Evaluating the Linear Viscoelasticity of Vitrimers Using Start-up and Cessation Tests

03 June 2024, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Stress relaxation experiments are often performed on reprocessable polymer networks to evaluate their characteristic relaxation time, which represents the bond lifetime in the absence of structural contributions. While traditional cessation tests employ the application of an instantaneous small strain, the strain amplitude and the rate of strain applied during startup are known to influence the subsequent stress relaxation behavior. Here we illustrate this phenomenon using vitrimers with characteristic bond exchange times spanning seconds to hours. Our experiments show that controlling the dimensionless strain amplitude and shear rate applied during startup is critical to obtaining the true distribution of relaxation times for non-Maxwellian materials. In particular, consistent with rheology performed on thermoplastics, we find that experiments performed at small Deborah numbers, the dimensionless start-up timescale, and small Weissenberg numbers, the dimensionless accumulated strain, result in a stress relaxation time consistent with that observed in SAOS tests.

Keywords

vitrimer
covalent adaptable network
reprocessable polymer network
rheology
linear viscoelasticity

Supplementary materials

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Description
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Supporting Information
Description
Additional rheology data and fitting procedures, thermal characterization, tearing energy measurements, evidence of edge fracture
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