The In ! uence of Modacrylic and Metal Protective Fibres in the Mixture on the Mechanical Properties of Ring Spun Yarns for Protective Textiles

The research is focused on the infl uence of the fi re resistant modacrylic (MAC) fi bres in the ring-spun yarn mixture with cotton (CO) fi bres and of the conductive metal fi bres (MTF) in the ring-spun yarn mixture with polyester (PES) fi bres on the mechanical properties in the region of lower loads. Analysed yarns are intended for the protective clothing production (fi re resistant and electrically conductive clothing). The viscoelastic behavior of yarns in the fi eld of lower loads under the specifi c stress/extension curve which amounts to 5 cN/tex, reaching the weight of 85 g. The results of the research show that the incorporation of MAC fi bres in the yarn from the mixture of 55% MAC/45% CO fi bres increases the region of elastic deformations (the stress and extension in the yield point), on the other side the MAC fi bres in the yarn mixture decrease the elasticity modulus level. The incorporation of MTF (stainless stell) fi bres in the yarn mixture consisting of 75% PES/25% MTF decreases the region of elastic deformations (about 10%), however the region of elastic deformations lies very close to the chosen stress value under the specifi c stress/extension curve – 5 cN/tex or 85 g.


Izvleček
Raziskava je usmerjena na vpliv ognjevarnih modakrilnih vlaken v prstanski preji iz mešanice modakrilnih in bombažnih vlaken in elektroprevodnih kovinskih vlaken v prstanski preji iz mešanice poliestrskih in kovinskih vlaken na mehanske lastnosti v območju manjših (uporabnih) obremenitev.Analizirane preje so namenjene za izdelavo zaščitnih oblačil (ognjevarnih in elektroprevodnih), tako se raziskava osredinja na viskoelastično območje manjših obremenitev na krivulji napetost/raztezek, tj.pri napetosti 5 cN/tex, kar pomeni obremenitev mase 85 g.Raziskava je pokazala, da ognjevarna modakrilna vlakna (MAC) v mešanici iz 55 % modakrilnih 45 % bombažnih vlaken vplivajo na povečanje elastičnega območja (napetost in raztezek v meji polzišča), na drugi strani pa vplivajo na znižanje modula elastičnosti prstanske preje.Vsebnost MTF (iz nerjavnega jekla) vlaken v mešanici iz 75 % PES in 25 % MTF vlaken vpliva na zmanjšanje elastičnega območja za okrog 10 %, na drugi strani pa se vrednosti elastičnega območja gibljejo v mejah območja manjših (uporabnih) obremenitev na krivulji specifi čna napetost/raztezek, ki znaša 5 cN/tex oziroma 85 g.Ključne besede: modakrilna vlakna, kovinska vlakna, prstanska preja, mehanske lstnosti, viskoelastične lastnosti 1 Introduction e protection becomes nowadays very important taking into account the industrial developments and the strong need to increase the workwear clothing production, especially in the eld of protective clothing.e protective textiles have extraordinary importance for the European textile and clothing industries as well as the end users.Protective textiles show high-tech character and are used mainly in the industrial segments.e expected average increase in Europe in the eld of protective textiles production amounts to around 4% [1][2][3].Novel developments with complex protection requirements are, apart from the protection against electromagnetic radiation, also directed to the protective clothing for electricians working on energized plants with the risk of exposure to very high arcing ames.e facts presented above have encouraged the direction of the research in regard to the mechanical behavior of the ring-spun yarn from ame resistant and electrically conductive yarn mixtures.Certain authors dealt with the ame retardant properties of yarns and fabrics.In recent years, many researchers are interested also in electrical and conductive properties of bres and fabrics intended for protective clothing [4][5][6][7].Approximately 90% of global ber consumption is processed into yarns, with 57% of the entire production consisting of yarns from chemical bres.About 8% of the yarn production belongs to the organic bres intended for protective clothing, while inorganic bres present around 1% of yarn production intended for protective clothing [8].
