Key Engineering Materials Vol. 1059

Abstract: Natural fiber reinforced biopolymer composites have gained attention due to their eco-friendliness, biodegradability, sustainability, and mechanical properties. In this study, hemp fiber-reinforced polybutylene succinate (PBS) composites were prepared with various fiber loadings ranging from 0 to 40 wt%, with increments of 10 wt%. The hemp fibers were treated with NaOH to remove impurities on fiber surface. The thermal and rheological properties of hemp fiber/PBS composites were analyzed. The results indicated that the addition of hemp fiber significantly enhanced the rheological properties, with increased fiber concentration. However, the thermal properties of the composites did not improve with the addition of hemp fibers because of the lower thermal stability of natural fibers. The optimal hemp fiber concentration in PBS matrix was 30 wt% since it provided a balance between thermal and rheological properties.

Abstract: This study investigates the fabrication and characterization of composites made from high-density polyethylene (HDPE) and alkali-treated Saccharum munja fibers (SMF) at varying fiber concentrations (0 wt%, 5 wt%, and 10 wt%) using a twin extruder-based 3D printing process without any blending material other than fiber and matrix. The fibers were treated with 5 wt% NaOH solution to enhance surface properties and fiber–matrix adhesion. Comprehensive characterization was performed, including mechanical testing (tensile and flexural), thermal analysis (thermogravimetric analysis (TGA), differential scanning calorimetry (DSC)), morphological evaluation (scanning electron microscopy (SEM)), crystallinity evaluation (X-ray diffraction (XRD)), and functional groups identification (Fourier transform infrared spectroscopy (FTIR)). Additionally, four-dimensional X-ray microscopy (FDXM) was employed to assess void content in the composite samples. Alkali treatment significantly influenced the composite's crystallinity, thermal stability, and mechanical performance. The study demonstrates the effective utilization of natural fibers in HDPE matrices for making sustainable composite materials using additive manufacturing.

Abstract: Hemp fibers, naturally rich in cellulose and possessing a porous structure with abundant hydroxyl groups, offer strong electrolyte uptake, while the favourable interactions between Zn²⁺ ions and hydroxyl groups help suppress dendrite growth. In this study, cellulose was extracted from hemp through alkaline treatment and bleaching, followed by blending with sodium alginate to fabricate the separator. SEM and chemical composition analyses confirmed effective fiber separation and cellulose purity, whereas XRD, FTIR, and TGA verified the crystalline structure, functional groups, and thermal stability, respectively. The hemp-derived cellulose fibers were processed into separators with Rapid-Köthen sheet former. Zinc plating/stripping tests demonstrated stable cycling from 0.5 to 8 A cm^-2 and more than 3000 cycles at 5 A cm^-2, indicating strong potential for aqueous Zn-ion battery applications.

Abstract: This study investigates the mechanical behavior of epoxy composites reinforced with hybrid water hyacinth fibers and powder to develop sustainable epoxy-based hybrid composites. Epoxy resin (YD-535) and hardener (TH-7255) were mixed at a 100:35 weight ratio. Water hyacinth fibers were incorporated at a fixed 5 vol%, while powder with particle sizes of 250–425 µm was added at 5, 10, 15, and 20 vol%. The composites were fabricated using the casting method and evaluated according to ASTM standards for tensile, flexural, impact, and hardness properties. The results reveal that tensile strength peaked at 10PF, while all powder-reinforced samples exhibited higher tensile modulus than the fiber-only composite. Flexural modulus increased significantly at 5PF and 10PF, demonstrating the stiffening effect of particulate fillers. Impact strength decreased at lower powder contents but improved at 10PF. Hardness increased progressively with powder loading, with 20PF achieving the highest value. These findings highlight the effectiveness of hybrid reinforcement in enhancing the mechanical performance of epoxy composites.

Abstract: Lightweight and sustainable materials for protective systems are increasingly required to replace conventional synthetic composites. This study investigates the blast response of banana fibre–epoxy composite panels, with and without graphite particulate reinforcement, for potential bomb blanket applications. Panel-scale specimens (25 cm × 25 cm × 2 cm) were subjected to controlled explosive loading using Plastic Explosive (P.E.) No. 4 initiated by PETN detonators. Relative deflection behaviour was evaluated using high-speed visual observation and a dough medium indicator. Graphite-reinforced panels showed reduced apparent peak deflection, lower residual deformation, and improved structural integrity compared to non-graphite panels. The enhanced performance is attributed to improved stiffness, crack deflection, and fibre–matrix cohesion induced by graphite addition. These findings indicate that banana fibre–graphite epoxy composites have potential as sustainable protective materials for bomb blanket applications.

