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MARCIN BCZEK*), JAROSAW JANICKIInstitute of Textile Engineering and Polymer MaterialsUniversity of Bielsko-Bialaul. Willowa 2, 43-309 Bielsko-Biala, Poland

Supermolecular structure and selected properties of PA 6/LCO

modified fibres

Summary The objective of the research presented in this paper was to analyze the influence ofthe LCO Liquid Crystalline Oligoester (LCO) on the supermolecular structure, thermal and me-chanical properties of new fibres prepared from PA6 and LCOblends.Small angle X-ray scattering(SAXS) and wide angle X-ray diffraction (WAXS) methods were used to determine the structure ofLCO modifier and the crystal and lamellar structure of PA 6 matrix of the fibres. Based on DSC

measurements thermal properties of these fibres were analyzed. Some results of mechanical testswere also presented. All results of investigations into supermolecular structure, thermal and me-chanical properties of PA 6/LCO fibres were compared with the results obtained for unmodifiedPA 6 fibres.Keywords: supermolecular structure,modified fibres, liquid crystalline oligoester, tensile strengthparameters.

STRUKTURA NADCZSTECZKOWA I WYBRANE WACIWOCI MODYFIKOWANYCHWKIEN PA 6/LCOStreszczenie Analizowano wpyw dodatku oligoestru ciekokrystalicznego (LCO) na strukturnadczsteczkow, waciwoci termiczne i mechaniczne wkien formowanych z mieszaniny PA 6i LCO (95/5). Wykorzystujc dyfrakcyjne metody SAXS i WAXS zbadano struktur zarwnomodyfikatora LCOwkienpoliamidowych (rys. 3), jak i samej matrycy PA 6 (tabela 2). Na podsta-wie uzyskanych wynikw bada rentgenowskich zaproponowano model struktury nadczstecz-kowej modyfikowanych wkien PA 6/LCO (rys. 10), w ktrym ujawnia si charakterystyczne roz-mieszczenie domen modyfikatora w matrycy polimerowej. Na podstawie bada DSC porwnanorwnie waciwoci termiczne wkien PA 6 oraz modyfikowanych wkien PA 6/LCO (rys. 10,11) a take wybrane ich waciwoci mechaniczne.Sowa kluczowe: struktura nadczsteczkowa, wkna modyfikowane, oligoester ciekokrystalicz-ny, parametry wytrzymaociowe.

Polyamides are essential materials in fibres produc-

tion for textiles and technical uses. However, for thosefields of applications extremely high strength parametersas well as excellent dimensional stability are required. Inorder to improve polymer properties they are reinforcedwith glass fibres or with very high strength and highmodulus liquid crystalline polymers LCPs. During thelast decades, liquid crystalline polymers were presentedas new compounds with superior properties, as com-pared to conventional polymers. The search for melt-pro-cessable LCPs which are miscible with conventionalpolymers is still a great challenge in polymer science [1].Blending thermotropic liquid crystalline polymers with

semi-crystaline thermoplastic polymers to form in situpolymer composites is very attractive because LCP acts a

reinforcing element in the blends and its addition to a

polymer matrix has a significant impact on the physicaland mechanical properties of the final product [27]. Itshould be noted that the melting temperature of most li-quid crystalline polymers is too high for processing semi-crystalline thermoplastic polymers. In order to reducethemelting and transition temperature new liquid crystal-line oligoesters (LCO), with a much shorter chain thantypical liquid crystalline polymers and with flexible unitsin the main chain, were synthesised, resulting in a de-crease of their melting temperature. Due to its relativelylow melting temperature LCO can be used as a propercompound for processing with semicrystalline thermo-

plastic polymers [810].The main goal of the investigations presented in thispaper was to determine the influence of the LCO on thesupermolecular structure of the fibres which were pre-

POLIMERY 2011, 56, nr 9 637

*) Author for correspondence; e-mail:mbaczek@ath.bielsko.pl

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pared from the polyamide 6 and liquid crystalline oligo-ester blend (PA 6/LCO). X-ray diffraction methods wereused to characterize the supermolecular structure of thepolymer matrix of fibres: WAXS was used to characterizecrystalline polymorphs and crystallinity of the PA 6 ma-trix, while parameters of the lamellar structure were ex-tracted from the SAXS patterns. Thermal properties arediscussed in the context of Differential Scanning Calo-rimetry (DSC) results and some results of the mechanicaltests are presented as well. The morphological parame-ters of unmodified PA 6 fibres are included for compa-rison.

