Effects of environmentally friendly degumming methods on some surface
properties, physical performances and dyeing behaviour of silk fabrics
DOI: 10.35530/IT.071.04.1675
TUBA TOPRAK PERVIN ANIS
MINE AKGUN
ABSTRACT – REZUMAT
Effects of environmentally friendly degumming methods on some surface properties, physical
performances and dyeing behaviour of silk fabrics
In this paper, the effect of degumming processes on the physical performance, surface properties and colour
coordinates of silk fabrics at high temperature and enzymatically, which was developed as an alternative to conventional
method, has been investigated. Degummed silk fabrics were compared in terms of weight loss, bending length, tear and
breaking strength, surface roughness and friction coefficient. After these tests, acid dyeing was performed to observe
different degumming methods effect on dyeing behaviour of degummed silk fabric. The colour coordinates were
evaluated by L*, a*, b*, C*, h0, K/S, and ∆E* values. The results revealed that despite insignificant differences between
conventional and alternative methods in terms of physical performance and surface properties, the conventional method
gave slightly better results than the others. There were no significant differences in colour depth between the two
processes. These reasons showed that the alternative method could be used instead of the traditional method and a
more sustainable process has been designed.
Keywords: degumming, enzyme, environmentally friendly, friction, roughness, silk 
Influența metodelor ecologice de degomare asupra unor proprietăți de suprafață, performanțe fizice
și comportamentul la vopsire al țesăturilor din mătase
În această lucrare, a fost analizată influența proceselor de degomare la temperatură ridicată și prin procedeu enzimatic,
realizate ca o alternativă la metoda convențională, asupra performanței fizice, proprietăților de suprafață și coordo- 
natelor colorimetrice ale țesăturilor din mătase. Țesăturile din mătase degomate au fost comparate din punctul de
vedere al pierderii de masă, lungimii de încovoire, rezistenței la sfâșiere și rupere, rugozității suprafeței și coeficientului
de frecare. După aceste teste, a fost realizată vopsirea cu coloranți acizi, pentru a se observa influența diferitelor metode
de degomare asupra comportamentului la vopsire al țesăturii din mătase degomată. Coordonatele colorimetrice au fost
evaluate prin valorile L*, a*, b*, C*, h0, K/S și ∆E*. Rezultatele au relevat faptul că, în ciuda diferențelor nesemnificative
dintre metodele convenționale și cele alternative în ceea ce privește performanța fizică și proprietățile de suprafață,
metoda convențională a dat rezultate puțin mai bune decât celelalte. Nu au existat diferențe semnificative de intensitate
a culorii între cele două procese. Aceste argumente au demonstrat că metoda alternativă ar putea fi utilizată în locul
metodei tradiționale și a fost proiectat un proces mai sustenabil.
Cuvinte-cheie: degomare, enzimă, ecologic, frecare, rugozitate, mătase
INTRODUCTION together [9–11]. Fibroin and sericin proteins differ
Because of its comfort, elegance, sensuousness, lus- from each other in amino acid percentages and con-
ter, glamour and excellent mechanical properties, silk figurations. The fibroin formed by amino acids with
fiber is called “Queen of Textiles” and has been used about 76% non-polar side groups surrounds by
for 5000 years [1–6]. Although the annual production sericin which consist 75% amino acids with polar
of silk fiber is not very high, it remains a special fiber groups [4, 12–13]. Fibroin is a dense structure of
used in high value textile products. Increasing B-sheet microcrystals, whereas sericin is an amor-
demand for natural fibers to meet environmental and phous structure [3, 14]. These differences in configu-
consumer demands will lead to an increase in the ration and composition of the fibroin and sericin make
use of this fiber [7]. it possible for fibroin to contribute to the strength and
The silk fibers obtained from the silk worm and it con- stiffness, while the sericin that holds the fibroin
sists of mainly sericin (20–30%), fibroin (65–75 %). together makes it more water soluble than fibroin
There is about 5% water, wax, pigments, sugars, and [6, 15–17]. While sericin causes the fiber to become
mineral salts in the silk fiber [4, 8]. Sericin covers a stiff and harsh, it also hinders luster and whiteness of
pair of fibroin filaments and allows them to stay the silk, and prevents penetration of solutions used in
industria textila˘ 380 2020, vol. 71, no. 4
textile wet processes [18]. Therefore, sericin has to EXPERIMENTAL WORK
be removed to make silk fiber the ideal fiber for tex- Material
tile industry [9]. In the process of removing sericin
A fine-medium weight (76 g/m2) 100% silk plain woven
from the fiber, degumming, sericin is hydrolyzed and fabric was used. This raw silk fabric was provided by
the amide bonds in the protein molecules are broken Bursa İpek. The fabric properties are shown in table 1. 
