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Propriétés Thermiques Des Matériaux Polymères

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Propriétés Thermiques Des Matériaux Polymères
Propriétés thermiques des matériaux polymères 1-Résumé

La température de transition vitreuse (Tg) est probablement la propriété thermique la plus importante des polymères. Elle permet de déterminer la plage de température d'utilisation d'un polymère. On constate en effet, une diminution importante du module d'élasticité aux environ de la Tg. La Tg est influencé par plusieurs facteurs. Une faible masse moléculaire, des chaînes de polymères plus rigide, la présence de gros groupement latéraux ou de groupement latéraux fortement polaire sont tous des facteurs provoquant une augmentation de la Tg. La présence d'une légère ramification diminue la Tg alors qu'une ramification très dense l'augmente. Un degré élevé de cristallinité a aussi pour effet d'augmenter la Tg (plus la cristallinité augmente, plus la Tg augmente). Finalement, la présence de plastifiant peut également faire grandement varier la Tg. Il existe plusieurs méthode pour mesurer la Tg. Parmi celles-ci, on retrouve la méthode DSC et la méthode DMA.

La température de fusion est également une propriété importante. La température de fusion est la température à laquelle la partie cristalline du polymère "fond". Les facteurs qui ont une influence sur la Tg ont, pour la plus part, également une influence sur la température de fusion. On peut mesurer la Tg par la méthode DSC.

Les température de cristallisation, de fléchissement sous charge, de déformation et de ramollissement sont également des propriétés thermiques dont la connaissance de la valeur est très utilise dans le cadre du design d'une pièce en matériau polymère.

Les élastomères sont une classe particulière des matériaux polymère. On pourrait dire qu'ils sont à mi-chemin entre les thermoplastique et les thermodurcissable parce qu'ils ont certaines caractéristiques des deux classes. La vulcanisation est un procédé qui permet de modifier grandement les propriétés thermique et mécanique des élastomères.
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