Jocelyne Ferret

Talc as nucleating agent of polypropylene: morphology induced by lamellar particles addition and interface mineral-matrix modelization

The efficiency of talc used as nucleating agent (0.5% by weight) in polypropylene (PP) was determined taking into account the particle size d50, particle morphology and BET specific surface areas. These findings were compared to a mineral with similar properties, pyrophyllite. Talc samples with the finest particle sizes induce a significant increase in the starting crystallization temperature of PP and irrespective of the particle size d50, pyrophyllite was found to be less efficient than talc. X-Ray results show that PP oriented crystallization due to talc or pyrophyllite addition, corresponds to an epitaxial growth whereby the mineral c*-axis is merged with the PP b*-axis. Microscopic observations revealed that in the presence of talc, nuclei density of PP increased strongly. In addition, a large number of nuclei was observed to appear everywhere on the talc surface. A PP-talc interface model is proposed by matching the (001) talc plane and the (010) PP plane. In this model, 3% of PP cell accommodation on talc is necessary with a 15° angle between PP chains elongation and the crystallographic directions of talc. Hexagonal rings on talc surface are believed to represent hydrogen bonds with PP methyl groupings. This fine structure relation between talc and PP is discussed, and is used to characterize the differences observed between the efficiency of talc and that of pyrophyllite.

Evaluation of talc morphology using FTIR and H/D substitution

Abstract Deuteration (H/D substitution at 200ºC) was performed on powders of two ground talcs of different particle shapes (different basal/lateral surface ratios). Results indicate that the deuteration process is only efficient on lateral talc surfaces, and suggest that the hydrogens located in the hexagonal ring of the talc basal surfaces are not exchanged. The FTIR spectra collected from the two talc samples show that it is possible to discriminate between particles with the same specific surface area but with different basal/lateral surface ratios using the deuteration process.

Fine-probing the crystal-chemistry of talc by MAS-NMR spectroscopy

Magic-Angle-Spinning Nuclear Magnetic Resonance (MAS-NMR) spectroscopy was used to probe the crystallographic environment of Si, Al, F and H in 14 natural talc samples originating from different localities and containing various, small amounts of iron (Fe2O3 (total) < 2 wt %). We show that iron induces strong variations in NMR spectra and that even very low quantities can be used as an indirect NMR parameter to characterize in detail the crystal-chemistry of talc. Conversely, their correlations with full width at half height (FWHH) in MAS-NMR spectra for 29Si, 27Al, 1H, and 19F obtained from these 14 talc samples allow for rapid estimations of the total iron content. Finally we highlight how, by simply recording Mossbauer, NIR and NMR spectra, one can obtain an accurate structural formula of talc, which is a necessary parameter for uses in specific industrial applications.

Cation site distribution in clinochlores: a NIR approach

Abstract A near infrared (NIR) spectroscopy approach was undertaken to collect information on the Al cationic distribution in tetrahedral and octahedral sites in natural chlorite (clinochlore) samples. Structural formulae were established using electron microprobe and Mossbauer spectroscopy. A band located near 7115 cm-1 was attributed to the overtone of OH fundamental stretching mode of Mg2AlOH and increases with the total Al amount. Good correlation was obtained between the (SiAl)O-OH vibration band area and tetrahedral Al content, making it easy to partition Al (and thus Fe3+) between octahedral and tetrahedral sites.

Structure of the {001} talc surface as seen by atomic force microscopy comparison with X-ray and electron diffraction results

In this study the surface structure of a centimetre sized crystal of talc from the Trimouns deposit (Ariege, France) was imaged by atomic force microscopy. The direct image shows detailed characteristics of clay tetrahedral surfaces. The unit-cell dimensions obtained 30 using atomic force microscopy (aor = 5.47±0.28 and bor = 9.48±0.28 A) are found to be slightly higher, with an increased uncertainty, than those obtained using X-ray diffraction (aor = 5.288±0.007 and bor = 9.159±0.010 A) and selected-area electron diffraction (aor = 5.32±0.03 and bor = 9.22±0.05 A). Talc has a quasi-ideal surface, clean of strong 34 structural distortion as compared to most of other clay minerals and unlikely surface 35 relaxation. The observation on the obtained image of apparent cell dimension enlargement is 36 then more likely attributed to instrumental artefacts, also responsible for scattered values of unit-cell parameters rather than related to any surface structural features.