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Hydrogen bonds between two cellulose molecules 55 . The pairs of covalent and hydrogen bonds are indicated by -and ⋅⋅⋅. Grey lines are the covalent bonds that form the cellulose chains.
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Teknolojinin gelişmesiyle konut fiyat tahmini için kullanılan yöntemlere yapay sinir ağları yöntemi de eklenmiştir. Bu çalışmada Eskişehir ilinde satılık konut fiyatlarının tahmininde yapay sinir ağlarının kullanılması araştırılmıştır. Konutların büyüklüğü, oda sayısı, birinci katta bulunup bulunmadığı, konutun bulunduğu binadaki toplam kat sayısı,...
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... This could have been due to both the Coi bark and Coi pulp fiber being very long and stiff with small lumens and thick cell walls, as the preferred Runkel ratio and flexibility should not be above 1.00 and not below 0.50, respectively (Tofanica et al. 2011). Retulainen et al. (1998) stated that long fibers usually possess thick cell walls due to a mature lignified fiber cell wall. Even though Coi pulp fiber was stiff, as seen in Fig. 6(a), it could still be felted naturally on a washing screen to make a strong wet sheet (or mat). ...
The Siamese people utilized the bark of the Coi tree (Streblus asper Lour.) to manufacture paper approximately 330 years ago. However, there are no studies yet related to the chemical properties of Coi bark as well as the morphological properties of Coi bark fiber and Coi pulp fiber. This research paper discussed such properties of Coi bark. The results indicated that Coi bark possessed a chemical composition that could potentially be used for pulp production, although it contained a high value of ash content, due to many calcium particles in the bark. Even though Coi pulp fibers were very long and stiff, with small lumens and thick cell walls, they could be felted naturally on a washing screen to make a strong wet sheet. This was due to a high felting power of fibers derived from a high value of fiber length and slenderness ratio. Therefore, the handsheets produced from Coi pulp fiber were obtained without chemical and beating treatments. These observations mean that both the archaeological and industrial applications of Coi bark, i.e., an ancient Samud Coi preservation and a new potential source of pulp fiber, are possible.
... However, extensibility can be affected by modifying properties of individual fibres through mechanical refining, which introduces deformations, internal and external fibrillation in fibres affecting their flexibility, tensile stiffness, shrinkage, and bonding behaviour (Jackson 1967;Mohlin et al. 1996;Seth 2005;Zeng et al. 2013;Khakalo et al. 2016). Fibre network properties are affected by stresses during wet straining and the drying process (Retulainen et al. 1998;Wahlström and Fellers 2000), and free shrinkage of paper during drying is known to promote the fibre network's elongation properties (Fujiwara 1956;Page 1971;Htun and de Ruvo 1981;Htun et al. 1989;Waller and Singhal 1999). Elevated temperature and moisture can be used to soften the fibres, which decreases stiffness and enhances the elongation potential of paper (Goring 1963;Salmén and Back 1977;Back and Salmén 1982;Caulfield 1990;Haslach 2000). ...
Elongation is an important property of many packaging board and paper grades. Paper with high extensibility could provide an alternative for oil-based packaging materials. Micro-(CMF) and nanofibrillated (CNF) cellulose are known to increase the strength of a paper, but their effect on the drying shrinkage and elongation is not well-studied. In this work, paper was reinforced with fibrillated material. Added fibrillated material increased the drying shrinkage, which was generally proportional to the increase of paper elongation before breakage. Results differed depending on the fibrillated material and how it was added to paper (wet-end addition or spray application). The papers were dried unrestrained in order to achieve the highest elongation potential for the paper. Spray application of CMF increased elongation by 13%, while wet-end additions increased elongation by 20% and also strength by 10%, but only with high dosages. Spray application of oxidized-CNF improved elongation by 33%, while wet-end applications increased only strength by 20%. Thus, boosting the drying shrinkage with fibrillated cellulose is one potential way to increase elongation and 3D formability of paper.
... Mechanical pulp differs in many respects from chemical pulp (Retulainen et al. 1998;Lehto 2011). While there are several differences between these types of pulps, from the strength perspective, the main differing factors are the fiber properties and fines content. ...
