|Ph.D Student||Rosen Kligvasser Jasmine|
|Subject||Investigation of Controlled Migration of Antifog|
Additives from Thin Polyolefin Films
|Department||Department of Polymer Engineering||Supervisors||Professor Emeritus Moshe Narkis|
|Professor Yachin Cohen|
|Professor Emeritus Raphael Semiat|
|Full Thesis text|
The use of plastic films, in particular polyethylene, is ubiquitous in a variety of applications, especially in packaging and agriculture. In order to change and/or improve different properties, additives are incorporated into polymeric systems. When added to a polyethylene film, the additives migrate to the films' surface and their concentration decreases; over time the additive’s effect desists. Extended performance is necessary to avoid frequent substitution of polyethylene films in various applications (e.g. greenhouses plastic coverings, food packaging), resulting in reducing plastic waste and contributing to environmental sustainability. This research focuses on three kinds of additives. Antifog additives reduce the surface tension of the film surface thus mitigating fog formation due to water droplets that have deleterious effects such as light scattering in greenhouse covers or a spoilt appearance in food packaging. UV absorbers reduce the damaging effect of UV radiation by its absorbance, and antimicrobial additives increase the shelf life of packaged goods by inhibiting bacterial growth. The main thrust of this research is the synergetic combination of organic molecules with inorganic nanoparticles in polymer nanocomposites for enhanced functionality. In this study, different polymer nanocomposites were fabricated by organic (antifog) modification of nanoparticles and incorporating them in linear low density polyethylene matrix. The modified nanoparticles serve as an additive with different functionalities: antifog when using silica nanoparticles; antifog and UV absorber when using titania nanoparticles; antifog, UV absorber, and antimicrobial agent when using zinc oxide nanoparticles. The modification reaction, the modified nanoparticles, and the composite systems were analyzed, studied, and scaled-up. 2 The main objective of this research was to develop an effective and long lasting wettability upon polyolefin thin films surface. Fourier transform IR and NMR measurements confirm the existence of the modified nanoparticles. An optimal modification degree was investigated; it was discovered that low modification degrees exhibit better and durable antifog performance than high modification degrees, as well as no modification at all (neat antifog, or a simple blend between antifog and nanoparticles). An evaluation test procedure for antifog performance presents an extended duration of the modified additives' activity. Solar exposure tests reveal effective UV protection when using titania and zinc oxide nanoparticles. Antimicrobial tests show reduced bacterial growth when using zinc oxide nanoparticles. An accelerated migration tests and diffusion coefficients calculations reveal that the migration rate is strongly dependent on the nature of the bond between the antifog and the nanoparticles, as well as the strong affinity between the attached and unattached antifog fractions. The addition of the modified nanoparticles to polyethylene matrix did not significantly influence film properties, such as viscosity, thermal stability and tensile properties, in contrast to the addition of neat antifog; thus, this process can be applied on a semi-industrial scale (extrusion). The extrusion process considerably enhanced the film properties such as antifog activity, optical and mechanical properties. A morphological study showed that a fine dispersion of the modified nanoparticles in the polymeric matrix is crucial for achieving enhanced and prolonged performance of the different additives, while retaining film properties.