Chlorinated rubber, bonding

Treatment of natural rubber with chlorine gives a product, chlorinated rubber, with a maximum chlorine content of 65% corresponding to the empirical formula C10H11CI7. Such a compound corresponds neither to a hypothetical simple addition to the double bond (Figure 30.6 (I)) nor to a product with a-methylenic substitution in addition (II). 

Chlorination of natural rubber (NR) is carried out with chlorine in carbon tetrachloride solution at 60-90°C to yield a chlorinated rubber containing about 65% chlorine, which corresponds to 3.5 chlorine atoms per repeat unit. The process is complex and includes chlorine addition to the double bond, substitution at allylic positions, and cyclization. Chlorinated rubber has high moisture resistance and is resistant to most aqueous reagents (including mineral acids and bases). It is used in chemical- and corrosion-resistant paints, printing inks, and textile coatings. Bromination of butyl rubber is also practiced [Parent et al., 2002]. 

Chlorinated rubber is also an effective bonding agent. It can be used for bonding neoprene, nitrile and natural rubbers to metals. Phenol formaldehyde resins have been used alone or in conjunction with chlorinated rubbers, but curing time is lengthy. 

In particular, they found enhanced bonding between metal surfaces and resins such as acrylics (solvent- and water-based), epoxy chlorinated rubbers, silicones, and polysulphides. It was noted that titanium complexes caused colouration with phenolics, whilst zirconium complexes did not. 

Chlorinated rubber resins are produced by the chlorination of synthetic and natural rubbers. The chemical structure shown in Fig. 13.3 is synthesized by the addition of chlorine to unsaturated double bonds until the resin contains 65% chlorine. These resins have similar properties to those of vinyl resins. Plasticizers are added to increase elasticity and resin adhesion. These coatings are resistant to water but have poor resistance to sunhght. 

Uses Bonding agent for bonding rubber doughs, sol n. coatings, and solv.-based dips to a variety of syn. textiles, rec. for adhesives, esp. those based on polychloroprene and on chlorinated rubbers Properties Dk. bm. low vise, liq. dens. 1070 kg/m (20 C) 54% act. Toxicoiogy Harmful by inh. irritating to skin, eyes, and respiratory tract may cause sensitization by inh. 

Chlorine treatment of natural rubber gives chlorinated rubber III. Since the products contain up to 65% chlorine, substitution obviously occurs along with addition across the double bonds (since the latter would only lead to a theoretical maximum of 51%C1). As indicated by spectroscopic studies, some cyclization to cyclohexane structures occurs also. Chlorinated rubber solutions are Used as adhesives for diene rubber-metal laminates. 

It is possible to make a whole series of derivatives of rubber. First one can add atoms to the double bond the products, obtained with Clg and HCl, being well-known. Apart from this however, substitution also occurs so that chlorinated rubber may be represented by... 

Chlorinated rubber resins include those resins produced by the chlorination of both natural and synthetic rubbers. Chlorine is added to unsaturated double bonds until the final product contains approximately 65% chlorine with the chemical structure shown in Figure 12.2. Since the final product is a hard, brittle material with poor adhesion and elasticity, a plasticizer must be added. The volume of solids of the coating is somewhat higher than that of a vinyl therefore, a suitably protective chlorinated rubber system often consists of only three coats. 

Acetone and methyl ethyl ketone are components of solvent blends in urethane, nitrile rubber, and neoprene industrial adhesives. Acetone is the primary solvent in resin-type adhesives and pressure sensitive chlorinated rubber adhesives. Methyl isobutyl ketone is a solvent component for nitrile rubber and acrylic adhesives as well as in polyvinyl chloride and polyvinyl chloride-polyvinyl acetate copolymer bonding adhesives. Again, the desired evaporation rate of the adhesive formulation will often determine the ketone selected. 

Epoxidizedsoybean oil (ESO) is produced via conversion of the double bonds of soybean oil with peracids or peroxides, resulting in more reactive oxirane or epoxide moieties, promoting chemical reactions [230-232]. ESO is normally used to plasticize and/or stabilize poly(vinyl chloride) (PVC), chlorinated rubber, and PVOH emulsions [231, 232]. The effects of ESO as a PLA plasticizer were reported elsewhere [230, 233, 234]. In summary, ESO lowered Tg, cold crystallization temperature Tm. enthalpy of cold crystallization (AHcc), tensile strength, and tensile... 

The bond between rubber and the metal surface is essentially a mechanical one achieved by the use of various resins and chlorinated rubbers, which when heated and crosslinked within their mass form a rigid network. Subsequent application of a high temperature directly to the area of the bond will result in the loosening of the grip of the primer material, and under the application of a load the bond will fail. This method is sometimes used to reprocess metals from components which have been rejected by quality tests. 

Chlorinated rubber resins tend to undergo dehydrochlorination that is, a hydrogen atom on one segment of the polymer molecule joins with a chlorine atom on an adjacent segment to form hydrogen chloride. When they split off from the polymer molecule, a double bond forms in their place. In the presence of heat and light, this... 

Nitrile rubber is used preferably for contact adhesives with improved plasticizer resistance. Polyisobutylene is used in pressure-sensitive adhesives. Butyl rubber is sometimes added to pressure-sensitive and hot-melt adhesives, although it is mainly used in sealing compounds. Epoxy resins and reactive (meth)acrylate adhesives (reactive adhesives) are modified with polychloroprene, butyl, and nitrile rubber. Chlorinated rubber is added in small quantities to contact adhesives and also to rubber-to-metal bonding agents for improving the adhesion properties. 

Jaeger and Korb" described the use of added carboxyl nitrile rubber to modify a standard rubber-to-metal adhesive containing chlorinated rubber and phenolic resin and thereby enhance the rubber-to-metal bonding capability. Cylinders of natural rubber were bonded by vulcanization for 25 min at 145°C and 70 kg/cm. The bond strength for the control adhesive was 59 kg as compared to 74 kg for the modified adhesive. This adhesive was also used successfully for bonding cw-polybutadiene rubber and nitrile rubbers to steel, aluminum, and brass adherends. The Dunlop Rubber Company patent claims the use of a butadiene... 

Ex. 3. Natural, Hycar, Paracril, and butyl and neoprene mbbers are bonded to seven metals/alloys with an adhesive comprising 50 parts of a chlorinated rubber ( Alloprene B) and 100 parts of Vulcabond TX (XIII) dissolved in 150 parts of ethylene dichloride. Bonds to copper and Monel metal were inferior. Information is provided on the effect on bond strength of accelerator, loading types (carbon blacks, white fillers) in the bonded stocks, and the age of the fully formulated adhesive. 

---