A novel tenter-frame device for real-time monitoring during biaxial stretching of polyethylene

Biaxial stretching of polymeric films, which typically occurs in a semi-solid state, involves the application of shear and elongational force fields along two main directions and is a common technology in several applications. To understand the effect of the processing conditions on the final properties, it is crucial to monitor the development of the crystal structure and orientation throughout the stretching process. While there is considerable literature on the uniaxial processing of PE materials, only a small number of research studies have been conducted on biaxially oriented polyethylene (BOPE) film processing. Given the complex and costly nature of designing biaxial devices, several potential solutions exist within the literature. However, most of these do not meet the needs of in-situ investigations. The objective of this manuscript has been the development of a cost-effective device that enables in-situ analysis during biaxial stretching of polyethylene cast sheet samples. The potential of the so-designed device has been demonstrated by carrying out in-situ small X-ray scattering (SAXS) analysis during stretching tests at 125 °C on an LLDPE pre-cast sheet sample.