Optimized Dyeing Process for Enhancing the Functionalities of Spent Coffee Dyed Wool Fabrics Using a Facile Extraction Process

Abstract

Spent coffee grounds are the byproduct of coffee brewing and are generally discarded as waste. However, spent coffee has high levels of organic compounds that have multiple biological effects, including antibacterial and antioxidant activities. In this light, spent coffee grounds were tested for fabric dyeing to both functionalize as well as color the fabrics. The dyeing solution was prepared by extracting spent coffee grounds collected from a local coffee house by using a manual espresso machine. The spent coffee extract was applied to wool fabrics using a laboratory infrared dyeing machine. After the dyeing process was completed, the fabrics were mordanted with a tannic acid aqueous solution. To optimize the dyeing conditions, the times and temperatures during the process were varied, and the functionalities and other properties including color and strength of the wool fabrics dyed with the spent coffee extract were investigated. The wool fabrics dyed with the spent coffee extract were significantly colored, and the color withstands the effect of washing and light exposure. Moreover, the dyeing process with the spent coffee extract and the mordanting process with tannic acid gave the wool fabrics antibacterial and antioxidant properties.

Full text

polymers
Article
Optimized Dyeing Process for Enhancing the
Functionalities of Spent Coffee Dyed Wool Fabrics
Using a Facile Extraction Process
Jihyun Bae 1and Kyung Hwa Hong 2, *
1College of Human Ecology, Department of Clothing and Textiles, Hanyang University,
Seoul 04763, South Korea; jbae2@hanyang.ac.kr
2College of Natural Science, Kongju National University, Chungnam 32588, South Korea
*Correspondence: hkh713@kongju.ac.kr; Tel.: 82-41-850-8305
Received: 1 March 2019; Accepted: 25 March 2019; Published: 28 March 2019


Abstract:
Spent coffee grounds are the byproduct of coffee brewing and are generally discarded as
waste. However, spent coffee has high levels of organic compounds that have multiple biological
effects, including antibacterial and antioxidant activities. In this light, spent coffee grounds were
tested for fabric dyeing to both functionalize as well as color the fabrics. The dyeing solution was
prepared by extracting spent coffee grounds collected from a local coffee house by using a manual
espresso machine. The spent coffee extract was applied to wool fabrics using a laboratory infrared
dyeing machine. After the dyeing process was completed, the fabrics were mordanted with a tannic
acid aqueous solution. To optimize the dyeing conditions, the times and temperatures during the
process were varied, and the functionalities and other properties including color and strength of
the wool fabrics dyed with the spent coffee extract were investigated. The wool fabrics dyed with
the spent coffee extract were significantly colored, and the color withstands the effect of washing
and light exposure. Moreover, the dyeing process with the spent coffee extract and the mordanting
process with tannic acid gave the wool fabrics antibacterial and antioxidant properties.
Keywords: wool; spent coffee; tannin; dyeing; antibacterial property; antioxidant property
1. Introduction
Approximately 7.4 million tons of coffee is produced each year and it is the most consumed
luxury table beverage in the world. Coffee is also the second most traded commodity by volume
after petroleum, indicating that the economic impact of coffee is substantial [
1
]. In 2017 in Korea
alone, approximately 26.5 billion cups of coffee were consumed. Considering the population of Korea,
approximately 512 cups of coffee were consumed per person in 2017. Korea’s coffee market exceeded
10 trillion KRW (ca. 8.76 billion USD) for the first time in 2017. This market size is more than three times
greater than it was 10 years ago [
2
]. Since coffee consumption has increased so dramatically, the amount
of spent coffee grounds produced after brewing coffee cannot be ignored. In contrast to the rapid
growth of the coffee market, the development of efficient treatments for spent coffee grounds is difficult
because there is no established system for collecting and recycling spent coffee grounds [
3
]. Spent
coffee grounds are not just food garbage; they are also a major cause of environmental pollution since
they produce a large amount of methane gas, which has an adverse effect on global warming. The effect
of methane gas is assumed to be approximately 2.5 times worse than that of carbon dioxide, and the
amount of carbon dioxide produced by spent coffee grounds is approximately 1.6 times more than that
produced by black tea [
4
]. However, spent coffee grounds still contain many functional components,
such as phenolic compounds, terpenes, caffeine, and Maillard reaction products. Therefore, treatment
of this bio-waste by simply burying it in a landfill or incinerating it may be wasting a valuable resource.
Polymers 2019,11, 574; doi:10.3390/polym11040574 www.mdpi.com/journal/polymers

Polymers 2019,11, 574 2 of 11
Our group recently conducted a study on the dyeing and finishing of cotton and wool fabrics
by using spent coffee extract prepared by the extraction method suggested by Mussatto et al. [
5
].
This method was reported to be effective for extracting active components from spent coffee grounds.
