Polyurethanes adhesive shear strength

The physical properties of polyurethane adhesives result from a special form of phase separation which occurs in the cross-linked polyurethane stmcture. The urethane portions of polyurethanes tend to separate from the polyol portion of the resin, providing good shear strength, good low temperature flexibiUty, and high peel strength. Catalysts such as dibutyltin dilaurate [77-58-7], stannous octoate [1912-83-0], l,4-diazabicyclo[2.2.2]octane... 

Chlorinated Polyether. This thermoplastic resists most solvents and is attacked only by nitric acid and fuming sulfuric acids. Thus, it is not capable of being solvent-cemented. Chlorinated polyether parts can be bonded with epoxy, polyurethane, and polysulfide-epoxy adhesives after treatment with a hot chromic acid solution. Tensile shear strength of 1270 psi has been achieved with an epoxy-polysulfide adhesive. 

Various adhesives can be used to bond polyphenylene oxide to itself or to other substrates. Parts must be prepared by sanding or by chromic acid etching at elevated temperature. Methyl alcohol is a suitable solvent for surface cleaning. The prime adhesive candidates are epoxies, modified epoxies, nitrile phenolics, and polyurethanes. Epoxy adhesive will provide tensile shear strength on abraded polyphenylene oxide substrates of 600 to 1300 psi and 1300 to 2200 psi on etched (chromic acid) substrates.71... 

An emulsion polymer-isocyanate adhesive, a crosslinked polyvinyl acetate adhesive, a resorcinol-formaldehyde adhesive, a phenol-resorcinol-formalde-hyde adhesive, and an acid-catalyzed phenolic-formaldehyde adhesive developed bonds of high shear strength and wood failure at all levels of acetylation in the dry condition. A neoprene contact bond adhesive and a moisture-curing polyurethane hot-melt adhesive performed as well on acetylated wood as untreated wood in tests of dry strength. Only a cold-setting resorcinol-formal-... 

Polyurethane adhesives are typically more flexible than epoxies, with good shear and high peel strengths on metals and engineering thermoplastics. These types of adhesives are particularly well-suited for joining substrates with dissimilar coefficients of thermal expansion and for securing various types of inserts in composite panels. 

Castor oil-based polyurethanes have ten times more lap shear strength than commercially available wood adhesives. Castor oil-based polyurethanes are widely used as adhesives in the biomedical and other fields. Castor oil-based polyurethane is also reported to be biocompatible and has been used successfully as a material for making artificial bone. Polyurethanes based on a castor oil-modified polyol and a PEG chain extender... 

Polyurethanes are among the better adhesives for cryogenic applications. Room temperature-curing polyurethane adhesives in current use provide higher ultimate shear and tensile stress and higher peel and shock properties at -253°C than the earlier polyurethanes. This situation is the inverse of what happens to most structural adhesives. The polyurethane adhesives increase in strength at -253°C, but become weaker at ambient and higher temperatures, as shown in Table 10.3. ... 

When all the conditions are optimum, particularly the polyurethane to robber ratio, then the chemistry and nature of the precipitated phase is altered and a degree of blend synergy takes place, which leads to an improvement in the adhesive shear properties, compared with a standard CTBN-tonghened system, coupled with a marked increase in peel strength, particularly under dynamic loading conditions. 

Keywords Adhesive modulus Adhesys expert system Co-axial joints Compression Concealed joints Creep Elastic limit Epoxy Epoxy composite Einite element analysis Glue line thickness Goland and Reissner Hart-Smith Heat exchanger Hooke s Law Joint designs Joint thickness Lap shear strength Peel Plastic behaviour Polyurethane Pipe bonding Shear stresses Shear modulus Stress distribution Thick adherend shear test Tubular joints Volkersen equation Young s modulus... 

Fig. 5. Temperature dependence of tensile relaxation modulus E(t) and lap shear strength (MMM-A-132) for a polyurethane block copol3nner adhesive.

Polyurethane and epoxy-nylon systems offer outstanding cryogenic properties. Polyurethane adhesives are easily processable and bond well to many snbstrates. Peel strength ranges from 22 Ib/in at 75° to 26 Ib/in at -423°F, and the increase in shear strength at... 

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