低含量聚乳酸对微孔发泡聚丁二酸丁二醇酯泡孔结构的改善

通过挤出制备了可生物降解聚丁二酸丁二醇酯(PBS)和3种聚乳酸(PLA)含量(7 wt%、15 wt%和20 wt%)的PBS/PLA共混物样品,采用超临界二氧化碳作为物理发泡剂对样品进行间歇发泡,研究发泡样品的泡孔结构,并分析其形成机理.在120oC发泡温度(Tf)下,借助PLA对PBS熔体黏弹性尤其是熔体强度的改善,获得了分布较均匀、形状较规则、直径较小(平均值约10μm)的微孔;共混物发泡样品的直径分布明显变窄,且符合高斯分布,这归因于细小的PLA相较均匀地分布于PBS基体中.进一步地,研究Tf对PBS和PLA含量为15 wt%的PBS/PLA共混物发泡样品泡孔结构的影响.结果表明,加入15 wt%的PLA使PBS的Tf下限从115oC降低至110oC,并显著改善了较高Tf(120和125oC)下制备的发泡样品内泡孔结构的均匀性.

Improving Cellular Structure of Microcellular Poly(butylene succinate) via Adding Low Content of Poly(lactic acid)

A new strategy was proposed to improve foaming properties of poly(butylene succinate) (PBS) via blending it with low content ofpoly(lactic acid) (PLA).Biodegradable PBS/PLA blend samples with PLA content of 7 wt％,15 wt％ and 20 wt％ and pure PBS sample were prepared using a single-screw extruder with a chaotic mixing screw developed in our group.The samples were then foamed using supercritical carbon dioxide as physical foaming agent in a batch process.The cellular structure of the foamed samples was investigated,and its formation mechanism was analyzed.At foaming temperature (Tf) of 120 ℃,the foamed PBS sample exhibited an irregular cellular structure and wider cell diameter distribution (5-30 μm).Adding low PLA content (7 wt％,15 wt％ or 20wt％) obviously improved the foaming properties of the PBS.Microcells were developed with more uniform distribution,more regular shape,and smaller diameter (with a mean value of about 10 μm) for all the foamed blend samples.This is attributed to improved storage modulus,complex viscosity and especially melt strength of the PBS induced by added PLA.Moreover,the cell diameters for the foamed blend samples exhibited a much narrower distribution (4-18 μm) and followed Gaussian distribution,resulting from good dispersion of the PLA microdomains.Further,the effect of the Tf on the cellular structure ofmicrocellular samples of the PBS and the blend with 15 wt％ of PLA was investigated.As for the PBS,the lower Tf limit for foaming was dictated by its higher crystallinity degree,whereas the upper one by its low melt strength.Specifically,the lower Tf limit was 115 ℃.When lowering the Tf to 110 ℃,only a few sparse cells appeared in the foamed PBS sample,which was inferred to be developed at the core of spherulite.Raising the Tf to 120 or 125 ℃,the wall of some cells was ruptured.Adding 15 wt％ of PLA shifted the lower Tflimit of the PBS from 115 ℃ to 110 ℃,and obviously improved the cellular structure uniformity and decreased the cell diameters for the foamed samples prepared at relatively high Tfs (120 and 125 ℃).