METHOCEL™ - Thickeners for Architectural Coatings ...

Thicken Latex Paints with METHOCEL&#;

The market for architectural paints and coatings has seen substantial growth over the last decade due to growing populations, a growing housing market, and increased infrastructure spending. Increased demand for high-performance, eco-friendly coatings has driven the market toward water-based paints. While latex technology has come a long way over the last 60 years, formulations must still be optimized to meet the performance criteria of consumers. The precise control of viscosity and rheology METHOCEL&#; additives provide is critical for maximizing the performance of latex paints. 

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What Is METHOCEL&#;? 

METHOCEL&#; products are cellulose-based thickeners made of water-soluble methylcellulose (MC) and hydroxypropyl methylcellulose (HPMC), which compose a family of polymers called cellulose ethers. These water-soluble polymers are derived from cellulose that comes from natural wood or cotton linters. While these additives find use in many different applications, they are used to effectively thicken latex paints. METHOCEL&#; thickeners impart a number of benefits to paints, detailed below. 

Stability

The expiration of latex paints is typically determined by a loss of viscosity and pigment suspension. The shelf life of latex paints can be extended when METHOCEL&#; is used as a thickener and pigment stabilization additive. Although METHOCEL&#; is a cellulose-based thickener, it is more resistant to enzymes released by microbes than other cellulose-based thickeners. In addition to pH stability from pH 3 to 11, paints containing METHOCEL&#; thickeners maintain a uniform viscosity regardless of age or pH. Additionally, METHOCEL&#; thickeners can be used to boost the viscosity of latex paints that have thinned due to spoilage. 

Easy Application

Due to their pseudoplastic nature, METHOCEL&#; cellulose ethers provide more than just thickening. They impart a pseudoplastic rheology that enables the exceptional application of paints. When paints use METHOCEL&#; thickeners, viscosity increases at rest, improving the loading of the paint onto brushes and rollers when they are dipped in. When the paint is brushed or rolled onto surfaces, shear forces decrease viscosity, allowing for easier application. After the paint is applied, viscosity decreases to prevent dripping or sagging. &#;&#;&#;&#;&#;&#;&#;

Film Durability

Water-based architectural coatings are regularly subjected to harsh conditions. They need to withstand cleaning chemicals, scrubbing, rain, and condensation. METHOCEL&#; additives in water-based paints and coatings help improve paint film durability and resistance to chemicals and moisture. Addition, flow, leveling, and spreadability are also improved, reducing pinhole formation and increasing film uniformity over surfaces with varying porosity. 

Sustainability

Being derived from cellulose, METHOCEL&#; imparts bio content in formulations and provides a future-focused advantage in terms of driving product sustainability. Many other thickeners and additives that provide the functionality detailed so far are derived from nonrenewable raw materials, such as petroleum. 

Selecting the Proper Grade of METHOCEL&#;

The selection of METHOCEL&#; thickeners is governed by two main criteria: viscosity, which is associated with molecular weight, and degree of substitution. These criteria can be identified by the grade nomenclature. An example is presented below. 
 

Substitution

Chemically speaking, METHOCEL&#; cellulose ethers are cellulose polymers with hydroxyl functional groups substituted for methoxyl and hydroxypropyl functional groups. The degree and nature of cellulose functional group substitution varies and can be identified by the first letter in the name of the grade. 
  Chemistry A E F J K Methyoxyl substitution, %  27.5-31.5 28.0-30.0 27.0-30.0 16.5-20.0 19.0-24.0 Hydroxypropyl substitution, %  0 7.0-12.0 4.0-7.5 23.0-32.0 25.0-32.0
The amount and type of cellulose substitution lend to differences in the cellulose ethers' organosolubility and thermal gelation temperatures. In general, the organosolubility of METHOCEL&#; thickeners increases as hydroxypropyl substitution increases, and the thermal gelation temperature of METHOCEL&#; decreases with increasing methoxyl substitution. Organic solvents may be used in latex paint formulations to increase film-formation properties. Therefore, the &#;J&#; and &#;K&#; thickeners are typically recommended as they are compatible with most cosolvents used to improve film formation. 

Chemically speaking, METHOCEL&#; cellulose ethers are cellulose polymers with hydroxyl functional groups substituted for methoxyl and hydroxypropyl functional groups. The degree and nature of cellulose functional group substitution varies and can be identified by the first letter in the name of the grade.The amount and type of cellulose substitution lend to differences in the cellulose ethers' organosolubility and thermal gelation temperatures. In general, the organosolubility of METHOCEL&#; thickeners increases as hydroxypropyl substitution increases, and the thermal gelation temperature of METHOCEL&#; decreases with increasing methoxyl substitution. Organic solvents may be used in latex paint formulations to increase film-formation properties. Therefore, the &#;J&#; and &#;K&#; thickeners are typically recommended as they are compatible with most cosolvents used to improve film formation.

