Physical Phenomena of Thermoplastic Articles in the Vicinity of Their Glass Transition Temperatures
It is well known that environmental conditions impact the performance of thermoplastic articles, therefore requiring selection of appropriate raw materials. Nevertheless, frequently due to business reasons, when selecting a material, the rigor of understanding the fundamental physical events responsible for the desired performance is shortchanged. In this study, we investigate the effects of cyclic heat history on the dimensional stability of articles made with commercial grade rigid thermoplastic resins, particularly, in the temperature range close to the material’s glass transition temperature, as more materials are used in hot & arid environments. The two physical events identified as most relevant to desired article performance are the relaxation of the processinduced residual stresses within the material and the dynamic phenomena brought about by the material’s coefficient of thermal expansion, CTE. We find that the periodic development of convexconcave surfaces on an article matches the periodic development of a non-uniform temperature gradient within the article. We demonstrate that this periodic heat exposure leads to an irreversible concave deformation of the article’s exposed surface. Moreover, articles exhibit this deformation phenomenon regardless of the level of the initial process-induced stresses. We offer explanations of these behaviors and discuss their practical implications.
John Bell, Cheng Yan, Lin Ye and Liangchi Zhang
S. Kharchenko and J. Huang, "Physical Phenomena of Thermoplastic Articles in the Vicinity of Their Glass Transition Temperatures ", Advanced Materials Research, Vol. 32, pp. 25-28, 2008