Understanding the Origin of the Low Cure-Shrinkage of Polybenzoxazine Resin by Computational Simulation

TL;DR

This study uses molecular dynamics simulations to investigate why polybenzoxazine resins exhibit near-zero volumetric shrinkage during curing, providing insights into their physical properties and the underlying mechanisms behind their low shrinkage.

Contribution

The paper offers a detailed computational analysis of PBZ resins' physical and mechanical properties, elucidating the causes of their low shrinkage during curing, which was previously not well understood.

Findings

Validated MD model with experimental data

Identified physical factors contributing to zero shrinkage

Provided data for future process modeling of PBZ composites

Abstract

Thermoset resin-based composite materials are widely used in the aerospace industry, mainly due to their high stiffness-to-weight and strength-to-weight ratios. A major issue with the use of thermoset resins in fiber composites is the process-induced residual stresses that are formed from resin chemical shrinkage during the curing process. These residual stresses within the composite material ultimately result in reduced durability and residual deformations of the final product. Polybenzoxazine (PBZ) polymer resins have demonstrated near-zero volumetric shrinkage during the curing process. Although the low shrinkage of PBZ is promising in terms of reduced process-induced residual stresses, little is known about the physical causes. In this work, Molecular Dynamics (MD) simulations are performed with a reactive force field to predict physical properties (gelation point, evolution of network, mass density, volumetric shrinkage) and mechanical properties (Bulk modulus, Shear modulus, Young's modulus, Poisson's ratio, Yield strength) as a function of crosslinking density. The MD modeling procedure is validated herein using experimental measurements of the modeled PBZ resin. The results of this study are used to provide a physical understanding of the zero-shrinkage phenomenon of PBZ. This information is also a critical input to future process modeling efforts for PBZ composites.