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, and while latex technology has come a long way over the last 60 years formulations still need to be optimized to meet performance criteria of consumers.  The precise control of viscosity and rheology provided by METHOCEL™ is critical  to maximizing the performance of latex paints.


What is METHOCEL™?


METHOCEL™ cellulose ethers are a family of water soluble methylcellulose (MC) and hydroxypropyl methylcellulose (HPMC) polymers that are used to effectively thicken latex paints.  Latex paints thickened with METHOCEL™ offer a number of benefits.

Stability

Expiration of latex paints is typically determined by a loss of viscosity and loss of pigment suspension.  The shelf life of latex paints can be extended when METHOCEL™ is used as a thickener and rheology modifier.  METHOCEL™ is more resistant to enzymes released by microbes than other cellulose thickeners.  This and pH stability from pH 3 to 11 allow for METHOCEL™ thickened latex paints to maintain uniform viscosity regardless of age or pH.  Additionally, latex paints that have lost viscosity due to spoilage can be rethickened with METHOCEL™ to achieve a proper and stable viscosity.

Easy Application

 Due to the pseudoplastic nature of METHOCEL™, latex paints thickened with the polymers exhibit exceptional application properties.  METHOCEL™ improves the loading of the paint onto brushes and rollers.  In addition, flow, leveling,  and spreadibility are improved due to the rheology modifier.

Film Durability

Water based architectural coatings are subjected to harsh conditions on a regular basis.  They need to be able to withstand cleaning chemicals, scrubbing, rain, and condensation.  The addition of METHOCEL™ to water based paints and coatings helps to improve the durability and resistance to chemicals and moisture.  Additionally, pin-hole formation is reduced and film uniformity is improved over surfaces with varying porosity.
 

Selecting the Proper Grade of METHOCEL™


Selection of METHOCEL™ grades is determined by two main criteria: viscosity (molecular weight) and degree of substitution.  These criteria can be identified by the nomenclature of the grade.  For example:

 

Sustitución

METHOCEL ™ son polímeros basados en celulosa que han tenido grupos funcionales hidroxilo sustituidos por grupos funcionales metoxilo e hidroxipropilo. El grado y la naturaleza de la sustitución varían y se pueden identificar por la primera letra del nombre del grado.

Quimica A E F J K
% MeO 27.5-31.5 28.0-30 27.0-30.0 16.5-20.0 19.0-24.0
% HP 0 7.0-12.0 4.0-7.5 23.0-32.0 25.0-32.0

La cantidad y el tipo de sustitución dan lugar a diferencias en la organosolubilidad y las temperaturas de gelificación térmica de los polímeros. En general, la organosolubilidad de METHOCEL ™ aumenta a medida que aumenta la sustitución de hidroxipropilo, y la temperatura de gelificación térmica de METHOCEL ™ disminuye al aumentar la sustitución de metoxilo. En las formulaciones de pintura de látex, se recomienda típicamente la química "J" y "K", ya que son compatibles con la mayoría de los codisolventes utilizados para mejorar la formación de películas.

Viscosity

The viscosity of solutions produced by METHOCEL™ in water varies from grade to grade based on the molecular weight of the polymer.  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 1000.  For example the grade listed above, J75MS, would have a viscosity of 75,000 mPa*s at 2% in water.  The viscosity of METHOCEL™ solutions will also vary based on the concentration in which they are added and the solvent selection.  The graph below shows viscosity of common METHOCEL™ grades in DI water at varying concentrations.

 

Otro factor importante a considerar con respecto a la reología de las soluciones que contienen METHOCEL ™ es que la pseudoplasticidad aumentará a medida que aumente el peso molecular del polímero y la concentración. Los gráficos a continuación resaltan esta relación.

Surface Treatment
The final attribute that needs to be considered when selecting a METHOCEL™ grade is surface treatment.  Grades of METHOCEL™ that are denoted with an "S" after the viscosity are surface treated for delayed hydration.  These will not hydrate and begin to thicken until a pH adjustment of the solution has occurred to raise the pH to 9.  This allows for the METHOCEL™ to be adequately dispersed in the solvent prior to hydration and prevents any clumping.

Preparación de Soluciones de METHOCEL ™

Polvos Sin Tratar

Los polvos METHOCEL ™ sin tratar son solubles en agua fría y algunos disolventes orgánicos; sin embargo, primero deben disolverse completamente en el agua para evitar la formación de grumos. Los polvos METHOCEL ™ no son solubles en agua caliente. La dispersión de polvos no tratados se puede realizar mezclando METHOCEL ™ con 1/3 del volumen requerido de agua calentada a 90 ° C. Una vez que el METHOCEL ™ se dispersa uniformemente, el volumen restante de agua se puede agregar como hielo o agua fría. Esto reduce la temperatura de la dispersión a la temperatura a la que el METHOCEL ™ se vuelve soluble en agua y el polvo comienza a hidratarse y aumenta la viscosidad.

 

Polvos de Superficie Tratada

Los grados de METHOCEL ™ tratados en la superficie se han tratado con glioxal y se pueden agregar directamente a sistemas acuosos de pH neutro y dispersarse con bastante facilidad con agitación suave. Una vez que la superficie tratada con METHOCEL ™ se dispersa uniformemente, la hidratación se puede activar mediante un ajuste del pH con una pequeña cantidad de base a 8.5-9.0. Una vez que se completa la hidratación, el pH del sistema se puede ajustar y debería ser estable entre 3 y 11. Debido a la facilidad de uso, los grados de METHOCEL ™ con tratamiento superficial generalmente se recomiendan para su uso en pinturas y revestimientos de látex.

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 to thicken paints and coatings METHOCEL™ offers improved stability versus other cellulose based polymers, increased dry film durability, easier brush loading, improved spreadability,a nd decreased splattering.  Contact us to discuss your upcoming architectural coating formulations or click the link below to view all commercially available grades of METHOCEL™.

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