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METHOCEL™ Binders and Additives for Water-Based Adhesives

logo-iff@2x-200px.png Water-based adhesives are one of the fastest-growing adhesive formats due to the advantages they provide in terms of safety and sustainability by eliminating VOCs and flammability risks. These adhesives are typically easy to apply and achieve the required level of durability and performance to suit a variety of applications.

METHOCEL™ for Water-Based Adhesives


METHOCEL™ is a naturally derived binder and rheology-modifying additive manufactured by IFF that has widespread utility in water-based adhesives. Produced from cellulose obtained from southern white pine or cotton linters, the METHOCEL™ product line encompasses an array of methylcellulose and hydroxypropyl methylcellulose grades. IFF maintains a large portfolio of these grades to offer water-based adhesive formulators the highest flexibility needed to customize viscosity, compatibility, and workability for their formulations.

METHOCEL™ products are preferred binders and rheology modifiers in water-based adhesives because they provide several key benefits, as follows:
 
  • Good adhesive and cohesive strength through hydrogen bonding
  • High green strength through reversible thermal gelation properties
  • Increased application efficiency through shear-thinning rheology modification

Hydrogen Bond Reactivity

Chemically, METHOCEL™ is similar in structure to cellulose but with substitutions of methyl chloride or propylene oxide and methyl chloride made to hydroxy groups to yield methylcellulose or hydroxypropyl methylcellulose respectively, as viewed in the picture below. As cellulose is not naturally water soluble, these substitutions help increase water solubility and make METHOCEL™ compatible with water-based systems.

Methocel-processing.png


Even with these substitutions, several hydroxyl groups usually do not get substituted. These remaining hydroxyl groups participate in hydrogen bonding to increase adhesive properties. Hydrogen bonding increases the cohesive strength of adhesives made using METHOCEL™ when the hydroxyl groups react with other hydroxyl groups on the METHOCEL™ polymer. Similarly, these hydroxyl groups can bond with surfaces the adhesive joins, increasing adhesion. These interactions make METHOCEL™ an ideal binder in water-based adhesive systems.

Reversible Thermal Gelation


The methoxy substitution on METHOCEL™ also provides significant green strength to adhesives through reversible thermal gelation. While METHOCEL™ is soluble in cold water, it is insoluble in water heated to 50°C–90°C, depending on the grade used. This is identified as the incipient gelation temperature. As the solution cools, the solubility of METHOCEL™ is restored, allowing for reversible gelation, as viewed in the graph below. By this mechanism, METHOCEL™ functions as a rheology modifier at colder temperatures and a gelling additive at higher temperatures.
 
Methocel-gelation.png
Gelation of 2.0% aqueous solution of METHOCEL™ A-series grade, heating at 0.25°C/min

This thermal gelation property is useful in adhesive applications since most water-based adhesives are exposed to heat to evaporate water and initiate cure. As heat is applied, the physical strength of the adhesive increases because METHOCEL™ induces gelation, allowing for higher durability in the early stages of cure, leading to better integrity after the adhesive is cured.

Shear-Thinning Rheology Modification


In cases where adhesives are applied to vertical or overhead surfaces, it is important to ensure that the adhesives do not sag or drip for efficient application and waste prevention. When METHOCEL™ is present in water-based solutions, such as a water-based adhesive, it imparts shear-thinning rheology. This shear-thinning rheology depends on the molecular weight of the METHOCEL™ polymer and the concentration present in the solution, as shown below.
 
Methocel-shear-thinning.png
Apparent viscosity versus shear rate, 2% aqueous solutions, 20°C Apparent viscosity versus shear rate for aqueous solutions of 4,000 mPa·s with various METHOCEL™ concentrations


The shear-thinning rheology that METHOCEL™ imparts is useful because it allows for easy spreading or spraying of the adhesives onto vertical or overhead surfaces under high shear. When shear is removed and the adhesive is set on the surface, the viscosity will rebuild to provide thickening, preventing the adhesive from sagging or dripping and leading to better workability and less waste.

Example Applications


The properties outlined above for METHOCEL™ make it useful for a host of water-based adhesives. Below are examples where METHOCEL™ is valued as a binder or rheology modifier in these formulations.

