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Abstract—The current research studied the effect of
degumming conditions on the properties of PLA and silk yarns
aiming to get the actual influence of the process on each fiber
which would later be combined together into a blended fabric.
The degumming conditions with 10 g/l wetting agent were
employed at pH 5, 7 and 10 at various temperatures of 70, 80
and 90oC for 15 min. The most effective degumming was
recommended at 70oC and pH 10. Too high temperature (90
oC)
brought about an eroded fiber surface and deteriorated the
fabric strength. The PLA/silk blended fabrics were prepared
into different fabric structures and their properties i.e. strength,
density and stiffness, were investigated. The fabric properties
before and after degumming under a recommended conditions
were compared.
Index Terms—Poly (lactic acid), silk, blended fabric,
degumming.
I. INTRODUCTION
Nowadays an eco-friendliness of textile products becomes
a key interest not only in development of the textile industry
but also for product end-users who are conscious of
environment conservation and human safety regarding the
use of textile products. For this reason, natural fibers are still
popular in textile production. However, some important
textile properties cannot be provided by natural fibers e.g.
outstanding strength and easy-care properties, whereas
synthetic fiber can render those key properties satisfactorily
to the textile products. Therefore, synthetic fibers are still in
demand with seldom replacement being achieved.
Polyester fiber (poly (ethylene terephthalate), PET) is the
fiber with outstanding textile properties. It is from petroleum
resource, hence, it has been claimed to take part in global
warming problem, being the same as other petroleum-based
fibers. Recently, poly (lactic acid) or PLA, a greener
polyester fiber was developed and it was expected to replace
PET commodities. PLA fiber can be made by melt and
solution spinnings [1] but the former process is more popular.
It can be used in apparel and nonwoven applications for
textiles. It can be processed in the textile production but
milder processing conditions are employed for PLA as
Manuscript received October 14, 2012; revised January 2, 2013. This
work was supported by The National Innovation Agency (NIA), Thailand. A
partial funding was supported by Department of Textile Science, Faculty of
Agro-Industry, Kasetsart University, Thailand.
J. Suesat is with the Department of Textile Science, Faculty of
Agro-Industry, Kasetsart University, 50 Ngamwongwan Rd., Ladyao
Subdistrict, Chatuchak, Bangkok, 10900 Thailand (e-mail: Jantip.s@
ku.ac.th).
S. Ujjin is with the Kasetsart Agricultural and Agro-Industrial Product
Improvement Institute, Kasetsart University, 50 Ngamwongwan Rd.,
Ladyao Subdistrict, Chatuchak, Bangkok, 10900 Thailand (e-mail: aapsdu@
ku.ac.th).
compared with PET. Like PET, it can also be dyed with
disperse dye [2]-[4]. Nevertheless, it was reported that the
strength of PLA fiber was relatively inferior to that of PET
[5], [6]. Therefore, a further investigation focuses on
blending PLA with other textile fibers so as to improvement
the strength and also other essential properties [7].
Bombyx Mori silk is a cultivated silk composes of two
main compositions, i.e. sericin and fibroin. Silk fibroin is a
protein filament gluing together by sericin gum. Before
taking silk filament for exploitation in textiles, the silk
filament needs to be degummed in a hot alkaline soap
solution to remove sericin away. The degumming process,
thus, is the main pretreatment step for silk. Silk is a luxurious
fiber with quite high price compared with other common
textile fibers. Blending silk with PLA has been paid attention
because PLA is a biodegradable synthetic fiber derived from
plant and it is encouraging for green textile products where
PET should be replaced by the greener ones. Dyeing PLA and
silk yarns with natural dyes was investigated in our previous
work [8]. In this research, we aimed to study silk blending
with PLA fiber to create a new textile blended fabric. By
blending with the cheaper fiber, PLA, it would help to reduce
the cost in silk fabric production with new properties
generated. As PLA is rather sensitive to alkaline hydrolysis,
the effect of degumming process for silk was studied on both
PLA and silk at various conditions to investigate the optimum
degumming condition for PLA/silk blended fabric with
satisfactory degumming efficiency and less damage to the
fibers. The properties of the PLA and silk yarns after
degumming were examined. The PLA/silk blended fabrics
with various structures were studied their properties.
