Lenzinger Berichte 89 (2011) 50 � 59

THERMAL AND SORPTION STUDY OF FLAME�RESISTANT FIBERS

Ksenija Varga1,2, Michael F. Noisternig3, Ulrich J. Griesser3, Linda Alja�4 andThomas Koch5

1Christian�Doppler Laboratory for Chemistry of Cellulosic Fibers & Textiles, University of Innsbruck, Austria 2Lenzing AG, Fiber Science & Development Department, Werkstraße 2, A�4860 Lenzing, Austria

Phone:+43 7672 701 2757; Fax:+43 7672 918 2757; E�Mail: k.varga@lenzing.com 3University of Innsbruck, Institute of Pharmacy, Pharmaceutical Technology, Innrain 52c, A-6020 Innsbruck,

Austria4Faculty of Natural Sciences & Engineering, University of Ljubljana, Slovenia

5TU Wien, Institute of Materials Science & Technology, Favoritenstraße 9-11, A-1040 Vienna, Austria

The characterization of FR fibers andfabrics is of crucial importance givingthe main accent to the thermal behaviorof materials in practical use. Since FRfabrics are often made from a verylimited number of materials, it isimportant to use fibers which providegood physiological comfort. LenzingFR® fibers are characterized by thermaland sorption methods in comparisonwith other flame�resistant materials. DSC and TGA are important means tostudy thermal properties of textiles.DSC spectra provide changes of heat

release during decomposition whileTGA show weight loss of the testedmaterials, but no specific pyrolysis ofthe products. Dynamic sorption analysisin broad humidity range show highsorption of cellulosic Lenzing FR® andlower for synthetic materials.Visualization of the residues ofcombusted materials by SEM confirmsthe theory of different decompositionmechanisms during heat exposure.

Keywords: Lenzing FR®, FR fibers,protective wear

__________________________________________

Introduction

Safety of human beings has been animportant issue all the time. A growingsegment of the industrial textiles industryhas therefore been involved in a number ofnew developments in fibers, fabrics andprotective clothing. Major innovations inthe development of heat�resistant fibers and flame�protective clothing for fire-fighters, foundry workers, military andspace personnel, and for other industrialworkers who are exposed to hazardousconditions have been carried out. For heatand flame protection, requirements rangefrom clothing for situations in which thewearer may be subjected to occasionalexposure to a moderate level of radiantheat as part of normal working day, toclothing for prolonged protection, wherethe wearer is subjected to severe radiantand convective heat to direct flame.

In the process of accomplishing flameprotection, however, the garment may beso thermally insulative and water vaporimpermeable that the wearer may begin tosuffer discomfort and heat stress. Bodytemperature may rise and the wearer maybecome wet by sweat. Attempts havetherefore been made to develop thermaland flame protective clothing which can beworn without any discomfort [1, 2].

This paper provides an overview of mostlyused fibers for thermal and flameprotection. The thermal behavior of suchfibers is studied by using followingthermal methods: thermogravimetry(TGA) and differential scanningcalorimetry (DSC). Scanning electronmicroscopy (SEM) images showed theresidues of the fibers after combustion.

Lenzinger Berichte 89 (2011) 50 � 59

Sorption study highlights the importanceof using cellulosic flame�retardant fibers in the protective fiber blends.

Thermal behavior of fibersThe effect of heat on textile materials canproduce physical and chemical changes.The physical changes occur at the glasstransition )( gT , and melting temperature

)( mT in thermoplastic fibers. The chemical

changes take place at pyrolysistemperature )( pT at where thermal

degradation occurs. The combustion is acomplex process that involves heating,decomposition leading to gasification (fuelgeneration), ignition and flamepropagation.A self�sustaining flame requires a fuel source and a means of gasifying the fuel,after which it must be mixed with oxygenand heat. When a fiber is subjected to heat,it pyrolyses at pT and volatile liquids and

gases, which are combustible, act as fuelsfor further combustion. After pyrolysis, ifthe temperature is equal or greater thancombustion temperature cT , flammable

