Epoxy resin Hardener systems

Figure 3.35. A correlation plot of rheological gel time (from crossover of G and G") and the maximum in chemiluminescence (CL) intensity over the temperature range 140-200 °C for the following epoxy-resin/hardener systems o, Tactix 742/27% DDS A, Shell 1153/22% DDS and Shell 1071/27% DDS. Adapted from Kozielski et al. (1995).

Figure 3.50. The relationship between PCI score and percentage cure as determined by DSC for the epoxy-resin/hardener system DER 332/Jeffamine T-403 in the following mixing ratios o, 100/45 and X, 100/55. Aust et al. (1997). Copyright 1997 by Society for Applied Spectroscopy reproduced with permission of Society for Applied Spectroscopy.

When formulating a system for optimum abrasion resistance, both the epoxy/resin hardener binder system and the filler blends used appear to have an influence. The simulation of abrasive service loads on industrial floor toppings in a laboratory is not simple, and numerous wear test machines have been devised. Correlation between different wear test machines is not always good, although most... 

The products of the chemical degradation of PETP with triethylene tetramine and triethaneolamine can be used as epoxy resin hardeners, it is demonstrated. Products of PETP aminolysis with triethylene tetramine and aminoglycolysis with triethanolamine, were characterised using NMR and rheometric measurements. Characteristics of the crosslinking process for the system epoxy resin/ PETP/amine degradation product, and epoxy resin/TETA for comparison were investigated by DSC. Three classes of liquid epoxy resins based on bisphenol A, bisphenol F and epoxy novolak resins were used in the experiments. 16 refs. 

This is a simplification of the process occurring in a curing resin-hardener system and a detailed discussion may be found in Pascault et al (2002), Williams et al (1997) and Inoue (1995). The main parameter that it is important to control in the reactive phase separation is the diameter of the elastomer particle. This is because the toughness of the resulting network is controlled by the energy-absorbing mechanisms such as particle cavitation and rubber bridging of cracks. Also of importance is the limitation of the effect of the rubber dispersed phase on the critical properties of the cured epoxy resin such as the stiffness and Tg. This will be affected by the extent to which the rubber dissolves in the matrix-rich phase. 

The most widely used epoxy systems are those which are based on pure epoxy resins, hardened with a curing agent. Curing of epoxy resins containing two epoxy groups per molecule can be readily accomplished by the addition of primary polyamines, such as ethylene diamine, diethylene triamine, triethylene tetramine, tetra-ethylene pentamine, etc. Aliphatic polyamines produce cured resins with the greatest chemical resistance. However, these systems have inadequate durability, weather resistance and film-forming properties. They are sensitive to humidity, errors in addition rates are quite possible, and the catalysts are relatively toxic. 

Some low molecular weight chemicals, such as, the conventional epoxy resin hardener methyl tetrahydrophthalic anhydride that can stay as a remnant in the system, can cause immunologic contact urticaria . 

Diluents. These are generally incorporated to reduce the viseosity of the freshly mixed adhesive to offset the effect of the filler. This may be required to improve handling and spreading characteristics or to allow filler additions which tend to reduce cost. Other properties of the fresh and hardened adhesive can be affected by the use of diluents, for example pot life, flexibility and glass transition temperature. If the diluent is non-reactive, such as solvents which remain in the cured system, the net result is a deterioration of chemical and mechanical properties such as increased shrinkage and reduced adhesion. Reactive diluents containing epoxy compounds are capable of combining chemically with the resin/hardener system. 

The rate of cure is temperature dependent and many formulations stop curing altogether below a temperature of about 5 °C. If carefully formulated the change in volume between the uncured resin-hardener system and the fully cured polymer can be very low. This property, together with their relatively high strength and claimed resistance to moisture and chemical attack, forms the basis of the use of epoxy resins as structural adhesives. 

