Factors influencing the adsorption of stabilizers onto carbon black: Flow microcalorimetry studies

The surface activity of various kinds of carbon black toward phenolic antio xidants and hindered amine light stabilizers (HALS) was examined by using f low microcalorimetry (FMC). Phenolic hydroxyl and ester groups were found t o be the moieties responsible for the adsorption activity of primary phenol ic antioxidants onto the carbon black surfaces. Furthermore, a difference i n the degree of phenolic hydroxyl hindrance by alkyl groups was found to be the main factor affecting the adsorption activity of the phenol group. A d ifference in the degree of substitution of the piperidine amine, as well as the number and type of functionality per molecule, are important factors t hat were found to influence the adsorption activity of HALS. Data from adso rption studies using model compounds, some of which represented functional portions of the stabilizer molecules, reflected behavior similar to that ob served with the stabilizers. In addition, these latter results showed that FMC analysis can yield potentially useful information beyond that given by the usual parameters such as BET surface area, I-2, DBP, and CTAB adsorptio n values. Differences in the behavior between types of carbon black were ev ident and showed that the specific surface area is not the most important f actor in the adsorption/desorption activity. but also the chemical nature o f the surface. From the activity observed for model compounds, it was deduc ed that the presence of secondary and tertiary amine in the backbone and br anch structures also has an important role in the adsorption activity of po lymeric HALS. In general, the observed quantities can be related to the val ues of adsorption/desorption energy and to the molar mass of the probe.