It involves placing the spent coffee grounds in a 60% aqueous methanol solution and shaking the
solution for 60 min in a water bath at 60
◦
C [
6
,
7
]. The study showed that the fabrics treated with
the spent coffee extract displayed a good antioxidant capacity and significant antibacterial activity,
especially towards Gram-positive bacteria. In particular, the spent coffee extract showed strong color
fastness in the fibers containing amide groups in their polymers (such as those found in wool fiber).
This strong color manifestation indicates that spent coffee grounds may be an effective material for fiber
dyeing and functionalization. Recently, we found that higher concentrations of effective components
such as total phenolics and total condensed tannins are present in the spent coffee extract prepared
by a typical espresso machine than in the extract prepared via a methanolic extraction [
5
–
7
]. Thus,
machine extraction may be a good extraction method for fiber dyeing because it does not require
methanol, a toxic solvent, which would need to be evaporated from the extract for fabric applications
such as dyeing. In the present study, spent coffee extract prepared by using an espresso machine was
used for wool dyeing, and the optimal dyeing conditions were investigated. In addition, tannic acid
was used as a mordant in the fabric to improve its functionalities and the coloring effect of the spent
coffee extract on the wool fabric. In addition, tannic acid is well known as an eco-friendly mordant and
many researchers have been using it for attaining high quality natural dyeing along with imparting
multifunctional properties from textile dyes [8,9].
2. Materials and Methods
2.1. Sample Material and Chemicals
A commercially available scoured wool fabric (ISO 105-F01; plain woven 125 g/m2) was
prepared (Testfabrics Inc. West Pittston, PA, USA). Spent coffee grounds (Coffea arabica L.) were
supplied from a local coffee house in Gongju, Korea. Folin-Ciocalteu reagent, gallic acid (
≥
97%),
vanillin (99%), (+)-catechin hydrate (
≥
98%), potassium iodate, sodium bicarbonate, formic acid,
acetonitrile, trigonelline, protocatechuic acid, tannic acid (ACS reagent, Mw: 1701.20), chlorogenic
acid, and caffeine were purchased from Sigma-Aldrich (St. Louis, MO, USA). Free radical DPPH
(1,1-diphenyl-2-picrylhydrazyl) was purchased from Calbiochem (San Diego, CA, USA). All reagents
were used as received without further purification.
2.2. Extraction of Spent Coffee Grounds to Prepare the Dyeing Solution
A manual espresso machine (Gaggia Gran Prestige, Milano, Italy) at a pump pressure of 15 bar
was utilized for extracting dying solution from the spent coffee. The extract was used as a stock
solution for the dyeing of fabrics in this study.
2.3. Dyeing Process
Wool fabrics were cut into 30 cm
×
30 cm pieces, and each piece was immersed in a vessel
containing the stock solution of the spent coffee extract (bath ratio = 1:30). A laboratory infrared
(IR) dyeing machine (Daelim Starlet Co., Ltd; Gyeonggi-do, Korea) was used for the dyeing process.
The temperature of the dyeing bath was gradually increased (ca. 3
◦
C/min) up to the designated
temperature (60, 90, and 120
◦
C), and then that temperature was maintained while the vessels were
rotated at 45 rpm for the designated dyeing time (30, 60, 90, and 120 min). The dyed wool fabrics were
thoroughly rinsed with deionized water and squeezed using a padder to obtain 100 wt % of a specified
wet pick-up rate.

Polymers 2019,11, 574 3 of 11
2.4. Mordanting Process
The wool fabrics dyed with the spent coffee extract were subsequently mordanted as follows.
After being squeezed with a padder, the damp wool fabrics were put into vessels containing a 1 wt %
tannic acid aqueous solution (bath ratio = 1:30). The vessels were then shaken at 130 rpm for 60 min at
85
◦
C. The wool fabrics were next thoroughly rinsed with deionized water and dried in a convection
oven at 60 ◦C.
