Various PVDF/PMMA (poly(vinylidene fluoride)/poly(methyl methacrylate)) blends were selected for mechanical testing in compression. At low PVDF content (less than 50/50 w/w), the blends remain amorphous and PVDF and PMMA are fully miscible. In PVDF‐richer blends, PVDF crystallizes in part, leading to a PMMA‐enriched homogeneous amorphous phase. In this study, the degree of crystallinity was set at equilibrium by appropriate annealing of the samples before testing. Mechanical analysis was focused on the low deformation range, and especially on the yield region. Depending on the test temperature and blend composition, three types of response were identified, depending on whether plastic deformation is influenced: 1) by the PMMA secondary relaxation motions, 2) by the PVDF/PMMA glass transition motions, or 3) by the crystallite‐constrained PVDF chains.
After extensive studies starting in the 1970s in relation to miscibility and piezoelectric properties, the blends of poly(vinylidene fluoride) (PVDF) and poly(methyl methacrylate) (PMMA) have been revisited with the aim of assessing their mechanical behavior. Depending on the amount of PVDF, either amorphous or semicrystalline blends are produced. Typically, the blends remain amorphous when their PVDF content does not exceed 40 wt. %. Blend composition influence on the values of the glass transition temperature, Tg, and on its mechanical expression, Tα, is extensively discussed. Then, emphasis is put on the stress-strain behavior in tension and compression over the low deformation range covering the elastic, anelastic, and viscoplastic response. The reported data depend, as expected, on temperature and strain rate and also, markedly, on blend composition and degree of crystallinity. Molecular arguments, based on the contribution of the glass transition motions are proposed to account for the observed behavior. Thanks to the understanding of phenomena at the molecular level, accurate models can be selected in the view of mechanical modeling.
Résumé -Analyse moléculaire du comportement mécanique de polymères plastifiés -Les effets de la plastification sur le comportement mécanique ont été étudiés sur deux familles de matériaux à base de poly(méthacrylate de méthyle) (PMMA) et de poly(chlorure de vinyle) (PVC). Le PMMA a été mélangé avec du poly(fluorure de vinylidène) (PVDF) dans des proportions massiques en PVDF variant de 0 à 40 %, compositions pour lesquelles ces échantillons sont totalement amorphes. Le di-octylphtalate (DOP) a été mécaniquement dispersé dans le PVC dans des proportions massiques en DOP variant de 0 à 20 %. Le comportement en relaxation des échantillons a été étudié par analyse thermique différentielle avec une rampe de température de 10 °C·min -1 et par analyse dynamique mécanique à une fréquence de 1 Hz sur une plage de température allant de -100 °C jusqu'à 150 °C. Les courbes contrainte -déformation ont été réalisées en compression à une vitesse de déformation de 2.10 -3 s -1 . L'analyse des données a révélé le rôle déterminant des mouvements de relaxation β dans le comportement plastique. En considérant la partie non élastique du travail fourni, une corrélation a été trouvée entre cette quantité et les mouvements de relaxation α et β. Abstract -Molecular Analysis of the Mechanical Behavior of Plasticized Amorphous PolymersPlasticization effects on the mechanical behavior were investigated on two families of materials based on poly(methyl methacrylate) (PMMA) and poly(vinyl chloride) (PVC), respectively. For this purpose, PMMA was blended with poly(vinylidene fluoride) (PVDF) by co-precipitation from solution, all over the
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