"HPMC" redirects here. For other uses, see HPMC (disambiguation)
Hypromellose (INN), short for hydroxypropyl methylcellulose (HPMC), is a semisynthetic, inert, viscoelastic polymer used in eye drops, as well as an excipient and controlled-delivery component in oral medicaments, found in a variety of commercial products.[1][2]
As a food additive, hypromellose is an emulsifier, thickening and suspending agent, and an alternative to animal gelatin.[3] Its Codex Alimentarius code (E number) is E464.
Chemistry
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Hypromellose is a solid, and is a slightly off-white to beige powder in appearance and may be formed into granules. The compound forms colloids when dissolved in water. This non-toxic ingredient is combustible and can react vigorously with oxidizing agents.[4]
Hypromellose in an aqueous solution, like 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 the concentration is, the more viscous or less flexible the resulting mass is)[citation needed].
Uses
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There are many fields of application for hypromellose, including:[5]
Use in whole grain breads
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Agricultural Research Service scientists are investigating using the plant-derived HPMC as a substitute for gluten in making all-oat and other grain breads.[citation needed] 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.
Use in construction materials
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HPMC is used primarily in construction materials like tile adhesives and renders[7] 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 now DuPont, formerly manufactured under Dow Wolff Cellulosics GmbH.[8]
Ophthalmic applications
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Hypromellose solutions were patented as a semisynthetic substitute for tear-film.[9] Its molecular structure is predicated upon a base celluloid compound that is highly water-soluble. Post-application, celluloid attributes of good water solubility reportedly aid 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.[10] 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
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In addition to its use in ophthalmic liquids, hypromellose has been used as an excipient 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.[11] It is also used as a binder[12] and as a component of tablet coatings.[13][14]
Test methods
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Various benchmark tests are used to qualify hypromellose:
Viscosity test methods
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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 viscosimeters 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:
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Degree of substitution
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Degree of substitution is the average level of methoxy substitution on the cellulose chain. Since there are maximum three possible sites of substitution with each cellulose molecule, this average value is a real number between 0 and 3. However, degree of substitution is often expressed in percentages.
Molar substitution
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Molar substitution is the average level of hydroxypropoxy substitution on the cellulose chain. Since hydroxypropoxy base can be attached to each other on side chains and does not each require a base substitution site on the cellulose molecule, this number can be higher than 3. However, molar substitution is also often expressed in percentages.
Moisture
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Since all cellulose ethers are hygroscopic, they will absorb moisture from surroundings if left exposed from original packaging. Thus, moisture must be tested and weight corrected to ensure adequate amount of dry active material are apportioned for usage. Moisture is tested by weighing a sample of X grams on an analytic scale, and drying the sample in an oven at 105 °C for 2 hours, then weighing the sample again on the same scale.
See also
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References
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The construction industry has experienced massive growth in incorporating new materials to enhance the output and overall performance of construction products. Among such trendy innovations is the gypsum plaster.
However, one of the ingredients that serve as the gypsum plaster&#;s bedrock, particularly in stability and thickening property, is cellulose.
In this article, we&#;ll briefly examine the roles of Hydroxypropyl Methyl Cellulose &#;HPMC&#;in the production of gypsum plaster.
Before we dive in, let&#;s quickly integrate you with gypsum plaster and the characteristics of Hydroxypropyl Methyl Cellulose &#;HPMC&#;.
What is Gypsum Plasters?
Widely known as hydrous calcium sulfate among chemists, gypsum itself is a water-soluble naturally occurring mineral. It exists freely in nature as crystals and can be located among layers of limestone and shale.
On the other hand, gypsum plaster is produced by heating gypsum at a very minimal temperature to achieve evaporation. The dehydrated gypsum known as Plaster of Paris (POP) is pulverized and heated at about 150&#;. The dry POP powder hardens when you add water to form gypsum plaster. The concentration can be applied over concrete, brick, or block to further strengthen it.
Characteristics of Cellulose&#;HPMC&#;
HPMC cellulose exists as white, non-ionic cellulose ether. In its powdery form, it&#;s odorless and tasteless. It&#;s soluble in water and other organic content such as ethanol, propanol, and dichloroethane. However, it is insoluble in acetone, diethyl ether, and anhydrous alcohol.
When in an aqueous solution, HPMC offers high stability, transparency, and surface activity. Heating makes the Hydroxypropyl Methyl Cellulose (HPMC) precipitate for gels due to its thermal gelation properties.
How does cellulose work in gypsum products?
1. High water retention
Hydroxypropyl Methyl Cellulose &#;HPMC&#;has a high water-holding capacity. This attribute makes it useful to improve resistance, prevent cracking, and enhance gypsum plaster&#;s overall appearance. It also boosts surface uniformity, lubrication, and adhesion when applied to gypsum plaster in putty and other construction works.
2. Thickening property
Hydroxypropyl Methyl Cellulose &#;HPMC&#;is the right material for you if you want to increase the tensile strength of gypsum plaster and other construction material. It acts as an interface agent. That is, it improves gypsum plaster flexural strength and increases bonding strength.
3. Highly stable
Hydroxypropyl Methyl Cellulose &#;HPMC&#;'s outstanding film-forming properties and high resistance to degrading enzymes help stabilize gypsum plaster pH and enhance its salt discharge performance.
Others include dispersibility, constructability, and adhesive strength. Also, Hydroxypropyl Methyl Cellulose &#;HPMC&#;has effects on the setting time, pumpability, and workability of gypsum plaster composition. Overall, it enhances construction efficiency and guides against weathering after exposure of building surfaces to water-soluble salts.
All these make Hydroxypropyl Methyl Cellulose &#;HPMC&#;an integral part of the gypsum plaster every construction worker must-have.
To order your cellulose, Michem Chemicals is your one-stop shop for quality Hydroxypropyl Methyl Cellulose &#;HPMC&#;and other construction products. Check-in-here with us today to book a free session with our experts for your Construction-Chemicals material needs.
The company is the world’s best Hydroxypropyl Methylcellulose For Gypsum Plasters supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.