2.5. Analysis of the Spent Coffee Extract
The antioxidant compounds in the spent coffee extract were analyzed by high-performance liquid
chromatography (HPLC) using a diode array detector (Agilent Technologies, 1260 Infinity, Waldbronn,
Germany). A Kinetex 5-
µ
m C18 column (150 mm
×
4.6 mm i.d., Phenomenex, Torrance, CA, USA)
was employed at 40
◦
C. The antioxidant compounds were separated by a gradient mobile phase
consisting of (A) 0.1% formic acid and (B) acetonitrile at a flow rate of 1 mL/min. The gradient
was programmed as follows: 0–10 min, 15%–37% B; 5–10 min, 37%–80% B; 10–12 min, 80%–100%
B; and 12–13 min, 100%–15% B. The major antioxidant compounds were identified based on the
similarities between their experimental retention times and ultraviolet-visible (UV-Vis) spectra and
those of pure authentic standards (trigonelline, gallic acid, chlorogenic acid, and caffeine). The total
phenolic content in the spent coffee extract was measured by the colorimetric method described by
Singleton and Rossi [
10
]. Folin–Ciocalteu reagent (2.5 mL, previously diluted with water 1:10, v/v)
and 2 mL of 75 g/L aqueous sodium carbonate were added to 0.5 mL of an aqueous solution of the
extract. The mixture was kept at 50
◦
C for 5 min, and after cooling, the absorbance was measured at
760 nm (Biomate5 spectrophotometer, Thermo, Waltham, MA, USA). The total phenolic content was
calculated in terms of gallic acid equivalents (GAE) from the calibration curve of gallic acid standard
solutions (2–40
µ
g/mL) and is expressed as mg gallic acid equivalent (GAE)/mg of extract (on a dry
basis). The total tannin content in the spent coffee extract was determined by the vanillin/HCl method
described by Broadhust and Jones [
11
] with some modifications. An aliquot of the extracts (1 mL) was
added to the vanillin reagent (2 mL), which had been prepared by dissolving vanillin in methanol
(0.5%, w/v). Aqueous HCl (2 mL, 4%, v/v) was added to the mixture, and then the mixture was
incubated in the dark. The absorbance was measured at 500 nm after 20 min of incubation. Different
concentrations (500–3000
µ
g/mL) of (+)-catechin standards were used to calculate the condensed
tannin content. The total tannin content was expressed as mg of tannic acid equivalents (TAE)/mL.
All samples were analyzed in triplicate, and the mean value was calculated.
2.6. Characteristics of the Fabrics Dyed with the Spent Coffee Extract
Color properties, in terms of the L*, a*, and b* values, and color differences,
∆
E, of the dyed
fabrics were investigated using a spectrophotometer (CM-2500d, Konica Minolta, Inc., Osaka, Japan).
The color strength (K/S) values were assessed using the Kubelka–Munk Equation (1):
K/S =(1−R)2
R(1)
In the above equation, R is the decimal fraction of the reflectance of the dyed fabric.
Color fastness was investigated as follows: color fastness to washing (ISO 105 C06: 2010, A2S,
30 min mechanical wash at 40
±
2
◦
C in 0.4% European Colorfastness Establishment (ECE) reference
detergent and 0.1% sodium perborate tetrahydrate solution with 10 steel balls); color fastness to light
(ISO 105 B02: 2014, Xenon-arc lamp, blue scale). All tests were conducted at least in triplicate for
all samples.
The shrinkage rate of dyed fabrics was determined based on the fabric count values measured via
fabric analyzing glass, and calculated using Equation (2):

Polymers 2019,11, 574 4 of 11
Shrinkage (%)=D−P
D×100 (2)
In the above equation, D and P represent the fabric count values of dyed fabrics and pristine
fabrics, respectively.
The tensile strength of the fabrics was measured by the cut strip method (modified ASTM D5035)
only in the weft direction using an Instron 5543 system (Norwood, MA, USA); 300 mm/min, gauge
length: 50 mm, specimen width: 25 mm.
Fourier transform infrared (FT–IR) spectrometry was performed using a Spectrum 100 Optica
FT–IR instrument (PerkinElmer, Waltham, MA, USA) with a resolution of 4 cm
−1
. The FT–IR
measurements were carried out using an attenuated total reflectance (ATR) technique.
The ability of the dyed fabrics to impede microbial growth and retention was tested using
Staphylococcus aureus (ATCC 6538; a Gram-positive bacterium) and Klebsiella pneumoniae (ATCC 4352;
a Gram-negative bacterium) cultures according to an established protocol (KS K 0693).
Reduction of bacteria (%)=(B−A)
B×100 (3)
In the above equation, A and B represent the surviving bacterial cells (colony-forming units mL-1)
on the plates inoculated with the bacterial solution derived from the dyed fabric and a control solution
derived from untreated fabric, respectively.
The antioxidant activity of the dyed fabrics was measured with DPPH using a previously reported
method [
12
]. More details are presented in our previous papers [
6
,
7
]. Lower absorbances of the
solutions indicated higher DPPH scavenging abilities. The DPPH scavenging ability was calculated
using Equation (4).
DPPH ·scavenging activity (%)=C−S
C×100 (4)
In the above equation, S and C represent the absorbance at 517 nm of the sample from the dyed
fabric and that of the control from the untreated fabric, respectively.
