Mechanical, thermal, and fire retardant properties of poly(ethylene terephthalate) fiber containing zinc phosphinate and organo-modified clay
J Therm Anal Calorim
Mechanical, thermal, and fire retardant properties of poly(ethylene terephthalate) fiber containing zinc phosphinate and organo-modified clay
Mehmet Dog˘an 0 1 2
Selahattin Erdog˘an 0 1 2
Erdal Bayramlı 0 1 2
0 E. Bayramlı Department of Chemistry, Middle East Technical University , 06531 Ankara , Turkey
1 S. Erdog ̆an E. Bayramlı (&) Department of Polymer Science and Technology, Middle East Technical University , 06531 Ankara , Turkey
2 M. Dog ̆an Department of Textile Engineering, Erciyes University , 38039 Kayseri , Turkey
The effect of zinc bisdiethylphosphinate (ZnPi) and organoclay on mechanical, thermal, and flame retardant properties of poly(ethylene terephthalate) (PET) fiber was investigated. ZnPi was preferred due to its fusible character at spinning temperature and organoclay was used for synergistic interaction. The mechanical, thermal, and flame retardant properties of fibers were examined by tensile testing, thermogravimetric analysis (TG), and micro combustion calorimeter (MCC). The tensile strength of the PET fiber reduced with the addition of both ZnPi and organoclay. The TG results showed that the inclusion of ZnPi increased the char residue. The MCC results showed that the addition of organoclay increased the barrier effect of formed char which depends on char amount, thickness, and integrity and reduces the maximum heat evolved during the test. This result was also important in terms of showing that the organoclay was effective in thermally thin samples.
PET; Fiber; Flame retardancy; Micro combustion calorimeter
Poly(ethylene terephthalate) (PET) fiber is the largest
volume synthetic fiber produced worldwide due to its low cost,
convenient processability, and its high performance. It finds
a variety of use area, such as textile apparel fibers, furnishing
fabrics, tyre cord, car seat belts, water bottles, and carpets for
their attractive properties. It also finds application area in
outdoor and sports wear when used as microfiber [
A flame retardant PET-based textile can be obtained
(1) during polymerization adding phosphorous containing
monomers, (2) during spinning adding flame retardants into
spinning dope, and (3) by finishing treatment especially
thermosol method [
]. Although the flame retardant fiber
production with melt-processable additives is likely to be
cheaper and have higher wash fastness than the
conventionally produced flame retarded textile articles, it has some
drawbacks such as finding suitable flame retardant which
must be used below 15 wt% to minimize its effect on fiber
textile properties. Accordingly, the nanotechnology and the
synergy between different flame retardants gain importance
for the production of flame retardant fiber by reducing the
total amount of flame retardant additive [
Different kinds of nanoparticles, especially layered
silicates due to their plate-like structure, are used with and
without conventional flame retardants to increase the flame
retardant behavior of polymeric materials. The most
significant effect of the addition of layered silicate is the reduction
of peak heat release rate (PHRR) which is a function of
sample thickness. They are not so effective in textile
applications when used alone compared to polymeric fire
retardants due to their thermally thin structure which has only the
pyrolysis zone and promotes volatilization rather than
the formation of carbonaceous-silicate layer. In spite of the
reduction of PHRR, total heat release rate (THR), time to
ignition (TTI), UL-94, limiting oxygen index (LOI) is not
influenced much by the presence of layered silicates [
The flame retardant properties of nanoparticle containing
fibers are widely investigated [
]. It follows from these
studies that there is only limited success obtained when
nanoparticles are used without any conventional flame
retardants. New trends are focused on the use of
nanoparticles for their synergistic effect with melt-processable flame
retardant additives in fiber applications [
In this study, the flame retardant PET fiber is produced via
melt spinning process adding organic phosphinate-based
flame retardant with and without organoclay. Organic
phosphinates commercialized as metal salts of phosphinates are a
novel class of phosphorus-based flame retardants for
thermoplastics. Like other phosphorus compounds, it is believed
that organic phosphinates show their flame retarding effect
both in the condensed and gas phase. The previous studies
showed that the predominant mechanism changed with the
type of polymer and synergistic agents [
bisdiethylphosphinate (ZnPi) is the most widely used one
especially for polyesters. ZnPi that is fusible at spinning
temperature is used as flame retardant additive and
organomodified clay is used for its synergistic effect. The state of
dispersion of layered silicate into PET was monitored by
X-ray diffraction (XRD) and transmission electron
microscopy (TEM). The mechanical properties of fibers were
determined by tensile testing. The thermal and flame retardant
properties of fibers were determined by thermogravimetric
analysis (TG) and micro combustion calorimeter (MCC).
