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The Role of Cellulose Nanofibrils in Structure Formation and Drying Stress Development of Pigment Coating Layer

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dc.contributor.advisor이학래-
dc.contributor.author오규덕-
dc.date.accessioned2017-07-13T17:43:53Z-
dc.date.available2017-07-13T17:43:53Z-
dc.date.issued2017-02-
dc.identifier.other000000141793-
dc.identifier.urihttps://hdl.handle.net/10371/121087-
dc.description학위논문 (박사)-- 서울대학교 대학원 : 산림과학부, 2017. 2. 이학래.-
dc.description.abstractCoating structure is one of the important factors determining pigment coated paper quality including printability. The structure is influenced by the type or composition of pigment, binder, and additives. Even though the pigment and binder determine the structure of the coating layer most significantly, a small amount of additives can also influence the structure. In this study, cellulose nanofibrils (CNF) were used as an additive of the coating color. CNF was selected as an additive because it is a potential material to thicken the coating color. The effect of CNF on the coating color and coating layer was suggested compared to carboxymethyl cellulose (CMC) that has been used as a traditional thickener. Initially, the rheological properties of the coating color were investigated to understand the effect of CNF on the microstructure of the coating color. Drying kinetics was evaluated using the multispeckle-diffusing wave spectroscopy (MS-DWS) technique to suggest structure formation in the coating layer. Stress development was evaluated to investigate the effect of CNF on shrinkage of the coating layer. In addition, surface characteristics of the coating containing CNF were evaluated. Finally, CNF was applied to coated paper to investigate the change of in the optical, structural, and absorption properties of the coated paper.

CNF coating showed lower elastic behavior than CMC coating because there was no interaction between the particles in the coating color containing CNF. The microstructure of the coating color influenced the drying process. The particles in the CNF coating color moved freely because CNF did not form a structural network and increase the viscosity of the aqueous phase. The movement of the coating components, however, was greatly restricted by CMC because it created a network structure and increased the viscosity of the aqueous phase. CNF made the coating layer porous in a different manner than CMC. The voluminous characteristics of CNF made the coating layer porous.

CNF coating showed different stress development behavior compared to CMC. The drying stress of the coating layer increased with the addition of CMC because of the loosely packed structure of CMC coating, which increased the total shrinkage of the coating layer after the solidification point and the shrinkage of the precipitated CMC during drying. The stress of the CNF coating, however, was lower than that of the CMC coating because of the less structured CNF coating and the low shrinkage characteristics of cellulose. The CNF coating showed much lower gloss than the CMC coating due to its water absorbing characteristics. The swollen CNF caused a rough surface because the shrinkage of CNF proceeded until the end of the drying process.

The CNF coating gave lower coated paper gloss than that of the CMC coating due to non-uniform shrinkage, which came from the gel-like structure of CNF. To improve the gloss of the coated paper, the coated paper was made with a low coat weight and under high shear rate. The gloss and roughness of the coated paper were similar for the CNF and CMC coatings. In addition, the surface defects in the coated paper diminished. The CNF coating greatly improved ink absorption compared to CMC coating in the ink absorption test and the modified Vandercook press test by forming a porous coating layer due to its low shrinkage characteristics. The small amount of CNF addition can promote the absorption rate and uniformity of coated paper without changing the material properties.
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dc.description.tableofcontentsChapter1 Introduction 1
1. Introduction 2
2. Objectives 6
3. Literature reviews 8
3.1 Rheological properties of coating color 8
3.2 Consolidation of coating layer 12
3.3 Stress development of coating layer 18
3.4 Absorption characteristics and mottle of coated paper 23

Chapter2 Rheological Properties, Drying Kinetics and Pore Characteristics of Coating Layer by Cellulose Nanofibrils 27
1. Introduction 28
2. Experimental 30
2.1 Materials 30
2.2 Formulation and preparation of coating color 32
2.3 Sedimentation of coating color 32
2.4 Low shear viscosity and dewatering of coating color 33
2.5 Rheological properties of coating color 33
2.6 Drying kinetics of coating layer 34
2.7 Pore structure of coating layer 38
3. Results and Discussion 39
3.1 Sedimentation of coating color 39
3.2 Low shear viscosity and water retention of coating color 43
3.3 Rheological properties of coating color 47
3.4 Drying kinetics of coating layer 60
3.5 Pore characteristics of coating layer 71
3.6 Drying process 77
4. Summary 79

Chapter3 Stress Development and Surface Characteristics of Coating Layer by Cellulose Nanofibrils 81
1. Introduction 82
2. Experimental 83
2.1 Materials 83
2.2 Formulation of coating color 83
2.3 Evaluation of stress development during drying 83
2.4 Gloss of coating layer 85
2.5 Moisture content of coating components during drying 85
2.6 Observation of coating layer surface 85
3. Results and Discussion 86
3.1 Drying stress of coating layer 86
3.1.1 Effect of CMC 86
3.1.2 Effect of CNF 89
3.1.3 Effect of latex content 93
3.2 Surface characteristics of coating layer 97
3.2.1 Surface morphology of coating layer 97
3.2.2 Gloss of coating layer 100
4. Summary 104

Chapter4 Effect of Cellulose Nanofibrils on Surface and Absorption Characteristics of Coated Paper 105
1. Introduction 106
2. Experimental 108
2.1 Materials 108
2.2 Formulation of coating color 108
2.3 Coating on base paper and coat weight of coated paper 110
2.4 Gloss and roughness of coated paper 111
2.5 Ink absorption ratio 111
2.6 Vehicle absorption test 111
2.7 Observation of coated paper using FE-SEM 114
3. Results and Discussion 115
3.1 Gloss and roughness of coated paper 115
3.2 Ink absorption ratio 119
3.3 Absorption uniformity of coated paper 121
3.4 Surface characteristics of coated paper 128
3.5 Double-coated paper 133
4. Summary 138

Chapter5 Overall Conclusions 139
References 144
초록 157
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dc.formatapplication/pdf-
dc.format.extent6219003 bytes-
dc.format.mediumapplication/pdf-
dc.language.isoen-
dc.publisher서울대학교 대학원-
dc.subjectPore structure-
dc.subjectdrying stress-
dc.subjectink absorption-
dc.subjectrheological properties-
dc.subjectcellulose nanofibrils-
dc.subjectcarboxymethyl cellulose-
dc.subject.ddc634-
dc.titleThe Role of Cellulose Nanofibrils in Structure Formation and Drying Stress Development of Pigment Coating Layer-
dc.typeThesis-
dc.description.degreeDoctor-
dc.citation.pages158-
dc.contributor.affiliation농업생명과학대학 산림과학부-
dc.date.awarded2017-02-
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