Polyurethanes compressive strength

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. 

Before we leave this descriptive chapter and explore the simple molecular chemistry that allows the diversity of applications, we must discuss a departure from traditional applications for polyurethanes. Readers will notice that the above discussion of applications focuses exclusively on physical properties we have painted a picture of polyurethanes that indicates the only reason to use them is their tensile or compressive strength. Based on Figure 2.21, polyurethane is capable of holding things together, protecting them, or fostering comfort. 

It is important to note that the compressive strength is controlled by the chemistry to some degree, of course, but other than that, the phenomena are physical. Cell structure, density, and other physical factors control properties of the material. It must be noted, therefore, that with the exceptions of composites, the polyurethanes... 

In most cases, the factors that affect tensile properties also affect the compressive strength of a polyurethane. This is most easily depicted in a graph such as Figure 3.12 that shows compressive strengths of foams. 

The addition of small amounts (ca 0,6%) of cellulose esters removes exudate by absorption, and also reduces the tendency to crack (Ref 17) polyurethanes remove exudate and double the compressive strength of the case (Ref 8), or impart finer crystal structure to the TNT matrix (Ref 33). Exudation is also, discussed in a limited-access report (Ref 11)... 

Compressive strengths were performed on a number of foam samples in accordance with ASTM 1621. The results obtained were comparable to other polyurethane foams prepared from conventional polyols and diisocyanates. 

Cunningham et al.199-203 investigated the use of starches and dextrins as extenders for polyurethane foams. Starch generally had little effect on the foam density, while compressive strength moderately decreased with increasing starch content. Hydrophilic foams prepared using starch were suggested to have useful horticultural... 

Very interestingly, Harding ound that the compressive strengths of polyurethane and polystyrene foams in one case and of polyurethane and phenolic foams in another case display the same dependence on the height-to-width ratio over a range from 1/2 to 2/1, despite the fact that the volumetric weights of these materials are... 

Fig. 12. Effect of temperature on compressive strength o at different height-to-width ratios h/D of polyurethane foam cells aspect ratios (1) 3/5, (2) 1/1, (3) 5/3...

Fig. 13. Effect of height-to-width ratio h/D of cells on compressive strength of rigid foamed polymers based on (1) polyurethane, y = 48 kg/m, polystyrene, y = 32 kg/m (2) polyurethane, y = 32 kg/m (3) polyurethane, y = 24kg/m phenolic resin, y = 32kg/m and aj, are the compressive strengths perpendicular and parallel to the direction of foaming...

This Navy specification covers a single class of foam, nominal density 2.0 Ib/ft rigid unicellular polyurethane foam, and the materials required for preparation by the foam-in-place technique. Requirements cover density, compressive strength, volume change after heat aging, humidity aging, compressive set, unicellularity (% open cells, max.), oil resistance, and fire resistance. 

Typical properties of RPUMRPE mortar in comparison to the hybrid recycled polyester (HRPE) mortar and recycled polyester (RPE) are presented in Table 6. The HRPE is hybrid polymer of recycled polyester and polyurethane which comes from F2 hybrid resin part A made by Amoco. The RPE is recycled polyester made by Alpha corporation. The bond, tensile and compressive strength, modulus of elasticity and shrinkage of these three kinds of polymer mortar were measured at 4, 8, 12, and 24 hours respectively. 

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