ACULYN(TM) 28 Rheology Modifier

ACULYN™ 28 Rheology Modifier is a Hydrophobically-modified Alkali Soluble Emulsion (HASE). HASE polymers are synthesized from an acid/acrylate copolymer backbone and a monomer that connects the hydrophobic groups as side chains. The polymer is made through emulsion polymerization.

ACULYN™ 28 Rheology Modifier is synthesized from acrylic acid, acrylate esters and a beheneth-20 methacrylate ester. The general structure for ACULYN™ 28 Rheology Modifier is shown to the right.

R_x = Acyl chain from 1 to 18 carbons

• ACULYN™ HASE rheology modifiers are able to thicken by two mechanisms that can act simultaneously and are synergistic, i.e. by the effect of charge-induced polyelectrolytic chain extension and by association of hydrophobe groups.
• When the acid groups present in the ACULYN™ HASE molecules are neutralized with inorganic bases or organic amines, they become anionically charged and water-soluble. ACULYN™ 28 Rheology Modifier thickens above pH 5.5. ACULYN™ HASE rheology modifiers dissolve and swell due to charge-charge repulsion.
• When ACULYN™ HASE polymers swell, the pendant hydrophobic groups are free to build associations with one another and with other hydrophobes available in the formulation, such as surfactants, particulates, emulsion droplets and dyes. This phenomenon creates a network structure that results in a significant viscosity build.

These associative structures can also act to stabilize and disperse particulates in a formulation.

And because of the ethoxylated hydrophobic group on the rheology modifier, ACULYN 28 can also act as a primary emulsifier for some emulsion systems, such as water resistant sunscreens, to minimize the level of surfactant or emulsifier.

ACULYN™ 28 Rheology Modifier possesses many properties that make this polymer highly desirable for use in personal care, as shown by the data presented below.

Rheology

• The highly associative nature of ACULYN™ 28 Rheology Modifier has a significant affect on the viscosity of formulations, one that is much stronger than that created by the addition of electrolytes.
• The presence of the C22 hydrophobe causes solutions of ACULYN™ 28 Rheology Modifier to be very pseudoplastic with a high yield value, in general showing a high degree of shear thinning. The high yield value also allows the thickener to stabilize suspensions while still being pourable.
• In applications such as two part hair dye products, the shear profile allows for easy application with penetration of the dye, while reducing the dripping or running of hair dye products when developed and applied to the scalp.
• The shear thinning behavior in the following graph is measured in water and the behavior can change in formulations.

Effect of Shear on ACULYN™ 28 Rheology Modifier at Various Concentrations

In the above graph, the sheer profile is shown for various concentrations of ACULYN™ 28 Rheology Modifier (as solid polymer) using a Brookfield Rheometer.

Compatibility

Salt Tolerance

ACULYN™ 28 Rheology Modifier exhibits outstanding salt tolerance. The polymer can significantly build viscosity even in the presence of 1.6% sodium chloride. This performance attribute makes ACULYN™ 28 Rheology Modifier the ingredient of choice in formulations that contain high levels of electrolytes, such as shampoos and shower gels, when the sodium salts of surfactants are employed, or when some raw materials have salt as a trace component.

Effect of Salt Concentration on Gel Viscosity of ACULYN™ 28 Rheology Modifier

• Polymer concentration: 0.7% solids
• Neutralized with ammonium hydroxside to pH 8.5
• Brookfield LVT, 12 rpm, LV spindle set

pH Tolerance

The thickening effect of ACULYN™ 28 Rheology Modifier develops above pH 5.5, when the polymer becomes solubilized and polymer chain extension occurs. In the following graph, where ammonium hydroxide was used as the neutralizing base, the viscosity reaches a maximum and remains steady over a pH range from 6 to 12. This profile will be similar for any neutralizing base.

Profile for Viscosity Versus pH for ACULYN™ 28 Rheology Modifier

19% polymer solids aqueous solutions neutralized with hydroxide, Brookfield RVT DV I, 10 rpm, Heliopath spindle set.

