Effect of alkali and silane surface treatments on the mechanical and physical behaviors of date palm seed-filled thermoplastic polyurethane eco-composites

In this study, eco-grade thermoplastic polyurethane (TPU), which includes 46% renewable content, was reinforced with date palm seed (DPS). Alkali and silane surface treatments were applied to DPS to increase the compatibility between DPS and TPU matrix. The oil of DPS was removed before treatments and surface functionalities of modified and pristine DPS samples were examined by Fourier transform infrared spectroscopy. Composites were fabricated using melt blending method and injection molding processes. Test samples of composites were characterized using tensile test, hardness test, water absorption study, dynamic mechanical analysis (DMA), melt flow index (MFI) test, thermogravimetric analysis, and scanning electron microscopy (SEM). According to test results, silane treatment led to remarkable improvement for mechanical performance of composites attributed to improvement of compatibility and interface adhesion between DPS and TPU. DMA results implied that higher storage modulus and glass transition temperature were achieved for treated DPS-containing composites compared to pristine DPS filled ones. Thermal stability of flexible segment of TPU increased with the addition of DPS regardless of surface treatment. Additionally, DPS loadings caused significant increase in MFI value of unfilled TPU. Silane-treated DPS-containing composite yielded the lowest water uptake value among samples due to the hydrophobicity of silane layer. Enrichment of interface adhesion of DPS to TPU matrix was confirmed by SEM micrographs of composites. Silane-treated DPS-containing composite displayed higher results among produced composites since the increase in interfacial interactions with TPU was achieved by silane treatment for DPS surface.

Automated summary

In this study, eco-grade thermoplastic polyurethane (TPU) with 46% renewable content was enhanced with date palm seed (DPS). Surface treatments, including alkali and silane treatments, were applied to the DPS to improve its compatibility with the TPU matrix. The results showed that the silane treatment significantly improved the mechanical properties of the composites due to the enhanced compatibility and interface adhesion between DPS and TPU. The treated DPS-containing composites exhibited higher storage modulus and glass transition temperature compared to the composites filled with pristine DPS. The addition of DPS also increased the thermal stability of the flexible segment of TPU, regardless of the surface treatment. Moreover, the DPS loadings caused a significant increase in the melt flow index (MFI) value of unfilled TPU. The silane-treated DPS-containing composite exhibited the lowest water uptake value among the samples, indicating its hydrophobicity. The SEM micrographs confirmed the improved interface adhesion between DPS and TPU in the silane-treated composite.