Session: 12-16-02: General Session

Paper Number: 69891

Start Time: Wednesday, 10:15 AM

69891 - Experimental Characterization of Hygrothermal Aging: Competition Between Thermo-Oxidation and Hydrolysis Phenomena 

Evaluation of the durability of elastomers for structural applications has been a subject of interest among the research community for long. All polymeric materials undergo degradation when in contact with aggressive environmental agents like humidity, water, and temperature. This rate of degradation should increase with the increasing intensity of the environmental factors involved. The rate and extent of degradation can be monitored by changes in constitutive behavior through mechanical and chemical properties. Accelerated thermal, hydrolytic and hygrothermal aging are among the most common modes of process-related degradation, leading generally to chain scission, crosslinking phenomena, and reduced resistance to fracture stress, and strain.

Thermo-oxidation involves degradative effects of high temperature in presence of oxygen; hydrolytic aging considers the effect of water and temperature; and hygrothermal aging combines all of the above sub-phenomena of oxygen, heat, and moisture movement. Oxidation reactions are known to encourage crosslink development while high temperature and water ingress in material is expected to retard the material through chain scission mechanism. Our experimental results indicate that hygrothermal aging can be considered as a consequence of competitive damage accumulation of two concurrent aging mechanisms, namely; i) thermo-oxidative, and ii) hydrolytic aging.

In this work, the effects of accelerated thermo-oxidative, hydrolytic and hygrothermal aging on the mechanical and chemical properties of a flexible polyurethane-based (PUB) adhesive are presented. The adhesive is extensively used in the automobile industry, particularly as a glass sealant. PUB is inevitably exposed to the hygrothermal environment during service life and the integrity of the matrix interface is most vulnerable. This study focuses on weighing and comparing the effects of different aging environments on material behavior; it showed that hygrothermal aging is a competition between two sub-aging phenomena i.e. thermo-oxidation and hydrolytic aging. Microscopic behavior under environmental exposure remains elusive and will require a deeper look in future studies. Samples were exposed to 0%RH, 80%RH, and submerged conditions in distilled water. Uniaxial tensile tests, Differential Scanning Calorimetry (DSC) analysis, cross-link analysis, and swelling tests were carried out on as-received and aged samples. All mechanical tests were found to be in good agreement with the chemical results. The accelerated aging process was conducted at different temperatures (60̊C, 80̊C, and 95̊C) and for different exposure durations of 1, 10, 30, and 90 days. Our experimental study confirms that the effect of hygrothermal aging on Material behavior can be considered as the result of competition between thermo-oxidation and hydrolytic aging environments. The total mechanical and environmental damage incurred by specimens is a collaborative effect of all exposure environments involved i.e. aging time, temperature, oxygen, water, and humidity.

Presenting Author: Mamoon Shaafaey Michigan State University

Authors:

Mamoon Shaafaey Michigan State University
Amir Bahrololoumi Michigan State University
Hamid Mohammadi Michigan State University
Sharif Alazhary Michigan State University
Roozbeh Dargazany Michigan State University