Surfactant Synergies

• Given that ACULYN™ 28 Rheology Modifier is an associative thickener, its thickening efficiency can be significantly affected by the presence of surfactants. The type of surfactant and its concentration play a key role in the rheological properties of the polymer-surfactant system. The measurements of viscosity vs. surfactant concentration generally show an increase in viscosity for ACULYN™ 28 Rheology Modifier-surfactant systems.
• A nonionic surfactant with a high HLB (Hydrophobic Lipophilic Balance), such as C9-11 pareth-12, typically produces a significant increase in viscosity at low concentrations of surfactant that decreases at higher surfactant concentrations. A nonionic surfactant with a low HLB, such as C14-15 pareth-74, leads to a gradual increase in viscosity, which will remain at a higher level even at higher surfactant concentrations.
• In the case of an anionic surfactant such as Sodium Laureth Sulfate (SLES), there is usually a small increase in viscosity at very low surfactant concentrations followed by a gradual decrease at higher surfactant concentrations. The longer alkyl chain in ACULYN™ 28 Rheology Modifier reduces the decrease as compared to many other rheology modifiers.

Clarity in the Presence of Surfactants

Solutions of ACULYN™ 28 Rheology Modifier and various surfactants maintain their clarity. The table on the next page shows the clarity of solutions as can be seen from the NTU (Nephelometric Turbidity Units) readings above for each of the polymer / surfactant solutions. A solution with a reading below 10 NTUs would be clear. The pH of these solutions was adjusted to 8.5 with ammonium hydroxide, and each system was equilibrated to 20 to 25°C.

Clarity of ACULYN™ 28 Rheology Modifier (1% Active) with Different Surfactants

1. NTU = Nephelometric Turbidity Units, a measure of clarity. Lower numbers correspond to a higher degree of clarity.
A reading of 0 to 10 is clear, 10-20 is almost clear, 20-50 has a slight haze.

Performance

Extremely Efficient Thickener

The viscosity of neutralized aqueous solutions of ACULYN™ 28 Rheology Modifier as a function of the concentration of solids is shown in the graph opposite. The viscosity of solutions increases with increasing concentration, but even at low concentrations, the viscosity is increased significantly with ACULYN™ 28 Rheology Modifier.

Viscosity of Neutralized ACULYN™ 28 Rheology Modifier with Increasing Concentration

Polymer aqueous solutions neutralized with hydroxide to pH 8.5, Brookfield RVT DV II, 10 rpm, Heliopath spindle set

Clarity of Solutions

The formulation of crystal clear gel products for hair and skin is an important global trend. Based on the low NTU values of the instrumental transparency measurements of aqueous ACULYN™ 28 Rheology Modifier gels, we recommend the use of this product for the preparation of crystal clear formulations.

Solution Clarity of ACULYN™ 22 Rheology Modifier, ACULYN™ 23 Rheology Modifier and ACULYN™ 28 Rheology Modifier Gels

0.7% polymer solides aqueous solutions, Neutralized with ammonium hydroxide to pH 8.5.

Thickening of Alcohols and Polar Solvents

ACULYN™ 28 Rheology Modifier can be used to thicken polar solvents such as ethanol, isopropanol or propylene glycol.

Thickening of 25% Ethanol with ACULYN™ 28 Rheology Modifier

Environmental, Health and Safety Record

ACULYN™ 28 Rheology Modifier is considered non-toxic by single oral and dermal exposure, produces minimal to no irritation to the eyes and skin, a non-sensitizer, nonmutagenic in the Ames assay and non-toxic to aquatic organisms, as well as non-irritating or sensitizing in Human Patch testing. This material is safe and appropriate for use in a broad range of rinse-off and leave-on personal care applications.

Disposal Considerations

Dispose in accordance with all local, state (provincial) and federal regulations. Empty containers may contain hazardous residues. This material and its container must be disposed in a safe and legal manner.

Keep from freezing; material may coagulate. The minimum recommended storage temperature for these materials is 1°C/34°F. The maximum recommended storage temperature is 49°C/120°F. These materials may coagulate if exposed to temperature outside this range. The coagulation process is irreversible.