e number of natural disasters such as oodings, landslides and res are unfortunately increasing in the last few years.With the increasing of disasters, the need of functional textiles, i. e. the protective clothing for re ghters, rescuers, civil protection, police is also increasing.at is the main reason for choosing the research which deals with so-called protective ring-spun yarn loading behavior.A growing segment of the industrial textiles industry has therefore been involved in a number of new developments in bres, fabrics and protective clothing.For heat and ame protection, requirements range from clothing for situations in which the wearers may be subjected to occasional exposure to a moderate level of radiant heat as part of their normal working day, to clothing for prolonged protection, where the wearer is subject to several factors such as radiant and convective heat, to direct ame, for example the re ghter's suit.
e e ect of heat on a textile material can produce physical as well as chemical change.In thermoplastic bres, the physical changes occur at the glass (Tg), and melting temperature (Tm), while the chemical changes take place at pyrolysis temperatures (Tp) at which thermal degradation occurs.Textile combustion is a complex process that involves heating, decomposition leading to gasi cation (fuel generation), ignition and ame propagation.Fibres with LOI (limiting oxygen index) greater than 25% are ame retardant.For protective clothing, however, there are additional requirements, such as protection against heat by providing insulation, as well as high dimensional stability of the fabrics, so that, upon exposure to the heat uxes that are expected during the course of the wearer's work, they will neither shrink nor melt [1,2].e bres could be classi ed into two categories: Inherently ame-retardant bres, such as ara-mid, modacrylic, polybenzimidazole (PBI), Panox (oxidised acrylic) or semicarbon, phenolic, asbestos, ceramic etc. chemically modi ed bres and fabrics, for exam-ple, ame retardant cotton, wool, viscose and synthetic bres.Electromagnetic radiation has become the fourth most serious source of public pollution in addition to noise, water and air.It is claimed that the electromagnetic waves a ect human health and the performance of electrical and electronic devices.Textile materials made with conductive bres and yarns can shield the large part of the electromagnetic waves and protect health of the humans and animals.Conventional textile fabrics are poor electrical conductors.Conducting yarns are used to produce fabrics for electromagnetic shielding and electrostatic charge dissipation.Such yarns and fabrics are increasingly used in applications where exibility and conformability are important.Demand for these products has increased rapidly.Conductive yarns are produced from metal bres which have high electrical conductivity, such as stainless steel and copper.ey are produced by mixing metal bres with chemical bres, cotton and viscose bres; these increase the electrical conductivity of the fabric, thus eliminating electrostatic charges and preventing static loading on the fabric [1][2][3].

