Effect of Hydrophilic and Hydrophobic Interactions on the Rheological Behavior and Microstructure of a Ternary Cellulose Acetate System

Abstract

The effect of hydrophilic and hydrophobic interactions on the rheological and microstructural behavior of cellulose acetate (CA) in a ternary CA, N,N-dimethylacetamide (DMA), nonsolvent (alcohol) system was examined. Increasing nonsolvent concentration increased the viscosity and dynamic viscoelastic properties of the system. At a critical nonsolvent concentration, a sol-gel transition was observed, which was dependent on nonsolvent structure. Increasing the available hydrogen bonding groups within the nonsolvent led to higher modulus (stronger gels) and a sol-gel transition at lower nonsolvent concentration. Likewise, increasing the alkyl chain length (hydrophobicity) of the nonsolvent also enhanced the viscoelastic properties; however, hydrogen bonding, specifically the ability to hydrogen bond donate was critical for gel formation. For all gels studied, the elastic modulus shifts to higher values with increasing hydrophilicity and hydrophobicity of the nonsolvent and exhibits a power-law behavior with nonsolvent content. All of the gels exhibit similar fractal dimensions; however, confocal images of the different systems reveal distinct differences. Increasing the hydrophilicity of the nonsolvent led to a more uniform denser gel microstructure, whereas increasing the hydrophobicity resulted in a larger more heterogeneous network structure despite the increase in moduli.

Effect of processing conditions on gel formation in ternary cellulose acetate systems

“…The ternary systems exhibited Newtonian behaviour at low shear stress followed by shear thinning as shear stress increased ( Fig. 1), consistent with previously reported results (Appaw et al 2007;Kadla and Korehei 2010).…”

Controlled Morphology and Mechanical Characterisation of Electrospun Cellulose Acetate Fibre Webs

“…The presence of hydroxyl and acetyl groups in CA gives rise to strong intra-and intermolecular interactions, predominately H-bonding. Intermolecular H-bonding results in bridging the adjacent CA structural entities [16]. With concentrations less than 13% (w/v), it is proposed that the interactions between adjacent CA molecules (intermolecular H-bonding) are not strong enough for fibre formation that is, the critical chain entanglement concentration for fibre formation was not reached.…”

Modification of Thermal and Mechanical Properties of PEG-PPG-PEG Copolymer (F127) with MA-POSS

“…Elevated temperatures increased the thermal energy for polymer chain rearrangement and where the mPEG- g -chitosan sol-gel transition driven by hydrophobic interactions, the mPEG- g -chitosan chains formed aggregates, resulting in the formation of a gel network. A study by Kadla and Korehei explained the effect of hydrophilic and hydrophobic interactions on rheological behaviour and gel microstructure [6]. Increasing the alkyl chain length (hydrophobicity) enhanced the viscoelastic properties and resulted in a larger, more heterogeneous, network structure despite the increase in moduli.…”