down [15]. Degumming, which causes a 20–25 %
reduction in the weight of the fiber [3, 19], can be car- Table 1
ried out with water under high pressure [20], by boil-
ing in a soap-alkaline [8, 21–22] or acidic mediums CONSTRUCTIONAL PROPERTIES OF SILK FABRIC
[23–25], or enzymatically [4, 17]. The magnetic field SAMPLE
also was used for degumming by Valu [26]. The rec- Parameters Warp Weft
ommended method is to boil with soap in the pres-
Yarn count (Nm) 151 151/2
ence of alkali, but the chemicals used make it non-
environmentally friendly [21, 27–29]. Yarn density (thread/cm) 26 18
The -NH and -COOH groups in the chemical struc- Yarn twist (T/m) Non-twisted 2482
ture of the silk fiber enable this fiber to be dyed with
acid, basic, metal complex, mordant, natural, and The commercial acid dye (Lanaset Red 2B), wetting
reactive dyes. The interaction between the dyestuff agent (Albaflow Jet) and leveling agent (Albegal)
and the silk fiber occurs with ionic or covalent bonds. were kindly provided by Huntsman Cooperation,
The choice of dyes depends on the shade, bright- Turkey. Sodium sulfate, acetic acid, sodium bicar-
bonate and Marseilles soap were analytical reagent
ness and fastness grade properties. Acid dyes are grades. Savinase 16L, protease (Novozymes), which
used mostly and they are easily absorbed into fibers was produced from Bacillus sp was used in enzyma-
and washing fastness is poor to moderate [19, 21, tic degumming processes. 
30–32].
Finishing processes to impart various handling and Method
performance properties gain to textile materials such Degumming and dyeing
as smoothness, stiffness, softness, crease recovery, The degumming processes were grouped into three
dimensional stability, and strength can also be done groups: boiling off with soap in alkaline medium,
to change the frictional resistance of fabrics. Friction enzymatic degumming, and high temperature (HT)
resistance is influential on abrasion, wear resistance, degumming. Marseilles soap was used in the con-
degree of consolidation and shrinkage properties, ventional process based on comparing the effective-
especially the key of the fabrics. Friction properties ness of the other degumming processes. Silk fabrics
were treated conventionally with 3.5 g/l Marseille
are also important in determining roughness,
soap, 2.5 g/l sodium bicarbonate (pH 9.5) at 95oC for
smoothness and other surface characteristics. While 45 min with an LR value of 25:1. For degumming with
friction studies have been carried out on metals in the enzymes in all experiments 8% enzyme was used in
past, non-metals, which are the elastomers, plastics, pH 8.5 medium which was adjusted with sodium
and fibers, friction characteristics have begun to be bicarbonate and was recommended by Novozymes.
studied in detail, and even this century can be called The conditions of the enzymatic degumming were
the “renaissance of tribology”. Friction, a surface 50oC for 20 min (LR 25:1). The HT degumming pro-
phenomenon, has long been used for the objective cesses were operated at the 110oC for 20 and 30
measurement of surface smoothness. Although fric- minutes and named as HT 20’ and HT 30’, respec-
tion is a surface property, it is also influenced by the tively. For enzymatic and conventionally degummed
bulk property and therefore the changes in the friction fabrics, neutralization process was operated with
are also sensitive to the type of yarn mechanical acetic acid. Finally, all degummed fabrics were rinsed
o
properties, fabric structure, finishing process and also water at 70 C for 10 minutes two times.
