Polyurethanes Dynamic properties

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. 

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

DMA is an analysis technique used to determine the dynamic properties of the elastomers [13, 14]. Dynamic properties of the elastomeric materials are important because they influence the performance of certain parts such as wheels and tyres. This method determines the storage modulus G (elastic behaviour), loss modulus G (energy dissipation), tan 8, loss compliance ]" and glass transition temperature (Tg) values. The Tg of the soft segment can determine the low temperature behaviour of polyurethane elastomers. This is not only influenced by the nature of the soft... 

So one can maximise the benefit from ultra-low monol PPG polyols in urethane systems such as MDI/BDO cured elastomers by understanding their fundamental differences in comparison to other high-performance polyols like PTMEG. A detailed look at the effect of the polyol MWD on the mechanical and dynamic properties of polyurethanes follows. 

Polyol Molecular Weight Distribution Effect on Mechanical and Dynamic Properties of Polyurethanes... 

Another important feature of these polyols is their narrow MWD. Low polydispersity results in lower viscosities in both the polyol and isocyanate-terminated prepolymers. Polyol MWD has a significant effect on the mechanical and dynamic properties of polyurethane and polyurethane/urea systems. Broad-MWD polyols such as PTMEG or polyester polyols contain significant amounts of hard-segment diol, which limits their softness. Acclaim polyols contain no hard-segment diol and thus have inherent superior properties in soft systems. They can be made to approximate broad-MWD polyols such as PTMEG by incorporation of a low MW glycol. 

The dynamic properties of polyurethane composites made with treated rubber particles can also be very similar to those of the unfilled polyurethane. Comparison of d5mamic mechanical analysis (DMA) curves for composites composed of surface-modified rubber particles in polyurethane and corresponding curves for the unfilled polyurethane show nearly identical hysteretic heating. End products, such as wheels and rollers, made in either unfilled pol5mrethane or in composites comprising treated rubber particles/pol)mrethane have essentially identical heat build-up in dynamic applications. 

Polyurethane roll covers were introduced to the paper industry at the end of the 1980s. The outstanding mechanical and dynamical properties make polyurethane the most suitable material for soft elastomeric covers in press positions. Depending on paper quahty and press design, high open surfaces up to 45 % with grooves, blind drilled holes or suction holes, as well as combinations thereof are used. An example of surface design is shown in Fig. 5.11. 

In fast running machines the dynamic heat build up in the cover limits the application of elastomeric materials. Polyurethane polymers, based on special formulations with excellent dynamic properties, ensure good performance in these applications with minimal heat build up. An example of such an application is the substitution of grooved steel rolls by elastomeric covers in shoe presses. 

Phenolics are consumed at roughly half the volume of PVC, and all other plastics are consumed in low volume quantities, mosdy in single apphcation niches, unlike workhorse resins such as PVC, phenoHc, urea—melamine, and polyurethane. More expensive engineering resins have a very limited role in the building materials sector except where specific value-added properties for a premium are justified. Except for the potential role of recycled engineering plastics in certain appHcations, the competitive nature of this market and the emphasis placed on end use economics indicates that commodity plastics will continue to dominate in consumption. The apphcation content of each resin type is noted in Table 2. Comparative prices can be seen in Table 5. The most dynamic growth among important sector resins has been seen with phenoHc, acryUc, polyurethane, LLDPE/LDPE, PVC, and polystyrene. 

We achieved, that by contact of polyurethane foam with water solution of molybdophosphate, contain by pH 1-2,5 mixture of saturated (5 NMR P=-3.20 p.p.m. apply to 85 % H PO ) and unsaturated monovacant (x=0-t-4) (5 NMR P = -0,96 p.p.m.) heteropolycomplexes Keggin staicture, equilibrium discharge in the direction produced of saturated heteropolycomplex of Dowson stmcture and on the surface of polyurethan foam formed 18-molybdo-2-phosphate acid ( P = -2,40 p.p.m. in ether extract). The formed surfaces heteropolycomplex is stable for action 1 M solution of strong acids and basics and have ion exchanged properties in static and dynamic conditions to relation to macro and micro amount of M(I) ... 

Thermal and thermomechanical analyses44 are very important for determining die upper and lower usage temperature of polymeric materials as well as showing how they behave between diose temperature extremes. An especially useful thermal technique for polyurethanes is dynamic mechanical analysis (DMA).45 Uiis is used to study dynamic viscoelastic properties and measures die ability to... 

Mechanical properties. See also Dynamic mechanical analysis (DMA) of polyamides, 138 of polyester LCPs, 52 of polyurethanes, 242-244 of semicrystalline aromatic-aliphatic polyesters, 45 Mechanical recycling, 208 Medical applications, for polyurethanes, 207... 

In an NMR analysis of the effects of /-irradiation induced degradation on a specific polyurethane (PU) elastomer system, Maxwell and co-workers [87] used a combination of both H and 13C NMR techniques, and correlated these with mechanical properties derived from dynamic mechanical analysis (DMA). 1H NMR was used to determine spin-echo decay curves for three samples, which consisted of a control and two samples exposed to different levels of /-irradiation in air. These results were deconvoluted into three T2 components that represented T2 values which could be attributed to an interfacial domain between hard and soft segments of the PU, the PU soft segment, and the sol... 

A comparative stndy is made of the properties of energy absorbing foams nsed in passenger protection in cars, with particular reference to dynamic impact and compression strength. Materials examined inclnde polyurethanes, PP, PS and polyphenylene oxide/PS. 7 refs. 

There are a number of other physical properties that are very important to the optimum performance of polyurethane other than the normally quoted ones in trade literature. These include temperature, dynamic, and hysteresis properties. 

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. 

Extensive dynamic mechanical property studies have been carried out on hydrogen-bonded (81) and nonhydrogen-bonded (60,82) polyurethanes. Several secondary relaxations were found in addition to the major hard- and soft-segment transitions. Molecular mechanisms could... 

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