Additives toughened adhesives

Interleaving strips made from ductile short fibers, notably Kevlar fiber mat, and an adhesive (Browning and Schwartz, 1986) provide extra energy required during delamination crack propagation due to additional toughening mechanisms such as... 

According to Kinloch, the addition of 1-8 wt.% of nanosilica particles with an average diameter of around 20 nm to a typical rubber-toughened adhesive, based... 

Recent studies at NASA Langley Research Center have been directed towards the toughening of higher temperature thermoset addition polyimides (4,5). ATBN and silicone elastomers have been incorporated into an addition polyimide adhesive, LARC-13 (6,7), which is a candidate for bonding metals such as titanium and graphite/polyimide... 

Information on particular types of adhesive may be found in articles cited above and in the following entries Hot melt adhesives. Selection of adhesives. Silicone adhesives addition cure. Silicone adhesives condensation cure. Toughened adhesives. 

Unmodified Epoxide adhesives are versatile materials, but like many polymers below their Glass transition temperatures, they suffer from low resistance to impact and peel forces. In Toughened adhesives, some means of addressing such problems were discussed in general terms. This article considers the basis of toughening in epoxies, and related articles (cross-referenced herein) discuss the types of toughening additives employed. 

With the incorporation of the new surface-insensitive additives which allow rapid curing on acidic and porous substrates such as wood and paper, and the marketing of these versatile adhesives in the consumer sector, the number of applications where cyanoacrylates are used is limited only by the ingenuity of the user. The new toughened adhesives with improved heat and humidity resistance and dynamic performance are already encroaching into areas where epoxies were once the only choice. Versatility... 

Acryhc stmctural adhesives have been modified by elastomers in order to obtain a phase-separated, toughened system. A significant contribution in this technology has been made in which acryhc adhesives were modified by the addition of chlorosulfonated polyethylene to obtain a phase-separated stmctural adhesive (11). Such adhesives also contain methyl methacrylate, glacial methacrylic acid, and cross-linkers such as ethylene glycol dimethacrylate [97-90-5]. The polymerization initiation system, which includes cumene hydroperoxide, N,1S7-dimethyl- -toluidine, and saccharin, can be apphed to the adherend surface as a primer, or it can be formulated as the second part of a two-part adhesive. Modification of cyanoacrylates using elastomers has also been attempted copolymers of acrylonitrile, butadiene, and styrene ethylene copolymers with methylacrylate or copolymers of methacrylates with butadiene and styrene have been used. However, because of the extreme reactivity of the monomer, modification of cyanoacrylate adhesives is very difficult and material purity is essential in order to be able to modify the cyanoacrylate without causing premature reaction. 

Interestingly, this same effect has been observed for the addition of a rubber toughening agent to ethyl cyanoacrylate-based adhesives, as was reported previously. The rubber must contain enough latent acid functionality on the polymer backbone or in an additive to inhibit the thermally activated decomposition of the alkyl cyanoacrylate adhesive polymer. 

Adhesives formulated from tile 2-cyanoacrylic esters typically contain stabilizers and thickeners, and may also contain tougheners, colorants, and other special property-enhancing additives. 

Over the past several decades, significant advances have been made in developing epoxy-based adhesives having improved performance over these early adhesive systems. These improvements were made possible by (1) the incorporation of toughening additives into epoxy resin formulations and (2) the use of multifunctional epoxy resins primarily for high-temperature applications. These innovations are discussed in later chapters. 

Compared to the carboxylated nitrile elastomer additives, the use of thermoplastics has primarily been focused on the aerospace industry. On a cost per pound basis, the two-phase nitrile additives offer the best combination of property improvement without negative impact. The thermoplastic additives, however, may offer better high-temperature performance, but they are more difficult to formulate and to process as adhesives. As a result, the cost of these adhesives is generally much higher than that of other toughened epoxy mechanisms. 

The high-temperature resins described above provide the main elements in the adhesive formulator s recipe. However, there are also additives, fillers, etc., that can further enhance the thermal properties of more conventional epoxy adhesives. These additional components improve thermal resistance by providing oxidation resistance, toughening, and control of bond line stress. 

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