No abstract

Various aspects of soft paraffins, with the main emphasis on their rheological properties, are considered in a review of 119 references. Rheological test methods currently used are critically appraised in sections on penetrometry, continuous shear viscometry, oscillatory testing and creep analysis. The chemical nature, microscopic structure, miscellaneous methods of standardisation, formulation and work softening of petrolatums are reviewed. The textural properties of soft paraffins are discussed; a master curve of the rheological conditions operative during spreading on the skin is presented.

The rheology of six grades of white soft paraffin B.P. at 25° has been investigated using continuous shear viscometry and a creep viscometer. Temperature effects between 25° and 50° have been measured in continuous shear, and activation energies from 14·0 to 25·3 k cal mol−1 (58·6 to 105·9 k J mol−1) have been determined. Working the samples on a triple roller mill at 25° was found to decrease the apparent viscosity and, initially, to increase the yield stress. Five of the grades were linear viscoelastic, one was non‐linear viscoelastic. The nature of ductility and its relation to measured rheological parameters have been discussed. Creep viscometry data gave a better correlation with the manufacturer's data than did continuous shear measurements.

The maleation of conventional and metallocene linear low density polyethylenes by reactive extrusion has been explored with a view to defining the conditions necessary for a robust process that provides both high grafting efficiencies (>80%) and minimal degradation or cross‐linking. The dependence of grafting efficiency on various operating parameters (maleic anhydride level, maleic anhydride:initiator ratio, throughput rate, direction of screw rotation, temperature) has been established. Literature methods for characterization of the grafted product based on FTIR or 1H NMR analysis have been critically examined with respect to their ability to distinguish between single unit and oligomeric maleic anhydride grafts and found to yield ambiguous results.