Aggregation of modified celluloses in aqueous solution : transition from methylcellulose to hydroxypropylmethylcellulose solution properties induced by a low molecular weight oxyethylene additive

• Temperature effects on viscosity and aggregation behaviour of aqueous solutions of three different cellulose ethers: methylcellulose (MC), hydroxypropylmethylcellulose (HPMC) and ethyl(hydroxyethyl)cellulose (EHEC), were investigated using viscosity and dynamic light scattering measurements as well as Cryo-TEM. In all cases increasing temperature reduces the solvent quality of water, which induces aggregation. It was found that the aggregation rate followed the order EHEC > HPMC > MC, suggesting that cellulose ethers containing some bulky and partly hydrophilic substituents assemble into large aggregates more readly than methylcellulose. This finding is discussed in terms of the organization of the structures formed by the different cellulose ethers. The temperature-dependent association behavior of cellulose ethers was also investigated in a novel way by adding diethyleneglycolmonobutylether (BDG) to methylcellulose aqueous solutions. When the concentration of BDG was at and above 5 wt%, methylcellulose adopted HPMC-like solution behaviour. In particular, a transition temperature where the viscosity was decreasing, prior to increasing at higher temperatures, appeared and the aggregation rate increased. This observation is rationalized by the ability of the amphiphilic BDG to accumulate at non-polar interfaces, and thus also to associate with hydrophobic regions of methylcellulose. In effect BDG is suggested to act as a physisorbed hydrophilic and bulky substituent inducing similar constraints on aggregation as the chemically attached hydroxypropyl groups in HPMC and oligo(ethyleneoxide) chains in EHEC.

Ämnesord

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

NATURVETENSKAP  -- Kemi -- Fysikalisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Physical Chemistry (hsv//eng)

Nyckelord

methylcellulose

hydroxypropylmethylcellulose

ethyl(hydroxyethyl)cellulose

cellulose ethers

diethyleneglycolmonobutylether

BDG

hydrophobic interactions

aggregation

dynamic light scattering

Cryo-TEM

viscosity

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