4. Conclusions
There is significant interest to re-introduce natural dyeing into present technical production scale for textile colouration. For the extraction of plant material a huge amount of plant material has to be handled in the dyehouse, which is a major drawback for a wider future use of such dye sources. The production of a concentrated dyestuff containing product was achieved by use of simple methods, which contain extraction, precipitation, sedimentation, filtration and drying. The processes require only basic equipment and thus can be installed at the site of farming and harvesting. This technique has significant potential to replace the direct extraction of plant material in the dyehouse. In addition quality standardisation for improved reproducibility of the colour depth and shade can be done at the stage of dyestuff production.
The mass of dry residue that can be produced per kg of plant material is limited by the rather low dyestuff content present in the plant. In the given examples an average value of 3–4% of the dry plant mass was found to be formed by addition of FeSO4·7H2O solution. A concentration of 7.2 mM (2 g L−1) FeSO4·7H2O was found to be sufficient to form a solid precipitate with an Fe-content of 5% w/w and 45% w/w TPH (as gallic acid monohydrate equivalents).
The solid dyestuff is soluble in diluted acid and yields dyeing results which are comparable to the dyeings obtained with direct use of plant material extracts.
Highly concentrated dyestuff solutions up to 100 g L−1 dyestuff are required for continuous dyeing procedures. At present the low concentration of dyestuff in the extract limits the possible application techniques for dyehouses, thus mainly exhaust dyeing procedures are used. This limitation can be overcome when concentrated dyestuff product is available, which permits production of higher concentrated dye solutions and thus allows application in a wide range of different dyeing techniques.