the conditions used during testing [33]. The woven silk fabrics were dyed using exhausting
In this study, weight loss, bending lengths, tear and method under laboratory conditions. In the dyeing
breaking strengths of the silk fabrics have been inves- experiments, the fabric samples weighed 10 g and
the liquor ratio was 25:1. The dyebaths contained 2%
tigated for the possibility of environmental degum-
owf (on-weight-fabric) acid dye, 1 g/l penetration agent,
ming with using enzyme and high temperature condi-
5% owf sodium sulphate, and 1% owf acetic acid. In
tions as alternatives to conventional degumming. Silk the dyeing bath at 40–50oC containing acetic acid
fabric handling is one of the most attractive features and sodium sulphate fabric was treated for ten min-
for customers. That’s why surface characteristics were utes. Then, acid dye was put into the bath and the
analysed via surface roughness and friction coeffi- temperature was raised to 80–85oC at a rate of
cients after degumming processes. Differences cre- 1oC/minute. The dyeing was continued at this tem-
ated by different degumming processes on the dyeing perature for 60 minutes to allow good penetration of
properties of silk fabrics have also been investigated. the dyes and level dyeing. Later the samples were
industria textila˘ 381 2020, vol. 71, no. 4
taken out of the dyeing tubes and were rinsed with under test was mounted on the sled (mass of sled:
hot (70oC) and cold water (30oC) for 10 minutes, 200 g) and standard abrasive wool fabric was mount-
respectively. After rinsing the samples were left to dry ed on the moving plate (the test speed: 150 mm/min;
under laboratory conditions. the measurement length: 150 mm) of the coefficient
The degumming processes were performed with tester. Friction measurements were performed in
ATAÇ Dyetech Sample Dyeing Machine and the warp and weft directions of fabric samples under test.
ATAÇ Mini Bobbin Dyeing Machine (MBB01-02F). Three measurements were recorded in each direc-
For dyeing process, ATAÇ Dyetech Sample Dyeing tions and the mean was calculated.
Machine was used. The raw silk fabric was used Colour measurement
without further treatment for all experiments for com- The colour coordinates of samples were measured
parison. Each experiment was performed by non- by Konika – Minolta 3600D reflectance spectropho-
dyed silk fabric at three times. tometer coupled to a PC, at wavelengths between
The effects of degumming methods and dyeing were 400 and 700 nm under D 65 / 10° illuminant with
analysed with the following tests. specular component included (SCI mode). The per-
Bending length centage reflectance values at the wavelength of max-
Bending lengths of fabrics were measured according imum absorption (500 nm) were recorded. The con-
to “Standard Test Method for Stiffness of Fabrics ventionally treated fabrics were taken as the
ASTM D 1388-96” test method by SDL ATLAS Fabric standards and the other fabrics were taken as the
Stiffness Tester M003B. samples when calculating the colour differences.
Tear strength CIELAB (1976) equation 2 was used to calculate
The Power Tear (SDL ATLAS M008HE) was used to colour differences:
measure the tear strengths according to “Textiles- DE*
2
CIELAB = √ (DL*)2 + (Da*)2 + (Db*)2 (2)
Tear properties of fabrics – Part 1: Determination of
where DL* is the lightness difference, Da* – red/green
tear force using ballistic pendulum method
(Elmendorf) (TS EN ISO 13937-1:2000)”. difference, Db* – yellow/blue difference.
Breaking strength The K/S value was calculated for the wavelength cor-
The Shimadzu AG-X plus was used for measuring responding to the maximum absorption value. The
the breaking strengths of the fabric via ASTMD 1682-64. DE* was calculated according to CIELAB 1976 equa-
Surface roughness test tion 3:
2
Surface roughness values of silk samples were mea- (1 – R)K/S =             (3)
sured by a roughness tester (Accretech Surfcom 2R
130A) and surface roughness values were recorded where R is the decimal fraction of the reflectance of
according to ISO 4287-1997. The measurement was fabric, K – the absorption coefficient, S – the scatter-
performed on steady state without causing any fur- ing coefficient.
ther tension on the sample. Three roughness mea-
surements were made on each direction (warp and RESULTS AND DISCUSSION
weft) with the selected measurement parameters of Weight loss
50 mm evaluation length (0.8 mm cut-off value) and
1.5 mm/s measurement speed. Three measurements Figure 1 shows the average weights of the fabrics
were recorded in each directions and the mean was after different degumming methods.