EXPERIMENTAL

Materials

The blend for fibre formation was prepared from PA 6andliquidcrystallineoligoesterwith95%ofPA6and5%of LCO by weight. Commercial PA 6 Tarnamid T27(Azoty-Tarnw, Poland) with a density of 1140 kg/m3 anda melt flow index of MFI= 12 g/min was used. The LCOwas provided by the Centre of Polymer and Carbon Ma-terials of the Polish Academy of Sciences, Zabrze. In themolecular structure of LCO, aromatic rings of the meso-gen are bonded with ester groups, while the aliphaticend-groups consisting of eleven carbon atoms are con-nected with the aromatic ring by ester bonds, as shown inFormula (I).

The preparation of the blend consists of three essentialstages: blending, extrusion, and annealing at a tempera-ture above Tm of LCO and below Tm of polymer matrix[9, 10].

Formation of fibres

Unmodified PA6 fibres and fibres from the PA6/LCO95/5 blend were formed by using the prototype sin-gle-head laboratory extruder. The extruders head con-sists of a spinneret with a single hole of diameter f =0.2 mm. Fibre-forming materials were melted in a masscylinder and extrudered under the pressure of 0.7 MPa.During the formation process the temperature of thespinneret was set at 230 C. The fibres were spun with atake-up velocity of 70 m/min.

Methods of testing

The SAXS/WAXS investigations of the LCO modi-fier were carried out using the synchrotron beamline ofthe X33 double focusing camera of the EMBL in Hasylab,atthestorageringDORISIIIoftheDESYinHamburgata

wavelength of 0.15 nm. During the real-time measure-ments SAXS patterns were simultaneously recordedevery 6 seconds giving a temperature resolution of 1 Cper pattern, using a delay line detector. TheSAXS intensi-ties were normalized to the intensity of the primary beamand corrected for the detector response. Finally, an aver-aged melt pattern was subtracted from each curve to eli-minate background scattering.

Static WAXS measurements of powdered rawfibres were performed on a URD6 Seifert diffractometer.CuKa radiation was used at 40 kV and 30 mA. Monochro-matisation of the beam was obtained by means of a nickelfilter and a pulse-height analyser. A scintillation counterwas used as a detector. Investigations were performedover the range of angles from 5 to 60 using steps of 0.1.Experimental diffraction patterns were corrected for thepolarization and Lorentz factor. After the subtraction of

the incoherent scattering and a linear background, thecurves were resolved into the crystalline peaks and theamorphous halo using the method described by Hin-deleh & Johnson [11, 12] and OPTIFIT software [13]. Thefraction of the crystalline phase was calculated from theratio of the integral intensities of crystalline peaks to thetotal scattering intensity:

xI

I Ic

c a

=+

(1)

where: Ic the intensity scattered by the crystalline regions,Ia the intensity scattered by the amorphous regions.

Small-angle X-ray scattering investigations for

fibres were performed by means of a MBraun camerawith conventional Kratky collimation system. The frontofthecamerawasdirectlymountedonthetopofthetubeshield of the stabilized Philips PW 1830 X-ray generator.The X-ray tube was operated at a power of 1200 W. CuKaradiation was used; monochromatisation was performedby a Ni-b filter and a pulse-height discriminator. Scat-tered radiation was recorded using an acquisition time of900 s by means of MBraun PSD50 linear position-sensi-tive detector (1024 channels with a channel-to-channeldistance of 52 nm). The experimental SAXS curves werecorrected for sample absorption and de-smeared for

collimation slit distortion by means of the 3DVIEWMBraun computer program. On the basis of the SAXScurves basic parameters of the lamellar structure of thepolymer matrix of fibres were obtained using the correla-tion function approach [1416]. The normalized correla-tion function was calculated, using the OTOKO program[17], from the following equation:

(2)

where: I(s) the scattering intensity function, r a distancein real space, s the modulus of the scattering vector (s =2sinq/l), where l the X-ray wavelength and 2q the scatter-ing angle.

