Cross-linking epoxy

Because the heat distortion temperature of cured epoxy resins (qv) increases with the functionality of the curing agents, pyromellitic dianhydride is used to cross-link epoxy resins for elevated temperature service. The dianhydride may be added as a dispersion of micropulverized powder in liquid epoxy resin or as a glycol adduct (158). Such epoxies may be used as an insulating layer in printed circuit boards to improve heat resistance (159). Other uses include inhibition of corrosion (160,161), hot melt traffic paints (162), azo pigments (163), adhesives (164), and photoresist compounds (165). 

The calculated equilibrium network moduli of elasticity and experimental moduli measured in the rubbery state10,34) of different epoxy-amine networks show quantitative agreement. This means that the real structural nonuniformity of cross-linked epoxy-aromatic amine polymers exists only at the level of statistical deviations of network structure from the ideal one. A comparison of Ecalc and E p is shown in Fig. 4. 

Glassy polymers with highercohesiveness, like polycarbonate and cross-linked epoxies, preferentially exhibit shear yielding [7], and some materials, such as rubber-modified polypropylene, can either craze or shear yield, depending on the deformation conditions [8]. Application of a stress imparts energy to a body which... 

Cross-linked epoxy resin (thermoset of bisphenol A diglycidyl ether). 

Highly cross-linked epoxy resins combine high strength stiffness thermal, chemical, and environmental stability adhesion low weight processability excellent creep resistance and favorable economics. These resins are widely applied as coatings, casting resins, structural adhesives, and matrix resins of advanced composite materials. The broad spectrum of applications ranges from the automotive and aerospace industries to corrosion protection and microelectronics. 

The inhibitor should be capable of being transported through a cross-linked epoxy resin matrix. 

At high extents of cure, the ACp per unit mass may become vanishingly small and undetectable by scanning calorimetry. This finding largely accounts for the unusually effective plasticization of cross-linked epoxies by water. 

Other multiblock copolymers contain slloxanes as blocks, and others are based on cross-linked epoxy resin systems (35). 

In contrast to tertiary amine hardeners, which, as shown, cross-link epoxide resins by a catalytic mechanism, polyfunctional primary and secondary amines act as reactive hardeners and cross-link epoxy resins by bridging across epoxy molecules. 

Solvents used for paint removal are able to dissolve or considerably swell physically drying binders (e.g., vinyl chloride copolymers, cellulose nitrate, polyacrylates) and chemically cross-linked coatings (e.g., oil-based paints, dried alkyd resins, cross-linked polyester-melamine resins, cross-linked epoxy and isocyanate coatings) [14.237]. A combination of dichloromethane with low-boiling ketones or esters is particularly suitable. Small amounts of high-boiling solvents with a low volatility (e.g., tetrahydronaphthalene, solvent naphtha, methyl benzyl alcohol, or benzyl alcohol) are added to these mixtures to retard evaporation and increase the solvency. Modern paint removers do not contain chlorinated hydrocarbons, they are formulated on the basis of high boilers (e.g., dimethylformamide, dimethyl sulfoxide, propylene carbonate, and yV-methylpyrrolidone) in combination with alcohols and aromatics, or consist of aqueous, frequently alkaline or acidic systems. 

Epoxy resins form a durable protective coating only when polymerized with amine, polyamide, or esterified fatty acids. Coal-tar epoxies are modified with coal-tar fiUer to improve moisture resistance. Coatings highly resistant to solvents, acids, and alkahs are based on phenoHc cross-linked epoxies. These coatings are used to protect process equipment. When the phenolformaldehyde constituent of phenol is used to cross-hnk epoxy resin instead of amine, the coating has improved resistivity to alkahs. 

Vak Vakil, U. M., Martin, G. C. Yield and fracture behaviour of cross-linked epoxies. J. Mater. Sci. 28 (1993) 4442 50. 

To be suitable for powder coatings, resins should melt for pigmentation at temperatures well below that required for cross-linking, should be brittle and amenable to dry milling when cold, should be stable in the presence of cross-linker when stored at room temperature and, at stoving temperatures, should melt and fall rapidly in viscosity before cross-linking. Epoxy resins admirably meet these requirements. 

Anhydrides cross-link epoxy resins by reacting first with the hydroxyl groups. Carboxyl groups are produced in the process and these then react with the epoxy ring. Stoving is at 180-200° C. 

Experimental restoration of inserted relaxation operators and testing of their prediction ability were made for cross-linked epoxy amine polymers from diglycide ether of bisphenol-A (DGEBA), which was solidillcated by stoichiometric amounts of 1-ami-nohexane (AH) and hexamethylenediamine (HMDA) in variation of their molar ratio from 0 to 2 with pitch 0.5. 

Information about the quantity of cross-linked polymers strain properties in their one or another physical state with known assessment of mechanical tensions is nesessary, for choice of the optimal cross-linked polymer matrix and high strength Dberglass products. In the network of search solutions of this problem was developed and conDrmed by experiments with cross-linked epoxy amine polymers, a new mathematical account of nanofragment cross-linked polymers pliability [1]. A pur-... 

Journal of Polymer Science Polymer Physics Edition 32, No.3, Feb. 1994, p.395 08 TOUGHENING OF A HIGHLY CROSS-LINKED EPOXY RESIN BY REACTIVE BLENDING WITH BISPHENOL A POLYCARBONATE. I. 

Cross-linked epoxy resins are combustible and their burning is self-supporting. They require mainly reactive flame-retardants, such as tetrachloro- or tetrabromobisphenol-A and various halogenated epoxides. Even the cross-linking agent may be flame-retardant, as in the case of chlorendic anhydride, tetrabromo- or tetrachloro-phthalic anhydride, or possibly phosphorus compounds. Halogenated agents can be supplemented with antimony trioxide. 

The time-dependent component of polymer response is of extreme importance to the use of structural adhesives which are required to sustain either permanent or transient loads. At temperatures well below the adhesive s Ig, overloading is far more likely to lead to stress rupture than to creep(5). However, at temperatures close to or at Tg, some creep of loaded joints is to be expected. Recalling Chapter 2, highly cross-linked epoxies which are cured at elevated temperature possess the best resistance to creep. 

Many different aliphatic and aromatic polyamines are available for cross-linking epoxy resins. Some of these are ethylenediamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, and many others. Among the aromatic polyamine are / -phenylene diamine, /n-phenylene diamine, 4,4 -diaminodiphenyl-methane, and diaminodiphenylsulfone. 

Many cyclic acid anhydrides are used industrially for cross-linking epoxy resins. These are mono and polyanhydrides. Following are some typical commercially used anhydrides ... 

---