Biocolourant applications in textiles, plastic and wood coatings

During the spring first biocolourant application tests and pilots with different materials were carried out in the BioColour-project.

Natural indigo colored plastic and wood coatings

HAMK research team focuses on applications of biocolourants in solid materials such as plastic and wood. These materials are often subject to corrosion and different weather conditions in their use, which makes the study of long-term durability of colourants especially important. This spring HAMK-team have focused on testing bio-based PLA plastic and wood coatings dyed with natural indigo from woad (Isatis tinctoria)  

For testing the coloration properties of PLA, Polylactic acid granules were extruded into colored filaments with various amounts of synthetic and woad-based natural indigo (the main photo features filaments coloured with woad-based indigo). The filaments have then been granulated, and injection molded into samples and are on their way to artificial weathering tests. In the tests that will be carried out this summer, the pigments’ durability in the plastic will be studied by exposing the samples to UV-light and water condensation. Color, gloss and hyperspectral properties of the samples will be measured before, during and after the testing period.

Wooden test specimens coated with indigo dyed paints and lacquer. There are also reference samples containing commercial pigments

HAMK-team has also carried out artificial weathering tests for linen-based coating oil, paint and varnish colored with woad-based natural indigo, synthetic indigo and commercial pigments. For the tests, wooden samples were painted with the colored coatings and are currently being exposed to UV-light, water condensation and water spray. The changes of color, gloss and spectral properties of the samples due to the exposure to weather-like conditions will be used for assessing the performance and usability of natural indigo as a pigment in wood coatings.

Dyeing methods for textiles using food by-products

In May, coloring studies on food by-products were carried out in the BioColour laboratory of the University of Helsinki. The first tests were made using the skins of yellow and red onion (Allium cepa) as a dye source and cotton knit as the dyed material.

Onion skins contain flavonoid-structured dyes, in addition to which the red onion also contains anthocyanin dyes to produce the red color typical of this variety. By varying the dyeing conditions, such as temperature, acidity of the solution, and mordant agent, the color shade of the dyed material was varied greatly. The onion skins are rich in dyes and produced strong shades on the cotton. Next step is to study the color fastness of the dyed materials, on the basis of which choices will be made to further develop the dyeing method. The goal is to be able to implement small-scale business piloting next autumn.

Liquid dye extracts from yellow and red onion skins (Allium cepa).
The diverse colours from onion skins generated by varying the dyeing conditions.

Industrial level yarn and fabric dyeing with woad-plant

To be able to use natural dyes in an industrial scale manufacturing, tests with applied methods are needed. The dyeing process needs to be adjusted according to existing machinery and very often is it not an “optimal” process for the dye type as it is in the small scale lab equipment. Kirsi Niinimäki from Aalto University team lead the industrial level dyeing pilots.

Yearn dyeing with the automated dyeing machine at Lappajärvi dye-works. Up to 300 kg of material can be dyed at once.

The tests were carried out using woad (Isatis tinctoria), that gives a nice Indigo type blue colour and that was cultivated in Finland by project’s business partner Natural Indigo Finland. The dye was used in a liquid form. Dyeing was tested both in Värisävy (fabric dyeing) and in Lappajärven värjäämö (Lappajärvi dye-works, yarn dyeing) during spring 2020 and tests were very succesfull.

Linen yarn dyed with woad (Isatis tinctoria).

Riikka Alanko, interaction coordinator of the project