638 POLIMERY 2011, 56, nr 9

( )2cos

0

2

0

2

=

dsI(s)s

dsrI(s)s

(r)

CH3(CH2)10 C O

O

C O

O

O C

O

O C (CH2)10CH3

O

(I)

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Two-dimensional SAXS measurements were carriedout using a 0.5 m long Kiessig-type camera which wasequipped with a pinhole collimator and a Kodak imagingplate as a recording medium. The camera was coupled toa Philips PW 1830 X-ray generator (CuKa, operating at50 kV and 35 mA) equipped with a capillary collimator.To obtain 2D-SAXS patterns exposed imaging plates (ex-posure time 40 min) were read with a PhosphorImager SIsystem (Molecular Dynamics).

Thermal properties of the investigated sampleswere examined by Differential Scanning Calorimetry(DSC). Calorimetric investigations were carried out witha TA Instruments Thermal Analysis System 5100 equip-ped with a MDSC Calorimeter 2920 and RCS cooling sys-tem. The temperature was calibrated with the meltingpoint of indium (156.6 C) and the enthalpy was cali-brated with indium (28.4 J/g). The measurements were

performed in the temperature range 20250 C, usingTA standard aluminium pans, in an atmosphere of nitro-gen (flow 40 ml/min) with a heating and cooling rate of10 C/min. The weights of the examined samples wereabout 5 mg. Registration sensitivity was above 0.2 W.The thermograms were evaluated by means of the Uni-versal V2.6D (TA Instruments) software. DSC curveswere presented in a standard arrangement, illustratingthe heat flow as the function of sample temperature. Thecrystallinity index was determined on the basis of themeasurements of enthalpy of melting from the followingequation:

k = DD

H

H100(3)

where:DH the enthalpy of melting of the fibre,DH100 theenthalpy of 100 % crystalline PA 6, the value being assumed is230.1 J/g [18].

Tensile strength parameters of the fibres were de-fined by means of the tensile testing machine INSTRON5544 Single Column. The machine consisted of a press--stretching head for fibres for a static load cell rating 10 Nwith the indication error 1.0 %. The tensile testing machinewas connected to the computer equipped with MERLIN

software. The measurements were taken at ambient tem-perature for sample lengths of 10 mm. The tensile speedwas30mmmin-1 and 20 tests were made for each sample.On the basis of the measurements the basic mechanical pa-rameters of fibressuch as initial modulus breaking tenacityand breaking elongation were determined.

RESULTS AND DISCUSSION

Thermal behaviour and supermolecular structure ofthe LCO modifier

The thermal behaviour of LCO was analysed usingDSC measurements. Table 1 presents the results of ouranalysis of the DSC heating and cooling curves of theoligoester collected at a rate 10 C/min.

The values of Tm, DHm and Ti, DHi correspond to thetwo main endothermal signals, melting and isotropi-sation, respectively, which are observed in the heatingDSC curve. When a cooling run was performed after ini-tial heating,exothermal peaks were observed which werecharacterized by the values of T

c, DH

cand T

i, DH

i, respec-

tively.

T a b l e 1. Transition temperatures and enthalpies obtained

from DSC measurements during heating and cooling LCO*)

Heating Cooling

Tg, C Tm, CDHmJ/g

Ti, CDHiJ/g

Tc, CDHcJ/g

Ti, CDHiJ/g

40.6 118.7 17.5 156.6 2.3 114.8 11.0 155.0 2.6

*) Tg, Tm, Tc, Ti glass transition, melting, crystallization and isotro-pisation temperatures, respectively, DH

m

, DTc

, DHi

the enthalpiesof melting, crystallization and isotropisation, respectively.

