Resins, polyamide, components

Materials that can be used as main components of thermoplastic adhesives are vinyl acetate, polyvinyl alcohol, polyvinyl acetal, ethylene-vinyl acetate copolymer (EVA), vinyl chloride, acrylic resin, polyamide, cellulose, alfa-olefin resin, and waterborne isocyanate resin. 

Because of the capacity to tailor select polymer properties by varying the ratio of two or more components, copolymers have found significant commercial appHcation in several product areas. In fiber-spinning, ie, with copolymers such as nylon-6 in nylon-6,6 or the reverse, where the second component is present in low (<10%) concentration, as well as in other comonomers with nylon-6,6 or nylon-6, the copolymers are often used to control the effect of sphemUtes by decreasing their number and probably their size and the rate of crystallization (190). At higher ratios, the semicrystalline polyamides become optically clear, amorphous polymers which find appHcations in packaging and barrier resins markets (191). 

Only a few commercial uses for TDA per se have been found. In epoxy curing appHcations, 2,4- I DA has been used as a component of a eutectic mixture with short chain aUphatic glycidal ether resins (46) as well as by itself (46,47) TDA (46) and single isomers (47) are also used as amine curatives. TDA can be used as a chain extender in polyurethanes (48,49). TDA is cited as a monomer in making aromatic polymers with unique properties, eg, amorphous polyamides (50), powdered polyamides (51), and low melting, whoUy aromatic polyamides (52). 

The most important coating appHcation for the nonreactive polyamide resins is in producing thixotropy. Typical coating resins such as alkyds, modified alkyds, natural and synthetic ester oils, varnishes, and natural vegetable oils can be made thixotropic by the addition of dimer acid-based polyamide resins (see Alkyd resins). Specialty high performance coating appHcations often requite the properties imparted by dimer acid components. 

The minimum service temperature is determined primarily by the Tg of the soft phase component. Thus the SBS materials ctm be used down towards the Tg of the polybutadiene phase, approaching -100°C. Where polyethers have been used as the soft phase in polyurethane, polyamide or polyester, the soft phase Tg is about -60°C, whilst the polyester polyurethanes will typically be limited to a minimum temperature of about 0°C. The thermoplastic polyolefin rubbers, using ethylene-propylene materials for the soft phase, have similar minimum temperatures to the polyether-based polymers. Such minimum temperatures can also be affected by the presence of plasticisers, including mineral oils, and by resins if these become incorporated into the soft phase. It should, perhaps, be added that if the polymer component of the soft phase was crystallisable, then the higher would also affect the minimum service temperature, this depending on the level of crystallinity. 

Suitable curatives for the polysulfide-epoxy reaction include liquid aliphatic amines, liquid aliphatic amine adducts, solid amine adducts, liquid cycloaliphatic amines, liquid amide-amines, liquid aromatic amines, polyamides, and tertiary amines. Primary and secondary amines are preferred for thermal stability and low-temperature performance. Not all amines are completely compatible with polysulfide resins. The incompatible amines may require a three-part adhesive system. The liquid polysulfides are generally added to the liquid epoxy resin component because of possible compatibility problems. Optimum elevated-temperature performance is obtained with either an elevated-temperature cure or a postcure. 

Mori et al. [87] analysed the components of polyamide resins by GC after silylation with the aid of BSA. About 10-mg portions of the samples are dissolved in 0.15 ml of acetonitrile in a 10-ml flask and 0.03 ml of triethylamine and 0.15 ml of BSA are added gradually. The flask is connected to a reflux condenser and heated at 90°C for 30 min with the elimination of the excess of air humidity. Another 0.15 ml each of BSA and acetonitrile are added gradually and the flask is heated for 30 min. The solution is then made up to a known volume with acetonitrile and 10 pi are injected into the gas chromatograph. Binding of the hydrochloric acid produced makes necessary the addition of triethylamine to the reaction mixture. In order to separate TMS derivatives, Mori et al. used a 2-m column packed with 5% of neopentyl glycol succinate on Celite 545 at 160°C, and a relative error of 4.4% was obtained for the quantitative analysis. The same column coated with SE-30 or Apiezon L failed. 

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