volatile liquids burn in the presence ofoxygen to give products such as carbondioxide and water. When a textile isignited heat from an external source raisesits temperature until it degrades. The rateof this initial rise in temperature dependson: the specific heat of the fiber, itsthermal conductivity and also the latentheat of fusion (for melting fibers) and theheat of pyrolysis.In protective clothing, it is desirable tohave a low propensity for ignition from aflaming source or, if the item ignites, aslow fire spread with low heat outputwould be ideal. In general, thermoplasticfibers such as polyamide or polyesterfulfill these requirements because theyshrink from the flame. If they burn, theyburn with a small and slowly spreadingflame and ablate.For protective clothing, however, there areadditional requirements, such as protectionagainst heat by providing an insulation, aswell as high dimensional stability of

fabrics. Upon heat exposure, they areexpected to support the wearer�s work; they should not shrink or melt, and if thendecompose, from char. These requirementscannot be met by thermoplastic fibers andso resource must be made from aramidfibers, flame�resistant cellulosics or wool. It may also be noted that the aramid fiberswith their high limited oxygen index (LOI)and high thermal stability, have not beenfound suitable for preventing skin burns inmolten metal splashes because of theirhigh thermal conductivity. The mode ofdecomposition and the nature of thedecomposition products (solid, liquid andgaseous) depend on the chemical nature ofthe fiber, and also on the type of appliedfinishes or coatings. If the decompositionproducts are flammable, the atmosphericoxygen raises ignition, with or withoutflame. When the heat evolved is higherthan that required for thermaldecomposition, it can spread the ignition tothe total material destruction.In addition to the fiber characteristics andfabric finish, several garmentcharacteristics also influence the thermalprotection. For a given fabric thickness,the lower the density, the greater is thethermal resistance. This applies on char�forming fibers such as cellulosics andwool. Hence, thicker fabric made fromcellulosics or wool or other non�melting fibers give good thermal protection,whereas the thicker thermoplastic fibers�fabric produce burns. Thermal propertiesof some fibers are given in Table 1 [1].Concerning the environmental point ofview, Horrocks et al. developed ananalytical model for understanding theenvironmental consequences of usingflame�retardant textiles. An environmental rank value is given at each stage in themanufacturing process and product life ofeach flame�retardant fibers and fabrics. The results show that each of the elevengeneric fibers analyzed showed anenvironmental index value within therange of 32�51 % where 100 denotes the worst environmental position possible [3].

Lenzinger Berichte 89 (2011) 50 � 59

Materials for flame protection

Flame-resistant CellulosicsInherently flame�resistant viscose fibers are produced by incorporating FRadditives (fillers) in the spinning dopebefore extrusion. For example:phosphorous additives, polysilicic acid orpolysilicic acid and aluminum [1].

Lenzing AG currently produces LenzingFR® which contains phosphorus / sulfur�containing additives [4].

Rüf et al. patented a new procedure forproducing TENCEL® fibers with reducedflammability. The invention relates to acellulosic molded body containing acellulose / clay nanocomposite. The claycomponent of said nanocompositecomprises a material selected from thegroup consisting of unmodified hectoriteclays and hydrophilically modifiedhectorite clays [5].There are also viscose fibers withincorporated polysilicic acid available onthe market [1].

Flame-retardant PolyesterThere are three methods of renderingsynthetic fibers flame retardant: use of FR

co-monomers during co�polymerization, introduction of an FR additive duringextrusion and application of flameretardant finishes or coating. Additives andco�monomers are halogen- or phosphorus�based [1].

Flame-retardant AcrylicLike other synthetic fibers, acrylic fibersshrink when heated, which can decreasethe possibility of accidental ignition.However, once ignited they burnvigorously accompanied by black smoke.Halogen�based and particularly bromine derivatives or halogen� or phosphorus�containing co�monomers are the most effective flame retardants used in acrylicfibers. A number of spinning dopeadditives are also known to render acrylicfibers flame retardant, for example estersor antimony, tin and their oxides, SiO2,halogenated paraffins, halogenatedaromatic compounds and phosphoruscompounds [1].

AramidsAromatic polyamides char above 400 °Cand can be exposed to temperatures up to700 °C. Meta�aramid fibers have been developed for protective clothing forfighter pilots, tank crews and astronauts.

Table 1. Thermal and flame�retardant properties of some fibres [1].