Modacrylic bres
Modacrylic bres are chemical bres which are composed of less than 85% but at least 35% by weight of acrylonitrile units and have excellent chemical, sun light and ame resistance.

Metal bres
Metal bres are bres produced from metals, which may be used alone or in combination with other substances.Metal bres are produced mainly from aluminum, stainless steel and nickel.eir melting point stands at approximately 1426 °C.
eir speci c breaking stress stands at around 22.3 cN/tex, with breaking elongation lower than 1% and they are chemical and thermal resistant.
ey are also excellent electrical conductors, rather than stainless steel which is poor conductor, and may be used for resistance heating.Metal bres have higher melting point and are more heat resistant than ordinary bres.In addition, they are ame resistant and are used mainly for protective fabrics, carpets, upholstery, work clothing and protective clothing [10][11][12][13][14][15][16][17].
e research focuses on the in uence of the re resistant modacrylic (MAC) bres in the mixture of 55% MAC/45% CO (MAC/CO) bres and the conductive metal bres (MTF) in the mixture of 75% PES/25% MTF (PES/MTF) bres on the mechanical and viscoelastic properties of the ring-spun yarn.Since the yarns analysed are intended for the protective clothing production, the research focuses on the mechanical behavior of the yarns analysed.e research focuses on the eld of lower loads under the speci c stress/extension curve which amounts to 5 cN/tex, wherein the stress presents the weight of around 85 g.With that purpose the two-plied re resistant ringspun yarn from 100% cotton bres (100% CObres) and the mixture of modacrylic and cotton two-plied yarn in the percentage ratio of 55%/45% were analysed in the rst part.Furthermore, the research focuses on the ring-spun yarn from the 100% PES bres and the electrically conductive yarn from mixture of PES and metal bres with the ratio of 75%/25%.In the experimental part the mechanical properties (speci c stress and extension) were analysed and yarn quality (unevenness) such as yarn imperfections (the mass irregularity CV m , thin and thick areas/1,000 m, neps and yarn hairiness).e yarn quality was measured on the Uster Tester, while the mechanical properties of analysed yarns were measured on Statimat Tester.e viscoelastic properties (elasticity modulus, the yield point) were calculated from the speci c stress/extension curve using DINARA® so ware [9].

