Effect of preexisting crazes on the dynamic viscoelasticity of poly(methyl methacrylate)

Abstract

The effect of preexisting crazes on the storage modulusE′ and the loss tangent tanδ was investigated by using two types of pre-crazed specimens of poly(methyl methacrylate) in which plastic deformation by crazing had proceeded to different degrees under a 1 -butanol environment. The measurements were conducted both in air under a constant heating rate and in an environment of methanol at room temperature. In air no significant difference can be found between the viscoelastic properties of the pre-crazed and the uncrazed specimens, even when all the pre-crazes entirely heal up aboveTg. In methanol two different trends are observed in response to the degree of pre-crazing. In a specimen which is damaged to some degree by crazes, a reduction inE′ and an increase in tanδ followed by methanol absorption are suppressed in comparison with the uncrazed specimen. On the other hand,E′ and tan δ of a specimen with heavy damage by crazes take almost the same values as those of an uncrazed specimen during exposure to methanol. These observations suggest that in some cases the preexisting crazes act as a rigid second phase to maintain the overall stiffness of the polymer against the plasticization effect of penetrants.