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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 stainless steel: see steel.
stainless steel

Any of a family of alloy steels usually containing 10–30% chromium. The presence of chromium, together with low carbon content, gives remarkable resistance to corrosion and heat.
 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.  rubber (CR) 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 of the surface of the vulcanizate by chlorination chlorination Public health Addition of chlorinated compounds to drinking water as disinfectants. Cf Ozonation. .

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 as a chlorinating agent. This material is available in preweighed (3 g) tablets for household use.

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 suitably diluted with MEK Noun 1. MEK - a terrorist organization formed in the 1960s by children of Iranian merchants; sought to counter the Shah of Iran's pro-western policies of modernization and opposition to communism; following a philosophy that mixes Marxism and Islam it now attacks the  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 thiourea

a goitrogenic agent used in industry as a photographic fixative. Mode of action is as for thiouracil.
 or its derivatives absorb water to a considerable degree as a result of the in situ production of the very deliquescent del·i·quesce  
intr.v. del·i·quesced, del·i·quesc·ing, del·i·quesc·es
1.
a. To melt away.

b. To disappear as if by melting.

2.
 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 oscillations See Cortical 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 IIT - Integrated Information Technology , Haifa, Israel
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Title Annotation:Tech Service
Author:Rigbi, Zvi
Publication:Rubber World
Date:Aug 1, 2004
Words:435
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