Hielscher – Ultrasound Technology

Wax Emulsions with Power Ultrasonics

  • When wax is dispersed as nano droplets with a very homogeneous distribution, a stable wax emulsions is obtained.
  • Ultrasonic homogenizers generate high shear forces and are reliable and robust systems to produce stable wax nano-emulsions.
  • Hielscher Ultrasonics’ high-shear ultrasonicators deliver superior emulsions for various industries.

Ultrasonic Wax Emulsions

Ultrasonic shear creates nano-dropletsUltrasonically generated high shear forces deliver the required energy to produce nano-sized wax emulsions, e.g. stable paraffin wax nanoemulsions.
Sub-micron and nano emulsions and dispersions can be formulated using a combination of various waxes in order to obtain a superior product with very high functionalities (e.g. lubriaction, water resistance, scratch resistance etc.).
The high shear forces of ultrasonic homogenizers enable to produce stable ready-to-use wax formulations with particles at equilibrium. The ultrasonic emulsification results in nano-sized particles and a uniform distribution.

Ultrasonic emulsifier deliver superior results:

  • very small droplet sizes with less than 100nm
  • stable emulsions
  • extended shelf life (mechanical stability)
  • higher efficacy
  • precise process control

Ultrasonic Paraffin Wax Nanoemulsion

How to prepare a stable Paraffin Wax Emulsion
The nano-sized wax emulsion is formulated from molten paraffin wax (as oil phase), distilled water, and anionic SDS as surfactant. In order to form a coarse pre-mixture, wax, water and surfactant are homogenized using a magnetic stirrer at 1000 rpm. Therefore, the surfactant (concentration 10 mg/ml of emulsion) and water are mixed in a beaker and heatet to approx. 65–70ºC. Then, the paraffin wax is drop-wise added by keeping a 0.2 oil-phase volume fraction under magnetic stirring.
After complete addition of the paraffin wax, the coarsely pre-mixed emulsion is sonicated with an ultrasonic bench-top homogenizer UIP1000hdT (1000W, 20kHz) for approx. 15 min. The ultrasonic emulsification process results in a nano waxemulsion with a very high stability.

Glass flow cell at UIP1000hdT ultrasonic emulsifier for the production of wax emulsions (Click to enlarge!)

Wax emulsion in ultrasonic inline reactor

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Surfactants

Wax emulsions can be stabilized by either a steric mechanism (using nonionic emulsifiers) or by an electrostatic mechanism (using ionic emulsifiers, most often anionics). Combining anionic and nonionic emulsifiers provides the emulsion the optimum stability because wax particles are protected through both stabilization mechanisms. This is referred to as the electro-steric stabilization mechanism.
For the emulsification of waxes, various emulsifiers or surfactants, which can be anionic, cationic or non-ionic, can be used. The most commonly used surfactants are fatty alcohol ethoxylates as non-ionic surfactants since they offer an extraordinary stability against hard water, pH-shocks and electrolytes. For other specific material characteristics, various other are used, e.g. anionic surfactants for better hydrophobicity or cationic surfactants for better adhesion.
Note: The smaller the droplets, the more surfactant is required to cover the droplet surface since the V/S ratio of spheres is the following: S/V = 3/R. For any increase, x*l or x*r in length or radius, the increase in surface area is x squared (x2) and the increase in volume x is cubed (x3).

Formulating with Wax Emulsions and Dispersions

Ultrasonic homogenizers are not only used to form wax emulsions / dispersions – they are used to process the wax emulsions in further steps to incorporate the emulsion as an additive into the final product (e.g. coatings, laquers, paints, cosmetics etc.).

Heavy-Duty Ultrasonic Homogenizers

Hielscher Ultrasonics is worldwide renowned supplier of high-power ultrasonic homogenizers. Our ultrasonicators can be found worldwide as reliable and robust “work horses” in the chemical, pharma, cosmetic and food industry. Hielscher’s industrial-grade ultrasonicators create very high amplitudes of up to 200µm (and higher on demand) in order to generate intense cavitation and high shear. As result, ultra-fine nano emulsions and dispersions with very narrow particle distributions are produced. Our high-power ultrasound systems help you to obtain superior quality of your wax formulations.
The robustness of Hielscher’s ultrasonic equipment allows for 24/7 operation at heavy duty and in demanding environments.

The table below gives you an indication of the approximate processing capacity of our ultrasonicators:

Batch Volume Flow Rate Recommended Devices
0.5 to 1.5mL n.a. VialTweeter
1 to 500mL 10 to 200mL/min UP100H
10 to 2000mL 20 to 400mL/min UP200Ht, UP400St
0.1 to 20L 0.2 to 4L/min UIP2000hdT
10 to 100L 2 to 10L/min UIP4000
n.a. 10 to 100L/min UIP16000
n.a. larger cluster of UIP16000

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Hielscher's ultrasonicators from lab to industrial scale deliver the required sonication power for nanoemulsions. (Click to enlarge!)

