Heat Transfer in Polypropylene‐Based Foams Produced Using Different Foaming Processes

Abstract

This paper presents the characterization of the cellular structure and thermal conduction behaviour of polypropylene foams produced using different foaming processes, with the aim of selecting the best possible PP foam thermal insulator. Thermal conductivity results have shown that the global heat transfer behaviour is controlled by the relative density. For relative densities higher than 0.2, thermal conductivity differences were insignificant, the data being predicted by the mixture's rule and Russell's model. In the low density range, all of the proposed models underestimated the overall conductivity, the effect of the processing method being more significant, slight differences being observed between foams produced by extrusion and those produced by gas dissolution with higher cell sizes and anisotropies. Foams with finer cellular structures showed to be better insulating materials.

Thermal conductivity anisotropy in polypropylene foams prepared by supercritical CO2 dissolution

“…The most oriented honeycomb-like CO 2 dissolution foams (relative density ¼ 0.08 and AR ¼ 9.3) displayed a thermal conductivity value in the axial direction of 0.265 W m À1 K À1 , very close to that of solid PP, the highly elongated cells facilitating heat flow through the sample in the axial direction. Although this had previously been given as a possible explanation for the higher thermal conductivity of these foams measured in the standard mode compared to that of similar relative density extrusionproduced foams with an almost isotropic-like structure [2], only by separating both components it was possible to demonstrate the contribution of the induced cell orientation to the increase in thermal conductivity.…”

Multifunctional nanocomposite foams based on polypropylene with carbon nanofillers

“…The use of fillers with functional characteristics, such as high transport properties (high thermal and/or electrical conductivities), could promote the formation of foams with improved mechanical and functional properties, further extending the field of application of polymers. [3][4][5][6][7][8] The nanometric size of some fillers could be used to impart functional characteristics to polymer foams at low filler concentrations, related to their expected high surface interaction with polymer molecules, for instance acting as effective local mechanical reinforcements of the foam cell walls. 9,10 In the case of platelet-like nanosized fillers, good barrier properties may also be expected, limiting the escape of gas during expansion and facilitating foam stabilization.…”

Foaming behavior, cellular structure and physical properties of polybenzoxazine foams

“…Thermal conductivity ( λ ) was determined using the transient plane source (TPS) method, successfully applied to characterize the real conductivity of polymeric cellular materials 24–26…”

“…To finally relate the changes in temperature during the test with thermal conductivity, the equation for heat conduction, assuming the conditions reported by Log et al . and Gustavsson et al ., was applied 24–28…”