The experimental study was carried out for clarifying the thermal property of reinforced PA 66. Anisotropy in linear thermal expansion coefficient (α) was related to the aspect ratio (λ) of the reinforcements, which is defined as the ratio of the length to the radius. The α was measured for disks which were injection molded from the PA 66 reinforced with reinforcement of λ=1, 4 and 10. For all the reinforced PA 66, the anisotropy in α was significantly large, while it was negligible in unreinforced PA 66. The direction of minimum α was along the flow direction of the melted polymer in the injection molding in the case of λ=4 and λ=10. On the other hand, the direction of minimum α was transverse to the flow direction in the case of λ=1. The cause of the difference in the direction of the minimum α was discussed by considered orientation state and density distribution of the reinforcements.

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