| Abstract: | Alkaline and alkaline earth salts of either dimercaptans obtained by duplication of o-mercaptobenzoic acid with α, ω-diols or of o-mercaptobenzoic acid have been synthesized. Their efficiency has been studied with respect to induction time before change in melt viscosity and crosslinking rate assessed with Haake plasticorder equipped with a Rheomix 600 internal mixer. Then efficiency with respect to crosslinking was also characterized by the assessment of the insoluble fraction in tetrahydrofuran. Mechanical properties of uncrosslinked and crosslinked PVC were compared at different temperature through either static tests with high strain as creep and tensile tests or dynamic test in the elastic domain. Except for creep resistance, crosslinking does not improve mechanical properties of plasticized PVC at temperature lower than 80°C if insoluble fraction in tetrahydrofuran is lower than 100 % by weight. Because chemical crosslinking leads to the existence of two interpenetrated networks, a physical one and a covalent one, the temporary physical network governs the properties until the melting of ordered domains, whereas the covalent network governs the properties if temperature rises above the melting temperature of the crystalline populations. To improve mechanical properties of crosslinked PVC at room temperature, the crosslinking density of the covalent crosslinks must be higher than the density of physical crosslinks. Such a situation is reached if insoluble fraction in tetrahydrofuran becomes 100 % by weight. |
