Intermolecular interactions of chitosan: Degree of acetylation and molecular weight

The degree of acetylation (DA), which determines as the molar proportion of N-acetyl-D-glucosamine units on chitosan, characterizes the physical, chemical, and biological properties of chitosan. Thus, DA can be a critical factor in the utilization of chitosan. Nevertheless, quantitative studies on the molecular interactions of chitosan as a function of DA are lacking. Here, we directly measured the molecular interaction (adhesion and cohesion) of molecularly thin chitosan films, dependent on the molecular weight and DA, using a surface forces apparatus. Using low molecular weight (LMW,-5 kDa) and high molecular weight (HMW,-135 kDa) chitosan, we obtained several DA ranges through a reacetylation method. The interactions of LMW chitosan were greatly influenced by the intrinsic charge of the chitosan units, whereas for HMW chitosan, chain flexibility was found to be the major factor affecting molecular interaction Taken together, our comprehensive data provides a holistic understanding of the interaction mechanism of chitosan

In-Depth Study of the Interaction Mechanism between the Lignin Nanofilms: Toward a Renewable and Organic Solvent-Free Binder

Lignin is an abundant biorenewable resource with an annual production of 50 million metric tons. Despite the abundance and high potential for applications, only ???2% of the produced lignin was used for industrial applications. One of the main reasons for the low applicability is the lack of fundamental studies. In particular, the molecular binding mechanism of lignin is a key for the development and design of lignin into higher-value products. In this study, the interaction forces between homogeneous lignin nanofilms as thin as a phenylpropane unit monolayer (???11 ??) are directly measured using a surface forces apparatus (SFA) at various concentrations of intervening electrolyte solution. The measured adhesion force decreases with increasing electrolyte concentration, the inverse of what would be expected according to the electric double layer theory. These findings, along with detailed analyses using Derjaguin???Landau???Verwey???Overbeek (DLVO) and hydrophobic theories, strongly indicate that hydrophobic interaction accounts for a large proportion of the interaction forces. Additional measurements between methyl-terminated self-assembled monolayer and lignin film confirm that hydrophobic interactions dominated the overall interaction potential of lignin films. Furthermore, lignin-supplemented activated carbon composites show enhanced compressive strength, which indicates the potential use of lignin as an ecofriendly reinforcing binder