Rheological , Colour and Processing Properties of Polypropylene Masterbatches for Nanocomposite Fibre Preparation

Asia’s current dominance of the global production of standard types of chemical fi bres requires the sophistication of European fi bre and textile products. Modifying the mass or surface of materials using nanotechnologies is one of the most promising ways to ensure the special, monoand multi-functionally modifi ed fi bre properties of clothing and technical textiles. The permanent antimicrobial treatment of fi bre mass represents one the most desired functional modifi cations of chemical fi bres. It involves the use of an antimicrobial additive masterbatch with the appropriate rheological, colour and processing properties required for the preparation of antimicrobial modifi ed fi bres. This article presents the results of our study of the eff ect of two types of nanoadditives (nanosilica and nanocalcium carbonate) as potential carriers of an AMB active ingredient, and the eff ect of stearic acid, polyethylene glycol and propylene oxide as various dispersing systems on the rheological, colour and processing properties of polypropylene nanoadditive masterbatches. The obtained experimental results are evaluated in terms of the suitability of the properties of prepared nanoadditive masterbatches for the preparation of nanocomposite polypropylene fi bres.


Izvleček
Sedanja azijska prevlada v svetovni proizvodnji standardnih tipov kemičnih vlaken zbuja potrebo po bolj izpopolnjenih evropskih vlaknih in tekstilnih izdelkih.Modifi kacija polimerne mase ali površine materialov z nanotehnologijo je eden najperspektivnejših načinov, kako zagotoviti posebno funkcionalizacijo vlaken, oblačil in tehničnih tekstilij.Trajna protimikrobna obdelava vlaken je med najbolj zaželenimi funkcionalizacijami kemičnih vlaken.Vključuje uporabo nanofunkcionalnega polipropilenskega koncentrata z dodatki protimikrobnih aditivov z ustreznimi reološkimi, barvnimi in predelovalnimi lastnostmi, ki so potrebne za pripravo protimikrobno modifi ciranih vlaken.V članku so predstavljeni rezultati študije vpliva dveh vrst nanoaditivov -nanokremena in nanokalcijevega karbonata kot potencialnih nosilcev protimikrobne aktivne sestavine ter različnih disperzijskih sistemov -stearinske kisline, polietilenglikola in propilenoksida za uravnavanje reoloških, barvnih in predelovalnih lastnosti polipropilenskega koncentrata z nanoaditivom.Rezultati preizkusov so ovrednoteni glede na ustreznost lastnosti pripravljenih koncentratov z nanoaditivi za pripravo nanokompozitnih PP-vlaken.Ključne besede: nanokremen, nanokalcijev karbonat, stearinska kislina, polietilenglikol, propilen oksid, barvne in predelovalne lastnosti 1 Introduction e global production of textile bres increased by 2.0% in 2015 to 94.9 million tonnes, with an increase in chemical bre production by 4.0% to 69.8 million tonnes and a decrease in natural bre production by 3.1% to 25.2 million tonnes [1,2].e production of polypropylene (PP) bres increased by 1.3% in 2015 to 5 million tonnes (excluding spunbonds, meltblowns and tapes) [1].e textile market is expected to continue expanding in the future to reach 106 million tonnes in 2020 and almost 139 million tonnes in 2030. is translates to a further increase in the volume of the global production of man-made bres to 75 million tonnes in 2020, at an average annual growth rate of 4% [3,4].Asia enjoys a dominant position in the global production of standard man-made bres, having held an 87.5% share of production in 2015 [1]. is dictates the need to sophisticate European bre and textile products in today´s highly competitive environment.In particular, this involves the development of special, modi ed, mono-and multifunctional active bres and textiles necessarily characterised by their high functionality, diversi cation, exibility and highly e ective and environmentally acceptable production [5,6].e most promising way to ensure the sophisticated properties of textiles is to modify their mass or surface using nanotechnologies.e most important nanotechnological procedures in the area of textiles include the nano-treatment of surfaces and the addition of nanoparticles/ nanomaterials to bres during extrusion (nanocomposite bres).Using such procedures, mono-or multi-functional properties of bres can be achieved even at low concentrations of nanoadditives, which is also very bene cial in economic terms [6,7].Permanent functional modi cations of chemicalbres are mainly achieved by adding a functional additive masterbatch to the basic polymer during the spinning process.e incorporation of an additive into the PP bre mass is thus always preceded by the preparation of a functional additive masterbatch with a PP carrier and an appropriate dispersing system, which ensures a high degree of dispersion of the modi er in the bre mass.In addition, the masterbatch must have appropriate rheological and processing properties (i.e. it should not reduce the technological stability of bre preparation processes) and should not signi cantly a ect the colour properties of bres.A masterbatch is added to PP pellets in a pre-de ned volume during the spinning process.e mixture is then melted, homogenised and spun into the form of PP bres.Functional modi cations of chemical bres that ensure the protective, hygienic and comfort properties of textiles are the most desired in the textile industry.
is group mainly facilitates the permanent antimicrobial (AMB) modi cation of bres [8][9][10][11][12][13][14][15][16][17].Today's market o ers AMB additives with an average particle size in the micro range of 2-4 µm, or polymer dispersions of those additives [18][19][20][21][22].Among AMB nanoadditives, only metal Ag nanoparticles are known, and their use has recently encountered environmental obstacles.It is assumed that the use of a nanoadditive as a carrier of an AMB active ingredient with a much higher speci c surface than current microadditives will result in the more even spread of the AMB active ingredient on the surface of the inorganic carrier.At the same time, AMB e ciency will be achieved at even proportionally lower concentrations compared with microadditives, with a positive impact on the technical and economic aspects of the production of AMB bres modi ed in the mass.
is article presents the results of our study of the e ect of two types of nanoadditives as potential carriers of an AMB active ingredient, and the e ect of various dispersing systems on the rheological, colour and processing properties of PP nanoadditive masterbatches.e obtained experimental results are evaluated in terms of the properties of prepared nanoadditive masterbatches for the preparation of nanocomposite PP bre.

