Hypromellose
Encyclopedia
Hypromellose short for hydroxypropyl methylcellulose (HPMC), is a semisynthetic, inert, viscoelastic polymer
used as an ophthalmic lubricant, as well as an excipient
and controlled-delivery component in oral medicaments, found in a variety of commercial products.
As a food additive
, hypromellose is an emulsifier, thickening
and suspending agent, and an alternative to animal gelatin. Its Codex Alimentarius
code (E number
) is E464.
s when dissolved in water. Although non-toxic, it is combustible and can react vigorously with oxidising agents.
Hypromellose in an aqueous solution, unlike methylcellulose
, exhibits a thermal gelation property. That is, when the solution heats up to a critical temperature
, the solution congeals into a non-flowable but semi-flexible mass. Typically, this critical (congealing) temperature is inversely related to both the solution concentration of HPMC and the concentration of the methoxy group within the HPMC molecule (which in turn depends on both the degree of substitution of the methoxy group and the molar substitution. That is, the higher the concentration of the methoxy group, the lower the critical temperature. The inflexibility/viscosity
of the resulting mass, however, is directly related to the concentration of the methoxy group (the higher is the concentration, the more viscous or less flexible is the resulting mass).
scientists are investigating using the plant-derived HPMC as a substitute for gluten
in making all-oat and other grain breads. Gluten, which is present in wheat, rye and barley is absent (or present only in trace quantities) in oat and other grains. Like gluten, HPMC can trap air bubbles formed by the yeast in bread dough, causing the bread to rise. Although it has not been widely studied, it is predicted that whole grain breads made with HPMC will have cholesterol-lowering effects. http://www.ars.usda.gov/is/pr/2010/100225.htm
Functionally HPMC is very similar to HEMC (hydroxy ethyl methyl cellulose) Trade names include Methocel and Walocel. The global leading producer is Dow Wolff Cellulosics GmbH.
in oral tablet and capsule formulations, where, depending on the grade, it functions as controlled release agent to delay the release of a medicinal compound into the digestive tract.
It is also used as a binder and as a component of tablet coatings.
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
used as an ophthalmic lubricant, as well as an excipient
Excipient
An excipient is generally a pharmacologically inactive substance used as a carrier for the active ingredients of a medication. In many cases, an "active" substance may not be easily administered and absorbed by the human body; in such cases the substance in question may be dissolved into or...
and controlled-delivery component in oral medicaments, found in a variety of commercial products.
As a food additive
Food additive
Food additives are substances added to food to preserve flavor or enhance its taste and appearance.Some additives have been used for centuries; for example, preserving food by pickling , salting, as with bacon, preserving sweets or using sulfur dioxide as in some wines...
, hypromellose is an emulsifier, thickening
Thickening agent
Thickening agents, or thickeners, is the term applied to substances which increase the viscosity of a solution or liquid/solid mixture without substantially modifying its other properties; although most frequently applied to foods where the target property is taste, the term also is applicable to...
and suspending agent, and an alternative to animal gelatin. Its Codex Alimentarius
Codex Alimentarius
The Codex Alimentarius is a collection of internationally recognized standards, codes of practice, guidelines and other recommendations relating to foods, food production and food safety. Its name derives from the Codex Alimentarius Austriacus...
code (E number
E number
E numbers are number codes for food additives that have been assessed for use within the European Union . They are commonly found on food labels throughout the European Union. Safety assessment and approval are the responsibility of the European Food Safety Authority...
) is E464.
Chemistry
Hypromellose is a solid, and is a slightly off-white to beige powder in appearance and may be formed into granules. The compound forms colloidColloid
A colloid is a substance microscopically dispersed evenly throughout another substance.A colloidal system consists of two separate phases: a dispersed phase and a continuous phase . A colloidal system may be solid, liquid, or gaseous.Many familiar substances are colloids, as shown in the chart below...
s when dissolved in water. Although non-toxic, it is combustible and can react vigorously with oxidising agents.
Hypromellose in an aqueous solution, unlike methylcellulose
Methylcellulose
Methyl cellulose is a chemical compound derived from cellulose. It is a hydrophilic white powder in pure form and dissolves in cold water, forming a clear viscous solution or gel. It is sold under a variety of trade names and is used as a thickener and emulsifier in various food and cosmetic...
, exhibits a thermal gelation property. That is, when the solution heats up to a critical temperature
Critical point (thermodynamics)
In physical chemistry, thermodynamics, chemistry and condensed matter physics, a critical point, also called a critical state, specifies the conditions at which a phase boundary ceases to exist...
