Thermal Conductivities of Long Glass Fibre (LGF) Composites in the solid and melt state
May 31st, 1999
Paper to 15th Annual Polymer Processing Conference, ‘s-Hertogenbosch, Netherlands, 31st May-4th June 1999
S F Bush and F G Torres
Abstract
The work reported here results from a long term research programme on LGF composites under the generic name of Self Assembling FIbre REinforcement (SAFIRE) in which fibre reinforcing mats are created in the melt during its passage through the process equipment. Previous reports from this laboratory have described results [1, 2, 3] obtained from LGF loaded granules manufacture, from pipe and sheet extrusion, and from injection and blow moulding, all of which have been developed at the industrial scale.
Besides changes in mechanical properties relative to unreinforced grades, LGF polypropylene exhibits very different thermal behaviour compared with unreinforced polypropylene. Broadly speaking, heat distortion temperatures increase by 7 oC for every 1% v/v glass fibre and thermal conductivity normal to the predominant flow plane increases by a factor of 2 for about 6% v/v.
The original theory [1] of the fibre reinforcing mats is based on the idea of the number of fibre-fibre touches (N) creating a coherent structure approximately according to the formula N = A.c.ld. In order to understand how the mat structure affects the thermal conductivity of the composite, thermal conductivity experiments have been carried out in the steady state at temperatures in the range 50-200 oC using an improved Lee’s Disc apparatus. The reinforcing fibre mats have also been characterised using a scanning electron microscope (SEM) and the average number of touches between the fibres has been calculated and compared with the theoretical equation. The paper proposes a model for thermal conductivity of LGF reinforced composites based on the touch and fibre orientation concepts.
References
[1] Bush S F, Yilmaz F, Zhang P F, Plastic & Rubber Composite Process Applications, Impact strengths of injection moulded polypropylene long-glass-fibre composites, 24 (1995) 139-147
[2] Bush S F, Tonkin J D, Short and Long Term Behaviour of Long Glass Fibre Reinforced Polyolefins, Antec Technical Papers, 43 (1997) 3081-3086
[3] Bush S F, Torres F T, Erdogan E S, Mechanical Properties of Discrete Long Glass Fibre Reinforced Polymer Sheets and their Application to the Thermoforming Process, Proceedings of 7th International Fibre Reinforced Composites Conference (1998) 237-244