In this study, hemp particle (HP)-reinforced polypropylene (PP) matrix composites containing two sieve-defined HP fractions, HP_90 (≤90 µm) and HP_150 (>90 µm and <150 µm), at weight ratios of 10-30% were produced, and the effects of HP addition on the mechanical, tribological, thermomechanical, and thermal properties of PP were investigated. Tensile test results showed that increasing the content of the HP_150 fraction increased the stress at yield and elastic modulus but decreased the strain at yield. The highest mechanical performance was obtained for the composite containing 30 wt. % of the HP_150 fraction. SEM images supported the lower agglomeration of the HP_150 fraction. The results of the adhesive wear test showed that the lowest and most stable COF was obtained for the composite containing 30 wt. % of the HP_150 fraction. The DMA results showed that the storage modulus values increased over the entire temperature range with the addition of HP, with the highest values obtained for the composite containing 30 wt. % of the HP_150 fraction. DSC analysis showed that the addition of HP did not cause a significant change in the T m of PP but affected the X c,rel of the PP phase in the composites. At the same HP ratios, higher X c,rel was obtained with the HP_150 fraction. The results revealed that the particle-size range is a determinant of reinforcement efficiency and that the finer fraction does not always lead to superior composite performance. Although additional processes to obtain the finer HP_90 fraction are costly and energy-intensive, composites containing the HP_150 fraction were found to exhibit superior performance. Therefore, it was concluded that the optimum particle-size range in natural particle-reinforced composites should be determined not only by the surface area approach but also by considering the agglomeration tendency and stress transfer efficiency together.
PA80, a partially crosslinked form of natural rubber, was blended with a polar synthetic rubber (acrylonitrile butadiene rubber (NBR)) in variable proportions via a three-step dry rubber mixing procedure. The effect of PA80 in imparting superior processability and retaining the physical properties of NBR vulcanizates was evaluated to select an optimum blend proportion appropriate for extrusion applications. The polarity mismatch between PA80 and NBR was minimized and the blend properties were improved with a suitable compatibilizer (polychloroprene rubber). The fast-curing accelerators resulted in uniform rheological characteristics. A partial replacement of NBR with PA80 (up to 30 phr) satisfactorily maintained the mechanical and transport properties with minimum deviation. Under similar proportions, the thermal behaviour of the blends was also measured and was comparable with the NBR reference system. Moreover, the filler dispersion was found excellent for all the samples studied. The effect of PA80 in improving the processability was evident from the smoother appearance and lower die swell of extruded profiles. So, a strategy of blending synthetic rubbers with an optimum level of a secondary elastomer like PA80 is highly recommended to achieve a good balance of technical properties, cost-effectiveness and processability.
3D printing has recently emerged as a rapidly evolving manufacturing technique that enables the production of intricate geometries with ease. This investigation delves into the development of a virgin PETG-CF composite filament that incorporates 20% short carbon fibres in order to improve the mechanical performance of printed parts. The DOE framework was employed in conjunction with a hybrid Grey Relational Analysis method to optimise five critical printing parameters: layer thickness, infill density, printing temperature, raster angle, and printing speed. The optimisation was done using an L27 orthogonal array. Components that were printed with the most optimal process parameters were subjected to an annealing heat treatment to improve crystallinity and increase molecular chain mobility. This step was taken to further enhance the properties. Optimal parameters were determined to be 0.2 mm layer thickness and 75% infill density, as optimisation revealed that infill density and layer thickness were the most noteworthy variables. As opposed to the least effective parameter combinations, the tensile strength (TS) increased by 108.36%, the impact strength by 200%, and the surface roughness decreased by 81.94% under these conditions. Following optimisation, annealing at 90 degrees C for 200 min results in a 21.8% increase in tensile strength (TS), a 33.3% increase in impact strength (IS), and a marginal reduction in surface roughness (SR) (3.11%). These findings verify that thermal annealing substantially enhances mechanical performance, albeit with only a modest enhancement in surface quality.
Fused filament fabrication (FFF) is widely used to produce polymer-based parts, particularly bioscaffolds, though mechanical performance depends heavily on process parameters. In the present study, a Taguchi L9 orthogonal design is used to examine the influence of printing angle, infill percentage, and layer thickness on tensile strength and torsion-induced shear stress of PLA + parts. Experimental results demonstrated that the printing angle exerts the strongest influence on both mechanical responses; specifically, increasing the angle from 0 to 90° caused a substantial decline in both tensile and shear strength. SEM analysis of the broken surfaces further confirmed the underlying failure mechanisms. Samples printed at 0° exhibited ductile tearing and strong interlayer bonding, while 90° samples failed in a brittle manner along weak interlayer boundaries. ANOVA results revealed that the printing angle accounts for 89.28% of the variation in tensile strength and 62.66% in shear stress, while the infill percentage emerges as a more critical factor for shear strength. The optimal process parameters, consisting of a 0° printing angle, approximately 60% infill density, and a layer thickness of 0.1 mm, yielded maximum tensile strength of 48.02 MPa and shear strength of 30.67 MPa. Following this optimization, porous scaffolds with 0–90° and 0–45° internal architectures were fabricated using these parameters and evaluated under compression. Experimental results revealed that the scaffold with a 0–90° arrangement possessed a compressive load-bearing capacity more than three times greater than that of the 0–45° scaffold.
This study investigates the influence of fabric hybridization and stacking sequence on the physical, mechanical, and thermo-mechanical behavior of polyester-based laminates reinforced with glass (G) and kenaf (K) fibers. Using the hand lay-up route, five different four-layer laminates (GGGG, GKGK, GKKG, KGGK, and KKKK) were fabricated. The GGGG laminate demonstrated superior mechanical performance compared to the KKKK laminate. Among the hybrid configurations, the GKKG laminate achieved the highest tensile strength (79.89 MPa), flexural strength (91.39 MPa) and impact strength (53.36 KJ/m 2 ). Dynamic Mechanical Analysis (DMA) results revealed that, the GKGK laminate exhibited a higher storage modulus than KGGK, while the GGGG laminate attained the maximum loss modulus (691 MPa). Conversely, the KKKK laminate showed the highest damping peak (0.271). Thermal stability was further evaluated for GGGG, KKKK, and GKKG laminates. TGA results indicated greater thermal stability for GGGG, while KKKK exhibited earlier degradation, primarily associated with the thermal decomposition of its lignocellulosic constituents. Scanning electron microscopy (SEM) revealed matrix cracking, fiber pull-out, and interfacial debonding as the primary failure mechanisms, while Fourier transform infrared spectroscopy (FTIR) showed chemical interactions between fibers and matrix in the developed composites.
