Rubber-based adhesive physical properties

With rubber base adhesives, it is necessary to prevent their properties from changing during service life. Oxidative changes induced by thermal, ozone exposure and UV light can dramatically affect service life of rubber base adhesives. More precisely, the rubber and the resin are quite susceptible to oxidative degradation. Environmental and physical factors exert detrimental effects on rubber base adhesive performance. These effects can be mitigated by the incorporation of low levels of stabilizers during the fabrication process of the adhesive. 

Rubber based adhesives are used in a myriad of applications which are familiar to the consumer. Tile and paneling adhesives are examples of these adhesives used in home construction. The largest use of mbber-based adhesives is in laminated furniture manufacmre. Representative physical properties of mbber-based adhesives are shown in Table 27.4. The adhesives are characterized as having low to moderate shear strength and high peel strength. 

The difference between plasticizers and tackifiers is somewhat arbitrary and the effect of this difference is described below in the section on Physical Properties. Plasticizers are typically lower in molecular weight and melting or softening point than are tackifiers. Hydrocarbon oils including aromatic, naphthenic, and paraffinic are commonly used with rubber-based adhesives. Phthalates, such as dioctyl phthalate or dibutyl phthalate, are more typically used in small amounts with acrylics. Since plasticizers are usually low molecular weight compounds, there is often more latitude in the chemical types that will be compatible with the base pol5mier because of the contribution from entropy of mixing. 

The viscoelasticity and surface tension of adhesives are physical properties that are independent of the specific chemical composition. Therefore, the relations discussed for rubber-based adhesives are also valid for polyacrylates [218] and other elastomeric bases. 

Phenolic based adhesives are outstanding in their wetting characteristics and strength. In the unmodified form, however, they tend to be brittle. To overcome this problem, phenolic based adhesives usually contain a rubber modifier to increase the crack resistance of the adhesive. The first modified phenolic contained polyvinyl butyral and was known as the "Redux" adhesive. Many modern phenolic adhesives contain nitrile rubbers (copolymers of acrylonitrile and butadiene) as the modifiers. An example of a phenolic based film adhesive is AF-30 which is listed in Table 1 along with its physical properties. This film... 

The most typical adhesive solvents are those based on elastomers, compounds characterized by the fact that they have a strong natural adhesiveness, especially in respect of themselves (the phenomenon of self-adhesion, the instantaneous adhesion of two films of glue after almost total evaporation of the solvent, is the basis for the composition of the contact glues especially neoprene-based (Fletcher 1971)). The basic chemical composition of neoprene synthetic rubber is polychloroprene (O Fig. 14.6). The polymer structure can be modified by copolymerizing chloroprene with, for example, 2,3-dichloro-1,3-butadiene to yield a family of materials with a broad range of chemical and physical properties. 

PP has also been blended with various proportions of recycled nitrile rubber (rNBR) crumb in the presence of a co-agent (trimethylolpropane triacrylate, TMPTA) [8]. The level of TMPTA used was 3 phr based on the amount of nitrile rubber (NBR) and crosslinking of the mixtures achieved using electron-beam irradiation at a level of 40 kCy. The irradiation process was found to improve both the interfacial adhesion between the phases in the blend and their physical properties when these were compared with non-irradiated samples. 

The concept of rubber reversion protection by using biscitraconimidomethylbenzene, trade name Perkalink 900, is discussed. The advantages of using this chemical in NR based adhesion compounds was examined. The effects of its use on adhesion to textiles, cure characteristics physical, mechanical and thermal properties are discussed. 14 refs. 

The conunon polymers for plastics, rubbers and fibers have been produced at a large industrial scale. It appears difficult to modify them from the early stage of the preparation route. Currently, most of modificatimis either via physical methods or via chemical treatments are based on their structure—property relationships. The specific functimial polymers for coatings, adhesives, adsorption resins and filtration membranes occupy a relatively small market, and their modifications often start from monomer synthesis. 

Block copolymers with incompatible blocks which are able to microphase separate are good candidates for PSA properties. Indeed, blends of ABA triblocks and AB diblocks, where the rubbery midblock of the ABA is the majority phase and the glassy endblocks self organize in hard spherical domains and form physical crosslinks, are widely used as base polymers for PSA. The actual adhesives are always compounded with a low molecular weight tackifier resin able to swell the rubbery phase and dilute the entanglement network. Linear styrene-rubber-styrene copolymers, with rubber being isoprene, butadiene, ethylene/propylene or ethylene/butylene, are the most widely used block copolymers in this category. 

Nitrile polymers have found a varied number of applications in the adhesive area. These applications are based on the excellent elastomeric properties of the polymer coupled with its polarity which gives the material good solvent resistance and compatibility with other polar materials. The various commercially available physical forms of nitrile polymers (slab rubber, crumb rubber, liquid rubber and latex) have also increased the ease of processing of the material and broadened the application base. In an attempt to review this broad area, the applications have been subdivided into three parts. In the first section applications involving solely nitrile rubber as the base polymer as well as miscellaneous nitrile rubber blends are reviewed. Due to the large number of applications involved, nitrile rubber/pheno-lic blends have been separated into the second section. For the same reason, nitrile rubber/ epoxy blends are covered separately in the third section. 

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