Characterization of the ethylene-vinyl acetate copolymer and the influencing parameters of the weld in intravaginal rings

Sammanfattning: The aim of this thesis was to characterize the mechanical and thermal properties of three different ethylene vinyl acetate (EVA) polymers with varying vinyl acetate (VAc) content and to investigate the influential parameters when welding the polymer into intravaginal rings. A second purpose in this study was to compare two different produced EVA polymers with the same VAc content to find thermal and structural differences. Since the weld is a crucial part of the production of a thermoplastic based IVR it is of high interest to gain knowledge and experience on how the material behave upon a second heating and what parameters affect the strength and robustness of the rings. The study was made by first investigating the properties of the EVA polymers with 9, 28 and 40% VAc content by running samples in a DSC. A modelling study was then made to get knowledge and to find interesting temperatures and times for the welding part of the thesis. The polymeric fibers were welded into IVRs while alternating the important parameters time, temperature and VAc content. To evaluate the welding, tensile testing was carried out and the stress and elongation at break were analyzed. The analysis and results showed clear trends where the elongation and stress at break increased with the welding time for the EVA9 and EVA28 IVRs. For EVA40 the trends in the results were not as clear. Conclusions made in this thesis are that the VAc content parameter has a large effect on the weld strength where the elongation at break will increase with increasing amount of VAc content. The stress at break will increase with a decreasing amount of VAc content. For IVRs made of EVA28 welded at 100°C the time needs to reach at least 20 seconds to result in a good weld. EVA9 IVRs need to be welded at a higher temperature than 110°C but the material shows a clear trend with increasing elongation and stress at break with increasing time, thus it can be concluded that the time is an important parameter for the welding process.