Materials and methods
In the research, two-plied ring-spun yarn from 100% cotton bres and the mixture of modacrylic and cotton bres in the ratio of 55% modacrylicbres and 45% cotton bres were analysed in the rst part (short MAC/CO).While in the second part, the research concentrates on the single ringspun yarn from the 100% PES bres and the yarn from mixture of PES and metal bres, with percentage ratio of 75% PES/25% MTF (short PES/ MTF) bres.
e yarns analysed were produced in Predilnica Litija from short staple bres.e neness of the single-and two-plied yarns amounts to 16.67 tex.
e two-plied yarn from 100% cotton bres and the mixture of modacrylic and cotton bres in the ratio of 55% modacrylic bres and 45% cotton bres is wound, doubled and twisted with 720 and 660 twist per meter in the S-direction (counterclockwise direction).
e yarn quality and irregularity, yarn imperfections (the mass irregularity CV m in percents, the number of thin and thick areas/1000 m, the number of neps) and yarn hairiness were measured on the Uster Tester, while the mechanical properties (stress and extension) were measured on Statimat tester.On the Uster Tester the yarn is passed through the electric eld of a measuring capacitor.Mass variation of the yarn causes the disturbance of the electric eld which is converted into electric signal.e viscoelastic properties such as elasticity modulus and the yield point were calculated using DINARA® so ware [9].e scanning electron microscope (SEM) view of analysed ring-spun yarns from the mixture of MAC/ CO and the mixture of PES/MTF bres is presented in the Figure 1.Table 1 presents the basic properties of raw material ( bres), while Table 2 presents the basic properties of yarns.e irregularity (quality) of yarn is measured on the Uster Tester (Table 3).e analysis of speci c breaking stress (Table 4) of the yarn from the mixture of MAC/CO bres has the lowest value which amounts to 13.3 cN/tex.e speci c breaking stresses of the 100% MAC and the 100% cotton yarns are higher (15.8 cN/tex and 23.0 cN/tex).
e yarn from the mixture of MAC/CO bres has the lowest speci c breaking stress (13.3 cN/tex) mainly due to the very high di erence between the speci c breaking stresses of cotton bres (43.9 cN/ tex) and modacrylic bres (24.8 cN/tex).at results in the speci c breaking stress level decrease of the MAC/CO yarn, from 23.0 cN/tex (100% cotton yarn) and 15.8 cN/tex (100% MAC yarn) to 13.3 cN/ tex (MAC/CO yarn).
e MAC/CO yarn has the breaking extension of 5.8% and similar values are measured with the 100% CO yarn, while the breaking extension is the highest with the 100% MAC yarn (18.7%).
the re protection of the MAC/CO yarn is dominant, MAC bres exert the LOI index between 33-34% (the limit of ame resistant bres of LOI index is 25%) and ensure re and heat resistance of the protective clothing produced from that yarn.
e speci c breaking stress of MAC/CO yarn is only about 2% lower than with 100% MAC yarn, but the incorporation of cotton bres in the yarn (45% of cotton bres in the mixture) is very important from the point of view of comfort properties (water vapor permeability, air permeability, thermal conduction, etc.) of the yarn intended for the protective clothing.On the other hand, the results of the mechanical and physical properties of yarn (coe cient of the variation of mass, thick and thin areas/1000 m, neps, hairiness) which are listed in Table 3, show that the variation in mass per unit length along the yarn (CV m ) is similar and amounts to 9.7% (100% MAC yarn) and 9.8% (MAC/CO yarn).e number of thick and thin areas increases from zero (100% MAC yarn) and one (100% cotton yarn) to 17 (thick areas/1,000 m) and 29 (neps/1,000 m) of MAC/CO yarn, meaning the yarn from the mixture is nonuniform.e irregularity of yarn has a profound inuence on the appearance of yarn and fabric.In contrast, the yarn from the mixture of MAC/CObres is less hairy (hairiness of 100% MAC yarn is 7.8, while the hairiness of the MAC/CO yarn is 6.4).
e main reason of low hairiness lies in the di erent lengths of the MAC bres (38 mm) and cotton bres (34 mm).e percentage of longer MACbres in the yarn mixture is higher (55%) and prevents the transport of shorter cotton bres from the inner to the upper (sheath) side of the yarn.On the other hand, lower hairiness of the MAC/CO yarn a ects the higher abrasion resistance and better appearance of the yarn.
e second part of the research is directed to the mechanical properties of protective single PES/ MTF yarn (Table 4) with MTFs which are re resistant, heat resistant and have high conductivity.
e results of the speci c breaking stress show that the PES/MTF yarn has lower speci c breaking stress (21.8 cN/tex) than the 100% PES yarn (34.5 cN/tex).
e metal bres (stainless steel) are coarser (2.7 dtex), longer (60 mm) and thinner (7 µm) than the PES bres ( neness 1.5 dtex, length 38 mm and e results of the yarn quality (coe cient of the variation of mass, thick and thin areas/1000 m, neps, hairiness) are measured with the 100% PES yarn (Table 3).e results of the yarn quality show that the variation in mass per unit length along the yarn (CV m ) amounts to 11.8 and is higher than with the 100% MAC yarn, 100% cotton yarn and MAC/ CO yarn, however the number of thick and thin areas/1000 m and hairiness are lower than with the MAC/CO yarn.

