Polysaccharide beads and films for controlled release of agricultural compounds and water decontamination

Abstract

Massive amounts of agricultural, industrial, medical and domestic water worldwide are polluted by different types of contaminants that harm the environment and impact human health. Films and beads made from abundant inexpensive polysaccharides have been shown to be effective sorbents that can be utilized for the removal of contaminants from effluent. In addition, these materials can also function as vehicles for controlled release of chemicals for targeted applications. As a result, polysaccharides properties have been exploited in various fields of research in the biomedical, pharmaceutical, cosmetic, food and agricultural industries due to their unique physicochemical characteristics. In the first part of this research, alginate beads were formed by combination with either starch, one of two types of cellulose, or xylan as fillers and investigated for their effectiveness as sorbents in waste water remediation processes. Their capacity for water uptake, their sorption capabilities for a model cationic pollutant and their charge density was studied in relationship to their composition and their surface characteristics. The effect of drying the beads in air or lyophilizing on their average diameters was assessed by optical microscopy and differences in morphology were observed by scanning electron microscopy. Their interaction with water was evaluated using low-field NMR spectroscopy. It was found that nanocrystalline cellulose had the most influence on the beads’ sorption capacity for cationic contaminants while xylan admixture created beads with the highest water sorption after lyophilization. In the second part of this research, polysaccharide beads formulated from alginate, cellulose powder, cellulose nanocrystals (CNC), starch and xylan were reinforced with kaolin and surface-modified with polyethylenimine (PEI), a positively-charged polyelectrolyte. Addition of kaolin improved the mechanical strength of the beads. Modification of the surface of the beads with PEI facilitated better control of the release rate of the plant growth regulator, phenylacetic acid (PAA). The physical properties of the beads were characterized by optical and scanning electron microscopy (SEM), and their mechanical strength was determined using an Instron® 5565 Tensile Testing Machine. Cumulative release of PAA was measured by UV-Vis spectroscopy. In the third research project, pectin blended with four other types of anionic polysaccharides, including alginate, carrageenan, xylan and xanthan, were crosslinked with zinc acetate and formed into thin films. In addition, a negatively charged polyelectrolyte, poly(4-styrenesulfonic acid-co-maleic acid) sodium salt (PSSMA) was coated on the film surface with the goal of increasing the capture of cationic contaminants. The average film thickness was measured using a digital micrometer. Surface morphologies and elemental analysis were obtained by energy dispersive spectroscopy connected with scanning electron microscopy. The swelling ratio and the mechanical properties of the films were investigated in relationship to their composition and PSSMA coating. The sorption of model cationic pollutants clearly improved for coated films and showed to be predominantly based on the interaction of positively and negatively charged groups between film/coating and contaminants.