50 Years of Image Analysis

On the nature of

Paper is a material known to everybody. It has a network structure consisting of wood fibres that can be mimicked by cooking a portion of spaghetti and pouring it on a plate, to form a planar assembly of fibres that lie roughly horizontal. Real paper also contains other constituents added for technical purposes.This review has two main lines of thought. First, in the introductory part, we consider the physics that one encounters when 'using' paper, an everyday material that exhibits the presence of disorder. Questions arise, for instance, as to why some papers are opaque and others translucent, some are sturdy and others sloppy, some readily absorb drops of liquid while others resist the penetration of water. The mechanical and rheological properties of paper and paperboard are also interesting. They are inherently dependent on moisture content. In humid conditions paper is ductile and soft, in dry conditions brittle and hard.In the second part we explain in more detail research problems concerned with paper. We start with paper structure. Paper is made by dewatering a suspension of fibres starting from very low content of solids. The processes of aggregation, sedimentation and clustering are familiar from statistical mechanics. Statistical growth models or packing models can simulate paper formation well and teach a lot about its structure.The second research area that we consider is the elastic and viscoelastic properties and fracture of paper and paperboard. This has traditionally been the strongest area of paper physics. There are many similarities to, but also important differences from, composite materials. Paper has proved to be convenient test material for new theories in statistical fracture mechanics. Polymer physics and memory effects are encountered when studying creep and stress relaxation in paper. Water is a 'softener' of paper. In humid conditions, the creep rate of paper is much higher than in dry conditions.The third among our topics is the interaction of paper with water. The penetration of water into paper is an interesting transport problem because wood fibres are hygroscopic and swell with water intake. The porous fibre network medium changes as the water first penetrates into the pore space between the fibres and then into the fibres. This is an area where relatively little systematic research has been done. Finally, we summarize our thoughts on paper physics.

http://iopscience.iop.org/article/10.1088/0034-4885/69/3/R03/pdf

The physics of paper

Different types of microfibrillated cellulose (MFC) and fines suspensions were produced, characterized, and then added to a papermaking pulp suspension. High and medium molar mass cationic polyelectrolytes were used as fixatives. The drainage behavior of the pulp suspensions with additives were evaluated against the strength properties of hand sheets made thereof. The effects of salt concentration, pH, fixative type, dosage and type of fibrillar material on drainage were examined. All the MFC and fines samples produced had clearly different properties due to their dissimilar production methods, and they also introduced specific responses on the measured drainage and paper strength. Generally, the addition of MFC decreased the drainage rate of pulp suspension and increased the strength of paper. However, it was shown that by optimum selection of materials and process conditions an enhancement of the strength properties could be achieved without simultaneously deteriorating the drainage.

Effect of microfibrillated cellulose and fines on the drainage of kraft pulp suspension and paper strength

The effect on the physical properties of TMP handsheets by adding microfibrillated cellulose (MFC) is investigated. 26 TMP handsheet series were made with 4% addition of MFC produced by grinding or homogenization. Analysis of particle size distribution of the MFC showed that homogenization yields a bimodal distribution curve, while grinding gives a log normal distribution. The produced MFC had hydrodynamic particle sizes in the range 30–150 μm, and homogenization produced MFC with the largest particles. Addition of MFC to handsheets increased the tensile index and air resistance. MFC made by homogenization had a larger effect on the tensile index than MFC made by grinding (7–21% and 11–34% strength increase respectively), suggesting that the strengthening mechanisms of the two MFC qualities are different. The addition of MFC reduced the light scattering coefficient (a loss of 8% for the worst case), opacity and brightness of the sheets. Theoretical consideration regarding addition of fillers to maintain the optical properties showed that one still may get a 10% increase in tensile index. The use of MFC as strength enhancer in commercially produced paper is discussed.

