| Because of its good biocompatibility and biodegradability, poly(lactic acid)(PLA) has broad application prospects in the packaging materials, biologicalmedicine and other fields. However, it is not ideal for industrial application of PLA.Pure PLA has relatively brittle property and low melt-strength which lead to thefailure in foaming. Nanocrystalline cellulose (NCC) is a kind of natural andrenewable organic nano-particals with some excellent properties, such as high length-diameter radio and high strength. Modifying PLA with NCC can not only improvethe performance, but also enlarge its application scope. PLA and NCC, derived frombiomass resources, are biodegradable after being abandoned and meet the concept of“sustainable development” and “green packaging”.Based on the matrix—PLA, the reinforced phase—NCC, and the compatibilizer—polyethylene glycol (PEG), PLA/NCC composite was prepared by melt-blending.The chemical structure and hydrogen bonding of compound system was analyzed byfourier infrared spectrometry (FTIR) and the results showed that the hydrogenbonding not only existed between PEG and PLA, but also between exposed NCC andPLA. The hydrogen bonding of temperature dependence which was tested by variabletemperature-FTIR demonstrated that hydrogen bonding strength was stability at a lowtemperature, but weakened when more than60℃. The crystallization of compoundsystem was studied by X-ray diffraction (XRD). In addition, the dynamicthermomechanic analysis (DMA) revealed NCC increased the storage modulus butalmost did not influence Tg, and PEG reduced the storage modulus and Tg, improvedthe flexibility of composite.Degradation experiment was conducted in phosphate buffer (PBS) with37℃and7.4pH. The degradation performance was explored through the water absorptionrate, mass loss, thermo-gravimetric analysis (TGA) and so on. The research indicatedthat adding NCC and PEG decreased the hydrophilic angle, increased the surfaceemergency, and improved the water absorption rate. And adding NCC and PEG alsoboosted the degradation rate and shortened the period of degradation. When degraded for60days, the mass loss rate of PLA/N/P-16was4.7times that of pure PLA, andthe molecular weight reduced by37.2%. The TGA curves showed that the rate ofthermal degradation improved after PLA being reinforced by NCC and PEG.However, the thermal decomposition temperature remained above300℃, whichcould still meet the requirement of production.At last, PLA/NCC microcellular foaming material was prepared by supercriticalCO2, the foaming process parameters were optimized, and the effects of NCC andPEG on the foaming system were analyzed by scanning electron microscopy (SEM).The study indicated that the best bubble structure was obtained at the condition of2h,100℃and16MPa. NCC could develop the foaming performance by improving themelt strength, and moreover NCC played a role of heterogeneous nucleation in thefoaming system. In a certain range, the bubble density increased with the content ofNCC increasing. When adding4%NCC, ideal microcellular foaming material with abubble diameter of3.79μm and a bubble density of3.11×1010cell/cm3was obtained.PEG, which had no direct effect on bubble nucleation and growth, mainly played arole of compatibilizer to improve the microcellular foaming performance. |
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