FibregT [ C ]

Glass

transition

mT [ C ]

Melt

pT [ C ]

Pyrolysis

cT [ C ]

Combustion

LOI

[ % ]

Viscose (CV) - - 350 420 18.9

Cotton (CO) - - 350 350 18.4

Wool (WO) - - 245 600 25

Polyester (PES) 80-90 255 420 �477 480 20�21.5

Acrylic (PAN) 100 >320 290 >250 18.2

Modacrylic (MAC) <80 >240 273 690 29�30

Meta�aramid (AR) 275 375 310 500 28.5�30

Para�aramid (AR) 340 560 590 >550 29

Lenzinger Berichte 89 (2011) 50 � 59

The meta�aramid nonwovens are also used for hot gas filtration and thermalinsulation. Para�aramid fibers are used for ballistic and flame protection. Generally,meta�aramides are used in heat protective clothing. However, para�aramid fibers are added to improve the mechanicalstability [1].Meta�aramid fibers are blended with Lenzing FR® and FR�treated wool.

PolyimideAnother aromatic copolyamide fiber ispolyimide (brand name P84®; produced byEvonik Industries). The fiber does not meltbut becomes carbonized at 500 °C withLOI value 36�38 %. The application of high�performance P84® fibers includeprotective clothing, as a sealing or packingmaterial, for hot gas filtration and inaviation and space including aircraftseats [1].

PhenolicsMelamine polymer is obtained bycondensation reaction between melamineand formaldehyde. The cross�linked polymer is then spun to melamine fibers.They can be used in continuous service at200 °C. Above 370 °C, thermaldegradation result in char formation ratherthen molten drip [1].

ModacrylicFR modacrylic fiber is a copolymer ofacrylonitrile, vinyl�chloride or vinyliden�chloride in ratio of 60:40 wt% along with asulphonated vinyl monomer [1].

Aim of our workDSC and TGA are important means tostudy thermal properties of textilematerials, fabrics and fibers. However,DSC spectra provide changes oftemperature of the material in pyrolysisand the changes of heat release, but noother thermal properties. TGA can showweight losses of fibers and fabrics underdifferent temperature, but not the concretepyrolysis processes and products. In thisstudy, DSC and TGA were employed to

study the energy and mass changes ofvarious FR fibers during temperatureincrease. The use of these FR fibers inclothing requires sufficient physiologicalcomfort. Therefore, FR fibers have toprovide good sorption properties.Additionally to the thermal study, moisturesorption isotherms and WRV (waterretention value) measurements were doneon FR samples to have a notion about thephysiological behavior of FR fibers in use.By SEM, the visualization of fiber residueafter burning was conducted.

Experimental

Materials

In this work, thermal behavior of LenzingFR® fibers was compared with flame�retardant polymers. The characteristics ofused samples are given in Table 2.

Table 2. Fibres used for thermal and sorptionstudy.

Fibre Type Characteristics

Titer [dtex] /

Length [mm]

Lenzing FR® 2.2 / 51

Lenzing Modal® 1.3 / 38

TENCEL® 1.3 / 38

Meta�aramid 1.7 / 50

Para�aramid Fabric

Modacrylic 2.8 / 38

Polyimide 2.2 / 53

Melamine 2.2 / 90

Flame�retardant

polyester

7.0 / 60

Methods

Thermal analysisThermogravimetric Analysis (TGA)Approximately 20 mg of compressedfibers rolled in a small ball were placed in

Lenzinger Berichte 89 (2011) 50 � 59

the sample pan. The temperatureprogramme was set from 23 °C until600 °C with a heating rate 10 Kmin-1. Allmeasurements were done under airatmosphere to get more realistic resultssince oxygen is needed to burn the fibers.Before measurements all fibers werecarded to ensure maximum homogeneityof the fibers and better reproducibility ofthe results. A TA instruments TGA 2050was used.

Differential Scanning Calorimetry (DSC)10�12 mg of fibers were compressed and placed in the sample pan. Four holes weremade in the sample lid to allow the off�gases to escape. Heating rate was set at10 Kmin-1. For these experiments, standardpan and standard lids were used (pan900786.901; lid 900779.901). Preparationof samples for DSC is more sensitive thanfor TGA and more attention had to be paidto the sample preparation. Two parallelmeasurements were done and the averagevalue was calculated. An untreated samplewas also measured in parallel in order toinvestigate the effect of the incorporatedpolymers on the temperature stability.

Sorption studyDynamic Sorption AnalysisMoisture sorption measurements weredone on dynamic sorption analyzer (SPS11 Analyser, Projekt�Messtechnik, Ulm, Germany). The measurements of the fibersamples by dynamic sorption analyzerwere described in detail by Okubayashi etal. [6]. In brief, the atmosphere in theanalyzer was conditioned at 25 °C and 0 %relative humidity (RH) until equilibriumwas achieved. Then, the moisture cyclewas started increasing the RH in 10 % RHsteps (interval method). The maximalachieved RH was 90 % for measurementsat 25 °C.

