Aqueous based surfactant compositions

Details Aqueous based surfactant compositions Aqueous based surfactant compositions

1996-07-17

2001-01-23

Douyon, Lorna M. (Department: 1751)

Cleaning compositions for solid surfaces, auxiliary compositions

Cleaning compositions or processes of preparing

Liquid composition

C510S337000, C510S340000, C510S418000, C510S470000

Reexamination Certificate

active

06177396

ABSTRACT:

INTRODUCTION
The present invention relates to concentrated aqueous based surfactant compositions containing high levels of surfactant and/or electrolyte which would normally provide either a product with an undesirably high viscosity, or one which separates into two or more phases on standing, or exhibits signs of excessive flocculation of the surfactant.
Liquid laundry detergents have a number of advantages compared with powders which have led to their taking a substantial proportion of the total laundry detergent market. The need to suspend sparingly soluble builders such as sodium tripolyphosphate, or insoluble builders such as zeolite in the pourable aqueous surfactant medium led to the development of structured surfactants. These are pseudoplastic compositions in which the structurant is a surfactant or a surfactant/water lyotropic mesophase.
The introduction of compact powders containing higher concentrations of active ingredient than the traditional powders has challenged the trend towards liquids. There is a market requirement for more concentrated liquids to meet this challenge, and in particular concentrated aqueous surfactant compositions containing dissolved or suspended builder salts. The addition of high levels of surfactant and/or dissolved electrolyte can promote flocculation of the structured surfactant resulting in high viscosities and/or instability.
The problem of suspending water-insoluble or sparingly soluble pesticides in a fluid medium has called for new approaches to avoid the use of environmentally unacceptable solvents. Structured surfactant systems represent one such approach. Flocculation of the systems, together with crystal growth of the suspended solids has, however, been a serious limitation on the development of suitable products.
Dyes and pigments, which are water-insoluble or sparingly soluble also need to be suspended in pourable liquid concentrates to avoid handling fine powders when preparing dyebaths, or to provide printing inks.
Attempts to suspend dyes and pigments in structured surfactants have been hindered by the tendency of the surfactant structure to flocculate or break down in the presence of the polyelectrolytes which are commonly added to pigments prior to milling, and which act as milling aids.
Cosmetic, toiletry and pharmaceutical formulations also frequently require the preparation of stable suspensions of dispersed solids or liquids in a pourable aqueous medium which may require to be highly concentrated with respect to electrolyte, surfactant or both, or incorporate polyelectrolyte.
Oilfield drilling muds are used to lubricate drill bits and to transport rock cuttings from the bit to the surface. Structured surfactants have been found to provide the required rheology and solid suspending power. Such muds require to be able to tolerate very high electrolyte concentrations, e.g. when the borehold penetrates a salt dome. They usually contain weighting agents such as barite, calcite or haematite to facilitate penetration to great depths. However in the final stages of drilling these are often replaced by completion fluids which contain soluble weighting agents such as calcium chloride or bromide. These dissolved alkaline earth metal electrolytes are highly flocculating toward most surfactant structures.
The ability to concentrate liquid detergent or other surfactant systems was once limited by the tendency of most surfactants to form viscous mesophases at concentrations above 30% by weight, based on the weight of water and surfactant. Mesophases, or liquid crystal phases, are phases which exhibit a degree of order less than that of a solid but greater than that of a classical liquid, e.g. order in one or two, but not all three dimensions.
Up to about 30% many surfactants form micellar solutions (L
1
-phase) in which the surfactant is dispersed in water as micelles, which are aggregates of surfactant molecules, too small to be visible through the optical microscope.
Micellar solutions look and behave for most purposes like true solutions. At about 30% many detergent surfactants form an M-Phase, which is a liquid crystal with a hexagonal symmetry and is normally an immobile, wax-like material. Such products are not pourable and obviously cannot be used as liquid detergents. At higher concentrations, e.g. above about 50% by weight, usually over some concentration range lying above 60% and below 80% a more mobile phase, the G-phase, is formed.
G-phases are non-Newtonian (shear thinning) normally pourable phases, but typically have a viscosity, flow characteristic and cloudy, opalescent appearance, which render them unattractive to consumers and unsuitable for use directly as, e.g., laundry detergents. Early attempts to suspend solids in typical G-phases were unsuccessful, giving rise to products which were not pourable. However thin mobile G=phases, having a relatively wide d-spacing have been reported, which are capable of suspending solids to form pourable suspensions.
At still higher concentrations e.g. above about 70 to 80% most surfactants form a hydrated solid. Some, especially non-ionic surfactants, form a liquid phase containing dispersed micelle size droplets of water (L
2
-phase). L
2
phases have been found unsuitable for use as liquid detergents because they do not disperse readily in water, but tend to form gels. They cannot suspend solids. Other phases which may be observed include the viscous isotropic (V) phase which is immobile and has a vitreous appearance.
The different phases can be recognised by a combination of appearance, rheology, textures under the polarising microscope, electron microscopy and X-ray diffraction or neutron scattering.
DEFINITIONS
The following terms may require explanation or definition in relation to the different phases discussed in this specification: “Optically isotropic” surfactant phases do not normally tend to rotate the plane of polarisation of plane polarised light. If a drop of sample is placed between two sheets of optically plane polarising material whose planes of polarisation are at right angles, and light is shone on one sheet, optically isotropic surfactant samples do not appear substantially brighter than their surroundings when viewed through the other sheet. Optically anisotropic materials appear substantially brighter. Optically anisotropic mesophases typically show characteristic textures when viewed through a microscope between crossed polarisers, whereas optically isotropic phases usually show a dark, essentially featureless continuum.
“Newtonian liquids” have a viscosity which remains constant at different shear rates. for the purpose of this specification, liquids are considered Newtonian if the viscosity does not vary substantially at shear rates up to 1000 sec
−1
.
L
1
phases are mobile, optically isotropic, and typically Newtonian liquids which show no texture under the polarising microscope. Electron microscopy is capable of resolving the texture of such phases only at very high magnifications, and X-ray or neutron scattering normally gives only a single broad peak typical of a liquid structure, at very small angles. The viscosity of an L
1
-phase is usually low, but may rise significantly as the concentration approaches the upper phase boundary.
L
1
phases are single, thermodynamically stable phases and may be regarded as aqueous solutions in which the solute molecules are aggregated into spherical, rod shaped or disc shaped micelles, which usually have a diameter of about 4 to 10 nanometers.
“Lamellar” phases are phases which comprise a plurality of bilayers of surfactant arranged in parallel and separated by liquid medium. They include both solid phases and the typical form of the liquid crystal G-phase. G-phases are typically pourable, non-Newtonian, anisotropic products. They are typically viscous looking, opalescent materials with a characteristic “smeary” appearance on flowing. They form characteristic textures under the polarising microscope and freeze fractured samples have a lamellar appearance under the electron microscope. X-ray diffraction

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