Thickeners
Rheology modifying is one of the crucial issue in fluids. Thickeners play an important role in this part. Wide range of thickeners can be used for this purpose, but the most common ones including cellulosic, ASE and HASE, fumed silica, HEUR (polyurethane thickeners). Different industries like Paints and Coatings, Ink, etc. can take advantage of these products.
Thickeners are known as rheology modifiers which are able to increase viscosity. furthermore, they can provide with different features like water retention, increasing open –time, scrub resistance, anti-sagging, etc.
The most common thickeners in paints and coatings, resins and water-based adhesives:
- Cellulose thickeners
- Acrylate thickeners (ASE and HASE)
- Polyurethane thickeners (HEUR)
Cellulose thickeners
Cellulose thickeners are chemical compounds derived from Cellulose ether families that are able to absorb water highly. In addition to increasing viscosity, they offer different properties e.g. stability, water retention, open-time, color development, etc.
The pros of these thickeners are compatibility with different formulations and also different range of pH, but one of the cons of them is poor levelling effect. Further, these thickeners are not resistant to microorganism’s attack. Hence, suggested to use in – can preservatives to prevent contamination.
Types of cellulose thickeners:
- Hydroxyethyl cellulose (HEC)
- Methyl Hydroxy ethyl cellulose (MHEC)
- Hydroxy propyl methyl cellulose (HPMC)
- Ethyl Hydroxy ethyl cellulose (EHEC)
- Carboxymethyl Cellulose (CMC)
Hydroxyethyl cellulose (HEC): This thickener is applied for various industries including paints and coatings, adhesives, resins, cosmetics, detergents, etc. In paint and resin industry, Hydroxyethyl cellulose offers better feature comparing other Cellulose ether derivatives. The characteristics are as follows:
- Minimum effect on resin and paint gloss
- Pigment compatibility
- Better water retention
- Spatter resistance
Acrylate thickeners
Polyacrylate thickeners are acrylic copolymer emulsions. they are based on ASE (Alkali Swellable emulsions) and HASE (Hydrophobically Modified Alkali Swellable emulsions). these rheology modifiers can increase viscosity. Thanks to their liquid delivery form it is easy to incorporate. furthermore, due to their chemical structure they will not face microorganism attacks. By increasing pH to alkali range, they would absorb water and swell, and this process causes thickening effect.
Difference between ASE and Associative acrylate thickeners (HASE) -which are also known as Hydrophobically Modified Alkali Swellable Emulsions, is that HASE contain hydrophobic groups that result more thickening efficiency, and improve scrub resistance.
Polyurethane thickeners (HEUR)
Polyurethane thickeners or Hydrophobically modified Ethylene oxide – based Urethane, are one of the innovative products among water – based thickeners. They can offer various features and provide good characteristic such as, levelling, scrub resistance, etc. moreover they perform in different range of pH and also will not face microorganism attack.
Fumed Silica
Fumed silica (CAS number 112945-52-5), also known as pyrogenic silica because it is produced in a flame, consists of microscopic droplets of amorphous silica fused into branched, chainlike, three-dimensional secondary particles which then agglomerate into tertiary particles. The resulting powder has an extremely low bulk density and high surface area. Its three-dimensional structure results in viscosity-increasing, thixotropic behavior when used as a thickener or reinforcing filler.
These products can be applied in:
- Coatings
- Printing Inks
- Adhesives
- Cosmetics
- Silicone elastomers (Like RTV, HTV)
- Food and Pharmaceutical products
Generally fumed silica is divided to two main groups, including hydrophobic and hydrophilic.
The other factor that can divide fumed silica to different grades is specific surface area and common grades are 150 m2/g, 200 m2/g, etc. The bigger surface area is, the more viscosity they give.
