Light and heat fast modified Mimosa23 November 2009
Tanac specialise in providing the leather industry with Mimosa based products farmed from their FSC certified plantations of Acacia in Brazil. By modifying the extract they have devised new high-performance extracts for upholstery and upper leathers
Mimosa or Acacia are native Australian species introduced to southern Brazil in the 1920s and rapidly becoming a sustainable economic product. At present, there are 150,000 hectares of Acacia forests in Brazil of which 30,000 hectares belong to Tanac. There are also more than 30,000 small farms, which supply Tanac with enough bark to produce 36,000 tons of vegetable products per year. These products are used in various areas such as the production of leather and adhesives as well as in water and effluent treatment.
The forests belonging to Tanac are certified by the FSC (Forest Stewardship Council), which guarantees a sustainable raw material complying with
the most stringent environmental regulations. Conventional Mimosa extracts are versatile and provide a variety of characteristics such as naturally light colouration, low acid and salt content, low viscosity and natural pH ranging from 4.0 to 5.0. They also provide stability to hydrolysis and electrolytes, good resistance to iron salts, fast penetration and stability to damage caused by microorganisms.
In spite of their wide application and versatility, the Mimosa extracts which are available on the market do not fully satisfy all the needs of upholstery leather makers, especially those of automotive leather. Thanks to its chemical structure, Acacia tannin is a natural antioxidant (figure 1), being often used to this end. This feature alters the colouration of the leather produced when exposed to light or heat.
Production of furniture, automotive, aviation and aquatic upholstery articles as well as footwear upper and leathergoods requires a high specification. The demand for these leather types is growing, particularly if they have good physical and environmental credentials. Characteristics such as light shades and heat and lightfastness are important. The products currently used to this end are not extracts but ground products obtained from irregular sources and contain impurities (some insoluble ones) that affect the quality of the final goods.
By means of chemical modification of Mimosa extracts, lightfastness may be increased so that significant leather colouration changes do not occur after upholstery articles have been produced. These alterations take place through chemical modification where specific radicals are added to the original molecule so that they provide the extract with the capacity to reduce oxidation when exposed to sunlight or other sources of light, resulting in a lower degree of colour alteration.
Organic chemical reactions are the best way to provide heat and light stability to raw materials by using efficient protective groups. These groupings prevent electronic resonance between the B aromatic link and its free hydroxyls thus stabilising the molecular structure and guaranteeing a lower degree of alteration of the extract colour and, consequently, that of the leather tanned with new modified Mimosa (such as Tanac’s Supertan LTA).
Using modified Mimosa with such characteristics makes it possible to produce tanned and retanned leather where a light colour as well as heat and lightfastness are possible.
These additional properties are added to other favourable characteristics of Mimosa extracts such as fast penetration, smooth open grain, good filling and excellent softness. Figure 2 shows a significant improvement in heat and lightfastness when using modified Mimosa compared with standard Mimosa extract. In figure 2 the samples were treated with heat, natural and UV light and the discolouration measured.
The colouration provided by modified Mimosa and Tara are quite similar.
Physical, chemical and mechanical tests carried out on automotive upholstery leather, comparing modified and standard products, showed a significant improvement in the results obtained from the article that used modified Mimosa compared to regular Mimosa extract. It may also be noted that both products reached
the parameters required in OEM upholstery leathermaking including a significant increase in the tensile strength in the sample, which used modified Mimosa as the retanning agent.
Taking into consideration that the production of upper leather accounts for more than 50% of global leather consumption and that this market is evolving fast as far as quality of the final goods are concerned, Tanac have also developed modified Mimosa as a sustainable alternative for the market.
Table 1 highlights the results of the physical and mechanical tests carried out on footwear leather samples. It shows an improvement in the results obtained from leathers where modified Mimosa was applied compared to standard Mimosa extracts.