Session: 12-07-01: Mechanics of Soft Materials
Paper Number: 95230
95230 - Experimental Characterization of Polyurethane Adhesive: Independence of Environmental and Mechanical Aging
Assessment of the durability of elastomers for structural applications has been of much interest among the literary circles for quite some time. 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 growing intensity of the ambient environmental agents involved. On the other hand, during service life, these materials are also subjected to mechanical loading in one way or the other. The rate and extent of degradation can be accessed by scrutinizing the changes in constitutive behavior of material 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.
In this experimental study, our goal is to separate environmental degradation from mechanical damage. For this purpose, we selected a flexible polyurethane-based (PUB) adhesive which is commonly used as a glass sealant in the automotive industry. The under-study adhesive was aged in a controlled laboratory environment in thermo-oxidative (0%RH), hydrolytic aging, and hygrothermal (80%RH) aging environments. The damage and decay mechanisms have been used to draw a distinction between environmental degradation and mechanical damage. The test methods were adopted as elaborated in the relevant ASTM D412 standard. Material characterization included gravimetric measurements to observe water uptake, uniaxial cyclic tensile tests, dynamic mechanical analysis (DMA), cross-link density analysis (CLD), and scanning electron microscopy (SEM) tests on as-received and aged samples. Aging was conducted at three different temperatures (60◦C, 80◦C and 95◦C) and four different exposure durations (1, 10, 30, and 90 days). Data collected during gravimetric measurements indicate that during aging in desalinated water, water uptake increases linearly with the square root of the aging duration which agrees with Fick’s second law. Increasing water uptake is proportional to decreasing tensile strength and toughness of the material. The total mechanical and environmental damage is a synergized effect of all exposure conditions and parameters involved i.e. aging time, temperature, oxygen, water, and humidity. The test results from tensile tests and variation in material behavior were analyzed in conjunction with chemical test results to show that environmental damage is superposed on top of the mechanical damage, and thus, they are separable. This study will help to better understand the degradation mechanics involved in environmental and mechanical loading conditions. The chemistry and mechanics of the polymer degradation were found to be in good agreement with each other.
Presenting Author: Mamoon Shaafaey Michigan State University
Presenting Author Biography: Mamoon Shaafaey completed his BSc in Civil Engineering from National University of Sciences and Technology (NUST), Pakistan in year 2011. He joined MSU in Fall 2017 for masters in Structural Engineering and graduated in Summer 2019. Mamoon is continuing his pursuit of knowledge as a PhD student in the department of Civil & Environmental Engineering MSU since Fall 2019 under supervision of Dr Roozbeh Dargazany, and has been contributing as a member of High Performance Materials Group. Presently he is studying the constitutive behavior of adhesives in hydrolytic and hydrothermal aging conditions.
Authors:
Mamoon Shaafaey Michigan State UniversityAmir Bahrololoumi Michigan State University
Roozbeh Dargazany Michigan State University
Experimental Characterization of Polyurethane Adhesive: Independence of Environmental and Mechanical Aging
Paper Type
Technical Paper Publication