II. MATERIALS AND METHOD
A. Materials
The 40 Ne PLA yarn was purchased from Hebei Tianlun
Textile Co. Ltd, China. The 20-denier Bombyx Mori silk yarn
was obtained from Chul Thai Silk, Co. Ltd. Sera Wash, a
nonionic wetting agent, was supplied by DyStar, Co. Ltd.,
Thailand.
B. Effect of Degumming Conditions on PLA and Silk Yarns
The effect of degumming on the properties of silk and PLA
yarns was studied by treating the yarns in the solution
comprising 10 g/l Sera Wash (wetting agent) for 15 min at
various pHs of 5, 7 and 10. Degumming temperatures were
varied to 70, 80 and 90oC. The %weight loss of the yarns was
determined from the weight of the yarn after degumming
comparing with the initial yarn weight. Tensile strength of
the degummed PLA and silk yarns was measured by
Shimadzu Autograph AGS-J series with the gauge length of
Effect of Fabric Structure and Degumming Conditions on
the Properties of PLA/Silk Blend
Jantip Suesat and Suchada Ujjin
International Journal of Bioscience, Biochemistry and Bioinformatics, Vol. 3, No. 2, March 2013
106
60 mm and crosshead speed of 300 mm/min. The whiteness
of the degummed yarns was assessed by McBeth ColorEye
7000 spectrophotometer. The surface morphology of the
degummed yarns was collected by JEOL JSM-5800 LV
scanning electron microscope (SEM).
C. Preparation of the Woven Fabrics Containing PLA and
Silk Yarns with Different Fabric Structures
The woven fabrics containing PLA and silk yarns in the
structure were prepared. The detail of each structure is
depicted in Table I. The 20/3 denier silk yarn was used as a
warp for all fabrics. The structures 1-4 are the PLA/Silk blend
with different weft PLA yarns, viz. 40/2, 40/3, 40/4, 40/5Ne,
meaning that the 40Ne PLA yarns are plied together
according to the number after / symbol while those of 5-6 are
the 100% silk fabrics but different in silk yarn structure,
being used as a weft. The fabrics were prepared by means of
rapier power loom. All the fabrics was taken to measure their
propertied, viz. density (weight/unit area), strength and
stiffness. The strength of the fabrics was obtained from
Shimadzu Autograph AGS-J series. The fabric stiffness was
indicated in terms of flexural rigidity. By measuring the
bending length of the fabrics along the weft direction
according to BS 3356 standard test method, the flexural
rigidity could be calculated.
TABLE I: STRUCTURES OF PLA/SILK BLENDED FABRICS
Fabric
parameters
Fabric structure
PLA/Silk Silk
1 2 3 4 5 5
1 Warp-Silk
yarn (denier)
20/3 20/3 20/3 20/3 20/3 20/3
2 Weft-PLA
yarn (Ne)
40/2 40/3 40/4 40/5 - -
3 Weft-silk yarn
(Denier)
- - - - 20/6 20/10
4 PLA:silk ratio 3.80:1 3.98:1 5.06:1 5.32:1 - -
5 Fabric density
(g/m2)
101.4 121.1 140.9 235.5 83.93 98.72
6 Warps/inch 99 103 103 103 99 99
7 Wefts/inch 66 57 47 42 78.6 75
D. Effect of Degumming Conditions on the Properties of
PLA/Silk Blended Fabrics
The prepared fabrics with different structures were taken
to study the influence of degumming on their properties. The
effect of degumming condition was investigated by treating
the fabrics in a bath containing 10 g/l Sera Wash (wetting
agent) at pH 10 and liquor ratio of 20:1. Degumming was
performed at 70oC for 15 min. The degummed fabrics were
left to dry at room temperature and then their properties, viz.
density, strength and stiffness, were measured.
