Rubber, tackiness

The consequences of oxydative and thermal breakdown of a polymer are discolouration, surface roughening, embrittlement, etc. for rubbers tackiness, followed by embrittlement. For electrical applications oxidation goes accompanied by a strong increase in the dielectric losses, and a decrease in insulation resistance and breakdown strength. 

A typical example is total monomers. 100 sodium stearate, 5 potassium persulfate, 0.3 lauryl mercaptan, 0.4 to 0.7 and water, 200 parts. In this formula, 75 parts of 1,3-butadiene and 25 parts of 4-methyl-2-vinylthiazole give 86% conversion to a tacky rubber-like copolymer in 15 hr at 45°C. The polymer contains 62% benzene-insoluble gel. Sulfur analysis indicates that the polymer contains 21 parts of combined 4-methyl-2-vinylthiazole (312). Butadiene alone in the above reaction normally requires 25 hr to achieve the same conversion, thus illustrating the acceleration due to the presence of 4-methyl-2-vinylthiazole. 

In appearance and on handling the material is somewhat intermediate between a wax and a rubber. It is also semi-tacky. Like isotactic polypropylene it is attacked by oxygen but unlike the isotactic material it swells extensively in aliphatic and aromatic hydrocarbons at room temperature. It is also compatible with mineral fillers, bitumens and many resins. 

Among the different pressure sensitive adhesives, acrylates are unique because they are one of the few materials that can be synthesized to be inherently tacky. Indeed, polyvinylethers, some amorphous polyolefins, and some ethylene-vinyl acetate copolymers are the only other polymers that share this unique property. Because of the access to a wide range of commercial monomers, their relatively low cost, and their ease of polymerization, acrylates have become the dominant single component pressure sensitive adhesive materials used in the industry. Other PSAs, such as those based on natural rubber or synthetic block copolymers with rubbery midblock require compounding of the elastomer with low molecular weight additives such as tackifiers, oils, and/or plasticizers. The absence of these low molecular weight additives can have some desirable advantages, such as ... 

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-grade resins are mostly in the softening point range 70-100°C R B. A deviation of 5-10°C in softening point may cause problems. The softening point of a resin affects the properties of adhesives. Hence, for pressure-sensitive rubber adhesives the decrease in the softening point of the resin produces a more tacky adhesive with less cohesive strength. 

A wide range of substrates can be bonded. The inherent tackiness of natural rubber enables it to coat most non-polar substrates (mainly plastics and rubbers). 

Solvent-borne adhesives. Although the NR polymer is inherently tacky, tack-ifying resins are generally added to improve bonding to polar surfaces. Because the solids content in these adhesives is lower than 35 wt%, they are not suitable for gap filling. The quick-grab (cements) adhesives are particular because they contain about 65 wt% rubber, and set within a few seconds under finger pressure. 

All grades of regular butyl rubber are tacky, rubbery and contain less unsaturation than natural rubber or styrene-butadiene rubber. On the other hand, low molecular weight grades of polyisobutylene are permanently tacky and are clear white semi-liquids, so they can be used as permanent tackifiers for cements, PSAs, hot-melt adhesives and sealants. Low molecular weight polyisobutylenes also provide softness and flexibility, and act as an adhesion promoter for difficult to adhere surfaces (e.g. polyolefins). 

The BR and PIB adhesives have permanent tack but relatively low cohesive strength. Cohesive strength is provided by adding natural rubber, fillers or tacki-fiers. Furthermore, these adhesives have excellent resistance to chemicals, oils and ageing. 

Modern bonding systems usually consist of a primer coat, often with a secondary tie coat, plus a tacky solution to assist in the application of the rubber. The bonding systems currently in use are usually suitable both for autoclave vulcanisation and vulcanisation at 100°C with atmospheric pressure steam or hot water. Ambient vulcanisation bonding systems have to be chemically active at the lower temperatures and are therefore specialist in nature. 