MCC is a new small scale instrument which measures
flame retardant behavior via a mimic of fire-type conditions
through pyrolysis and oxygen consumption calorimetry.
Oxygen consumption calorimetry works via Thornton’s rule,
which is an empirical relationship that gives the average heat
of consumption of oxygen with typical (C, H, N, and O)
gases, liquids, and solids. Specifically, on average 1 g of
oxygen gives of 13.1 ± 0.7 kJ of heat when it reacts with
typical organic materials to produce water, carbon dioxide,
and nitrogen [
Dry fiber grade PET was obtained from Kordsa Global
(I˙stanbul, Turkey). ZnPi, Exolit OP 950, was kindly obtained
from Clariant (Frankfurt, Germany). It is fusible at about
220 C with 24.9 J g-1 enthalpy of melting which is
measured by differential scanning calorimeter (Mettler Toledo
DSC 1 Star System) under nitrogen atmosphere at a heating
rate of 10 C min-1. Cloisite 30B, organoclay, was
purchased from Southern Clay Products Inc. (Gonzales, TX,
USA). It was organically modified with methyl, tallow,
bis2-hydroxyethyl, quaternary ammonium by the supplier.
Preparation of monofilament PET fibers
The pre-dried PET pellets are mixed with ZnPi and/or clay in
a twin screw microextruder (15 mL microcompounder ,
DSM Xplore) coupled with winding unit (DSM Xplore) at
100 rpm at 285 C. After the completion of mixing, the twin
screw extruder is brought to force controlled mode which
ensures a uniform polymer melt flow. The diameter of the die
is 0.25 mm. The spinning speed was 200 m min-1. After
spinning process, as-spun monofilaments were obtained with
varying diameters of 56–66 lm. There is no additional
cooling applied to the extrudate except for the ambient
conditions (25 C). The as-spun fibers are drawn at 90 C
with a constant draw ratio of 3.
The state of dispersion of layered silicate in PET was made by
XRD and TEM. XRD scan was performed by Rigaku DMAX
2200 diffractometer in the reflection mode using an incident
X-ray wavelength of 1.542 A˚ at a scan rate of 1 min-1 over
the range of 2h = 1 –10 . Ultra-thin sections (nominally
100 nm) were sliced using an ultra-microtome (Leica EM
UC6) with a diamond knife. Films transferred to 400 mesh
copper grids were observed under a high-resolution electron
microscope (TEM), FEI Tecnai G2 Spirit BioTWIN, operated
at 80 kV acceleration voltage. The measurement of the tensile
properties of monofilaments was carried out following the
standard ASTM D 3822 on a tensile testing machine of Lloyd
LR 5 K with a load cell of 10 N. All the tests were made at
room temperature at about 25 C. The length of the samples
was 20 mm and the deformation rate was 20 mm min-1. All
the results represent an average value of twenty tests with
standard deviations. For the calculation of stress values, the
diameter of fiber samples was measured with digital
microscope (Veho VMS-004) using imaging software. The
diameters of monofilaments were measured at 20 different places
on fiber sample and an average value is listed in Table 1 with
standard deviations. TG was carried out on Perkin Elmer
Diamond TG/DTA at a heating rate of 10 C min-1 up to
800 C under nitrogen flow of 50 mL min-1. The fire
retardant properties of fiber samples were tested with the MCC
(Govmark Organization Inc., Farmingdale, NY), at 1 C s-1
heating rate under nitrogen from 200 to 600 C using method
of ASTM D7309 (pyrolysis under nitrogen). Each sample was
run in triplicate to evaluate reproducibility of the flammability
measurements. No additional conditioning of the samples was
attempted prior to testing. The photograph of char residues
remained after MCC test was obtained via optical microscopy
(Nikon Coolpix S4).
