Performance Evaluation of Optimized Fiber Length on the Mechanical and Thermal Performance of Composite Sunroof Panels Using Plumbago zeylanica 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.