David Spence

David Spence (September 26, 1881 – September 24, 1957) 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.

Biography David was the son of the Rev. Alexander Spence (Minister of the Church of Scotland) and his wife, Agnes Spence nee Barclay (who were married in Scoonie on 15 Jun 1876). He was born at 7:00 am on 26 September 1881 at The Manse at Udny, Aberdeen County, Scotland. He was "vaccinated as per certificate dated December 18th 1881".

Spence earned his PhD from the University of Jena in Germany in 1906. Three years later, he accepted a position as the research lab director at the Diamond Rubber Company in Akron, Ohio. There, he succeeded in synthesizing isoprene for use in synthetic rubber. He left the company in 1914, and started the Norwalk Tire & Rubber Company, where he was vice president and manager until 1925. He retired in 1931, after which he continued to do his own rubber research.

During his career, he was responsible for developing several different processes: he developed accelerators for the vulcanization process; a process to devulcanize rubber; a system to extract natural rubber from guayule; and a process to modify the physical properties of rubber. During World War I, Spence headed the National Research Council's Rubber Division, and he was a consultant to the War Production Board during World War II. In 1941, he became the first recipient of the Charles Goodyear Medal.

Scientific career

Organic accelerators

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.

Development of guayule as a rubber alternative Throughout World War II, the allied forces suffered from a shortage of latex rubber, due to Japan cutting off America's access to the Malaysian rubber plantations. Spence, along with other allied scientists, scrambled to secure another natural rubber resource. Latex derived from Parthenium argentatum, more commonly called Guayule, was an ideal candidate as a replacement rubber due to the properties of the vulcanized rubber produced from Guayule, which were similar to the rubber produced from Malaysian rubber plantations. Latex from Guayule was first prepared in 1876, via a solvent extraction of the latex using acetone, and this extraction process was used commercially by the Diamond Rubber Company up until the 1930s. However, the acetone extraction process was too expensive to meet the large rubber demand brought on by World War II, creating a push to develop more conventional mechanical processing methods to extract the latex. Therefore, additional rubber supplies were needed in order to avert a rubber shortage. This would present a serious vulnerability in the American war machine, as rubber was used to manufacture a wide variety of war materials. President Roosevelt commissioned the American rubber and petroleum industries to quickly design and implement synthetic rubber replacements, leading to rapid expansion of both these industries. Due to his involvement in the synthesis of the isoprene monomer, Spence was the first recipient of the Charles Goodyear Medal. While observing devulcanization, Spence noticed that the decomposition products were dependent on the oxygen content in the system, and that, without oxygen, the rubber failed to devulcanize. Based on these observations, Spence developed an oxygen, sulfur, and accelerator free vulcanization process by using organic oxidizers such as quinones or organic peroxides. Spence's vulcanization process required placing the latex mixture in a pH 7 buffered solution, and applying an organic oxidizer agent to the mixture under an inert atmosphere of nitrogen. Prior to Spence's method, the dyes were applied during the processing of the rubber. This proved too expensive and was limited by thermal decomposition of the dyes. Submerging the rubber products in an adsorbent bath of amine dye, sodium hydrate, sodium chloride, and sulfuric acid allowed for the dyes to be bound covalently to the rubber matrix. The amines in solution reacted with primary amines in the rubber matrix to form azo dyes on the rubber fibers. This methodology of dyeing rubber was found to be applicable to raw, vulcanized, and other manufactured rubber products.