Khwanpipat Thanawat, Seadan Manus, Suttiruengwong Supakij
Department of Materials Science and Engineering, Faculty of Engineering and Industrial Engineering, Silpakorn University, Nakhon Pathom 73000, Thailand.
Department of Physics, Faculty of Science, Silpakorn University, Nakhon Pathom 73000, Thailand.
Materials (Basel). 2018 Jul 5;11(7):1139. doi: 10.3390/ma11071139.
The improvement of the rate of crystallization and crystallinity of poly (l-lactic acid) (PLLA) is one of the key performance elements for PLLA to perform better at the higher temperature than its heat deflection temperature (around 60 °C). The organic nucleating agent compounds are one of the interesting choice as they can offer the clarity of products. On the other hand, the nucleated PLLA can be prepared using a low molecular weight poly (d-lactic acid) (PDLA). The aim of this work was to explore the effect of an unsaturated amide compound and PDLA as single and mixed nucleating agents used for PLLA. The crystallization rate and kinetics were investigated and compared for the synthetic unsaturated amide compound (,′-ethylenebis (10-undecenamide) (EBU)) and commercial hydrazide compound (tetramethylenedicarboxylic dibenzoylhydrazide (TMC-306)). PLLA samples was prepared by melt-mixing with TMC or EBU incorporated with peroxide. The influence of different nucleating agents loading on thermal properties, crystallization behaviors, and rheological properties of PLLA were explored by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The results showed that the addition of EBU or TMC 0.5 phr could pronouncedly increase the crystallinity of PLLA from 3.80% to 24.84% and 8.61%, respectively. The crystallization peak appeared at 112.3 °C in the cooling scan at the rate 7 °C/min when addition EBU and peroxide into PLLA. This indicated that EBU acted as an efficient nucleating agent for PLLA. In isothermal crystallization run at 110 °C, it was found that the overall crystallization rate of nucleated PLLA with TMC or EBU was much faster than neat PLLA. The crystallization half-time indicated that the existence of TMC or EBU could slightly decrease to 2.90 and 1.96 min, respectively compared to neat PLLA (4.60 min). Finally, a low molecular weight PDLA with different contents between 3 and 7 wt % was added in PLLA with EBU and peroxide to investigate the effect of mixed nucleating agents. The crystallization rate of the incorporation of PDLA/EBU/peroxide into PLLA was discussed with the proposed crystallization mechanism. The results revealed the stereocomplex temperature peak at 207 °C as well as normal melting temperature of PLLA. The kinetics of growth crystallization, the crystallization half-time of PLLA at 110 °C was reduced from 4.60 min to 1.96 min (when adding EBU alone) and to 2.62 min (when using mixed PDLA and EBU).
提高聚（L-乳酸）（PLLA）的结晶速率和结晶度是使PLLA在高于其热变形温度（约60℃）的温度下表现更优的关键性能要素之一。有机成核剂化合物是一个有趣的选择，因为它们能使产品保持透明。另一方面，可使用低分子量的聚（D-乳酸）（PDLA）制备成核PLLA。这项工作的目的是探究不饱和酰胺化合物和PDLA作为PLLA的单一及混合成核剂的效果。研究并比较了合成的不饱和酰胺化合物（N,N'-亚乙基双（10-十一碳烯酰胺）（EBU））和市售酰肼化合物（四亚甲基二羧酸二苯甲酰肼（TMC-306））的结晶速率和动力学。通过将TMC或EBU与过氧化物一起熔融共混来制备PLLA样品。利用差示扫描量热法（DSC）和动态力学分析（DMA）探究了不同成核剂用量对PLLA热性能、结晶行为和流变性能的影响。结果表明，添加0.5 phr的EBU或TMC可分别使PLLA的结晶度显著从3.80%提高到24.84%和8.61%。当向PLLA中添加EBU和过氧化物时，在7℃/min的冷却扫描中，结晶峰出现在112.3℃。这表明EBU是PLLA的有效成核剂。在110℃的等温结晶过程中，发现添加TMC或EBU的成核PLLA的整体结晶速率比纯PLLA快得多。结晶半衰期表明，与纯PLLA（4.60 min）相比，TMC或EBU的存在可分别略微降低至2.90和1.96 min。最后，在含有EBU和过氧化物的PLLA中添加3至7 wt%不同含量的低分子量PDLA，以研究混合成核剂的效果。结合提出的结晶机理讨论了PDLA/EBU/过氧化物加入PLLA后的结晶速率。结果揭示了207℃的立体复合温度峰以及PLLA的正常熔点。在110℃下，PLLA的生长结晶动力学、结晶半衰期从4.60 min降低至1.96 min（单独添加EBU时）和2.62 min（使用PDLA和EBU混合时）。