3. Results
3.1. Analysis of the Components of the Spent Coffee Extract
Four compounds were identified in the spent coffee extract by comparing their retention times
and UV-Vis spectra with those of authentic standards (pure chemicals). Although a tiny peak appeared
near the retention time corresponding to protocatechuic acid in Figure 1b, its UV-Vis spectrum was
not identical with that of protocatechuic acid. This revealed that there is no protocatechuic acid in
the spent coffee extract prepared in this research, even though the functional compound is known to
exist in coffee extract [13]. The other four identified peaks were phenolic compounds (gallic acid and
chlorogenic acid) and nitrogenous compounds (trigonelline and caffeine). Among the compounds
identified, caffeine was the most abundant in the spent coffee extract. These results are consistent with
previous studies [
6
]. The total phenolic content and total tannin content in the spent coffee extract
were 2.63 g/L(GAE) and 10.20 g/L(TAE), respectively. For comparison, the total phenolic and total
tannin content in the spent coffee extract prepared using methanolic method were 2.00 g/L(GAE) and
0.61 g/L(TAE), respectively, according to our previous study [
6
,
7
]. Therefore, it was found that all the
functional compounds extracted by the espresso machine are present in much greater quantities than
those extracted by the methanolic method.

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Polymers 2019, 11, x FOR PEER REVIEW 4 of 11
Fourier transform infrared (FT–IR) spectrometry was performed using a Spectrum 100 Optica
FT–IR instrument (PerkinElmer, Waltham, MA, USA) with a resolution of 4 cm−1. The FT–IR
measurements were carried out using an attenuated total reflectance (ATR) technique.
The ability of the dyed fabrics to impede microbial growth and retention was tested using
Staphylococcus aureus (ATCC 6538; a Gram-positive bacterium) and Klebsiella pneumoniae (ATCC 4352;
a Gram-negative bacterium) cultures according to an established protocol (KS K 0693).
Reduction o
f
bacteria (%) = (B − A)
B × 100 (3)
In the above equation, A and B represent the surviving bacterial cells (colony-forming units mL-
1) on the plates inoculated with the bacterial solution derived from the dyed fabric and a control
solution derived from untreated fabric, respectively.
The antioxidant activity of the dyed fabrics was measured with DPPH using a previously
reported method [12]. More details are presented in our previous papers [6,7]. Lower absorbances of
the solutions indicated higher DPPH scavenging abilities. The DPPH scavenging ability was
calculated using Equation (4).
DPPH ⋅ scavenging activit
y
(%) = C−S
C × 100 (4)
In the above equation, S and C represent the absorbance at 517 nm of the sample from the dyed
fabric and that of the control from the untreated fabric, respectively.
3. Results
3.1. Analysis of the Components of the Spent Coffee Extract
Four compounds were identified in the spent coffee extract by comparing their retention times
and UV-Vis spectra with those of authentic standards (pure chemicals). Although a tiny peak
appeared near the retention time corresponding to protocatechuic acid in Figure 1b, its UV-Vis
spectrum was not identical with that of protocatechuic acid. This revealed that there is no
protocatechuic acid in the spent coffee extract prepared in this research, even though the functional
compound is known to exist in coffee extract [13]. The other four identified peaks were phenolic
compounds (gallic acid and chlorogenic acid) and nitrogenous compounds (trigonelline and
caffeine). Among the compounds identified, caffeine was the most abundant in the spent coffee
extract. These results are consistent with previous studies [6]. The total phenolic content and total
tannin content in the spent coffee extract were 2.63 g/L(GAE) and 10.20 g/L(TAE), respectively. For
comparison, the total phenolic and total tannin content in the spent coffee extract prepared using
methanolic method were 2.00 g/L(GAE) and 0.61 g/L(TAE), respectively, according to our previous
study [6,7]. Therefore, it was found that all the functional compounds extracted by the espresso
machine are present in much greater quantities than those extracted by the methanolic method.
(a) (b)
Figure 1. High-performance liquid chromatograms of standards (a) and spent coffee extract (b) at 258
nm. 1: trigonelline; 2: gallic acid; 3: protocatechuic acid; 4: chlorogenic acid; and 5: caffeine.
Figure 1.
High-performance liquid chromatograms of standards (
a
) and spent coffee extract (
b
) at
258 nm. 1: trigonelline; 2: gallic acid; 3: protocatechuic acid; 4: chlorogenic acid; and 5: caffeine.
3.2. Fourier Transform Infrared (FT–IR) Spectra of the Wool Fabrics Dyed with the Spent Coffee Extract
The FT–IR spectra of the wool fabrics dyed with the spent coffee extract and mordanted with
tannic acid are shown in Figure 2. Wool fabrics are made from protein fibers containing various
functional groups, such as carboxyl (–COOH), amino (–NH
2
), and hydroxyl (–OH) groups [
14
]. Thus,
all wool fibers displayed similar absorption bands at 3283 cm
−1
(N–H and O–H), 2873 cm
−1
(–CH
2
),
1634 cm
−1
(amide I), 1512 cm
−1
(amide II), and 1229 cm
−1
(amide III). However, new peaks at 1312
cm
−1
and 1037 cm
−1
were observed in the spectra of the wool fabrics dyed with the spent coffee extract
and mordanted with tannic acid. These bands are presumed to be driven by the C–O stretching of the
ester attributed to tannin in the wool fabrics dyed with spent coffee extract and mordanted with tannic
acid. This is because the new bands were more intense after mordanting with tannic acid, as shown in
Figure 3. Tannin is very soluble in water, and the hydrolyzable tannins break down via hydrolysis
to give gallic acid, a type of phenolic compound [
15
–
17
]. Therefore, a significant amount of phenolic
compounds was chemically attached to the wool fibers through the mordanting process as well.
