“Synergistic Enhancement of Thermomechanical and Chemical Properties in Carbon Fiber-Reinforced Composites via Modified Polyester–Epoxy Hybrid Matrix”

This study presents the synthesis and development of β-naphthol derived tri-functional epoxy-based modified unsaturated polyester resins (UPRs) through reactions with maleic anhydride and a series of dibasic acids. The chemical structure and physicochemical characteristics of the synthesized resins were systematically analyzed using Fourier transform infrared (FT-IR) spectroscopy, epoxy equivalent weight (EEW), gel permeation chromatography (GPC), and viscosity measurements. Carbon fiber-reinforced composites were fabricated using the hand lay-up technique, employing methyl ethyl ketone peroxide (MEKP) as the curing initiator. The resulting composites were evaluated for their mechanical, thermal, and chemical performance. It was observed that UPRs derived from aromatic dibasic acids exhibited comparatively higher molecular weight, improved thermal resistance, and enhanced mechanical properties relative to those derived from aliphatic counterparts. The composites demonstrated tensile strength in the range of 120.4–127.5 MPa and flexural strength of 213.1–223.4 MPa, indicating excellent structural integrity and resistance to deformation. Rockwell hardness values (141.2–149.2 MPa) confirmed good surface rigidity, while Izod impact strength (10.12–12.4 J/cm) reflected satisfactory toughness and energy absorption behavior. The activation energy (Ea), ranging from 4.84 to 9.20 kcal/mol, suggests moderate curing reactivity along with acceptable thermal stability of the system. Scanning electron microscopy (SEM) analysis revealed improved interfacial adhesion between the carbon fibers and the blend (modified UPR+ commercial epoxy) resin matrix, contributing to the enhanced overall performance. The findings clearly indicate that β-naphthol-based modification significantly improves the functional properties of unsaturated polyester resins, highlighting their potential for advanced high-performance carbon fiber-reinforced composite applications.