Elastomer hand casting

The elastomers were prepared using the one-shot process by the hand-casting technique at a pot life of 1.5 minutes. 

The compositions, processability and properties of elastomers prepared using the one-shot process are given in Tables 9.10 to 9.12. For the 4000-MW, EO-capped diol, the upper hardness processability limit via hand casting is about 85 Shore A as indicated by the green strength in Table 9.10. Machine casting using a shorter pot life (30 to 45... 

Processing of polyurethanes is different from other elastomers in that most polyurethanes are cast into a mold. The mixing of the pre-polymer and curative can be done with specially designed machines in large shops or by hand in small shops or for small runs. 

The tensile data obtained from the cast elastomers are summarised in Table 8.3, plotted and shown in Figure 8.2. From this figure, it can be seen that the 100% modulus and % elongation decreased for the HER-TG materials compared to HQEE and HER-HP chain extenders. On the other hand, the 200% and 300% modulus values were higher for HER-HP and HER TG-210 extenders compared to HQEE and the values were lower for the other technical grade materials. Except for HER-LIQ extender, all HER based... 

On the other hand, a gradual increase in tensile strength and compression set values is observed for cast elastomers containing more amorphous hard segment contents. 

Some of the advantages of polyurethane elastomers vs. conventional rubber are improved abrasion resistance, better tear resistance, transparency, ozone resistance, and pourability for cast molding and curing. On the other hand, polyurethane elastomers possess disadvantages such as poor high-temperature service, poor resistance to certain chemicals, poor resistance to hot, moist environments, and sometimes higher material costs. 

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