Application of amber filler for production of novel polyamide composite fiber

Abstract

The present investigation is connected to the field of medical textiles, which includes the development and application of composite fibers. The aim of the paper is the processing and investigation of polyamide 6 (PA6)–amber composite fibers. The use of amber filler for the preparation of a new type of polymer composite fiber is described in detail for the first time. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and granulometry testing were used to test the structure and the size of the prepared amber particles. The obtained amber particles were characterized by an average size of up to 3 µm and a regular shape. Fourier transform infrared (FTIR) spectroscopy investigations showed that amber in the dispersed state does not change its chemical structure and contains one of the active compounds—succinic acid. The effect of the amber filler inclusion on the melt-spinning routes of fully drawn yarns (FDY) and pre-oriented yarns (POY) was determined. Amber composite fibers general use is medical fabric (compression socks and tights); it is biocompatible with skin cells.

Full text

Original article
Application of amber filler for production
of novel polyamide composite fiber
Sergejs Gaidukovs
1
, Inga Lyashenko
2
, Julija Rombovska
3
and Gerda Gaidukova
4
Abstract
The present investigation is connected to the field of medical textiles, which includes the development and application of
composite fibers. The aim of the paper is the processing and investigation of polyamide 6 (PA6)–amber composite fibers.
The use of amber filler for the preparation of a new type of polymer composite fiber is described in detail for the first
time. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and granulometry testing were used to test
the structure and the size of the prepared amber particles. The obtained amber particles were characterized by an
average size of up to 3 mm and a regular shape. Fourier transform infrared (FTIR) spectroscopy investigations showed
that amber in the dispersed state does not change its chemical structure and contains one of the active com-
pounds—succinic acid. The effect of the amber filler inclusion on the melt-spinning routes of fully drawn yarns (FDY)
and pre-oriented yarns (POY) was determined. Amber composite fibers general use is medical fabric (compression socks
and tights); it is biocompatible with skin cells.
Keywords
amber fiber, fabric formation, fabric manufacture, fabric processing, fabric fabrication, spinning, fabric composites, amber
Increasing interest in novel functional textile materials
has multiplied the investigations dedicated to the pro-
cessing of diverse composite fibers.
1–4
An efficient and
versatile melt-spinning process is widely used for com-
posite fiber manufacturing.
5
However, serious issues
during the melt spinning of composite fiber are possi-
ble—increased melt viscosity, agglomeration of the par-
ticles and blockage and breaking of the fiber during the
winding. Recently, the incorporation of different fillers
(clay, carbon and oxide particles) into polymer fibers
has found intense research interest.
6–9
Modern and
functional textiles have also increased demand for the
new particulate filler formulations. In this investigation,
the use of a novel amber filler with specific properties
for polymer composite fiber preparation is described in
detail for the first time.
In nature, amber is in the shape of different sized non-
regular pellets; even large sized monoliths weighing up to
several hundreds of grams. Amber was developed from
the pine tree (Pinus succinifera) fossil resin during the
Paleogene period as a result of a specific fossilization
process—polycondensation of resin acids and ter-
penes.
10
The main fossilization conditions were long-
term pine forest oxidation in soil, and further redeposi-
tion in the weakly oxidizing alkaline environment of
coastal areas, lagoons and delta sediments. Diagenesis
during the fossilization process promoted the develop-
ment of the oxygen-containing compounds in amber.
11,12
Many researchers have discussed amber in the con-
text of geology and chemistry.
13–24
They have reported
1
Riga Technical University, Faculty of Material Science and Applied
Chemistry, Institute of Polymer Materials, Latvia
2
Riga Technical University, Faculty of Mechanical Engineering, Transport
and Aeronautics, Institute of Biomedical Engineering and
Nanotechnologies, Research Lab of Biotextile Materials, Latvia
3
Morphology Laboratory, Faculty of Medicine, Riga Stradins University,
Latvia
4
Riga Technical University, Faculty of Material Science and Applied
Chemistry, Institute of Applied Chemistry, Latvia
Corresponding author:
Inga Lyashenko, Riga Technical University, Faculty of Mechanical
Engineering, Transport and Aeronautics, Institute of Biomedical
Engineering and Nanotechnologies, Research Lab of Biotextile
Materials, Pulka street 3/3-20, Riga LV 1007, Latvia.