The results from Table 1 reveal that the LCO modifierexhibits the ability to form a thermotropic mesophase inthe temparature range 118156 C. The mesophase wasdetected both during the heating and cooling processes,which is typical for an enantiotropic liquid crystal com-pound [8].

In order to determine the supermolecular structure ofa thermotropic LCO and its changes accompanying the

heating to the melt time-resolved SAXS/WAXS measure-ments during heating and cooling were performed. Fig. 1presents selected SAXS and WAXS curves of the LCOduring heating.

The WAXS/SAXS curves exhibit characteristic phe-

nomena: a strong crystalline peak and a very weak amor-phous halo in the WAXS data as well as the first diffrac-tion maximum in SAXS curve occurs in the same tempe-rature range (25123 C). The crystalline peak in the

POLIMERY 2011, 56, nr 9 639

1.0 1.5 2.0 2.5 3.0 15 20 25 30

0.000

0.004

0.008

0.012

0.016

0.020WAXSSAXS

160 C150 C

145 C

140 C

123 C120 C

110 C75 C

25 C

2 , degq

Intensi

ty,a.

u.

Fig. 1. Time resolved SAXS and WAXS scattering patterns ofLCO during heating

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WAXSdata disappears at 123 C while the seconddiffrac-tion maximum in the SAXS data occurs in the tempera-ture range 104160 C.

The WAXS patterns registered from 25 C to 123 C,involving a strong cystalline peak and a very weak amor-phous halo indicate the presence of a well-ordered struc-ture while scattering curvesregisteredat higher tempera-tures indicate the liquid crystalline state of LCO.

The angular position (2q) of the peak observed onSAXS curves is connected to the supermolecular struc-ture of the oligoester involving different electron densi-ties of two phases, which are separated by a repeat dis-tance (d-space). The d-space values, based on the positionof the first and the second peak (which corresponds tosolid crystalline state and liquid crystalline state, respec-tively) were calculated using Braggs law and theseresults are presented in Fig. 2.

Fig. 2 shows that d-space values corresponding to thefirst peak of the SAXS curves are constant (4.5 nm) andthey are characteristic for a well-ordered solid state of the

LCO. The values of d-spacing, based on the angular posi-tion of the second SAXS peak, steadily decrease from3.8 nm (104 C) to 3.6 nm (123 C) as a result of the in-crease of chain flexibility during heating. According toour SAXS results the transition occurs at a temperature of123 C since the value of d-spacing is constant.

Such SAXS patterns with two diffraction maxima andcorresponding changes of d-space values are characteris-tic of the smectic liquid crystal structure [8, 10, 19].

WAXS studies of supermolecular structure ofPA 6/LCO 95/5 fibres

Theresultsof the wide angle scattering measurementswere analysed with respect to the crystalline structure ofa PA 6 matrix of fibres and the concomitant changes

caused by the addition of a small amount of the LCOmodifier; subsequentely both sets were compared. TheWAXS curves of both PA 6/LCO 95/5 and PA 6 fibres arereported in Fig. 3.

The scattering patterns reveal the existence of thewell-known polymorphism of the PA 6 matrix in bothsamples. Both diffraction curves exhibit the two mediumdiffraction peaks at 2q = 20.3 and at 2q = 23.7, a weakpeakat2q = 11 anda strong peakat 2q = 21.6. These twomedium peaks are a distinctive feature of the a-crystalpolymorph of PA 6 and both the weak and the strong

peaksstandfortheg-crystal polymorphof PA6 [2], whichgenerally is not thermodynamically stable in polyamidesand being predominant only under fast cooling condi-

tions during spinning of the fibres. The analysis of thecurves reveals that the intensities of all the peaks men-tioned above slightly decrease by introducing LCO in thesample. Such changes point to a decrease of the index of

640 POLIMERY 2011, 56, nr 9

20 40 60 80 100 120 140 1603.0

3.2

3.4

3.6

3.8

4.0

4.2

4.4

4.6

4.8

5.0

Temperature, C

d-Spacing,n

m

2

1

Fig. 2. d-Spacing for LCO: in solid state (1), in liquid crystal-line state (2)