Abstract: Duckweed (Lemnaceae) is a rapidly growing aquatic plant with promising potential as a bio-based feedstock for composite materials due to its high cellulose and biomass productivity. To enable its utilization in material engineering applications, proper preprocessing is essential to ensure stability, uniformity, and compatibility with polymer matrices. Drying represents a critical step in this processing chain, yet the drying behavior of duckweed remains insufficiently characterized. This study investigated convective hot air drying of duckweed at 60 °C for 5–7 h, focusing on thin-layer modeling, effective moisture diffusivity, color stability, and energy efficiency. Six thin-layer models were evaluated, with the Midilli et al. model providing the best fit (R² > 0.998, lowest RMSE). Effective diffusivity increased with drying time, while energy consumption rose only slightly. Color analysis revealed reductions in L* and b* and an increase in a*, with ΔE stabilizing after 6 h, identifying this as the optimal drying duration balancing energy efficiency, product stability, and quality. The results provide essential drying parameters for duckweed processing, thereby supporting its future application as a sustainable candidate material in composite engineering.

Abstract: This study examines the mechanical properties of epoxy composites reinforced with water hyacinth powder, aiming to utilize aquatic biomass waste as a sustainable reinforcement material. Water hyacinth powder with a particle size of 250–425 µm was incorporated into the epoxy matrix at 5, 10, 15, and 20 vol%. The composites were fabricated through casting, followed by room-temperature curing and post-curing at elevated temperatures. Mechanical tests, including tensile, flexural, impact, and hardness measurements, were conducted according to relevant ASTM standards. The results showed that low filler contents, particularly 5–10 vol%, enhanced tensile strength, tensile modulus, and hardness due to improved stress transfer and matrix stiffening. However, flexural strength and impact resistance decreased as filler loading increased, mainly due to particle agglomeration and interfacial defects. Overall, the findings indicate that water hyacinth powder is a promising reinforcement at moderate contents, offering potential for lightweight, non-structural composite applications while supporting sustainable material development.

Abstract: This study aims to utilize sugarcane bagasse, an agricultural by-product, for the production of cellulose nanofibers. The preparation process combines deep eutectic solvent (DES) treatment with chemical oxidation methods. The objective is to develop sugarcane bagasse cellulose nanofibers (SBCNFs) using a green approach that ensures high yield and low energy consumption. The resulting SBCNFs are incorporated into polylactic acid (PLA) to create environmentally friendly products with net-zero carbon potential, as well as biocomposites that exhibit high thermal resistance and mechanical strength, thereby increasing the product's added value. The results show that DES effectively removes lignin and hemicellulose from sugarcane bagasse. The fibers obtained through DES treatment were successfully oxidized via chemical methods, yielding nanofibers with diameters ranging from 18.9 to 26.7 nm. Furthermore, the heat deflection temperature (HDT), tensile strength, and impact strength of the SBCNF/PLA composites reached 116.7°C, 62.5 MPa, and 27.2 J/m, respectively.

Abstract: The purpose of this study was to investigate the effect of welding energy on tensile strength the physical appearance of rupture of the weld interface by the ultrasonic welding for bamboo strip material in welding 3 conditions of interlayer on weld interface, which are water, Low-Density Polyethylene (LDPE) plastic, and without adding anything. The bamboo strips are made of 3 years old bamboo internode of Dendrocalamus sericeus genus from Thailand at the middle zone, which was dried at temperate 105 °C in the oven and then cut by hand knife into bamboo strip with the size of 0.5 x 5 x 50 mm³. All 3 welding conditions were performed by ultrasonic machine under the same fixed force at 50 daN and fixed amplitude at 60% while the 6 different conditions, while the welding energy was varying with 50 J, 100 J, 200 J, 300 J, 400 J, and 500 J. The tensile strength determined according to the ASTM D3379 standard, and the paper grip technique was applied. The results indicated that all 3 welding conditions were nearly identical in strength when considering the optimal welding energy, with the tensile strength in range of 15-50 MPa. However, the values obtained under all conditions still provide much lower tensile strength compared with untreated bamboo bundles, which were in the range of 250-480 MPa. The damage on the weld interface was from slipping of the bamboo strips in under weld and normal weld conditions, or damage from burning on bamboo strips in over weld condition, not rupture by tensile force on the bamboo strips weld interface. However, the outcome of this study was small-scale, and the durability was not conducted. Therefore, it is suggested that ultrasonic welding for bamboo strips or other natural materials is required to add water to enhance the tensile strength and physical appearance of the welding.

Abstract: This paper evaluates the environmental sustainability of a carbon fibre reinforced composite panel manufactured using a bio-based, recyclable and reprocessable epoxy resin synthetized from phloroglucinol, compared to one produced with traditional epoxy, through life cycle assessment. Results show a 2.42% reduction in global warming potential and an 80.7% decrease in freshwater eutrophication, enabled by bioremediation from brown algae cultivation, the source of phloroglucinol. However, increases of 1.67% and 9.76% in human toxicity for carcinogenic and non-carcinogenic categories, respectively, were observed due to solvent use at laboratory scale, which still requires optimization. The findings highlight the potential of bio-refinery processes for carbon-neutral composites, identifying key challenges for future development and scale-up.