Adhesion To Dry CelluloseBy Nazir Khan

Outline History of adhesion in celluloseIntroduction to adhesion bondsImportance of adhesion to celluloseTheories for adhesion to celluloseHydrophobic vs. hydrophilic Cellulose adhesion on the nanoscale Cellulose adhesion bonding in paper Cellulose adhesion bonding in films Future of adhesion to dry cellulose

History of Adhesion in CelluloseAdhesion in cellulose-based fiber materials for paper as old as 5000 years.Egyptians invented papyrus parchments.Ref: Gardner, Douglas. Adhesion and Surface Issues in Cellulose and Nanocellulose. Journal of Adhesion Science and Technology 22 (2008) 545567

Introduction to Adhesion Bonds Adhesion is the tendency of certain dissimilar molecules to cling together due to attractive forces.Strength of adhesion between two materialsMaterials that wetSurface energy

Importance of Adhesion to Cellulose Cellulose has great importance in their current and future applications of papermaking, composites and nanocomposites.

Example: The mechanical performance of composites, is dependent on the degree of dispersion of the fibers in the matrix polymer and intensity of fiberpolymer adhesion interactions.

Adhesion theories to Cellulose Several theories have been proposed to provide an explanation for adhesion phenomena. The bonding phenomenon is the sum of a number of forces.Adhesion theories that have been examined in the bonding of cellulose fibers.Ref: Gardner, Douglas. Adhesion and Surface Issues in Cellulose and Nanocellulose. Journal of Adhesion Science and Technology 22 (2008) 545567

Adhesion theories to cellulose Mechanical interlocking caused by the mechanical anchoring of the adhesive in the pores and the uneven parts of the surface.Electrostatic forces, as they relate to the difference in electonegativities of adhering materials.Diffusion which is related to the interpenetration of molecular chains at the interface.

Adhesion theories to celluloseWeak boundary layers referring to the accumulation of air bubbles or low molecular weight compounds from the adhesive, the adherents or the surroundings at the interface

Adsorption and wetting which are related to highly localized intermolecular forces.

Adhesion theories to CelluloseFeatures that contribute to adhesion Each feature adds to the overall complexity of adhesionAdhesion of particles to a surface Ref: Sczech, Ronny. Molecularly smooth cellulose surfaces for adhesion studies. Journal of Colloid and Interface Science 301 (2006) 376385

Hydrophobic Versus HydrophilicThe hydrophilic and hydrophobic nature of cellulose is based on its structural anisotropy.

The hydrophilic behavior of cellulose is due to the location of hydroxyl groups at the equatorial positions of the glucopyranose rings.

Ref: Gardner, Douglas. Adhesion and Surface Issues in Cellulose and Nanocellulose. Journal of Adhesion Science and Technology 22 (2008) 545567

Hydrophobic Versus HydrophilicThe axial direction of the glucopyranose ring is hydrophobic because atoms of CH bonds are located on the axial positions of the ring. Ref: Gardner, Douglas. Adhesion and Surface Issues in Cellulose and Nanocellulose. Journal of Adhesion Science and Technology 22 (2008) 545567

Cellulose Adhesion on the NanoscaleThe ease of adhesion between pulp fibers that occurs during papermaking poses challenges to processing cellulose on the nanoscale. The hydrogen bonds present on the surface of nanofibers or nanorods or of cellulose are the key for a better manageability.Ref: Gardner, Douglas. Adhesion and Surface Issues in Cellulose and Nanocellulose. Journal of Adhesion Science and Technology 22 (2008) 545567

Cellulose Adhesion on the Nanoscale There are four types of nanocellulose depending on their manner of fabrication these include: (1) bacterial cellulose nanofibers(2) cellulose nanofibers by electrospinning(3) microfibrillated cellulose fibers and (4) nanorods or cellulose whiskersRef: Gardner, Douglas. Adhesion and Surface Issues in Cellulose and Nanocellulose. Journal of Adhesion Science and Technology 22 (2008) 545567

Nanoscale cellulose adhesion prepared by bacterial celluloseBacterial cellulose is more ordered than standard celluloseThe inter- and intra-molecular binding and/or adhesion is accomplished through hydrogen bonding. Low degree of polymerization may limit the adhesion through interpenetrating networks or mechanical interlocking.

Nanoscale cellulose adhesion prepared by electrospinningThe surface characteristics of the electrospun cellulose fibers are strongly dependent on the solvent used to dissolve the cellulose The most important criteria of dissolving ability of any solvent is the value of interaction energy of this solvent with cellulose

Nanoscale cellulose adhesion prepared by microfibrillated cellulose Interactions that take place in a composite between the reinforcement and the matrix. Studies showed that the tensile strength and tensile modulus increased when the cellulosic fibers were added.

Nanoscale cellulose adhesion prepared by cellulose whiskersWhiskers of cellulose have a hydroxyl-rich surface and in contact with relatively polar surfaces will form hydrogen bonds.

Chemical modifications of the surface of cellulose whiskers that increase its hydrophobicity include surface acylation and silylation.

Ref: Gardner, Douglas. Adhesion and Surface Issues in Cellulose and Nanocellulose. Journal of Adhesion Science and Technology 22 (2008) 545567

Cellulose Bonding in PaperAdhesion theories that have been examined in the bonding of cellulose fibers in paper

The adsorption of hydrophobic materials on cellulose fibersGardner, Douglas. Adhesion and Surface Issues in Cellulose and Nanocellulose. Journal of Adhesion Science and Technology 22 (2008) 545567

Cellulose Bonding in Paper The bonding of cellulose fibers in paper relies primarily on hydrogen bonding.Bond strength can also vary greatly depending on the methods used to prepare the fibers Hydrogen bonding between fibers requires close proximity between adjacent hydroxyl groups (0.250.35 nm).

Cellulose Adhesion in FilmsMany researchers have prepared model surfaces of cellulose films using spin coating and spin casting processes.The final thickness of cellulose films is dependent on the cellulose concentration of the solution.

Cellulose Adhesion in Films Differences in the adhesion properties between different degrees of crystalline order

A surface with a lower degree of crystalline order has a higher possibility for reorientation of the surface groups Ref: Sczech, Ronny. Molecularly smooth cellulose surfaces for adhesion studies. Journal of Colloid and Interface Science 301 (2006) 376385

FutureA number of studies have promoted the properties of nanocellulose composites such as lightweight, strength, biodegradability. However, only handful specific applications have shown strong results. Therefore, more future research should be spent on researching real world applications, where the properties and economic justifications are better than existing materials.

Thank You!!!Any questions???

*****This is adhesion of cellulose on the nanoscale. I am not going to discuss the importance of nanoscale technology, but I am going to discuss how adhesion of cellulose works on the nanoscale. *****