Fungicides
16 August 2008Fungicides are an essential component of leather manufacture to prevent the occurrence of mould on part processed and finished leather. If used correctly and sourced from a reputable supplier, fungicides used within the leather making process present no risk to the consumer. This article by BLC Leather Technology Centre Ltd discusses the typical fungicides used in leather processing.
In the production and distribution of leather, two types of biodeterioration are encountered: bacterial (which generally applies to hides and skins in the early stages of the process) and fungal (which usually applies after tannage has taken place). Fungal biodeterioration can affect leather both in part-processed condition within the tannery and after it has been made into and distributed as a fully finished article. Fungal deterioration is apparent from the growth on the leather of moulds. Moulds are part of the group known as fungi - a group of unique organisms that sit uneasily between microbiology and botany. They are neither filamentous bacterium nor are they similar to green plants. There are many strains of mould that are capable of growing on leather, but often the presence of one strain suppresses the appearance of others. Aspergillus niger, for example, usually results in the inhibition of other strains, although the others are quite capable of widespread growth in the absence of A. niger. Like all living organisms they need certain basics to grow and multiply: a source of moisture and a source of nutrient. In wet-blue leather the source of moisture is clear. In finished leather the moisture content is very much lower and the growth of mould is less, but when transporting leather between different climatic zones, or if storing leather in an inappropriate manner, moisture build up in certain areas, such as just inside any packaging, can readily lead to the growth of mould. Many of the process chemicals used in the manufacture of leather act as nutrients for mould growth, examples include ammonium salts, phosphates, surfactants, fatliquoring agents and other organic agents. The appearance of the mould growth is related to the type of mould present. In the minds of many people mould is usually associated with green/grey growths. Tanners, however, may also be familiar with the red spots or red discolouration caused by Paecilomyces ehrlichii, P. aculeatum, P. purpurogenum and P. roseopurpureum. In poorly controlled drying operations, where the humidity remains high or air circulation is poor, other types of growths may also be found, giving rise to other coloured appearance such as green, yellow-brown, dark-brown and grey. Strains associated with damage arising from poor drying control, include A. ochraceus, A. wentii, P. rugulosum, P. funiculosum, P. variotii and V. glaucum. Fungicides are the chemicals used to control or, better still, prevent mould growth and those used in the leather industry fall into two broad chemical families; phenolics, (which include CMC, OPP and TCP) and heterocyclics (which include TCMTB, OITZ, BMC and DIMTS). In general, fungicides interfere with the fungal germination and penetration process or inhibit fungal growth and reproduction within plant tissues. More specifically, fungicides may interfere with cell division, may inhibit the activity of certain enzymes, or may alter the function of cell membranes. As a measure of effectiveness fungicides should be demonstrated to have the following properties:
- high activity
- a broad antimicrobial spectrum
- compatibility with leather and with process liquors
- stability on leather
- non-discolouring
- environmentally acceptable
- low toxicity to humans and other warm-blooded animals
- cost effectiveness
- 1. C Hauber, H P Germann, 1997. The addition of fungicides in chrome tannage and their penetration, absorption and distribution in the wet-blue. World Leather, May 1997, pp75-82
- For further information contact BLC Leather Technology Centre Ltd on info@blcleathertech.com