|M.Sc Student||Koranit Shlosman|
|Subject||Investigation of Migration of Antifog Additives through|
Thin LLDPE Films
|Department||Department of Polymer Engineering||Supervisors||Professor Emeritus Narkis Moshe|
|Professor Emeritus Semiat Raphael|
|Full Thesis text|
This work describes novel methods for controlling the migration, mechanism and rate of antifog (AF) additives from linear low density polyethylene (LLDPE) films. Controlled migration was achieved using a compatibilizer based on maleic anhydride by chemical crosslinking, peroxide (reactive compounding) and vinyl silane modification. Bulk and surface properties of compression molded films of LLDPE blends were characterized using Fourier transform infrared spectroscopy (FTIR). Thermal properties were investigated using thermal gravimetric analysis (TGA) and differential calorimetry analysis (DSC). A new method for quantification of AF content in LLDPE films during accelerated migration tests was developed using FTIR. The diffusion coefficient was calculated using an accelerated migration test protocol and antifog properties were characterized using "hot fog" and "cold fog" tests. Compression molded films were also characterized for their morphology using high resolution scanning electron microscopy (HRSEM), and rheological properties were measured using a parallel plate rotational rheometer.
The following conclusions were deduced based on this work:
v The addition of a compatibilizer, LLDPE-g-MA and SMO (antifog additive) has shown a significant decrease of SMO migration rate. It was shown that addition of only 3 phr LLDPE-g-MA is sufficient to significantly decrease SMO migration. Correspondingly, the calculated SMO diffusion coefficient is reduced by one order of magnitude for the LLDPE systems containing compatibilizer. These results well correlate with results obtained by the hot fog test.
v Improvement of LLDPE thermal stability containing 3phr LLDPE-g-MA and 1phr SMO was also achieved. It seems that the higher thermal stability of the system is due to good dispersion of SMO in the LLDPE matrix.
v Ethanol extraction has shown a successful grafting of the studied antifogs: SMO, PEG methacrylate, PEG dimethacrylate and PEG methyl ether methacrylate. Peroxide grafting of GMO was not succesful, appearently due to decomposition of the GMO molecules.
v It was found that 2-steps compounding of LLDPE with SMO and peroxide where LLDPE was compounded with SMO, followed by compounding with peroxide, is much better than 1- step compounding of the polymeric system, in which all the components were pre-mixed and compounded.
v GMO was succssefuly modified by methacryloxy propyl tri-methoxy silane. Accelerated migration tests have shown that the modified GMO migrates slower than unmodified GMO and corresponds to a diffusion coefficient smaller by one order of magnitude.
v A crosslinked LLDPE system containing sorbitan monostearate (SMS) was produced, attaining better creep resistance, antifogging performance and slower migration rate than the non-crosslinked LLDPE system containing SMS.