, the solution congeals into a non-flowable but semi-flexible mass. Typically, this critical (congealing) temperature is inversely related to both the solution concentration of HPMC and the concentration of the methoxy group within the HPMC molecule (which in turn depends on both the degree of substitution of the methoxy group and the molar substitution. That is, the higher the concentration of the methoxy group, the lower the critical temperature. The inflexibility/viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
of the resulting mass, however, is directly related to the concentration of the methoxy group (the higher is the concentration, the more viscous or less flexible is the resulting mass).
Uses
There are many fields of application for hypromellose. These are not limited to the following:- Tile Adhesives
- Cement renders
- Gypsum products
- Pharmaceutical
- Paints & Coatings
- Food
- Cosmetics
- Detergents & cleaners
- Eye Drops
Use in whole grain breads
Agricultural Research ServiceAgricultural Research Service
The Agricultural Research Service is the principal in-house research agency of the United States Department of Agriculture . ARS is one of four agencies in USDA's Research, Education and Economics mission area...
scientists are investigating using the plant-derived HPMC as a substitute for gluten
Gluten
Gluten is a protein composite found in foods processed from wheat and related grain species, including barley and rye...
in making all-oat and other grain breads. Gluten, which is present in wheat, rye and barley is absent (or present only in trace quantities) in oat and other grains. Like gluten, HPMC can trap air bubbles formed by the yeast in bread dough, causing the bread to rise. Although it has not been widely studied, it is predicted that whole grain breads made with HPMC will have cholesterol-lowering effects. http://www.ars.usda.gov/is/pr/2010/100225.htm
Use in construction materials
HPMC, sometimes known as Hypromellose, is used primarily in construction materials like tile adhesives and renders where it is used as a rheology modifier and water retention agent.Functionally HPMC is very similar to HEMC (hydroxy ethyl methyl cellulose) Trade names include Methocel and Walocel. The global leading producer is Dow Wolff Cellulosics GmbH.
Ophthalmic applications
Hypromellose solutions were patented as a semisynthetic substitute for tear-film. Its molecular structure is predicated upon a base celluloid compound that is highly water soluble. Post-application, celluloid attributes of good water solubility reportedly aids in visual clarity. When applied, a hypromellose solution acts to swell and absorb water, thereby expanding the thickness of the tear-film. Hypromellose augmentation therefore results in extended lubricant time presence on the cornea, which theoretically results in decreased eye irritation, especially in dry climates, home, or work environments. On a molecular level, this polymer contains beta-linked D-glucose units that remain metabolically intact for days to weeks. On a manufacturing note, since hypromellose is a vegetarian substitute for gelatin, it is slightly more expensive to produce due to semisynthetic manufacturing processes. Aside from its widespread commercial and retail availability over the counter in a variety of products, Hypromellose 2% solution has been documented to be used during surgery to aid in corneal protection and during orbital surgery.Excipient/tableting ingredient
In addition to its use in ophthalmic liquids, hypromellose has been used as an excipientExcipient
An excipient is generally a pharmacologically inactive substance used as a carrier for the active ingredients of a medication. In many cases, an "active" substance may not be easily administered and absorbed by the human body; in such cases the substance in question may be dissolved into or...
in oral tablet and capsule formulations, where, depending on the grade, it functions as controlled release agent to delay the release of a medicinal compound into the digestive tract.
It is also used as a binder and as a component of tablet coatings.
Test Methods
Various benchmark tests are used to qualify hypromellose:- ViscosityViscosityViscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
- Degree of substitution (DS)
- Molar substitution (MS)
- Salt content
- Moisture
Viscosity test methods
Because hypromellose solution is a non-newtonian solution and exhibits pseudoplastic, more specifically, thixotropic behavior, various test methods are available, and the results of different methods and viscosmeters do not necessarily correspond to each other. Also, due to viscometer acceptable ranges of error, viscosity is typically given as a mean, or as a range. Typical viscosity test will specify the following:- Solution concentration (1%, 2%, 1.9% bone dry, etc.)
- Viscometer (Brookfield LV or RV, Höppler falling ball, Haake Rotovisco, etc.)
- Viscometer spindle number (1 ~ 4 for Brookfield LV, 1 ~ 7 for Brookfield RV, etc.)
- Solution Temperature (20 °C, 25 °C, etc.)