W.J.M. Douglas
Professor, Chemical Engineering Department
Research interests: Formation, Coating, Drying, Calendering and Paper Quality. Novel Drying Technologies: transport phenomena, superheated steam or air as drying medium, paper properties improvement, uncoated and coated paper. Simulation of pressing and drying of paper. Drying nonuniformity. Printability and mechanical properties control through formation and drying. Image analysis - based partitioning of formation nonuniformity into components as a function of scale of formation. Papermaking parameters - paper formation - paper properties relations. Calendering: rheological behavior of paper in the high-speed in-nip region for development of predictive CD control of calendering.
Awards: Fellow, American Institute of Chemical Engineers; Fellow, Chemical Institute of Canada; Victor Marquez Award, Interamerican Confederation of Chemical Engineering; Best Paper Award, 1998 and 1999, Drying Technology Journal; Jules Stachiewicz Medal, New Technologies for Drying Paper; Jukka Lehtinen Memoria Prize, Paper drying technology; Honorary Doctorate, Institut National Polytechnique de Grenoble.
Recent publications
Heat of Desorption of Water from Cellulosic Materials at High Temperature. Li, R., Bond, J.-F., Douglas, W.J.M. and Vera, J.H., Drying Technol.13, 999-1012 (1995).
Drying Paper in Superheated Steam. Douglas, W.J.M., Drying Technol. 12, 1341-1344 (1994).
Measurement of Paper Strain in the Nip of an Experimental Calender. Browne, T.C., Crotogino, R.H., and Douglas, W.J.M., J. Pulp Paper Sci., 20, J266 J271 (1994).
Equilibrium Moisture Content of Cellulosic Materials at High Temperature. Li, R., Douglas, W.J.M. and Vera, J.H., Drying Technol.,12, 823-847 (1994).
Research highlight
EFFECT OF BASESTOCK FORMATION ON COATED PAPER QUALITY
The effect on quality of LWC coated paper which derives from base sheet formation was determined for basestocks from three LWC producers. The formation of these basestocks was characterized using our new “components of formation-scale of formation” method, patented by McGill and recently commercialized as the PaperPerFect formation analyzer. On this basis the formation components of these three basestocks showed distinctly different patterns. Coated paper quality, in terms of the local nonuniformity of the coating layer, was found to relate well to basestock formation as determined by this new method.
Two comprehensive studies have provided quantitative evidence of the effect of base sheet formation on coating layer nonuniformity and thereby on coated paper print mottle. As the formation characterization techniques used in these studies are too complex for general use, we tested the utility of our new formation method for application to this base sheet formation-coated sheet quality problem. Formation test instruments which have been available until now provide some single-number index of average formation. Our PaperPerFect analysis technique, which partitions formation nonuniformity into 10 components over the range of scale of formation 0.6 to 37 mm, has been demonstrated in a series of 12 recent publications to be superior to single-number formation index instruments.
Coating, drying and calendering conditions were fixed in order to isolate the effect of formation for basestock three sources, identified here as from companies A, B & C. This basestock was blade coated in our lab to 7.1 g/m2 under conditions paralleling industrial practice. The pigment was a 50:50 mixture of delaminated clay and #2 clay, used with a standard butadiene-styrene latex binder. The coated paper was soft-nip calendered in the laboratory of a coated paper producer.
For basestock from companies A, B and C, Figure 1 shows the results for formation quality for each basestock as a “paper formation line” normalized to the average of the 3 sources. Higher numbers mean lower nonuniformity, better formation. For a normalized component of formation a value of 1.1 means that at this scale of formation the nonuniformity of formation is 10% less than for the mean of the 3 basestocks. Thus at the smallest scale of formation, 0.6 mm, basestock B is seen to have a formation which is better by 10% than the mean of the three basestocks. However, the data shows that at larger scales, basestock A becomes much better than the other two. By the highest scale of formation, 37 mm, the formation of basestock A is seen on Figure 1 to be more than twice as good as that of B or C, i.e. has less than half (0.7/1.65) the formation nonuniformity of B or C. There is no answer to the question: which basestock has better formation, B or C? The components of formation show basestock B has better formation up to 3 mm scale of formation, C is better from 5 to 14 mm scale, while at higher scale there is no significant difference in formation. Single-number formation index instruments miss this reality entirely.
The coating layer was isolated by the burn-out test. Images of the coating against the blackened base sheet were acquired by two scanners, of resolution 5 and 170 µm pixel size. The coefficient of variation of light reflectance at both levels of resolution showed the same deterioration (increase in COV) going from basestock A to C to B, with most of the degradation in coating layer nonuniformity occurring from basestock A to C. This coating superiority of basestock A correlates with the formation superiority of basestock A at scale of formation above 1 mm, which indicates that formation nonuniformity at 1 mm or smaller scale of formation is not important for coating quality. As the coating layer from basestock C is better than B, while the formation quality of B and C reverses at 3 mm scale, this suggests that coat weight uniformity may be controlled by base sheet formation for scale of formation above 3 mm. From this promising initial exploration a more extensive study (larger sample size) is now required to determine the precise range of scale of formation which controls coat weight quality for LWC paper. Doing so will enable a LWC producer to control papermaking parameters during basesheet production, using these specific formation components as a guide to producing higher quality coated paper.
Further details are available from S.J. Hashemi, F. Forel, J.-P. Bernié & W.J.M. Douglas, Proc. Advances in Paper Coating, Prague, November 2000
Figure 1. Normalized PaperPerFect components of formation of the three basestocks.
