Rapid Degradation of Poly(lactic acid) with Organometallic Catalysts

Poly(lactic acid) (PLA) is an effective sacrificial material for the creation of vascular networks in thermoset polymers and composites. The high thermal stability of PLA limits its applications as an embedded sacrificial template in high-temperature-resistant thermoset matrices. Here, we demonstrate faster and more efficient PLA degradation at temperatures lower than previously reported using two organometallic catalysts: tin(II) oxalate (Sn(Oxa)) and tin(II) acetate (Sn(Ac)2). We process Sn(Oxa) by two separate methods to obtain a significant difference in the specific surface area (SSA) of the catalyst particles and compare PLA degradation performance in a thermogravimetric analysis (TGA) instrument. Changing the SSA of Sn(Oxa) by a factor of ∼20 reduces the PLA degradation onset temperature by 37 °C. The total degradation time of PLA films also decreases after blending with Sn(Oxa) having a higher SSA. We also find Sn(Ac)2 lowers the degradation onset of PLA by 53 °C compared to Sn(Oxa) with a similar SSA. In addition, Sn(Ac)2 decreases the time for complete degradation of PLA films by an order of magnitude compared to Sn(Oxa) at 200 °C. Films with a significantly lower Sn(Ac)2 concentration compared to Sn(Oxa) degrade much faster at lower temperatures up to 160 °C. Finally, PLA films with different loadings of Sn(Ac)2 are embedded in an epoxy thermoset matrix and subsequently vascularized at elevated temperatures in a vacuum oven. Microchannel formation is observed at 170 °C using Sn(Ac)2, reducing the temperature required for vaporization of embedded sacrificial polymer compared to Sn(Oxa) catalyst. Sn(Ac)2 can potentially reduce the energy, time, and amount of catalyst required for degrading PLA into volatile products for sacrificial applications.