Date

2015

Document Type

Thesis

Degree

Master of Science

Department

Polymer Science and Engineering

First Adviser

Pearson, Raymond A.

Other advisers/committee members

Chan, Helen M.

Abstract

Hexagonal Boron Nitride has been shown to enhance thermal conductivity in polymer composites more so than conventional ceramic fillers. However, to see a significant increase in thermal conductivity a high loading level of the advanced ceramic is often needed which can have an adverse effect on the mechanical behavior of the composite part. Applications for thermal management using thermal interface materials (TIM) continue to grow with thermoplastic injection molded parts emerging as an area for market growth. There is a growing need for published technical data in this particular area of application.In the current study, the thermal conductivity and mechanical behavior of hexagonal Boron Nitride (hBN) loaded thermoplastic composites is investigated. The main objectives of this work is produce a novel data package which illustrates the effects of hBN, loaded at high concentrations, across several different thermoplastic resins with the ultimate goal being to find a desirable formulation for specific thermal management applications. The desired properties for such applications being high thermal conductivity and high electrical resistivity with a minimal decrease in mechanical properties. Hexagonal BN cooling filler agglomerates were compounded into polypropylene (PP), nylon-6 (PA-6), and thermoplastic elastomer (TPE) via twin-screw extruder at 3 different loading levels. Injection molded samples were produced and characterized to show varying degrees of thermal conductivity and mechanical strength. Results from this research showed that in all cases, the thermal conductivity increased with increasing levels of hBN addition. The largest increases in thermal conductivity were seen in the PA-6 and TPE systems with the possible indication of exceeding the percolation threshold inthe TPE system. This is hypothesized to occur due to the preferential migration of hBN to form conduction pathways around the elastomeric domains in the TPE matrix. Though TPE produced sizeable gains in thermal conduction it was the most negatively affected in terms mechanical strength with no increase in modulus and a drastic drop in tensile strength. The introduction of hexagonal boron nitride has the least impact on the mechanical properties in the PA-6 matrix. It is from these experimental results that a composite part comprised of a nylon-6/hBN system would be recommended as the most suitable for use thermal interface management applications due to its significant gains in thermal conductivity and minimal loss of mechanical strength, though this conclusion would only be applicable on a specific case basis.

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