Water Retention ValueThe WRV value denotes the amount ofwater held inside the fiber after wettingand centrifuging. The measurements wereperformed following a Lenzing protocol

TIIL�PRÜFANWEISUNG 092/00. Thefiber sample (0.35 g) was weighed in thecentrifuge glass and wetted for 10 minutesin deionized water (15 mL). After that, thesample was centrifuged for 15 minutes at3000 rpm and weighed immediately (mw).Then the samples were dried for 24 h at105 °C and weighed again (md). The WRVwas calculated according to Equation (1).The value expresses the water amount heldin the pores inside the fibers.

(Eq. 1)

Visualization of burned fibersLenzing FR®, modacrylic, FR polyesterand meta�aramid fibers were burned and viewed under SEM. The samples wereAu�coated for 60 s. A Hitachi S�400 SEM was used with a relatively low acceleratingvoltage of 5 kV to prevent beam damageof the samples.

Results and discussion

Thermal analysisMass change by TGATGA is a basic method for characterizationof flame�retardant materials under high�temperature environments. By the firstderivation of the mass change curve it ispossible to determine the temperature atwhich the degradation rate is the highest(the peak of the first derivation). In thiswork this temperature is defined asdegradation point [7].The TGA plots of examinated fibers areshown in Figure 1, Figure 2 and Figure 3.Plots of standard and modified cellulosicsare summarized in Figure 1. There are nodifferences in degradation point betweenTENCEL® and Lenzing Modal® (305 °C).At 450 °C the whole cellulose is burned.Very good results in heat protection showLenzing FR® fibers. The thermaldecomposition of Lenzing FR® fibersoccurs in two steps: the first point is at250 °C (most of the FR�agent reacts) and the second degradation point is 458 °C. At

100%d

dw

m

mmWRV

Lenzinger Berichte 89 (2011) 50 � 59

the temperature 250 °C to 700 °C, thematerial degrades slowly with a residue of8 % (w/w) at 700 °C.

Phosphorous containing FR agentsincorporated in Lenzing FR® fibers workaccording to following principle: duringburning, a protective layer is formed on thesurface of fabric by the production ofpolyphosphoric acid and carbonization,e.g. by release of water. TheseP�containing FR agents have to decompose before the cellulosedecomposes. If the decomposition ofcellulose occurs at 305 °C (derived fromTGA curves), then the P�agents have to decompose below this temperature to forma protective layer [8].In Figure 2 the traces of syntheticpolymers show significantly higherdegradation points than measured forcellulosics. The role of high�performance polymers is not to react before the basicmaterial (like in the case of cellulose), thento postpone the melting point to highertemperatures. The heat energy is spent onmelting of polymer or on radical reactionlike in FR polyester. The tested samplesdegrade at two major points: 431 °C and517 °C which indicate that variousmodifications are present in the polymer.Para�aramid degrades at 521 °C. Meta�aramid, due to the meta�position of aromatic rings is less stable then para�aramid. Meta�aramid degrades at 476 °C. The physical action of the meta�aramid fiber when exposed to a heat source is thatthe fiber itself absorbs heat energy duringthe carbonization process. The fiber swells

and thickens in size and seals openings inthe garment fabric helping to eliminate airmovement and heat transfer to the interiorskin area. As both the fiber and the fabricthicken together this increases theinsulating barrier and therefore reducesheat transfer to the wearer.Polyimide (brand name P84®) is morestable then meta�aramid and FR polyester. It degrades at 510 °C.

TGA plots of other high�performance synthetic fibers melamine and modacrylicare shown in Figure 3. Both melamine andmodacrylic fibers degrade in two majorsteps. Modacrylic is less stable thanmelamine. Modacrylic degrades at 236 °C(first point) and 503 °C (second point).The two�step degradation of this polymer is explained by the formation of acrylicand modacrylic (halogen containing)components in a ratio approx. 60:40 wt%.Halogens contained in modacrylic work onthe principle of radical reaction. Theacrylonitrile component works on theprinciple of char formation. Melamine alsodegrades in two steps: 363 °C and 617 °C.The thermal degradation in melamineresults in char formation rather thanmolten drip.

Figure 1. TGA graph of cellulosics.

