Development of Hybrid Composite Utilizing Micro-Cellulose Fibers Extracted from Date Palm Rachis in the Najran Region

Environmental effects can be reduced by using renewable resources in various applications. The date palm fibers (DPF) used in this study were extracted from waste date ranches of the Najran region by retting and manual peeling processes. The biocomposites were developed by reinforcing the silane-treated DPF (SDPF) at different wt.% in eugenol phthalonitrile (EPN) and difunctional benzoxazine (BA-a) copolymer. The impact strength, tensile, flexural, and dynamic mechanical properties and thermogravimetric analysis were evaluated to understand the mechanical, thermomechanical, and thermal properties. Results confirmed that 30 wt.% SDPF-reinforced poly (EPN/BA-a) composites produced the highest mechanical and thermomechanical properties, and were considered optimized SDPF reinforcement. Furthermore, hybrid composites with 30 wt.% SDPF and 15 wt.% silane-treated glass fibers (SGF) reinforcement having different lamination sequences were also studied. The lamination sequences showed a significant impact on the mechanical and thermomechanical properties, as properties were further enhanced by adding a core layer of SGF in hybrid composites. However, the thermal properties of SDPF/SGF laminates were higher than SDPF biocomposites, but the SGF lamination sequence did not produce any impact. According to the limiting oxygen and heat resistance indexes, the developed SDPF/SGF laminates are self-extinguishing materials and can be used in temperature-tolerant applications up to 230 °C.

Effects of Processing Parameters for Vacuum-Bagging-Only Method on Shape Conformation of Laminated Composites

Complex composite structures manufactured using a low-pressure vacuum bag-only (VBO) method are more susceptible to defects than flat laminates because of the presence of complex compaction conditions at corners. This study investigates the contribution of multivariate processing parameters such as bagging techniques, curing profiles, and laminate structures on laminates’ shape conformation. Nine sets of laminates were produced with a concave corner and another nine sets with a convex corner, both with a 45° inclined structure. Three-way analysis of variance (ANOVA) was performed to quantify thickness variation and spring effect of laminated composites. The analysis for concave and convex corners showed that the bagging techniques is the main factor in controlling the laminate thickness for complex shape applications. The modified (single) vacuum-bag-only (MSVB) technique appeared to be superior when compared to other bagging techniques, exhibiting the least coefficients of variation of 0.015 and 0.016 in composites with concave and convex corners, respectively. Curing profiles and their interaction with bagging techniques showed no statistical significance in the contribution toward laminate thickness variation. The spring effect of laminated composites was investigated by calculating the coefficient of determination (R2) relative to that of the mold. The specimens exhibited a good agreement with R2 values ranging from 0.9824 to 0.9946, with no major data offset. This study provides guidelines to reduce thickness variations and spring effect in laminated composites with complex shapes by the optimum selection of processing parameters for prepreg processing.

Development of highly performant hybrid materials based on phthalonitrile resin for a simultaneous ballistic and nuclear shielding protection

In this study, a new high-performance hybrid material was designed targeting an efficient ballistic and nuclear shielding protection. To achieve this goal, a typical highly performant thermosetting resin, namely the phthalonitrile (PN) resin, was reinforced with Kevlar fibers (KF-29), as continuous phase, and erbium oxide (Er2O3) nanoparticles, as discontinuous phase. The reinforcing phases underwent a silane surface modification to create a fully connected network aiming an improved stress transfer between the constituents. The mechanical investigations through tensile and bending testing confirmed the positive effect of the addition of an increasing amount (up to 20 wt%) of the Er2O3 nanoparticles. The hybrids also provided excellent gamma rays shielding performances with a screening ratio of about 33% for a 3 cm thick sample. In the meantime, the ballistic tests evaluated under the National Institute of Justice standard (NIJ standard-0101.06-IIA) also highlighted an improved kinetic energy absorption following the increase in the amounts of the discontinuous phase. Overall, this study unraveled for the first time ever the benefits obtained from a fully connected hybrid network in the field of ballistic and radiation protection.

Temperature effect on compression property of multiaxial warp-knitted composites

The wind turbine blades are exposed to various environments all the year round, especially temperature variations during the four seasons. To study the influences of temperatures on the mechanical properties of composite materials, the compression property in the 0°, 45°, and 90° directions of the multiaxial (triaxial and quadaxial) glass fiber warp-knitted composites at −30°C, 0°C, 20°C, and 40°C was analyzed, respectively. The stress–strain curves, strength, modulus, failure strain, and the relationship between strength and temperature were obtained. The results indicated that the compression performance decreased with the increase of temperature, and the effect of temperature on quadaxial composite was more significant than that of the triaxial composite. In addition, the failure mechanisms were also analyzed according to the fracture modes and scanning electron microscopic morphologies of composites.