Characterization and RSM-Based Modeling of Sustainable Malva sylvestris L./Polypropylene Composites

Abstract

Malva sylvestris L. was evaluated as a potential sustainable lignocellulosic filler for polypropylene-based composites. Composites containing two particle size fractions and filler loadings ranging from 5 wt% to 20 wt% were produced through thermokinetic mixing and compression molding. Chemical, morphological, thermal, and mechanical characterizations were performed to determine the influence of filler incorporation on composite performance. The results showed that increasing filler content reduced tensile and flexural strengths by up to 27.2% and 29.6%, respectively, due to limited interfacial compatibility between the hydrophilic filler and hydrophobic polymer matrix. In contrast, the tensile and flexural moduli increased by up to 15.6% and 18.0%, respectively, indicating enhanced stiffness through restricted polymer chain mobility. Thermal analysis revealed improved thermal stability, with the onset degradation temperature increasing by approximately 35 °C at the highest filler loading. The filler particles also acted as heterogeneous nucleating sites, promoting earlier crystallization without substantially altering the degree of crystallinity. Mechanical properties were successfully modeled using response surface methodology. Linear model provided the most accurate predictions for tensile strength, whereas quadratic models better represented tensile modulus and flexural behavior. These findings demonstrate that Malva sylvestris L. is a promising renewable filler for lightweight polymer composites.