Results and discussion
To evaluate the morphology achieved by the organoclay in
the polymer matrix after spinning process, XRD and TEM
Fig. 4 HRR curves of the fibers
have been carried out. The XRD patterns and TEM image
of composite is given in Figs. 1 and 2, respectively. Closite
30B shows a peak at 2h = 4.9 corresponding to basal
spacing of 17.9 A˚ . PET–ZnPi–clay composite shows a
peak at 2h = 8.8 corresponding to basal spacing of
10.03 A˚ . The peak at higher angles indicates a sort of
collapse of the structure in some parts of the clay due to
degradation of organic modification which starts to degrade
at 180 C [
] high processing temperature. No
intercalated or exfoliated structure seen at TEM images which
supports this conclusion. As a result, polymer molecules
are unable to intercalate between the silicate sheets and a
phase separated composite is obtained.
Tensile tests on monofilament fiber samples were made to
investigate the effect of flame retardant additives on the
mechanical properties of fibers. Youngs’ modulus (E),
stress at break values (r), and elongation at break values (e)
at given draw ratios are listed in Table 1. The addition of
Fig. 5 Photograph of char
residues remained after
ZnPi slightly reduces the E, r, and e values of fiber due to
its fusible character at spinning temperature. The addition
of organoclay further reduces the E, r, and e values of fiber
due to the formation of phase separated structure
(microcomposite). In this structure, clay platelets do not exfoliate
and nanocomposite structure does not form. The poor
interfacial adhesion between organoclay and PET further
deteriorates the mechanical properties of fiber samples.
TG curves of composites are shown in Fig. 3 and the
relevant data are given in Table 2. According to Fig. 3 and
Table 2, the mass loss of pure PET takes place in a single
step, with a maximum of mass loss rate at 444 C by
leaving high amount of char residue at 800 C. The
inclusion of ZnPi and organoclay does not significantly
modify the degradation path of PET except for the small
reduction in T5% and Tmax values which arises from the
degradation of ZnPi and the organic constituents added to
clay. The addition of ZnPi increases the char yield due to
the formation of phosphorus species like phosphonates,
phosphates in the condensed phase [
Micro combustion calorimeter
The char yield, HRR peak, THR, and char character
obtained from the MCC are listed in Table 3. The HRR
curves of the fibers and the photograph of the char residues
are shown in Figs. 4 and 5, respectively. All samples show
high char yields. Both PET and ZnPi containing PET gives
shiny black char that forms a foam-like structure which
centers itself in the middle of crucible. With the addition of
organoclay, black shiny foam-like structure is formed and
sticks to the crucible. Parallel with the TG results, the
inclusion of ZnPi reduces the maximum degradation
PET and ZnPi containing PET show a sharp spike of
HRR curve. The peak HRR values of PET ranging from
479 to 516 W g-1 with an average of 503 W g-1 and total
HR values ranging from 15.8 to 16.5 kJ g-1 with an
average of 16.1 kJ g-1. With the addition of 10 wt% ZnPi,
the average peak HRR increases to 531 W g-1 and average
total HR reduces to 15.8 kJ g-1. This result shows that the
inclusion of ZnPi does not improve the barrier effect in
spite of higher amount of char. The organoclay containing
sample shows a broad distinct two peak HRR curve.
