Cross-linking thermal effects

Shao et al. (2005a) also used ethylenediamine (EDA) to cross-link Pis based on its unique linear structure, small molecular volume, and the potential of its functional groups to react with Pis. Thermal annealing processes at 100°C and 200°C were also performed on the membranes in order to study their effects on the separation performance of EDA-cross-linked Pis. The permeation results demonstrated that the EDA cross-linking can effectively decrease the permeability and increase the selectivity of Pis for He/N2 and H2/N2 separations. However, there were no such increases for O2/N2 selectivity, and CO2/CH4 selectivity was found to decrease with cross-linking. The gas transport properties of the EDA-cross-linked and then thermally treated Pis also show high selectivity for He/N2 and H2/N2 separations. 

B. Likozar, Z. Major, Morphology, mechanical, cross-linking, thermal, and tribological properties of nitrile and hydrogenated nitrile rubber/multi-walled carbon nanotubes composites prepared by melt compounding the effect of acrylonitrile content and hydrogenation, Applied Surface Science, ISSN 0169 332 257 (2) (November 1, 2010) 565-573. http //dx.doi.Org/10.1016/j.apsusc.2010.07.034. 

Sulfur-containing chemicals such as dimorpholinyl disulfide (DTDM) and tetraethylthiuram disulfide (TMTD) are not only effective accelerators, but they can also be used as sulfur donors. As such, they are effective ia controlling sulfur cross-link length to form primarily moao- and disulfide cross-links. These short cross-links are more thermally stable than conventional sulfur curing and thereby provide better heat and set resistance. 

In summary, formalin-treated does not significantly perturb the native structure of RNase A at room temperature. It also serves to stabilize the protein against the denaturing effects of heating as revealed by the increase in the denaturation temperature of the protein. However, formalin-treatment does not stabilize RNase A sufficiently to prevent the thermal denaturation of the protein at temperatures used in heat-induced AR methods as shown by both DSC and CD spectropolarimetry. This denaturation likely arrises from the heat-induced reversal of formaldehyde cross-links and adducts, as shown in Figure 15.4 of Section 15.4. Further, cooling formalin-treated RNase A that had been heated to 95°C for 10 min does not result in the restoration of the native structure of the protein, particularly in regard to protein tertiary structure. 

---