Soil degradation behavior of ramie/thermoset poly(lactic acid) composites

A new thermoset PLA resin was synthesized. The structure and performance of the thermoset PLA resin were characterized by Fourier transform infrared spectroscopy (FTIR), 1H Nuclear Magnetic Resonance (1H-NMR), 13C Nuclear Magnetic Resonance (13C-NMR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) testing methods. The results indicate that thermoset PLA resin has been synthesized successfully, and the thermal stability of thermoset PLA is better than that of linear PLA. Thermoset PLA resin and ramie/thermoset poly(lactic acid) (PLA) composites were prepared by casting and hot-pressing, respectively. The degradation behavior was evaluated by surface morphology observation, scanning electron microscope (SEM), pH detection and FTIR analysis. The results show that the thermoset PLA resin fully degrades after 20 days, and the degradation rate of ramie/thermoset PLA composites is only 45.27% after 30 days, which is lower than that of thermoset PLA. The reason is due to that ramie fabric as the barrier hinders the moisture and microorganisms enter the interior of the composites. Moreover, according to the FTIR analysis, the ester groups of thermoset PLA are firstly hydrolyzed, and thermoset PLA is decomposed into low molecular weight oligomers. Then thermoset PLA and oligomers are continuously hydrolyzed by moisture and microorganisms until mineralized into H2O and CO2. Besides, the soil pH value detection proves that no acidic or alkaline harmful degradation products are produced during the soil degradation process.