Rubber, natural production

Cure Characteristics. Methods of natural rubber production and raw material properties vary from factory to factory and area to area. Consequentiy, the cure characteristics of natural mbber can vary, even within a particular grade. Factors such as maturation, method and pH of coagulation, preservatives, dry mbber content and viscosity-stabilizing agents, eg, hydroxylamine-neutral sulfate, influence the cure characteristics of natural mbber. Therefore the consistency of cure for different grades of mbber is determined from compounds mixed to the ACSl formulation (27). The ACSl formulation is as follows natural mbber, 100 stearic acid, 0.5 zinc oxide, 6.0 sulfur, 3.5 and 2-mercaptobenzothiazole (MBT), 0.5. 

The calender was developed over a century ago to produce natural rubber products. With the developments of TPs, these multimillion dollar extremely heavy calender lines started using TPs and more recently process principally much more TP materials. The calender consists essentially of a system of large diameter heated precision rolls whose function is to convert high viscosity plastic melt into film, sheet, or coating substrates. The equipment can be arranged in a number of ways with different combinations available to provide different specific advantages to meet different product requirements. Automatic web-thickness profile process control is used via computer, microprocessor control. 

Hevea rubber is undoubtedly one of the unique crops of history and of all agriculture, and one of the most interesting. It is not easy to produce rubber. Research is the tool by which it is possible to grow vast acreages of the tree as a profitable crop. This could never have been done without the past /and present intensive investigations of careful scientists over more than 30 years. Repeated reference in the literature indicates that diseases are the limiting factors in natural rubber production, and that planters owe a debt to disease-control workers. 

Natural rubber is readily attacked by oxygen. Copper and manganese, if present in amounts greater than the specified 0.001%, greatly accelerate oxidation. There are, however, naturally occurring antioxidants in natural rubber that help preserve it until vulcanization. All vulcanized natural-rubber products contain added antioxidants to ensure satisfactory life. 

F. Natural Rubber. Natural rubber products have low resistance to hydrocarbons and relatively high permeability to gases and moisture. Natural-rubber goods are often more flexible than those made of synthetic rubber and have excellent tensile strength. 

Results of RIPT, modified Draize test, and human maximization tests have been accepted as valid by regulatory agencies however, some sponsors routinely use one of the methods described and defend its use as the standard of the industry . FDA reviewed details of sensitization procedures and developed a guidance document (1999) for evaluating skin sensitization to chemicals in natural rubber products. 

Jordan and King (1977) proposed modifying the challenge procedure to two consecutive 48-h patch periods. The modified Draize test has recently been selected as the test of choice for chemicals in natural rubber products by the FDA. Tests for the transdermal products are currently being evaluated by the FDA. 

Buehler EV (1964) A new method for detecting potential sensitizers using the guinea pig. Toxicol Appl Pharmacol 6 341 Center for Devices and Health (1999) Guidance for Industry and FDA Reviewers/Stuff Premarket notification [510(K)] Submission for Testing for Skin Sensitization to Chemicals in natural Rubber Production. U.S. Department of Health and Human Service, FDA... 

A more recent Dutch retail survey looked at the migration of A-nitrosamines, A-nitrosatable substances and 2-mercaptobenzothiazole (MET) from 19 samples of teats and soothers. In addition to these species, screening work was also carried out for any other potential migrants. The majority of the teats and soothers were found to be based on sihcone mbber, and the extractable substances were found to be siloxanes. The remaining samples were natural rubber and only one was found to be above the permissible limits, and that was for nitrosatable substances at 0.23 mg/kg. MET was found in only one of the natural rubber products and this was below the migration limit of 0.3 mg/teat. 

A.O.N. Panikkar, V.K.G. Nair, and V.C. Markose, "Breeding and tree improvement", in P.N.Radhakrishna Pillay Ed., Handbook of Natural Rubber Production in India, Rubber Research Institute of India, Kottayam, Kerala, 1980. 

E Yip. Residual extractable proteins and allergenicity of natural rubber products. In Latex Protein Allergy The Latest Position. Brickendonbury, United Kingdom Crain Communications Ltd, Rubber Consultants, 1995, pp. 33-39. 

Fair to good aging Cured products often will outperform natural rubber products, but uncured products made from emulsion polymers can degrade rather quickly if not compounded for UV, ozone, and oxygen resistance. Block copolymers are typically better in the uncured state than standard SBR, but still require protectant additives for extended exposure conditions. 

NATURAL SOURCES Natural rubber occurs in over 200 species of plants. However, only one tree source, Hevea Brasiliensis, is of commercial importance, and it accounts for over 99 percent of the world s natural rubber production. 

Chloroprene rubber, polychloroprene (CR). A syniheXic rubber produced by polymerization of chloroprene (2-chlorobutadiene, CH2=CCl—CH = CH 2). High weather and chemical resistance, better oil resistance than that of natural rubber products. Some applications building sheets, belts, cable insulations, technical rubber goods, contact adhesives. Trade names Baypren (FRG), Neoprene (USA). 

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