A tensile flow stress model for oriented polypropylene

• Published in: Polymer engineering and science 1988-06, Vol.28 (11), p.740-742
• Main Authors: Tate, K. R., Perrin, A. R., Woodhams, R. T.
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Machinery and processing; Miscellaneous; Plastics; Polymer industry, paints, wood; Technology of polymers
• ISSN: 0032-3888; 1548-2634
• DOI: 10.1002/pen.760281106

Many solid‐phase processing and forming operations for polymers require tensile stretching forces to produce flow. To make forming operations practical, a knowledge of the flow stress of the polymer is required. This paper presents a simple formulation for predicting the flow stress of polypropylene In the oriented direction as a function of the controlling parameters, which are strain rate, temperature, and deformation ratio. It will be shown that the experimental flow stress data may be formulated in a way that is similar to the constitutive laws for metals. Equations for metals relating flow stress Lo strain rate, flow stress to strain, and flow stress to temperature are compared with an equivalent formulation for oriented polypropylene. The experimental conditions, chosen to develop the constitutive equations, reflect practical forming conditions, The deformation ratios (i.e., strains) were varied from 6 to 14. The strain rates imposed were between 10 and 1000% per min. Most of the tests were conducted in the temperature range 150 to 160°C, although a few were conducted at 130°C.