Email: inga.lasenko@rtu.lv
Textile Research Journal
2016, Vol. 86(20) 2127–2139
!The Author(s) 2015
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DOI: 10.1177/0040517515621130
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the chemical structure and properties of the amber
regarding its origin, deposition and fossilization condi-
tions. Beck et al.,
25
Lambert et al.
26
and Mills et al.
27
have demonstrated by the use of spectroscopy and
chromatography methods that amber’s chemical com-
position is not stoichiometric and consists, on average,
as follows: 79% Q, 10.5% Mand 10.5% N. Amber also
contains up to 12 chemical elements: Ni, Cu, Mg, Fe,
Na, Ca, Mn, Al, Si, Au, N and S. Their content is in
traces up to 0.75%.
Basic structural elements of amber are high molecu-
lar weight aromatic and hydroaromatic compounds,
which contain double-associated carboxyl, hydroxyl
and ester groups.
10–12
Amber consists of three types of
compounds: (1) terpenoids and sesquiterpenoids; (2)
succinites (succinic acid, succinoabietin acid, abietin
acid, levopimaric acid, palustrin acid, neoabietin acid,
dextropimar and isodextropimar acids, dehydroabietin
acid, dehydroisopimar acid, sandaracopimar acid and
diagaten acids); and (3) polyethers, which are developed
as a result of the condensation of soluble acids with
alcohol that is formed by the reduction of acids.
25–27
Several authors reported solubility investigations of
the different amber types in diverse organic sol-
vents.
28–31
Solubility can vary in very broad ranges,
from 6–63%. The solubility of amber depends on the
intensity of the fossilization process. Under ambient
conditions, amber is insoluble in water.
Hazelwood
32
and other authors have reported on the
excellent bioactivity and biocompatibility properties of
amber.
33,34
The active compound of amber is succinite
(succinic acid). Its content is 3–8 % in Baltic amber.
Succinic acid plays a significant role in metabolism
(Krebs cycle), and also takes an important part in
intramithohondrial hemoglobin synthesis.
32–34
Like
simple mono- and dicarboxylic acids, succinic acid
is not considered dangerous, according to the
Registration, Evaluation, Authorisation and restriction
of CHemicals (REACH) safety data sheet for Baltic
amber powder (EC 232-520-0). Agarwal et al.
35
dis-
cussed that succinic acid and its derivatives can be
used in medicine as anxiolytic, antispasmer, antiplegm,
antiphogistic and antitumor agents. Succinic acid is a
strong electron donor.
36,37
Mie et al.
38
reported that
amber produces energy. It can give away free electrons
in order to maintain the energetic potential in cells with
aerobic respiration.
39–41
Archambault et al.
42
presented
the ability of amber to prevent the degradation of
dermal proteins and amber’s remarkable modulating
activity on the gene expression profile of human
dermal fibroblasts. The use of amber in cosmetic pro-
ducts was also reported.
43
Amber can be characterized
by its biostimulating effect on new cell formation in
skin. Amber stimulates skin and hair restoration.
44
Amber does not cause skin irritation and organism
sensitization.
42–44
Lyashenko et al.
45,46
also reported
that textile fabric impregnated with technologically
processed amber, investigated in vivo, does not show
irritation or caustic effect and also has a
biostimulating effect on the creation of new cell in
skin, subcutaneous tissue and skin derivatives, and it
promotes skin renewal.
Considering the chemical composition, thermal and
biocompatibility properties of amber, the aim of the
investigation is the processing of polyamide 6 (PA6)–
amber composite fibers. PA6 was chosen as a matrix for
amber composite fiber production due to its general use
in medicine fabrics (compression socks and tights) and
due to its biocompatibility with skin cells.
47
The next
aim of this work was to determine the effect of amber
filler inclusion on the melt-spinning routes of fully
drawn yarns (FDY) and pre-oriented yarns (POY).
The melt spinning conditions (temperature, velocity
and denier) have been investigated, considering also
the possible breaking susceptibility during the fiber
spinning process. Amber composite fiber’s tensile prop-
erties have been tested.
Materials and methods
Raw materials
Amber pellets (5 mm, Chemical Abstracts Service
(CAS): 9000-02-6 Enzyme Commission (EC): 232-
520-0) were obtained from the Kaliningrad region of
the Russian Federation. The raw pellets of the
amber and the prepared amber powder can be seen in
Figure 1.
PA6 RADIPOL S100-004Õis used in melt extrusion
processing. It is characterized with a low molecular
substance content of 0.9% and a melting temperature
of 220C.
