Polyurethanes tensile strength

Tensile Strength and Elongation. The tensile strength of latex mbber foam has been shown to depend on the density of the foam (149,177) and on the tensile strength of the parent mbber (177,178). At low densities the tensile modulus approximates a linear relation with density but kicreases with a higher power of density at higher densities. Similar relations hold for polyurethane and other flexible foams (156,179,180). 

Compared with nylon 66 fibres, the polyurethane fibres (known as Perlon U) have a tensile strength at the higher end of the range quoted for nylon 66, they are less prone to discolouration in air, are more resistant to acid conditions and they have a lower moisture absorption. On the debit side they are less easy to dye, are hard, wiry and harsh to handle and have too low a softening point for many applications. They are currently of little importance but have found some use in bristles, filler cloths, sieves and a few other miscellaneous applications. 

As another example, a synergistic enhancement of tensile strength has been reached in blends of a sulfo-nated polyacrylonitrile terpolymer (SPAN) with a polyurethane (PU) cationomer [23]. Maximum enhancement was achieved at a blend composition of 30/70 (PU/ SPAN). At this blend composition, the tensile strength was raised from an initial value of 78.5 MPa to 196 MPa and the strain-to-fracture was at its highest. The en-... 

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%. ... 

Tensile strength ABS, methacyrylate-butadiene-styrene, polyurethanes, ethylene-vinyl acetate... 

Maji et al. [136] have examined the effect of 30B loading on the mechanical properties of hyperbranched polyurethane (PU) nanocomposites. The extent of clay loading was varied from 2 to 16 phr. The nanocomposite containing 8 wt% 30B clay shows a 100% increase in the tensile strength as compared to unmodi-fied-clay-filled samples. Above 8 wt% clay loading, the mechanical properties decrease. The efficiency and good dispersion of 30B in the hyperbranched PU40... 

We will conclude this chapter with a commercial perspective of polyurethanes. It will be useful to see the research that has taken place in this field over the past 70 years. The intent was to devise a polymer system with physical characteristics of flexibility, tensile strengths, and other factors that could be applied in the development of useful devices. We will discuss chemical features in subsequent chapters. 

In the first two chapters, we introduced polyurethane, not from the traditional chemistry view, but from the perspective of researchers desirous of a system to solve problems not typically addressed directly by polyurethanes. It has rarely been the intent of researchers in polyurethane to develop anything but a physical polymer system. Increasing tensile strength and controlling rigidity, flammability, sofmess, and hardness guided formulation development. 

It is important to note that tensile strength is controlled by density, of course, but tensile strength is otherwise a molecular phenomenon. Molecular weight, cross-linking, and other chemistiy level factors affect tensile properties. We should note that, with the exception of composites, the polyurethanes we will design based... 

Other tests are cited in ASTM 3574 and other standards, but they are of less importance in the context of how we will use them. Among parameters tested are resilience, fatigue/durability, flammability, and creep. A polyurethane devised to meet our primary objectives of density, tensile strength, compression, air flow, etc., will probably lead to values for these other properties that will have to be adjusted on a systems basis. 

While Table 3.3 deals with elastomers, it is important to mention that the effect of MDI illustrated in the table applies to MDI foams as well. Figure 3.7 shows the effect on the tensile strength of the polyurethane of increasing amounts of MDI. The increase in hard segments increases the brittleness but does not improve the strength of the polymer, as reflected in the elongation figures. The increase also exerts positive effects on the compression of the foam as noted in the next section. 

FIGURE 3.7 Effect of increase in hard segments on tensile strength of a polyurethane. 

One additional factor must be covered. While not classically polyurethane-specific in nature, it is nonetheless a useful tool. The use of a filler can produce a marginal effect on tensile strength. Adding particles to a matrix reduces the tensile... 

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