PBPU Elastomer Network Architecture Determination via Corresponding States Analysis of Mechanical Behavior

TL;DR

This study investigates how the R=[NCO]/[OH] ratio influences the structural topology of PBPU elastomer networks, using stress-elongation behavior modeling and analysis of network defects, revealing non-correlation between chain size and crosslink density.

Contribution

It introduces a combined modeling approach with a normalized Mooney-Rivlin representation to analyze network topology and defect effects in PBPU elastomers based on R ratio variations.

Findings

Network defects increase with R in the <1 regime.

Non-correlation between chain size and crosslink density.

Stress-elongation behavior reveals structural topology insights.

Abstract

In this work we examine the effect of R=[NCO]/[OH] in the R=<1 regime, on the resultant structural topology of polybutadiene polyurethane (PBPU) elastomer networks based on hydroxy-terminated polybutadiene (HTPB). We employ stress-elongation behavior and its modeling, as a tool. We examine this property via a combination of our model for the finite chain phantom networks incorporating the HTPB structural information, with the slip-tube model from the literature, suitably modified phenomenologically. We implement a further normalized Mooney-Rivlin (MR) representation (corresponding deformation states plots), to remove any magnitude bias on the model parameters. The now revealed curvatures of all the MR plots, in turn, reveals the non-correlation between the chain size and crosslink density. This discrepancy occurs due to the R-dependent majority presence of network defects due to sol effects (as obtained from swelling experiments) and non-load bearing pendant branches on the load-bearing network chains.