Latex-Based Adhesives


METHOCEL™ provides value in latex-based adhesives as a thickener to increase viscosity to the desired level while imparting shear-thinning rheology. When METHOCEL™ is added to latex-based adhesives, it also facilitates better dry times and increases wet-tack strength due to the thermal gelation properties described above. In addition, it provides better stabilization for inorganic, insoluble fillers and additives, such as pigments. Since METHOCEL™ is nonionic, it is compatible with various latex adhesive formulations.

Carpet Backsizing Compounds


These compounds are typically used with carpets made from synthetic fibers, such as nylon and polyester, to prevent dimensional shrinkage or stretching and mitigate curling during carpet installation. METHOCEL™ provides value in these compounds by thickening the adhesive to keep it within the carpet glue line instead of seeping into the carpet backing. The thermal gelation properties METHOCEL™ offers also help the adhesive set faster and dry quickly when heated.

Leather-Processing Adhesives


These adhesives are used to bond leather hides to glass or porcelain surfaces to prevent shrinkage during drying processes. Compared to starch, commonly used in these types of adhesives, METHOCEL™ provides an advantage as a rheology modifier and binder with better water retention and initiates thermal gelation, creating stronger bonds.

Plywood Laminating Adhesives


METHOCEL™ is used in adhesives to laminate plywood because they deliver excellent viscosity control and impart shear-thinning rheology, both of which increase workability. Since plywood lamination involves bonding veneers together under pressure and heat, the thermal gelation properties of METHOCEL™ increase the green strength and durability of the adhesive during assembly and early cure. Thermal gelation also helps prevent the adhesive from soaking too deeply into the veneers during curing.

Wallpaper Paste


In dry-mix wallpaper pastes, METHOCEL™ is used as the primary binder to improve wet tack. It also functions as a rheology modifier to help control viscosity to the desired level. The wet tack METHOCEL™ provides enables it to adhere various paper types to the wall while being easily repositionable prior to curing. The repositioning is possible because solutions containing METHOCEL™ also have good lubricity.

METHOCEL™ Grades


Selecting the appropriate METHOCEL™ grade depends on the viscosity requirements of the adhesive application, thermal gelation properties, and desired solution preparation technique. METHOCEL™ grades are appended with a letter indicating the polymer’s degree of methoxy and hydroxpropyl substitution, as viewed below.

Methocel-substitutions.png


In general, METHOCEL™ grades with higher methoxy content have lower thermal gelation temperatures. Thus, if thermal gelation is a property to be leveraged, grades with higher methoxy substitution should be selected. If an organic solvent will be present as a cosolvent in adhesive formulations, grades with high hydroxypropyl and methoxy substitution will have better solubility.


Apart from the substitution level, the viscosity is another determining factor in selecting a grade for thickening properties. Below is a list of select grades for adhesives with corresponding viscosities. It should be noted that the molecular weight of the polymer corresponds with the viscosity, which also corresponds with how pronounced the shear-thinning properties are. Therefore, a grade should be selected with this in mind when choosing a shear-thinning rheology modifier. Click on the grades below for a full description and more information.
 

Grade Viscosity (2% in water, cPs) Gelation Temperature (°C)
A15LV 15 50–55
A4C 400
A4M 4,000
F50 50 58–65
F4M 4,000
J12MS 12,000 62–68
J75MS 75,0000
K4M 4,000 70–90
K15M 15,000

Several other METHOCEL™ options are available. More information and a full list of METHOCEL™ grades can be found here.


The letter S in the J12MS and K75MS grade names indicates that the grade’s surface is modified with glyoxal to delay hydration until the pH is adjusted to 9. This can help with complete dispersion prior to hydration to prevent clumping. For more information on the significance of this and to help create solutions of METHOCEL™, visit this page for an instructional video.

Summary


METHOCEL™ is an ideal binder and rheology modifier additive for various water-based adhesive formulations. It is naturally derived from cellulose and enables good hydrogen bonding, thermal gelation properties, and shear-thinning rheology. These properties make METHOCEL™ ideal for adhesives because they facilitate high adhesive and cohesive strength, impart excellent green strength, and reduce dripping and sagging on overhead and vertical surfaces. Click below to request more information or a sample of METHOCEL™ for your adhesive application.

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