End User Focus: Bentonite’s clay cleanse

Published: Tuesday, 22 November 2011

Sustainability issues, a rise in allergy prevalence and the EU’s REACH directive are all encouraging the use of bentonite-based additives in the detergent industry, as Dr Andreas Werner discusses

Industrial minerals are traditionally a key factor in the manufacture of detergents. In volume terms, sodium sulphate, soda ash and zeolites play a major role, while considerably lower quantities of bentonite-based speciality additives are also used. Giving rise to innovative detergent formulations, the demand for these additives has been growing at an exceptionally high rate for many years. Worldwide sales of laundry care products are currently recording average annual growth rates of 2.5%, while the demand for bentonite-based detergent additives is increasing at well over 3% a year.

Concentrated growth market

According to Euromonitor International, the global laundry care market currently generates a sales volume in the order of some $70bn, with detergents alone accounting for 75% of this figure. The competitive environment is inevitably intense. A glance at the market structure shows that the four largest suppliers already hold a total market share of around 55%. In view of the economic and ecological challenges facing the industry, this concentration will no doubt continue to increase over the next few years.

One of the main priorities for manufacturers is ensuring the sustainability of their products Ð in the broadest sense of the word. Apart from the chemicals inherent in detergents, numerous other aspects also determine their eco-balance. These range from the resources used in production and the amount of packaging and transport required, to the energy and water consumed during the actual washing process. Added to these are challenges such as a growing consumer demand for detergents that are as natural as possible and for the most part hypoallergenic.

New statutory regulations are also a response to the eco trend. These include for instance the Registration, Evaluation and Authorisation of Chemicals (REACH) directive, which has been in force in the European Union since 2008. In terms of ingredients, REACH now demands the highest possible degree of transparency from manufacturers. At the same time, new fabrics and performance textiles create a need for ongoing development on the part of detergent producers. In the search for solutions to this list of requirements, focus is increasingly directed at speciality additives based on the natural clay mineral bentonite. The reasons for this lie in the mineral«s properties, which are both versatile and exceptional.

Bentonite: origin & properties

The term bentonite stems from an American geologist by the name of Knight. Around 1890, he discovered an unusual layer of clay near Fort Benton in the US state of Wyoming and named the material bentonite, after the place where it was found.

From a geological viewpoint, bentonite is a sedimentary rock originating under certain physical and chemical conditions from weathered drifts of volcanic ash. Large deposits are found mainly in hollows and fluvial plains in almost all parts of the globe. Conditions influencing its creation did however vary from place to place, giving rise to the many different qualities of bentonite found today.

In most cases, the clay mineral was formed by sedimentation - this being the reason for the lenticular form of many bentonite beds, which are generally found near the Earth’s surface.

Highly valued as an industrial mineral, this clay owes its exceptional properties to its chemical composition. In addition to accessory minerals, such as quartz, feldspar, mica and calcite, bentonite essentially consists of the clay mineral montmorillonite. In chemical terms, this is a layered aluminium silicate made up mainly of silicon, aluminium and oxygen atoms. The silicon and aluminium ions are surrounded by oxygen ions, resulting in the formation of three-layered silicate lamellae comprising a SiO4 tetrahedron on each outer side and an octahedral layer of hydrated aluminium oxide in the centre. Bentonite is therefore classed as a so-called triple-layered silicate. Each crystal is made up of some fifteen to twenty of these lamellate layers.

Inside each individual lamellate stack, trivalent aluminium in the octahedral layer is replaced by divalent ions, such as magnesium. This gives rise to an excess negative charge which is neutralised by incorporating exchangeable cations into the intermediate layer.

In addition to this exceptional surface charge distribution, the lamellate structure of the crystals is a key factor contributing to the mineral’s specific properties. The individual crystal lamellae are only one nanometer thick, their diameter reaching dimensions of between 100 and 800 nanometers. This structure lends bentonite inherent adsorptive and bonding powers which, compared with other substances, are extremely high.

In order to utilise these properties for technical applications, for instance in the detergent industry, they are strengthened by way of selective chemical after-treatment - this being referred to as ‘activation’. Depending on the intended application, bentonite undergoes either acid or alkali activation, the latter process also being used to manufacture detergent bentonite.

The principle of alkali activation is based on an ion-exchange reaction during which the incorporated alkaline earth ions are replaced by alkaline ions. These particles accumulate on the edges and intermediate layers of the lamellae and hydrate upon contact with water. This causes inner-crystalline swelling, accompanied by significant expansion of the interlayer spacing. As a result, there is a tremendous increase in the inner surface area, which explains the high adsorption and retention capacity of activated detergent bentonite. Added to this is a whole series of other useful properties, which are outlined below based on specific product-related examples.