The lowest weight was obtained by conventional
calculated.
method. It was worth noting that this process showed
Ra is the arithmetical average of absolute values of a very high degumming efficiency. The conventional
the profile variations (peaks and valleys) from the
process caused about 25% weight losses indicated
mean line in the evaluation length [34–36]. This value the target value for complete degumming, as
was calculated using equation 1: obtained under standard conditions with soap and
 1R   n y alkali. Without enzymes, the HT 30’ degumming pro-a = ni=1|  i |                       (1) cess loss was very close to the conventional treat-
where n is the number of samples along the evalua- ment and differences between them was negligible
tion length and yi – (surface height) deviation.
Friction coefficient test 
The static and kinetic friction coefficients used to
evaluate the friction characteristics of the fabrics
were measured according to ASTM D 1894-14: 2014
standard on a Labthink Param MXD-02 friction coef-
ficient test device. 
Static and kinetic friction coefficients of the silk fabric
were measured by fabric-to-fabric friction by using
standard abrasive wool fabric (ASTM D 4966) (i.e.
friction coefficients of sample were measured by silk Fig. 1. Weights of silk fabrics after different degumming
fabric-to-abrasive wool fabric). The silk fabric sample processes
industria textila˘ 382 2020, vol. 71, no. 4
(≈ 5%), owing to the highest treatment temperature.
Compared to HT 30’, the HT 20’ caused almost 5%
less weight loss because the time was less than 10
minutes. Degumming loss with enzyme was approxi-
mately same with the HT 20’ process. The protease
enzyme used in this study allowed a 10 % difference
to the targeted loss of weight (≈ 25%) under the
adopted experimental conditions.
Bending length
Fig. 3. Tear strengths of degummed silk fabrics
The bending length values, one of the performance with various degumming processes
characteristics, are shown in figure 2.
with each other, the lowest results were obtained with
the conventional process. The possible reason for
the highest tear strength loss was not only the sericin
in the amorphous structure but also the fibroin struc-
ture in the crystalline structure was damaged in the
conventional degumming process which operated
under alkaline conditions [1]. The HT 20’ and HT 30’
conditions gave higher tear strength values in the
weft direction than the enzymatic process. It could be
Fig. 2. Bending length values of silk fabrics after different seen that ten minutes difference between the HT pro-
degumming processes cesses did not cause any significant change in the
tear strength values both of the direction. When
effects of degumming processes on the tear strength
The silk fabrics degummed with conventional method
values at the weft and warp directions were com-
showed the lowest bending lengths since the sericin
which gives the fabric hardness was removed at the pared to the raw fabrics, the differences in the weft
maximum amount. There were no significant differ- direction were more pronounced, which was thought
ences between these values for HT 20’ and HT 30’. to have stemmed from the two-ply weft yarn. 
The bending length values obtained by the enzy-
Breaking strength
matic process were slightly higher because the enzy-
matic process removed the sericin less than HT 20’ – The effect of degumming processes under investiga-
HT 30’ and the conventional methods, whereas the tion could be realized by comparing the breaking
success of this method was significantly prominent strength, which was one of the physical properties of
when compared with the raw fabric. Moreover, this the fabric, is shown figure 4. 
result indicated that enzymatic degummed fabric Based on breaking strength, the raw silk fabrics had
structure was harder than the others, except raw. By the highest strength, implied that the sericin rein-
comparing the fabrics degummed with the conven- forced to the fabric, so the removing sericin with var-
tional and environmentally friendly methods, it was ious degumming methods led to a decrease in the
possible to observe that the latter exhibited a bit breaking strength. This reduction was the most in
harder fabrics, especially enzymatically treated one. conventional process as expected because the
These results were parallel to the weight loss values sericin was removed at the most amount in the con-
of the fabrics, and the fabrics exhibited the greatest ventional process (figure 1). Another possible reason
and least weight loss gave the lowest and the highest for this loss was the conventional process conditions
bending lengths, respectively. This could be inter- caused fiber degradation [1]. When HT 20’, HT 30’,
preted as the fabric became softer when sericin
moved away from the fabric, thus reducing the bend-
ing length of the fabric because sericin gives the fab-
ric rigidity.