Viscosity

The viscosity of solutions produced by METHOCEL&#; in water varies from grade to grade based on the molecular weight of the polymer. Many options exist to provide the paint formulator with the right level of thickening needed per application. The mean viscosity of a solution of 2% METHOCEL&#; in water is reported in each grade by a number and a "multiplier" letter, with C being 100 and M being .  For example, the grade listed above, J75MS, would have a viscosity of 75,000 mPa*s at 2 wt% in water.  The viscosity of solutions thickened with METHOCEL&#; will also vary based on the concentration in which they are added and the solvent(s) used.  The graph below shows the viscosity imparted by common METHOCEL&#; grades in DI water at varying concentrations.

 

Another important factor to consider regarding the rheology of solutions containing METHOCEL&#; is that pseudoplasticity will increase as the polymer&#;s molecular weight and concentration increase. This means that the viscosity of solutions with higher&#;molecular weight METHOCEL&#; thickeners will become lower as shear increases. The graphs below highlight this relationship. 

 

 

Surface Treatment

The final attribute to consider when selecting a METHOCEL&#; grade is the surface treatment. METHOCEL&#; cellulose ethers denoted with an &#;S&#; after the &#;multiplier&#; letter for viscosity have a glyoxal surface treatment applied to the cellulose polymer for delayed hydration. Here, the cellulose polymer will only begin to hydrate and provide thickening after the pH is adjusted to at least 9. This allows for METHOCEL&#; to be adequately dispersed in the solvent prior to hydration, preventing clumping and insufficient thickening of paint and coating formulations. 

Preparing Solutions of METHOCEL&#;

Untreated Powders

Untreated METHOCEL&#; powders are only soluble in cold water and some organic solvents. For water-based solutions, they must first be thoroughly dispersed to prevent clumping. METHOCEL&#; powders are not soluble in hot water. Dispersion of untreated powders can, therefore, be achieved by mixing METHOCEL&#; with one-third of the required volume of water heated to approximately 90°C. Once METHOCEL&#; is evenly dispersed, the remaining volume of water can be added as ice or cold water. This lowers the temperature to a level at which the METHOCEL&#; thickener will be water-soluble, thus allowing it to begin to hydrate and thicken the solution. 

Surface Treated Powders

Surface-treated METHOCEL&#; thickeners can be added directly to pH-neutral aqueous systems and dispersed rather easily with mild agitation. Once the surface-treated METHOCEL&#; is evenly dispersed, hydration can be triggered by adjusting the pH to 8.5&#;9.0 with a small amount of alkali. Once hydration is complete, the pH of the system can be readjusted. Solutions with METHOCEL&#; are stable from pH 3 to 11. Due to the relative ease of preparation, surface-treated grades of METHOCEL&#; are typically recommended for use in latex paints and coatings. 

Conclusion

METHOCEL&#; cellulose ethers are a useful tool for formulators of water-based architectural paints and coatings to optimize and control the viscosity and rheology of formulations. When used as thickening additives in paints and coatings, METHOCEL&#; offers improved viscosity and pigment stability, increased dry film durability, easier brush loading, improved spreadability, and decreased dripping and sagging. Being cellulose-based polymers, METHOCEL&#; also increases the bio content in paint and coating formulations.

METHOCEL&#; cellulose ethers are a useful tool for formulators of water-based architectural paints and coatings to optimize and control the viscosity and rheology of formulations. When used as thickening additives in paints and coatings, METHOCEL&#; offers improved viscosity and pigment stability, increased dry film durability, easier brush loading, improved spreadability, and decreased dripping and sagging. Being cellulose-based polymers, METHOCEL&#; also increases the bio content in paint and coating formulations. Click here to view all the available METHOCEL&#; grades. Alternatively, contact us below to discuss the METHOCEL&#; rheology modifiers for your architectural paint formulation.

Hydroxypropyl methylcellulose (HPMC) is a polymer compound obtained by chemically modifying natural plant cellulose. It has good water solubility, non-toxicity, odorlessness and good biocompatibility. Therefore, it is widely used in paint, construction, pharmaceuticals, food and other fields. In the paint industry, HPMC plays a vital role as a thickener, which can improve the performance, stability and processing technology of paint.

1. The role of HPMC as a paint thickener

HPMC plays the following roles as a thickener in paint:

(1) Increase the viscosity of the paint

HPMC can absorb water and swell in water-based paints mainly through its polymer chain structure, increase the interaction between molecules, and thus increase the viscosity of the paint. The increase in viscosity improves the rheological properties of the paint and enhances the coating performance of the paint. Specifically, HPMC can make the brushing and spraying performance of the paint smoother and avoid excessive sagging or dripping.