100 200 300 400 500 600 7000

20

40

60

80

100 Lenzing FR®

TENCEL®

Lenzing Modal®

Temperature [°C]

Degradation

Lenzing FR®

= 250 °C

TENCEL®

= 305 °C

Lenzing Modal®

= 305 °C

AIR

Figure 2. TGA plots of synthetic FR fibers.

100 200 300 400 500 600 7000

20

40

60

80

100Para-aramidMeta-aramidPolyimideFR polyester

Temperature [°C]

AIR

DegradationPara-aramid=521 °CMeta-aramid=476 °CPolyimide=510 °CFR polyester=431 °C/517 °C

Lenzinger Berichte 89 (2011) 50 � 59

Energy changes by DSCThe heat released or absorbed during thethermal conversion is measured by DSC.

In Figure 4, DSC traces of cellulosics areshown. At the beginning of themeasurement, there is a small endothermicpeak due to the water evaporation.Both standard and Lenzing FR® showexothermic peaks while those for LenzingFR® are significantly smaller and narrowerdue to the phosphorous/sulfur basedagents.DSC plots of high�temperature polymers are shown in Figure 5. Exothermic peaksare not measured at these samples, whichindicate that the exothermic reaction whichstarted at 350 °C is still ongoing at 600 °C.

The DSC traces of melamine andmodacrylic show first smaller peaks(where char is formed) and the reaction isfinished (Figure 6). The second part of thethermal degradation is melting. Like inother high�performance fibers, the melting of melamine occurs at the beginning of thereaction.

If we compare TGA and DSC data, thecorrelation of the degradation points of thetemperatures show exact fitting. Thecombination of these two analyticalmethods provides a very useful tool infiber characterization and productdevelopment.

Sorption studyWater vapor sorptionDynamic sorption analysis is a veryprecise method for materialcharacterization. It covers the whole range

100 200 300 400 500 600-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

Para-aramidMeta-aramidPolyimid

Temperature [°C]

Endo Up

Figure 5. DSC Plots of synthetic FR fibers.

100 200 300 400 500 600-16

-14

-12

-10

-8

-6

-4

-2

0

MelaminModacrylic

Temperature [OC]

Endo Up

Figure 6. DSC plots of melamine andmodacrylic fibers.

Figure 4. DSC Plots of cellulosics.

100 200 300 400 500 600-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

2

Lenzing FR®

TENCEL®

Lenzing Modal®

Temperature [°C]

Endo Up

Figure 3. TGA plots of melamine and modacrylicfibers.

100 200 300 400 500 600 7000

20

40

60

80

100 MelamineModacrylic

Temperature [OC]

AIR

Degradation

Melamine=363 °C / 617 °C

Modacrylic=236 °C / 503 °C

Lenzinger Berichte 89 (2011) 50 � 59

of relative humidities, where the 50�70 % RH range is relevant for physiologicalcomfort. So the comparison of thematerials in this paper focuses on thishumidity range. All isotherms showsigmoid�shaped curves, which are typical for hygroscopic materials. In Figure 7,TENCEL® and Lenzing Modal® show thehighest sorption (9 � 13 %) where the sorption capacity of Lenzing FR® isslightly lower due to the incorporatedadditives (7 � 11%). The isotherms of synthetic fibers are rather linear (Figure 8).In the humidity range 50 � 70 %, meta�aramid and melamine absorb 5 � 6% H2O.Para�aramid and polyimide absorb 2 � 3 % and the lowest sorption is measured formodacrylic � only 0.5 to 1 %.

Water retention values (WRV)Parallel to the vapor sorption, sorption ofliquid water is measured for textilematerials which refers to the porosity of

the materials (Table 3 and Table 4). AsTENCEL® is more porous than LenzingModal®, the WRV is higher. The valuesdecrease slightly with incorporation of FRparticles. Like in vapor sorption, WRVvalues for synthetics are significantlylower. The sorption is in this case higherfor melamine and meta�aramid fibers.

Table 3. WRV of standard and modifiedcellulosics.

Table 4. WRV of synthetic FR fibers.

From this results it can be concluded thatthe application of hygroscopic FR fibers inprotective clothing is crucial to providegood wear comfort of protective textiles.

