This work is a contribution to the study of the curing of silicone prepolymers (hydroxyfunctional polydimethyl siloxanes) and the physical properties of the resulting networks. The kinetics of curing of one of the prepolymers has been studied with a simple new inexpensive piece of equipment i.e the Vibrating Needle Curemet~r (VNC). The order of reaction with respect to crosslinker and catalyst concentration has been determined to be unity and 0.24 respectively while an attempt has been made to determine the order of reaction with respect to silanol group concentration in the prepolymer. The effect of. crosslinker and catalyst concentration was observed to check the validity of the Lake and Thomas theory; namely that tear strength at a particular condition is proportional to the square root of the molecular weight between crosslinks. It has been found that varying crosslinker concentration is a better way to test this theory. Surprisingly the detailed physical properties such as tear and tensile of the supposedly different prepolymer networks showed little relationship to the molecular weight. The effect' of blending short and long chain polymers i.e bimodality, and that of the concentration of the crosslinker on the physical propert; es has been investigated. It became apparent that in addition to bimodality, the physical properties are dependent upon the amount of cross1inker used for curing This is a factor which has not previously been reported. It has also been shown that unfortunately, contrary to expectation bimodality has adverse effects on the physical properties of the highly filled networks. In the case of the tensile properties, the stress strain curves were analysed in light of tne phenomenological Mooney - Rivlin (MRL) and Martin, Roath and Stiehler (MRS) equations. Apart from successfully applying these theories to stress-strain curves, the structure factors of networks have been' obtained. These theories have been used in parallel to check and compare the results of one technique with the other. However, in the case of the filled HOPDMS networks it is evident that only the MRS equation can successfully describe the stress-strain data. The stress-strain data for the various HOPDMS filled networks have been compared with one another in terms of Young's modulus from their practical point of view.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:276881 |
| Date | January 1990 |
| Creators | Shah, Gul Bali |
| Publisher | Cardiff University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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