Cm. Liauw et al., The use of flow micro-calorimetry and FTIR techniques for characterising filler/organic acid interactions, COMPOS INTE, 5(6), 1998, pp. 503-514
Reaction of filler grade magnesium hydroxide (Martinswerke Magnifin H10) wi
th oleic acid (cis 9-octadecenoic acid) and stearic acid (octadecanoic acid
) has been investigated using flow micro-calorimetry (FMC) and solution ads
orption isotherm methods (both from heptane). Diffuse reflectance Fourier t
ransform IR spectroscopy (DRIFTS), sedimentation volume measurements and X-
ray diffraction were also carried out on the isolated and dried adsorption
isotherm treated samples.
Stearic acid adsorbed to a greater extent (24 mg g(-1)) than oleic acid (12
mg g(-1)) and this is likely to correspond to vertical adsorption of both
acids based on measured filler surface area and adsorbate molecular area. I
t is considered that stearic acid forms a layer more than one molecule in t
hickness and was shown by X-ray diffraction, in the dry state at least, to
exhibit structural order. Oleic acid adsorbs as a single molecular layer wi
th any additional (i.e. excess) acid present probably reacting fully with t
he magnesium ion, thus forming the double salt which then di;solves in the
heptane. Magnesium stearate is not soluble in heptane. FTIR analysis of the
supernatant liquors for the oleic acid treated filler showed no free acid,
only magnesium oleate.