Vannier et al. [
] showed that ZnPi degrades in two step
under air with maximum degradation rate at 417 C for
first step and 486 C for second step. Accordingly, the
small peak seen at about 434 C is probably due to the
decomposition of ZnPi. With the addition of organoclay
total HR value increases to 16.6 kJ g-1 and peak HRR
reduces to 329 W g-1 which corresponds to 62 %
reduction with respect to ZnPi containing PET fiber. The
reduction in peak HRR value is only observed in the
organoclay containing PET fiber samples due to the their
plate-like structure which increases the barrier effect of
foamed char structure arising from the degradation of PET
and ZnPi. Although this barrier reduces mass and heat
transport and slows down the escape of the flammable
volatiles generated during combustion, the total HR value
does not decrease since the amount of fuel source does not
decrease. It is a well-known fact that the flame retarding
effect of layered silicates is a function of sample thickness
and it increases as the sample thickness increases. These
results show that the layered silicates are also very
effective when used with char forming polymers in thermally
In this study, we investigate the flame retardant behavior of
PET fiber containing ZnPi and/or organoclay. It is observed
that the inclusion of ZnPi slightly deteriorates the
mechanical properties of PET fiber due to its fusible
character at melt spinning temperature. The inclusion of
organoclay further reduces the mechanical properties due
to the formation of phase separated structure. The addition
of ZnPi increases the char yield with formation of
phosphorus species in the condensed phase. According to MCC
results, the addition of organoclay reduces the HRR values
of fiber by increasing the barrier effect of the foamed char
1. Mclntyre JE . Synthetic fibers: nylon, polyester, acrylic, polyolefin . Cambridge: CRC Press; 2000 .
2. Lewin M. Handbook of fiber chemistry . New York: CRC Press; 2007 .
3. Weil ED , Levchik SV . Flame retardants for plastics and textiles . Munich: Hanser Publications; 2009 .
4. Levchik SV , Weil ED. Flame redardancy of thermoplastic polyesters-a review of the recent literature . Polym Int . 2005 ; 54 : 11 - 35 .
5. Zhang S , Horrocks AR . A review of flame retardant polypropylene fibres . Prog Polym Sci . 2003 ; 28 : 1517 - 38 .
6. Horrocks AR , Kandola BK , Davies PJ , Zhang S , Padbury SA . Developments in flame retardant textiles-a review . Polym Degrad Stab . 2005 ; 88 : 3 - 12 .
7. Morgan AB , Wilkie CA. Flame retardant polymer nanocomposites . Hoboken: Wiley; 2007 .
8. Kiliaris P , Papaspyrides CD . Polymer/layered silicate (clay) nanocomposites: an overview of flame retardancy . Prog Polym Sci . 2010 ; 35 : 902 - 58 .
9. Samyn F , Bourbigot S , Jama C , Bellayer S . Fire retardancy of polymer clay nanocomposites. Is there an influence of the nanomorphology? Polym Degrad Stab . 2008 ; 93 : 2019 - 24 .
10. Bourbigot S , Duquesne S , Jama C . Polymer nanocomposites: how to reach low flammability . Macromol Symp . 2006 ; 233 : 180 - 90 .
11. Morgan AB , Wilkie CA. Flame retardant polymer nanocomposites . New York: CRC Press; 2010 .
12. Erdem N , Cireli AA , Erdogan UH . Flame retardancy behaviors and structural properties of polypropylene/nano-SiO2 composite textile filaments . J Appl Polym Sci . 2009 ; 111 : 2085 - 91 .
13. Vargas AF , Orozco VH , Rault F , Giraud S , Devaux E , Lopez BL . Influence of fiber-like nanofillers on the rheological, mechanical, thermal and fire properties of polypropylene: an application to multifilament yarn . Compos Part A . 2010 ; 41 : 1797 - 806 .
14. Horrocks AR , Kandola BK , Smart G , Zhang S , Hull TR . Polypropylene fibers containing dispersed clays having improved fire performance. I. Effect of nanoclays on processing parameters and fiber properties . J Appl Polym Sci . 2007 ; 106 : 1707 - 17 .
15. Rault F , Pleyber E , Campagne C , Rochery M , Giraud S , Bourbigot S , Devaux E . Effect of manganese nanoparticles on the mechanical, thermal and fire properties of polypropylene multifilament yarn . Polym Degrad Stab . 2009 ; 94 : 955 - 64 .
16. Rault F , Campagne C , Rochery M , Giraud S , Devaux E. Polypropylene multifilament yarn filled with clay and/or graphite: study of a potential synergy . J Polym Sci Part B Polym Phys . 2010 ; 48 : 1185 - 95 .
