Experimental and numerical investigation into mechanical degradation of polymers

Abstract

Polymers have myriad uses in the modern world, but their advantageous properties can be compromised by degradation induced via moisture absorption. This work presents a novel reduced order numerical model for the mechanical behavior and degradation of polymers, along with experimental results, illustrating the influence of water absorption on 3D printed and injection molded nylon 6. The nylon 6 specimens are immersed in water at 21∘C and 70∘C, temperatures above and below the glass transition temperature. Both the water absorption behavior and the influence of the absorbed water on thermomechanical and tensile properties are investigated. The hygroscopic nylon 6 absorbs up to 10% water when immersed at 21∘C. The rate of absorption for the 3D printed specimens is higher than that of the injection molded specimens at both temperatures. This absorbed water enhances polymer chain mobility and results in significantly lower storage modulus and glass transition temperatures after only 1 day of immersion. Consequently, as much as 30% reduced modulus and strength are observed during this period. The constitutive model capably captures the degradation of polymer mechanical behavior as a function of water concentration for both materials and temperatures investigated.