Study On Rheology And Degradation Characteristics Of PPC And PLA/PPC Blends

Poly(propylene carbonate)(PPC) is a new biodegradable thermoplastic material, which easily subjects the degradation due to high temperature and high shear during the processing, and then affects its performance. In this work, degradation of PPC at different processing conditions(temperature, time, environment and shear) was investigated by rheological method. Poly(lactic acid)(PLA) is also an excellent biodegradable material. But it is brittle and its melt strength is low. PPC possesses complementary characteristics with PLA. Therefore, in order to improve the performance of PLA, the rheological characteristics and impact resistance of PLA/PPC blends were studied. The main research results were showed as:1. Comparing and analyzing rheological characteristics of three PPCs with different molecular weight, it was shown that:increasing PPC’s molecular weight, the linear viscoelastic region widened, shear thinning behavior was more obvious and the disentangle time of polymer chains increased. According to the Cox-Merz rule, the steady shear modulus could be obtained from dynamic modulus. It was found that zero shear viscosity could be obtained through Carreau-Yasuda(Osc) model.2. Combined with time-temperature superposition(TTS) principle, the degradation behavior of PPC could be investigated by high temperature and high shear in rheometer. When temperature was less than170℃, the rate of PPC’s thermal degradation was slow; When temperature was higher than170℃, the PPC’s degradation would be apparent. PPC was hardly affected by the shear at150℃; While increasing of temperature above150℃, the degradation of PPC was more seriously due to high shear. Comparing PPC with different molecular weight, PPC with low molecular weight was less affected by shear. The result of nuclear magnetic resonance(13C-NMR) and infrared analysis(FTIR) showed that the degradation of TT structure was dominant only by shear, and the degradation of HH structure was dominant only by temperature. Comparing TT and HH structure, the degradative rate of HT structure was slow.3. For PLA/PPC blends, the introduction of PPC increased the complex viscosity and enhanced the melt strength of blends. For example, when PPC’s content was10%, η*of blends increased by about one time more than that of PLA. When PPC’s content was less than30%, impact strength, tensile stress and elongation increased with increasing PPC’s content. For example, when PPC’s content was10%, impact strength of blends increased by about50%more than that of PLA. The improvement of PLA’s toughening performance and melt strength by adding PPC with high molecular weight was more obvious.