Polyamide hardeners

One can rationalize a need for small rubber inclusions in some of the newer approaches to waterborne and high solids epoxy coating systems. Water-thinned epoxy coating compositions are described (48) where the two-component system consists of a nitrile rubber modified epoxy resin in the epoxide component and a styrene/ butadiene/methylmethacrylate latex modifier for an emulsion-based polyamide hardener component. Showing improved adhesion, impact and water resistance, the paint has good wetting characteristics and can be formulated to a high solids content at low viscosity. 

Water-based epoxy primers are ideal for damp porous substrates, as such primers will penetrate to an adequate depth to ensure good adhesion and produce a sound surface for bonding. Emulsifiable resins and hardeners are available, and the better systems deactivate the emulsifier system during cure to ensure that the cured system is not unduly water sensitive (Section VI.A). Solventless epoxy primers are used for bonding new concrete to existing concrete. Polyamide hardeners are preferred because of their ability to cure satisfactorily in the presence of water. Accelerators and diluents may be added, but fillers are generally omitted. The primer is applied to the existing concrete, and the fresh concrete cast before the resin has set (Section VI.B). 

Perhaps, the earlier materials found to have a useful capacity for adhesive bonding underwater depended upon the use of a stoichiometric excess of water-scavenging polyamide hardener in an epoxide-based adhesive. This approach can lead to the production of effective joints in the short term, but formulations of this type, which are hydrophilic in the uncured state, are also likely to absorb significant amounts of water in the cured condition. It is a widely accepted view that the extent of joint weakening in susceptible joints, quite apart from the consequences of plasticization, is a function of the water-uptake characteristics of the adhesive (see Glass transition temperature). The consequence is therefore likely to be that such joints will show poor durability in the presence of water, when rapid uptake of water may lead to equally rapid degradation of both cohesive and interfacial properties (see Durability fundamentals). 

Fig. 6. Stress-strain curves of Epikote 628 hardened by (a) K61 and (b) polyamide hardener at 77 K before and after irradiation. 1 - preirradiation 2 - 30 h irradiation at 5 K 3 - 8 h irradiation at 5 K and warm-up to R.T.

Some products may cause allergies or dermatitis, such as cement, epoxy resins and polyamide hardeners, etc. The safety data sheets also warn about these risks. 

With the epoxide resins the hardness and flexibility of the cured mass depends upon the chemical structure of the hardener used. A number of different hardeners are available giving not only altered physical properties but also setting times from a few minutes to several hours. When polyamide hardeners are mixed with epoxide resins the proportions may be varied either side of the 50/50 level less hardener making the set resih more rigid, while more hardener produces a more flexible product. In this sense the word hardener would appear not to be a good descriptive choice. 

The two-part epoxy adhesive, readily available in hardware stores or other consumer outlets, comes in two tubes. One tube contains the epoxy resin, the other contains an amine hardener. Common diamine room temperature epoxy curing agents are materials such as the polyamides, available under the trade name Versamid. These polyamides are the reaction products of dimer acids and aUphatic diamines such as diethylenetriamine [111-40-0] ... 

Polymers. AH nitro alcohols are sources of formaldehyde for cross-linking in polymers of urea, melamine, phenols, resorcinol, etc (see Amino RESINS AND PLASTICS). Nitrodiols and 2-hydroxymethyl-2-nitro-l,3-propanediol can be used as polyols to form polyester or polyurethane products (see Polyesters Urethane polymers). 2-Methyl-2-nitro-l-propanol is used in tires to promote the adhesion of mbber to tire cord (qv). Nitro alcohols are used as hardening agents in photographic processes, and 2-hydroxymethyl-2-nitro-l,3-propanediol is a cross-linking agent for starch adhesives, polyamides, urea resins, or wool, and in tanning operations (17—25). Wrinkle-resistant fabric with reduced free formaldehyde content is obtained by treatment with... 

Other. 2-Nitro-1-butanol is an excellent solvent for many polyamide resins, cellulose acetate butyrate, and ethylceUulose. It can be utilized in paint removers for epoxy-based coatings. 2-Hydroxymethyl-2-nitro-l,3-propanediol is usebil for control of odors in chemical toilets. Its slow release of formaldehyde ensures prolonged action to control odor, and there is no reodorant problem which sometimes is associated with the use of free formaldehyde. 2-Hydroxymethyl-2-nitro-l,3-propanediol solutions are effective preservative and embalming fluids. The slow Uberation of formaldehyde permits thorough penetration of the tissues before hardening. 

Molded polyamide surfaces can be hardened by grafting with Ai,Ai-diallylacrylamide [3085-68-5] monomer under exposure to electron beam (159). AijAZ-DiaHyltartardiamide [58477-85-3] is a cross-linking agent for acrylamide reversible gels in electrophoresis. Such gels can be dissolved by a dilute periodic acid solution in order to recover protein fractions. 

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. 

For solvent-based ambient cure systems polyamides are often the hardeners of choice. For heat-cured systems, anhydrides are used to provide higher heat-resistance systems but at the expense of flexibiHty. 

For the high temperature systems, dicyandiamide and aromatic-amine hardeners are frequendy used. For room temperature systems, polyamide aminoamide, and aliphatic-amine hardeners are preferred. 

P.B.15 1 is also applied in polystyrene, polyamide, polycarbonate (in which it is heat stable up to 340°C), PUR foam materials, and cast resins. It should be noted, however, that the hardening of cast resins which are based on unsaturated polyesters is usually much retarded. 

P.B.15 3, like stabilized a-Copper Phthalocyanine Blue, markedly affects the hardening of unsaturated polyester cast resins. The list of applications also includes PUR foam materials, office articles, such as colored pencils, wax crayons, and water colors, as well as spin dyeing of polypropylene, polyacrylonitrile, secondary acetate, polyamide, polyester, and viscose. Used in polyester spin dyeing, P.B.15 3 satisfies the thermal requirements of the condensation process (Sec. 1.8.3.8). 1/3 and 1/25 SD samples equal step 7-8 on the Blue Scale for lightfastness. Textile fastnesses, such as stability to wet and dry crocking are perfect. 

Epoxy coatings. A high solids two-component epoxy coating was prepared (Ciba Geigy Araldiate 6010 epoxy/Polyamide 840 hardener) and spray-applied to CRS and aluminum (Table 8). The coating was cured at 25°C and 50% relative humidity for 7 days. 

Thermoplastic A resin or plastic compound that can be repeatedly softened by heating and hardened by cooling. Examples of thermoplastics are acetal, acrylic, chlorinated polyether, fluorocarbons, polyamides (nylons), polycarbonate, polyethylene, polypropylene, polystyrene, some types of polyurethanes, and vinyl resins. 

The interesting molecular mass range for technical applications lies between a Mr value of 200,000 to 400,000 for the thermoplastic polyvinyl plastics and between 15,000 and 25,000 for the polyamides. For polyesters which are used as precursors for hardened crosslinked plastics, the optimum molecular mass lies around 2000 to 4000. 

Samples of plasticised PVC coatings backed with a thin polyamide fibre cloth used for arm and head rests of trains were analysed after both normal use in service and artificial ageing at 100 C. Two parameters were studied the effects of temperature inside the train and the influence of the polyurethane foam inside the rests. Plasticiser loss due to migration during ageing led to hardening of the... 

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