TIME-DEPENDENT RESPONSE OF POLYCARBONATE AND MICROCELLULAR POLYCARBONATE

Microcellular polycarbonate is a novel cellular material with cells on the order of 10 mu m in diameter and a cell density on the order of 10(9) cells per cm(3). In this study the room temperature creep response of microcellular polycarbonate is experimentally determined and compared with the creep behavior of polycarbonate. The viscoelastic response of polycarbonate and microcellular polycarbonate is characterized using Schapery's theory of nonlinear viscoelasticity. Polycarbonate exhibited a nonlinear creep response at stress levels above 24.13 MPa, while the nonlinear behavior in microcellular polycarbonate was initiated at lower stress levels. Creep strains of microcellular polycarbonate contain a significantly higher viscoplastic component compared with the unfoamed material.