This research studies the effect of thermal, thermo-oxidative and thermomechanical degradation conditions on the melt rheological, chemical and thermal properties of PLA at temperatures around its normal processing temperature. Thermal and thermo-oxidative degradations were conducted on a rheometer by using nitrogen or air as gas, respectively, and the thermomechanical degradation was performed on a mixer equipped with two counter-rotating rollers. Dynamic oscillatory rheology, TGA, DSC and FTIR were performed on PLA samples subjected to different degradation conditions: temperature (180, 200 or 220 °C), time (15, 30 or 60 min), atmosphere (air or atmosphere) and the application of mechanical stress or not. Thus, rheological results indicate the synergic effect that temperature, mechanical stress and time exerts on the extent of chain scission phenomena, which was also corroborated by FTIR results; however, the individual contribution of mechanical stress diminishes gradually with the degradation time, being more pronounced for higher degradation temperature. In addition, degree of crystallinity (χ_c) turned out not to be a suitable parameter for comparing degraded samples, since all of them became amorphous after degradation. Instead, glass transition (T_g) and cold crystallization (T_cc) temperatures as well as the cold crystallization enthalpy (ΔH_cc) reveal that the chain scission phenomena makes degraded samples easier to crystallize. Finally, TGA results point out a worsening of the PLA thermal stability, with lower values of the characteristic temperatures (T_5% and T_max) for degraded samples.

这项研究研究了热，热氧化和热机械降解条件对PLA正常加工温度附近的熔体流变学，化学和热学性质的影响。分别通过使用氮气或空气作为气体在流变仪上进行热和热氧化降解，并在配备有两个反向旋转辊的混合机上进行热机械降解。在具有不同降解条件的PLA样品上进行了动态振荡流变学，TGA，DSC和FTIR的研究：温度（180、200或220°C），时间（15、30或60分钟），大气（空气或大气）及其应用机械应力与否。因此，流变学结果表明温度，机械应力和时间影响断链现象的程度，FTIR结果也证实了这一点；然而，机械应力的个体贡献随着降解时间而逐渐减小，对于更高的降解温度而言更为明显。另外，结晶度（χ_c）并不是比较降解样品的合适参数，因为所有样品在降解后都变成非晶态。取而代之的是，玻璃化转变（T_克）和冷结晶（T _CC）的温度以及冷结晶焓（ΔH _CC）表明断链现象使得降解的样品更容易结晶。最后，TGA结果表明PLA的热稳定性变差，降解样品的特征温度值较低（T _5％和T _max）。