Methyl Hydroxy Ethyl Cellulose (MHEC)

MHEC or HEMC is a non-anionic cellulose ether which is produced by reaction of alkali cellulose with Methylene Chloride and Ethylene Oxide under a pressure reactor in the absence of air at about 40 deg to 50 deg celsius. Then the reactor is vented, excess NaOH is neutralized and purified by appropriate means. After purification, cellulose is dried, granulated or grounded or surface treated according to the requirements.

MHEC is used as a water retaining agent in various construction applications like cement based wall putty, gypsum based wall putty, cement motors, gypsum spray plasters, tile adhesives.

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Derivatives

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.

Molar & Degree of Substitution

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

Solubility

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.

Gelation

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).

Mixed Methyl Cellulose Ethers

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.

Rheology

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.

Viscosity Chart



Cellulose Ether
( HEC, HPMC, MHEC )

2% Viscosity NDJ-1

2% Viscosity Brookfield RV

2% Viscosity Hoppler

60000 cP

30000 cP

60000 cP

75000 cP

35000 cP

75000 cP

100000 cP

45000 cP

100000 cP

150000 cP

55000 cP

150000 cP

200000 cP

65000 cP

200000 cP