Polyurethane finishes properties

REZTHANE U-PF products are aqueous polyurethane finishes designed for pad application for a wide range of upgrading end uses. They all have excellent properties in resistance to degradation in washing and dry cleaning. 

The urethane linkage is resistant to alkalis and thus urethane oils and alkyds have better alkali resistance than ordinary alkyds. This is usually accompanied by better water resistance. Urethane oils and alkyds possess a property common to all polyurethane finishes good abrasion resistance. It is claimed that they are superior to oils and alkyds for the dispersion of difficult organic pigments and carbon black, but in pigmented form they are prone to chalk and lose gloss earlier than normal alkyds and oleoresinous finishes. 

Dr. Manfred Schdnfelder illustrated the effects of polyurethane finishes on the mechanical properties of the plastic. The abstract describes the propagation of a crack from the coating through to the plastic substrate. 

Some commercial durable antistatic finishes have been Hsted in Table 3 (98). Early patents suggest that amino resins (qv) can impart both antisHp and antistatic properties to nylon, acryUc, and polyester fabrics. CycHc polyurethanes, water-soluble amine salts cross-linked with styrene, and water-soluble amine salts of sulfonated polystyrene have been claimed to confer durable antistatic protection. Later patents included dibydroxyethyl sulfone [2580-77-0] hydroxyalkylated cellulose or starch, poly(vinyl alcohol) [9002-86-2] cross-linked with dimethylolethylene urea, chlorotria2ine derivatives, and epoxy-based products. Other patents claim the use of various acryUc polymers and copolymers. Essentially, durable antistats are polyelectrolytes, and the majority of usehil products involve variations of cross-linked polyamines containing polyethoxy segments (92,99—101). 

Polyurethane, thermoset TSUs have du-rometers range from soft cushion to glass hard with superior wear resistance. Use includes skateboard wheels, solid tires, floor coatings, marine finishes, etc. A major use for soft-foam is automotive bumpers another is upholstery. Property improvements are made with different added fibers and fillers in... 

In recent years, blown oils have found their way into the polyurethane industry. The additional hydroxyl content introduced through the oxidation process makes the oils more reactive toward isocyanates [82]. The oils can usually be incorporated at low levels into conventional formulations with little compromise to the mechanical properties of the finished polyurethanes. Blown oils have since found utility in carpet backing, insulation foams, and other polyurethane products [83]. At least a... 

The characteristics of the three most common thermoset resin systems used in pultrusion are compiled in Table 11.2 [3]. It is noteworthy that unreinforced polyesters and vinylesters shrink 7-9% upon crosslinking, whereas epoxies shrink much less and tend to adhere to the die. These epoxy characteristics translate into processing difficulties, reduced processing speed, and inferior component surface finish. It is normal practice to use resin additives to improve processability, mechanical properties, electrical properties, shrinkage, environmental resistance, temperature tolerance, fire tolerance, color, cost, and volatile evaporation. It is normally the resin, or rather its reactivity, that determines the pulling speed. Typical pulling speeds for polyesters tend to be on the order of 10-20 mm/s, whereas speeds may exceed lOOmm/s under certain circumstances. Apart from the resins characterized in Table 11.2, several other thermosets, such as phenolics, acrylics, and polyurethanes, have been tried, as have several thermoplastics (as will be discussed in Sec. 11.2.6). 

Very strong bonding between polyurethane and metal is needed in items such as polyurethane mounts. When metal is used as reinforcement or for location and stabilization, a very good bond is needed to form the bridge between the rigid metal and the elastic properties of the polyurethane. Ideally, a test that could be performed on the finished product is desirable, but in practice this is often not the case. 

Isocyanates react with polyether polyols to produce polyurethane foams. The amount of polyether polyol required varies widely depending on the desired properties of the finished urethane however, a typical flexible urethane contains about 55% propylene oxide and a typical rigid urethane contains about 30% [9]. 

Fillers are used in adhesives to improve physical properties, to control rheology, and to lower cost. The most common polyurethane fillers are calcium carbonate, talc, silica, clay, and carbon black. A more rigorous treatment of this subject can be found in Katz and Milewski [47]. Fumed silicas and carbon blacks are used primarily as thixotropes in application areas that require a nonsagging bead. Calcium carbonates, clays, and talcs are used to improve the economics of an adhesive formulation. A major concern using fillers with urethane prepolymers is the moisture content associated with the fillers. Fillers typically must be dried prior to use with urethane prepolymers or isocyanates. Hygroscopic fillers should be avoided, as moisture introduced by the filler can lead to poor shelf stability of the finished product. 

Where the coating itself does not provide all the desired properties, top coats or top finishes will be applied as a final environmental barrier, providing UV stability, durability, inertness and self-cleaning attributes. Top finish choices include acrylics, acryUcs/polyurethanes and PVF films. 

Hydroxy-terminated liquid polybutadienes are prepared for reactions with diisocyanates to form elastomeric polyurethanes (see Chapter 6). Such materials can be prepared by anionic polymerizations as living polymers and then quenched at the appropriate molecular weight. These polybutadienes can also be formed by a free-radical mechanism. The microstructures of the two products differ, however, and this may affect the properties of the finished products. To form hydroxy terminated polymers by a free-radical mechanism, the polymerization reactions may be initiated by hydroxy radicals from hydrogen peroxide. 

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