Silanization of Starch and Its Effect on Cross-Linking and Mechanical, Dynamic, Hydrophobic, and Aging Properties of Polymeric Compositions Containing Natural Rubber

In recent years, the search for more sustainable fillers for elastomeric composites than silica and carbon black has been underway. In this work, silanized starch was used as an innovative filler for elastomeric composites. Corn starch was chemically modified by silanization (with n-octadecyltrimethoxysilane) via a condensation reaction to produce a hydrophobic starch. Starch/natural rubber composites were prepared by mixing the modified starch with elastomer. The morphology, hydrophobicity, and chemical structure of starch after and before modification were studied. The results showed that starch after silanization becomes hydrophobic (θ_w = 117.3°) with a smaller particle size. In addition, FT-IR spectrum analysis confirmed the attachment of silane groups to the starch. The modified starch dispersed better in the natural rubber matrix and obtained a more homogeneous morphology. The composite achieved the best dynamic (ΔG' = 203.8 kPa) and mechanical properties (TS_b = 11.4 MPa) for compositions with 15 phr of modified starch. In addition, the incorporation of silanized starch improved the hydrophobicity of the composite (θ_w = 117.8°). The higher starch content allowed the composites to achieve a higher degree of cross-linking, resulting in better resistance to swelling in organic solvents. This improvement is due to enhanced elastomer-filler interactions and reduced spaces that prevent solvent penetration into the material's depths. The improved mechanical properties and good dynamic properties, as well as improved hydrophobicity, were mainly due to improved interfacial interactions between rubber and starch. This study highlights the potential and new approach of silane-modified starch as a sustainable filler, demonstrating its ability to enhance the mechanical, dynamic, and hydrophobic properties of elastomeric composites while supporting greener material solutions for the rubber industry.