Dark Sulfur: Quantifying unpolymerized sulfur in inverse vulcanized polymers

Abstract

Elemental sulfur is produced as a by-product of the refining process of the petrochemicals industry. This generates an excess of sulfur each year that currently goes unused. A process known as inverse vulcanization allows polymeric mate-rials to be formed from elemental sulfur, stabilised with organic comonomers or crosslinkers. The resultant high sulfur content polymers have shown many interesting and unique properties, and are being investigated for a growing number of applications. However, the techniques regularly used to determine if free unreacted sulfur, as S8, remains in the mate-rials only detect the crystalline, and not the amorphous form. Here is presented a detailed study on the identification and quantification of free amorphous sulfur present within inverse vulcanized polymers, both immediately after synthesis and after a period of aging, in which free sulfur is shown to increase over time. The potential for post-aging regeneration, by applying heat to stimulate homolytic disulphide cleavage, is also investigated.