Rapid and solvent-free synthesis of pH-responsive graft-copolymers based on wheat starch and their properties as potential ammonium sorbents.

A rapid and cost-effective reactive extrusion (REx) method was employed in this study as an alternative technique for the graft-copolymerization of non-food grade native wheat starch with acrylamide, and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) monomers, with a total starch/monomer ratio of 3:1, using twin-screw extrusion technology. The influence of AMPS content ratio on the REx process was monitored using specific mechanical energy, die pressure and torque values recorded during the extrusion. The as-prepared starch-copolymers were characterized using ATR-FTIR, NMR, TG-DSC, and elemental analysis. An average grafting efficiency and monomer conversion of ~61 and ~86%, respectively, was achieved within 5 min of extrusion at a high starch concentration (0.75:1 w/w starch-water). The copolymer with starch/acrylamide/AMPS weight ratio of 75:20:4 showed the highest swelling capacity in water, while behaving similarly to polyelectrolyte networks in the presence of free ions in both NaCl and NH4Cl solutions. A steady NH4+ adsorption capacity was also recorded for these starch-copolymers within the pH range of ~5.5-8.5, which exceeded those of the natural sorbents. These findings indicate the suitability of the starch-copolymers as potential precursors of effective sorbents, thus confirming the feasibility of using REx to produce pH-responsive hybrid copolymers based on wheat starch at low-cost.

Synthesis of starch graft-copolymers via reactive extrusion: Process development and structural analysis.

To promote the large-scale production of starch-based biomaterials, we developed a method of synthesis based on reactive extrusion that combines the benefits of continuous manufacturing with the use of green chemistry principles. This paper describes the grafting of four different types of starches with acrylamide monomers via free radical copolymerization using twin-screw extrusion technology. The elemental analysis confirmed the success of this method, with an average monomer conversion of 80% and grafting efficiency of ˜74% across all samples. The 13C-NMR/1H-NMR and ATR-FTIR analysis revealed that the type of starch substrate used strongly influenced the mechanism of the grafting reaction. Thermal analysis (TG/DTG-DSC) indicated that the graft-copolymers thermal stability was influenced by the amylose-amylopectin content ratio. Swelling tests suggested that cationic modification of the substrate is a promising approach to produce stimuli-responsive graft-copolymers via reactive extrusion. The proposed method has proved to be a viable alternative for the production of starch-copolymers.

Rapid removal of ammonium from domestic wastewater using polymer hydrogels.

To date, technologies to recover ammonium from domestic wastewater from the mainstream have not found widespread application. This is largely due to the low ammonium concentrations in these wastewater streams. This paper reports on the use of polymer hydrogels for rapid sorption of ammonium from domestic wastewater coupled with efficient regeneration by mild acid washing. The sorption capacity of the hydrogel was 8.8-32.2 mg NH4-N/g, which corresponds to removal efficiencies ranging from 68% to 80% NH4-N, increasing proportionally with the initial ammonium concentration. It was, however, unaffected by changes in pH, as the sorption capacity remained constant from pH 5.0-8.0. Importantly, effective regeneration of the hydrogels under mildly acidic conditions (i.e. pH 4.0) was demonstrated with minimal loss in sorption performance following multiple sorption/desorption cycles. Overall, this study highlights the potential of low-cost polymer hydrogels for achieving mainstream ammonium recovery from domestic wastewater.

Extrusion induced low-order starch matrices: Enzymic hydrolysis and structure.

Waxy, normal and highwaymen maize starches were extruded with water as sole plasticizer to achieve low-order starch matrices. Of the three starches, we found that only high-amylose extrudate showed lower digestion rate/extent than starches cooked in excess water. The ordered structure of high-amylose starches in cooked and extruded forms was similar, as judged by NMR, XRD and DSC techniques, but enzyme resistance was much greater for extruded forms. Size exclusion chromatography suggested that longer chains were involved in enzyme resistance. We propose that the local molecular density of packing of amylose chains can control the digestion kinetics rather than just crystallinity, with the principle being that density sufficient to either prevent/limit binding and/or slow down catalysis can be achieved by dense amorphous packing.

The fabrication and characterization of biodegradable HA/PHBV nanoparticle-polymer composite scaffolds.

This study reports the fabrication and characterization of nano-sized hydroxyapatite (HA)/poly(hydroxyabutyrate-co-hydroxyvalerate) (PHBV) polymer composite scaffolds with high porosity and controlled pore architectures. These scaffolds were prepared using a modified thermally induced phase-separation technique. This investigation focuses on the effect of fabrication conditions on the overall pore architecture of the scaffolds and the dispersion of HA nanocrystals within the composite scaffolds. The morphologies, mechanical properties and in vitro bioactivity of the composite scaffolds were investigated. It was noted that the pore architectures could be manipulated by varying phase-separation parameters. The HA particles were dispersed in the pore walls of the scaffolds and were well bonded to the polymer. The introduction of HA greatly increased the stiffness and strength, and improved the in vitro bioactivity of the scaffolds. The results suggest these newly developed nano-HA/PHBV composite scaffolds may serve as an effective three-dimensional substrate in bone tissue engineering.