Preparation of amber micro-size particles
The first stage of the amber particle preparation was
their purification by the flotation process. The flotation
process was based on the difference in densities of the
amber and the impurities. It separated the amber from
the crystalline minerals (quartz) and the amorphous
impurities (silica). The flotation device consists of the
two flotation chambers equipped with a foam
picker device and a compressed air supply device. The
flotation camera was fed with deionized water
(density ¼1.00 g/cm
3
) at a temperature of 20C. The
particles of ash rose to the water’s surface and were
collected. The amber had a density of 1.08 g/cm
3
,soit
remained at the bottom of the chamber. The second
flotation chamber was fed with a NaCl salt–water solu-
tion (density 1.02 g/cm
3
, NaCl 200 g/l) at a temperature
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of 30C. The amber pellets floated on the surface of the
water, but quartz, mica and feldspar, which had the
highest density, remained at the bottom of the cham-
ber. The amber pellets were collected with the foam
picker, transported into the oven and dried for 10 min
at 45C.
The amber pellets were first ground with a planetary
ball-mill Pulverisette 5 Fritsch (Germany). The amber
(45 g) was ground in a 250 ml agate bowl with 15 x
20 mm SiO
2
balls. The speed was 400 rpm, and the
duration was 10 min. The processed amber was used
in the next grinding step, which was performed on
mill devices 01-HD Attritor, Union Process and
01-HDDM Attritor, Union Process (USA). The
second grinding was performed with 3 or 5 mm YTZÕ
media. The third grinding was performed with
0.4–0.6 mm YTZÕmedia. The processing rates were
600 and 1900 rpm, respectively. The tank volume
was 1400 ml. The slurry temperature during the process
was 16C. The tank was continuously cooled with the
circulating water. The slurry was sampled by granulo-
metry testing every 30 and 60 min. After the grinding,
the amber was dried in an oven for 48 h at a tempera-
ture of 45C, resulting in the dry amber powder
(Figure 1(b)). It was stored in a tightly closed container
and desiccator without access to moisture and sunlight.
Methods
In the present investigation, we focus on the prepara-
tion of the amber particles applicable for melt extrusion
processing. The amber particles have been manufac-
tured by the three-stage grinding technology and char-
acterized by granulometry, Fourier transform infrared
(FTIR) spectroscopy, scanning electron microscopy
(SEM) and atomic force microscopy (AFM).
A Particle Size Analyzer 90 Plus with ZetaPALS
from Brookhaven Instruments Corporation was used
for the particle granulometry test. AFM measurements
of the experimentally prepared amber particles were
performed in the non-contact mode with a scanning
probe atomic force microscope, CP-II VEECO
Instruments (USA). The structure and shape of the
amber particles and the fibers were observed with a
SEM TESCAN Mira\LMU Field-Emission-Gun. The
accelerating voltage was 15 kV.
FTIR is a common method for the determination of
bonding in amber material samples.
16,25
FTIR spectra
were recorded on a Varian Scimitar 800 FTIR spectro-
meter. The measurement range was 400–4000 cm
1
with an accuracy of 4cm
1
using KBr as the beam
splitter. Samples were prepared by mixing the amber
particles with dried anhydrous KBr (Merck, Germany).
A KERN MRS 120-3 was used to control the moist-
ure of the amber pellets and powder.
The tensile properties of the amber fiber were tested
on a Zwick/Roell (Germany) with the grip separation
rate of 5 mm/min and the distance between the grips of
100 mm.
The calorimetric tests of the obtained amber parti-
cles were carried out on a differential scanning calori-
metry (DSC) 204 F1 Phoenix instrument. Specimens
about 10 mg in weight were heated, by using nitrogen
as a purge gas with the flow rate of 40 ml/min in the
temperature range from 25–300C. The heating ran at a
rate of 20C/min. The glass-transition temperature T
g
was calculated from the experimental heating curve.
The thermogravimetric tests of the obtained amber
particles were performed on a NETZSCH TG 209 F1
Iris instrument. Specimens about 10 mg in weight were
heated in nitrogen up to 800C. The material thermal
stability was evaluated from the weight-loss heating
curves. The thermal degradation temperature was cal-
culated by using the NETZSCH PROTEUS original
software.
Extrusion processing of the amber composite fiber
We have investigated a two-step extrusion technology
for amber–polymer composite, which admits a
Figure 1. Photos of (a) initial amber pellets and (b) prepared amber powder.
