Understanding the Effect of Water in Polyamides: A Review

Abstract

Polyamides (PAs) are repeatedly exposed to environments of varying humidity throughout their service life. Due to their hygroscopic nature, moisture diffusion can alter the polymer properties, sometimes irreversibly. It has been previously found that the effect of transport of water on the structure, morphology, and physical properties of polymers is not negligibly small. In certain semi-crystalline polyamides, the diffusion coefficient has been shown to be governed by the local chain dynamics (β relaxation). The final molecular weight of PAs achieved after melt processing is a result of the equilibrium between the forward and reverse polycondensation depending on the water concentration. With the growing demand for unreinforced and reinforced polyamides as well as polyamide fibers in high-performance applications, it is critical to understand the physics of the interaction between water molecules and polymer or composite systems. This article reviews the existing literature about polyamide-water interactions with a focus on the governing physical laws of moisture transport within the polyamide matrix, drying kinetics, and dynamics of water in the polymer system. The implications of moisture on the processing and properties of the polyamides class of materials are also discussed, suggesting the need for best practices in instrumentation and control.

Keywords:

• Moisture
• diffusion
• plasticization
• polycondensation
• hydrolysis
• polyamide-water interactions

Acknowledgments

The authors would like to thank Dr. Jo Ann Ratto Ross (Deputy Director CCDC SC-HEROES, Senior Materials Engineer) for her mentorship to Varun Venoor and critical feedback on this article.

Disclosure statement

There are no conflicts to declare.

Additional information

Funding

This review article was funded in part by the U.S. Army Combat Capabilities Development Command Soldier Center (CCDC Soldier Center) and Harnessing Emerging Research Opportunities to Empower Soldiers (HEROES) under contract #W911QY-17-2-0004 SLIMM Project MN-1 titled “New thermoplastic materials using microcrystalline cellulose”, and UMASS President’s Office Technology and Commercial Ventures Fund.