long fiber thermoplastic pellets (LFTP) are composite materials that consist of thermoplastic and discontinuous reinforcement fibers with an aspect ratio more than critical aspect ratio. LFTP are high modulus, high strength and excellent impact resistance. Normally, commercial LFTP were produced by hot melt impregnation process or combinding between pultrusion and extrusion process. In this research, Thermoplastic pultrusion process was used for production of LFTP. The thermoplastic pultrusion process is uncomplicated process and machine less than hot melt impregnation process. The glass fibers were used in LFTP as a reinforcement and polypropylene (PP) fibers were used as a matrix of LFTP. General full factorial design of experiment was used to determine the optimal condition for un-impregnation on specimen from pultrusion process of LFTP. The study focused on three factors including the filling ratio, the molding temperature and pulling speed. The specimens were investigated on impregnation of resin in LFTP by microscope. The results show that un-impregnation decreased with an increase of filling ratio. Un-impregnation decreased with an increase of molding temperature. Finally, un-impregnation had increased with an increase of pulling speed. However, the void content has a little effect to molding temperature and pulling speed, or they have not almost effect. From statistical analysis, the optimal condition for the pultrusion process of LFTP was filling ratio of 104.73 %, molding temperature of 230 °C and pulling speed of 10 cm/min, which was given the lowest un-impregnation value of 5.85 %.

Long fiber thermoplastic pellets are pellets containing discontinuous reinforced fibers and a matrix, offering excellent mechanical properties, good processability, recyclability, and low cost. Typically, commercial LFTP is manufactured through the hot melt impregnation process, combining extrusion and pultrusion. Although there is a thermoplastic pultrusion process for LFTP production, characterized by a simple machine and an easy method, its mechanical properties have not yet approached those of commercial LFTP. In improving the mechanical characteristics of LFTP manufactured via thermoplastic pultrusion, this research employed polypropylene-graft-maleic anhydride as a coupling agent during the injection molding procedure. The LFTP is composed of polypropylene material reinforced with glass fiber. Mechanical and physical properties of the LFTP were investigated by introducing PP-g-MAH at concentrations of 4, 8, and 12 wt% through injection molding. The results revealed that, at a 4 wt% concentration of PP-g-MAH, the LFTP composites exhibited heightened tensile, flexural and impact strengths. However, these properties began to decrease upon exceeding 4 wt% PP-g-MAH. The enhanced interfacial adhesion among glass fibers, induced by PP-g-MAH, contributed to this improvement. Nonetheless, excessive amounts of PP-g-MAH led to a reduction in molecular weight, subsequently diminishing the impact strength, tensile modulus, and flexural modulus. In LFTP composites, both tensile and flexural strengths exhibited a positive correlation with the PP-g-MAH concentration, attributed to improved interfacial adhesion between glass fibers and polypropylene, coupled with a reduction in fiber pull-out. Based on morphological analysis by SEM, the incorporation of PP-g-MAH improved interfacial bonding and decreased fiber pull-out. The presence of maleic anhydride in the LFTPc was confirmed through the utilization of FTIR spectroscopy. Mechanical properties of LFTP containing 4 wt% PP-g-MAH were found to be equivalent to or superior to those of commercial LFTP, according to the results of a comparative analysis.