(2) Improve the rheological properties of coatings

The application of HPMC in coatings can significantly improve their rheological properties, especially at high concentrations and low shear rates, and can maintain good viscosity and stability. This is very important for the processing of coatings under different process conditions, especially for the construction effect when brushing on large areas. By adjusting the concentration and molecular weight of HPMC, the fluidity of the coating can be regulated, so that it is not easy to flow too fast during use, and can maintain suitable construction properties.

(3) Improve the horizontal spreading of coatings

The thickening effect of HPMC in coatings is not only to increase viscosity, but also to improve the leveling of coatings. Horizontal spreading refers to the ability of the coating to be evenly distributed on the surface of the substrate after brushing without causing mottled or uneven phenomena. HPMC increases the surface tension and optimizes the flow characteristics of the coating, so that the coating forms a uniform and smooth coating film on the surface of the substrate.

(4) Prolong the open time of the coating

As a thickener, HPMC also has the function of prolonging the open time of the coating. The open time refers to the time that the coating remains operable during the application process. Prolonging this time helps to prevent the coating from drying too quickly during the brushing process, which leads to uneven coating or brush marks. HPMC improves the evaporation rate of the coating, allowing the water-based coating to maintain an appropriate viscosity for a longer period of time, ensuring a smoother coating process.

Additional resources:
1,3-Dimethylurea CAS# 96-31-1 - SincereChemical

For more information, please visit Hydroxypropyl Methylcellulose For Paints.

(5) Enhance the stability of the coating

The thickening effect of HPMC also helps to enhance the dispersion stability of the coating, especially in the water-based coating system, it can stabilize solid particles such as pigments and fillers, prevent sedimentation, and extend the storage period of the coating. By adjusting the molecular weight and degree of substitution of HPMC, the stability of the coating can be optimized so that it will not stratify or precipitate during long-term storage.

2. Application of HPMC in water-based coatings

Water-based coatings have been widely promoted in recent years due to their environmental protection, non-toxicity, and low pollution. The application of HPMC in water-based coatings is particularly important. It not only acts as a thickener, but also plays an important role in the following aspects:

(1) Improve fluidity and workability

The fluidity of water-based coatings is often affected by the water content and solid content. HPMC can adjust the rheology of water-based coatings to maintain a higher viscosity at low shear rates, thereby ensuring that the coating has good workability during coating. In addition, HPMC can also optimize the thixotropy of the coating, that is, the coating has a certain viscosity in a static state, but can quickly reduce the viscosity during the application process to facilitate flow.

(2) Improve the water resistance of water-based coatings

HPMC molecules contain hydrophilic groups, which can enhance the affinity of water-based coatings for water. During the drying process of the coating, HPMC can effectively reduce the problem of coating cracking caused by rapid evaporation of water, thereby improving the water resistance and adhesion of the coating.

(3) Enhance the transparency and gloss of the coating

Due to its high solubility, HPMC can help water-based coatings maintain high transparency and gloss. In some special coating applications, such as varnishes and clear coatings, the use of HPMC can maintain the clarity of the coating and improve the gloss of the final coating.

3. Application of HPMC in oil-based coatings

In oil-based coatings, HPMC is mainly used as a thickener and rheology regulator. Although HPMC itself is highly water-soluble, its good thickening effect in oil-based coatings is still widely used. In oil-based paints, HPMC can effectively adjust the viscosity of the paint, improve the brushability and sprayability of the paint, and also improve the stability of the paint, prevent pigment sedimentation, and reduce the stratification of the paint.

4. Advantages of HPMC as a thickener

Compared with traditional thickeners, the application of HPMC in paints has the following significant advantages:

Good environmental protection: HPMC is a derivative of natural cellulose and does not contain harmful substances, so it is safer to use in paints and does not pollute the environment.

Strong water solubility: HPMC has good solubility and stability in water-based paints, can provide ideal thickening effects, and will not affect other properties of the paint.

Excellent construction performance: HPMC can effectively improve the construction performance of the paint, avoid premature drying and uneven coating, and is suitable for different coating process requirements.

Improve storage stability: HPMC can stabilize the physical and chemical properties of the paint and reduce the precipitation phenomenon that may occur during storage.

As a paint thickener, HPMC can not only increase the viscosity of the paint and improve the rheology, but also enhance the stability, leveling and construction performance of the paint. It is widely used in water-based paints and oil-based paints. By adjusting its molecular structure and concentration, the performance of the coating can be flexibly adjusted to meet the production needs of different types of coatings. With the increasing demand for environmentally friendly and low-pollution coatings, the application prospects of HPMC will be broader and it will become one of the key functional additives in the coatings industry.

If you want to learn more, please visit our website HPMC For Tile Adhesive.