Bond Strength Modifiers

Some additives, or combinations of additives, have been disclosed as impact or heat shock resistance promoters for cyanoacrylates. For example, a variety of alkyl and aryl polycarboxylic acids and anhydrides have been described as impact resistance promoters. The property measured was impact strength on steel according to ASTM D-950. In this test, an improvement in adhesion will result in an improved impact strength. These formulations show little or no improvement over a control in tests for fracture toughness. In other words, these additives are adhesion promoters, not 

Adhesion promoter Typical range (%) in Adhesive Formulation Improvement of OLS strength on CRS (%) Reference 

A common feature of all of the adhesion promoters discussed here is the presence of one or more carboxylic acid groups, anhydrides, or phenolic hydroxyls. Presumably these groups complex with the metal surface during bonding and/or coreact with the cyanoacrylate during polymerization. Also, the improvement in adhesive performance can be attributed to improved adhesion, regardless of the manner in which that performance is measured. 

Internal plasticization has been attempted through the use of monomer mixtures. Probably the earliest recognition of and attempt to solve the brittleness problem appeared in a patent issued to Shearer and Coover. This patent described the use of mixtures of monomers, such as ethyl or methyl and cyclohexyl cyanoacrylates. No quantitative data were offered to support the contention that these monomer mixtures do, in fact, provide 

A variety of external plasticizers have also been suggested for cyanoacrylates. Among these are alkyl esters of aliphatic monocarboxylic acids such as cyanoacetates aliphatic dicarboxylic esters, such as malonates, adipates, and sebacates triaromatic phosphates such as tricresyl phosphate acyl triesters of glycerine dialkyl alkylphosphonates and alkyl phthalates. Joyner and Coover state that limiting the plasticizer concentration to less than 5% will not retard the cure speed, from 5 to 20% will retard the cure rate, and over 20% plasticizer concentration seriously slows the cure rate of the adhesive. 

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In addition to polyamide, lamination inks ordinarily contain modifiers such as polyketone resin, plasticizer, and wax to impart specific properties such as block resistance and increased bond strength. Because laminating inks are usually reverse-side printed and end-up sandwiched between films, gloss is not a primary requirement. Water-base laminating inks that will meet the U.S. EPA emission requirements and have the correct functional properties are currently under development. 

Bond strength can vary from a temporary bond (non-curing compound) to a substrate tearing bond (using phenolic-modified curing products). Solvent-borne CR adhesives can be formulated to have very short open times for fast production operations or to retain contact bond characteristics for up to 24 h. Heat and solvent reactivation can be used to re-impart tack to dried surfaces. 

The fluorine atom, by virtue of its electronegativity, size, and bond strength with carbon, can be used to create compounds with remarkable properties. Small molecules containing fluorine have many positive impacts on everyday life of which blood substitutes, pharmaceuticals, and surface modifiers are only a few examples. 

The production of moisture resistant particleboard by treatment with a maleic anhydride -glycerol mixture and using phenol formaldehyde as the matrix material has been investigated (Fujimoto etal., 1987). Boards prepared from modified wood showed considerable improvements in modulus of elasticity and internal bond strength when compared to control boards. Composites made from aspen fibres modified with SA, MA or acetic anhydride using phenol-formaldehyde (PF) or polypropylene as binder have also been studied (Clemons etal., 1992 Rowell etal., 1993b). The reaction of wood with MA was found to proceed at a slower rate than with SA. The volume increase due to modification... 

Hill and (letin (2000) modified the surfaces of wood veneers with methacrylic anhydride (Figure 6.6a) and formed lap joints using either styrene or methyl methacrylate in the presence of the free radical initiator azoisobutyronitrile. Significant improvements in bond strength were found when compared to unmodified wood. 

Figure 1.10 shows the relationship between bond strength and degree of covalence in cation-oxygen bonds for cations with 18, 36, and 54 electrons (note that in table 1.9 the parameters of equation 1.48 are identical for the three isoelectronic series). By combining equation 1.48 with a modified form of Donnay s (1969) equation ... 

Most latex-modified mortars and concretes have good adhesion to most substrates (tile, stone, brick, steel and aged concrete) compared to conventional mortar and concrete. In general, bond strength in tension and flexure increases with an increase in the polymer-cement ratio,... 

Cements that harden by the loss of solvent generally are to be avoided because the solvent can be lost only be diffusion thru the expl. Diffusion may be slow and the solvent may modify the properties of the expl. Two types of cement that have been used for this purpose are catalytic setting cements, like epoxy resins, and contact cements. Compatibility of the materials to be used should be checked. Compatibility of epoxy resins with most explosives depends upon the catalyst or hardener used (Ref 8). Data regarding bond strengths and other pertinent properties also have been compiled (Refs 5 6)... 

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