III. RESULTS AND DISCUSSION
A. Effect of Degumming Conditions on PLA and Silk
Yarns
The properties of PLA and silk yarns after being
degummed at different conditions are demonstrated in Table
I. The whiteness of silk yarns increased considerably when it
was degummed at pH 10. This was in accompanying with the
loss of fabric weight and reduced strength when compared
with those at pH 5 and 7. No weight and strength losses were
noticed when degummed the yarns at pH 5 and 7. This result
points out that degumming silk at pH 10 gives a high
whiteness but impairs the yarn strength. For PLA, it is a
manmade fiber, so the degree of whiteness is much higher
than the silk yarn. The whiteness of the yarn increased
slightly when the pH of degumming process increased from 5
to 7 and 10. No signified effect was observed when varied the
degumming temperatures. The extent of weight loss did not
changed significantly except that at 90oC and pH 10, about
twofold of yarn weight was lost as compared with the 80oC
counterpart. This weight loss result was correspondent to the
strength reduction of PLA at 80-90oC and pH 10. It was
reported that PLA could be damaged in a hot alkaline
solution [9-10]. Alkaline hydrolysis takes place and the
damage on PLA fiber is claimed to be surface erosion where
the hydrolysis causes a gradual erosion of the fiber surface
and fiber then becomes thinner [10]. This brings about a
reduction in weight and strength of PLA fiber. When
compared between the influence on silk and PLA, it can be
seen that the effective degumming can be achieved for PLA
and silk at 70oC and pH 10 with a whiteness improvement
and less strength loss. This result elucidates that the optimum
degumming condition of 70oC at pH 10 for 15 min could be
practically viable for PLA/silk blended fabric.
TABLE II: PROPERTIES OF PLA AND SILK YARNS AFTER BEING DEGUMMED UNDER DIFFERENT CONDITIONS
Degumming conditions Silk PLA
pH Temp Weight loss
(%) Whiteness
Strength
(N/denier)
Weight loss
(%) Whiteness
Strength x10-3
(N/denier)
control 0 34.22 0.043 0 55.23 9.4
5 70 0 34.23 0.043 0.40 58.02 9.2
5 80 0 34.73 0.041 0.28 63.07 9.1
5 90 0 34.91 0.040 0.14 64.34 9.2
7 70 0 34.59 0.043 0.38 64.56 9.4
7 80 0 36.23 0.041 0.33 63.99 9.9
7 90 0 38.60 0.045 0.14 62.44 9.9
10 70 17.51 55.63 0.038 0.64 63.19 1.03
10 80 19.08 56.20 0.038 0.68 63.41 8.7
10 90 19.19 55.79 0.036 1.20 62.82 8.6
International Journal of Bioscience, Biochemistry and Bioinformatics, Vol. 3, No. 2, March 2013
107
70oC 80oC 90oC
pH 7
70oC 80oC 90oC
pH 10
Fig. 1. SEM photographs of PLA yarns degummed under pH 7 and 10 conditions at 70, 80 and 90oC
The SEM photographs of PLA yarn degummed at pH 7
and 10 at varying temperatures are shown in Fig. 1. Phillips et
al. [9-10] reported that PLA could undergo a serious bulk
erosion even under neutral pH but from our result in Table 1,
there was no strength loss observed for degumming at pH 7,
the SEM photographs also showed no change in fiber surface
morphology. In the meantime, degumming in alkaline
conditions at 90oC caused a damage to the surface of PLA
fiber. Some crack marks and erosion could be noticed. This
SEM results corresponded to the strength reduction
mentioned before. Erosion of fiber surface makes the fiber
become thinner and subsequently, weaker. A less damage
was found for 80oC but a slight surface erosion could be seen.
It also confirms that degumming process at pH 10 at 80-90oC
is too vigorous for PLA/silk blended fabric as it could harm
PLA.
B. Effect of Degumming Conditions on the Properties of
PLA/Silk Blended Fabrics
The results in the previous section have told that
degumming process for PLA/silk blended fabric should be
done using 10 g/l wetting agent at pH 10 and temperature of
70oC. This recommended degumming condition was used for
PLA/silk blended fabrics in this section. Table III shows the
properties of PLA/silk blended fabrics. Each no. of fabric
structure contained different PLA and silk composition and
structures. The fabrics no. 1-4 were the PLA/silk blend with
20/3 denier silk yarn as a warp and PLA yarn as a weft but
with different number of yarns plying together. The fabrics
no. 5-6 were 100% silk fabrics with different weft structures.
