发泡聚乳酸流变性能及泡孔结构的研究

Study on Rheological Behavior and Cell Structure of Foamed Polylacic Acid

采用偶氮二甲酰胺（AC）做为发泡剂，直接通过挤出过程制备聚乳酸（PLA）泡沫塑料，通过显微镜照片、HAKKE流变仪观察和研究了工艺条件对其泡孔结构的影响。结果表明，发泡剂与成核剂的增加能降低发泡PLA的表观密度，增加其泡孔密度。流变试验表明纯PLA与发泡PLA熔体在低剪切速率下都呈现剪切变稀现象，发泡后PLA熔体的黏度会下降10％～30％。发泡剂含量在4％以下时，泡孔直径随发泡剂含量增加而减小；发泡剂含量增加到5％及以上时，PLA熔体强度过小，泡孔会过于密集而导致塌陷和串泡。成核剂的加入能够明显降低PLA熔体强度，异相成核使得泡孔直径较均相成核大，但前者泡孔密度较后者小。

Porous polylactic acid foamed by azodicarbonamide was prepared on a single-screw extruder. The effects of influencing factors （nucleating and foaming agent） on the cell structure and the rheological behavior of the melt were investigated using microscope and HAKKE rheometer. The apparent density of the porous PLA decreased （pore density increased） with increasing content of nucleating and foaming agent. HAKKE rheometer showed that neat and foamed PLA were both shear-thinning at low shear rates. Compared with the neat PLA, the viscocity of foamed PLA was 10 % -30 % lower. When the content of foaming agent was below 4 %, pore diameter decreased as foaming agent increased; when the content of foaming agent was higher than 5 %, the pore collapsed and merged because of the low melt strength. The melt strength of foamed PLA decreased obviously with the addition of nucleating agent. The diameter of the pores for heterogeneous nucleation was bigger than that of homogeneous one, while the pore density of the former was smaller than the latter.