Preparation of PP masterbatches
PP masterbatches with a 10.0 wt.% nanoadditive concentration were prepared on a laboratory Werner-P eiderer ZDSK 28 twin-screw extruder, with a vacuum zone and screw diameter of 28 mm, and equipment for premixing the preparation from powdered PP, nanoadditives and a dispersing system.e PP premixes were compounded, and the resulting extrudates cooled and pelletised.In order to compare the e ect of the types of nanoadditives and dispersing systems used, the preparation process was carried out at a constant screw rotation speed of 250 min -1 and a constant extrusion temperature of 220 °C.

Rheological properties
Rheological properties were measured using a Gottfert RG20 capillary rheometer at temperatures of 230, 240 and 250 °C.A capillary with a circular diameter of L/D = 30/1 in the range of shear rates from 180 to 4500 s -1 was used, with the masterbatch pre-heated over a period of ve minutes.Based on various piston shi ing rates and the measurement of the pressure gradient, uncorrected dependences of shear stress and viscosity on the shear rate for the evaluated masterbatches were generated to determine a ow consistency index (K) and a ow behaviour index (n), applying the Ostwald de Waele power law (Equation 1): , where τ represents shear stress and D represents the shear rate.
All masterbatches are polymer materials with a non-Newtonian behaviour.All measured rheological parameters were thus corrected using the Rabinowitsch correction [23].An Arrhenius-type equation was used for the calculation of the ow activation energy of masterbatches (Equation 2): where η represents absolute viscosity, R represents the gas constant, T represents absolute temperature and E represents ow activation energy.Viscosity was determined at three temperatures: 230, 240 and 250 °C, while the viscosity and ow activation energy of masterbatches were evaluated at shear rates of 500 s -1 and 1000 s -1 .