In the rubber industry tackiness means the ability of uncured rubber compounds to stick together under moderate pressure. Tackifiers improve adhesion and joint... 

We might well expect this differing stereochemistry to have a marked effect on the properties of the polymer, and this is borne out by the two naturally occurring polyisoprenes, natural rubber and gutta percha. The former, which before vulcanisation is soft and tacky, has all cis junctions in its chains while the latter, which is hard and brittle, has all trans junctions. 

Table V. Tackiness of various types of polybutadienes as determined by the test procedure of Ref. 14. Compound (phr) rubber 100 carbon black 50 aromatic...

A textile material used to prevent the tacky surfaces of unvulcanised rubber from adhering. The liner is often treated to permit easy release from the rubber. 

Vulcanization The treatment of natural rubber with sulfur to reduce its tackiness and improve its strength and elasticity. Invented independently by C. Goodyear and N. Hayward in the United States in 1839, and by T. Hancock in London in 1842-1843. Various chemicals other than elemental sulfur are effective, for example, sulfur monochloride, selenium, and p-quinone dioxime. 

This fungicide, as well as certain other organics, does not cause the tacky condition of latex said to be induced by copper contaminations. In Brazil and Costa Rica, rubber planters use much Dithane for nursery spraying. There are still some who prefer a certain amount of copper spray, but in Costa Rica, at least, the organic material is much more acceptable. It is also used for leaf disease on old trees in tap, being held for some special reason. Probably 10 tons of Dithane are used in the Western Hemisphere annually for control of South American leaf disease, and somewhat less than half as much of so-called insoluble copper sprays are still being applied. 

In 1838 Macintosh and Hancock at Goodyear discovered how to take tacky naturai rubber from rubber trees and react it with suifur in the presence of heat to vuicanize the rubber to a nonstick compound that couid be usefui for items such as boots, rain coats, and tires. Synthetic rubber research started between Worid Wars I and II and progressed very quickly after World War II. The modern birth of soiid synthetic poiymers for commerciai products may be traced to Hyatt in 1868. He discovered how to react cellulose nitrate and camphor to produce a hard piastic that was used to fabricate billiard balls because ivory had become scarce. 

After compounding, the stock is sheeted out in a roller mill and extruded into sheets or pelletized. This new rubber stock is tacky and must be coated with an antitack solution, usually a soapstone solution or clay slurry, to prevent the sheets or pellets from sticking together during storage. 

Toy balloons were introduced by Thomas Hancock in 1825 as a do-it-yourself kit that consisted of a rubber solution and a syringe. Vulcanized toy balloons were initially manufactured by J.G. Ingram of London in 1847. The vulcanizing caused the balloons to be nontacky and not susceptible to becoming excessively tacky on hot days. Montgomery Ward had balloons in their catalog by 1889. 

Rubber becomes brittle in cold weather and tacky in hot weather, and it is odorous and perishable. It also has very low tensile strength and low resistance to abrasion. One of the major advances in the improvement of rubber was in the discovery by Charles Macintosh in Scotland in 1820 that coal-tar naphtha is a cheap and effective solvent for rubber. He placed a solution of rubber and naphtha between two fabrics, and in so doing he covered up the sticky or brittle surfaces that had been common in earlier single-texture garments treated with rubber. Macintosh patented the process in 1823. These double-textured waterproof cloaks, which were first introduced to the public in 1824, have been known ever since as mackintoshes. 

Vulcanization heating rubber in the presence of sulfur to remove its tackiness and improve its quality... 

Isobutylene is more reactive than n-butene and has several industrial uses. It undergoes dimerization and trimerization reactions when heated in the presence of sulfuric acid. Isobutylene dimer and trimers are use for alkylation. Polymerization of isobutene produces polyisobutenes. Polyisobutenes tend to be soft and tacky, and do not set completely when used. This makes polyisobutenes ideal for caulking, sealing, adhesive, and lubricant applications. Butyl rubber is a co-polymer of isobutylene and isoprene containing 98% isobutene and 2% isoprene. 

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