Modelling of effective thermal conductivity of polymer matrix composite foams with biaxially aligned filler networks

Abstract

Recent research revealed potentials to develop polymer matrix composite foams filled with thermally conductive filler network as light-weight thermal management materials. Since polymeric foams are commonly used for thermal insulation, the concept of thermally conductive polymer matrix composite foams seems to be counter-intuitive, and the underlying factors that govern polymer matrix composite foam's effective thermal conductivity (k eff ) were not clear. In this context, this paper develops new models to predict polymer matrix composite foams' k eff and to elucidate the dependence of k eff on their cellular morphology. Linear low density polyethylene-hexagonal boron nitride composite foams were used as case examples to verify the model. The model demonstrated that the composite foam's k eff would be promoted when the volume expansion was over a threshold percentage. At low hexagonal boron nitride loadings (e.g. 10 vol.%) and fixed cell size, linear low density polyethylene-hexagonal boron nitride foams' k eff increased with volume expansion percent through an increase in cell population density. Constrained foaming with preferential expansion in the heat flow direction also enhanced their k eff .

Polyolefinic nanocomposite foams: Review of microstructure-property relationships, applications, and processing considerations

“…In actuality, the underlying mechanisms governing the conductivity of foamshow the solid (unfoamed) polymer and the gases entrapped in the cells contribute to the composite conductivity of the foam as a whole -are more complex, and are found to be different for open-celled and closed-celled foams. [104][105][106][107][108][109][110][111][112] These mechanisms may be further impacted by the presence of additives and the crystalline orientation of the polyolefin during foaming. 11,23,82,106,107 Several theoretical and empirical models that have been proposed to predict the thermal conductivity of multi-material systems -including series and parallel, Russel and Maxwell 109 and other models 106,[110][111][112] -may be employed to understand the thermal conductivity of foams.…”

“…In actuality, the underlying mechanisms governing the conductivity of foams – how the solid (unfoamed) polymer and the gases entrapped in the cells contribute to the composite conductivity of the foam as a whole – are more complex, and are found to be different for open-celled and closed-celled foams. 104–112 These mechanisms may be further impacted by the presence of additives and the crystalline orientation of the polyolefin during foaming. 11,23,82,106,107…”

“…[104][105][106][107][108][109][110][111][112] These mechanisms may be further impacted by the presence of additives and the crystalline orientation of the polyolefin during foaming. 11,23,82,106,107 Several theoretical and empirical models that have been proposed to predict the thermal conductivity of multi-material systems -including series and parallel, Russel and Maxwell 109 and other models 106,[110][111][112] -may be employed to understand the thermal conductivity of foams. The macroscopic (measurable) thermal conductivity k of the foam has contributions from not only conductive heat transfer processes through the connected (solid) domains of the foam microstructure and through the gas phase, but also from convective heat transfer through the gases entrapped within the cells as well as radiative heat transfer between disconnected cell-walls and voids.…”

Lightweight Polyethylene/Hexagonal Boron Nitride Hybrid Thermal Conductor Fabricated by Melt Compounding Plus Salt Leaching

“…Leung et al [ 13 ] reported the effects of foam volume expansion and cell size on the λ value of resultant polyethylene (PE)/hBN foams. Besides, there are literatures dealing with the theoretical work of filler included in PTCs [ 9 , 14 ]. Although notable experimental and theoretical progress have been made in this area, the obtained thermal conduction abilities of PTCs are still far away from meeting industrial applications needs.…”

Strain-induced oriented crystallization of UHMWPE: Enhanced thermal conductivity through molecular chain alignment

“…13 Recently, foaming-induced extensional stress field was used to align thermally conductive filler in polymer composites to increase their k eff . [14][15][16] This promote the formation of a three-dimensional thermally conductive network throughout the bulk material. Ghariniyat et al integrated this technique and post-foaming elastic recovery of thermoplastic polyurethane to fabricate flexible thermally conductive TPU-hexagonal boron nitride (hBN) composites.…”