Cell Morphology and Improved Heat Resistance of Microcellular Poly(L-lactide) Foam via Introducing Stereocomplex Crystallites of PLA
Cell Morphology and Improved Heat Resistance of Microcellular Poly(L-lactide) Foam via Introducing Stereocomplex Crystallites of PLA
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DOI：
10.1021/ie504345y
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发表时间：
2015-03-11
影响因子：
4.2
通讯作者：
Han, Changyu
中科院分区：
文献类型：
--
作者：
Jia, Pin;Hu, Jie;Han, Changyu
制备具有良好泡孔结构和高耐热性的聚L-乳酸（PLLA）泡沫是拓宽其应用的关键。通过熔融共混的方法，将具有较高熔点和热稳定性的立体复合微晶（SC）引入到PLLA泡沫材料中，并与不同量的聚D-乳酸（PDLA）进行共混。比较了纯PLLA和PLLA/PDLA共混物在共混和成型过程中形成的晶体结构。结果表明，纯PLLA没有明显的结晶现象，而PLLA/PDLA共混体系中有SC生成。采用DSC、WAXD、FTIR和SEM等技术研究了PLLA和PLLA/PDLA复合材料在CO2饱和发泡过程中的晶体结构和形态变化。结果表明，与纯PLLA相比，SC具有较高的熔融峰、较高的热稳定性和较小的晶畴尺寸，且不随CO2饱和和发泡过程而进一步发展，但CO2饱和导致PLLA和PLLA/PDLA共混物形成介晶结构。在随后的发泡过程中，介晶结构转变为更稳定的结构。所得PLLA/PDLA泡沫相对于PLLA泡沫表现出泡孔密度和泡孔结构均匀性的显著且同时的增加。耐热性测试表明，PLLA/PDLA泡沫塑料的耐热性优于PLLA泡沫塑料，这是由于PLLA/PDLA泡沫塑料中SC具有较高的熔点、热稳定性和成核能力。
The preparation of poly(L-lactic acid) (PLLA) foam with well-defined cell structure and high heat resistance is critical to broaden its applications. In this study, the stereocomplex crystallites (SC) with higher melting point and heat stability were introduced into PLLA foam by melt blending the PLLA with different amounts of poly(D-lactic acid) (PDLA). The crystal structures of pure PLLA and PLLA/PDLA blends formed during the blending and molding process were compared. It was found that no obvious crystallization was detected in pure PLLA, while SC formed in PLLA/PDLA blends. Crystal structure and morphology evolution of PLLA and PLLA/PDLA during the CO2 saturation and foaming process were investigated by combination of DSC, WAXD, FTIR, and SEM techniques. The results suggested SC had a higher melting peak, higher thermal stability, and smaller crystal domain size in relation to the homocrystal of PLLA, and it did not further develop with the CO2 saturation and the foaming processes, while the CO2 saturation induced the formation of the mesomorphic structure in PLLA and PLLA/PDLA blends. The mesomorphic structure transformed into the more stable a form in the following foaming process. The resultant PLLA/PDLA foam exhibited a significant and concurrent increase in cell density and cell structure uniformity relative to PLLA foam. The heat resistance measurement presented that thus-prepared PLLA/PDLA foams had better heat resistance than PLLA foam, which was attributed to the higher melting point, higher heat stability, and higher cell nucleation ability of SC in PLLA/PDLA foams.