A novel and universal surfactant15 November 2003
BASF took up the challenge to find an environmentally-friendly degreasing agent which did not rely on solvents or nonylphenolethoxylates. Using the synergies provided by the different sectors within BASF Performance Chemicals and also working with the University of Cologne, an innovative and universal surfactant, Eusapon OD, was developed. The following paper is by Dr Gunther R Pabst and Philippe Lamalle.
Introduction Processing with surfactants, both water and solvent-based, is the state of the art in the degreasing of animal skins and hides. Beside the use of solvents, nonylphenol ethoxylates (NPEs) are the most effective ones, not least in terms of their cost-performance ratio. The degradation products of NPEs exhibit high aquatic toxicity and biological accumulation, however. For this reason, the European Union has prohibited products containing NPEs in concentrations exceeding 0.1% by weight for the majority of applications with effect from 2005 (Directive 2003/53/EC). The more eco-friendly method would be a water-based process employing fatty alcohol ethoxylates (FAEs). However, the result of this water-based process is often either unsatisfactory, particularly for very greasy sheep and pig skins, or uneconomical. To date, none of the alternative surfactants have matched the outstanding cost-performance ratio of NPEs for industrial use. There is a technical, economical and environmental need worldwide for a novel degreasing agent and Eusapon OD from BASF can meet this need. Eusapon OD is a novel surfactant, exclusively developed and produced for the leather and fur industry with outstanding added value for tanners: * Universal surfactant * Best degreasing and good soaking effect * Extremely low quantities required and therefore very economical * Simple application * Provides even and bright dyeing * Positive effect on waterproofing Furthermore, Eusapon OD is an environmentally-friendly surfactant for the leather and fur industry with the following advantages for the environment: * Readily biodegradable * Very environmentally friendly due to low dosage * Fulfils all relevant environ-mental EU directives The approach taken for the development of Eusapon OD was the exploitation of synergies within and outside BASF. A study of the degreasing mechanism was carried out in co-operation with the University of Cologne for a better understanding. The working group was headed by Prof R Strey. Although degreasing has been known for many years to take place in a four-step-process: 1. penetration of the surfactant into the pelt 2. dissolving of the grease 3. transport of the grease into the external float and, finally, formation at least temporarily of a stable emulsion of the grease in the process float to permit separation of the grease from the skin The degreasing mechanism itself has not been fully understood. In co-operation with the University of Cologne, BASF succeeded in discovering the degreasing mechanism essential to the development of the novel degreasing agent Eusapon OD (see Figure 1). 1. penetration of the surfactant into the skin 2. dissolving of the grease by formation of a nanophase 3. transport of the grease to the surface of the skin and 4. conversion of the nanophase into a macroemulsion for draining the grease into the float The nanophase was observed in the float of the depickling step in the presence of two other phases in a conventional sheepskin degreasing process: * a lower phase, mainly consisting of water * an upper phase, mainly consisting of grease and * a middle phase, containing water, grease and the main part of the surfactant All phases were almost clear. Under visible light, we observed light scattering of the clear middle phase. The nanophase can be visualised by certain microscopes. The nanosponge-like structure has a cavity diameter of less than 50 nanometres (5x10-8m, 1/1000 of the thickness of a human hair). Nanophases containing water, grease and surfactant show a sponge-like structure with an immense inner surface (like that of a microfibre towel) and a stability over a wide temperature window. This leads to an outstanding capability for dissolving grease and fat under varying application conditions (see Figure 2). The product development strategy was to pre-select products according to their ability to form nanophases during application and to form stable macroemulsions. Further properties, particularly ease of biodegradation without aquatoxic metabolites, low eco-toxicity, ready-to-use characteristics and low foaming also had to be taken into account. The pre-selection was assisted by robot-aided high-throughput screening (HTS) and computer-aided molecular product design (MPD). Approximately 5,000 candidate surfactants were tested by HTS and approximately 100 novel substances designed by MPD. High-throughput screening was performed by a fully automated robot-driven device. Surfactants in different ratios, water and grease were metered automatically into glass vessels. Following homogenisation at 37°C, the homogeneity and phase separation between water and oil were recorded automatically by transmission and reflection measurement. Information was thus first obtained on suitable surfactant structures and surfactant mixtures capable of forming nanophases and stable emulsions. Screening was followed by computer-aided design to find the optimal product. This objective had to be achieved within a single alcohol component for reasons of cost and quality in production (see Figure 3). Compared to a standard NPE, Eusapon OD delivers superior performance in the solubility and foaming tests. Eusapon OD dissolves in water immediately and generates less than half the amount of foam. These properties are important for an easy handle and 'ready-to-use' characteristics. The application properties of Eusapon OD are also outstanding. Eusapon OD can be used in all types of leather and fur processing: * sheep and pig skin: soaking, liming, pickling, tanning and degreasing * fur: soaking and degreasing (wool and skin) * cattle hide: soaking, liming, pickling and tanning Sheepskin processing: Comparative trials of a standard NPE and Eusapon OD in degreasing of sheepskins revealed greatly superior fat extraction and a better phase separation of the float by Eusapon OD, which consumed only half the quantity compared to NPE (Figure 4). Furthermore, the biodegradability of the residual degreasing float is much better, as shown by a lower chemical oxygen demand (COD) and a higher biological oxygen demand within 5 days treatment (BOD5) (see Figure 5). Overall, Eusapon OD exhibits superior grease extraction, improved physical properties and dyeing shades during sheep and pig skin processing, and adds a lower pollution charge to the float by being twice as efficient as NPEs. Fur processing: Wool degreasing has always presented a problem in fur processing which appears in the form of yellowish wool and dull dyeing. The solution is Eusapon OD, which delivers an exceptionally clean wool whilst requiring only 40% of quantity of NPE. A further advantage is that Eusapon OD can be used for both wool and skin degreasing. Cattle hides beamhouse: An additional, very important topic is the effect of a degreasing agent upon the waterproofing. Conventional surfactants are known to have a negative influence upon the water-repellence of leathers. However, less surfactant results in uneven dyeing. The application of Eusapon OD overcomes these disadvantages. It not only positively influences the waterproofing, but also provides an even dyeing at the same time. Eusapon OD delivers a very balanced and increased waterproofing effect over the whole skin. Leathers processed with Eusapon OD exhibit very uniform distribution of readings, documented by increased and equalised numbers of flexes in the Maeser test. The fat extraction of Eusapon OD is superior by 30%, whilst using only half the quantity. This means that Eusapon OD is > 2.5 times more efficient in grease removal for cattle hides than a standard NPE. Summary Eusapon OD is a novel degreasing and soaking agent with unique application properties for all types of leather and fur. The outstanding properties in comparison to a standard NPE are shown in Figure 6. For the development of Eusapon OD, synergies have been exploited within and outside BASF leading to co-operation plus teamwork!