Rubber product stability

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 early practical application of antioxidants was connected with the development of rubber production. The rubber is easily oxidized in air, and the first antioxidants were empirically found and used to stabilize it [1]. Empirical search for antioxidants was performed by Moureu and Dufresse [2] during the First World War. These researchers successfully solved the problem of acrolein stabilization by the addition of hydroquinone. They explained the retarding action of the antioxidant in the scope of peroxide conception of Bach and Engler (see Chapter 1). They proposed that the antioxidant rapidly reacts with the formed hypothetical moloxide and in such a way prevents the autoxidation of the substrate. 

Uses. Intermediate in the manufacture of EDTA catalytic agent in epoxy resins dyes, solvent stabilizer neutralizer in rubber products... 

Benzylpenicillin is incompatible with rubber products and metal ions. Stability is affected by alcohols, surfactants, oxidizing and reducing agents, macrogols and other hydroxy compounds, glycerol, glycols, some paraffins and ointment bases, preservatives such as chlorocresol or thiomersal, blood and blood products, and antibacterials such as amphotericin, cephalosporins, and vancomycin. Injections of benzylpenicillins and aminoglycosides should be administered separately. 

The Arrhenius treatment has been applied to aging studies on rubber (13), to predict the life of a polyester-glass laminate (14), to predict product stability of a thermosetting resin alone and in combination with two additives (15), in permanence tests on paper (16), to multi-component systems in which the principal component is paper (17), and to study the influence of temperature on the relative contributions of the oxygen-independent and oxygen-dependent processes to the total rate of newsprint deterioration (18-20). 

Cefoxitin is a broad spectrum, semi-synthetic cephamy-cin antibiotic. The free acid form is a white, crystalline, practically insoluble solid and therefore the decision was made to use the sodium salt to provide a sterile solution for intravenous administration. It was soon evident that the sodium salt of cefoxitin would have limited stability in solution and would not lend itself to the formulation of a marketable solution product. Stability studies highlighted the advantages of sterile crystalline solid over amorphous freeze-dried product, and also the need for rubber stopper screening studies to eliminate interactions between sodium cefoxitin powder and rubber, and finally the profound effect of oxygen on the coloration rate of the product. 

Traditionally, ophthalmic liquid products were packed in glass containers fitted with rubber teats for the eye dropper. Glass containers have (limited) use today when there are product stability or compatibility issues which exclude the use of flexible plastic containers made of polyethylene or polypropylene. Most liquid eye products on the market are plastic containers fitted with nozzles from which, by gentle squeezing, the contents may be expressed as drops. 

N.S. Allen and A. Parkinson, Polymer Degradation and Stability, 1983, Vol. 5, No. 3, p. 189 cit. from D. Wright, Failure of Plastics and Rubber Products. Causes, Effects and Case Studies Involving Degradation. Rapra Technology Ltd., UK, 2001, pp. 84. 

Overcure stability is the steadiness of the compound s physical properties in the cured state under conditions of prolonged overcure. With thick article cures, some compounds are unavoidably exposed to overcure conditions. Certain compounds may not have good overcure stability. For example, many compounds based on natural rubber will decrease in modulus after peaking at the optimal cure when left at extended exposure times to the cure temperature. This decrease in modulus from overcure is called reversion. Also some compounds appear never to reach a cure plateau but continue to increase in modulus indefinitely at the cure temperature. This quality is commonly referred to as marching modulus. Obviously, the compound s overcure stability is very important in a rubber production facility. 

A proposed expansion of the company s styrene-butadiene rubber production will require an additional 10,000 tons/yr of butadiene as a raw material. For many years, butadiene has been manufactured by dehydrogenating butene or butane over a catalyst at appropriate combinations of temperature and pressure. It is customary to dilute the butene feed with steam (10 to 20 mol HjO/mol butene) to stabilize the temperature during the endothermic reaction and to help shift the equilibrium conversion in the desired direction by reducing the partial pressures of hydrogen and butadiene. The current processes suffer from two major disadvantages ... 

At present tubular turbulent apparatus system of divergent-convergent design is used in ethylene-propylene rubbers production at the stages of catalytic system decomposition, removing of catalyst from polymer and introduction of stabilizer-antioxidant into rubber solution [78, 79]. 

ZnO is especially effective in gelation of the latex foam with sufficient stability making it to be useful in the production of latex foam rubber products. 

Rubber-based products permeate our lives, forming part of the many materials used for personal, domestic and industrial purposes. Rubber may be natural, synthetic or a mixture of the two. Since the vast majority of rubberized materials are unlabeled, it is difficult to determine whether a product contains natural or synthetic rubber. The overlap between rubber and plastic further complicates the matter, especially since plastics contain many of the same catalysts, stabilizers, antioxidants and pig-ments/dyes that are present in rubber products. Fregert (1981) listed a number of naphthylamines, substituted para-phenylenediamines, alkylphenols and hydroquinone derivatives, which are utilized in the manufacturing of both rubber and plastic. Although completely cured plastics are rare sensitizers, fully cured rubber products produce allergic reactions as the sensitizers in rubber can leach out or bloom over time. 

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