Alkyl polyglucosides: A class of its own

Excerpt: THE abundance of carbohydrates and the fact that they are both natural and renewable has evoked lot of interest in the last few years in carbohydrate derived surfactants.

THE abundance of carbohydrates and the fact that they are both natural and renewable has evoked lot of interest in the last few years in carbohydrate derived surfactants. Non ionic alkyl olyglucosides commonly known as alkyl poly glucosides {APG} has attracted as highly efficient and mild surfactants and combines many advantages of non ionic and anionic surfactants. APG exhibit extraordinary properties such as low surface tension, high surface activity, rich and stable foam, good compatibility properties with other class of surfactants, stable surface activity in high electrolyte concentration. The ability of exhibit more solubility than the typical alcohol ethoxylates makes a perfect fit for textile and household laundry applications. Detergent formulations based on APG are also more stable than the above referred ethoxylates over a wide range of temperatures and can also be effectively used in combination with anionic surfactants.

At present, a variety of routes are used for synthesis of this surfactant but the methods of one and two step processes are used for industrial production. Alkyl polyglycosides containing C8 - to C18 -alkyl radicals can entirely or in part be prepared from renewable raw materials.. These materials have to meet high aesthetic requirements for textile processing - household and cosmetic applications. APG of different hydrocarbon chain lengths can be prepared using an indirect method involving condensation of fatty alcohol with dextrose. The chemical structures of the prepared compounds can be confirmed using different spectroscopic techniques, primarily Fourier transform infrared spectroscopy, nuclear magnetic resonance and mass spectroscopy. The surface properties of the solutions containing different concentrations of the prepared APGs can be determined at different temperatures. The results of the spectroscopic analysis demonstrate that these materials are prepared through the correct techniques, producing pure materials. The results of the critical micelle concentration (CMC) determination demonstrate that the surface properties of these compounds depend mainly on the nature of their hydrophobic component.

Process optimization particularly in the use of long chain alcohols, such as dodecanol, tetradecanol etc. has resulted in distinct improvements. Fatty alcohols can be obtained either from the petrochemical {synthetic alcohols} or natural or renewable resources {oils and fats}. Fatty alcohol blends are used in the production and synthesis of alkyl polyglucosides to build up the hydrophobic part of the molecule. Depending on the desired alkyl chain length of the fatty alcohols, the main feed stocks are oils and fats of coconut or palm kernel for the C 12 /14 range and tallow, rapeseed oils for the C16/18 fatty alcohols. The hydrophilic part of the alkyl polyglucoside molecule is derived from a carbohydrate, based on starches from corn, wheat or potatoes. Double alcohol exchange steps are omitted in one step process, where there are no level of alkyl poly glucosides exists in products with leading to a simple process. In the new process dodecyl poly glucoside can be synthesized by glucose and dodecanol using para tolune sulphonic acid as a catalyst. The most preferred molar ratios is 6:1 ratios of lauryl alcohol and glucose.at 120c under pressure of 5 of Another class of novel surfactants is the alkyl polyglucosides. As far as the production is concerned, processes based on Fisher synthesis have been successfully adopted.

Physical characteristics

Their hydrophilic and hydrophobic parts are clearly separated. The hydrophilic group in an APG molecule usually consists of one to five condensed glucoside parts (DP = 1–5). The hydrophobic group in APG molecules is an alkyl chain containing usually from six to eighteen carbon atoms. Surface activity depends both on the hydrophilic part and the hydrophobic part, although to varying degrees. Surface activity of surfactants is determined primarily by the chain length.

The hydrophilic part affects adsorbability to a lesser extent. However, it affects solubility in polar solvents. Depending on the structure of the molecule, alkyl polyglucosides exhibit different solubility in various solvents. The compounds with the degree of polymerization (DP) from 1 to 5 containing alkyl chains whose length is from 6 to 14 carbons are soluble in water. The molecules with 16 to 22 carbon atoms are oil-soluble. In general, increasing the degree of polymerization increases solubility in a polar medium while lengthening of the alkyl chain increases solubility in a non-polar medium.. From the viewpoint of the application of APGs as additives improving lubricating properties of water, these compounds must be both water-soluble and highly surface active. The adsorption of APGs on the surfaces of friction couples results in the formation of a surface structure whose composition will determine the formation of a lubricant film.

The physicochemical properties of alkyl polyglucosides are interesting. They occur in the form of monomers at low concentrations and produce micelles above the critical micelle concentration (CMC) usually of the order of hundredths of a percent. Aqueous solutions of alkyl polyglucosides may appear in the form of lyotropic liquid crystals at the concentrations of above 30 %.

Properties of Alkyl Polyglucosides

  • Produced from natural, renewable resources
  • Non ionic surfactant
  • Compatible with all other surfactant classes
  • Excellent eco toxicological profile
  • Ethylene oxide free
  • Sulfate free
  • Readily biodegradable

Conclusions

Alkyl polyglucosides (APGs) surfactants find applications in various branches of industry. APG surfactants are increasingly gaining importance because of its unique surfactant properties in combination with very good biodegradability,

Author Details

C.N. Sivaramakrishnan