The natural dyeing industry has been faced with increasing demands, being spurred by constant needs for environment- and body-friendly clothing products among modern consumers. Natural dyeing has been attracting attention as a next-generation technology in green textile. Dyestuffs need to be diversified for technological development activation in order to meet the increasing demands for natural dyeing. This study thus extracted dyeing solutions from the petals, leaves, and twigs of the rose of Sharon, the national flowers of South Korea, and investigated their dyeing properties for the development of various natural dyestuffs.
In the study, the investigator set out to apply the dyeing solutions extracted from the petals, leaves, and twigs of the rose of Sharon to cotton, one of the representative plant-based environment-friendly materials, and silk, one of the representative animal-based materials, let colors express themselves in various ways, and conduct scientific assessments of them in terms of color difference, color fastness(fastness against washing, dry cleaning, friction, sunlight, and sweat), and functionality(deodorant property and antibacterial activity), thus providing basic data for researches on environment-friendly dye manufacturing technologies as part of the efforts to discover new natural dyes and establish a national system for natural dyes and also for the activation of natural dying industry, standardization of natural dyeing process, and a support system of national certification.
The findings were as follows: as for the dyeing properties of rose of Sharon leaves for silk, the dye uptake level recorded the highest 2.16 at 90℃ and after 60 minutes. As for the property of a dyeing solution according to the pH conditions of dyebaths, the dye uptake level recorded the highest 4.87 at pH3 and started to drop after the peak. As for dyeing properties according to the concentration of a dyeing solution, the dye uptake level recorded the highest 2.16 at 100% concentration. Dyeing equilibrium reached 2.92 after two or three times of repetitive dyeing. As for results according to mordants and mordanting methods, the dye uptake level recorded the highest 4.12 for Sn pre-mordanting and the highest 3.08 for Fe post-mordanting.
The study also examined the dyeing properties for the rose of Sharon leaves for cotton, dyeing equilibrium reached 0.81 at 50℃ and 0.85 after 40 minutes and also 60 minutes, based on which the conditions were set at 50℃ and 60 minutes in the following experiments. As for dyeing properties according to the concentration of a dyeing solution, the dye uptake level recorded the highest 0.85 at 100% concentration. Dyeing equilibrium reached 1.02 after three times of repetitive dyeing and 1.06 after four times of repetitive dyeing. The investigator also processed fabric with tannin acid and did combination dyeing with gardenia seeds, barberry roots, and onions to improve the dye uptake level of rose of Sharon leaves for cotton. As for dyeing materials processed with tannic acid, K/S was 0.85 in no dyeing and rose to 1.01 since. It was 5.66, 4.15, and 16.91 for combination dyeing with gardenia seeds, barberry roots, and onions, respectively, which indicates that the dye uptake level improved. As for results according to mordants and mordanting methods, the dye uptake level recorded the highest 1.22 for Sn pre-mordanting and the highest 1.09 for Fe post-mordanting. Colors were in the Y and R family.
As for the fastness of rose of Sharon leaves, fastness against washing was excellent with color change in grade 4 and contamination in grade 4 or 5; fastness against dry cleaning was also excellent with both contamination and color change in grade 4 or 5; fastness against friction was excellent, as well, in grade 4 or 5 in a dry or wet state; fastness against sweat was also excellent with color change in grade 4 or 5 in an acid or alkali state and good with contamination in grade 4 in an acid or alkali state; and fastness against sunlight was rather low in grade 2.
The deodorant property of rose of Sharon leaves was good at up to 90% after 120 minutes. rose of Sharon leaves turned out to have no antibacterial activity as reported in previous studies.
The investigator did combination dyeing with petals so as to increase the antibacterial activity of hibiscus leaves and found that the dye uptake level rose to 6.13, which suggests that combination dyeing with petals resulted in antibacterial activity. The color was 3.8R, much influenced by the color of petals, which was 3.8R.
As for the dyeing properties of hibiscus flowers for silk, the dye uptake level dropped according to temperature, recording 5.52, 4.93, and 4.78 at 40℃, 60℃, and 80℃, respectively. Dyeing equilibrium reached 5.52 and 5.57 after 30 and 50 minutes, respectively, based on which the conditions were set at 40℃ and 30 minutes for the following experiments. As for the property of a dyeing solution according to the pH conditions of dyebaths, the dye uptake level was 3.64 at pH3 and made a sharp drop since then. As for dyeing properties according to the concentration of a dyeing solution, the dye uptake level recorded the highest 5.52 at 100% concentration. Dyeing equilibrium reached 9.39 for four times of repetitive dyeing and 9.52 for five times of repetitive dyeing. As for the results according to mordants and mordanting methods, the dye uptake level recorded the highest 4.12 for Sn pre-mordanting and the highest 3.08 for Fe post-mordanting. The color gamut was broad in the range of 8.1R to 3.8R, which indicates that a hibiscus petal is a pleochroic dye.
As for the dyeing properties of hibiscus flowers for cotton, the dye uptake level recorded 1.89 at 50℃ and after 60 minutes and started to drop after that, based on which the conditions were set at 50℃ and 60 minutes for the following experiments. As for dyeing properties according to the concentration of a dyeing solution, the dye uptake level recorded the highest 1.89 at 100% concentration.
Dyeing equilibrium reached 2.33 for four times of repetitive dyeing and 2.34 for five times of repetitive dyeing. The fabric was processed with milk to improve the dye uptake level. The results show that K/S was 1.85 in no dyeing and rose to 2.03 after the processing. As for the results according to mordants and mordanting methods, the dye uptake level recorded 1.22 for Sn pre-mordanting and 1.08 for Fe post-mordanting. The colors were diverse in the Y and R family, which suggests that a hibiscus petal is a pleochroic dye.
As for the fastness of hibiscus flowers, fastness against washing was low in color change at grade 1 or 2 and excellent in contamination at grade 4 or 5; fastness against drying cleaning was excellent with both contamination and color change in grade 4 or 5; fastness against friction was also excellent in grade 4 in a dry state and grade 4 or 5 in a wet state; fastness against sweat was good with both color change and contamination in grade 3 or 4 in an acid or alkali state and contamination; and fastness against sunlight was rather low in grade 1 or 2.
The deodorant property of hibiscus flowers was excellent at up to 99% after 120 minutes. As for their antibacterial activity, it was 99.9% for both Staphylococcus aureus and pneumoniae. The results suggest the possibilities of hibiscus petals as an environment-friendly natural dye.
As for the dyeing properties of hibiscus twigs for silk, they were 3.80, 5.25, 5.65, 6.12, and 7.05 after one, two, three, four, and five times of dyeing. The dye uptake level was 2.16 after one time of dyeing. The investigator mixed the dyeing solution of twigs with that of leaves to improve the low dye uptake level and found that the dye uptake level was 4.06. When the dyeing solutions of hibiscus twigs and leaves are mixed and used together, they will make a good natural dye.
Representing the nation, the rose of Sharon has long been considered as the national flowers. However, its status is dependent on common law, not being codified. It has been used as street trees, for decorative purposes, or to make Deokeum tea. If it is applied to natural dyeing, its applicability will further expand. The results of the present study will offer educational materials about natural dyeing with the rose of Sharon to the public and students.
In addition, its proven functionalities(deodorant property and antibacterial activity) will help to produce high value added environment-friendly products. Those findings demonstrate the possibilities of the rose of Sharon as an environment-friendly dye.