Date of Award
12-2025
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Packaging Science
Committee Chair/Advisor
Gregory Batt
Committee Member
Duncan Darby
Committee Member
James Gibert
Abstract
Closed cell expanded polyethylene (EPE) foams are widely used for protective packaging due to their high energy absorption properties and recyclability. However, these foams can be subjected to sustained compressive stresses (13.78 - 36.20 kPa), depending on density and application, leading to time-dependent deformation (creep). Creep reduces cushioning performance, making its understanding critical for effective protective packaging. Two standards, ASTM D3575 and ASTM D2221, define methods for conducting compressive creep tests on foam materials, with test durations extending up to 1000 hours. Accelerated methods such as Time Temperature Superposition (TTS) and the Stepped Isostress Method (SSM) have been explored for polymer foams. However, TTS is not suitable for closed cell foams, which are not thermorheologically simple, while SSM, though applicable, does not utilize the intrinsic viscoelastic relationship between creep and stress relaxation. This study evaluates whether short-term stress relaxation experiments can reliably predict longterm creep behavior of expanded polyethylene foams, effectively determining if a 1000-hour creep test can be replaced by a 22-hour stress relaxation test. Preliminary characterization established that stress relaxation in EPE foams can be explained by viscoelastic and gas diffusion mechanisms. Foam cell structure was characterized by optical microscopy, and mechanical behavior evaluated via uniaxial creep and stress relaxation tests. Stress relaxation of four EPE specimens was accurately modeled using a three-term Prony series, which represents the Generalized Maxwell Model, attributing behavior to polymer viscoelasticity and gas diffusion. Furthermore, creep predictions derived from short-term (22-hour) stress relaxation data were found to plateau off early showing a missing mechanisms. Obtaining parameters from fitting a logarithmic drift correction factor to 168 hours of compressive creep data, enabled us to accurately reproduce measured creep behavior out to 1000 hours. These findings establish stress relaxation as a viable accelerated testing method for EPE foams and increase understanding of the mechanisms that define creep behavior.
Recommended Citation
Seelig, Andrew M., "Predicting Long-Term Creep Behavior Using Short-Term Stress Relaxation Data in Expanded Polyethylene Foam" (2025). All Theses. 4672.
https://open.clemson.edu/all_theses/4672
Author ORCID Identifier
0009-0006-5625-0406