0 10 20 30 40 50 60

gPA6/LCO 95/5

PA6

g

a

a

Inten

sity

2 , degq

Fig. 3. Comparision of WAXS curves for unmodified and modi-fied polyamide fibres

10 20 30 40 50 60

0

20

40

60

80

100

120

2q, deg

A2

A1

a

g

ag

Intensity

,cp

s

Fig. 4. WAXS curve of PA 6 fibres resolved into individualcrystalline peaks and the amorphous components (A1 and A2)

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order of the crystalline structure of the polymer matrixfor the PA 6/LCO 95/5 fibres. The crystallinity of PA 6 ascalculated from equation (1), based on WAXS curves re-solved into crystalline peaks and an amorphous halo, isequalto39%forPA6/LCO95/5and41%forPA6,respec-tively. The value of the degree of crystallinity of the modi-fied fibres was calculated only with respect to the PA 6matrix (Fig.4 presents WAXS curves of PA 6 resolved intoindividual crystalline peaks and the amorphous compo-nents).

SAXS studies of the supermolecular structure ofPA 6/LCO 95/5 fibres

The results of the SAXS experiments are analysed interms of the lamellar structure of a PA 6 matrix of modi-fied fibres changes as introduced by the LCO additive.

Small angle scattering curves of both modified andunmodified polyamide fibres are presented in Fig. 5.

The SAXS curve of a PA 6 sample exhibits only onewide diffraction peak (1.64) corresponding to the long

period of the lamellar structure of the polyamide. How-ever, the curve of PA 6/LCO 95/5 sample exhibits two dis-tinct peaks: a first one (1.55) from PA 6 and the secondone (1.96) from the LCO modifier. This clearly points tothe fact that the polymer matrix of the modified fibreskeeps its lamellar structure in the presence of the oligo-ester. Moreover, the angular position of the LCO peak inthe data of the modified fibre (corresponding to d-spacevalue4.5nm)isthesameasinthecaseoftheSAXSdataofthe oligoester (in the solid state) in the absence of the PA 6matrix (see Fig. 1). This means that the LCO keeps its ex-cellent dimensional stabillity even in thepolymermatrix.

To compare the parameters of thelamellar structure ofthe PA 6 matrix of both fibres, based on SAXS curves, thecorrelation functions were calculated from equation (2).A typical correlation function as obtained for PA 6 fibres

is shown in Fig. 6. The calculation of the long period Lp ofthe structure is based on the position of the first maxi-

mum in the function. Other structural parameters like thecrystalline lamellae (lc) and the amorphous layer thick-ness(la) are also calculated on the basis of this function asshown in Fig. 6. The values of the structural parameters,which are calculated for both investigated fibres arepresented in Table 2.

T a b l e 2. The values of parameters of the lamellar structure of

PA 6 matrix of investigated fibres,determined by SAXSmethods

Sample Lp, nm lc, nm la, nm

PA 6 5.4 *) 5.2 2.0 3.2

PA 6/LCO 95/5 5.7 *) 5.3 1.9 3.5

*) Long period calculated from Braggs law based on angular posi-tion of the PA 6 peak on the SAXS curve.

The results from Table 2 show that Lp, lc and la valuesfor the modified and the unmodified sample are compa-rable. It means that the lamellar structure of the polymermatrix of PA 6/LCO 95/5 fibres practically depends on theconditions of the formation of the fibres and is not mark-edly affected by the presence of the LCO modifier. More

details, particularly concerning the distribution of LCOdomains in PA 6 matrix of modified fibres are obtainedfrom the 2D-SAXS measurements. The 2D-SAXS patternsof both PA 6 and PA 6/LCO 95/5 fibres are presented inFig. 7.

