ABSTRACT STRUCTURAL MAPPING OF PAPER TOWELS: COMPARISON OF TWIN LASER PROFILOMETRY AND SYNCHROTRON X-RAY MICRO-COMPUTED TOMOGRAPHY by Yan Huang This investigation was to compare the structural properties, of commercial available single ply paper towels, as they vary in X-Y plane. The focus was to quantify the differences in selected regions of interest, as measured by two analytical methods, non-contact Twin Laser Profilometry (TLP) and synchrotron X-ray micro-computed tomography (XRμCT). The thickness and out-of-plane deformation (OPD) distributions were mapped using a TLP and XRμCT. The XRμCT samples were further used to calculate for the mass center surface. TLP enables web structures to be mapped to a micrometer resolution over 12.5mm regions. Synchrotron X-ray microtomography method provides sub-micrometer resolution of the complete volumetric structure (1.4mm1.4 mm thickness (μm)) for the imaged region. The features of individual fibers are revealed by XRμCT method, so that the true surface geometry may be quantified. STRUCTURAL MAPPING OF PAPER TOWELS: COMPARISON OF TWIN LASER PROFILOMETRY AND SYNCHROTRON X-RAY MICRO-COMPUTED TOMOGRAPHY A Thesis Submitted to the Faculty of Miami University in partial fulfillment of the requirements for the degree of Master of Science Department of Paper and Chemical Engineering by Yan Huang Miami University Oxford, Ohio 2010 Advisor: Dr. D. S. Keller Reader: Dr. D. W. Coffin Reader: Dr. S. Lalvani Contents 1. Introduction ................................................................................................................................... 1 2. Back ground .................................................................................................................................. 5 2.1 Tissue paper grade ............................................................................................................... 5 2.2 Tissue and towel manufacture ............................................................................................. 5 2.2.1 The forming section ................................................................................................. 5 2.2.2 Drying: Conventional wet pressing (CWP) and the Yankee dryer ........................... 7 2.2.3 Drying: Through-air-drying (TAD) .......................................................................... 8 2.2.4 Embossing .............................................................................................................. 10 2.3 Scale ranges that are important ......................................................................................... 11 2.4 Characterization of towel structure ................................................................................... 12 2.4.1 Measurement of local grammage ........................................................................... 13 2.4.2 Measurement of local paper thickness ................................................................... 14 2.4.3 Measurement of local density map ......................................................................... 15 2.5 The analysis of paper structure in three dimensions ......................................................... 16 2.6 Synchrotron X-ray tomography and image processing ..................................................... 19 2.7 Measurement of z-direction density distribution .............................................................. 22 3. Problem statement and objective: ............................................................................................... 24 4. Experimental Methods ................................................................................................................ 25 4.1 Materials ........................................................................................................................... 25 4.2 Thickness mapping............................................................................................................ 29 4.3 Synchrotron X-ray micro-computed tomography (XRμCT) ............................................. 31 4.3.1 High resolution synchrotron X-ray micro-computed tomography imaging ........... 31 4.3.2 Tomographic file and image processing ................................................................. 32 4.3.3 Surface definition and algorithm of generating thickness and OPD maps ............. 36 4.3.4 Threshold value defining: ....................................................................................... 37 4.4 Statistical analysis ............................................................................................................. 38 5. Result and Discussion ................................................................................................................. 40 5.1 Conventional wet creping (CWP) samples ....................................................................... 40 5.1.1 Twin Laser Profilometry (TLP) .............................................................................. 40 5.1.2 Synchrotron X-ray micro-computed tomography (XRμCT) .................................. 43 5.1.3 Comparing TLP and XRμCT maps ........................................................................ 46 5.2 Through air drying (TAD) samples ................................................................................... 50 5.2.1 TLP ......................................................................................................................... 50 5.2.2 XRμCT ................................................................................................................... 53 5.2.3 Comparing TLP and XRμCT maps ........................................................................ 56 5.3 Comparison of CWP and TAD paper towels ..................................................................... 60 5.3.1 Thickness distribution ............................................................................................ 60 5.3.2 Void regions ........................................................................................................... 64 5.3.3 The relative thickness reduction ............................................................................. 66 5.4 Density distribution ........................................................................................................... 67 6. Conclusion and Future Work....................................................................................................... 72 ii 7. Reference .................................................................................................................................... 74 Appendix I: Incident light photographs .......................................................................................... 78 Appendix II: XRCTomographs ..................................................................................................... 81 Appendix III: Thickness and out-of-plane deformation map from TLP and XRμCT …………….89 Appendix IV: Thickness comparison of CWP and TAD samples……………………………...…93 Appendix V: Void percentage………………………………………………………………...……95 iii LIST OF TABLES Table 1-1 The hierarchical structure of paper of interest 2 Table 2-1 Some reported 3D image acquisition devices used in the analysis of paper structure 17 Table 2-2 Classification of some image acquisition devices and their effective resolution 17 Table 4-1 Samples for TLP scanning and submitted to ESRF for XR-Tomographic Imaging 25 Table 5-1 Comparison of void percentage 65 Table 5-2 The reduction ratio of thickness of the pressed to non-pressed region based on different process 66 iv LIST OF FIGURES Figure 1-1 The Relationship of paper making process to product properties 2 Figure 2-1 Configuration of tissue forming section. 6 Figure 2-2 Schematic of tissue web being dried and creped on a Yankee dryer 7 Figure 2-3 Schematic representations of fiber changes as a web on a Yankee dryer is creped 8 Figure 2-4 Tissue web being dried on a through-air-dryer 9 Figure 2-5 Schematic of morphology of fiber changes as a web passed a through air dryer 9 Figure 2-6 Schematic of the shape of tissues after different embossing processes 10 Figure 2-7 Void surface volume created by features in tissue and towel papers 11 Figure 2-8 Important scale of towel paper 11 Figure 2-9 Site of European Synchrotron Radiation Facility 21 Figure 4-1 Light photographs of CWP towel samples A1, A8 and A7 27 Figure 4-2 Light photographs of TAD towel samples B6, B8 and B7 28 Figure 4-3 Schematic of TLP instrument 29 Figure 4-4 Schematic of the XRμCT experimental set-up 31 Figure 4-5 Three dimensional volumetric structure of two typical CWP samples A1 and A8 34 Figure 4-6 Three dimensional volumetric structure of two typical TAD samples B6 and B8 35 Figure 4-7 Schematic of algorithm calculating thickness and OPD map and one slice out of 2048 36 Figure 4-8 Median thickness value to threshold of sample B9 38 Figure 4-9 Median thickness value to threshold of sample A1 38 Figure 5-1 Structural maps obtained from TLP for CWP sample A1 41 Figure 5-2 Frequency distribution of thickness values for CWP sample A1 42 Figure 5-3 Structural maps obtained from XRμCT for CWP sample A1 44 v Figure 5-4 OPD of A1 with white oval sketching the creping patterns; the three dimensional volume; a slice out of 2048 (illustrating creping feature) 45 Figure 5-5 Thickness map correlation of CWP sample A1 47 Figure 5-6 Thickness probability distributions of sample A1 from TLP and XRμCT 48 Figure 5-7 Deformation map correlation of CWP sample A1 49 Figure