Tear strength
The main effect of degumming processes for fabric
tear strengths are given in figure 3.
It could be seen that the starting with tear strength of
the raw silk fabric (43.19 N) for weft direction, it
increased after degumming processes. This increase
in tear strength could be explained by removing the
sericin which prevents the ability of the yarns to move
together against the tear force applied to the fabric. Fig. 4. Breaking strengths of degummed silk fabrics
When the degumming processes were compared
industria textila˘ 383 2020, vol. 71, no. 4
and enzymatic degumming processes were com- density and count of warp and weft yarns. During the
pared among themselves, it was seen that the HT measurement of the roughness in the warp direction,
processes had lower breaking strength values. It had the stylus probe of the roughness measurement
also turned out that the difference in the process device moves on the cross direction on each of the
times of HT processes did not cause any significant thread spacing of individual weft yarns in the fabric
change (≈ 2–4 %). Since the working conditions in structure.  Taking into consideration that the weft yarn
the enzymatic process were milder and the amount density constituting the fabric were lower than the
of sericin removed from the fiber by this process was warp yarn density, this state caused higher thread
less, so the least strength loss was seen in this spacing of individual weft yarns, as a result the
method. Although this loss was the least in the enzy- roughness values of fabrics obtained from the warp
matic process compared to other degumming pro- direction were determined to be higher than the
cesses, the loss of strength was about 32% com- roughness values of fabrics obtained from the weft
pared to the raw silk fabric. Since two-ply yarn was direction. An increase in yarn density decreased the
used in the weft direction, it was seen that the gaps between the yarn peaks, giving a decrease in
strength of this direction was higher than the warp surface roughness [35–36]. Also, the coarse struc-
direction. ture of weft yarn (weft yarn thickness two times high-
er than the warp yarn) could have led to a higher yarn
Surface roughness peaks on the surface during the measurement of the
In figure 5, the changes in the surface roughness val- roughness in the warp direction, and as a result the
ues of the weft and warp directions of the silk fabrics, fabric surface roughness increased in the warp direc-
in accordance with the different sericin removing tion.
methods, are presented.
Friction coefficients
In figure 6, the changes in the friction coefficient val-
ues of the weft and warp directions of the silk fabrics,
in accordance with the different sericin removing
methods, are presented. The raw fabric gave the low-
est friction coefficient values in both directions and
these values increased after degumming processes.
Sericin in raw silk fabric provided low friction coeffi-
cient values because it made fabric structure stiffer
and it had not adhesive feature which occurs by fab-
ric-to-fabric friction. After the degumming process, it
was observed that this process made the silk fabric
Fig. 5. Surface roughness values of silk fabrics with feel smoothly handle and increased potential of the
various degumming processes fabric to stick or cling to the other surfaces. As a
result of this, the friction coefficient values of silk fab-
rics increased after degumming processes. When the
In order to evaluate the effect of sericin on the sur- degumming processes were compared in both direc-
face roughness, it was observed that the raw fabric tions, it was observed that the friction coefficient val-
had a higher surface roughness compared to the ues were almost close to each other in the warp
conventionally degumming method by which the direction, but the values of the friction coefficients
sericin was removed at the maximum amount were slightly more pronounced in in the weft direc-
through the fabric. In the conventional method, it was tion. When the differences between the degumming
considered that the sericin-removed fibroin has a processes in the weft direction were analysed, it was
smoother surface because of its lower results. It was seen that the amount of sericin left on the fabric sur-
thought that higher values were obtained in the face was related to the friction coefficient. It could be
enzymatic process than other degumming methods
because the sericin on the surface cannot be
removed completely and properly. The surface
roughness results at HT processes were lower than
the enzymatic process and but they were higher than
the conventional process. The data of HT 30’ indicat-
ed that sericin was more uniformly removed from the
surface than HT 20’. In general, these results showed
that sericin increased the surface roughness of the
fabrics, that is, all degumming processes made the
surface of the fabrics smoother. 
