Polymeric adhesives

USSR Pat. 544,663 (1977) SMyarskii (to State Scientific Research and Design Institute of Polymeric Adhesives). 

The Nitro-dur system, marketed by Key Pharmaceuticals, Inc., contains nitroglycerin in acryUc-based polymeric adhesives with a cross-linking agent for polymer stabiUty. This depot of dmg provides a continuous source of active ingredient. An impermeable backing prevents release of nitroglycerin away from the skin. The systems are individually sealed in a paper polyethylene-foil pouch (81). 

A completely polymeric adhesive minimizes the risk of skin irritation or sensitization by the lower molecular weight additives. 

Bitton R, Ben-Yehuda M, Davidovich M, Balazs Y, Potin P, Delage L, Colin C, Bianco-Peled H (2006) Structure of algal-born phenolic polymeric adhesives. Macromol Biosci 6 737-746 Bolwell GP, Davies RD, Gerrish C, Auh C-K, Murphy TM (1998) Comparative biochemistry of the oxidative burst produced by rose and French bean cells reveals two distinct mechanisms. Plant Physiol 116 1379-1385... 

Other advantages of polymeric adhesiveness over that by small molecules, at the same degree of wetting, are the substantial fraction of covalent bonds which lie in the immediate first plane adjacent to the interface, allowing to bridge small flaws by chains, and encouraging stress dissipation and transmission through their loops away from the interface. 

Charge and ionization of the polymer. Anionic polymers provide better efficiency than cationic or uncharged polymers with respect to both adhesiveness and toxicity [35]. Furthermore, polymeric adhesives with carboxyl groups are preferred over those with sulfate groups [36]. 

Concentration of the polymeric adhesive. In general, the more concentrated the poly-merie adhesive, the lower its bioadhesive strength. The coiled molecules become solvent poor in a concentrated solution which, in turn, reduces the available chain length for interpenetration into the mueus layer. Therefore, a critical concentration of the polymeric adhesive is required for optimum bioadhesion [37]. 

This work was supported by the Virginia Institute for Material Systems (VIMS) and the NSF Science and Technology Center High-Performance Polymeric Adhesives and Composites (NSF grant number DMR-912004). The authors would like to thank Dr. Po-Jen Shih and Mr. Todd Bullions for their assistance is preparing this chapter. 

Metals such as aluminium, steel, and titanium are the primary adherends used for adhesively bonded structure. They are never bonded directly to a polymeric adhesive, however. A protective oxide, either naturally occurring or created on the metal surface either through a chemical etching or anodization technique is provided for corrosion protection. The resultant oxide has a morphology distinct from the bulk and a surface chemistry dependent on the conditions used to form the oxide 39). Studies on various aluminum alloy compositions show that while the oxide composition is invariant with bulk composition, the oxide surface contains chemical species that are characteristic of the base alloy and the anodization bath40 42). 

Comyn [1] has pointed out that maximum bond strength and consequently greater adhesion between the substrate and polymer could be achieved with a monolayer of silane bound to both the adherend and adhesive. The current investigation was undertaken to evaluate the possibility of monolayer level depositions on silicon substrates by employing a few w -functionalized alkanoyl-substituted derivatives of APTES which will provide polar moieties as well. The interactions of these functionalized silanes covalently immobilized on silicon with octadecylamine and octadecanoic acid, used as models for basic and acidic polymeric adhesives, were also examined in this study. Characterization of the silanized surfaces as well as studies on their interactions with the above two chemical probes were carried out through ellipsometric and XPS measurements. 

Department of Chemistry and Center for High Performance Polymeric Adhesives and Composites, 2108 Hahn Hall, Virginia Tech, Blacksburg, VA 24061- 0344, USA... 

Many epoxy adhesives are capable of being B-staged. A B-staged resin is one in which a limited reaction between the resin and hardener has taken place so that the product is in a semicured but solid state. In the B-staged state, the polymeric adhesive is still fusible and soluble. On additional heat curing, the adhesive will progress from the B stage to a completely cured state. This will usually be accompanied by moderate flow. 

Adhesive compounding also occurs at the end-user level. This is generally done when the end user cannot find a product to meet his or her individual needs, to reduce cost associated with a middleman, or to make use of other materials (e.g., scrap resin, fillers, etc.) that are generated during the course of business. Epoxy adhesives are more conducive to the end user or in-house processor than other polymeric adhesives because of the ease with which the liquid resins can be mixed with other ingredients. Many of these operators buy raw materials from various suppliers and do their own blending and formulating. 