Gaidukovs et al. 2129
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homogeneous distribution of amber particles in a PA6
matrix.
A twin-screw extruder, Berstorff ZE25-38D
(Germany), was used for the PA6 and the amber par-
ticles melt compounding. The settings were the follow-
ing: screw speed of 300 rpm, barrel temperature of
240C, melt temperature of 265C and mass flow of
10 kg/h. The PA6–amber fiber (hereinafter, the amber
fiber) melt spinning was performed with a single-screw
extruder lab line at the Institut fu
¨r Textiltechnik (ITA)/
Aachen University. The POY configuration was as fol-
lows: process speed of 2000–4500 m/min, titer up to 300
den (final), filament count of (0.5) 1.0–4.0 dpf (final),
elongation of 60–250%, tenacity of 1.7–3.4 g/den and
yarn uniformity (USTER) of <1%. The configuration
for the FDY was as follows: process speed of 2000–
4500 m/min, titer up to 1.200 den, filament count of
1.0–10.0 dpf, tenacity of 3.5–6 g/den and yarn unifor-
mity (USTER) of <1%.
Results and discussion
Characterization of the amber particles
Figure 2 shows the granulometric curves and volume-
size histograms of the amber particles at the different
grinding stages. As could have been expected, in the wet
grinding condition the particles size is smaller than in
the dry condition;
48
the particle size decreases up to
500 mm in the first grinding stage (dry), up to 180 mm
in the second grinding stage (wet) and up to 0.5 mmin
the third grinding stage (wet).
Figure 3 shows the relationship between the amber
particle size and the grinding time. In the wet grinding
stage, the average size of the particles reduce very fast
from the initial 180 to 10 mm, according to the observa-
tion of Kotake et al.
49
that the fine grinding has pro-
gressed fast in the wet grinding conditions, with the
small balls. The amber particle size slightly starts to
increase during the longer grinding times; this increase
Figure 2. Granulometric curves and volume-size histograms of amber particles: (a) after the first grinding stage, (b) after the second
grinding stage and (c) after the third grinding stage.
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is generally caused by the aggregation of elementary
particles.
50
Figure 4 shows SEM micrographs of the obtained
amber particles. The amber particles are characterized
by the irregular shape, obtained after the grinding. The
size of the amber particles after the dry grinding is
about 200–500 mm (Figure 4(a)). The wet grinding has
significantly reduced the particle size (Figure 4(b)
and (c)). It has been reported that the particles have
a tendency to agglomerate during the grinding.
50
Figure 4(d) shows that the obtained amber particles
are agglomerates of the particles with the size of
0.1–1 mm. Figure 5 shows the AFM micrographs of
the amber particles at different magnifications, which
Figure 3. Grinding time influence on amber particle size for (a) the second grinding stage and (b) the third grinding stage.
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also shows that the agglomerates consist of the small
particles. The agglomeration also has promoted some
smoothing of the amber particle edges and the develop-
ment of the more spherical particle shapes.
50
We concluded that 30 min of grinding was sufficient
to produce the best particle results, considering their
size, shape and agglomeration, which was measured
by SEM, AFM and granulometry.
The Figure 6 shows the FTIR spectra of the initial
amber and the obtained amber particles after the wet
grinding. The horizontal shoulder observed in the inter-
val 1160–1260 cm
1
corresponds to the characteristic
absorption band of Baltic amber.
16
An intense absorp-
tion band observed at 1158 cm
1
indicates the presence
of C-O bonds. Both spectra show also the broad
absorption band at 3400 cm
1
, indicating the -OH
groups of the alcohol and/or carboxylic acids and/or
absorbed water. The alkyl group has two similar
intensity bands at 2926 and at 2867 cm
1
. The band
between 1420 cm
1
and 1460 cm
1
and the band
between 1375 and 1385 cm
1
correspond to -CH
2
and
-CH
3
group vibrations, respectively. FTIR spectra
absorption bands at 3040, 1640 and 887 cm
1
corre-
spond to exocyclic methylene groups.
