Rheological Properties of Emulsions Stabilized by Cellulose Derivatives with the Addition of Ethyl Alcohol

Abstract

The paper presents the results of research on the rheological properties and stability of oil-in-water emulsions containing cellulose derivatives: methylcellulose, hydroxyethylcellulose, and hydroxypropylmethylcellulose. The continuous phase of the emulsion was a 70% ethanol (EtOH) solution by volume. The dispersed phase consisted of mineral, linseed, and canola oils (20% by volume). Rheological measurements were performed in both steady and oscillatory flow. Emulsion stability was assessed on visual observation and changes in droplet diameter over a period of 5 months after preparation. Relatively stable emulsions were obtained without the addition of low-molecular-weight surfactants, exhibiting viscoelastic properties. The presence of ethanol in the continuous phase significantly slowed down the processes of emulsion sedimentation or creaming, as well as droplet coalescence. The reasons for the slow phase separation were linked to changes in density and zero-shear viscosity of the continuous phase caused by the addition of EtOH. All emulsions were highly polydisperse, and the addition of methylcellulose and hydroxypropylmethylcellulose further led to the formation of strongly flocculated emulsions. Droplet flocculation resulted in highly viscoelastic fluids. In particular, for emulsions containing hydroxypropylmethylcellulose, the ratio of the storage modulus to the loss modulus approached a value close to 0.1, which is characteristic of gels.

Keywords: cellulose derivatives; emulsions; emulsions stability; viscoelsticity.

Figure 1

Sample photos of the emulsion taken 45 days after preparation: (a) HEC 1.5% wt./EtOH, (b) MC 1.5% wt./EtOH, (c) HPMC 0.7% wt./EtOH.

Figure 2

Viscosity curves for aqueous polymer solutions and polymers in water/ethanol mixtures (70% vol. EtOH).

Figure 3

G′ and G″ moduli (a) and tan δ = G″/G′ (b) as a function of oscillation frequency ω for polymers in water/ethanol mixtures.

Figure 4

G′ and G″ moduli and tan δ = G″/G′ as a function of oscillation frequency ω for emulsions with (a) linseed oil, (b) canola oil, (c) mineral oil.

Figure 5

Sample photos of emulsions with added polymers/EtOH mixtures and various oils after preparation: (a) HEC/EtOH—canola oil, HEC 1.5% wt., (b) HEC/EtOH—linseed oil, HEC 1.5% wt., (c) HEC/EtOH—mineral oil, HEC 1.5% wt., (d) MC/EtOH—canola oil, MC 1.5% wt., (e) MC/EtOH—linseed oil, MC 1.5% wt., (f) MC/EtOH—mineral oil, MC 1.5% wt., (g) HPMC/EtOH—canola oil, HPMC 0.7% wt., (h) HPMC/EtOH—linseed oil, HPMC 0.7% wt., (i) HPMC/EtOH—mineral oil, HPMC 0.7% wt.

Figure 6

Comparison of the dependence of complex viscosity on oscillation frequency for emulsions containing linseed oil (LO), canola oil (CO), and mineral oil (MO) (emulsions with the addition of HEC (2% wt.) and EtOH (70% vol.)).