All the materials to be tested for shelf life are stored in unopened containers. Storage in containers that have been opened exposes the resin to oxygen and humidity that, depending on the type of resin, could drastically reduce the shelf life and affect final properties. Most polymeric adhesives and sealants and their components have a shelf life greater than 6 months at room temperature. However, some one-component adhesives need to be stored at refrigerated conditions to have a practical shelf life. 

The use of SSL or lignosulphonates in other polymeric adhesive systems has also been examined [e.g., with polyacrylamide, proteins/aldehydes, polyethylene oxide, polyethylene imine, epoxides, melamine, styrene oxide, polyisocyanates (55)]. So far, these procedures, for different reasons, have not led to any major practical application (36). It would, however, be interesting to reexamine some of these processes using not crude spent sulphite liquors, but instead those purified by membrane filtration. 

The replacement of petroleum-derived (nonrenewable) sources of adhesive raw materials with renewable sources will follow three basic strategies 1) renewable materials will be used to replace part of the required petroleum-derived adhesive systems, 2) new polymeric adhesives will be synthesized from renewable materials and totally replace petroleum-derived adhesive systems, or 3) the adhesives systems now based on petroleum-derived materials will continue to be used, but the adhesive raw materials will be derived from renewable sources instead of from nonrenewable ones. Carbohydrates are very versatile chemicals that can be utilized in all three strategies as demonstrated by the preceding discussion. 

Graft copolymers combine the properties of their polymeric constituents and as such are polymer alloys, which open a vast field of new polymeric species. This is why active research along these lines is performed in many academic and industrial research laboratories all over the world. However, only few applications have reached a commercial level today. They involve the production of specific polymeric adhesives, perm-selective membranes, bio-medical devices and the surface modification of certain products. 

The transformation of liquid monomers to solid adhesive involves an increase in molecular size and molecular weight through polymerization. The increase in molecular weight of the polymeric adhesive is responsible for the attainment of adequate mechanical properties, cohesive strength, impact strength, etc., and should, therefore, be allowed to proceed to the required levels during bond formation. 

Another interaction occurs between dipoles in molecules. Dipoles arise when the electrons of a chemical bond between atoms are not shared equally, thus creating positive and negative charge centers in the molecule. The interaction forces between permanent dipoles of polar molecules depend on the strength of the two dipoles, and decrease with the sixth power of the distance between their centers. Clearly, the dipolar interaction of polymeric adhesives will be strong when they carry polar chemical groups. 

An example of this effect is given in where the time to failure of a polymeric adhesive is measured for various applied Gi values. The corresponding creep modulus values for the various times were then obtained. From Eq. (37) ... 

Addition of typical crosslinking agents,such as 20% diallyl phthalate, 10% ethylene glycol dimethacrylate, 1% maleic anhydride or 1% itaconic anhydride, to the isobutyl 2-cyanoacrylate so that after curing a more rigid,insoluble, hydrolytically stable polymeric adhesive might be formed,does not increase the strength of the dentin-poly(methyl methacrylate) joint. Perhaps the cross-linked adhesive possesses decreased resistance to the thermal shock encountered by the test specimens. 

The initial drop in adhesion strength occurred rapidly, often in a matter of hours. The drop may reflect a plasticizing effect of moisture, similar to that observed in polymeric adhesives (4.5). 

For the reaction mechanism described above the term polymerization has become established. Adhesives curing in this way are therefore called polymerization adhesives. 

Apart from polyaddition and polymerization adhesives, a third kind of adhesive that shows a special reaction mechanism during the curing process exists. They should be mentioned for the sake of completeness, although they are less important compared to the systems mentioned so far. Their characteristic is the fact that a byproduct arises in the formation of the polymers from the monomers, which has to be considered in curing. The central molecule of these adhesives is formaldehyde... 

Acrylic adhesive A polymerization adhesive deriving from acrylic acid. 

Double bond In organic chemistry, the combination of two carbon atoms by two valencies (C=C). The double bonds are the prerequisite for curing of polymerization adhesives. 

Polycondensation In contrast to polyaddition and polymerization adhesives, a byproduct, for example, water, develops during curing. Apart from the application of heat, adequate pressurizing of the adherends is required (see autoclave). 

In general, thermosets (crosslinked polymers below their Tg) are used as polymeric adhesives. The mechanical properties of an adhesive joint, therefore, depend strongly on the mechanical properties of thermoset resins, which will be discussed in Chapter 11. 

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