16
The first band
corresponds to an ethylene C-H bond, the second band
corresponds to a C ¼C double bond and the third band
corresponds also to the ethylene C-H bond. The exo-
cyclic methylene groups are present in the agathic and
communic acid. Carbonyl group absorption, in the
region of 1640–1740 cm
1
, is very complex with signifi-
cant overlap, which distorts the spectra and complicates
the interpretation of it. However, the absorption band
at 1738 cm
1
is overlapping with the bands at
1690 cm
1
and 1646 cm
1
(see Figure 6). The band at
1738 cm
1
corresponds to a C ¼O bond in ketones; the
band at 1690 cm
1
characterizes -CO groups in
Figure 4. Scanning electron microscopy (SEM) micrographs of amber particles: (a) particles after the first grinding stage, (b) particles
after the second grinding stage, (c) particles after the third grinding stage and (d) amber particle agglomerate.
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carboxylic acid. The strong band at 1738 cm
1
indicates
the presence of esters. Other spectrum bands of the
amber are much more difficult to interpret.
16
Melt spinning of the amber filament
The technological process of the amber filament
included the following steps: (1) the melt extrusion
with a twin-screw extruder of the PA6–amber 5 wt. %
composite; (2) the preparation of 1 wt. % composite
with a single-screw extruder from PA6–amber 5 wt.%
composition and (3) the melt spinning of the amber
fiber and its post-processing (lubrication and stretch-
ing). Figure 7 shows the schematic overview of the
melt extrusion spin routes of the amber fiber obtained
in the present investigation.
The proposed two-step extrusion processing was
chosen for the better dispersion of the amber particles
into the polymer matrix. The temperature of the extru-
sion equipment and the melt are the major process
parameters determining the viscosity of the polymer.
50
Then, the processing temperature of 255C was chosen
in a way that the polymer viscosity is low enough to
allow a stable melt processing and dispersion of the
amber particles. After several experimental trials
under different temperatures, we determined that for
PA6 the temperature of the extrusion was found
approximately 30–40C above the polymer melting
temperature, which corresponded to the reported inves-
tigations.
51
The extrusion compounding of the compo-
sites with 5 and 1 wt.% of the amber was without any
complications. Figure 8 shows the DSC and the
thermal gravim analysis (TGA) thermograms, which
testified that the amber’s T
g
and T
deg
are 153C and
454C, respectively. The amber particles can become
soft at the chosen processing temperatures,
23
which
promotes the blending within the polymer matrix.
52
The amber filament was obtained using a standard
melt spinning technology (Figure 7). The melt exits the
extruder at pressure levels around 80–110 bar and is
transported through heated pipes to the spin pump.
Before the spin pump, the process and throughput are
pressure controlled depending on the pressure at the
extruder head. From the spin pump and after, it is a
throughput-controlled process. The polymer is pumped
for filtration into the spin pack, which consists of the
multiple metallic non-woven layers. After passing
through all the filtration stages, the melt flows into
the capillaries of the spinneret. At the end of the capil-
lary, the melt exits and forms a filament. A laminar air
stream perpendicular to the fibers’ axis cools the
extruded filaments directly below the spinnerets.
5
Spinnerets with 12 capillaries per spin plate were
used. The details on the spinnerets geometry and the
filtering are listed in Table 1. The used spinneret gave
good results with the spin pressure, the filtering and the
filament formation. The throughput of the polymer
melt was calculated for 10 dtex per filament. The final
filaments counted 120 dtex at 2500 m/min. Per filament,
this result was about 30 g/min. The used spinning line
had two spin packs, which gave the total extruder
throughput of 3.6 kg/h.
Figure 5. Atomic force microscopy (AFM) micrographs of different magnifications of amber particles after the third grinding stage
(wet).
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After cooling, the amber fiber was lubricated with
the use of a spin-finish to reduce friction in the further
drawing. The processed spun fibers are drawn down
vertically by the one godet route (POY) and by the
two godets route (FDY), whereas the consecutive
godet revolves faster than the first one.
53
In Figure 7, blue lines represent a take-up
POY process. In the POY route, the process ran at
2500–3000 m/min with no solid-state drawing
between the godets. The only drawing of the filament
found a place just below the spinnerets in the melt
state of the material. The winding head was
winding the filament ends onto the paper tubes. The
characteristic relaxation after 24 h of the filament
on the bobbins was observed (Figure 9), which led to
the winding problems; the filament slid off the holder.
54
Figure 6. Fourier transform infrared (FTIR) spectra of (a) initial amber and (b) amber particles after grinding.
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Therefore, the winding process has been
modified further.