For all processes, when the weft and warp direction
roughness values were compared, it was observed
that the higher results were obtained in the warp Fig. 6. Friction coefficient values of silk fabrics
with various degumming processes
direction. This could stem from differences in the
industria textila˘ 384 2020, vol. 71, no. 4
Table 2
COLOUR COORDINATES OF SILK FABRICS WITH VARIOUS DEGUMMING PROCESSES
Process L* a* b* C* ho K/S ∆E*
HT20’ 49.10 50.25 17.32 52.98 19.01 8.20 0.53
HT30’ 49.28 50.39 17.47 53.27 18.79 8.24 0.46
Enz. 48.75 50.10 17.05 52.92 19.11 8.48 0.84
Conv. 49.42 50.60 17.09 53.41 18.66 8.68 -
interpreted that the remaining sericin on the surface gave similar values to those obtained from the con-
enhanced the irregularity, which in turn increased the ventional process. When the effect on the fabric
friction coefficient. strength values (tear and breaking strength) of the
different degumming processes were examined, it
Colour coordinates was seen that the most loss of strength was seen in
The colorimetric coordinates (L*, a*, b*, C*, ho), K/S, the fabric treated with conventionally where the
and ∆E* values of all the dyed fabrics are given in sericin was removed the most amount. The breaking
table 2. strength values of the enzymatically treated fabrics
The L* values given in table 2 revealed that the enzy- were highest.
matic degummed fabrics had the lowest L* values, When the effects of different degumming treatments
i.e. darker than the others. However, it seemed that on the fabric surface properties (roughness and fric-
the difference between these values and others was tion coefficient) were examined, it was seen that the
not very high. In table 2, it could be seen that the val- lowest surface roughness values were obtained by
ues of a* (redness) were higher than those of b* the conventional process. With the enzymatic pro-
(blueness) as expected because red dyestuff was cess, roughness values were high because of the
used. The a*, b*, C* and ho values for each process sericin remaining on the surface of fiber. When the
were very close to each other. It was also observed friction coefficient values were examined, it was
from the ∆E* values that the differences between
observed that the coefficient of surface friction of the
them were negligible (<1). The differences between
sericin-free fabric was increased. This was due to the
them were less than 1 could be interpreted as each
could be used as an alternative process. Moreover, sticking or clinging effect between the sericin and the
this was expected because the removed sericin other surface it touches, due to the softer handling of
amounts of alternative processes were about the the degummed fabric. It had been observed that the
same. Colour strength (K/S), which was the most different sericin removal processes gave nearly simi-
important parameter to test the quality measurement lar results on the fabric friction coefficients.
of a sample in terms of depth of the colour, showed After different degumming processes, the silk fabric
similar results to each other. Additionally, with the colour coordinates (L*, a*, b*, C*, ho, K/S and ∆E*)
help of alternative methods, levelled dyeing could be showed that the results obtained with degumming
achieved. processes results were similar to each other.
Although the highest colour difference value was
CONCLUSIONS 0.84 between conventional and enzymatic degum-
In this study, the effects of different degumming pro- ming, this difference value was also insignificant
cesses applied to 100 % silk woven fabric on the because it was below 1. 
mechanical properties (weight loss, bending length, As a result, it had been observed that degumming
tear strength, breaking strength), surface properties processes with alternative methods had no negative
(roughness and friction coefficient) and colour coordi- effects on the physical and surface properties of silk
nates (L*, a*, b*, C* , ho, K/S and ∆E*). fabrics. The colour coordinates and uniform dyeing
According to the results, despite the sericin was obtained by the dyeing after the application of these
removed at the most amount  by conventional methods to silk fabrics showed they could be alter-
method (as seen from the changes in the weight loss natively used. Furthermore, other advantages of
and bending length values), it had been found that environmentally degumming processes were the lack
the other alternative methods (HT and enzymatic) of chemical usage and short processing times.
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Authors:
TUBA TOPRAK, MINE AKGUN, PERVIN ANIS
Bursa Uludag University, Faculty of Engineering, Textile Engineering Department, Gorukle Campus,
16059, Nilufer, Bursa, Turkey
e-mail: akgunm@uludag.edu.tr, pervin@uludag.edu.tr
Corresponding author:
TUBA TOPRAK
e-mail: tubatoprak@uludag.edu.tr
industria textila˘ 387 2020, vol. 71, no. 4