Speciality bentonite for advanced 2-in-1 detergents

Among other things, bentonite-based speciality additives offer a major economic and ecological benefit in 2-in-1 detergents. The reason for these products is that, in the case of conventional detergents, residue settles on textile fibres during the laundry process, causing them to knot. This results in a hard, scratchy feeling on the skin.

To prevent this effect the industry initially developed fabric softeners, these liquid products being added during the final rinse cycle. Their cationic surfactants create a film around the fibres, making them resistant to any deposits and subsequent knotting. Today, the same effect can be obtained with 2-in-1 detergents - without added softeners and surfactant-free. This is made possible by using soft-touch bentonite, as offered for instance by German bentonite producer Sud-Chemie AG - a subsidiary of Clariant Group - under the Laundrosil brand.

Laundrosil is added to the manufactured product, forming an integral part of the detergent mixture. Upon contact with water, the lamellae are released from the additive’s crystal structure and attach themselves to the textile fibres, forming a protective layer measuring no more than a few thousandths of a millimetre. As a result, fibres can no longer become entangled.

The advantages are far-reaching and begin with wearing comfort. After washing, fabrics feel pleasantly soft. Unlike softeners containing surfactants, the soft-touch bentonite responsible for this feeling is however guaranteed not to cause allergic reactions. Added to this is another positive feature - whereas laundry treated with fabric softeners is slightly hydrophobic, products such as Laundrosil promote the water absorbing and releasing properties of textiles. This creates a more pleasant body climate.

Environment and cost considerations are also convincing aspects of 2-in-1 detergents, since consumers need only one product to achieve the same washing performance and softness, based on a significantly lower dosage. The final rinse cycle can also be entirely dispensed with, thereby saving considerable water resources - even in the case of modern automatic washing machines, by far the largest amount of water is required for the rinse cycle.

There are also significant savings to be gained by the manufacturer. Compared with producing a combination of detergent and softener, the amount of energy used and the costs incurred in manufacturing, packaging, transporting and warehousing 2-in-1 detergents are considerably lower. Speciality additives such as Laundrosil are meanwhile so sophisticated that they can be used in both dry detergent granules and liquid detergents. This is possible thanks to special dispersions which ensure that the bentonite particles remain stable, even in liquid solutions.

Even the reverse principle can meanwhile be realised with the aid of bentonite, allowing manufacturers to selectively combine certain advantages of powder and liquid detergents. An ideal example of this is Sud-Chemie’s Laundroclin product. Its free-flowing granules utilise the high adsorption capacity of bentonite and, depending on each manufacturer’s requirements, contain up to 50% of liquid, non-ionic surfactants, which are environmentally degradable. The granules immediately disintegrate in the suds, promptly releasing the active detergent ingredients. Other advantages of Laundroclin include extremely easy dosing during the manufacturing process, minimal cleaning of production equipment compared with other solutions and an above-average level of storage stability.

Challenges for industry suppliers

These and other bentonite-based additives increase value creation in the detergent industry and make a significant contribution to eco-friendly and economically attractive innovations in this market segment. Of vital importance for major, globally-positioned manufacturers are their additive suppliers, who also maintain a worldwide presence, supplying detergent additives of consistent high quality in all markets, in line with required specifications.

Another group of bentonite-based products - so-called pearls or speckles - draw particular attention to the nature of this challenge. Today, most washing powders are interspersed with these granules, whereby their main purpose lies in the marketing sector thanks to their individually defined colours. The vivid particles symbolise the performance potential of each product, strengthening its brand image. Specialised processing expertise is needed for their manufacture, as previously activated bentonite powder must be agglomerated to form larger customised particles and then distinctively coloured to achieve the desired optical differentiation from competitive products.

Dr Andreas Werner, Adsorbents business line, Sud-Chemie AG, Clariant Group.

Spotlight on Sud-Chemie

Sud-Chemie is the world’s leading supplier of customised detergent additives. The speciality chemical company recently became part of the Clariant Group, after the Swiss chemicals major acquired 96.15% of the company’s shares for €2bn ($2.92bn) in April this year.

The company is a major global supplier of bentonite with deposits in key regions such as Asia and Latin America and an annual capacity of over 1m. tonnes.

The Munich-based company’s bentonite-producing adsorbents business represents 59% of annual sales of €1.23bn (for 2010), with the remainder of the company focused on speciality catalysts.