The Thickening Duo: HEC vs HPMC in Paint Applications

Hydroxyethyl Cellulose (HEC) and Hydroxypropyl Methylcellulose (HPMC) are two titans in the world of thickeners, finding applications in everything from food additives to pharmaceuticals. But where they truly shine is in the world of paints. Both derived from cellulose, a natural polymer found in plants, they play a crucial role in influencing the consistency, workability, and overall performance of paints. However, the choice between HEC and HPMC for paint formulations hinges on understanding their subtle differences.

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The Allure of HEC: Solubility and Stability

HEC enjoys a certain popularity in paint formulations due to its superior water solubility compared to HPMC. This translates to a quicker and more consistent thickening effect, a valuable asset in production settings. Especially in water-based paints, faster and more even dispersion of the thickener leads to a smoother and more predictable paint consistency.

Beyond initial solubility, HEC boasts impressive viscosity stability. Paints are often exposed to a range of temperatures and pH levels during storage and application. HEC maintains a consistent level of thickness across this spectrum, ensuring the paint retains its desired flow and application characteristics. This stability becomes especially crucial for paints designed for diverse environments or those requiring extended shelf life.

Shear-Thinning Magic

Painters appreciate HEC for its shear-thinning behavior. This fancy term simply means that the viscosity of HEC decreases when subjected to shear stress, like brushing or rolling. In simpler terms, the paint flows more easily during application, making it easier to spread evenly. Once the shear stress is removed, the viscosity recovers, ensuring the paint stays put on the surface after application. This shear-thinning property allows for smooth application without compromising the paint&#;s ability to adhere and cover the surface.

Cost Consideration

Economics sometimes play a role in material selection. In certain paint formulations, HEC might be the more cost-effective option compared to HPMC. This factor, combined with its favorable solubility and viscosity profile, often makes HEC the preferred choice for paint manufacturers.

HPMC: A Worthy Contender

While HEC shines in specific areas, HPMC shouldn&#;t be underestimated.  It excels in providing excellent thickening properties and can be a suitable choice for specific paint formulations.

Here&#;s where a deeper understanding of HPMC&#;s strengths becomes valuable:

• Water Resistance: HPMC exhibits better water resistance compared to HEC. This characteristic might be advantageous for paints intended for exterior applications or environments with high humidity, where water absorption could compromise the paint&#;s integrity.
• Adhesion Promotion: HPMC can enhance the adhesion properties of paints, potentially improving their ability to bond to various surfaces. This could be beneficial for specific situations where better adhesion is crucial.

The Final Verdict: A Balancing Act

The choice between HEC and HPMC for paint formulations doesn&#;t have a clear-cut winner. It depends on the specific requirements of the paint and the desired properties. Here are some key factors to consider.

• Viscosity Profile: Does the paint require a consistent viscosity across a range of temperatures and pH levels? Or is shear-thinning behavior for better application crucial?
• Water Resistance: Is the paint intended for a high-humidity environment or exterior use where water resistance is a concern?
• Adhesion Needs: Does the paint require enhanced adhesion to a specific surface?
• Cost Considerations: Does the budget favor a more cost-effective option?

Choosing the Right Thickener

HEC and HPMC offer a diverse set of thickening properties for paint formulations. By understanding their individual strengths and weaknesses, paint manufacturers can make informed decisions to achieve the desired consistency, workability, and performance for their specific paints. Ultimately, the right choice lies in carefully evaluating the paint&#;s intended application and desired characteristics to select the thickener that delivers optimal results.

in this artical, we mainly talk about the application of HPMC in the coating and how does it work.

Hydroxypropyl methyl cellulose (HPMC) belongs to the group of cellulose ethers in which hydroxyl groups have been substituted with one or more of the three hydroxyl groups present in the cellulose ring. HPMC is hydrophilic (water-soluble), a biodegradable, and biocompatible polymer having a wide range of applications in constructions, dyes and paints, adhesives, coatings, agriculture, and textiles. HPMC is also soluble in polar organic solvents, making it possible to use both aqueous and nonaqueous solvents. It has unique solubility properties with solubility in both hot and cold organic solvents. HPMC possesses increased organo-solubility and thermo-plasticity compared to other methylcellulose counterparts. It forms a gel upon heating with a gelation temperature of 75&#;&#;90&#;.(From: sciencedirect)

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As the performance of hydroxypropyl methyl cellulose (HPMC) is similar to other water-soluble ethers, it can be used as a film-forming agent, thickener, emulsifier, and stabilizer for latex coatings and water-soluble resin coatings so that the coating film has good abrasion resistance, leveling, and adhesion, thereby improving its surface tension, stability to acids and alkali and compatibility with metallic pigments. Because HPMC has a higher gel point than MC, it has stronger resistance to bacterial erosion than other cellulose ethers. HPMC in the coating can be used as a thickener for water emulsion paints. HPMC also has good viscosity storage stability and dispersibility, so it is particularly suitable as a dispersant in emulsified coatings.

Examples of HPMC in the coatings industry are as follows:

The coatings prepared by hydroxypropyl methyl cellulose (HPMC) with various viscosities have good abrasion resistance, high-temperature resistance, anti-bacterial degradation, washing resistance, and acid-base stability; HPMC in the coating can also be used as a thickener for paint removers containing methanol, ethanol, propanol, isopropanol, ethylene glycol, acetone, methyl ethyl ketone or diketone alcohol; The emulsified paint prepared by HPMC has excellent wet abrasiveness; HPMC in the coating is better than HEC, MHEC, and CMC as coating thickeners.

HPMC in the coating with a high degree of substitution (DS is 1.76~2.15) has better anti-bacterial corrosion resistance than the low degree of substitution. It has stable viscosity when used in polyvinyl acetate thickener. Other cellulose ethers reduce the viscosity of the coating due to chain degradation during storage.

Paint remover can be formulated with water-soluble HPMC (28%~132% of methoxyl and 7%~12% of hydroxypropyl), dichloromethane toluene, paraffin, ethanol, methanol, and applied to a vertical surface with the required viscosity and volatility.

This paint remover can remove most conventional spray paints, varnishes, enamels, and certain epoxy esters, epoxy amides, catalyzed epoxy amides, acrylic esters, etc. Many paints can peel off within a few seconds, and some paints take 10-15 minutes or more. This paint remover is particularly suitable for wood surfaces.

The water emulsion paint can be composed of 100 component inorganic or organic pigments, 0.5-20 component of water-soluble alkyl cellulose or hydroxyalkyl cellulose, and 0.0-5 component of polyoxyethylene ether or ether ester. For example, 1.5 component of HPMC, 0.05 component of polyethylene glycol alkyl phenyl ether, 99.7 component of titanium dioxide, and 0.3 component of carbon black are mixed to obtain the colorant. Then stir the mixture with 10 of 50% solids polyvinyl acetate to get a coating and apply it on thick paper with a brush to form a dry film without any differences.

MelaColl&#; HPMC in  the Coating Industry

Our MelaColl&#; HPMC products provide the following features for coating applications:

• Improve water retention, sag resistance, crack resistance, and thickening effect.
• Enhance the adhesion of putty to various substrates
• Improve the consistency and stability of putty
• Provides putty with good workability
• Improves open time
• Improves hydrophobicity

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