Thermal conductivity polymer matrix

Metal Matrix Composites, Ceramic Matrix Composites, Carbon Matrix Composites, and Thermally Conductive Polymer Matrix Composites... 

The above equation should be used with caution, however, because it does not account for the quality of interfacial contact between the plastic and the filler system. Poor interfacial contact has the same effect as a thermal contact resistance and can result in a significant lowering in the ability of the highly conducting filler particles to transmit heat to the low-conductivity polymer matrix. What complicates the matter further is that these systems may possess good interfacial contact while the polymer matrix is molten but then become lower in thermal conductivity as interfacial contact resistance develops between the filler and the now-solidified polymer. This can be particularly confusing in the case of some filled semicrystalline polymers, where the appearance of the crystalline phase upon solidification should result in increased thermal conductivity, while the actual value appears to decrease. For this reason, it is considered safer to measure the thermal conductivity of filled materials. 

Applied Sciences, Inc. has, in the past few years, used the fixed catalyst fiber to fabricate and analyze VGCF-reinforced composites which could be candidate materials for thermal management substrates in high density, high power electronic devices and space power system radiator fins and high performance applications such as plasma facing components in experimental nuclear fusion reactors. These composites include carbon/carbon (CC) composites, polymer matrix composites, and metal matrix composites (MMC). Measurements have been made of thermal conductivity, coefficient of thermal expansion (CTE), tensile strength, and tensile modulus. Representative results are described below. 

All VGCF was graphitized prior to composite consolidation. Composites were molded in steel molds lined with fiberglass reinforced, non-porous Teflon release sheets. The finished composite panels were trimmed of resin flash and weighed to determine the fiber fraction. Thermal conductivity and thermal expansion measurements of the various polymer matrix composites are given in Table 6. Table 7 gives results from mechanical property measurements. 

Almost any known polymer or polymer mixture can be used in the capacity of a polymer matrix various additives may be introduced in the matrix to reduce melt viscosity, increase thermal stability of the composition or its plasticity, etc. A choice of a matrix is determined mainly by the operating conditions of a material and the desired physical-mechanical properties of a composite. One may state rather confidently that, other things being equal, the value of the CPCM conductivity does not depend on a choice of a polymer matrix [3]. 

Experimental results are presented that show that high doses of electron radiation combined with thermal cycling can significantly change the mechanical and physical properties of graphite fiber-reinforced polymer-matrix composites. Polymeric materials examined have included 121 °C and 177°C cure epoxies, polyimide, amorphous thermoplastic, and semicrystalline thermoplastics. Composite panels fabricated and tested included four-ply unidirectional, four-ply [0,90, 90,0] and eight-ply quasi-isotropic [0/ 45/90]s. Test specimens with fiber orientations of [10] and [45] were cut from the unidirectional panels to determine shear properties. Mechanical and physical property tests were conducted at cold (-157°C), room (24°C) and elevated (121°C) temperatures. 

The effect of blending LDPE with EVA or a styrene-isoprene block copolymer was investigated (178). The properties (thermal expansion coefficient. Young s modulus, thermal conductivity) of the foamed blends usually lie between the limits of the foamed constituents, although the relationship between property and blend content is not always linear. The reasons must he in the microstructure most polymer pairs are immiscible, but some such as PS/polyphenylene oxide (PPO) are miscible. Eor the immiscible blends, the majority phase tends to be continuous, but the form of the minor phase can vary. Blends of EVA and metallocene catalysed ethylene-octene copolymer have different morphologies depending on the EVA content (5). With 25% EVA, the EVA phase appears as fine spherical inclusions in the LDPE matrix. The results of these experiments on polymer films will apply to foams made from the same polymers. 

A series of low density polyolefin foams were manufactured and studied in terms of their thermal conductivity, cellular structure and polymer matrix morphology. In order to predict the thermal conductivity of a specified material a mathematical equation is presented. 26 refs. 

Properties of peroxide cross-linked polyethylene foams manufactured by a nitrogen solution process, were examined for thermal conductivity, cellular structure and matrix polymer morphology. Theoretical models were used to determine the relative contributions of each heat transfer mechanism to the total thermal conductivity. Thermal radiation was found to contribute some 22-34% of the total and this was related to the foam s mean cell structure and the presence of any carbon black filler. There was no clear trend of thermal conductivity with density, but mainly by cell size. 27 refs. 

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