Processing properties
e MFI of masterbatches was evaluated using a Dynisco Kayness capillary rheo-viscometer according to Standard EN ISO 1133 Plastics: Determination of the MFI of thermoplastic melts.Parameter lterability was evaluated using a ltration single-screw extruder with a screw diameter of 25 mm and a pore density of the ltration sieve of 16000 pores per cm 2 .e lterability of the dispersion (F) is expressed as ratio of an increment of the pressure (∆p) on the lter to a weight unit of the ltrate (m) at the de nite ltration conditions when: .
3 Results and discussion

Rheological properties
e appropriate rheological behaviour of a masterbatch melt is an important precondition for its use in the preparation of bres.e results obtained through our study of the e ect of the types of inorganic nanoadditives A and B and the e ect of the evaluated dispersing systems D1, D1+D2 and D5 (Table 1) on the basic rheological characteristics of melts of 10.0 wt.% PP masterbatches at temperatures of 230, 240 and 250 °C are presented in Tables 2 and 3. Compared to PP, a concentration of 10.0 wt.% of the dispersed particles of both types of nanoadditives reduces the viscosity of their PP masterbatch melts at the evaluated shear rates D, where the decrease in viscosity was more signi cant with the type B nanoadditive (Table 2, samples IV-VI).e decrease in the viscosity of nanoadditive masterbatch melts is advantageous as far as the degree of their dispersion is concerned with more viscous PP in the spinning process.e e ect of the types of dispersing systems on the viscosity of PP masterbatch melts is less signi cant.e highest decrease in viscosity for  both types of nanoadditives was observed with dispersing system D5 (Table 2, samples III and VI), while the lowest decrease was observed for D1 (Table 2, samples I and IV).
Compared to PP, a concentration of 10.0 wt.% of the dispersed particles of both types of nanoadditives has a signi cant and almost comparable e ect on the increase in the non-Newtonian characteristics of ow (decrease in the ow behaviour index n but an increase in parameter K and activation energy E A ) of PP masterbatches melts (Table 3).e e ect of the types of dispersing systems on the non-Newtonian ow characteristics of PP masterbatch melts is less signi cant.e most signi cant e ect was observed with dispersing system D1 (Table 3, samples I and IV).More signi cant is the e ect of the types of dispersing systems on the ow consistency index K of PP masterbatch melts (Table 3).Its increase towards PP was identi ed with the D1 system, while the D1+D2 system (sample II and V) has a K comparable with PP and the D5 system (sample III and VI) contributes to a decrease in K towards PP with both types of nanoadditives -silica and calcium carbonate.Both types of nanoadditives (A and B) increase the activation energy of melt ow of their 10.0 wt.% PP masterbatches towards the PP polymer carrier (Table 3).
at increase is more signi cant with the type A nanoadditive.e e ect of the type of dispersing system on the increase in the activation energy of the melt ow of PP masterbatches is most signi cant with the D1 dispersing system.It can be concluded from the above ndings that the most suitable is masterbatch VI with nanoadditive type B and the D5 dispersing system, in terms of the rheological characteristics of prepared PP nanoadditive masterbatches for the preparation of nanocomposite PP bre, as it has the lowest viscosity of all prepared masterbatches, intensi es the non-Newtonian ow characteristics the least, and has the lowest ow consistency index K and a low activation energy of the ow.

Colour properties
e appropriate colour properties of a PP nanoadditive masterbatch are another important precondition for its use in the preparation of nanocomposite PPbres.e results obtained through our study of the effect of the types A and B inorganic nanoadditives with the evaluated D1, D1+D2 and D5 dispersing systems on the colour properties of nanocomposite PP bres with a neness of 3.0 dtex are presented in Table 4.
e obtained results indicate various e ects of the evaluated nanoadditive types and nanoadditive concentrations, and the dispersing systems of their masterbatches on the colour properties of nanocomposite PP bres.e described e ects are not signi cant for the colour coordinates of colour gradient light -dark L* and for red -green a*.A signi cant e ect was observed on the colour coordinate of colour gradient yellow -blue b* with a shi to the yellow area. is resulted in a signi cant decrease in the WICIE whiteness index and an increase in the YIE-313/10 yellowness index of nanocomposite PP bres.It was important to determine that the used dispersing system contributes to an undesired change in the colour parameters of nanocomposite bres into the yellow area at the evaluated nanoadditive concentrations.e results in Table 4 indicate that masterbatch VI with the type B nanoadditive and type D5 dispersing system is most suitable for the preparation of PP nanocomposite bres in terms of the colour properties of the laboratory PP nanoadditive masterbatches.When it is used, the colour properties of nanocomposite PP bres with a nanoadditive concentration from 0.1 to 0.5 wt.% are practically comparable with the colour properties of pure PP bres.

