Surface characteristics and surface behaviour of polymer carbons—III: Surface acidity of polymer carbons

✍ Scribed by R.C. Bansal; Nirupama Bhatia; T.L. Dhami

• Publisher: Elsevier Science
• Year: 1978
• Tongue: English
• Weight: 423 KB
• Volume: 16
• Category: Article
• ISSN: 0008-6223
• DOI: 10.1016/0008-6223(78)90118-5

✦ Synopsis

Ah&act-Surface acidity of charcoals prepared by the carbonisation of PVDC, PVC, Saran, PF and UF polymers has been determined by titration with sodium hydroxide and sodium ethoxide. The surface acidity as determined by titration with 0.2N sodium hydroxide solution is found to be almost exactly equivalent to the amount of CO2 evolved on evacuation at 1200°C in case of the PVDC, PVC and Saran charcoals. However, for the PF and UF charcoals the base neutralisation capacity of the surface oxide is almost one half of the amount of CO* evolved.

The surface acidity decreases on evacuation at gradually increasing temperatures and the decrease at any temperature is exactly equivalent to the amount of CO* evolved at that temperature. The temperature interval at which the drop in acidity occurs appears to be the same as the temperature interval over which CO* is evolved from the sample. The oxygen desorbed as CO seems to have little effect on the surface acidity of these charcoals. The results have been explained on the basis of the existence of a cyclic ester which exists in two tautomeric forms. The keto form of the lactone explains the monobasic character of PF and UF charcoals while the enol form fits very well with the dibasic character of the acidic surface oxide on PVDC, PVC and Saran charcoals.