Solid-state drawing was used to reduce the amber
filament relaxation process observed through the POY
route. For this step, the amber filament was wound in
the FDY process (see the red line in Figure 7). The
winding speed was 2500 m/min, but, therefore,
the take-up speed of the Godet 1 was reduced, and
the filament was led over the secondary GodetDuo 2
in order to draw the filament at a temperature above
room temperature. The solid-state draw temperature
was above the glass-transition temperature of
the polymer. The draw ratios (DR) were varied between
factors 1.0 and 1.9.
The processing parameters for these FDY spinning
trials are collected in Table 2. The initial polymer melt-
spinning trial (0) was used as a reference. The first trial
(1) of the amber filament was unsuccessful. The fila-
ment breached off as the drawing stage occurred. The
total drawing ratio (TDR) was about 1.72. Then, the
more stable spinning trials with a TDR of 1.15 were
introduced. The average throughput was about
170 dtex or 15 dtex per filament. The parameter n
s
indicated the number of revolutions per minute of the
spinning pump; n
p
indicted the number of revolutions
per minute of the spin-finish pump. The spinning pump
was forwarding the melt toward the spinneret. The
spin-finish pump was covering the filament ends with
spin-finish after the spinning. For trials 2 and 3, the
revolution values were 18 and 14, respectively. Godet
1 together with an idler roll took over the filament ends
directly after the spinning. The speed of Godet 1 was
chosen to be nearly the same as the speed of the fila-
ment ends after the spinneret.
5
It was considered, that
Figure 8. (a) Differential scanning calorimetry (DSC) and (b) thermogravimetry (TG)/derivative thermogravimetric (DTG) analysis
curves of amber particles.
winder
air quench
extruder
spin pump
spinneret
filaments
Godet 1
Godet 2 GodetDuo 2
GodetDuo 1
polymer
amber
Figure 7. Schematic chart of the fiber melt-spinning routes;
red¼fully drawn yarns (FDY), blue ¼pre-oriented yarns (POY).
Table 1. Spinneret characteristics
Spin pack
Spin plate diameter 80
Number of capillaries per plate 12
Capillary diameter, mm 0.35
Capillary length, mm 0.7
Filter, mm 0.062
Steel sand, g 100
Steel sand corn size, mm 350–500
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GodetDuo 1 was heavily drawing the yarn ends
(DR ¼1.05–1.40), but GodetDuo 2 was additionally
slightly drawing the yarn ends (DR ¼1.04–1.06). The
DR was adjusted with the Godets and GodetDuo speed
in the range of 1746–3050 m/min. Godet 2 was relaxing
the filament ends at room temperature (DR ¼0.98–
0.99). The Godets were operating within the tempera-
ture range of 20–160C.
Additional spinning trials have been performed with
winding speeds of 3500–4000 m/min, which correspond
to the general winding process speeds of nylon 6.
55
The
winding process was fast enough to produce economic-
ally competitive amber fibers for production at scale.
Table 3 lists the tensile properties of the filaments
produced in the experimental melt-spinning trials.
Trial 0 resulted in the initial PA6 filament of medium
strength and high elongation.
53
Overall, it can be
stated, that the amber filament tenacity of 16.35 cN/
dtex decreases in comparison to the initial filament
tenacity of 32.09 cN/dtex. It corresponds to the lower
values of TDR for the amber filaments (TDR ¼1.15) in
comparison to the TDR of the initial polymer filament
(TDR ¼1.92). The elongation at breaking of the amber
filament is the lowest for trial 1. This finding is also in
good agreement with the main findings during the spin-
ning trials, where possible agglomeration of the amber
particles occurred, which can decrease the filament
tenacity and the elongation.
Generally, particle sizes should be less than one-
third the diameter of the mono-filament for continuous
composite fiber processing.
54
The size of amber particles prepared by our original
technology was less than 3 mm and less than eight times
the mono-filament diameter of 25 mm (see Figure 10).
It showed that the amber particle agglomerates
(<5mm, Figure 10(a)) and elementary particles
(<3mm, Figure 10(b)) have a round shape and are
homogeneously distributed on the surface of the fila-
ments. Amber particles cover about 20% of area of the
filaments. The result was calculated according to the
Table 2. Amber fiber processing parameters for spinning trials
Trial Godet 1 Duo 1 Duo 2 Godet 2 Winder
No. n
s
n
p
VT VT VT VT V
[rev] [rev] [m/min] [C] DR [m/min] [C] DR [m/min] [C] DR [m/min] [C] DR [m/min]
(0) 12 32 1564 20 1.02 1596 20 1.85 2952 160 1.04 3070 23 0.98 3000
(1) 16 32 1746 20 1.20 2095 80 1.40 2933 80 1.04 3050 23 0.98 3000
(2) 18 14 2156 20 1.05 2273 20 1.05 2387 40 1.06 2530 23 0.99 2500
(3) 18 14 2156 20 1.05 2273 20 1.05 2387 40 1.06 2530 23 0.99 2500
DR: draw ratio; T: temperature; V: speed.