Powerful 1.5kW ultrasonic processor UIP15000hd

Literature/References

  • Behrend, O.; Ax, K.; Schubert, H. (2000): Influence of continuous phase viscosity on emulsification by ultrasound. Ultrason Sonochem. 7(2), 2000. 77-85.
  • Hosseini S.; Tarzi B. G.; Gharachorloo M.; Ghavami M.; Bakhoda H. (2015): Optimization on the Stability of Linseed Oil-in-Water Nanoemulsions Generated by Ultrasonic Emulsification Using Response Surface Methodology (RSM). Orient J Chem 31(2), 2015.
3 Steps to Successful Ultrasonic Processing: Feasibility- Optimization - Scale-up (Click to enlarge!)

Ultrasonic Processing: Hielscher supports you from feasibility and optimization to commercial production!



Facts Worth Knowing

Wax

Waxes are defined as a diverse class of organic compounds that are hydrophobic, malleable solids at near ambient temperatures. Waxes are composed from various components including hydrocarbons (normal or branched alkanes and alkenes), ketones, diketones, primary and secondary alcohols, aldehydes, sterol esters, alkanoic acids, terpenes (squalene) and monoesters (wax esters). The chemical composition of waxes is complex and varies, but in general waxes contain a relatively high proportion of alkanes and the hydrocarbons have long or very long carbon chains (from 12 up to about 38 carbon atoms). They are solid in a large range of temperature (fusion point between 60°C and 100°C). When molten, they turn into a low viscosity liquid.
They are characterized by their insolubility in water but solubility in organic, nonpolar solvents. Waxes can be distinguished in natural (plant-, animal-derived), semi-synthetic and synthetic waxes.
For commercial production of waxes, crude oil is the main source.

The two most important petroleum wax types are paraffin and microcrystalline waxes:
Paraffin waxes mostly features a white, odorless, tasteless, waxy solid consistency, with a typical melting point between 46°C and 68°C (115°F and 154°F), and a density of approx. 900 kg/m3. It has a macrocrystalline structure and is insoluble in water, but soluble in ether, benzene, and certain esters. Paraffin waxes are derived from crude oil and contain between 20 and 40 carbon atoms.
Microcrystalline wax, also known as petrolatum, is used for manifold applications due to its odour, colour, oil content, consistency and oil-binding property.

α-olefin waxes are either synthetically derived from ethylene via Fischer-Tropsch synthesis with a Ziegler-Natta catalyst or via oligomerization of ethylene. Alpha-olefin waxes are most commonly used in lube oil additives, PVC lubricants, candles, oil-drilling chemicals and cosmetics.

Polyethylene Wax (PE-WAX) is an ultra low molecular weight polyethylene (ULMWPE) consisting of ethylene monomer chains. Polypropylene wax (PP-WAX) is a synthetic, crystalline low molecular resin.
Both, olyethylene and polypropylene waxes are homopolymers and are mainly used for the formulation of colourants for plastics.

Copolymer waxes such as derivates of ethylene vinyl acetate (EVA) and ethylene acrylic acid (EAA) are widely spread in the formulations of coatings, e.g. metallic basecoats.

Waxes and wax additives are widely used to lend a product lubrication/slip, rheology, abrasion resistance, anti-blocking/barrier, polish or matting, anti-oxidation resistance and/or water repellency.
Waxes are a widely used component in many industries, such as in the production of chemicals (e.g. fine & specialty chemistry), coatings, paints & inks, additives & modifiers, adhesives, plastics & PVC, tires & rubbers, construction & building, thermostatic control devices, packagings, food, and cosmetics.

Natural Waxes:

  • Animal Waxes: beeswax, lanolin, tallow, shellac, spermaceti
  • Vegetable Waxes: carnauba, candelilla, soy, castor, rice bran, bayberry, jojoba etc.

Mineral waxes:

  • Fossil Waxes: Ceresin, Montan, Ozocerite, Peat wax
  • Petroleum Waxes: paraffin, microcrystalline waxes, e.g. petrolatum

Synthesized Waxes:
Synthetic Waxes: ethylenic polymers e.g. polyethylene & polyol ether-esters; polyolefin waxes; fatty acid amide waxes; chlorinated naphthalenes; hydrocarbon type, e.g. Fischer-Tropsch

Wax Emulsion

A wax emulsion / wax dispersion is a stable mixture of one or several waxes in water. As waxes and aqueous liquids are normally immiscible, surfactants and a sophisticated mixing process, e.g. power ultrasound, are required in order to form a stable wax emulsion. In correct terms, a wax emulsion must be called a wax dispersion as waxes are solid at room temperature. But since wax emulsions / dispersions are prepared with molten waxes, the terms “emulsification” and “wax emulsion” are most commonly used for aqueous wax formulations, whilst the term “wax dispersion” mostly describes a solvent based wax formulation.

Emulsion

An emulsion is a liquid in liquid dispersion of two or more immiscible liquids.
An emulsion can occur in various types: w/o, o/w, w/o/w, o/w/o
The type of emulsion (w/o or o/w) can be examined by a dilution test. The emulsion can be only diluted with the continuous / external phase. Another method to identify the emulsion type is by conductivity testing. Ionic o/w emulsions do not conduct, whilst o/w emulsions conduct electric current.
For the use of the CoCl2 filter paper test, a filter paper is impregnated with CoCl2 and dried (blue color). The color of the CoCl2 filter paper turns into pink when an o/w emulsion is added.