National Activities - UK Sustainable Surfactants Renewable Feedstocks for the 21st Century - Recent successes - industrial applications. Why use polyhydroxyl- or carbohydrate-based surfactants?

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Competitive Industrial Materials from Non-Food Crops
Sustainable Surfactants: Renewable Feedstocks for the 21st Century
Wednesday 4 November 1998, Central Science Laboratory Agency, Sand Hutton, York

Recent successes - industrial applications. Why use polyhydroxyl- or carbohydrate-based surfactants?
Ingegard Johansson, Akzo Nobel Surface Chemistry AB, Sweden

Driving force for development:

• A need for environmentally benign, "green" and efficient surfactants from renewable sources.
• Technical needs in industrial applications.

Examples:

• Low foam
• Good wetting and cleaning
• Good penetration properties
• Solubility in highly concentrated caustic or electrolyte solutions
• Highly concentrated formulations to minimise transport and packing costs
• Waste water with low oil content

Strategy:

• Choose type of "green" surfactant, in this case alkyl glucosides (AG:s).
• Map structure-property relationship aiming at meeting technical needs.
• Focus on one application area.
• Match properties to get the best choice, probably a compromise between different demands.
• Fine-tune and test in the market to get feedback.
• Start marketing.
• Take the next application area etc.

Example of broad structure-property relationships for the alkyl polyglucosides:

• A range of glucosides (25 samples) were synthesised and characterised with 23 different parameters describing structure, physico-chemical properties, foaming, wetting and cleaning.
• This matrix was analysed using a Principal Component Analysis, which gave the most important descriptors for different responses or test results.
• Then responses like foaming, wetting and cleaning were modelled with the use of partial least squares of latent variables as a function of structure and physico-chemical properties.

Example 1 - application area: Adjuvants for the Agro area

Demands:

• Low foam, good wetting and spreading properties on a hydrophobic surface.
• Good penetration into the surface of the leaves.

Test results:

Good wetting and spreading as well as penetrating ability for medium chain alkyl glucosides were achieved. But the foam is too high. A compromise can be made with a branched C8-glucoside. Synergies were seen with ammonium sulphate.

Example 2 - application area: Cleaning and wetting in highly alkaline systems; Cleaning of hard surfaces and textile treatment

Demands:

• High efficiency as cleaning and wetting agent.
• Solubility in highly concentrated alkali or electrolytes.
• Low foam.
• Compatibility with complexing agents.
• Good separation of oil from the waste water .

Since the general structure-property relationships showed that high foam and good cleaning ability vary together, the combination low foam and good cleaning could not be found with a glucoside only. However, the AG:s are known to show good hydrotrope efficiency, i.e. to be good at co-operating with other surfactants and create clear formulations. The conventional nonionics based on ethylene oxide are extremely good wetting and cleaning agents but not soluble in highly alkaline solutions. The idea then was to look at combinations of these two categories of products.

Test results:

• A few nonionics were chosen for their good cleaning and low foaming properties.
• Alkyl glucosides of different alkyl chain lengths were compared as cosurfactants together with the chosen alkyl ethoxylates in alkaline cleaning formulations. The results showed the C6-glucoside to be the most efficient hydrotrope.

New questions that arose during the investigation:

• Why do these mixed solutions get cloudy when they are diluted?
• And how do they behave at different temperatures?

A new batch of tests was made with comparisons between C6-, C8-branched- and C8-straight glucosides together with a C 1 OE04 non-ionic in different electrolyte systems and in three different ratios (about 40 formulations basically). The effects of concentration and temperature was looked at for each of these formulations. A typical feature for the ethoxylates is their reverse temperature solubility, i.e. water solutions get cloudy and eventually separate when they are heated. The temperature at which this clouding takes place is called their cloud point temperature. For pure ethoxylates in water the cloud point is rather independent of concentration. With the glucosides the situation is very different. They seldom show cloud points and when they do, the cloud point is strongly dependent on concentration. So what happens when you mix them? It is found that the behaviour of the mixture is intermediate between a typical glucoside and an ethoxylate, with steep concentration borders at low concentrations. This means that at low concentration there is a mixing gap for all temperatures.

Conclusion:

The concentration of the "working" solution should be kept above the amount that gives a stable solution, but as close as possible since it is well known that cleaning and wetting for a non-ionic composition is most efficient close to a cloud point.

When the procedure is finished and the fluid is contaminated with oil and dirt a dilution will take the whole batch into the cloudy region and the oil will separate. A measurement according to the oil separation test SNV 1975:10 gave around 10 mg of mineral oil residue per litre of water after 2 hours separation as compared to a conventional hard surface cleaner which left about ten times more.

In many cases the solubility is higher in at high pH than in neutral solutions. This has been discussed in terms of the weak acidity of the OH-groups of the glucose part. It also gives a hint of why there is a synergy with ammonium sulphate with a possible interaction between the opposite charges.

Future possibilities:

Our impression is that the polyhydroxyl based surfactants offer many new properties both as such and in mixtures with other more conventional products. - The hydroxyl function gives a lipophobic character to the hydrophilic part of the molecule thus increasing the surface activity.

• The stiffness of the glucose ring gives other behaviour at the interfaces and also other interactions intermolecurlarly.
• The hydratization is different from that of the ethoxylates.
• The cloud point behaviour differs from the ethoxylate characteristics.
• The weakly acidic character is seen in the interactions with for instance cationic products as well as in the good solubility in high alkali.

All these differences create new possibilities in formulations and applications. Their properties are, in spite of the extensive patenting activity in this area, still not fully understood. To see and use the potential of these sustainable surfactants is a challenge for the future.

References:

1. I. Johansson, C. Strandberg, B. Karlsson, B. Gustavsson. Structure-property relationship for some alkyl glucosides. Proc. 4th World Surfactants Congress, 1996.
2. I. Johansson, C. Strandberg, B. Karlsson, G. Karlsson, K. Hammarstrand. Use of mixtures of alkyl alkoxylates and alkyl glucosides in strong electrolytes and highly alkaline systems. Industrial applications of surfactants IV. Editor: D.Karsa.

Contacts

Contact

• Sue FINLAY / DEFRA Organic Farming and Industrial Crops Division / UNITED KINGDOM

Participant

• LINK Secretariat BBSRC / UNITED KINGDOM

Speaker

• Ingegard JOHANSSON / Akzo Nobel Surface Chemistry AB SWEDEN