Microcellular extrusion‐foaming of polylactide with chain‐extender

Abstract

The effects of adding epoxy-functionalized chainextender (CE) and processing conditions such as die temperature on the cell morphology, volume expansion ratio (VER), open cell content (OCC), and crystallization of microcellular extruded polylactide (PLA) were investigated. When compared with pure PLA, the addition of talc decreased the average cell size and increased the cell density. Moreover, the simultaneous addition of talc and CE led to denser and more uniform cell structure up until 1.0% CE content. In general, the volume expansion ratio and open cell content of all the formulations decreased with the die temperature. The addition of talc decreased both VER and OCC, whereas the addition of CE increased both. The die temperature did not affect the degree of crystallinity significantly. The addition of talc increased the crystallinity, but the addition of CE decreased it. Finally, the molecular weight of PLA increased significantly with the addition of CE. FIG. 4. Variation of average cell size with (a) die temperature and (b) formulation. FIG. 5. Variation of cell density with (a) die temperature and (b) formulation. FIG. 8. Variation of degree of crystallinity with (a) die temperature and (b) formulation.

Foaming of Polylactide in the Presence of Chain Extender

“…Various properties of PLA, particularly its degree of crystallinity, the melting point, mechanical, rheological and barrier properties, can be controlled by varying the ratio of stereoisomers of L-and D-lactic acid [8,9]. Despite all the advantages of PLA, there are nevertheless some drawbacks, especially a low molecular weight, which affects the polymer melt viscosity, melt elasticity, mechanical and thermal properties [10,11]. One of the possible methods to increase the molecular weight is the use of chain extenders (CE) that cause a change from the linear to long chain branched structures [12].…”

“…It was also noted that in PLA 3251D, despite its low melt viscosity, the cellular structure can be successfully produced in a sufficiently low temperature. Pilla et al [10] studied the effect of chain extender CESAextend (CE) and talc on the structure of PLA. Addition of talc caused a reduction in the cell size and increased cell density in PLA.…”

The effect of two commercial melt strength enhancer additives on the thermal, rheological and morphological properties of polylactide

“…Najafi et al [21] prepared PLA-clay nanocomposites using polycarbodiimide, tris(nonyl phenyl) phosphate and Joncryl ADR-4368 as chain extenders. Liu et al [16], Corre et al [22], Mihai et al [23] and Pilla et al [24], employed a multi-functional epoxy-based chain extender (Cesa-Extend from Clariant) to give rise to branched structures of PLA. Recently, Han et al [25] used polysilsesquioxane microspheres as novel chain extenders to improve the thermal stability of PLA.…”

Characterisation of natural fibre reinforced PLA foams prepared by supercritical CO2 assisted extrusion

“…CEs have two or more functional groups such as hydroxyl, amine, anhydride, epoxy, carboxylic acid or isocyanate. Bifunctional CEs couple the two end groups of PLA, thereby lead to a linear polymer with somewhat higher molecular weight, while CEs of higher functionality give raise to branched structures with significantly improved rheological properties [2,3]. It was found by Wang et al [4] that molecular branching increases melt strength and elasticity, and thereby also the integrity of cells, cell density, and expansion ratio during extrusion foaming.…”

“…In PLA, improved crystallinity has been achieved by using different nucleation agents, such as talc, that increase the heterogeneous nucleation density [7]. It was shown by Pilla et al [2] that the simultaneous addition of talc and CE leads to increased cell density and more uniform cell structure. Fillers, such as wood particles [8] or clay nanoparticles [9] are also known to act as crystal nucleating agents and change the melt viscosity.…”