Soymeal is the prominent byproduct of soybean oil extraction and is mainly used as a high-protein source in animal feed. Saponins are also components of this soymeal. They have been associated with various health issues for livestock and are noted to negatively impact the taste and appeal to eat. The safe removal of saponins from soymeal can provide a sustainable source for saponins, and simultaneously provide a more desirable meal for livestock. The aim of this study was to investigate the feasibility of a saponin extract from soymeal as a naturally occurring coupling agent to improve the properties of fiber-based composites for food packaging. The first part of this study focused on determining the invasiveness of the saponin extraction on the meal. The isolation of saponins was proven via HPLC-MS, and a proximate composition analysis of soymeal post-extraction confirmed a nutritional content that was consistent with the initial meal. Second, this study focused on investigating the effectiveness of the saponin extract as a coupling agent. This effectiveness was shown for polylactic acid-soyhull composites based on an improvement of mechanical properties. The treatment of the filler with sulfuric acid prior to its inclusion into the polymer matrix improved the water vapor permeability, UV barrier, and thermal stability of the composites. With both treatments (saponin extract and acidification), mechanical, barrier, and thermal properties of composites were improved. This study shows that the saponin extract from soymeal has promise for potential as a coupling agent.
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