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Paprican Adjunct Professor, Department of Chemistry

Research interests: Physicochemical studies of the polymer solid state. Current or recent topics include: blends of cellulose with synthetic polymers, structure and morphology of cellulose fibres, light-induced degradation of lignin.

Awards: 1975, Fellow of the Chemical Institute of Canada; 1983, Fellow of the American Physical Society.

Recent publications

Proton Spin Diffusion Studies of Polymer Blends. 2. Blends of Cellulose with Either Poly(acrylo-nitrile) or Poly(4-vinylpyridine). D.L. Van der Hart, J.D. Barnes and R. St.John Manley, Macromolecules, 27, 2826 2836 (1994).

Research highlight

THE EFFECT OF SOLVENT ON MECHANICAL PULP YELLOWING INHIBITION BY A BENZOPHENONE-BASED ULTRAVIOLET ABSORBER

R.St.J. Manley
in collaboration with C. Heitner, J. Schmidt and P. McGarry

A water-soluble benzophenone ultraviolet absorber (UVA), 5-Benzoyl-4-hydroxy-2-methoxy-benzenesulfonic acid, (Uvinul MS40™) (Figure 1)

Figure 1. Structures of water-soluble UVAs.

when applied from ethanol, imparted the expected anti-yellowing protection to a bleached thermomechanical pulp (BTMP) handsheet. There was a dramatic loss of protection, however, when water was used to deliver this UVA. For a benzotriazole UVA, 5-benzotriazolyl-4-hydroxy-3-sec-butyl-benzenesulfonic acid, (Cibafast W™) this adverse water effect is minimal. Spectroscopic evidence indicates that the benzophenone UVA, Uvinul MS40™, and, to a lesser extent, the benzotriazole UVA, Cibafast W™, are partly ionized to the phenoxide form when added to cellulose fibres from water. We further characterised the species responsible by measuring excitation spectra shown in Figure 2. The excitation spectra indicate that the phosphorescent species has a maximum absorption at 380 nm for compound Uvinul MS40™ and at 395 nm with a shoulder at 424 nm in the case of Cibafast W™. It is evident from the differences in these spectra that two distinct species are responsible for the emission as is expected for two different UVAs. The spectra below were from samples where the UVAs were deposited from alkaline solution (pH 8.8). They are identical for samples from neutral solution except they have better signal to noise ratios. This matches nicely with assignment of the phospho­rescence to the triplet of the corresponding phenoxide ions.

Figure 2. Excitation spectra of Uvinul MS40™ and Cibafast W™.

At pH 7, significant phosphorescence occur for water-delivered Uvinul MS40™, whereas for Cibafast W™ the emission intensity is very weak (Figure 3). At pH 8.8, where there is substantial formation of phenoxide, the luminescence increases. This luminescence indicates that a significant portion of Uvinul MS40™ on the paper has lost the impor­tant intramolecular H-bond, and hence anti-yellowing activity. Our experiments suggest the poor performance of aqueous- Uvinul MS40™, is due to the disruption of the internal hydrogen bond, and partial formation of phenoxide ion. Thus, choice of solvent, aqueous or non-aqueous, is of crucial impor­tance when testing chemical additives for colour stabilisation of mechanical pulp.

Figure 3. At pH 7, the relative emission intensity of Cibafast W™

is lower than that of Uvinul MS40™, indicating a greater extent of ionization to phenolate for Uvinul MS40™. At pH 8, the increased concentration of phenolate causes increased phosphorescence intensity for both Cibafast W™ and Uvinul MS40™. The excitation wavelength, lexc, was 385 nm.