Both patterns exhibit symmetrical meridional peakstypical for the polymer matrix. The angular position ofthe maximum intensity of the peaks is 1.55 and 1.64 forPA 6/LCO 95/5 and PA 6 100, respectively. These resultsare in excellent agreement with the values of Lp of thelamellar structure of the matrix: 5.7 nm and 5.4 nm for PA6/LCO 95/5 and PA 6, respectively (see Table 2). In the

caseofthe2D-SAXSpatternoftheLCOmodifiedsample,beside meridional peaks, four diagonal-peaks are ob-served resulting from the presence of the LCO modifierin the sample. The 2q position of these peaks and their

POLIMERY 2011, 56, nr 9 641

0.5 1.0 1.5 2.0 2.5 3.00

1000

2000

3000

LCOd= 4,5 nm

PA6/LCO 95/5

PA6

2 degq,

In

tensi

ty,a.

u.

Fig. 5. SAXS curves for PA 6/LCO 95/5 and PA 6 fibres

0 3 6 9 12

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

l -a p c=L l

Lp

lcg

(

)

r

r, nm

Fig. 6. Correlation function for PA 6 fibres, from which theparameters of lamellar structure are determined

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orientation in relation to fibre axe direction were also de-termined. The 2q position (1.96) connected with thed-space of LCO, as expected, is the same as obtained from

SAXS curve in Fig. 5. The orientation of the LCO peaks isconnected with the distribution of the orientation of themesogens of LCO in relation to the fibre axis direction. Aquantitative estimation of the orientation of the meso-gens was obtained by considering an azimuthal plot ofSAXS scattering data (for a suitable range of 2q values).This plot is presented in Fig. 8 and makes clear that themean angle of the orientation is equal to 70.

Based on our results derived from the SAXS measure-ments, a model of the supermolecular structure of modi-fied fibres is proposed (Fig. 9). This model suggests thatthe liquid crystalline oligoester domains are distributedinto the interfibrillar areas of the polymer matrix as wellas slightly slipped between crystalline lamellae (into the

amorphous layer). Such a way of distribution of the LCOmodifier in PA 6 proves that the LCO in practice only in-fluences the amorphous layers thickness of PA 6 (seeTable 2). The proposed model also accounts for the de-gree of the preferred molecular orientation of the oligo-ester in the fibres.

Thermal properties of PA 6/LCO 95/5 fibres

The thermal behaviour of the modified PA 6/LCO 95/5fibres was studied by using differential scanning calori-metry. Theresults of theDSCmeasurements areanalyzed

in terms of changes of the basic thermal parameters of thepolymer matrix, such as melting temperature (Tm),enthalpy of melting (DHm), mass degree of crystallinity(k), crystallization temperature (Tc) and enthalpy of crys-tallization (DHc) caused by the addition of the LCO modi-fier.

The shape of the DSC curves (Fig. 10), obtained forboth modified and unmodified fibres during heating ofthe samples in the form as received (curve 1 and 2) issimilar and they contain only one endothermic peakwhich illustrates the melting of the crystalline phase ofthe polymer matrix. The minimum of the endothermic

peak occurs at 221.9 C for the modified sample, whereasfor the pure polyamide 6 sample it is only very slightlyshifted towards a lower value. Additionally, the endo-thermic effect measured by the value of the enthalpy of

642 POLIMERY 2011, 56, nr 9

a)

b)

Fig. 7. 2D-SAXS patterns for PA 6 (a) and PA 6/LCO 95/5 (b)fibres

0 90 180 270 360

70

fibre axe

PA6 lamellae

LCO mesogen

Azimuthal angle,

Intensi

ty

Fig. 8. Azimuthal plot showing the orientation of LCO meso-gen and polymer matrix lamellae in PA 6/LCO 95/5 fibres

70

1.9 nm

4.5 nm

5.3 nm

Fig. 9. Proposed model of the supermolecular structure ofPA 6/LCO 95/5 fibres based on results derived from SAXSmeasurements

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melting (DHm), and calculated only with respect to thepolymer matrix, decreases when the LCO modifier ispresent in the PA 6 matrix. The lower value of DHm indi-cates that the addition of the modifier causes a slight de-crease of the degree of ordering of the supermolecularstructure of PA 6. The degree of crystallinity, calculatedfrom equation (3), is 33.5 % and 35.5 % for fibres PA6/LCO 95/5 and PA 6, respectively.