Polymers 2019, 11, x FOR PEER REVIEW 5 of 11
3.2. Fourier Transform Infrared (FT–IR) Spectra of the Wool Fabrics Dyed with the Spent Coffee Extract
The FT–IR spectra of the wool fabrics dyed with the spent coffee extract and mordanted with
tannic acid are shown in Figure 2. Wool fabrics are made from protein fibers containing various
functional groups, such as carboxyl (–COOH), amino (–NH
2
), and hydroxyl (–OH) groups [14]. Thus,
all wool fibers displayed similar absorption bands at 3283 cm
−1
(N–H and O–H), 2873 cm
−1
(–CH
2
),
1634 cm
−1
(amide I), 1512 cm
−1
(amide II), and 1229 cm
−1
(amide III). However, new peaks at 1312 cm
−1
and 1037 cm
−1
were observed in the spectra of the wool fabrics dyed with the spent coffee extract and
mordanted with tannic acid. These bands are presumed to be driven by the C–O stretching of the
ester attributed to tannin in the wool fabrics dyed with spent coffee extract and mordanted with
tannic acid. This is because the new bands were more intense after mordanting with tannic acid, as
shown in Figure 3. Tannin is very soluble in water, and the hydrolyzable tannins break down via
hydrolysis to give gallic acid, a type of phenolic compound [15–17]. Therefore, a significant amount
of phenolic compounds was chemically attached to the wool fibers through the mordanting process
as well.
Figure 2. Fourier transform infrared-attenuated total reflectance (FT–IR-ATR) spectra of wool fabrics
dyed with spent coffee extract for 60 min as a function of dyeing temperature (all dying samples were
mordanted with 1 wt % tannic acid aqueous solution): (a) untreated, (b) 60 °C, (c) 90 °C, and (d) 120
°C.
Figure 2.
Fourier transform infrared-attenuated total reflectance (FT–IR-ATR) spectra of wool fabrics
dyed with spent coffee extract for 60 min as a function of dyeing temperature (all dying samples were
mordanted with 1 wt % tannic acid aqueous solution): (
a
) untreated, (
b
) 60
◦
C, (
c
) 90
◦
C, and (
d
) 120
◦
C.

Polymers 2019,11, 574 6 of 11
Polymers 2019, 11, x FOR PEER REVIEW 5 of 11
3.2. Fourier Transform Infrared (FT–IR) Spectra of the Wool Fabrics Dyed with the Spent Coffee Extract
The FT–IR spectra of the wool fabrics dyed with the spent coffee extract and mordanted with
tannic acid are shown in Figure 2. Wool fabrics are made from protein fibers containing various
functional groups, such as carboxyl (–COOH), amino (–NH
2
), and hydroxyl (–OH) groups [14]. Thus,
all wool fibers displayed similar absorption bands at 3283 cm
−1
(N–H and O–H), 2873 cm
−1
(–CH
2
),
1634 cm
−1
(amide I), 1512 cm
−1
(amide II), and 1229 cm
−1
(amide III). However, new peaks at 1312 cm
−1
and 1037 cm
−1
were observed in the spectra of the wool fabrics dyed with the spent coffee extract and
mordanted with tannic acid. These bands are presumed to be driven by the C–O stretching of the
ester attributed to tannin in the wool fabrics dyed with spent coffee extract and mordanted with
tannic acid. This is because the new bands were more intense after mordanting with tannic acid, as
shown in Figure 3. Tannin is very soluble in water, and the hydrolyzable tannins break down via
hydrolysis to give gallic acid, a type of phenolic compound [15–17]. Therefore, a significant amount
of phenolic compounds was chemically attached to the wool fibers through the mordanting process
as well.
Figure 2. Fourier transform infrared-attenuated total reflectance (FT–IR-ATR) spectra of wool fabrics
dyed with spent coffee extract for 60 min as a function of dyeing temperature (all dying samples were
mordanted with 1 wt % tannic acid aqueous solution): (a) untreated, (b) 60 °C, (c) 90 °C, and (d) 120
°C.
Figure 3.
FT–IR-ATR spectra of wool fabrics dyed with spent coffee extract at 90
◦
C for 60 min:
(a) untreated, (b) not mordanted, and (c) mordanted with 1 wt % tannic acid.
