Jedert Vodopivec*1, Stanka Grkman1, Meta Černič-Letnar2

COMPARISON BETWEEN STARCH AND METHIL CELLULOSE SURFACE COATING DURING THE LEAF CASTING TECHNIQUE Jedert Vodopivec*1, Stanka Grkman1, Meta Černič-Letnar2 1 Archives of the Republic of Slovenia, Ljubljana, Slovenia 2Pulp and Paper Institute - ICP. Ljubljana, Slovenia * corresponding author: [email protected]

1. Introduction Starch1 and water-soluble cellulose ethers2, are important additives in paper production, in paper surface sizing and coaling. They arc as well used in paper conservation as adhesives, paper coatings or strengthened, consolidates and also as cleaners.3 A research into the influence of starch and cellulose ether surface coating on the properties of paper formed during conservation by leaf casting was conducted within the framework of the applied research project4 "Optimization of conservation leaf casting technique". In this context the first part of individual properties of starch types and starch layers were studied and determined. After having compared the results, we were able to confirm the assumption that starch properties depend mostly on its origin (wheat, potato, corn). This part was presented at the ICOM-CC meeting in Ljubljana on March 2004.5

2. Experimental part In the next stage of the mentioned research project, paper samples were prepared in the same manner and with the same fibre composition as for the first part, the only difference was the coating where some methylcelluloses were applied and tested. Some typical physical properties of the tested samples were determined, and comparison with the results obtained with starch surface coated samples was performed. In the presentation the results of the comparison between starch and methylcellulose surface coatings applied during the leaf casting conservation technique, are presented. Due to financial restrictions only two samples of methylcellulose coating were possible to analyse. We selected one of the most frequently used products in paper conservation, a relatively low and medium viscosity was selected. The following samples of starches and MC were used: Sample 1: Sudsterke potato starch (Helios), Sample 2: Cerestar wheat starch , (Helios), Sample 3: Cerestar corn starch (Helios), Sample 4: Papiran SKM-42 corn cationic active starch (Helios), Sample 5: Drei hasen Weizenstarke wheat starch (Laursen), Sample 6: Jin Shofu Japanese wheat starch, Sample 7: CULMINAL MC 2000 (Hercules), Sample 8: CULMINAL MC 7000 (Hercules). Measurements and analysis of surface coated paper samples were conducted at the Pulp and Paper Institute in Ljubljana, according to ISO and TAPPI standards and ICP methods: - Basic physical-structural properties (grammage6, thickness, density, specific volume7, uniformity of the paper sheet - M/K-3D formation index8). - Mechanical properties (tearing resistance9, bursting strength10, folding endurance - MIT", stiffness -Clark12) - Surface properties (smoothness - Bekk13, porosity -Gurley14, contact angle - FibroDAT15). - Optical properties (ISO brightness16, opacity17, light scattering and light absorption18).

3. Results and Discussion 1. Starches and MC surface coatings on paper influence only the paper uniformity, which is shown as improvement of the formation index. Other basic physical structural properties were not affected. Figure I: The effect of starch and MC surface coatings on the uniformity of paper samples.

2. Mechanical properties in general did not improve much with starch and MC, except the folding endurance. Starch samples showed less improved values. A distinct improvement in double folds was observed with 1% potato starch (sample 1). The best results were obtained with samples coated with Culminal 7000 0,5% and Culminal 2000 1%. (fig. 2) 3. Measurements show that starch or MC surface coatings do not affect smoothness, but only porosity and hydrophilic properties. Results show that 1 %

Figure 2: The effect of starch and MC surface coatings on paper samples tested for folding endurance. concentrations of potato (sample 1), corn (sample 3), Japanese wheat starch (sample 6), Culminal 2000 (sample 7) as well as l% Culminal 7000 (sample 8) reduce porosity of paper structure. (Fig. 3) Figure 3: The effect of starch and MC surface coatings on the porosity of the paper samples.

Application of starch and MC on the surface of paper slightly decreases its hydrophilic properties. The surface becomes less wet absorbent, but still remains hydrophilic. The best results were obtained with 0,5 % Culminal 2000 (Sample 7). (Fig. 4)

Figure 4: The effect of starch and MC surface coatings on the hydrophilic/hydrophobic properties of the paper samples measured with contact angle - FibroDAT.

4. In general application of starch and MC docs not affect measured ISO properties. We noticed only some reduced values in opacity, which means higher transparency, on samples coated with 1% potato starch (Sample I) and with 0,5% Culminal 7000 (Sample 8), all the others samples show no change in opacity.

Figure 5: The effect of starch and MC surface coatings on the ISO opacity of the paper samples. 4. Conclusions With the comparison of analysed properties of leaf casled coated paper samples we examined the effect of starches and methylcellulose surface coatings on some typical physical properties used in paper testing. From the results conducted during the research we may be able to conclude that: - Not all starches arc suitable for surface coating application in the paper conservation lcafcasting procedure. - Potato starch coating (sample 1) show improved properties, but because of its great adhesion it is not adequate as coating during the lcafcasting. - Corn starches coatings (Sample 3 and 4) show no improvement on treated paper samples. - Wheat starches (Samples 2, 5 and 6) show the best results among analysed starches. - Starch and MC coatings improve paper formation. - MC, compared to starches improves some surface properties especially the hidrophobicity (contact angle) and the porosity of paper. - MC coated samples show the best results in folding endurance (double folds).

5. References 1. S. E. Bruun: Starch, Papermaking Science and Technology, Pigment Coating and Surface Si/ing of Paper. Finish Paper Engineers Association and TAPPI. Helsinki, Finland, 2002, 11, 241-229. 2. R. L. Feller, M. Wilt: Evaluation of Cellulose Ethers for Conservation, The Getty Conservation Institute, 1990, 3, 3-19. 3. J. Vodopivec, M. Černič-Letnar: Applying synthetic polymers to conserve cultural property on paper, Restaurator, 1990. 11,34-47. 4. M. Černič-Letnar, J. Vodopivec: Optimizing the Leafcasling Technique, Restaurator, 2004, 25, 1-14. 5. J. Vodopivec. S. Grkman, M. Čcrnič-Letnar, M. Beto Vlč: Effect of Stareli coating during the leaf-casting technique. Proceedings of the ICOM - CC Graphic documents meeting, Ljubljana, Slovenia. March 2004, 40-42. 6. ISO 536 - Paper and board - Determination of grammagc. 7. ISO 534 - Paper and board - Determination of thickness and apparent bulk density or apparent sheet density. 8. ICP method - M/K-3D Formation Index (M/K Formation tester/ floe analyzer). 9. ISO 1974 - Paper - Determination of tearing resistance. 10. ISO 2758 - Paper - Determination of bursting strength. 11. ISO 5626 - Paper - Determination of folding endurance. 12. TAPP1 451 - Flexural properties of paper (Clark stiffness). 13. ISO 5627 - Paper and Board - Determination of smoothness (Bekk method). 14. ISO 5636-5 - Paper and board - Determination of air permeance (medium range) - Part. 5: Gurley method. 15. TAPPI 558 - Surface wettability of paper (angle of contact method). 16. ISO 2470 - Paper, board and pulps - measurement of diffuse blue reflectance factor (ISO brightness). 17. ISO 2471 - Paper and board - Determination of opacity (paper backing) - diffuse reflectance method. 18. ISO 9416 - Determination of light scattering and absorption coefficients (using Kubclka-Munk theory).