Another observation resulting from the DSC analysis

of the fibres, repeatedly heated after the previous con-trolled supercooling from the melt (curve 3 and 4), is thepresence of two endotherms as compared to one endo-

therm in the as received samples. The minimum of the

first endothermic peak (curve 3 and 4) occurs at a tempe-rature close to 212 C for both samples and this endo-therm probably results from the melting of less perfectcrystallites of PA 6.

Next the process of non-isothermal crystallization ofthe polymer matrix of PA 6/LCO 95/5 fibres was analyzedby comparision of DSC thermograms (Fig. 11) obtainedfor both unmodified and modified fibres.

Both DSC cooling curves exhibit one exotherm: thecrystallization peak. The crystallization peak tempera-ture for both samples is almost the same while diffe-rences in the value of the enthalpy of crystallization DHc(calculated only with respect to PA 6) and the onset crys-tallization temperature (TcON-SET) are observed. Thehigher DHc and TcON-SET values for the PA 6/LCO 95/5sample probably result from the heterogeneous nuclea-tion due to the presence of the LCO modifier, which is ab-sent in the crystallization process of the PA 6 matrix.

Mechanical properties of PA 6/LCO 95/5 fibres

The results of the experimental investigation of theeffect of LCO modifier on the mechanical properties ofpolyamide 6 fibres are presented in Table 3.

T a b l e 3. The values of mechanical parameters of unmodified

and modified polyamide fibres*)

Sample Mp, cN/tex Wr, cN/tex er, %

PA 6 100 1.18 20.5 178.1

PA 6/LCO 95/5 1.99 26.8 184.2

*)Mp, Wr, er initial modulus, breaking tenacity and breaking elon-

gation, respectively.

The comparative analysis of the results shows thatpresence of the liquid crystalline oligoester has a positiveinfluence on all the investigated parameters of the fibres.The higher values of the initial modulus and of the tena-city, which are observed in the case of PA 6/LCO 95/5fibres mean that the LCO mesogen acts as a stiff andstrong element, which transfers part of the tensions fromthe matrix of the fibres. Consequently, modified fibres be-come more stiff and strong in relation to the unmodified

PA 6 fibres.CONCLUSION

This study indicates that the synthesised oligoesterwhich was used as a modifier of PA 6 fibres exhibits theability of thermotropic mesophase (smectic type) forma-tion. The solid crystalline state of LCO is observed in thetemperature range from 25 C to 123 C, and the liquidcrystalline state in the temperature range 118156 C.The crystalline and lamellar structure of the polymer ma-trix of the fibres formed from the PA6/LCO 95/5 blend, is

not markedly affected by the LCO modifier. The super-molecular structure of the PA 6/LCO 95/5 fibres, pro-posed in this study, reveals a specific distribution of theLCO domains in the polymer matrix. This specific distri-

POLIMERY 2011, 56, nr 9 643

212.3 C

211.9 C

221.2 C

220.4 C

221.9 C

221.5 C ( )Tm

77.1 J/g(*)calculated in respectto PA 6 matrix

81.7 J/g ( )DHmHea

tflo

w,W

/g

-2.1

-1.6

-1.1

-0.6

-0.1

Exo up200 205 210 215 220 225 230

Temperature, C

1

2

3

4

Fig. 10. DSC curves of unmodified (curves 1 and 3) and modi-fied polyamide (curves 2 and 4) fibres during heating at a rate of10 C/min registered for: samples in form as received (1 and2), samples after the previous controlled cooling from the melt

(3 and 4)

150 160 170 180 190 200 210Temperature, C

190.1 C ( on-set)Tc

191.4 C

187.1 C

187.0 C ( )Tc78.0 J/g (*)

75.7 J/g( )DHc

calculated in respectto PA 6 matrix

2.5

1.5

0.5

-0.5

Hea

tfl

ow

,W

/g

Exo up

1

2

Fig. 11. DSC curves of unmodified (1) and modified (2) poly-amide fibres during cooling from the melt at the rate of10 C/min

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bution of the stiff and strong rod-like mesogen of LCO inthe PA 6 matrix of the fibres causes a considerable in-crease in the values of the tensile strength parameters ofthe fibres.

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