Scalable Silane Functionalization of Grape Seed Biofillers for Improved Interfacial Compatibility in Polypropylene Composites

The growing need for more sustainable polymer materials has encouraged the use of agro-industrial residues as fillers in thermoplastic composites. This thesis investigates grape seed biofiller (GSF), obtained from defatted grape seed meal after grape seed oil extraction, as a renewable filler in polypropylene (PP) composites. Since GSF is hydrophilic and PP is non-polar, different silanization strategies were evaluated to improve filler–matrix compatibility. Amino silane (AS) and hexadecyl silane (HS) were applied through lab-scale silanization, in situ silanization during melt compounding, and turbomixer-assisted dry silanization. Untreated and silane-treated GSF samples were first characterized to assess the effects of silane functionality and treatment route on surface properties. Silanization modified the GSF surface, with HS producing a more pronounced increase in hydrophobicity due to its long alkyl chain. Treated and untreated GSF samples were then incorporated into PP by melt compounding and injection moulding to evaluate the composites. Overall, GSF mainly increased composite stiffness while reducing ductility, whereas silane-treated composites generally showed improved or maintained tensile strength compared with untreated PP/GSF. Thermal and morphological behaviour remained mainly governed by the PP matrix and filler dispersion, although route-dependent differences were observed among treated formulations. Untreated PP/GSF5 did not negatively affect PP thermal degradation, while changes in silane-treated composites were interpreted as modifications of the degradation profile rather than evidence of poor performance. In summary, GSF can be valorized as a biofiller in PP composites, and silanization can improve GSF–PP compatibility. The most suitable treatment route should be selected by balancing material performance, process simplicity, sustainability, and scalability.