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Effect of plasticizers on the mechanical properties of the film
Jun 21, 2018


Effect of plasticizers on the mechanical properties of the film

This can be quite profound and capable of making significant alterations to its properties, either advantageously or adversely. changes in relation to tensile properties can be summarized as follows:
Returning to the earlier proposed mechanism of plasticizer action, it can be seen that as a plasticizer interacts with a polymer the structure of that polymer will be modified so as to permit increased
segmental movement. The tertiary structure of the polymer will therefore be altered in such a way as to give a more porous, flexible and less cohesive structure. When a plasticized polymer is subjected to a tensile force it can be seen that this structure would be less resilient and would deform at a lower force
than without the plasticizer.
Aulton et al. (1981) have utilized an ‘Instron’ materals tester to evaluate the effect of a series of plasticisers on the mechanical properties of cast films of HPMC (Methocel E5). Of particular interest was the finding that low molecular weight PEG was a more efficient plasticizer for this polymer than
corresponding high molecular weight grades (Fig. 2.7). The authors also examined films using the technique of indentation. This showed that the introduction of plasticizer to the polymer film promoted increasing viscoelastic behaviour in the polymer. Indentation studies at low and high humidity also
provided experimental evidence for the plasticizing effect of water on HPMC films. Porter (1980) and Delporte (1981) are in general agreement with the findings of Aulton et al. (1981) and, interestingly,
Porter used a technique whereby the film for investigation was obtained by spraying and not by casting. Okhamafe & York (1983) have also studied the effects of PEG and HPMC films. Again they are in agreement with the findings of Aulton et al. (1981) in that PEG 400 was preferable to PEG 1000. This view was also held by Entwistle & Rowe (1979) using their technique involving polymer/plasticizer solution viscosity determination. Okhamafe & York (1983) also showed that polyvinyl alcohol (PVA)
had a quantitatively different effect on HPMC to that displayed by the PEGs. PVA decreases to a lesser degree, the decrease seen in tensile strength and the increase seen in elongation compared with the PEGs. The authors postulate an increasing crystallinity as a result of PVA addition to the film. It is also noted from the results
• Increase in strain or film elongation
• Decrease in elastic modulus
• Decrease in tensile strength.
Returning to the earlier proposed mechanism of plasticizer action, it can be seen that as a plasticizer interacts with a polymer the structure of that polymer will be modified so as to permit increased
segmental movement. The tertiary structure of the polymer will therefore be altered in such a way as to give a more porous, flexible and less cohesive structure. When a plasticized polymer is subjected to a tensile force it can be seen that this structure would be less resilient and would deform at a lower force
than without the plasticizer.










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