The density of each fabric marginally increased after
degumming due to fabric shrinkage resulting in a more
compact structure, the weight/unit area of the fabric was then
increased. A denser fabric structure brought about a stiffer
fabric. The flexural rigidity of each fabric increased after they
were degummed. The strength of the fabrics was also
increased after degumming as seen from the increment of
maximum tensile load applied in fabric strength testing. With
the same warp yarn, higher number of weft yarns plying
together imparted higher density, stiffness and strength to the
fabric both before and after degumming. This provides the
information that different fabric properties can be
manipulated by the fabric structure in order to gain a wide
variety of fabric textures and properties. This is anticipated
for the development of PLA/silk blended fabric to serve the
home textiles industry e.g. bedding, where luxurious silk
fabric is typically major products. PLA, a cheaper fiber, can
also do its function in the blend and also help to reduce cost
of the production.
TABLE III: PROPERTIES OF PLA AND SILK YARNS AFTER BEING DEGUMMED AT DIFFERENT CONDITIONS
No. Warp Weft PLA / Silk
ratio
Density (x10-2g/cm2) Tensile max load (N) Flexural rigidity
(x10-2 g.cm)
Pre degum. After
degum. Pre degum.
After
degum. Pre degum.
After
degum.
1. Silk 20/3 D PLA 40/2Ne 3.8 : 1 1.01 1.08 156.33 183.71 1.93 1.46
2. PLA 40/3Ne 3.98 :1 1.23 1.31 167.86 195.06 5.06 2.58
3. PLA 40/4Ne 5.06 :1 1.33 1.52 161.07 195.39 5.96 3.82
4. PLA 40/5Ne 5.32 : 1 1.43 1.51 161.40 199.00 8.36 4.50
5. Silk 20/3 D Silk 20/6 D - 0.69 0.91 224.95 250.24 2.72 5.76
6. Silk 20/10 D - 0.98 1.07 329.58 331.89 7.03 7.86
IV. CONCLUSION
From this research, it gives the idea that blending silk with
PLA could be technically viable. PLA, an alkali sensitive
fiber especially at elevated temperature, can tolerate the
alkaline degumming conditions need for silk pretreatment to
International Journal of Bioscience, Biochemistry and Bioinformatics, Vol. 3, No. 2, March 2013
108
remove sericin. The optimum degumming conditions are
recommended not to perform at the temperature as high as
90oC for the condition studied as hydrolysis reaction would
reduce PLA strength. Practical coloration of PLA/silk blend
can also be done industrially with a proper choice of
dyestuffs and processes. It is encouraging to develop this
PLA/silk blended fabric for producing green alternative
products with lower price as compared with the expensive
100% silk fabric.
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Jantip Suesat was born on 29th November, 1976 in
Thailand. She was graduated from University of
Manchester, Manchester, U.K. for her Ph.D. in
Textiles in 2004. After graduation, she started her
work as a LECTURER in textile science and
technology at Department of Textile Science, Faculty
of Agro-Industry, Kasetsart University, Thailand until
present. Her research interests are in the field of textile
chemical processing, i.e. pretreatment, dyeing, printing and finishing of
textiles. She has been intensively researching about poly (lactic acid), PLA,
fiber since her Ph.D. study at University of Manchester and still continues
the research work in this area up till now and has generated a number of
publications regarding PLA fiber. Her current researches concerns the
development of disperse dyeing of polyester, textile chemical finishing and
utilization of natural dye for textiles.
Suchada Ujjin is currently a SENIOR
RESEARCHER at the Kasetsart Agricultural and
Agro-Industrial Product Improvement Institute
(KAPI). She was graduated for her Master degree in
Plant Pathology from Kasetsart University in year
1980. She focuses her research interest in dyeing
textiles with synthetic and natural dyes. Development
of textile from silk is also her field of expertise. Along
with doing a research, she has also been working closely with the rural
communities where silk sericulture are located in terms of training and
development of local team to help strengthen local silk production
communities in Thailand. Her current research regards the development of
silk products, blending of silk with other textile fiber and natural dyes.
International Journal of Bioscience, Biochemistry and Bioinformatics, Vol. 3, No. 2, March 2013
109