Hydroxy Propylmethyl Cellulose

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Methyl cellulose and its alkaline oxide derivatives HPMC, MHEC & HBMC are non-ionic surface active water soluble polymers. This type of derivative is available in range of methyl & hydroxyalkyl substitution. The extended uniformity of methyl substitution and specific type of hydroxyalkyl substituent affects the solubility, suface activity, thermal gelation, and other properties of the polymer in the solution.

Cellulose Ether

Methyl DS

Hydroxyalkyl MS

MC

1.4-2.0

 

HPMC

1.1-2.0

0.1-1.0

MHEC

1.3-2.2

0.06-0.5

HBMC

>1.9

>0.04

 

MC with methyl DS less than about 0.6 is alkali soluble. From about 1.6-2.4 it is water soluble (most commercial grades), about 2.4, it is soluble in wide variety of organic solvents. MC solution is water start to gel at ~55oC, independent of molecular weight.

The gelation is a function of DS, rate of heating, and type and amount of additives such as salts. As the temperature increases, the viscosity initially decreases (typical behavior) and gelling temperature is reached, the viscosity sharply rises until the flocculation temperature is reached. Above this temperature the viscosity collapses. This process is reversible with temperature (110).

The mixed derivatives HPMC,MHEC & HBMC tend to precipitate rather than gel as the temperature increases. The higher the hydroxyalkyl substitution, the greater the tendency for precipitation. MHEC & HPMC tend to have higher gelation & flocculation temperature(110). The mixed derivatives are generally are more tolerant of added salts than MC itself.
HPMC & HBMC are tolerant of and are soluble in some organic solvents, especially lower alcohols & glycols.

Solution of MCs are pseudoplastic below the gel point and approach Newtonian Flow behavior at low shear rates. Above the gel point, solutions are very thixotropic because of the formation of three dimensional gel structure. Solutions are stable between pH 3.0-11.0, pH extremes will cause irreversible degradation. The higher substitution level of most MCs result in relatively good resistance to enzymatic degredation. MC & its mixed ethers are surface active cellulose ether having suface tension value as low as 44 mN/m(=dyn/cm) and interfacial tension values as low as 17 mN/m(=dyn/cm) against paraffin oil.



Cellulose Ether
( HEC, HPMC, MHEC, MC)

2% Aqueous Solution NDJ-1

2% Aqueous Solution Brookfield

60000

30000

75000

35000

100000

45000

100000

45000

150000

55000

200000

65000