The results of mechanical behavior of with loading
e results of speci c breaking stress and extension curve of bres and yarns from the 100% cotton, the 100% MAC and MAC/CO yarns are shown in Figure 2. Figure 3 shows the speci c stress/extension curve of the MAC/CO yarn with the 1 st , 2 nd and 3 rd derivatives of the speci c stress/extension curve.
e results of the speci c breaking stress and extension curve of bres and yarns from the 100% PES and the PES/MTF yarn are gured in Figure 4. e MAC/CO yarn demonstrates the lowest speci c breaking stress (13.3 cN/tex) and breaking extension (5.8%).e reason lies in the high di erence between the speci c breaking stresses and breaking extensions of the 100% CO and the 100% MAC yarn (see Figure 2).In other words, the speci c breaking stress decreases from 23.0 cN/tex (100% CO yarn) and 15.8 cN/tex (100% MAC yarn) to 13.3 cN/tex (MAC/CO yarn) (see Figure 2).e straight-shaped MAC/CO yarn speci c stress/ extension curve represents the yarn with high modulus.e MAC/CO yarn has a high resistance to loading in comparison with the 100% MAC yarn.
e high resistance of the MAC/CO yarn to loading re ects in the lower breaking extension.e 100% cotton yarn proves lower breaking extension, while the 100% MAC yarn, which has the highest breaking extension, consequently proves the lowest modulus.Figure 3: e speci c stress/extension curve of MAC/ CO yarn with the 1 st (Y1), 2 nd (Y2) and 3 rd (Y3) derivatives e rst derivative of the speci c stress/extension curve of MAC/CO yarn shows lower value of elasticity modulus (3.9 cN/tex) than 100% cotton yarn (4.3 cN/tex) (see Figure 3).e resistance of yarn on loading in the elastic region -the eld of elastic deformations of the MAC /CO yarn -is about 10% lower.e rst deformations in the yarn cause the moving of the bres in the sheath.at deformations are completely recoverable until they reach the yield point, which presents the limit of elastic region.e yield point is calculated from the 2 nd and the 3 rd derivative of the speci c stress/extension curve in the point where the 2 nd derivative is minimal or maximal and 3 rd derivative is zero.e speci c stress in Tekstilec 2015, letn.58(1), 23−32 The Infl uence of Modacrylic and Metal Protective Fibres in the Mixture on the Mechanical Properties of Ring Spun Yarns for Protective Textiles the yield point of the MAC/CO yarn is 7.83 cN/ tex, while the extension in the yield point amounts to 2.1%.On the other hand, the speci c stress in the yield point of the 100% cotton yarn is 5.42 cN/ tex, while the extension in the yield point amounts to 1.4%.
e results of viscoelastic parameters of the MAC/ CO yarn in comparison with results of 100% cotton yarn show that the incorporation of MAC bres in the yarn mixture decreases the elasticity modulus of the MAC/CO yarn by about 10%.On the other hand, the incorporation of MAC bres increases the yield point level by about 45%, consequently also increasing the eld of elastic deformations.e speci c stress in the yield point of the MAC/CO yarn is 7.83 cN/tex, thus being higher than the so-called stress value of 5 cN/tex (85 g), which was selected by this research.e PES/MTF yarn has lower modulus and o ers lower resistance to loading than the 100% PES yarn (see Figure 4).e reason lies in the speci c breaking stress level which is the consequence of the type of raw material and is lower with the PES/MTF yarn (21.8 cN/tex) than with the 100% PES yarn (34.5 cN/ tex).e metal bres (stainless steel) are coarser (2.7 dtex) and longer (60 mm) than the PES bres ( neness 1.5 dtex and length 38 mm).On the other hand, the MTFs are also thinner and have lower breaking extension (only 1%) than PES bres (18%) -see Table 2. e MTFs in the PES/MTF yarn break rst (they have the lowest breaking extension, 1%) and in uence the speci c breaking stress level decrease of the PES/MTF yarn.Consequently, the PES/MTF yarn has higher breaking extension than the 100% PES yarn.e PES/MTF yarn shows lower elasticity modulus in comparison with the 100% PES yarn.e rst derivative of the speci c stress/extension curve of the PES/MTF yarn (see Figure 5) shows higher value of elasticity modulus (8.67 cN/tex) than the MAC/CO yarn (3.9 cN/tex). is would suggest that the PES/MTF yarn ensures higher resistance to loading in the elastic region -in the eld of elastic deformations (see Figure 5).e elasticity modulus of the 100% PES yarn is even higher -9.64 cN/tex, which is about 10% higher than the elasticity modulus of the PES/MTF yarn.e speci c stress in the yield point of the PES/MTF yarn is 4.33 cN/tex, while the extension in the yield point amounts to 1.5%.e speci c stress and extension in the yield point of the 100% PES yarn amounts to 4.81 cN/tex and 1.5%.e both yield point levels are a little bit lower than 5 cN/tex (80 g) which represents the amount chosen as the limit of elastic extension by this research.
e results of the viscoelastic parameters (the elasticity modulus and the yield point) show that the elasticity modulus of the PES/MTF yarn is about 10% lower than with the 100% PES yarn.On the other hand, the limit of elastic region (the speci c stress and extension in the yield point) for the PES/MTF yarn is about 10% lower than with the 100% PES yarn.e MTFs prove very low breaking extension (1%) and only slight in uence on the yield point decrease.Under the yield point, which presents the numerical limit of elastic deformations, the rst movements of bres in the sheath appear.Above the yield point, the rst movements of the bres in the yarn core appear and consequently also the viscoelastic deformation (time-dependent deformations).
e speci c stress/extension curve changes its shape.
From the Figure 4 it can be deduced, that the PES/ MTF yarn has a lower eld of elastic deformations (under the yield point) than the 100% PES yarn.
e eld of viscoelastic region of the PES/MTF yarn is wider and nally reaches higher breaking extension (12.6%) than the 100% PES yarn (11.4%).

