Adhesion Properties of Cellulose Films
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ABSTRACT The adhesion properties were evaluated for untreated and modified cellulose (cellophane) films. Several functional groups were introduced on the film surfaces by plasma based treatments. All the films were characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). AFM was employed to study the adhesion properties using both standard silicon nitride tips as well as self-assembled monolayer (SAM) modified gold coated tips containing a variety of specific functional groups. The acetone extracted cellulose films, which are rich in -OH groups, were used as substrates. The adhesion force detected with -COOH terminated AFM tips (- 34.8 nN) was much larger than that with -CH 3 terminated AFM tips (-16.7 nN), which was attributed to the hydrogen bonding between -COOH and -OH functional groups. The adhesion force of -NH 2 terminated AFM tips on the acetone extracted cellulose film was higher at 42.92 nN. However, after surface modification of the cellulose films with argon and oxygen based plasma treatments, the adhesion force were decreased to 17.4 and 19.4 nN respectively as a result of greatly enhanced surface roughness. Hydrazine plasma treatment also was used to introduce -NH 2 groups on the film surfaces, and the strongest adhesion behavior was observed with AFM tips terminated with -COOH groups on the aminated film due to acid-base interaction. The argon and oxygen plasma treatment greatly increased the surface roughness, resulting in poor adhesion properties. Both surface roughness and chemical modification of the cellophane films affected the adhesion properties as measured by AFM force curves. INTRODUCTION
Lignocellulosic fibers are being used in new biobased composite materials. The applications of these composites could be greatly expanded by property enhancement through improved bonding and adhesion of the lignocellulosic and thermoplastic polymeric materials. Evaluation of adhesion of cellulose based material is therefore very important to future applications. The atomic force microscope (AFM) is a powerful tool for surface morphology characterization through force measurements [1]. The deflection of the AFM cantilever can be used to measure the forces. In this study, the adhesion properties were evaluated for untreated and modified cellulose (cellulose) films using AFM force curves. The interaction of fibers, fines, and other colloidal components of papermaking suspensions depend on the electrostatic, hydration, Van der Waals and other force acting between particles. Neuman et al. [2, 3] have recently studied two cellulose surfaces at a distance of up to 100 nm with a surface force apparatus (SFA) and they inferred that the repulsive forces were due to the presence of dangling charged cellulose chains or molecular fibrils. However, SFA is not generally suitable for direct surface characterization of cellulose surfaces because SFA is very experimentally demanding. Due to the extreme surface roughness and chemical heterogeneity of wood fibers and fines, we used regenerated c
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