Research Of The Foaming Extrusion For Pla

Poly(lactic acid) is an industrially mature, bio-sourced and biodegradable polymer, current applications of this material are limited as a result of its brittleness and its poor melt properties. This paper systematically studied the extrusion foaming process and cell opening mechanism of PLA, and found the method of controlling PLA cell open content. Against the low melt strength characteristics of ordinary PLA, this study extended PLA molecular chain by reaction extrusion with an epoxy chain extender to improve the melt strength and foaming properties of PLA.In this paper, using a foam-level PLA, Bio-plus302(abbreviated as B+302), the extrusion foaming process, cell opening mechanism and the method of controlling of PLA cell open content was studied. The temperature zone of120to145℃and the CO2content of7%to10%of low PLA density foam (<50kg/m3) was obtained. Accordingly, the head pressure should be kept at7MPa or more. Add low content of LLDPE to PLA, as an organic nucleating agent, the open cell content of PLA foam was effectively reduced.Two low melt strength of PLA,4032D and3052D, were modified by chain extending on reactive extruder to improve the melt strength and foaming properties. And the influence of chain extending on the molecular weight and its distribution, rheological properties, crystallization properties and foaming properties of PLA was discussed. The extended PLA showed higher the molecular weight than unmodified PLA. Compared to the unmodified PLA, the molecular weight of the extended3052D was increased by13%, the extended4032D was increased by40%. The chain extending greatly improved the melt strength of both PLA. The melt strength of extended3052D and4032D was4to6times higher than unmodified PLAs.Due to the chain extended, the crystallization ability of both PLA was slightly reduced. Since the weak crystallization ability of3052D system, the initial crystallinity of modified3052Ds was3%or less. The crystallization ability of4032D is stronger than3052D, its degree of crystallinity reduced about10%compared to unmodified4032D.Compared to the unmodified PLA, the chain extending greatly improved the foaming properties of both PLA. For modified3052D, the apparent density decreased by38%, the mean cell diameter reduced23μm and the cell density increased by an order of magnitude compared to the unmodified foam. The apparent density of4032D decreased by43%, the cell diameter reduced39μm and the cell density increased an order of magnitude compared to unmodified one.Finally, the comparison of foaming properties between the purchased foam level PLA and the modified two foaming properties of PLA (3052-2and4032-2) including foam density, cell morphology and cell open content was achieved.The crystallization rate and melt strength greatly influenced on the foaming temperature zone. Slow crystallization rate and high melt strength of the material means widely temperature region in the foaming process. The melt strength and melt elasticity greatly influenced on the foam properties, the higher melt strength and melt elasticity, meaning the low open cell content and finely cell foam was easily obtained.