The effect of surface chlorination on the mechanical properties of a CR vulcanizate.In a particular project, it was found necessary to laminate stainless steel sheets to a chloroprene chloroprene (klōr`əprēn') or 2-chloro-1,3-butadiene, colorless liquid organic compound used in the synthesis of neoprene and certain other rubbers. The structure of the chloroprene molecule is very similar to that of isoprene; the molecule contains two double bonds and is readily polymerized. rubber (CR CR The two-character ISO 3166 country code for COSTA RICA.) vulcanizate while
maintaining the total thickness of the laminate to within close
tolerance. The CR base being only slightly polar and therefore unlikely
to bond strongly if at all to the steel sheets, it was decided to
increase the polarity 1. The property of having two opposite poles, such as those possessed by a magnet, or of having opposite properties or characteristics. 2. The direction or orientation of positivity relative to negativity. Chlorine is an unpleasant and dangerous chemical to handle, and concentrated solutions are not normally available. It was therefore decided to use a solution of calcium hypochlorite calcium hypochlorite hypochlorite /hy·po·chlo·rite/ (-klor´it) any salt of hypochlorous acid; used as a medicinal agent with disinfectant action, particularly as a diluted solution of sodium hypochlorite. hy·po·chlo·rite (h n. as a chlorinating
agent. This material is available in preweighed (3 g) tablets for
household use. A white crystalline solid used as a bactericide, fungicide, and bleaching agent. The CR sheets were obtained by curing in a semi-positive mold to close tolerance in thickness. After cooling, they were immersed in a solution of 150 g of calcium hypochlorite dissolved in 10 liters of water at 60[degrees]C for 40 minutes. The CR sheets were rinsed in water and allowed to dry in air. The adhesive used was an epoxy resin activated by DETA DETA - Defense Economic Transition Assistance (SBA) DETA - Dielectric Thermal Analysis DETA - Dielectric Thermal Analyzer DETA - Diethylene Triamine DETA - Digital Education Teacher Academy suitably diluted with MEK MEK - Message Encryption Key MEK - Methyl Ethyl Ketone MEK - Mobiles Einsatzkommando (German: Mobile Police Force) MEK - Mojahedin-E Khalq Organization (Iran) in order to minimize the thickness of the glue line. This resulted in a very strong bond in which the rubber consistently tore before the bond failed. It is well known that CR compounds cured with zinc oxide and ethylene thiourea or its derivatives absorb water to a considerable degree as a result of the in situ production of the very deliquescent zinc chloride. It was therefore feared that the chlorination process would change the mechanical properties of the compound, particularly the low strain modulus, called the "zero" modulus. Accordingly, tensile strips were tested before and after chlorination and their zero modulii calculated (ref. 1). This was considered to be the most indicative property for objects which would be used in applications of very low amplitude oscillations. The results of the tests showed that the absorption of water for the short period of inmaersion was negligible and the mechanical properties only slightly affected. The results are shown in table 1. Conclusion Chlorination of CR vulcanizates is a surface process which enhances the polarity and does not affect the bulk of the rubber.
Table 1 - properties of CR compound before and
after surface chlorination
Before After
Tensile strength 1.778 kgf/[cm.sup.2] 1.693 kgf/[cm.sup.2]
Elongation 273 211%
Zero modulus .3258 kgf/[cm.sup.2] .3244 kgf/[cm.sup.2]
References (1.) Z. Rigbi, "On the determination of the zero modulus of rubber," Kautscuk + Gummi Kunststffe, Vol. 33, p. 1,011, 1991. Zvi Rigbi, Dept. of Chemical Engineering, Technion IIT, Haifa, Israel |
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