The use of microfibrillated cellulose produced from kraft pulp as strength enhancer in TMP paper

Fibre-based packaging materials are widely utilized all over the world. They have several important advantages in comparison with fossil-based packaging: biodegradability, recyclability, and renewability. However, fibre-based packaging cannot fully compete with plastic in its barrier properties. Also there are limitations regarding its shapes due to poorer formability. The deep-drawing forming process can be used for the production of advanced three-dimensional shapes from paper-based materials. Formability and related characteristics are essential for deep-drawing of paper-based materials. This paper aims to give an overview of the deep-drawing of paper-based materials with the emphasis on the experienced deformations, on the role of mechanical properties of materials in deep-drawing, and on the typical defects found in the shapes after the forming. Additionally, strategies are proposed to help mitigate common problems in deep-drawing.

https://ojs.cnr.ncsu.edu/index.php/BioRes/article/download/BioRes_07_3_Vishtal_Retulainen_Deep_Drawing_Paper_Material_Properties/1696

Deep-drawing of paper and paperboard: the role of material properties

The fines of chemical pulps have a strong tendency to intensify the interaction between fibres. This is mainly due to the increased density of the network. A sheet made of kraft fines has a remarkably high density, 1100 -1200 kg/m3, whereas a handsheet made of TMP fines has a rather low density, about 450 kg/m3. In this study several pulps were compared. The fines form a spectrum ranging from fines of bleached softwood kraft to the fines of mechanical pulp. The differences between softwood and hardwood kraft fines as well as between bleached and unbleached softwood kraft fines are rather small. Clearly larger differences are within the different fractions of a fines from a certain chemical pulp. In addition to the size of the fines particles the shape seem to be important factor. Only part of differences in the quality of the fines can be explained by the chemical composition. But the results indicate that the size shape and chemical composition of the fines fraction have inter-correlation.

Papermaking quality of fines from different pulps - the effect of size, shape and chemical composition

Retulainen, E., Moss, P . and Nieminen, K., Helsinki University of Technology Laboratory of Paper Technology Vuorimiehentie 1 SF-02150 Espoo Finland The fines of mechanical and chemical pulps have a character vecy distinct from their respective fibre fractions . The fines can be regarded as a special furnish component and the optimum quality and percentage of fines in the sheet depends on the properties of the fibre fraction used . An addition of suitable fines can improve remarkably the properties of a printing paper . This paper deals with the structural, optical and strength properties of fibre networks, as influenced by fibre coarseness and the introduction of different types of fines . The response of these networks to calendering is also studied . Fibre fractions of different coarseness and lignin content are used . Confocal laser scanning microscopy (CLSM) is used to determine the changes in the structure and microscopic roughness of the sheet . Preferred citation: E. Retulainen, P. Moss and K. Nieminen. Effect of fi nes on the properties of fi bre networks. In Products of Papermaking, Trans. of the Xth Fund. Res. Symp. Oxford, 1993, (C.F. Baker, ed.), pp 727–769, FRC, Manchester, 2018. DOI: 10.15376/frc.1993.2.727.

Effect of fines on the properties of fibre networks

Fibers and bonds

The effect of eucalyptus chemical pulp fines on filler retention and paper properties was examined. Different quantities and qualities of fines were studied, and the benefit of pre-mixing fines and fillers before addition, compared to separate addition, was evaluated. As expected, fines enhanced paper properties, but retarded the drainage. The qualities of fines had a strong influence on paper strength properties and drainage of the pulp furnish. Fillers did not retard drainage; they had a positive effect on optical properties but impaired paper strength. In general, the retention of fillers was minor compared to fines. Retention, strength and optical properties of resultant paper were improved by addition of pre-mixed fines and fillers to pulp furnish. This improvement was achieved at the cost of significantly reduced drainage.

Elias Retulainen

Papers

Deep-drawing of paper and paperboard: the role of material properties

Papermaking quality of fines from different pulps - the effect of size, shape and chemical composition

Effect of fines on the properties of fibre networks

Fibers and bonds

Effect of Chemical Pulp Fines on Filler Retention and Paper Properties