Adhesives condensation type

Acrylic adhesives cure by addition polymerization reactions. These chain reactions are initiated by the formation of free radicals that result in the adhesive curing by way of a very rapid polymer chain growth. This cure chemistry is significantly more rapid than a typical cure curve (i.e., condensation type) found in epoxy and urethane adhesives. A comparison of the cure profile of condensation (epoxy and urethane) versus addition... 

The two-part sihcone adhesive/sealants do not require moisture to cure and produce a superior deep-section cure. Two types are available addition-cure and condensation-cure. Addition of curing produces no by-products, can be heat-accelerated, produces negligible shrinkage, and provides the best high-temperature resistance of all silicone adhesives. Condensation-cure silicones are not easily inhibited and can be used on a greater variety of materials. ... 

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. 

Table II. Condensation-Type Adhesives and Prepreg Polymers for High-Temperature Applications...

Addition The first stage of curing, carried out at 200 C, is a condensation type. At the end of this the adhesive becomes a thermoplastic. A higher pressure and temperature stage (-290°C) is then used to consolidate the bondline and finalise the cure. These adhesives have a slightly lower oxidation resistance than the condensation types, which limits their service temperature to 260°C. 

TriaUyl Gyanurate Gure of Preformed Polymers. TAC and TAIC are often used in smaU amounts with vinyl-type and condensation polymers for cured plastics, mbber and adhesive products of high strength, and heat and solvent resistance. In some cases, chemical stabUity is also... 

Polyamide Resins. Another class of polyamide resins, in addition to the Hquid resins used as epoxy hardeners, are the thermoplastic type, prepared generaHy by the condensation reaction of polyamines with polybasic fatty acids. These resins find use in certain hot-melt adhesives, coatings, and inks. Diamines, typicaHy EDA (233), are the principal amine reactant however, tri- and tetramines are sometimes used at low levels to achieve specific performance. 

More recently, a modification of the system described by Kreibich has been used extensively in industry with good success. Part A of the adhesive is again a standard phenol-resorcinol-formaldehyde (PRF) cold-setting adhesive, with powder hardener added at its standard pH. Part B can be either the same PRF adhesive with no hardener and the pH adjusted to 12, or a 50 to 55% tannin extract solution at a pH of 12-13, provided that the tannin is of the condensed or flavonoid type, such as mimosa, quebracho, or pine bark extract, with no hardener [118,135-137], The results obtained with these two systems are good and the resin not only has all the advantages desired but also the use of vegetable tannins and the halving of the resorcinol content makes the system considerably cheaper [118,135-137]. 

The 6th material Is a condensation-cure product which has been previously used for medical Implant protection (I). As verified by lap shear tests, (described below), the first 3 elastomers provide minimal adhesion In the absence of a surface primer. The last 3 are self-prlmlng materials. To permit visual examination, we tried to select clear materials. All of the elastomers are clear except for types 5 and 6. 

The combined effect of attraction and repulsion forces has been treated by many investigators in terms borrowed from theories of colloidal stability (Weiss, 1972). These theories treat the adhesion of colloidal particles by taking into account three types of forces (a) electrostatic repulsion force (Hogg, Healy Fuerstenau, 1966) (b) London-Van der Waals molecular attraction force (Hamaker, 1937) (c) gravity force. The electrostatic repulsion force is due to the negative charges that exist on the cell membrane and on the deposition surface because of the development of electrostatic double layers when they are in contact with a solution. The London attraction force is due to the time distribution of the movement of electrons in each molecule and, therefore, it exists between each pair of molecules and consequently between each pair of particles. For example, this force is responsible, among other phenomena, for the condensation of vapors to liquids. 

D 5686 Standard Specification for Fiberglass (Glass Fiber Reinforced Thermosetting Resin) Pipe and Pipe Fittings, Adhesive Bonded Joint Type Epoxy Resin, for Condensate Return Lines... 

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