page_title: David Spence (rubber chemistry)
section_title: Organic accelerators
hierarchical_section_title: David Spence (rubber chemistry) / Scientific career / Organic accelerators
caption_attribution_description: English: traditional vulcanization process
context_page_description: David Spence was one of the pioneering rubber chemists. He helped the war effort during the Second World War by devising new ways of extracting natural rubbers from plants, and worked to improve the processing of the rubber. Over the course of his career, he worked to improve the dyeing processes for rubber products and the vulcanization of rubber, and in developing new accelerants for strengthening lower-quality natural rubber. In 1941, he became the first recipient of the Charles Goodyear Medal, awarded by the American Chemical Society.
context_section_description: In the early years of rubber production, high quality natural rubber was obtained from the tree, Hevea braziliensis, found in the regions bordering the Amazon river.  The high quality rubber exhibited desired properties, such as a high tensile strength (greater than 2800 psi) and a two-hour vulcanization time. Vulcanization is the process by which natural rubber is strengthened by cross-linking the different polymer chains, with either elemental sulfur bridges or other molecules known as accelerators. However, high quality natural rubber was expensive, with a price exceeding $1.50 per pound.  Diamond Rubber experimented with various additives, such as mercury iodide and aniline, in an attempt to improve the properties of lower quality rubber. The addition of only 2.5 to 6 percent of these additives improved the tensile strength of low quality rubber from 1800 psi to 2800 psi, and shortened the vulcanization time to a 90 minutes. However, these additives were detrimental to the lifetime of the rubber. In 1912, Spence was working with George Oenslager at Diamond Rubber to discover different additives to overcome these shortcomings. Working off of Oenslager's aniline additives, Spence discovered that p-aminodimethylaniline was a far superior accelerator, requiring only 0.5 weight percent added to the vulcanization process, to vastly improve the tensile strength of the rubber.  P-aminodimethylaniline was adopted as the accelerator of choice by the Diamond Rubber Company in 1912.
caption: Traditional sulfur dependent vulcanization with para-aminodimethylaniline as an accelerator
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