This work presents a mechanistic investigation of bio-oil-engineered epoxy matrix reinforced with natural fibers, focusing on the role of cross-link density and interfacial strengthening in governing multiscale composite performance. Epoxy matrices were modified using bio-derived oils at varying concentrations and reinforced with alkali-treated natural fibers to fabricate composite laminates via hand lay-up processing. Comprehensive characterization spanning Molecular (FTIR), Microstructural (SEM), Thermal (TGA), and Mechanical (Tensile, Flexural, Impact, ILSS) scales was performed to establish structure–property relationships. The results reveal that controlled bio-oil incorporation significantly alters the epoxy compositional architecture, leading to an optimal balance between cross-link density and molecular mobility. At intermediate bio-oil content, enhanced cross-linking and improved fiber–matrix interfacial adhesion result in substantial improvements in Tensile (80%), Interlaminar Shear (130%), and Impact Strength (350%) compared to the unmodified system. At higher bio-oil concentrations, a reduction in cross-link density promotes increased ductility but compromises stiffness and load-bearing capacity, indicating a clear stiffness–toughness trade-off. Fractographic analysis confirms a transition from interfacial debonding to cohesive fracture and matrix yielding, highlighting the role of engineered interfaces in damage resistance. The findings demonstrate that bio-oil engineering provides a tunable strategy for designing sustainable, high-performance natural fiber composites with tailored mechanical and thermal characteristics.
This research examines thermal, thermoelectric transport, mechanical and flammability properties of nanocomposites prepared from Diglycidyl Ether of Bisphenol-A, a thermosetting epoxy resin (DGEBA) and nano coco peat carbon (NCPC) filler. The filler was derived from coco peat, a byproduct of coconut tree. Nano coco peat carbon composites (1% NCPCC, 3% NCPCC & 5% NCPCC) were fabricated by incorporating 1, 3 and 5 wt % of NCPC into a mixture of calculated quantities of DGEBA resin matrix and triethylenetetramine (TETA) hardener. Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and X-Ray Diffraction (XRD) methods were helpful in the interpretation of structural features of filler and nanocomposites. Thermal degradation stages of NCPC and nanocomposites during pyrolysis were assessed with the aid of Thermogravimetric Analysis (TGA). Thermal stability data indicated that 5% NCPCC was highly stable and 19.35% char residue was obtained at 800 °C. Resistivity of 1.442 × 10 4 Ω cm and conductivity of 6.933 × 10 -5 Ω −1 cm −1 obtained from thermoelectric measurements and Hall parameters by the van der Pauw method, signify the semiconducting behaviour of 5% NCPCC. 3% NCPCC possessed a maximum tensile strength of 44.35 MPa, determined according to ASTM D3039 standards, and 3% NCPCC exhibited the highest hardness value of 85, determined according to ASTM D2240 standards, respectively. Flammability was determined by the UL-94 vertical burning test, which showed that the 5% NCPCC composite had enhanced flame-resisting properties with a high amount of char formation, achieving V-2 grading with a Limiting Oxygen Index (LOI) of 26.88.
The growing demand for lightweight, sustainable gamma radiation shielding necessitates alternatives to traditional empirical design. This study employs a density functional theory (DFT)-guided strategy to develop a bio-based benzoxazine monomer synthesized from renewable eugenol and p-tert-butylaniline. DFT thermochemical calculations confirmed thermodynamic spontaneity (Delta G = -8.14 kcal/mol) and the exothermic nature (Delta H = -31.03 kcal/mol) of the monomer formation. Theoretical molecular geometries and predicted 1H NMR chemical shifts showed excellent agreement with experimental FT-IR and 1H NMR spectra, validating the predictive model. The monomer was thermally polymerized and reinforced with erbium oxide (Er2O3) at various loadings (5-20 wt%). Gamma radiation shielding measurements revealed that attenuation properties improved progressively with filler content. At 20 wt% Er2O3 loading, the composite achieved a superior mass attenuation coefficient of approximately 92.64 cm2/g, along with significantly enhanced linear attenuation and radiation protection efficiency compared to the neat polymer. These results demonstrate that combining DFT-assisted molecular design with high-Z rare-earth oxide reinforcement provides a highly effective route for engineering next-generation, sustainable radiation shielding materials.
In this work, four biphenyl diamine monomers bearing gradient steric hindrance from methyl and tert-butyl substituents were synthesized and copolymerized with 6FDA and CHDA dianhydrides to fabricate a series of colorless and transparent polyimide (CPI) films. The regulating mechanisms of substituent steric hindrance and dianhydride backbone on the optical, thermal, surface wetting and water absorption performances of the resulting CPIs were systematically investigated. The alkyl steric hindrance was proven to effectively suppress intermolecular charge-transfer complex (CTC) formation and improve the optical transmittance of films. Methyl-modified CPIs delivered superior comprehensive optical performance, while tert-butyl-incorporated systems exhibited enhanced thermal stability and hydrophobicity. Notably, asymmetric tert-butyl substituents introduced excessive molecular torsional distortion and aggravated yellowing of the films. Combined with time-dependent density functional theory (TD-DFT) calculations, the steric hindrance-induced anti-yellowing mechanism was clarified at the electronic level. Among all samples, the Y-2TB@6FDA film achieved a balanced performance of high transparency, outstanding thermal resistance and low water absorption (L* = 95.79, Td5% = 539 degrees C). This work offers a reliable molecular design strategy for developing high-performance CPI optoelectronic materials.
Unsaturated polyester resins (UPRs) are widely used thermosetting polymers; however, their inherent brittleness and limited thermal stability restrict their application in high-performance structural composites. In this study, a novel tetra-functional epoxy-based modification strategy was developed to enhance the performance of UPR systems. A tetra-functional epoxy resin was synthesized from hydroquinone, formaldehyde, and epichlorohydrin, followed by its reaction with maleic anhydride and various dibasic acids to prepare modified unsaturated polyester resins. Carbon fiber-reinforced composites were fabricated by the hand lay-up technique and cured using methyl ethyl ketone peroxide (MEKP). The modified composites exhibited tensile strengths of 123.4-130.2 MPa, flexural strengths of 212-230 MPa, Rockwell hardness values of 143.1-150, and Izod impact strengths of 12.5-15.2 J/cm. Among the developed composites, HTEC exhibited the highest tensile strength, flexural strength, hardness, and thermal stability, whereas HSEC showed the highest impact strength. Activation energy values ranged from 5.16 to 9.87 kcal mol-1. Scanning electron microscopy (SEM) revealed improved fiber-matrix interfacial adhesion, confirming the effectiveness of the tetra-functional epoxy modification in enhancing the overall performance of carbon fiber-reinforced composites for advanced structural applications.
