Polyurethane solvent free

Thermosetting epoxy and polyurethane chemically-cured liquid resins can provide, among other characteristics, superior abrasion resistance coatings. Solvent-free formulation applied by hot spray techniques can achieve film thicknesses of up to 5 mm. 

Recently a solvent-free dual-cure laminating adhesive based on the combination of polyurethane chemistry and EB cure was developed that exhibits improved properties compared to laminates prepared by either method alone. ... 

Spaans, C.J., Belgraver, V.W.. Rienstra, O.. De Groot, J.H., Veth, R.P.H., and Pennings, A.J., Solvent-free fabrication of micro-porus polyurethane amide and polyurethane-urea scaffolds for repair and replacement of the knee-joint meniscus. Biomaterials 21 2453-2460, 2000. 

While unaffected by water, styrofoam is dissolved by many organic solvents and is unsuitable for high-temperature applications because its heat-distortion temperature is around 77°C. Molded styrofoam objects are produced commercially from expandable polystyrene beads, but this process does not appear attractive for laboratory applications because polyurethane foams are much easier to foam in place. However, extruded polystyrene foam is available in slabs and boards which may be sawed, carved, or sanded into desired shapes and may be cemented. It is generally undesirable to join expanded polystyrene parts with cements that contain solvents which will dissolve the plastic and thus cause collapse of the cellular structure. This excludes from use a large number of cements which contain volatile aromatic hydrocarbons, ketones, or esters. Some suitable cements are room-temperature-vulcanizing silicone rubber (see below) and solvent-free epoxy cements. When a strong bond is not necessary, polyvinyl-acetate emulsion (Elmer s Glue-All) will work. 

Analytical studies of the PVC profile surface indicated that the reasons for failure of the adhesive bond between the PVC film and PVC profile in decorative film laminated structures, was finely dispersed lubricant and wax particles on the PVC profile. These contaminants prevented the build-up of bond forces at the interface between the adhesive and PVC profile. A biodegradable alkaline cleaning agent was developed to remove the contaminants, which, when combined with flame treatment and a solvent free polyurethane hot melt... 

Polyurethane crack-sealing systems are two-component, solvent-free materials. They are available in a range of viscosities and can be used to combat low-volume and high-volume leakage with equal success (Edwards, 1993a). 

Figure 10.9 The reaction pattern for epoxy-polyurethane modifications. Source Wellner, W., Gruber, H. and Ruttmann, G., New solvent free epoxy/polyurethane combinations, publication E 908-8122/850640 published by Bayer AG, Plastics and Coatings Division, D-5090, Leverkusen...

Reactive Polyurethane Hot-Melt Adhesives (Solvent-Free)... 

Chemical produces methylamine and its derivatives, and acrylic, polyurethane and polyester rapid cure and pressure-sensitive resins for solvent-free coating systems ... 

Andersson K., Gudehn A., Levin J.-O. and Nilsson C.-A. (1983) A comparative study of solvent and solvent-free sampling methods for airborne 4,4 -diphenylmethane diisocyanate (MDI) generated in polyurethane production. Am. Ind. Hyg. Assoc. J., 44, 802-808. 

Zebron is a polyurethane corrosion-resistant coating material available from ACO-Coatings. It is a solvent-free product that cures in cold wet conditions and can be rapidly applied to a high film thickness in one operation. The material provides a thick abrasion and water-resistant coating to steel or concrete. 

Depending on their chemical composition, polyurethane paints are formulated as two-component (two-pack) or one-component (one-pack) mixtures. They are applied from the liquid phase, which may be solvent-containing, aqueous, or solvent-free, or from the solid phase as a powder coating. They may be cured under a wide range of conditions drying above to stoving at ca. 200°C. 

Polyisocyanates differ as regards their chemical structure, reactivity, functionality, and isocyanate content. They are the principal curing constituent of two-pack polyurethane paints. Curing agent solutions have an isocyanate content of 5-16 wt%. Solvent-free, liquid curing agents may contain up to 30 wt% isocyanate. 

Curing with Atmospheric Moisture. Type 2 in Table 2.5. High molecular mass polyaddition products of polyols with excess diisocyanate contain reactive isocyanate groups. They are used to formulate one-pack polyurethane paints that cross-link with the formation of urea groups under the influence of atmospheric moisture to produce paint films with excellent resistance to chemical and mechanical attack. Solvent-free products and dissolved products with isocyanate contents of 5- 15% (based on the solid resin) are commercially available. 

