Accession Number : AD1031722

Title :   Molecular Dynamics and Morphology of High Performance Elastomers and Fibers by Solid State NMR

Descriptive Note : Technical Report,01 Sep 2015,31 May 2016

Corporate Author : University of Massachusetts - Amherst Amherst United States

Personal Author(s) : Hu,Weiguo

Full Text :

Report Date : 30 Jun 2016

Pagination or Media Count : 17

Abstract : Poly(p-phenylene-2,6-benzobisoxazole) (PBO) is an engineering fiber of extraordinary properties, but has been found to degrade quickly under moisture and ultraviolet light, which is a fatal flaw for soft body armor applications. The present report uses 31P solid-state nuclear magnetic resonance (ssNMR) spectroscopy to investigate the chemical structure and physical state of the residual phosphorous in PBO fiber, which has been long suspected to hydrolyze the benzoxazole bonds of PBO chains and cause the degradation. The residual phosphorous is found to be in the form of phosphoric acid (PA) and its various forms of hydrated or dehydrated derivatives. Moisture would drive the reaction along the direction of P2O5 - polyphosphoric acid - PA - water-bound PA, while increasing temperature would reverse the direction. Hydration increases the mobility of PA molecules and increases its damaging power, while higher temperature removes water and immobilizes PA. The residual P species are easily accessible by gas molecules but inaccessible by aqueous media. These studies provide direct evidence to confirm the proposed environmental degradation mechanisms in the literature, and point out future directions for mitigation of this crippling problem for PBO fiber, the otherwise superior fiber of choice for soft body armor applications.

Descriptors :   nuclear magnetic resonance , spectroscopy , MATERIAL DEGRADATION PROCESSES , body armor , physical properties , phosphorous , MOISTURE , FIBERS , Elastomers

Subject Categories : Atomic and Molecular Physics and Spectroscopy
      Elastomers and Rubber

Distribution Statement : APPROVED FOR PUBLIC RELEASE