Peel strength natural rubber adhesives

Other polymers used in the PSA industry include synthetic polyisoprenes and polybutadienes, styrene-butadiene rubbers, butadiene-acrylonitrile rubbers, polychloroprenes, and some polyisobutylenes. With the exception of pure polyisobutylenes, these polymer backbones retain some unsaturation, which makes them susceptible to oxidation and UV degradation. The rubbers require compounding with tackifiers and, if desired, plasticizers or oils to make them tacky. To improve performance and to make them more processible, diene-based polymers are typically compounded with additional stabilizers, chemical crosslinkers, and solvents for coating. Emulsion polymerized styrene butadiene rubbers (SBRs) are a common basis for PSA formulation [121]. The tackified SBR PSAs show improved cohesive strength as the Mooney viscosity and percent bound styrene in the rubber increases. The peel performance typically is best with 24—40% bound styrene in the rubber. To increase adhesion to polar surfaces, carboxylated SBRs have been used for PSA formulation. Blends of SBR and natural rubber are commonly used to improve long-term stability of the adhesives. 

Rubber base adhesives develop strength faster than most other polymeric types. Fig. 1 [3J shows the differences in the development of peel strength for several rubber polymers (without additional additives, except an antioxidant). Natural... 

Tackifying resins enhance the adhesion of non-polar elastomers by improving wettability, increasing polarity and altering the viscoelastic properties. Dahlquist [31 ] established the first evidence of the modification of the viscoelastic properties of an elastomer by adding resins, and demonstrated that the performance of pressure-sensitive adhesives was related to the creep compliance. Later, Aubrey and Sherriff [32] demonstrated that a relationship between peel strength and viscoelasticity in natural rubber-low molecular resins blends existed. Class and Chu [33] used the dynamic mechanical measurements to demonstrate that compatible resins with an elastomer produced a decrease in the elastic modulus at room temperature and an increase in the tan <5 peak (which indicated the glass transition temperature of the resin-elastomer blend). Resins which are incompatible with an elastomer caused an increase in the elastic modulus at room temperature and showed two distinct maxima in the tan <5 curve. 

The chemical nature of the tackifier also affects the compatibility of resin-elastomer blends. For polychloroprene (a polar elastomer) higher tack is obtained with a polar resin (PF blend in Fig. 27) than with a non-polar resin (PA blend in Fig. 27). Further, the adhesion of resin-elastomer blends also decreases by increasing the aromatic content of the resin [29]. Fig. 28 shows a decrease in T-peel strength of styrene-butadiene rubber/polychloroprene-hydrocarbon resin blends by increasing the MMAP cloud point. Because the higher the MMAP... 

Elastomer-based adhesives. Natural- or synthetic-rubber-based adhesives usually have excellent peel strength but low shear strength. Their resiliency provides good fatigue and impact properties. Temperature resistance is generally limited to 150 to 200°F, and creep under load occurs at room temperature. 

Experimental work has shown that a chemically depolymerized latex exhibits the characteristics of a pressure-sensitive adhesive." Good peel strength was found without the addition of resin, and as the low glass transition temperature of natural rubber was not affected by the reaction, these materials may be of interest in low temperature applications. Blends... 

Ex. 6 Multranil 176 polyurethane elastomer is dissolved at 20% by weight in a mixture of dry ethyl acetate and acetone, and 8.3 phr of Mondur TM (XII) (for natural and synthetic rubber adhesion) or 5 phr of Mondur CB-75 (XXIX) (for non rubber adhesion) is added. These combinations are versatile adhesives for bonding vulcanized rubber (natural and synthetic) to itself, leather, urethane, PVC, cork, wood, etc. Cure occurs at room temperature, and faster at elevated temperatures. At room temperature bond strengths (peel) are (imme-diate/after 3 days) rubber-to-rubber, 5.5—9.0/ 25 rubber-to-shoe sole leather, 5.5—7.3/24 shoe sole leather-to-shoe sole leather, 7.3—9.0/ 24 rubber-to-shoe sole leather, 9.5/24 Ib/in. width. 

In the literature, there are several reports that examine the role of conventional fillers like carbon black on the autohesive tack (uncured adhesion between a similar pair of elastomers) [225]. It has been shown that the incorporation of carbon black at very high concentration (>30 phr) can increase the autohesive tack of natural and butyl rubber [225]. Very recently, for the first time, Kumar et al. [164] reported the effect of NA nanoclay (at relatively very low concentration) on the autohesive tack of BIMS rubber by a 180° peel test. XRD and AFM show intercalated morphology of nanoclay in the BIMS rubber matrix. However, the autohesive tack strength dramatically increases with nanoclay concentration up to 8 phr, beyond which it apparently reaches a plateau at 16 phr of nanoclay concentration (see Fig. 36). For example, the tack strength of 16 phr of nanoclay-loaded sample is nearly 158% higher than the tack strength of neat BIMS rubber. The force versus, distance curves from the peel tests for selected samples are shown in Fig. 37. 

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