Of all the thermosetting plastics, epoxies are more widely used than any other plastic, in a variety of applications. There are resin/hardener systems (two-part) that cure at room temperature, as well as one-part systems that require extreme heat cures to develop optimum properties (e.g., 121°C and 177°C). Proper selection of various hardeners, resins, modifiers, and fillers allows the development of desired properties for a particular application. Because of the wide versatility and basic adhesive qualities, epoxies make excellent structural adhesives that can be engineered to widely different specifications. Essentially no shrinkage occurs during polymerization because epoxies are completely reactive producing no volatiles during cure. Epoxy adhesives can be formulated to meet a wide variety of bonding... 

Ethylenediamine is used in numerous industrial processes as a solvent for casein or albumin, as a stabilizer in rubber latex and as a textile lubricant. It can be found in epoxy-resin hardeners, cooling oils, fungicides, and waxes. Contact dermatitis from ethylenediamine is almost exclusively due to topical medicaments. Occupational contact dermatitis in epoxy-resin systems is rather infrequent. Ethylenediamine can cross react with triethylenetetramine and diethylenetriamine. Ethylenediamine was responsible for sensitization in pharmacists handling aminophylline suppositories, in nurses preparing and administering injectable theophylline, and in a laboratory technician in the manufacture of aminophylline tablets. 

Epoxy adhesives are thermosetting resins which solidify by polymerisations and, once set, will soften but not melt on heating. Two-part resin/hardener systems solidify on mixing (sometimes accelerated by heat), while one-part materials... 

Of all the thermosetting plastics, epoxies are more widely used than any other plastic, in a variety of applications. There are resin/hardener systems (two-part) that cure at room temperature, as well as one-part systems that require extreme heat cures to develop optimum properties (e.g., 121 °C and... 

The binder system of a plastic encapsulant consists of an epoxy resin, a hardener or curing agent, and an accelerating catalyst system. The conversion of epoxies from the Hquid (thermoplastic) state to tough, hard, thermoset soHds is accompHshed by the addition of chemically active compounds known as curing agents. Flame retardants (qv), usually in the form of halogens, are added to the epoxy resin backbone because epoxy resins are inherently flammable. 

In addition to electrical uses, epoxy casting resins are utilized in the manufacture of tools, ie, contact and match molds, stretch blocks, vacuum-forrning tools, and foundry patterns, as weU as bench tops and kitchen sinks. Systems consist of a gel-coat formulation designed to form a thin coating over the pattern which provides a perfect reproduction of the pattern detail. This is backed by a heavily filled epoxy system which also incorporates fiber reinforcements to give the tool its strength. For moderate temperature service, a Hquid bisphenol A epoxy resin with an aHphatic amine is used. For higher temperature service, a modified system based on an epoxy phenol novolak and an aromatic diamine hardener may be used. 

Conditions to be met in oven drying enamels depend also on the composition of the binder. Paint systems containing melamine-formaldehyde or urea-formaldehyde resins, for instance, harden by polycondensation with other resins, such as epoxy resins, short-oil alkyd or acrylic resins at elevated temperatures. Baking is carried out at temperatures between 100 and almost 200°C and may last from a few minutes to more than an horn. A general trend towards energy conservation has shifted public attention towards binders which require low baking temperatures. 

Materials Description. Three CIBA-GEIGY epoxy/hardener systems were studied Araldite 6010/906, Araldite 6010/HY 917 and Araldite 6010/972 with stoichiometries 100/80, 100/80 and 100/27, respectively. Araldite 6010 was a DGEBA epoxy resin. The hardeners 906, HY 917 and 972 were, respectively, methyl nadic anhydride (MNA), methyltetrahydro phthalic anhydride (MTPHA) and methylene dianiline (MDA). These systems were investigated previously for the matrix controlled fracture in composites (6-8). The curing cycles used can be found in (6). The ideal chemical structures of the systems are shown in Table I. Neat resins were thoroughly degassed and cast into 1.27 cm thick plates for preparation of test specimens. 

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