Influence of Montmorillonite and Clinoptilolite on the Properties of Starch/Minerals Biocomposites and Their Effect on Aquatic Environments

Abstract

This work has analyzed the properties of thermoplastic starch (TPS)-minerals biocomposites and their degradation on water bodies. The TPS-minerals biocomposites were prepared from cassava peels, residual glycerin, and minerals [montmorillonite (MMT) and clinoptilolite (CLI)]. The TPS and TPS-minerals biocomposites were characterized by scanning electron microscopy (SEM), tensile tests, and contact angle measurements. Moreover, microcosm degradation tests evaluated the release of dissolved organic carbon content (DOC) and total nitrogen (TN), carbon/nitrogen ratio (C/N), and heterotrophic bacteria count (HBC) in order to simulate the environmental effects of these biocomposites disposal. The SEM results showed the appearance of whole starch grains in TPS, which is an indicative of a partial thermo-plasticization. Furthermore, it was observed a surface roughness in all samples, with a possible better dispersion of mineral particles for TPS-MMT. This fact indicates an improvement of the tensile strength and elongation at break, when compared to the TPS-CLI. Both TPS-MMT and TPS-CLI presented lower contact angle values than TPS. These characteristics may assist in the microorganism access to the surface, favoring the degradation and the release of carbon and nitrogen. Microcosm degradation tests revealed an increase in DOC release from 18 to 98 mg L−1 for TPS-CLI after 24 h. Besides, there was an increase in TN release to 200% for TPS-MMT and TPS and 500% for TPS-CLI. The HBC presented a high growth after 12 h of contact, especially for TPS (3.4 ± 0.2 log CFU mL−1). Therefore, the TPS-minerals (clinoptilolite/montmorillonite) promoted better surface properties to the biocomposites, by making them biodegradable on aquatic environments, without unbalancing the nutrient loads among different environmental compartments.