Performance Evaluation of Optimized Fiber Length on the Mechanical and Thermal Performance of Composite Sunroof Panels Using <i>Plumbago zeylanica</i> Fiber

This study optimizes Plumbago zeylanica fiber (PZF) reinforced epoxy composites for sunroof applications using Response Surface Methodology (RSM). The optimal configuration result is 5 mm fiber length at 30% weight, which demonstrated superior mechanical and thermal performances. Tensile testing yielded 325.0 ± 8.2 N at a maximum load and 40.5 ± 1.2 MPa strength with a low standard deviation, indicating high consistency. Flexural strength reached 56.3 ± 2.1 MPa with a modulus of 4.15 ± 0.15 GPa, while impact strength was 43.75 ± 1.8 kJ/m2. Energy absorption was 12.5 ± 0.55 J. Thermal conductivity remained low at 0.216 ± 0.008 W/m K, with an excellent coefficient of variation of 0.46%. Solar radiation testing at 980 W/m2 revealed a 5.8°C internal-external temperature differential, achieving 14.9% thermal regulation efficiency. UV aging caused only 8% degradation after 1000 h, maintaining 92% tensile strength retention. Compressive strength was recorded at 953 MPa with a break distance of 5.85 mm. AFM showed a controlled surface morphology (Rq = 7.896 nm, Ra = 5.600 nm, Rpv = 58.826 nm). These consistent and statistically robust results validate the composite’s high reliability, making the 5-mm PZF-epoxy configuration a durable, thermally efficient, and sustainable sunroof alternative.