Visualization of burned fibers

SEM images of burned fibers support thetheory about the decompositionmechanism of various FR fibers. InFigure 9 images of five mainly usedprotective fibers are shown. Lenzing FR®

keeps shape after burning. A carbon�layer is formed on the surface and prevents thefibers from further burning. Modacrylicfibers shrink in the contact with flame andtear afterwards. FR polyester melts duringheat exposure, which is not an ideal optionsince molten fibers can stick to the skinand skin burns are possible. Meta�aramid fibers expand during the thermal treatment,(volume increase) and form a protectivebarrier which prevents from furtherburning of the fiber.

Fiber WRV [%]Lenzing FR® 48.6 ± 0.16TENCEL® 67.1 ± 0.51Lenzing Modal® 57.6 ± 0.95

Fiber WRV [%]Para�aramid 5.9 ± 0.19Meta�aramid 12.1 ± 0.80Polyimide 5.6 ± 0.26Melamine 11.8 ± 0.23Modacrylic 7.3 ± 0.17

Figure 8. Sorption isotherms of synthetic FR fibres.

0 10 20 30 40 50 60 70 80 90 1000

5

10

15

20

25 Para-aramidMeta-aramidPolyimideMelamineModacrylic

RH [%]

Figure 7. Sorption isotherms of cellulosics.

0 10 20 30 40 50 60 70 80 90 1000

5

10

15

20

25Lenzing FR

®

Lenzing Modal®

TENCEL®

RH [%]

Lenzinger Berichte 89 (2011) 50 � 59

Lenzing FR®

before burning after burning

Modacrylicbefore burning after burning

FR polyesterbefore burning after burning

Meta�aramid before burning after burning

Figure 9. SEM images of FR fibers before and after burning.

10 m 10 m

20 m

20 m

20 m30 m

300 m

70 m

Lenzinger Berichte 89 (2011) 50 � 59

Conclusions and Outlook

In this work, Lenzing FR® fibers werecharacterized by different analyticalmethods and their behavior in practical usehas been investigated in comparison toother protective fibers.

Thermal methods � DSC and TGA are precise tools for observing thermaldegradation � mass / energy changes with increasing temperature. The results of boththermal methods showed good correlation.Improved physiological performance ofprotective clothing is important and thestandards for protective clothing requirematerials with improved comfortproperties. Therefore, new developmentsin this segment are crucial to be at the stateof the art with the market trends.

The disadvantage of using synthetic fibersis associated with poor wear comfort. Theemphasis is placed on the use of LenzingFR® in workwear as best solution betweenfunctionality and comfort. This statementis supported by the sorption isothermsshowing high absorbency for cellulosicsand low absorbency for synthetics.

In the field of cellulosic materials, newestdevelopments have been focused on spun�dyed Lenzing FR®, especially in high�visibility colors for protective wear.

Acknowledgements

The authors gratefully acknowledge to Ms.Sandra Schlader (Kompetenzzentrum HolzGmbH) for SEM images and to Ms. AgnesUwaleke (Lenzing AG) for WRV data.

References

[1] Bajaj P.: Heat and Flame Protection,in Handbook of Technical Textiles(Ed. Horrocks R. A. & Anand, S.C.),Woodhead Publishing Limited(2000), ISBN 1 85573 385 4.

[2] Hull T. R. & Kandola B. K. (Ed.):Fire Retardancy of Polymers � New Strategies & Mechanisms, © RoyalSociety of Chemistry 2009, ISBN978�0�85404�149�7.

[3] Horrocks A. R., Hall M. E. &Roberts D: Environmentalconsequences of using flame�retardant textiles � a simple life cycle analytical model, Fire and Materials21 (1997), pp. 229�234.

[4] http://www.lenzing.com/fasern/lenzing-fr.html (19.06.2011).

[5] Rüf H., Firgo H. & Kroner G.:Cellulosic Molded Body, Method forManufacturing it and Use Thereof,US 2008/0233821 A1, 2008.

[6] Okubayashi S., Griesser U.J. &Bechtold T.: A kinetic study ofmoisture sorption and desorption onlyocell fibres, CarbohydratePolymers 58 (2004), pp. 293�299.

[7] Aljaz L., Varga K. & Koch T.: DSC& TGA Analysis of Lenzing FR®

Fibres, 41th International Symposiumon Novelties in Textiles, 27�29 May 2010, Ljubljana, Slovenia.

[8] Einsele U.: Über Wirkungsweise undsynergistische Effekte beiFlammschutzmittel fürChemiefasern, Lenzinger Berichte 40(1976), pp. 102�116.