Chemical treatment of poly(lactic acid) fibers to enhance the rate of thermal depolymerization

When heated, poly(lactic acid) (PLA) fibers depolymerize in a controlled manner, making them potentially useful as sacrificial fibers for microchannel fabrication. Catalysts that increase PLA depolymerization rates are explored and methods to incorporate them into commercially available PLA fibers by a solvent mixture impregnating technique are tested. In the present study, the most active catalysts are identified that are capable of lowering the depolymerization temperature of modified PLA fibers by ca. 100 °C as compared to unmodified ones. Lower depolymerization temperatures allow PLA fibers to be removed from a fully cured epoxy thermoset resin without causing significant thermal damage to the epoxy. For 500 μm diameter PLA fibers, the optimized treatment involves soaking the fibers for 24 h in a solvent mixture containing 60% trifluoroethanol (TFE) and 40% H ₂O dispersed with 10 wt % tin(II) oxalate and subsequent air-drying of the fibers. PLA fibers treated with this procedure are completely removed when heated to 180 °C in vacuo for 20 h. The time evolution of catalytic depolymerization of PLA fiber is investigated by gel permeation chromatography (GPC). Channels fabricated by vaporization of sacrificial components (VaSC) are subsequently characterized by scanning electron microscopy (SEM) and X-ray microtomography (Micro CT) to show the presence of residual catalysts.