Production of a concentrated natural dye from Canadian Goldenrod (Solidago canadensis) extracts

The dyestuff content in plant sources is rather low, usually in the order of a few % of the mass of dry plant material. Introduction of plant dyes into technical scale textile dyeing operations thus requires handling, extraction and disposal of huge amounts of plant material.The precipitation of a solid, dyestuff-containing residue by addition of FeSO4·7H2O to the aqueous plant extract yields a highly concentrated plant dye. In this work Canadian Goldenrod (Solidago canadensis) was used as representative case to study production of a concentrated solid plant dye. An iron content of 5% w/w of the dry precipitate was analysed by photometry (1,10-Phenanthroliniumchloride). The content of total phenolics (TPH) calculated as gallic acid monohydrate equivalents according the Folin-Ciocalteau method, was determined with 45% w/w.The dyestuff precipitate was tested in standard dyeing experiments. Shade and colour depth were found comparable to dyeings obtained with direct use of plant extracts. Use of a concentrated natural dye product offers new approaches with regard to standardisation of dyestuff quality, handling and applicable dyeing techniques.

► A solid natural dye product can be precipitated from Canadian Goldenrod extracts.
► Iron(II)sulphate can be used to precipitate natural colourants.
► Production of concentrated natural dyes is a key-step for technical use of natural dyes.
► Dyeing results with precipitated dye lake are comparable to direct use of plant extract.