Optimization of impact performance of chemically modified pineapple leaf fiber/guar gum/epoxy hybrid composites reinforced with nanofillers using CCD–grey relational analysis

Chemically treated pineapple leaf fiber (PALF), guar gum powder, nanofillers (h-BN, MWCNT and Al 2 O 3 ) and epoxy resin are used to fabricate hybrid composites, and their Izod impact performance is investigated using Central Composite Design (CCD). Unlike previous studies that primarily examined a single fiber treatment or an individual nanofiller system, the present work systematically compares three sequential PALF chemical treatments (PT, AT and AA) together with three nanofillers (h-BN, MWCNT and Al 2 O 3 ) within a unified CCD framework. In addition, CCD-based optimization is independently validated using Grey Relational Analysis (GRA), providing a statistically robust methodology for identifying the optimum composite formulation. The process parameters considered are (i) three PALF treatment conditions (PT, AT and AA), (ii) nanofiller types and (iii) fiber weight percentages. The parameters are optimized using Analysis of Variance (ANOVA), regression modeling, response surface methodology, while Grey Relational Analysis (GRA) is used as a complementary ranking method. The impact strength of the fabricated composites ranges from 6.11 to 10.32 kJ/m 2 , demonstrating the significant influence of fiber treatment, nanofiller type, and fiber loading. The developed regression model exhibits high predictive capability with a validation error generally within 5%. The maximum impact strength of 10.32 kJ/m 2 is obtained for AA-treated PALF/MWCNT/3 wt.% fiber loading, whereas the minimum value of 6.11 kJ/m 2 is observed for PT-treated PALF/h-BN/1 wt.% fiber loading. The optimal parameter combination is A3B2C2, with GRC and GRG values ranging from 0.33 to 1.00, respectively and the optimal formulation exhibits the highest GRG. Factor ranking (B > C > A) reveals that nanofiller type was the dominant parameter, followed by fiber weight percentage and fiber treatment. Confirmation experiments validate the optimization results, with the mean GRG (φm = 0.4825) increasing to a predicted ideal GRG of 0.955 under the A3B2C2 condition. The developed hybrid composites are promising for lightweight structural, automotive, transportation and impact-resistant engineering applications.