Date of Award
Master of Science (MS)
Heat sealing is one of several methods used to weld thermoplastic materials in packaging. Heat seals were made between Dow 501i LDPE and DuPont Nucrel 1202HC poly (ethylene co-methacrylic acid). The seals were exposed to sodium hydroxide solution so that the methacrylic acid sites of the DuPont Nucrel 1202HC were neutralized with a sodium ion. This was done to make diffusion measurements. Two side heated tooling sealing was used to make seals at 40 psi (276kPa), 1.0 second dwell, and temperatures ranging from 200oF (93.3oC) to 300oF (148.9oC). Energy dispersive x-ray spectroscopy, a function of scanning electron microscopy, was used to measure the presence of sodium and therefore diffusion of the methacrylic acid sites. The methacrylic sites are part of the polymer chain, and were tagged from the sodium hydroxide. It was possible to estimate polymer chain diffusion distance based on a sodium trace, as well as an oxygen trace. Then this method was used to measure diffusion on samples of 501i and 1202HC sealed at various temperatures. Diffusion was compared to seal temperature and to seal strength. The results of this study are different from previous findings. It was found that with this system diffusion distance is not correlated to seal strength. It was also found that for this system diffusion distance is not correlated with sealing temperature. However, it was found that both sodium and oxygen can be used to estimate diffusion in this polymer system.
Hendrickson, Mark, "Analysis of Diffusion in Heat Seals Using Energy Dispersive X-ray Spectroscopy" (2015). All Theses. 2278.