Gutta Percha and Related Materials

Chlorinated rubber is usually prepared by bubbling chlorine into a solution of masticated rubber in a chlorinated hydrocarbon solvent such as carbon tetrachloride. Hydrochloric acid is removed during the reaction. The solvent may be removed by vacuum or steam distillation or by precipitation of the derivative by a non-solvent such as petroleum. 

Chlorinated rubber is extensively employed in industrial corrosion-resistant surface coatings, for which purpose it is marketed by ICl under the trade name Alloprene. Although thermoplastic moulding compositions have been made by plasticising with the common ester plasticisers such as tritolyl phosphate they are of no commercial importance. 

Both rubber-styrene and rubber-methyl methyacrylate graft polymers have been produced on a pilot plant scale. The side chains have unit weights of the order of 5000 compared with values of 70 000-270 000 for the main rubber chain. 

A number of high molecular weight polyisoprenes occur in nature which differ from natural rubber in that they are essentially non-elastic. As with natural rubber they are obtained from the latex of certain plants but they differ in that they are either trans-l,4-polyisoprenes and/or are associated with large quantities of resinous matter. 

As with c -polyisoprene, the gutta molecule may be hydrogenated, hydro-chlorinated and vulcanised with sulphur. Ozone will cause rapid degradation. It is also seriously affected by both air (oxygen) and light and is therefore stored under water. Antioxidants such as those used in natural rubber retard oxidative deterioration. If the material is subjected to heat and mechanical working when dry, there is additional deterioration so that it is important to maintain a minimum moisture content of 1%. (It is not usual to vulcanise the polymer.) 

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Chemical nature Isolation of casein from milk Production of casein plastics Properties of casein Applications Miscellaneous Protein Plastics Derivatives of Natural Rubber Gutta Percha and Related Materials Shellac... 

Non-elastomeric chemical derivatives of natural rubber are discussed in Chapter 30 in which chemically related naturally occurring materials such as gutta percha and balata are briefly considered. 

Leakage around calcium hydroxide sealers has been studied experimentally, and findings have generally been satisfactory [34-36]. However, there have been some adverse reports [37], and these variations have been attributed to crucial differences in experimental methods [38]. Leakage appears to be related to both the solubility of the material and the questionable adhesion to both the dentine walls and the gutta percha points. The calcium hydroxide sealer Apexit, for example, was found to have a high solubility when set compared with other types of endodontic sealer [39] and, in some studies, sealer particles have been found to occur with the tissues at a considerable distance from the sample [40,41],... 

Two well-known natural materials are rubber and gutta percha which are cis and trans polyiso-prene, respectively (11.116). Other examples of terpenes are provided by poly prenols (10.63), vitamin A (10.64), certain components of essential oils and the closely related sterols. Terpenes are widespread in nature and many are cyclic compounds. 

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