Modified adhesives

Elastomeric Modified Adhesives. The major characteristic of the resins discussed above is that after cure, or after polymerization, they are extremely brittie. Thus, the utility of unmodified common resins as stmctural adhesives would be very limited. Eor highly cross-linked resin systems to be usehil stmctural adhesives, they have to be modified to ensure fracture resistance. Modification can be effected by the addition of an elastomer which is soluble within the cross-linked resin. Modification of a cross-linked resin in this fashion generally decreases the glass-transition temperature but increases the resin dexibiUty, and thus increases the fracture resistance of the cured adhesive. Recendy, stmctural adhesives have been modified by elastomers which are soluble within the uncured stmctural adhesive, but then phase separate during the cure to form a two-phase system. The matrix properties are mosdy retained the glass-transition temperature is only moderately affected by the presence of the elastomer, yet the fracture resistance is substantially improved. 

The type of chloroprene polymers used is perhaps best illustrated by the variety of special products, designed for adhesive appHcations, that Du Pont has developed. These are described ia Table 8. Standard polymer grades are also often used, especially to modify adhesive properties and to reduce cost. 

Bemabeu-Gonzalvez A., Pastor-Bias M.M., and Martm-Martmez J.M., 1998, Modified adhesion of rubber materials by surface migration of wax and zinc stearate, in Proceedings of the World Polymer Congress, 37th International Symposium on Macromolecules MACRO 98, Gold Coast, Australia, 705. Romero-Sanchez M.D., Pastor-Bias M.M., and Martm-Martmez J.M., 2001, Adhesion improvement of SBR rubber by treatment with trichloroisocyanuric acid solutions in different esters, Int. J. Adhes. Adhes., 21, 325-337. 

Moisture acts as a debonding agent through one of or a combination of the following mechanisms 1) attack of the metallic surface to form a weak, hydrated oxide interface, 2) moisture assisted chemical bond breakdown, or 3) attack of the adhesive. (2 ) A primary drawback to good durability of metal/adhesive bonds in wet environments is the ever present substrate surface oxide. Under normal circumstances, the oxide layer can be altered, but not entirely removed. Since both metal oxides and water are relatively polar, water will preferentially adsorb onto the oxide surface, and so create a weak boundary layer at the adhesive/metal interface. For the purposes of this work, the detrimental effects of moisture upon the adhesive itself will be neglected. The nitrile rubber modified adhesive used here contains few hydrolyzable ester linkages and therefore will be considered to remain essentially stable. 

Reacts by accelerating or retarding adhesive cure Properties of modified adhesive affect bond strength ... 

Special attention was granted to amphiphilic graft copolymers in which hydrophilic grafts are attached to a hydrophobic backbone (or vice versa). Such materials can be used as emulsifiers, compatibilizers, surface modifiers, adhesives, etc. and they may play a role in many industrial developments. 

Some of them (adhesives, coatings, foam plastics, and resins) use Mannich bases or their derivatives as structural components of the material, whereas all the listed branehes are concerned with the use of important additives (mainly antioxidants) or auxiliaries such as basic catalysts and accelerators. Specific functions are performed, for instance, by agents improving the adhesion of photopolymerizable paints and by accelerator-modified adhesion promoters for mbber-to-wirc adhesion." ... 

An example of an application of these special adhesives is their contribution to the construction of liquid gas tanks and tanker gas transport. Worldwide transport of this fuel would not be feasible from an ecological point of view without this adhesive technology, since the construction of large-scale tankers was first made possible by development and use of suitable insulation and bonding applications. The adhesives had to yield high-strength bonds, for instance at temperatures down to —160°C. This specification was met by use of these specially modified adhesives with an interpolation of PUR and silicone adhesives (MS adhesives), see details in Sect. 3.6. 

Additives. These specialty materials can be flow modifiers, adhesion promoters, stabilizers, plasticizers, etc. 

The permeability test samples were five-layer polyolefin plastic cylindrical containers with EVOH as the barrier material, modified adhesive layers on either side of the EVOH, and polyolefin layers as outer protection. The EVOH used was Evalca s EPF which has 32 mole percent ethylene. The layer thicknesses In the container sidewalls were 14/1/2/1/14 mils. 

A monolayer of adsorbates sandwiched between interfaces of solids can markedly modify adhesive and tribological properties. These monolayers are being investigated increasingly on the molecular level. 

Example 13.8 Urea-formaldehyde (UF) adhesive used in bonded wood products was modified by oopolymerizing 10 mol% urea derivative of dodecanediamine (DDDU). The fracture energies of wood joints made with the unmodified and DDDU-modified adhesives were found to be 130 and 281 J/m, respectively. Explain the enhanced fracture energy of the wood joint bonded with the modified adhesive. 

The test methods presently used to evaluate the adhesion of pressure-sensitive adhesives to release liners are modified adhesion tests, such as the 180° or 90° peel test, with the liner adhered to a test panel, or a T-peel test, where the sample is freely suspended while the tape is peeled at a controlled rate from the release liner. The values obtained by the latter method are alfected considerably by the stiffness of the liner, which alters the angle of peel. 

Nielson, PO., Properties of Epoxy Resins, Hardeners and Modifiers, Adhesives Age, Vol. 42, 1982. 

MAJOR APPLICATIONS Asphalt modifiers, adhesives, sealants, coatings, footwear, polymer modifers. 

Uses Corrosion inhibitor, dispersant, dewatering agent, emulsifier, rheology modifier, adhesion promoter, tiocculant for oil fields, metalworking, paints, inks, corrosion inhibitors, acid cleaning... 

Uses Modifier, adhesion promoter for industrial and architectural coatings... 

Chem. Descrip. Formaldehyde/toluenesulfonamide polymer Uses Modifier, adhesion promoter for coatings, lacquers, printing inks, adhesives, oil and gasoline resist, coatings Features Compat. with alkyds, acrylics, urethanes, nitrocellulose and vinyls... 

Chem. Descrip. Ethylene/vinyl laurate/vinyl chloride terpolymer with polyvinyl alcohol stabilizer and mineral filler antiblocking agent Uses Binder, water repellent in conjunction with inorg. binders in plasters. Joint mortars, troweling compds., tile and construction adhesives, adhesives for external insulation and finishing systems sole binder in plasters, paints, adhesives modifier, adhesion promoter, plasticizer, impact resist, aid for gypsum and anhydrite Features Imparts hydrophobic props. enhances adhesion, flex, str., plasticity, abrasion resist., and workability contains no soivs., plasticizers, of film-forming aids... 

Uses Corrosion inhibition, dispersants, dewatering, emuisification rhe-oiogy modifiers, adhesion promoters for oii fieids, metai working, paints, inks, anticorrosives, acid cieaning. fioccuiation Trade Names imidazoiine 18 NH... 

Uses Modifier, adhesion promoter for resins in adhesives and coatings extender in polyamide resins film-former in cosmetics adjuvant for SAN copolymer food pkg. in cellophane for food pkg. in side seam cements for food-contact containers in paper/paperboard in contact with aq./fatty foods... 

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