The use of novel inorganic and organic finishes

Introduction The BLC has announced the launch of an important new Networking project which was granted funding by the Engineering and Physical Sciences Research Council (EPSRC) in July 2001. The key philosophy behind this project programme is to bring together the retailer/manufacturer/tanners/chemical supply chain and researchers to provide exciting new products that the market demands. By incorporating all elements of the supply chain it is expected that research developments will be accurately targeted at the market needs. The Need for LeatherWeb Project The LeatherWeb project aims to proactively identify 'gaps' in the marketplace with regard to consumer expectations and future demands of leather, and to use this information to develop a responsive research programme which will give added value to the leather supply chain. From the limited data available, the recurring theme is one of consumers requiring leather items which have a more natural appearance but are more durable. Work programme overview There are two distinct, but symbiotic, aspects to the LeatherWeb project: * Collection and dissemination of customer/consumer data by electronic means - 'What are consumers current and future expectations of leather and leather products?' * Development and implementation of a research programme in response to consumer/customer needs and in line with the many factors that influence R&D strategy, as illustrated in Figure 1. What is the LeatherWeb? The LeatherWeb network is created from a large number (over 20 partners) of companies with a UK base but international reputation. These organisations will pool their knowledge and information to identify the future needs of the product leather. The LeatherWeb project relies heavily on a collaborative approach representing all parts of the leather supply chain from researcher to retailer. The technological/scientific area covered by this project is the investigation of the application of innovative approaches to leather finishing and the production of natural, durable leather, in response to consumer demands and needs. The proposed research is being carried out at BLC and the British School of Leather Technology and subsequently applied through the participating tanneries. Current Studies A focus point of the project was to produce natural-looking but durable leather as a direct result of the current consumer trend towards natural looking products. Whilst there are leather products which are marketed as durable products as a result of specific impregnantsi, the majority of unfinished leather products are characterised by poor abrasion resistance and water spot staining. In order to obtain the required performance specifications it is necessary to apply finishes, but these tend to reduce the natural aesthetics. Protein based finishes such as casein have been used as natural looking finishes but gave only limited resistance to water and limited abrasion resistance. The natural appearance of leather is probably related to a range of parameters such as visibility of the surface of the leather (eg grain), gloss, and feel of the material. In order to produce natural looking leather, a minimisation of the finish thickness, avoidance of pigments and the use of materials with suitable refractive indices and use of gloss modifiers, where necessary, are essential criteria. One class of material which is characterised by thin films (0.1-3mm) with good mechanical properties and suitable refractive index are inorganic-organic hybrids. Investigations have been made at BLC with the use of silica based materials as finishing agents. The simplest agent in this class is SiO2.nH20 which under suitable conditions of pH, temperature and concentration can polymerise (see Figure 2) and form a coherent film with good hardness. Due to their glassy nature, the films have very poor flexibility and are only suitable for coating inflexible substrates such as aluminium and glass.ii However, as a basis for comparison with more complex derivatives, finishing trials were undertaken using SiO2 with microscopy demonstrating their good film-forming properties (see Figure 3). Inorganic-organic hybrids which are essentially substituted derivatives of SiO2.nH20 were investigated more extensively as finishing agents. The chemistry of this broad class of materials offer a whole range of possibilities to obtain specific performance requirements depending on the number and functionality of the organic side chain(s) (see Figure 4). Because of the organic side chain the extent of crosslinking between silicon atoms is reduced with a resultant increase in flexibility. A range of inorganic-organic hybrids were selected based on differing functionalities. Initial scoping trials focused on investigating the effect of solid contents of the finishing material and the number of applications. A testing regime was applied to assess the films which included visual assessment, electron microscopy, wet and dry rubbing, flex testing, scuff resistance and lastometer testing the results. The results demonstrated that only one of the five hybrid materials had suitable finishing characteristics with the majority failing on wet rubbing, scuff resistance and lastometer testing. Hybrid 5 passed all the tests with the exception of flexing, despite the extremely thin coating, as highlighted in Figure 5. As a comparison, casein was demonstrated to pass all of the tests with exception of scuffing. In order to improve the flexing resistance of Hybrid 5 coated leather, trials were undertaken in combination with casein. The test results for this protein/ hybrid coated leather passed all of the tests, essentially combining the performance benefits of the Hybrid with the performance benefits of casein. Although the coating was necessarily thicker than with just Hybrid 5, the grain appearance of the leather was retained as shown in Figure 6. Further investigations using inorganic-organic hybrids are currently underway with the aim of improving their performance according to a more stringent testing regime.