Materials
Scoured wool fabric (ISO 105-F01; plain woven 125 g/m2) was purchased from Testfabrics Inc. (West Pittston, PA). The spent coffee grounds used in the research were arabica (Coffee arabica L.) coffee beans, which were dried in a conventional oven at 60 °C within 24 h after collection of the spent coffee grounds from a coffee house located in Gongju, Chung-nam province. For mordanting, tannic acid (ACS reagent) was purchased from Sigma-Aldrich (St. Louis, MO, USA), and to measure the antioxidant ability, DDPH (1,1-diphenyl-2-picrylhydrazyl) was obtained from Calbiochem (CA, USA).
Preparation method
Obtaining the spent coffee extract
The spent coffee extract was extracted from dried spent coffee grounds collected from the coffee house under a 15-bar pressure using a manual espresso machine (Gaggia Gran Prestige, Milano, Italy). A total of 5 L was extracted and was used as a stock solution for this research.
Dyeing
The wool fabrics were each cut into 30 cm × 30 cm pieces, put into the stock solution, and dyed using an infrared (IR) dyeing machine (Lab IR dyeing machine, Daelim Starlet Co., Ltd; Gyeonggi-do, Korea). The bath ratio was 1:30, and the bath rotational speed was 45 rpm. The dyeing temperature and time were 90 °C and 60 min, which were discovered to be optimal based on preliminary research. After dyeing, the wool fabrics were completely washed with deionized water and dehydrated using a padder to contain a consistent amount of water (100% wet pickup).
Mordanting
After dyeing, dehydrated wool fabrics were placed in containers containing aqueous 0, 0.25, 0.5, 1.0, and 2.0 wt% tannic acid solutions (bath ratio = 1:30). Then, the containers were shaken at 130 rpm for 60 min at 85 °C. After that, the wool fabrics were thoroughly rinsed with deionized water and dried in a convection oven at 60 °C.
Measurement and analysis
In order to identify the changes in the molecular structures in the fabric surfaces after dyeing, the bond structure was analyzed using an infrared spectrometer (Fourier-transform infrared spectroscopy, FTIR). The FTIR spectrum analysis device (100 FTIR spectrum, Perkin-Elmer MA, US) was used with a resolution of 4 cm−1, and attenuated total reflection was used to obtain the results.
The changes in the colors of the dyed samples were investigated using a photoelectric spectrophotometer (CM-2500d, Konica Minolta, Inc., Osaka, Japan) and the values of changes in colors (ΔE) were compared using L*, a*, and b* values. In addition, by using the Kubelka–Munk method, the color strength (K/S) values were derived.
Color fastness to washing (KS K ISO 105 C06:2010, A2S, washing temperature: 40 ± 2 °C, washing time: 30 min, 0.4% ECE standard solution +0.1% natrium used, 10 still balls) and color fastness to light (KS K ISO 105 B02:2010, xenon arc lamp, blue scale) results were obtained on request from the FITI Testing and Research Institute.
The ability of the dyed fabrics to prevent microbial growth and retention were tested using S. aureus (ATCC 6538; a Gram-positive bacterium) and K. pneumoniae (ATCC 4352; a Gram-negative bacterium) cultures according to an established protocol (KS K 0693).
$$Bacterial\,reduction\,\left( \% \right) = \frac{{\left( {B - A} \right)}}{B} \times 100$$
(1)
In the formula, each of A and B represents the surviving bacterial cells (colony-forming units in mL−1) on the plates inoculated with a bacterial solution derived from the dyed fabric and a control solution derived from untreated fabric, respectively.
For determining the antioxidant ability, the DDPH· method was used. DPPH· can measure radical activity by measuring the reduced speed of chemical response due to radical scavenging after its addition (Alger 1997). The radical scavenging activity was calculated using Eq. (2), and the detailed analysis method is provided in previous literature (Koh and Hong 2017a, 2018).
$$DPPH \cdot {scavenging\, activity} \,{\left( \% \right)} = \frac{{\left( {{\text{C}} - {\text{S}}} \right)}}{\text{C}} \times 100$$
(2)
Here, C and S refer to the values of absorbance at 517 nm after 1 h of resting in a dark room for the control sample and test sample in DPPH·/methanol solvents.