3.3. Apparent Colors of the Wool Fabrics Dyed with the Spent Coffee Extract
Dyeabilities of the wool fabrics dyed with the spent coffee extract and mordanted with tannic acid
were improved overall as the dyeing time and dyeing temperature increased. In particular, dyeing
temperature had a significant effect on the dyeability, while dyeing time negligibly did, as shown in
Figures 4and 5. In addition, the wool fabrics dyed with the spent coffee extract and mordanted with
tannic acid showed increasing a* values but decreasing b* and L* values as the dyeing time and dyeing
temperature increased, as shown in Table 1. This result indicates that reddish hue became dominant but
yellowish hue became faint in the wool fabrics as the dyeing time and dyeing temperature increased.
It appears that the brown pigments were primarily caused by melanoidins produced during the process
of roasting coffee beans. Melanoidins are brown compounds and are known to have several biological
activities, such as antioxidant, antimicrobial, anticarcinogenic, anti-inflammatory, antihypertensive,
and antiglycative activities. However, knowledge of melanoidins in coffee including the chemical
structures is still lacking [
18
]. On the other hand, it was observed that mordanting with 1 wt % tannic
acid has little effect on the color appearance of wool fabrics dyed with spent coffee extract, as shown in
Table 1. To identify the levelness of wool fabrics dyed with the spent coffee extract, we investigated the
color difference of two different points with at least 10 cm distance within each sample. Consequently,
any unlevelness was not noticed in the wool fabrics dyed with the spent coffee extract.
Polymers 2019, 11, x FOR PEER REVIEW 6 of 11
Figure 3. FT–IR-ATR spectra of wool fabrics dyed with spent coffee extract at 90 °C for 60 min: (a)
untreated, (b) not mordanted, and (c) mordanted with 1 wt % tannic acid.
3.3. Apparent Colors of the Wool Fabrics Dyed with the Spent Coffee Extract
Dyeabilities of the wool fabrics dyed with the spent coffee extract and mordanted with tannic
acid were improved overall as the dyeing time and dyeing temperature increased. In particular,
dyeing temperature had a significant effect on the dyeability, while dyeing time negligibly did, as
shown in Figure 4,5. In addition, the wool fabrics dyed with the spent coffee extract and mordanted
with tannic acid showed increasing a* values but decreasing b* and L* values as the dyeing time and
dyeing temperature increased, as shown in Table 1. This result indicates that reddish hue became
dominant but yellowish hue became faint in the wool fabrics as the dyeing time and dyeing
temperature increased. It appears that the brown pigments were primarily caused by melanoidins
produced during the process of roasting coffee beans. Melanoidins are brown compounds and are
known to have several biological activities, such as antioxidant, antimicrobial, anticarcinogenic, anti-
inflammatory, antihypertensive, and antiglycative activities. However, knowledge of melanoidins in
coffee including the chemical structures is still lacking [18]. On the other hand, it was observed that
mordanting with 1 wt % tannic acid has little effect on the color appearance of wool fabrics dyed with
spent coffee extract, as shown in Table 1. To identify the levelness of wool fabrics dyed with the spent
coffee extract, we investigated the color difference of two different points with at least 10 cm distance
within each sample. Consequently, any unlevelness was not noticed in the wool fabrics dyed with
the spent coffee extract.
Figure 4. Color strength (K/S) values of wool fabrics dyed with spent coffee extract at 90 °C as a
function of dyeing time (all dying samples were mordanted with 1 wt % tannic acid aqueous solution):
(a) untreated, (b) 30 min, (c) 60 min, (d) 90 min, and (e) 120 min.
Figure 4.
Color strength (K/S) values of wool fabrics dyed with spent coffee extract at 90
◦
C as a
function of dyeing time (all dying samples were mordanted with 1 wt % tannic acid aqueous solution):
(a) untreated, (b) 30 min, (c) 60 min, (d) 90 min, and (e) 120 min.

Polymers 2019,11, 574 7 of 11
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Figure 5. K/S values of wool fabrics dyed with spent coffee extract for 60 min as a function of dyeing
temperature (all dying samples were mordanted with 1 wt % tannic acid aqueous solution): (a)
untreated, (b) 60 °C, (c) 90 °C, and (d) 120 °C.
Table 1. Color values of wool fabrics dyed with spent coffee extract and mordanted with 1 wt % tannic
acid aqueous solution.
