Adhesives hydrolytic stability

Rider and Amott were able to produce notable improvements in bond durability in comparison with simple abrasion pre-treatments. In some cases, the pretreatment improved joint durability to the level observed with the phosphoric acid anodizing process. The development of aluminum platelet structure in the outer film region combined with the hydrolytic stability of adhesive bonds made to the epoxy silane appear to be critical in developing the bond durability observed. XPS was particularly useful in determining the composition of fracture surfaces after failure as a function of boiling-water treatment time. A key feature of the treatment is that the adherend surface prepared in the boiling water be treated by the silane solution directly afterwards. Given the adherend is still wet before immersion in silane solution, the potential for atmospheric contamination is avoided. Rider and Amott have previously shown that such exposure is detrimental to bond durability. 

In order to address these issues, a brief discussion of thermal, oxidative, and hydrolytic stability of urethanes will be offered, so as to aid the adhesion scientist in designing a urethane adhesive with the desired durability. 

As previously mentioned, some urethanes can biodegrade easily by hydrolysis, while others are very resistant to hydrolysis. The purpose of this section is to provide some guidelines to aid the scientist in designing the desired hydrolytic stability of the urethane adhesive. For hydrolysis of a urethane to occur, water must diffuse into the bulk polymer, followed by hydrolysis of the weak link within the urethane adhesive. The two most common sites of attack are the urethane soft segment (polyol) and/or the urethane linkages. Urethanes made from PPG polyols, PTMEG, and poly(butadiene) polyols all have a backbone inherently resistant to hydrolysis. They are usually the first choice for adhesives that will be exposed to moisture. Polyester polyols and polycarbonates may be prone to hydrolytic attack, but this problem can be controlled to some degree by the proper choice of polyol. 

Vinyl substituted cyclic hemlamidals 2 and their Interconvertible acetal precursors (eg. acrylamldo-butyraldehyde dimethyl acetal 1) were Incorporated as latent crosslinkers and substrate reactive functional comonomers In solution and emulsion copolymers. Some use and applications data for copolymers prepared with these new monomers are presented. They show low energy cure potential, long shelf life and high catalyzed pot stability In solvent and aqueous media, good substrate reactivity and adhesion, and good product water and solvent resistance. They lack volatile or extractable aldehyde (eg. formaldehyde) components and show enhanced reactivity and hydrolytic stability with amines and diol functional substrates. 

Polyt.V vinyl 2 pyrrolidinnne) (PVP) is undoubtedly the best-characterized and most widely studied (V-vinyl polymer. It derives its commercial success from its biological compatibility, low toxicity, film-forming and adhesive characteristics, unusual complexing ability, relatively inert behavior toward salts and acids, and thermal and hydrolytic stability. 

The toughness of an epoxy-nitrile adhesive is nearly equivalent to that of an epoxynylon adhesive. However, the epoxy-nitrile system has much better hydrolytic stability. Also, the low-temperature properties of an epoxy-nitrile adhesive are superior to those of epoxy-nylon adhesive. Table 7.3 illustrates the effect of nitrile addition on tensile shear and peel strength. 

The rate of reversion, or hydrolytic instability, depends on the chemical structure of the base polymer, its degree of crosslinking, and the permeability of the adhesive or sealant. Certain chemical linkages such as ester, urethane, amide, and urea can be hydrolyzed. The rate of attack is fastest for ester-based linkages. Ester linkages are present in certain types of polyurethanes and anhydride cured epoxies. Generally, amine cured epoxies offer better hydrolytic stability than anhydride cured types. 

Antipova and coworkers [193] increased the hydrolytic stability and adhesive strength of EPR by adding an epoxy resin, dicarboxylic acid anhydride and dialkyl tin dicarboxylate. The dialkyl tin dicarboxylate does not react with the double bonds in keto allyl groups but at radical sites, thus the replacement of labile hydrogen atoms by the two electronegative groups of organo tin ompounds results in an increase in EPR stability. 

