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Re: lifespan of hard rubber

Author: L. Omar Henderson
Date: 2007-05-01 13:47

Hard rubber goes through a process of vulcanization where a catalyst and heat cause the monomer chains to polymerize and form cross links between polymer chains. Hard rubbers begin to "decay" immediately after the vulcanization process. The time course depends on a lot of factors including exposure to ultra-violet light radiation, heat, and oxidizing agents in the air. The degree and ultimate structure of the polymerization reaction forming the hard rubber and subsequent tempering steps determine the final structure and its susceptibility to breaking of the cross links holding the rubber together. Modern rubber technology has improved the rate of "decay" of the polymerized chains - breaking of crosslinks and unravel ling polymerized chains, modern catalysts improve polymerization efficiency and complexity, UV inhibitor additatives have been included in rubber formulations, and now quality control steps analyze the structure of the rubber to form a blueprint characteristic of various batches of rubber which can help predict the longevity of the formulation.

Older catalysts like sulphur were adequate but relatively poor catalysts compared to modern exotic metal catalysts used to manufacture hard rubber. The purity of the starting material latex has also improved and changed over the history of rubber manufacture and a lot of the contaminants such as plant proteins found in older raw latex stock have been removed and the starting material further refined. The rubber trees themselves have been hybridized and the shift to different growing areas around the world has changed the quantitative makeup of latex stocks available today to make hard rubber. The type of catalyst used and the number and types of impurities in the starting latex stock determine the nodes of polymerization and therefore the resulting lattice structure of the final product. The lattice structure and blueprint signatures of antique hard rubbers is different than the lattice structures formed in todays hard rubber because of the impurities of starting materials used, catalysts, and type of vulcanization machinery available at the time. Whether the current "snapshot" of the "decayed" antique hard rubber is indicative of the beginning lattice and polymerization structure is a point of scientific conjecture.

Older hard rubber objects will "decay" faster than newer formulations because of the structure of the polymer formed using an excess of sulphur as a catalyst. We still have hard rubber mouthpieces in pretty good condition that were made 50-80 years ago so the lifetime of even these antique objects in long lived. There were probably more bad batches of rubber produced in earlier times and they may show more "decay" than similar batches made at the same time. Exposure of these items to heat, UV radiation, and oxidation elements probably causes a spectrum of "decay" characteristics even within a same batch of antique hard rubber examined today.

The bottom line answer - decay will and does happen but at a variable rate. Decay to fracture failure may take 25-100 years (or more) depending on the batch characteristics, formulation, and exposure to decay producing elements.
L. Omar Henderson
www.doctorsprod.com

Post Edited (2007-05-01 14:30)

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lifespan of hard rubber

Molloy

2007-05-01 13:05