The paper recycling sector has undergone major changes in recent years, particularly regarding the quantity and quality of various materials processed. Material originating from board grades will increasingly dominate the recycling market as the use of printing papers decreases and the amount of non-fiber elements increases. Users of recycled fiber material have to overcome three main challenges: price, quality, and availability. This paper focuses on the quality dilemma in terms of measurement needs and possibilities from the user viewpoint. It includes a discussion of the factors causing deterioration in the quality of paper used for recycling. Today, the average fiber age is low compared to what the fibers can tolerate. Therefore, the characteristic phenomena in the paper recycling loop are not caused by the degradation of individual fibers, but by a blending process in which different fiber grades and non-fiber components are blended in a non-optimal way. A novel method is introduced in this article for evaluating the quality of recycled fiber material using a new parameter, the fiber integrity value. Part 2 of this paper will focus on the application of this new parameter and demonstrates its correlation with paper properties.
... Poplars, especially aspen, have been successfully used in producing chemical and mechanical pulps (Sundholm 1998;Retulainen et al. 1998). The total carbohydrate fraction (i.e., holocellulose) found in wheat straw is approximately equal to that of hardwood because of straw's high hemicellulose content, which is primarily composed of pentose sugars. ...
The aim of this study was to determine the optimum combination of wheat straw and white poplar (P. alba) chemimechanical pulps (CMPs) for producing newsprint paper. The CMP was prepared separately from the two raw materials. Cooking conditions included 10%, 12%, and 14% chemical charge based on w/w oven dry raw materials, maximum cooking temperatures of 120, 140, and 160 °C, and cooking time of 45 min. Hydrogen peroxide was used for bleaching the selected pulp. The results indicated that screened pulp yields were in the range of 54.3% to 61% and 80.9% to 85.9% for 18 cooking trials of wheat straw and white poplar, respectively. Handsheet brightness reached up to 52.9% and 61.9% for wheat straw and white poplar, respectively. The highest breaking length and burst index were related to CMP produced from 25% white poplar/75% wheat straw pulp blend. The best tear index was obtained using a mixture of 50% white poplar and 50% wheat straw pulp. Averages of breaking length, burst and tear indices ranged between 4.61 and 3.80 km, 2.31 and 2.55 kPa•m2/g, and 7.29 and 11.1 mN•m2/g, respectively. The strength properties of handsheets were higher than those reported for commercial newsprint except the breaking length of 50%/50% blend.
... Poplars, especially aspen, have been successfully used in producing chemical and mechanical pulps (Sundholm 1998;Retulainen et al. 1998). The total carbohydrate fraction (i.e., holocellulose) found in wheat straw is approximately equal to that of hardwood because of straw's high hemicellulose content, which is primarily composed of pentose sugars. ...
The aim of this study was to determine the optimum combination of wheat straw and white poplar (P. alba) chemimechanical pulps (CMPs) for producing newsprint paper. The CMP was prepared separately from the two raw materials. Cooking conditions included 10%, 12%, and 14% chemical charge based on w/w oven dry raw materials, maximum cooking temperatures of 120, 140, and 160 °C, and cooking time of 45 min. Hydrogen peroxide was used for bleaching the selected pulp. The results indicated that screened pulp yields were in the range of 54.3% to 61% and 80.9% to 85.9% for 18 cooking trials of wheat straw and white poplar, respectively. Handsheet brightness reached up to 52.9% and 61.9% for wheat straw and white poplar, respectively. The highest breaking length and burst index were related to CMP produced from 25% white poplar/75% wheat straw pulp blend. The best tear index was obtained using a mixture of 50% white poplar and 50% wheat straw pulp. Averages of breaking length, burst and tear indices ranged between 4.61 and 3.80 km, 2.31 and 2.55 kPa • m 2 /g, and 7.29 and 11.1 mN • m 2 /g, respectively. The strength properties of handsheets were higher than those reported for commercial newsprint except the breaking length of 50%/50% blend.
... This can be explained by the drying shrinkage effect, because shrinkage of paper during drying is greatly dependent on the degree of swelling of the fibres. Shrinkage potential of the handsheet depends on fibre swelling and subsequent fibre shrinkage, on the number of fibre bonds where the fibre shrinkage is converted to axia (Retulainen et al. 1998). A linear correlation between shrinkage and elongation could be observed for wing defibrator treated fibres and Valley beaten fibres, as shown inFig. ...
Elongation at failure is an important but underrated functional property of paper. Traditionally, elongation has been of specific importance for sack and bag paper grades. Mechanical treatments at high consistency are known to induce fibre deformations that contribute to the elongation of paper. However, it is not clear to what extent different fibre deformations can improve the elongation of paper. The aim of this work was to investigate the influence of three mechanical treatments on fibre and paper properties. The wing defibrator, the E-compactor, and the Valley beater were used for treating chemical softwood pulp. It was found that the type and intensity of mechanical treatments significantly affect the formation of fibre deformations, and thus the resulting properties of paper. The combination of high-consistency wing defibrator treatment and subsequent low-consistency valley beating provided paper with high elongation potential and good strength properties without impairing the dewatering properties.
