Preparation of nanocomposites by swelling of a UV cured cycloaliphatic epoxy film in a silica precursor
International Journal of Plastics Technology, September 2014.
B. Kothandaraman, G. Malucelli, G. Camino.
1. Department of Rubber and Plastics Technology, MIT Campus, Anna University, Chennai, 600044, India and
2. Department of Applied Science and Technology, Politecnico di Torino, Alessandria branch, Viale T. Michel 5, 15121, Alessandria, Italy.
In this work, nano composites were prepared from a UV cured cycloaliphatic epoxy resin by swelling the cured film in tetramethoxysilane (TMOS) followed by exposure to humid atmosphere at an elevated temperature. The flexibility of the resin was tuned by using different modifiers, namely hexanediol-diglycidylether (HDGE) and a diglycidoxy terminated polydimethylsiloxane (GTMQ). Glycidoxypropyl trimethoxysilane (GPTS) was also added to the UV-curable mixture in order to promote the swelling of the cured films in TMOS, thus obtaining the silica phases through a sol–gel approach. The swelling was performed at different temperatures (40 and 80 °C); the subsequent hydrolysis and condensation reactions were carried out in dry and humid atmospheres at 80 °C. The obtained films were investigated through DSC and TGA analyses; their submicro- nano- morphology was assessed by SEM. The UV-cured films showed silica rich surfaces, the morphology of which was related to the presence of GPTS and of the reactive comonomers and to the experimental conditions adopted for the sol–gel process. The TMOS absorption and hence the subsequent hydrolysis-condensation processes seem to occur at the surfaces of the films probably due to the selective migration of the silicone chains towards the air interface. The pencil scratch hardness values too were found to increase after the sol–gel treatment on the films.
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The main advantage of sol-gel process is the ease with which this can be performed in spite of being a time consuming process. Sol-gel process on a cured polymer film can retain the flexibility of the film while stiffening the polymer by the nano filler. Further, it can reduce the probability of aggregation of nano particles in the nanocomposite. Further, the modification of the epoxy by silicone polymer can enable self organization of the dispersed in the desired region (in this case, the silicone phase). If migration of the silicone rich domain to the air interface of the film occurs, it can lead to formation of silica rich surfaces in the nanocomposite film which can retard burning, increase scratch resistance and may even give a path on the surface to conduct heat and electricity. Thus, nanodielectric films, with new set of properties can be prepared without the use of elaborate equipment.
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