17. Shanmuganathan K , Deodhar S , Dembsey NA , Fan Q , Patra PK . Condensed-phase flame retardation in nylon 6-layered silicate nanocomposites: films, fibers, and fabrics . Polym Eng Sci . 2008 ; 48 : 662 - 75 .
18. Bourbigot S , Devaux E , Flambard X . Flammability of polyamide6/clay hybrid nanocomposite textiles . Polym Degrad Stab . 2002 ; 75 : 397 - 402 .
19. Salau¨n F , Lewandowski M , Vroman I , Bedek G , Bourbigot S. Development and characterization of flame retardant fibres from isotactic polypropylene melt compounded with melamine formaldehyde microcapsules . Polym Degrad Stab . 2011 ; 96 : 131 - 43 .
20. Smart G , Kandola BK , Horrocks AR , Nazare S , Marney D. Polypropylene fibers containing dispersed clays having improved fire performance. Part II. Characterization of fibers and fabrics from PP-nanoclay blends . Polym Adv Technol . 2008 ; 19 : 658 - 70 .
21. Alongi J. Investigation on flame retardancy of poly(ethylene terephthalate) for plastics and textiles by combination of an organo-modified sepiolite and Zn phosphinate . Fiber Polym . 2011 ; 12 : 166 - 73 .
22. Yi J , Yin H , Cai X. Effects of common synergistic agents on intumescent flameretardant polypropylene with a novel charring agent . J Therm Anal Calorim . 2012 . doi: 10 .1007/s10973-012- 2211-z.
23. Xu T , Zhong Y , Liu Y , Yu H , Mao Z. Flammability properties of PI fabric coated with montmorillonite . J Therm Anal Calorim . 2012 . doi: 10 .1007/s10973-012-2549-2.
24. Levchik SV , Weil ED. A review of recent progress in phosphorus-based flame retardants . J Fire Sci . 2006 ; 24 : 345 - 64 .
25. Braun U , Schartel B. Flame retardancy mechanisms of aluminium phosphinate in combination with melamine cyanurate in glassfibre-reinforced poly(1,4-butylene terephthalate) . Macromol Mater Eng . 2008 ; 293 : 206 - 17 .
26. Isıtman NA , Gunduz HO , Kaynak C . Nanoclay synergy in flame retarded/glass fibre reinforced polyamide 6 . Polym Degrad Stab. 2009 ; 94 : 2241 - 50 .
27. Braun U , Schartel B , Fichera MA , Jager C . Flame retardancy mechanisms of aluminium phosphinate in combination with melamine cyanurate and zinc borate in glass-fibre-reinforced polyamide 6,6 . Polym Degrad Stab. 2007 ; 92 : 1528 - 45 .
28. Vannier A , Duquesne S , Bourbigot S , Alongi J , Camino G , Delobel R . Investigation of the thermal degradation of PET, zinc phosphinate, OMPOSS and their blends-identification of the formed species . Polym Degrad Stab . 2009 ; 495 : 155 - 66 .
29. Lyon RE , Walters RN , Stoliarov SI . Screening flame retardants for plastics using microscale combustion calorimetry . Polym Eng Sci . 2007 ; 47 : 1501 - 10 .
30. Yang CA , He Q , Lyon RE , Hu Y. Investigation of the flammability of different textile fabrics using microscale combustion calorimetry . Polym Degrad Stab . 2010 ; 95 : 108 - 15 .
31. Nagano Y , Sugimoto Y. Micro combustion calorimetry aiming at 1 mg samples . J Therm Anal Calorim . 1999 ; 57 : 867 - 74 .
32. Morgan AB , Galaska M. Microcombustion calorimetry as a tool for screening flame retardancy in epoxy . Polym Adv Technol . 2008 ; 19 : 530 - 46 .
33. Xie W , Gao Z , Pan W , Hunter D , Singh A , Vaia R . Thermal degradation chemistry of alkyl quaternary ammonium montmorillonite . Chem Mater . 2001 ; 13 : 2979 - 90 .