... Mechanical properties and strength of chemical pulp fibres change inconsistently with refining. Harsh industrial refining induce fibre deformations whereas gentle laboratory refining may remove structural discontinuities [183]. Dewatering in the wire part takes place under the action of gravity, the blades, the pressure of forming rolls (twin wire former) and the vacuum. ...
... 20: Structural changes involved in the Jentzen effect at fibre wall level[183] ...
Incorporation of recycled fibres in high value paper products can reduce costand environmental loads. Papermaking potential of cellulosic fibres decreaseswith recycling. The phenomenon of fibre hornification during pressing anddrying is normally held responsible for the loss in strength. To study the impactsof recycling on pulp, fibre and paper properties some non conventionalcharacterisation techniques like fibre saturation point, X-rays microtomography,environmental scanning electron microscopic observations, atomic forcemicroscope (PeakForce QNM mode) and inverse size exclusion chromatography(ISEC) were used. In order to achieve good reproducibility of ISEC measurements,a semi-automatic column fabrication pilot system was built. Thetechniques were first validated on refining process before being applied to therecycling process. In this study, it was found that fibre hornification alone cannot fully explain loss in strength during recycling. The loss in strength is muchmore complex and it is required to understand the morphological and ultrastructural changes associated with recycling. Fibre width, cell wall thickness,curl, kink, irregularities decreased during recycling. Fibre became hard andbrittle in dry state. Number of weak points in the fibre wall were increasedinitially and in the later recyclings. The increase in wet breaking length indicatesincreased surface friction and capillary forces with recycling. Decreasein bonded area during first recycle may be caused by the loss of fines and fibreflexibility whereas the increase afterwards may be linked to the lumen collapse.The strength of fibres did not decrease with recycling as shown by zero-spanbreaking lengths therefore the quality of bond may be deteriorated. It wasthought that the partially delaminated P/S1 layers may be responsible for theloss of paper strength. It is suggested since the significant change is associatedwith the pressing and drying of never dried pulp therefore the drying processneeds to be revisited. The delaminated layer should be restored so as to increasethe recyclability of the recovered fibres for high value paper. Influenceof recycled pulp blends on physical properties of paper was also studied. It wasrevealed that small quantity of recycled pulp can be used without significantlyaffecting the mechanical strength properties.
... Paper is a multi-scale composite material. It is constructed in the wet state from discrete tubular fibers which are bound to each other primarily through hydrogen bonds (Retulainen et al., 1998). The planar distribution of fiber centers is in general non-uniform. ...
... At the outset one must begin by considering the fiber mass which directly participates in interfiber bonding. Although not well understood, it is believed that during the drying of paper, fibers change dimension at the interfiber bond sites in a way which causes the fibers to form microcompressions or a saddle-shaped interface surface (Retulainen et al., 1998). It is certainly known that preventing shrinkage during drying decreases the elastic compliance of paper as shown in Fig. 9. Perhaps the inelastic compliance of this bond zone material is different from fiber segments which do not participate directly in interfiber bonding. ...
Stochastic two-dimensional elastic–plastic network models are used to represent the inelastic deformation behavior of well-bonded paper. Linear kinematic hardening is employed with an initial non-zero back stress to represent anisotropic fiber yield. Network models are used to simulate simple monotonic tension and simple cyclic tension of paper materials. The performance of the models is compared to experimental results and found to perform reasonably well. The results suggest that interfiber bonding must be explicitly accounted for to adequately describe the material. Some discrepancy between the model and experimental cyclic tension results is believed to be due to time-dependent strain recovery in the material which is not represented in the network models. Experimental results are also presented which show that simple tension failure in these materials occurs along a line of localized deformation in a majority of the samples. This line is generally observed to form immediately prior to failure and is oriented at a well-defined angle with respect to the loading direction.
... Interfibre bonding is essential for sheet strength, which, according to Stratton (1991), is a function of two factors: the strength of an individual fibre and the strength of the interfibre bonds. An interfibre bond can be defined as the zone where two fibres are so close to each other that chemical bonding, van der Waals' interaction or molecular entanglement can occur (Retulainen et al. 1998). Bonds hold fibres together and therefore contribute to the internal cohesion of paper. ...
