The Mechanism of Bonding

This review article considers processes by which the main components of wood have been reported to arrange themselves into various kinds of organized structures, at least to a partial extent. The biosynthesis of wood provides the clearest examples of such self-organization. For example, even before a cellulose macromolecule has been completely synthesized in a plant organism, the leading parts of the polymer chains already will have assembled themselves into organized crystals, i.e., nano-fibrils. This review then considers a challenge that faces industrial engineers: how to emulate the great success of natural systems when attempting to achieve favorable materials properties, process efficiency, and environmental friendliness when developing new engineered wood structures, barrier films, and other desired products composed of lignocellulosic materials. Based on the reviewed literature, it appears that the main chemical components of wood, even after they have been isolated from each other, still have a remnant of their initial tendencies to come back together in a somewhat non-random fashion, following mechanisms that can be favorable for the production of engineered materials having potentially useful functions.

Section: Dryingmentioning

confidence: 97%

Section: Irreversible Attributes Of Cellulosementioning

confidence: 99%

Self-assembly fundamentals in the reconstruction of lignocellulosic materials: A review

Hubbe

Trovagunta²,

Zambrano³

et al. 2023

“…At the limit where the two adjacent surfaces have come very close together, the value of P is predicted to become infinitely negative. Though the validity of using the equation may become questionable at that point, what is observed in practice is that the two adjacent surfaces tend to jump into molecular contact (Campbell 1959). This mechanism helps to explain why, during the process of papermaking, it is possible to achieve high levels of relative bonded area, with the formation of hydrogen bonds directly between the two surfaces (Campbell 1959;Page 1993).…”

Section: After Some Evaporationmentioning

confidence: 99%

“…Though the validity of using the equation may become questionable at that point, what is observed in practice is that the two adjacent surfaces tend to jump into molecular contact (Campbell 1959). This mechanism helps to explain why, during the process of papermaking, it is possible to achieve high levels of relative bonded area, with the formation of hydrogen bonds directly between the two surfaces (Campbell 1959;Page 1993). Another practical consequence of such forces is that flat plates of glass can become impossible to separate if they are placed in contact while droplets of water are present.…”

Section: After Some Evaporationmentioning

confidence: 99%

“…As can be seen with a cellulose sponge, a cellulosic filter contracts and stiffens upon drying and swells and softens upon wetting (Rey and Vandamme 2013). Stiffening of the cellulosic media upon drying can be attributed to closing of pores driven by capillary pressure (Campbell 1959;Page 1993;Rey and Vandamme 2013). Freeze-drying during the manufacturing of the cellulosic filter can help to avoid the complications of cellulosic filters stiffening and lowering filtration efficiency upon drying.…”

Section: Changes In Stiffness Of Mediamentioning

confidence: 99%

See 1 more Smart Citation

Performance factors for filtration of air using cellulosic fiber-based media: A review

Owens

Hubbe

2023

The filtration of air has attracted increasing attention during recent waves of viral infection. This review considers published literature regarding the usage of cellulose-based materials in air filtration devices, including face masks. Theoretical aspects are reviewed, leading to models that can be used to predict the relationship between structural features of air filter media and the collection efficiency for different particle size classes of airborne particulates. Collection of particles can be understood in terms of an interception mechanism, which is especially important for particles smaller than about 300 nm, and a set of deterministic mechanisms, which become important for larger particles. The effective usage of cellulosic material in air filtration requires the application of technologies including pulp refining and chemical treatments with such additives as wet-strength agents and hydrophobic sizing agents. By utilization of high levels of refining, in combination with freeze drying and related approaches, there are opportunities to achieve high levels of interception of fine particles. A bulky layer incorporating nanofibrillated cellulose can be used in combination with a coarser ply to achieve needed strength in a filter medium. Results of recent research show a wide range of development opportunities for diverse air filter devices containing cellulose.

Hornification in commercial chemical pulps: Dependence on water removal and hornification mechanisms

Sjöstrand

Karlsson

Barbier

et al. 2023

Understanding cellulose hornification provides crucial information regarding drying of pulp, paper, and other cellulosic materials as well as recycling them. By measuring drainage, fiber width, and water retention value of hardwood and softwood pulps before and after sheet forming and after different drying procedures at different achieved levels of solids, the hornification was evaluated. The water retention value was also measured for the pulps when dried from acetone to observe what happens when hydrogen bonds are not available in the liquid phase. The drainage and fiber width decreased with increasing solids content; the fibers became increasingly stiff with increased water removal. Water retention measurements indicated that hornification is a stepwise process with large drops in fiber flexibility as soon as the fibers are being processed and later after a certain amount of water has been removed. In sum, the fibers must achieve a certain solids content to show hornification, and hydrogen bonds in water draw the cellulose surfaces together to create hornification. The mechanism of hornification is believed to be driven by hydrogen bonds and related to the distance between cellulose chains inside the fiber wall. Other types of bonds are probably also present and help with the irreversibility of hornification.