Structure-Property Relationships in Coextruded Foam/Film Microlayers

Abstract

In this work, we have shown for the first time that assemblies of up to 64 alternating foam and film layers can be successfully made via the microlayer coextrusion technology. We have investigated the effect of some important processing variables on the foam-film structure, and have demonstrated how they can be optimized. With the optimum concentration of the right type of chemical blowing agent, the cell size can be significantly reduced for the polypropylene foam-film systems by increasing the number of layers. The foam layer density does not change significantly with increasing number of layers. Measurements of the cell density and cell volume indicate that enhanced nucleation and/or reduced coalescence is responsible for the reduction in cell size with an increasing number of layers. Constrained cell growth comes into play when a single cell/layer morphology is observed. Different types of polymers can be used as the film layer to alter the flexibility of the foam/film composite. The compressive behavior of the hard/hard polypropylene foam/polypropylene film system is similar to that of cork in terms of the compressive modulus, collapse stress, and densification strain. The tensile and compressive moduli increase with the increasing number of layers and this could be explained on the basis of an increase in the fraction of material in the cell walls, using the conventional Gibson-Ashby model. The soft/soft polyethylene foam/ethylene-styrene copolymer film system exhibits enhanced toughness in tension. The effect of the foam/film composition on the tensile and compressive moduli can be explained using the composite series and parallel models.

Preparation of a new foam/film structure poly (ethylene-co-octene) foam materials and its sound absorption properties

“…These foams were special due to their tendency to self-order into periodic structures under gravity or confinement, resulting in excellent properties such as mechanical properties, thermal insulation, sound absorption, etc. [14][15][16]. At present, ordered foams could be generated by the bubbling technique or self-assembly methods [2,[17][18][19].…”

The effect of strain-hardening on the morphology and mechanical and dielectric properties of multi-layered PP foam/PP film

“…The alternating foam/film morphology of cork was successfully mimicked with continuous microlayer co-extrusion technology developed by Ranade et al. [19], in which the film layer confines the bubble growth in the foam layer resulting in an alternating foam/film structure. The cell size was in the range of 50-300 µm and the foam density was as low as 0.3 g/cm 3 .…”

“…Three complementary approaches are possible in order to obtain a microcellular PP foam/film with improved foaming behavior and morphology that can mimic that of cork: the use of a nucleating agent, the incorporation of long chain branches, and processing via continuous microlayer co-extrusion [19][20][21][22][23][24][25][26][27][28][29][30][31][32]. A nucleating agent is helpful to nucleate and crystallize polypropylene earlier in the cooling process at a faster rate [20][21][22][23].…”

“…In this work, we build on the previous work of Ranade et al [19] and, using their methodology, we assess the influence of degree of long-chain branching of BPP on the morphology change of the multilayered foam/films, and consequently, on the mechanical and dielectric properties of the composite structures. …”

“…A two-component multilayer coextrusion system with layer multipliers was used to fabricate multilayer co-extruded film/foams. [19] Figure 1 shows schematic diagram of a two-component multilayer co-extrusion system and doubling of layers. The two-component multilayer co-extrusion system was composed of two extruders, two gear pumps, a 2-layer feed block, and layer multipliers to process two different components and determine the number of layers.…”