Melting and glass transitions in paraffinic and naphthenic oils

Naphthenic and paraffinic oils were analyzed by modulated differential scanning calorimetry (MDSC). The results showed several improvements in the analysis of thermal properties when compared with standard DSC. The glass transition temperature (Tg), the enthalpy relaxation at Tg, and the melting endotherms could be deconvoluted, and reversible melting could be identified. This allowed for an easier interpretation of the thermal properties of the oils. With MDSC, the Tgs in mineral oils were found to coincide with endothermic enthalpy relaxation, which is generally regarded as a melting endotherm with standard DSC. A decrease in heat capacity after Tg was attributed to the existence of rigid amorphous material. From \uc4cp at Tg and the oil molecular weight, the number of repeat units in the oil chains was estimated at less than 20. The Tg of a hypothetical pure aromatic oil was found to be similar to that for petroleum asphaltenes, and that for a naphthenic oil of infinite molecular weight to be similar to that of petroleum resins.Des huiles napht\ue9niques et paraffiniques ont \ue9t\ue9 soumises \ue0 une analyse enthalpique diff\ue9rentielle (AED) modul\ue9e. Les r\ue9sultats ont r\ue9v\ue9l\ue9 plusieurs am\ue9liorations dans l?analyse des propri\ue9t\ue9s thermiques par rapport \ue0 l?AED standard. La temp\ue9rature de transition vitreuse (Tg), la relaxation enthalpique \ue0 la Tg et les endothermes de fusion pouvaient \ueatre d\ue9convolu\ue9s, et une fusion r\ue9versible \ue9tait identifiable. On a pu ainsi interpr\ue9ter les propri\ue9t\ue9s thermiques de ces huiles. L?AED a mis au jour que les valeurs de Tg dans les huiles min\ue9rales co\uefncidaient avec la relaxation enthalpique endothermique, qui est g\ue9n\ue9ralement consid\ue9r\ue9e comme un endotherme de fusion selon l?AED standard. Une baisse de la capacit\ue9 calorifique apr\ue8s la Tg a \ue9t\ue9 attribu\ue9e \ue0 l?existence d?un mat\ue9riau rigide amorphe. Partant de cp \ue0 la Tg et de la masse mol\ue9culaire de l?huile, on a estim\ue9 \ue0 moins de 20 le nombre d?unit\ue9s de r\ue9p\ue9tition dans les cha\ueenes d?huile. La Tg d?une huile aromatique pure hypoth\ue9tique s?est r\ue9v\ue9l\ue9e semblable \ue0 celle des asphalt\ue8nes du p\ue9trole, et celle d?une huile napht\ue9nique d?une masse mol\ue9culaire infinie, \ue0 celle des r\ue9sines de p\ue9trole.Peer reviewed: YesNRC publication: Ye