Processing properties
e third important precondition for the application of a PP nanoadditive masterbatch in the preparation of nanocomposite PP bres is its suitable processing properties.e results of the evaluation of the processing properties of prepared laboratory PP masterbatches of the type A and B inorganic nanoadditives with the evaluated D1, D1+D2 and D5 dispersing systems are presented in Table 5.
e results of the evaluation of processing properties of the prepared PP masterbatches of inorganic nanoadditives in Table 5 prove that the prepared masterbatches are suitable for the preparation of nanocomposite PP bres in terms of viscosity and MFI.
However, in terms of the most important processing parameter of lterability, only nanoadditive B masterbatches (samples IV-VI) are suitable.e low lterability of these masterbatches shows the high degree of dispersion of the nanoadditive in the PP matrix.eir use will have no negative e ect on the technological stability of the bre preparation process.

Conclusion
is article presents the results of our study of the e ect of two types of inorganic nanoadditives (A and B) as potential carriers of an AMB active ingredient, and three dispersing systems (D1, D1+D2 and D5) on the rheological, colour and processing properties of PP nanoadditive masterbatches.e obtained experimental results are evaluated in terms of the suitability of the properties of prepared nanoadditive masterbatches for the spinning of nanocomposite PP bre.
e results showed that the types of inorganic nanoadditives and the types of dispersing systems used a ected the rheological, colour and processing properties of 10.0 wt.% PP nanoadditive masterbatches to various extents.We can conclude that nanoadditive masterbatches suitable for the preparation of nanocomposite PP bres must possess all appropriate rheological, colour and processing properties simultaneously.
us, of the six evaluated systems, only masterbatch VI with nanoadditive B (ultra ne precipitated calcium carbonate) and dispersing system D5 (condensation product of stearic acid and propylene oxide) was compliant.In rheological terms, the aforementioned masterbatch has the lowest viscosity, intensi es the non-Newtonian ow characteristics the least, and has the lowest ow consistency index K and low ow activation energy, which is convenient in terms of its dispersion degree with more viscous PP in the spinning process.It is also suitable in terms of colour, as when applied, the colour properties of nanocomposite PP bres with a nanoadditive concentration from 0.1 to 0.5 wt.% are practically comparable with the colour properties of pure PP bre. is masterbatch also has appropriate processing properties, in particular lterability.Its low value indicates a high degree of nanoadditive dispersion in the PP matrix. is masterbatch thus has no negative e ect on the technological stability of the preparation of nanocomposite PP bres.It follows from the above that inorganic nanoadditive calcium carbonate is a promising potential carrier of an AMB active ingredient for PP bre systems, provided that it is added in the mass of nanocomposite PP bres with PP masterbatch VI, i.e. with the use of a condensation product of stearic acid and propylene oxide as a dispersing system.

Table 1 :
Composition of laboratory PP masterbatches and the associated extrusion temperatures (T E )

Table 2 :
Viscosity (η) at shear rate (D) of PP and laboratory PP masterbatches determined from ow curves corrected using the Rabinowitsch correction

Table 3 :
Rheological parameters (K, n) and activation energies (E A ) of PP and laboratory PP masterbatches for viscous ow determined from I'll have to assume this all correct... ow curves corrected using the Rabinowitsch correction

Table 4 :
Composition and colour properties of pure PP and nanocomposite PP bres