Microcellular, definition

Microcellular elastomers16 bridge the gap between solid elastomers and low-density foams. Although they may appear to be noncellular, these materials have a microscopic cell structure and so are by definition high-density foams, with densities between noncellular solids and standard foams. The most commercially important applications include shoe soles, carpet backing, chair armrests,... 

The production of polyurethane involves the controlled polymerization of an isocyanate, a long-chain-backbone polyol and a shorter-chain extender or cross-linker. The reaction rates can be controlled through the use of specific catalyst compounds, well known in the industry, to provide sufficient time to pour or otherwise transfer the mix and to cure the polymer sufficiently to allow handling of the freshly demolded part. The use of blowing agents allows the formation of a definite cellular core (thus the term microcellular elastomer ) as well as a non-porous skin, producing an integral sandwich-type cross section. 

Microcellular foams are solids composed of relatively small cells. It is difficult to identify a universally accepted definition of the term "microcellular. Defining this term as "relatively small" is hardly quantitative. Aubert (1988) has defined microcellular foams as "foams whose cell or pore size is much smaller than that obtained in conventional foams." This is a subjective definition. The assertion is that traditional methods of foam formation can be used to produce foams with cells approximately 50 to 100 pm in diameter. This range in cell size serves as Aubert s basis for comparison. Aubert then defines microcellular foams as foams with cell diameters smaller than this, i.e., in the range of 10 pm or below. One author s attempt at defining "microcellular" illustrates this term s nebulous character. To provide a... 

While these previous studies offered valuable insights, demonstrating the continuous extrusion process of PLA foamed with supercritical CO2, the morphology achieved in foamed PLA failed to satisfy the definition of microcellular foam due to lower cell population density (less than 10 cells/ cm ) with cells being larger than 60 m in average size. Distinctions between these features and microcellular foam... 

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