In the case of abrasive freight goods, the interior of the car must be lined with a thick coat system consisting of solvent-free two-pack polyurethane or epoxy material. Toughness combined with flexibility results in a film that is highly resistant to abrasion. 

Certain components of domestic appliances are also coated with electrodeposition paints. Two-pack polyurethanes are applied if the dimensions of the parts are too large for the electrodeposition bath. These paints dry at ambient temperature to give films with similar properties to stoving acrylic enamels. Solvent-free powder coatings are also used to coat domestic appliances. Nowadays powder coatings and precoated metal (coil coating) are gaining more importance. 

Adhesives and sealants are manufactured from a variety of polymers. Their selection and their combinations used impact solvent selection. Most solvent systems are designed to optimize the solubility of the primary polymer. Adhesives can be divided into ones which bond by chemical reaction and ones which bond due to physical processes. Chemically reactive adhesives are further divided into three more categories for those that bond through polymerization, polyaddition, or polycondensation. Physically bonding adhesives include pressure sensitive and contact adhesives, melt, or solution adhesives, and plastisols. Polymerization adhesives are composed of cyanoacrylates (no solvents), anaerobic adhesives (do not contain solvents but require primers for plastics and some metals which are solutions of copper naphthenate), UV-curable adhesives (solvent-free compositions of polyurethanes and epoxy), rubber modified adhesives (variety solvents discussed below). 

Sealants are divided into groups according to the generic names of polymer base. The main groups include polyurethanes, silicones, acrylics, polysulfide and others (PVC, polybutylene, styrene-butadiene-styrene copolymers, polychloroprene, and several others). The amount of solvent used in sealants is controlled by the standards which previously divided sealants into two groups these below 10% VOC and those above. Recently, a provision was made to include water-based acrylics and the limit of VOC for class A sealants was increased to 20%. Polyurethane sealants and structural adhesives can be made without solvent (the first solvent-free polyurethane sealant was made in 1994). Solvents are added to reduce sealant viscosity and to aid in the manufacture of polymer. Typical solvents used are mineral spirits, toluene, and xylene. A small amount of solvent is emitted from curatives... 

In view of the above efforts, it is surprising that the majority of recent patents on adhesives are for solvent-based systems.The new inventions include a universal primer, an adhesive composition in which solvents have been selected based on Snyder s polarity (only solvents which belong to group III are useful in adhesive for automotive applications to avoid a deleterious effect on paint), a low VOC adhesive for pipes and fittings, a solvent-containing heat-resistant adhesive based on siloxane polyimide, a water-based polyimide adhesive,and two-component solvent-free polyurethane adhesive system for use in automotive door paneling. ... 

Recent inventions " are driven by product improvement needs and environmental aspects of application of these products. Janoski s patent describes a product which is an anhydrous blend of polymer and asphalt and is substantially solvent-free. This technology shows that it is possible for an ingenious designer to produce low viscosity materials without using solvents but by selecting the appropriate type and concentration of bituminous materials, polyurethane components, and plasticizers. 

In various asphalt processing methods, the rheological properties of the compounded asphalt are of primary importance. One invention shows how, by blending different fractions of crude oil, the processing properties can be optimized for pavement applications. In another recent invention,solvent-free polyurethane was compounded with asphalt. Such products have always contained substantial amounts of solvents to reduce viscosity to the level that allows the material to be cold applied with simple techniques. Using organoclay as compatibilizer for polyurethane and asphalt and a suitable plasticizer, elimination of solvent becomes possible. In addition to environmental safety, these products can be used safely on substrates which would otherwise be affected by solvents the formulation (e.g., polystyrene insulation boards). This is one example which shows that the benefits of solvent free systems go beyond the elimination of air pollutants. 

Powder coatings are completely solvent free. They are dry blends, so to speak, of pigments and binders. They are either applied with a fluidized bed or by electrostatic spraying onto the substrate to be coated. The most important binders are epoxides, sometimes alone and sometimes in combination with polyesters. Polyurethanes, polyesters combined with triglycidyl isocyanurates, and acrylates combined with oxazolines are also important. 

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