Water-resistant bonds

Oxane bonds between silane coupling agents and glass or metal oxides are rather easily hydrolyzed. For example, the Al-O-Si bond hydrolyzes rapidly in water, and yet very water resistant bonds between polymers and aluminum can be formed through silane primers. 

I once mentioned in a lecture that acid-base properties across the interface were not important in developing water resistant bonds to metal surfaces and cited the data of Table 7 [17]. Professor Fowkes was present and commented that there are numerous examples where acid-base reactions across the interface... 

Although not normally measured and not a requirement of an industry standard, the high wood failure values of the end-joints obtained with these adhesives are further evidence of water-resistant bonds. It was difficult to discern differ-... 

Conversion of the Microbially Produced Preadhesive to an Adhesive Protein. The polyphenolic protein purified from yeast adheres to a wide variety of surfaces including glass and plastic. The adherence probably results from the presence of many polar residues capable of hydrogen bonding and lysine residues that can form ionic interactions. However, this protein does not generate water-resistant bonds to surfaces nor does it have cohesive strength. For those purposes, it is necessary to convert at least a portion of the tyrosine residues to dopa and permit crosslink formation to occur after surface adhesion is achieved. That is, it is necessary to mimic the natural mussel process in which the dopa form of the polyphenolic protein is applied and then rapidly... 

A second type of urethane adhesive is currently being introduced to the U.S. construction industry. The adhesive was originally developed in Japan. The system is two component. The isocyanate component is a modified polymeric MDI. The cross-linkable component contains water with water-soluble or water-emulsifiable resins. The adhesive produces strong, water-resistant bonds and has shown promise as a possible lower cost substitute for resorcinol formaldehyde resins in the adhesion of laminated beams. The product is now being used in Japan to bond wood and various other porous substrates at the rate of about 10 million pounds per year. The first U.S. application of the product has been the bonding of wood doors. The opportunities for products of this type should be excellent in view of the ever-increasing governmental pressures on solvents. 

Cellulose acetate and cellulose acetate butyrate are water-clear and more heat-resistant, but less wata"-resistant, than cellulose nitrate. Cellulose acetate butyrate has better heat and water resistance than cellulose acetate and is compatible with a wide range of plasticizers. Cellulose nitrate is tough, develops strength rapidly, is water-resistant, bonds to many surfaces, and discolors in sunlight. The dried adhesive (nitrocellulose) is highly flammable. ... 

Requirements for adhesion of organic polymers to mineral surfaces in the presence of silane coupling agents have been well defined [5]. Water-resistant bonds to most mineral surfaces will be obtained if two requirements are met ... 

Simple addition of silanes to a rubbery polymer latex cannot impart water-resistant bonds to a mineral unless the silane deposits a resinous or tacky layer at the interface. A silane-modified resin or plasticizer will be effective if it can be retained as a separate phase in the emulsion and deposited as a primer layer on the mineral. 

A product, XZ8-5080, comprising 2% Z-6020 in Dow Latex 209 is recommended as a general instant primer for plaster. Wet plaster applied to virtually any surface primed with 2-5% dispersion of XZ8-5080 solids will develop a strong water-resistant bond. The primer may also be useful in adhesion of thermoplastic rubbers to mineral surfaces. 

Tough, develops strength rapidly, water-resistant bonds to many surfaces discolors in sunlight dried adhesive is flammable... 

Plate 20 A general view of a Grecon laminating machine which is used to bond resin-impregnated paper foils to chipboard prior to its subsequent use in furniture manufacture. An emulsion adhesive is applied to the board and dried with infra-red heaters. The foil to be bonded is pressed onto the board with heated rollers. The heat softens the dried adhesive and causes it to form a strong water-resistant bond on cooling. Production rates are high nine 12 x 6 (360 X 180 cm) boards are produced every minute. Material 083-1217 one-component emulsion adhesive manufactured by National Adhesives Resins Ltd. 

Adhesive, binder, and dcflocculant applications, which depend on the presence of polysilicatc ions, require silicates generally with ratios from 2.5 to 3.8. For ma.ximum adhesive strength the lower ratio types are used because they can be obtained with a higher concentration of solids. For more water resistant bond.s, the higher ratios arc needed. 

Polaqua 138 is a water-based primer specifically developed for water resistant bonds of polyethylene to aluminum foil by lamination or extrusion. It is applied by convmtitHial application methods (gravure, flexo, rod, roll, etc.) to the accepting substrate. The primer must be thoroughly and absolutely dry before introduction of the extrudate or lamination. Polaqua 138 should be applied as received using light application weights. 

The Si-O-Al bond, however, is not stable against water, but sets up an equilibrium in the presence of water to form A1 OH + Si OH. The silicone RTV mixtures invariably contain excess crosslinker which can form a resinous layer at the interface with aluminum. Thus, conditions are favorable (as described in the previous paper) for water-resistant bonds to aluminum, even though the bulk of the polymer is rubbery. The initial reaction of alkoxy silane with aluminum salts appears from this paper to be critical in setting up the initial adhesive contact. 

The greatest volume of wood adhesives for structural applications are thermosetting phenol-formaldehyde (PF) or urea-formaldehyde (UF) polymers or their derivatives. PFs are the commodity for exterior applications, while UFs are the commodity for interior applications. Because each composite product and the associated process may require a somewhat different resin, many variations of PF and UF resins are available. Isocyanate crosslinking resins are used to a lesser extent than PFs or UFs in manufactured board. Although these resins impart a durable, water resistant bond suitable for exterior application, the cost per pound of adhesive is greater than for PFs or UFs. 

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