Study on mobility of water and polymer chain in epoxy and its influence on adhesion

Abstract

AbstractThis paper presents a study on the mobility of water and polymer chains in epoxy materials and its influence on the rate of adhesion degradation in a humid environment. Solid state nuclear magnetic resonance (NMR) techniques (both 1H NMR and 2H NMR) were used to study the binding states of water within two epoxy formulations along with the possible plasticizing effects of moisture affecting the mobility of polymer chains. Absorbed water reduces the glass transition temperature of polymeric materials. However, the presence of moisture has no significant effect on the polymer chain mobility at temperatures below the reduced glass transition temperature. Water in an epoxy in its rubbery state above the glass transition has a much higher mobility than in a polymer in its glassy state. The mobility of water absorbed by a polymer in its rubbery state is similar to that of pure water. The translational mobility of water within epoxies was studied by measuring the diffusion coefficient of water in epoxies through the water uptake. Higher rotational mobilities of water and polymer chains in the rubbery state lead to a significant increase of the water diffusion coefficient in the rubbery state polymer matrix as compared to a polymer in its glassy state. The higher mobility of absorbed water and the higher mobility of polymer chains in epoxy lead to faster adhesion degradation during aging in a humid environment. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1–8, 2002