Dyeing conditions
L* a* b* ΔE
Temperature
(°C)
Time
(min)
Untreated 86.54 −0.59 12.68 -
Only mordanted 85.02 1.04 12.96 2.24
90
30 54.12 9.59 27.40 37.03
60 50.29 9.82 26.88 40.30
90 47.40 10.12 26.62 42.91
120 46.08 10.19 26.49 44.09
60
60
64.50 8.72 28.64 28.76
90 50.88 9.74 26.96 39.77
120 31.38 9.77 20.78 56.71
Considering the color fastness of the wool fabrics dyed with the spent coffee extract and
mordanted with tannic acid, the wool fabrics showed a high level of color fastness to washing (4.5
grade); in contrast, they exhibited somewhat inferior color fastness to light (3–4 grade), as shown in
Table 2. However, it was found that the levels of color fastness of the wool fabrics dyed with the spent
coffee extract and mordanted with tannic acid may be higher overall than those of fabrics dyed with
other natural pigments [19,20].
Table 2. Color fastness of wool fabrics dyed with spent coffee extract and mordanted with 1 wt %
tannic acid aqueous solution.
Dyeing conditions Color change to
washing
(Grade)
Color change to light
(Grade)
Temperature
(°C)
Time
(min)
90
30 4-5 3
60 4-5 3-4
90 4-5 3-4
120 4-5 3-4
60 60 4-5 2-3
Figure 5.
K/S values of wool fabrics dyed with spent coffee extract for 60 min as a function of
dyeing temperature (all dying samples were mordanted with 1 wt % tannic acid aqueous solution):
(a) untreated, (b) 60 ◦C, (c) 90 ◦C, and (d) 120 ◦C.
Table 1.
Color values of wool fabrics dyed with spent coffee extract and mordanted with 1 wt % tannic
acid aqueous solution.
Dyeing Conditions L* a* b* ∆E
Temperature (◦C) Time (min)
Untreated 86.54 −0.59 12.68 -
Only mordanted 85.02 1.04 12.96 2.24
90
30 54.12 9.59 27.40 37.03
60 50.29 9.82 26.88 40.30
90 47.40 10.12 26.62 42.91
120 46.08 10.19 26.49 44.09
60
60
64.50 8.72 28.64 28.76
90 50.88 9.74 26.96 39.77
120 31.38 9.77 20.78 56.71
Considering the color fastness of the wool fabrics dyed with the spent coffee extract and
mordanted with tannic acid, the wool fabrics showed a high level of color fastness to washing
(4.5 grade); in contrast, they exhibited somewhat inferior color fastness to light (3–4 grade), as shown
in Table 2. However, it was found that the levels of color fastness of the wool fabrics dyed with the
spent coffee extract and mordanted with tannic acid may be higher overall than those of fabrics dyed
with other natural pigments [19,20].
Table 2.
Color fastness of wool fabrics dyed with spent coffee extract and mordanted with 1 wt %
tannic acid aqueous solution.
Dyeing Conditions Color Change to Washing
(Grade)
Color Change to Light
(Grade)
Temperature (◦C) Time (min)
90
30 4-5 3
60 4-5 3-4
90 4-5 3-4
120 4-5 3-4
60
60
4-5 2-3
90 4-5 3-4
120 4-5 4

Polymers 2019,11, 574 8 of 11
3.4. Mechanical Properties of the Wool Fabrics Dyed with the Spent Coffee Extract
Shrinkage of the wool fabrics occurred through the dyeing and mordanting process, as shown
in Table 3. The shrinkage became intensified as the dyeing condition became progressively harsh, i.e.
higher temperature and longer time of the dyeing process. In particular, significant shrinkage of the
wool fabrics was induced by high-temperature dyeing. The mechanical strength of the wool fabrics
dyed with the spent coffee extract and mordanted with tannic acid also depreciated drastically after
the high-temperature dyeing at 120 ◦C. Considering the color appearance and mechanical properties
of the wool fabrics dyed with the spent coffee extract, it was discovered that the dyeing process at
90 ◦C for 90 min would be optimal conditions for wool fabrics.
Table 3.
Shrinkage and tensile strength of wool fabrics dyed with spent coffee extract and mordanted
with 1 wt % tannic acid aqueous solution.
Dyeing Conditions Warp Weft Fabric
Count
Shrinkage
(%)
Tensile
Strength (N)
Temperature (◦C) Time (min)
Untreated 60 48 2880 0 117
Only mordanted 60 49 2940 2.04 116
90
30 62 50 3100 7.10 122
60 63 50 3150 8.57 123
90 63 50 3150 8.57 126
120 62 51 3162 8.92 123
60
60
61 50 3050 5.57 125
90 63 50 3150 8.57 123
120 73 61 4453 35.32 76
3.5. Functional Properties of the Wool Fabrics Dyed with the Spent Coffee Extract
Tables 4and 5show the antibacterial activities of the wool fabrics dyed with the spent coffee
extract and mordanted with tannic acid. Overall, they showed significant antibacterial activities
against K. pneumoniae, a Gram-negative bacterium, as well as against S. aureus, a Gram-positive
bacterium. The effects of dyeing time and dyeing temperature were not significant. However, the
wool fabric dyed with spent coffee extract but without mordanting shows insufficient antibacterial
ability particularly to K. pneumoniae, as shown in Table 4(dyeing time 90*). Therefore, it was found
that the antibacterial activities of the wool fabrics dyed with the spent coffee extract were dramatically
enhanced by mordanting with tannic acid following the dyeing process.