... Fibre surfaces are chemically and geometrically complex structures and fibres most likely have a wide range of molecular bonding mechanisms: adhesion and fibre bonding cannot be explained by a single theory or principle, it must rather be conceived as a function of factors introduced in the different adhesion theories. Cellulose fibres may display a range of bonding mechanisms, from non-polar adsorption to strong hydrogen bonds, since the surface and bulk properties of fibres are not compatible (surface tension of cellulose is lower than expected because fibres contain 'buried' polar groups in addition to those on the surface) ( Retulainen 1997, Retulainen et al. 1998). Lepoutre (1986) concludes that adsorption theory and weak boundary layer (WBL) theory best correspond to actual phenomena in fibre bonding when explaining bond formation and bond failure. ...
... Instead, a significant factor seems to be the thickness of the mobile hydrated phase on the fibre surfaces (created by beating and fibre surface treatment, for example adsorption of polyelectrolytes or their complexes), which allows interaction between fibres even across relatively wide distances. In addition to hydrogen bonds, Van der Waals' forces have an important role in fibre bonding; cohesion of the wet web is based on Van der Waals' forces ( Retulainen 1997, Retulainen et al. 1998). Covalent and ionic bonds can also form between fibres if polymeric mediators (for example, formaldehyde cross-linking) are used. ...
The objective of this thesis work was to examine interfibre bonding and fibre segment activation as basic phenomena: how different papermaking processes affect bonding and activation, and in turn, how bonding and activation relate to the end properties of paper, especially to different mechanical properties. Fibre-to-fibre bonding is very well known and the variables that affect bonding have been widely studied over the years. Activation, however, has not been examined very extensively, so the objective of the experiments carried out in this thesis work was to investigate activation in a comprehensive way. By linking activation with a better known phenomenon, bonding, any findings can be verified in a scientifically reliable manner. Furthermore, the objective was to use common, widely used paper strength tests and analyses, and to study how well these can be used in examining bonding and activation. The findings of the thesis work confirm what has already been established about bonding and bond strength: raw material parameters such as the type of fibre, fibre treatments, pulp properties and process parameters all play a significant role in bonding and bond development. Factors such as internal and external fibrillation, fines, fibre swelling, increased flexibility and strength-increasing polymers contribute strongly to the initial bonding potential of fibres. These benefits seem to be extensively and negatively affected by drying stress. Different polyelectrolytes affected bonding positively, but more importantly, it seems that certain polyelectrolytes and their complexes may have the ability to change the relationship between bonding and activation, and may affect the behaviour of paper during drying. Fibre segment activation is also affected by fibre properties such as internal fibrillation, fibre strength, and the conformability and collapsibility of the fibres. Naturally, activation also requires sufficient bonding and bond strength. However, the drying strategy plays a major role for its development. In most sheets, activation increases linearly with increasing drying stress. In mechanical pulp sheets, the overall extent of activation is rather small, which can be explained by the poor swelling ability and conformability of mechanical pulp fibres, but contrary to what was believed before, fines present in mechanical pulp seem to have a significant effect on the activation of a mechanical pulp fibre network. Based on the results of this work, an explanation of the mechanism in which fines influence activation is put forward. Reports / Helsinki University of Technology, Laboratory of Paper and Printing Technology. Series A, ISSN 1796-7414; 29
Plant cell walls form an organic complex composite material that fulfils various functions. The hierarchical structure of this material is generated from the integration of its elementary components. This review provides an overview of wood as a composite material followed by its deconstruction into fibres that can then be incorporated into biobased composites. Firstly, the fibres are defined, and their various origins are discussed. Then, the organisation of cell walls and their components are described. The emphasis is on the molecular interactions of the cellulose microfibrils, lignin and hemicelluloses in planta. Hemicelluloses of diverse species and cell walls are described. Details of their organisation in the primary cell wall are provided, as understanding of the role of hemicellulose has recently evolved and is likely to affect our perception and future study of their secondary cell wall homologs. The importance of the presence of water on wood mechanical properties is also discussed. These sections provide the basis for understanding the molecular arrangements and interactions of the components and how they influence changes in fibre properties once isolated. A range of pulping processes can be used to individualise wood fibres, but these can cause damage to the fibres. Therefore, issues relating to fibre production are discussed along with the dispersion of wood fibres during extrusion. The final section explores various ways to improve fibres obtained from wood.
Keywords: biological material; plant fibre; cell wall; hemicellulose; molecular interactions; reinforced plastics; biobased composites
