Direct Resinification of Two (1→3)-β-D-Glucans, Curdlan and Paramylon, via Hot-Press Compression Molding

摘要

Hot-press compression molding was attempted to resinify two renewable source-derived linear (1→3)-β-D-glucan polymers, i.e., paramylon or curdlan via the generation of reactive aldehyde groups that tend to crosslink with hydroxyl groups of the glucans. As for the paramylon, the optimal molding temperature was found to be around 220 °C, keeping the pressure at 20 MPa for 3 min, due to its highly crystalline structure. On the other hand, the curdlan resin was producible in the temperature range of 180-240 °C at the same pressure and pressing time. Dynamic mechanical analysis revealed a large temperature dependence of the loss modulus, E'', for the paramylon- based polymer resin whereas the semi-crystalline curdlan resin was stable in terms of both the storage and loss moduli, E' and E'', up to 160 °C. The vaporization of the water formed during the molding, due to the thermal decomposition, and the adsorption of moisture due to the hydrophilic property of the paramylon affected the thermal stability. The curdlan resin exhibited flexural strength and modulus extremely superior to those of regenerated and esterified curdlan films, and even a little superior to those of polyamide-12. The strain at break was comparable to the yield strain of an epoxy resin. On the other hand, the paramylon-based polymer resin was producible, but the resinification property and thermal stability of the paramylon resin was inferior to the curdlan resin due to the former's highly crystalline structure.