General-purpose polyamides

The important members of the polyamide family, also known as nylons, and outline methods of manufacture, are given below. 

Other polyamides have been developed, including polyamide 4.6 (Dutch State Mines) which, as expected, has a melting temperature higher than that of PA 6.6, and is intended for service at temperatures above the ceiling for PA 6.6. 

Polyamide MXD-6 is the product of condensing metaxylylene diamine with adipic acid. This polymer has proved to be an outstanding gas barrier for example, at 100% relative humidity, it has lower oxygen permeation than ethylene-vinyl alcohol copolymer (30% ethylene). Otherwise, it is similar to 

Proteins are based on amino-acid condensates, i.e. they are polyamides, but they differ from the simple polyamides listed above, consisting of many monomers in a sequence which is unique to a particular protein. 

Polyamides of higher solubility can be made by copolymerization, which restricts crystallization. The common polyamides PA 6.6 and PA 6 are frequently of low molecular weight the resulting low viscosity requires special precautions during processing. Extrusion is important for PA 11 and PA 12. Polymers must be scrupulously dry before processing, otherwise hydrolytic degradation occurs, with consequent deterioration in properties. 

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Stiffness, resistance to deformation under constant applied load (creep resistance), resistance to damage by cyclical loading (fatigue resistance), and excellent lubricity are mechanical properties for which acetal resins are perhaps best known and which have contributed significantly to their excellent commercial success. General-purpose acetal resins are substantially stiffer than general-purpose polyamides (nylon-6 or -6,6 types) when the latter have reached equilibrium water content. 

An all aromatic polyetherimide is made by Du Pont from reaction of pyromelUtic dianhydride and 4,4 -oxydianiline and is sold as Kapton. It possesses excellent thermal stabiUty, mechanical characteristics, and electrical properties, as indicated in Table 3. The high heat-deflection temperature of the resin limits its processibiUty. Kapton is available as general-purpose film and used in appHcations such as washers and gaskets. Often the resin is not used directly rather, the more tractable polyamide acid intermediate is appHed in solution to a surface and then is thermally imidi2ed as the solvent evaporates. 

As the author pointed out in the first edition of this book, the likelihood of discovering new important general purpose materials was remote but special purpose materials could be expected to continue to be introduced. To date this prediction has proved correct and the 1960s saw the introduction of the polysulphones, the PPO-type materials, aromatic polyesters and polyamides, the ionomers and so on. In the 1970s the new plastics were even more specialised in their uses. On the other hand in the related fields of rubbers and fibres important new materials appeared, such as the aramid fibres and the various thermoplastic rubbers. Indeed the division between rubbers and plastics became more difficult to draw, with rubbery materials being handled on standard thermoplastics-processing equipment. 

A number of photopolymer printing plates are already known. Their basic structures are to combine one of the general purpose resins such as cellulose (1), polyamide (2J, polyester, poly urethane (3j, polyvinyl alcohol (4), synthetic rubber (5) and the like with photopolymerizing vinyl monomer, photopolymerization initiator and so on. Any one of the plates of such structures can be used as a press plate, but they can not be used as an original plate for duplicate plate owing to their insufficient hardness, toughness and the similar negative properties. 

As a family of curing agents for epoxy resins, the amidoamines are lower in viscosity than the polyamides. They exhibit very good adhesive properties due to their chemical structure and easy penetration. Amidoamine cured epoxy adhesives have shown very good properties on concrete and other porous substrates. They cure extremely well under humid conditions. In fact amidoamine cured epoxy formulations have been used to cure underwater in certain applications. A typical general-purpose room temperature curing epoxy-amidoamine system is described in Table 11.7. This adhesive is used as a general-purpose metal-to-metal adhesive and body solder in the automotive industry. 

As with amidoamine and polyamide cured adhesives, epoxy resins cured with aliphatic amines exhibit tensile shear strength that is dependent on the type of filler and concentration. Table 11.10 shows the effect of filler loading on strength of a simple general-purpose, room temperature curing epoxy adhesive composed of liquid DGEBA epoxy mixed with 10 pph of a tertiary amine. 

When the epoxy adhesive cannot be made flexible enough, the thermal conductivity and thermal expansion coefficient are controlled by appropriate fillers. General-purpose room temperature cured epoxy-polyamide adhesive systems can be made serviceable at low temperatures by the addition of appropriate fillers to control thermal expansion. 

General-purpose epoxy adhesive with amidoamine curing agents Effect of fillers on tensile shear strength of polyamide cured epoxy... 

These polyamidoamines are available from several suppliers worldwide (Cognis (Veramide ), Arizona Chemical (Uni-Rez ), Air Products (Ancamide ), and others) and are among the most common curatives in the general-purpose, do-it-yourself two-pack-age epoxy adhesives. They have a distinctive odor somewhat like popcorn and are easily recognized in adhesive formulations. The polyamide backbone does contribute to the overall good mechanical properties of the polyamide amine cured adhesives. 

LDPE, Low density polyethylene LLDPE, Linear low density polyethylene HDPE, High density polyethylene PP, Polypropylene PVC, Polyvinyl chloride GPS, General purpose polystyrene HIPS, High impact polystyrene SAN, Styrene acrylonitrile ABS, Acrylonitrile butadiene styrene PC, Polycarbonate PA, Polyamide PET, Polyethylene terephthalate. 

Fortunately, the deficiencies of both the classic thermosets and general purpose thermoplastics have been overcome by the commercialization of a series of engineering plastics including polyacetals, polyamides, polycarbonate, polyphenylene oxide, polyaryl esters, polyaryl sulfones, polyphenylene sulfide, polyether ether ketones and polylmides. Many improvements in performance and processing of these new polymers may be anticipated through copolymerization, blending and the use of reinforcements. 

Chem. Descrip. Polyethylene wax disp. in IPA Uses Surf, modifier, lubricant, abrasion resist, aid in coatings based on urethanes, polyamides, NC and blends Features General purpose reduces COF good compat. easy processing low matting and settling homogeneous particle size distribution Properties Fine particle size disp. 

CAS 1327-36-2 EINECS/ELINCS 215-475-1 Uses Reinforcing agent, extender in EPDM, SBR, nitrile, PVC, polyamides, most other polymers opacifier, TiOj extender, reinforcing agent in flat architectural interior/exterior paints, traffic paints Features General-purpose easy processing consistent cures and color good abrasion resist. 

Uses Polyamide for inks, coatings, adhesives Features General purpose resin exc. adhesion, water resist., gloss, high vise. neutral termination... 

Polyamides Good general-purpose, tough, strong material. Useful from -100°F to +300°F. 

General name given to a variety of grades that, except for general purpose grades, include impact modified polyamide 6,6. 

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