The bonding of 2-cyanoacrylates to mineralized tissues In an aqueous environment appears to be superior to that of other adhesives. The higher homologues of 2-cyanoacrylates may be useful clinically where an intermediate-term bone adhesive Is desired. The isobutyl ester Is the most effective 2-cyanoacrylate for bonding dentin to acrylic resin. Pretreatment of the dentin with dilute acid, addition of 2-cyanoacrylate polymer to the adhesive or application of a protective coating to the bonded surface increases the hydrolytic stability of the bond. 

In BPDA-PDA, the only hydrolysis observed was of anhydride. If the samples are cured to at least 400 °C to minimize the residual anhydride, the bulk polymer should be quite stable to hydrolysis. In this material, then, the major remaining concerns about hydrolytic stability center on the polymer-substrate interfaces whether possible polymer-metal interactions could result in the formation of hydrolytically unstable products and whether or not agents used to promote adhesion will retain their efficacy under humid aging. 

Other Materials. The acrylic D, Hypalon E, and Butyl F caulking compounds were too weak and tacky for the tensile testing technqiues employed and thus were not evaluated in these tests. (Peel adhesion tests, a topic of a future paper, were employed in monitoring the hydrolytic stability of these soft caulking compounds). 

Specific material characteristics (e.g., moisture and/or hot-curing adhesive) curing time, stability in storage, flexibility at low temperatures, hydrolytic stability, aging resistance, adhesion properties... 

Uses PU intermediate for PU castings, adhesives and coatings Features Offers exc. hydrolytic stability and solv. resist. gives harder coatings with better abrasion resist, and higher gloss Properties Gardner 2 liq. m.w. 800 dens. 9.2 Ib/gal vise. 7000 cps m.p. < 20 C acid no. 0.5 hyd. no. 140 Lexorez 5901-300 [Inolex]... 

Features High reactivity hydrophobic low glass transition temp. low color high clarity hydrolytic stability low temp, flexibility low moisture permeability resist, to aq. acids, bases exc. adhesion elec, insulation props. 

Uses Soft segment in formation of elastomers such as thermoplastic urethanes, polyether esters, polyether amides, coatings, adhesives and sealants, casting resins, and urethane foams Features Produces elastomeric end-prods, with hydrolytic stability, resist. to microbial attack, low temp, flexibility and elasticity Properties APHA 40 max. wax-like solid sol. in most org. solvs. barely sol. in water m.w. 650 sp.gr. 0.977 (40 C) acid no. 0.05 hyd. no. 166.2-179.5 flash pt. 215 C 0.025% water Storage Hygroscopic protect from moisture and air dry nitrogen blanket should be applied to open containers before resealing Polythix M [Poly-Resyn]... 

Chem. Descrip. Dimer acid-based polyester polyol Uses Building block for high-performance PU elastomers, coatings, adhesives modifier (increases flexibility, impact resist., toughness, hydrolytic stability) for industrial coatings (automotive, coil, textile, leather, wood lacquers)... 

Uses Urethane for textiles, artificial leather, furniture, flooring, industrial primers and coatings, and masonry sealants Features Exc. adhesion to plastics, metal, and wood produces coatings with exc. resist, to abrasion, UV and hydrolytic stability low VOC Properties Translucent disp. colloidal particle size dens. 8.98 Ib/gal vise. 200 cps flash pt. (PMCC) > 100 C pH 7-9 surf. tens. 49 dynes/ cm VOC 151.41 g/l Film props. tens. str. 6500 psi tens, elong. 450% (ultimate) anionic 40% solids Witcobond W-240 [Uniroyal]... 

Thus, minimizing the adhesive-substrate interphase tension is a necessary condition for obtaining both strong and liquid-resistant adhesive-bonded joints. But it is not necessarily sufficient, because the strength and the water resistance can be determined by various factors, such as internal stresses, low hydrolytic stability, etc. 

Properties M.w. 354.59 dens. 0.957 b.p. 119 C flash pt. 235 F ref. index 1.4110 Toxicology Toxic by inh., ing., skin contact severe eye irritant TSCA listed HMIS Health 3, Flammability 1, Reactivity 1 Storage Store under nitrogen Uses Adhesion promoter crosslinker additive to silane coupling agent formulations to enhance hydrolytic stability Manuf./Distrib. ABCR http //www.abcr.de-,... 

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