Epoxy resin/liquid natural rubber system: secondary phase separation and its impact on mechanical properties |
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Authors: | Viju Susan Mathew Christophe Sinturel Soney C George Sabu Thomas |
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Affiliation: | 1.Department of Chemistry,St. Thomas College,Kottayam,India;2.Centre de Recherche sur la Matière Divisée,Université d’Orléans,Orléans Cedex 2,France;3.School of Chemical Sciences,Mahatma Gandhi University,Kottayam,India |
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Abstract: | An investigation was carried out to explore the morphology and mechanical properties of diglycidyl ether of bisphenol A epoxy
resin (DGEBA) with liquid natural rubber possessing hydroxyl functionality (HLNR). Though modification of epoxies by synthetic
rubber has been extensively studied not much attention has been paid to liquid natural rubber. Photo depolymerisation of natural
rubber enables us to synthesise low molecular weight oligomers by varying the experimental parameters. Epoxy resin was cured
using nadic methyl anhydride as hardener in presence of N,N-dimethyl benzyl amine accelerator. Hydroxylated natural rubber of different concentrations is used as modifier for epoxy
resin. The addition of such chemically modified liquid rubber to an anhydride hardener–epoxy resin mixture has given rise
to the formation of a two-phase microstructure in the cured systems, consisting of spherical particles of liquid natural rubber
strongly bonded to the surrounding matrix, there by providing the required mechanism for toughness enhancement. Subinclusions
of epoxy resin were present in the elastomer domains as secondary particles (particle in particle morphology) as evidenced
from the SEM (scanning electron micrograph) photomicrographs. The origin of the so-called secondary phase separation is due
to the combined effect of hydrodynamics, viscoelastic effects of rubber phase, diffusion, surface tension, polymerisation
reaction and phase separation. In a dynamic asymmetric system, the diffusion of the fast dynamic phase is prevented by the
slow dynamic phase, and hence the growth of fast dynamic phase gets retarded due to the slow dynamic phase. In the case of
low viscosity blends the growth of fast dynamic phase turns fast and hence diffusion of fast dynamic phase cannot follow geometrical
growth and cannot establish local concentration equilibrium and hence double phase separation takes place. The double phase
separation is responsible for the enhanced impact and toughness behaviour of the blends. The mechanical behaviour of the liquid
rubber-modified epoxy resin was evaluated in terms of tensile and flexural properties. |
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