Figure 9. Post-relaxation after 24 h of the amber fiber on the
bobbins.
Table 3. Tensile properties of the amber fiber
Trial Properties
No. TDR Linear mass density Tenacity Elongation
[dtex] [cN/dtex] [%]
(0) 1.92 93.28 32.09 66.14
(1) 1.72 130.52 16.35 37.27
(2) 1.15 171.87 11.13 80.33
(3) 1.15 172.26 11.19 80.18
TDR: total draw ratio.
2136 Textile Research Journal 86(20)
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image analysis software (Image-ProÕ), which uses the
total area of the particles on the specific space.
Despite the lower strength of the amber fiber (16.35
cN/dtex) in comparison to the PA6 fiber without addi-
tives (32.09 cN/dtex), the strength is enough to prepare
the textile fabrics for medical application, because the
amber fiber is used in combination with other natural
(cotton, wool, linen, etc.) and synthetic (Lycra, nylon,
etc.) fibers.
56
It is designed to broaden the textile diver-
sity and to expand the medical textile assortment (com-
pression socks and tights). Fabrics containing amber
fiber can be used as medical textiles for external appli-
cations, when skin changes occur, including for skin
condition improvement for diabetics and for preventive
compression products. The Textile Industry Research
Association (AITEX) investigations (according to
OEKO-TEX Standard 100) approve that composite
amber fiber meets the human-ecological requirements
of the standard presently established for baby articles
(product class I, Certificate 2013LK0012).
57
OEKO-
TEX Standard 100 concluded positive medical impacts
of amber fibers concerning the skin: biocompatibility
and does not cause skin irritation and organism sensi-
tization. Amber fibers also have been tested with
in vitro cytotoxicity testing according to UNE-EN
ISO 10993-5: 2009; its satisfactory certificate MADE
FOR HEALTHÕNr 2014TM0281 issued by AITEX
is valid till 16.11.2016.
Conclusions
Amber filler with a particle size up to 3 mm (95 vol.%),
regular shape and without chemical degradation was
processed with a three step grinding process according
to performed investigations by granulometry, SEM,
AFM, DSC and TGA. The grinding conditions were
as follows: deionized water dispersion media, tempera-
ture of 16C, grinding time of 30 min and processing
rate of 1900 rpm.
The melt-spinning conditions testified the amber
filament relaxation after 24 h and demonstrated that
filaments slid off the holders in POY drawing. The
DR for FDY were varied between factors of 1.0 and
1.9. The stable spinning trials were with winding speeds
of 2500–3000 m/min and a TDR of 1.15. According to
the investigated spinning trials, the tensile properties of
the processed amber fiber (32.09 cN/dtex) decreased
about 2–2.8 times in comparison to initial the PA6
fiber (16.25 cN/dtex). The achieved strength of the
amber fiber is enough to prepare the textile fabrics for
medical application, because it is used in combination
with other natural and synthetic fibers.
SEM testified that the required elementary amber
particles were homogenously distributed on the surface
of the amber filaments, and the total cover area was
about 20%.
Amber composite fiber’s general use is medicine
fabric (compression socks and tights); it is biocompati-
ble with skin cells.
Declaration of conflicting interests
The authors declared no potential conflicts of interest with
respect to the research, authorship, and/or publication of this
article.
Funding
The authors disclosed receipt of the following financial sup-
port for the research, authorship, and/or publication of this
article: This research was funded through a Eureka/Micro
and Nano Technologies (MNT) ERA-Net European
Figure 10. Scanning electron microscopy (SEM) micrographs of (a) amber fiber and (b) of amber mono-filament.
Gaidukovs et al. 2137
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consortium, Project ‘‘Fundamental and Industrial Fossilized
Resin Research for the Production of Composite Material’’
Nr. E!5798. Support of this work for S Gaidukovs was pro-
vided by the Riga Technical University scientific research
project RTU ZP-2014/08.
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