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Rural Industries Research & Development Corporation
Enhancing the Unique Properties of Kangaroo Leather
Mark Looney, Ilias (Louis) Kyratzis, Yen Truong and Jacinta Wassenberg
RIRDC Publication No 02/105 RIRDC Project No CWT-1A
The commercial use of kangaroo meat and skins has developed into the largest native animal industry in Australia, estimated to be worth $200M and providing over 4000 jobs mainly in rural areas. One of the factors associated with the significant growth of the industry has been the decline in exporting raw skins and an increase in processing in Australia. Due to the unique skin morphology of kangaroo, leather produced is high in strength but remains lightweight and flexible which has resulted in increasing demand from the manufacturers of high-quality leather goods including footwear. Despite this uniqueness there is a strong push for continual improvement especially to protect the existing leather markets from potential competition from improving synthetic products.
The aim of this project was to determine the factors that affect leather strength during the various stages of processing kangaroo skins including the effects of preservation methods of the skins prior to processing at the tannery, pickle storage, chemical processing and mechanical operations carried out during the tanning and retanning processes. In addition to these factors the effects on strength of species (Red and Grey) and harvest season (winter, summer) were also investigated. Although the effect on the tensile and tear strength was examined during the course of the work, the majority of the report focused on the tear strength due to its significance in regards to leather quality. The results in this report were determined using commercial processes. The complexity of leather processes and the broad range of reagents that are available may mean that the findings may not apply to other processes.
The findings are summarised as follows:
The tear strength of the Western Australia red and grey skins appears to be intermediate between the Queensland red and grey skins.
The different preservation methods appear to only have marginal effects on strength.
Summer harvested skins show more variability in skin properties than winter harvested skins, especially within certain preservation groups.
Commercial pickled skins were able to be stored for periods of 6 months without losses in strength. Longer storage time, particularly at ambient Queensland temperatures resulted in losses in strength of greater than 10% and as high as 40% after 18 months in some cases.
Increased levels of chromium III salts added during the tanning stage or in the retanning, dyeing and fatliquoring step cause a decrease in tear strength. The potential loss of strength needs to be balanced against adequate long-term preservation, acceptable hydrothermal shrinkage temperature and the changes in handle of the final leather.
Tear strength is affected significantly during the retanning of the wet blue, with the resulting leather doubling in strength using the commercial process. Only marginal improvement in the tensile strength was evident going from wet blue to crust leather.
Tanning and retanning with organic based resins and syntans gave mixed results with most systems lowering strength, although, there were some exceptions. A modified polyaminecarboxylic acid provided an increase of 20% in tear strength and low levels of a dicyanamide resin increased tear strength when added either in the main tannage or in the retanning, dyeing and fatlquoring step. Glutaraldehyde in the main tannage was found to have a significant detrimental effect on the tear strength but in contrast, a modified glutaraldehyde reagent can offer a moderate improvement in the tear properties of the leather.
Fatliquors in the tanning and RDF process produced variable results. Modified fish oils, when compared to other types of fatliquors, were found to produce the leather with the best tear results. Some fatliquors such as sulfochlorinated paraffins were found to have a significant detrimental effect on tear strength. In the standard process used in the project, addition of fatliquors during the tanning process did not improve the tear strength of the final crust leather.
Significant improvements in tear strength ranging upto 63% could be obtained by incorporating certain types of waterproofing systems into the process as lubricating agents.
Addition of some of the waterproofing agents in the retan stage increases tear strength >20%, while addition late in the process, during the fatliquor stage, can increase tear strength by >50%. The required addition of chromium salts late in the process to fix the reagents and introduce waterproofing properties were found to significantly reduce the gains in tear strength from these systems.
In the neutralisation step, modifying the pH and time, to allow sufficient time for neutralising salts and fatliquors to penetrate, results in improved tear strength.
Colourants, dyes and pigments, added to the RDF were found to decrease tear strength in certain cases by >20%.
Preliminary work on the effect of drying on tear strength, suggests longer times or higher drying temperatures may improve tear strength. The observed behaviour of kangaroo appears to be different from that reported for bovine.
Overall the mechanical staking and shaving conditions examined generally cause a decrease in thickness but do not cause any significant change in strength of the leather.
The potential exists to gain improvements in strength by changing several factors during the course of the process. For example a dicyanamide resin increased strength by 18% and separately a waterproof agent increased strength by 43%. A combination of the resin and waterproof agent produced a 60% increase in tear strength compared to the standard process.
This value is comparable to the combined total of the two individuals trials and demonstrates the potential gains that may be achieved by small modifications to several parts of the process rather then one major change that may have a bigger impact on the properties of the leather.