Effect of mold temperature on mechanical properties of poly(ethylene terephthalate)

Abstract

Poly (ethylene terephthalate) is a semi-crystalline polymer, which has applications in both semi-crystalline and amorphous forms. It is being used extensively in preparing molded products. Different processing parameters like pressure and temperature directly affect the degree of crystallinity and the microstructure developed during molding. These parameters in turn affect the performance of the end product. In this research work, effect of mold temperature on microhardness and tensile properties of PET, in the temperature range of 130°C to 204°C, was determined. This range was selected based on crystal growth studies and the time required for complete crystallization at different crystallization temperatures. It was found that mold temperature has appreciable effect on microhardness and tensile properties. Microhardness increases linearly with mold temperature. This increase was attributed to the increase in crystallinity of samples and also to the development of thicker and more stable lamellar structure. It was found that most of the tensile properties correlate well with mold temperature. Tensile elastic modulus (ET) and Yield strain (ϵy) increase with mold temperature, Yield stress (σ y) tends to stabilize at 160°C and then increases. Strain at break (ϵb) decreases linearly with mold temperature, whereas, Stress at break (σb) remained constant at a value of 45 MPa within the mold temperature range of 130°C to 204°C. In general, most of the properties were found to correlate well with the crystallinity of the samples, suggesting that crystallinity is one of the main factors influencing the mechanical behavior of PET, other factors being crystal size and crystal thickness. Microhardness of the PET at different mold temperatures was correlated with tensile properties. Linear correlations between microhardness and tensile properties were obtained. These correlations are expected to help the PET industry, where they can be used to estimate the mechanical properties by simply measuring the hardness of the product.