Properties of polyurethane

The physical properties of polyurethane adhesives result from a special form of phase separation which occurs in the cross-linked polyurethane stmcture. The urethane portions of polyurethanes tend to separate from the polyol portion of the resin, providing good shear strength, good low temperature flexibiUty, and high peel strength. Catalysts such as dibutyltin dilaurate [77-58-7], stannous octoate [1912-83-0], l,4-diazabicyclo[2.2.2]octane... 

A. T. Chen, and co-workers, "Comparison of the Dynamic Properties of Polyurethane Elastomers Based on Low Unsaturation Polyoxypropylene Glycols and Poly(tetramethylene oxide) Glycols," Polyurethanes World Congress 1993, Vancouver, B.C., Canada, Oct. 10—13,1993. 

The physical properties of polyurethanes are derived from their molecular stmcture and deterrnined by the choice of building blocks as weU as the supramolecular stmctures caused by atomic interaction between chains. The abiHty to crystalline, the flexibiHty of the chains, and spacing of polar groups are of considerable importance, especially in linear thermoplastic materials. In rigid cross-linked systems, eg, polyurethane foams, other factors such as density determine the final properties. 

Table 11. Properties of Polyurethane/Elastomer Block Copolymers...

Table 27.2 Comparison of properties of polyurethane, nitrile and natural rubbers...

The physical properties of polyurethanes vary with the ratio of the polyol to the diisocyanate. For example, tensile strength can he adjusted within a range of 1,200-600 psi elongation, between 150-800%. ... 

Table 10.3 Properties of polyurethane/acrylic IPNs compared with blends and homopolymers...

The properties of polyurethanes can be tailored by prudent selection of their constituent monomers. They can be converted into elastic foams, which are widely used in upholstery, and are used as covers for the handles of various tools and implements, such as the soft touch grips on bail-point pens and power tools. 

What properties of polyurethanes make them an excellent choice for foamed seat cushions ... 

The properties of polyurethanes crosslinked in this way depend on the starting materials (polyol and diisocyanate) as well as on the additives and on the intensity of the mixing process. 

The effect of carboxylate and/or sulfonate ion incorporation on the physical and blood contacting properties of polyurethanes was studied by Cooper and collaborators [476-478]. Specifically, propyl sulfonate and ethyl carboxylate groups were grafted onto polytetramethylene oxide-based polyurethanes. Carboxylate polymers had no statistically significant effect on canine ex vivo blood contact response, but propyl sulfonate incorporation significantly reduced platelet deposition for very short blood contact times. 

In addition to providing the properties of polyurethane chemistry, the authors reported that HNIPUs also exhibit the chemical resistance of epoxy binders. Potential uses of HNIPUs include commercial application in paints, varnishes, adhesives, caulking compounds, flooring/industrial coatings, foams, and composite materials. 

While the properties of polyurethane as an extractant are useful, several problems make it less than ideal. Polyurethanes are far more specific than activated charcoal in removing contaminants. Charcoal separates particles by size, and while it has some specificity, it is well suited for mixtures of diverse chemistries (PAHs vs. halogenated hydrocarbons). Polyurethanes, however, operate on the principle that like dissolves like. They consist of hydrophobic isocyanates and hydrophobic polyalcohols. Thus, the molecules are hydrophobic. The polyalcohol backbone has some polarity, but it is hindered and therefore has a low net polarity. Inasmuch as the extraction effect is based, at least in part, on polarity, polyurethanes are most effective for nonpolar pollutants... 

Table 1. Dependence of the kinetic parameters of the reaction, the structural parameters of the network and the physico-mechanical properties of polyurethane elastomers on the molar fraction of OH groups in the monofunctional reagent21...

A. T. Chen, and co-workers, "Comparison of the Dynamic Properties of Polyurethane Elastomers Based on Low Unsaturation Polyoxypropylene... 

On the other hand, San Miguel and Duran (Ref 125) showed that the mechanical properties of polyurethane solid proplnt were degraded significantly by gamma irradiation dosages greater than 106 R. The tests used to determine the effects were by swelling, torsion, uniaxial tension and multiaxial tension... 

Therefore, Eq. (2.67) clearly reflects the existence of the gel-point, and the form of the function q(P,T) can be found. This last problem was solved elsewhere. It was shown that the whole range of experimental data on the viscous properties of polyurethane-based compounds used for reactive processing can be described by the following equation ... 

In order to describe changes in the rheological properties of polyurethanes during curing, the following equation was proposed and proved to be correct ... 

K. Kurita, N. Hirakawa, and Y. Iwakura, Synthetic polymers containing sugar residues, 7. Synthesis and properties of polyurethanes from D-cellobiose and diisocyanates, Makromol. Chem., 181 (1980) 1861-1870. 

There are a number of major factors that influence the final properties of polyurethanes. The most important of these are ... 

Polyethers give good mechanical properties with excellent hydrolysis resistance. PTMEG (C4) ether is generally superior to those of the PPG (C3) ethers. The properties of polyurethanes made with PPG ethers have been brought closer to the PTMEG materials with the use of end capping with ethylene oxide (EO) and the low monal materials (Acclaim). 

The current method of determining the energy properties of polyurethane is the Dynamic Thermal Mechanical Analyzer (DTMA). This instrument applies a cyclic stress/strain to a sample of polyurethane in a tension, compression, or twisting mode. The frequency of application can be adjusted. The sample is maintained in a temperature-controlled environment. The temperature is ramped up over the desired temperature range. The storage modulus of the polyurethane can be determined over the whole range of temperatures. Another important property closely related to the resilience, namely tan delta (8), can also be obtained. Tan (8) is defined in the simplest terms as the viscous modulus divided by the elastic modulus. 

The basic electrical properties of polyurethanes are good, but the polymer s tendency to absorb moisture can change the properties considerably. Polyurethanes are therefore not normally used as electrical insulators. They can be used in potting and encapsulating applications. Any applications involving mains power must be evaluated and approved by the relevant local electrical authority before use in the application. 

Wear is not a direct property of polyurethane but is the result of a complex system of materials being in contact, geometry of contact, operating conditions, and environment (Mardel et al., 1995). Polyurethanes find successful... 

Studies of the properties of polyurethanes, both physical and physicochemical, showed only that resilience had some direct relationship to wear. A relationship of (1- resilience)1-4, where resilience is expressed as a fraction, has been shown (Hutchings, 1987). No other relationship has been found for other properties for erosive wear between 30° and 90° (Hutchings, 1987). External factors that affect the erosive wear of the elastomers include ... 

Rubber can be formulated to meet most of the properties of polyurethanes. This is a complex capital and labor-intensive procedure. In most applications more than one property is needed, and polyurethanes provide many of these properties at one time. Rubbers that have the same or better properties than polyurethanes are detailed below. 

The load-bearing properties of polyurethanes are superior to that of conventional rubbers. The properties of the harder polyurethanes are superior to that of a rubber with the same hardness. To reach the 60 D to 70 D range, the conventional rubbers have to be very highly loaded or in the form of an ebonite (25% sulfur). Polyurethanes can be produced in this high range while maintaining the elastic properties that are also present in the lower-hardness materials. 

Polyurethanes have a combination of elastic and viscous properties that can be explained in standard engineering terms using DMA methods. Information can be obtained on the properties of polyurethanes that relates to the storage and dissipation of energy applied during use. 

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