Table 4.
Antibacterial activity of wool fabrics dyed with spent coffee extract at 90
◦
C as a function of
dyeing time (all dying samples were mordanted with 1 wt % tannic acid aqueous solution except 90*
sample).
Dyeing Time (min) Reduction % of S. aureus Reduction % of K. pneumoniae
Pristine wool 28.2 32.5
30 99.2 93.1
60 99.7 97.5
90 99.7 99.6
90 * 76.5 43.6
120 99.6 96.2
* Wool fabrics dyed with spent coffee extract but not mordanted.
Tables 6and 7show the antioxidant activities of the wool fabrics dyed with the spent coffee
extract and mordanted with tannic acid. All the wool fabrics dyed with the spent coffee extract and
mordanted with tannic acid showed antioxidant capacity greater than 93%, and the activities were
increased by a small amount with increased dyeing temperature (Table 7). However, it was observed

Polymers 2019,11, 574 9 of 11
that the antioxidant capacity is also primarily attributed to mordanting. This is because a significant
amount of phenolic compounds were attached to the wool fibers via the mordanting process. Phenolic
compounds are found in many plants and are known to possess diverse health-promoting effects such
as antimelanogenic, antioxidant, antineoplastic, and bacteriostatic properties [
21
–
23
]. It was reported
that chlorogenic acid is the major phenolic component in spent coffee extract, and gallic acid might be
abundant in the mordanting solution. Additionally, the non-phenolic compounds in coffee extracts,
such as caffeine and melanoidins, can also contribute to the antioxidant activity and scavenging of
hydroxyl radicals (a type of highly active reactive oxygen species (ROS)) [24].
Table 5.
Antibacterial capacity of wool fabrics dyed with spent coffee extract for 60 min as a function
of dyeing temperature (all dying samples were mordanted with 1 wt % tannic acid aqueous solution).
Dyeing Temperature (◦C) Reduction % of S. aureus Reduction % of K. pneumoniae
Pristine wool 28.2 32.5
60 99.6 94.1
90 99.7 97.5
120 99.9 99.2
Table 6.
Antioxidant activity of wool fabrics dyed with spent coffee extract at 90
◦
C as a function of
dyeing time (all dying samples were mordanted with 1 wt % tannic acid aqueous solution except 90*
sample).
Dyeing Time (min) DPPH Scavenging Activity (%)
Pristine Wool 59.65
30 94.28
60 94.46
90 94.83
90 * 59.65
120 94.68
* Wool fabrics dyed with spent coffee extract but not mordanted.
Table 7.
Antioxidant ability of wool fabrics dyed with spent coffee extract for 60 min as a function of
dyeing temperature (all dying samples were mordanted with 1 wt % tannic acid aqueous solution).
Dyeing Temperature (◦C) DPPH Scavenging Activity (%)
Pristine wool 59.65
60 93.59
90 94.30
120 95.13
4. Conclusions
Wool fabrics were dyed with spent coffee extract and mordanted with tannic acid to generate
functionalized and colored textiles and to recycle spent coffee grounds, which are a major component
of bio-waste. The spent coffee extract was simply prepared by using a manual espresso machine, and
the extract contained many functional compounds, including phenolic compounds (gallic acid and
chlorogenic acid) and nitrogenous compounds (trigonelline and caffeine). The spent coffee extract
significantly colored wool fabrics brown via the dyeing process, and the coloring effect was enhanced
by increasing the dyeing time and temperature. However, dyeing at extremely high temperature was
observed to deteriorate the mechanical strength of wool fabrics and, therefore, dyeing at 90
◦
C for
90 min would be the optimal condition for dyeing wool fabrics with spent coffee extract. On the other
hand, dyeing with the spent coffee extract alone imparted a limited level of functionality to the fabrics,
such as antibacterial activity and antioxidant capacity. However, mordanting with tannic acid after the

Polymers 2019,11, 574 10 of 11
dyeing process could enhance the functionalities of the wool fabrics dyed with spent coffee extract and
improve the color fastness of the fabrics to light.
Author Contributions:
Conceptualization, K.H.H.; methodology, K.H.H.; validation, K.H.H. and J.B.; formal
analysis and investigation, K.H.H.; writing—original draft preparation, K.H.H.; writing—review and editing, J.B.;
visualization, K.H.H. and J.B.; project administration and funding acquisition, K.H.H.
Funding:
This research was supported by the Basic Science Research Program through the National
Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning
(NRF-2016R1A1A3A04918760).
Conflicts of Interest: The authors declare no conflict of interest.
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