Conclusions
In regard to the research of the in uence of the re resistant modacrylic bres in the MAC/CO yarn and the conductive metal bres in the PES/MTF yarn on the mechanical and viscoelastic properties in the eld of lower loads (5 cN/tex), the following conclusions were drawn: e incorporation of re resistant MAC bres in Based upon the facts presented above, it could be • claimed that the incorporation of MAC (modacrylic) bres, which are re and heat resistant and intended for protective clothing, mostly increase the region of elastic deformations as well as the superior elastic properties of the MAC/CO yarn, as was predicted.On the other hand, the incorporation of MAC bres in the yarn decreases the elasticity modulus and increases the deformation level.
e incorporation of MTFs (metal-stainless steel • bres), which are heat resistant and conductive, in the PES/MTF yarn mostly decreases the region of elastic deformations (about 10%).On the other hand, the region of elastic deformations lies very close to the eld of lower loads under the speci c stress/extension curve which amounts to 5 cN/tex or 85 g.

Figure 1 :
Figure 1: e scanning electron microscope view (cross-sectional) of the ring-spun yarns from the mixture of MAC/CO (a) and the mixture of PES/MTF bres (b)

Figure 2 :
Figure 2: e speci c stress/extension curve of the 100% CO, 100% MAC and MAC/CO yarn

Figure 4 :
Figure 4: e speci c stress/extension curve of the 100% PES and PES/MTF yarn

Figure 5 :
Figure 5: e speci c stress/extension curve of the PES/MTF yarn with the 1 st (Y1), 2 nd (Y2) and 3 rd (Y3) derivatives Tekstilec 2015, letn.58(1), 23−32 The Infl uence of Modacrylic and Metal Protective Fibres in the Mixture on the Mechanical Properties of Ring Spun Yarns for Protective Textiles e capacitive sensor of Uster Tester is not able to measure the irregularity of special yarns containing electrically conductive material such a metallicbres, etc.

Table 1 :
e basic properties of bres Tekstilec 2015, letn.58(1), 23−32 The Infl uence of Modacrylic and Metal Protective Fibres in the Mixture on the Mechanical Properties of Ring Spun Yarns for Protective Textiles

Table 2 :
e basic properties of yarn's samples

Table 3 :
The Infl uence of Modacrylic and Metal Protective Fibres in the Mixture on the Mechanical Properties of Ring Spun Yarns for Protective Textiles e mechanical and physical properties of analysed ring-spun yarn Tekstilec 2015, letn.58(1), 23−32

Table 4 .
Table 4: e results of speci c breaking stress and breaking extension analysed bres and yarns Tekstilec 2015, letn.58(1), 23−32 The Infl uence of Modacrylic and Metal Protective Fibres in the Mixture on the Mechanical Properties of Ring Spun Yarns for Protective Textiles diameter 12.6 µm).Metal bres have also lower speci c breaking stress (22.3 cN/tex) in comparison with the speci c breaking stress of the PES bres (60 cN/tex), see Table 1.Consequently, the speci c breaking stress of the PES/MTF yarn is lower.
Tekstilec 2015, letn.58(1), 23−32 The Infl uence of Modacrylic and Metal Protective Fibres in the Mixture on the Mechanical Properties of Ring Spun Yarns for Protective Textiles 9%) in the MAC/CO yarn break rst (they lower breaking extension than MAC bres -18.7%) and in uence the breaking extension level decrease of the MAC/CO (5.8%) yarn in comparison with the breaking extension of MAC bres -18.7%.e incorporation of conductive MTFs decreases • the speci c breaking stress of the PES/MTF yarn (21.8 cN/tex) -the speci c breaking stress of the 100% PES yarn is 34.5 cN/tex, while the breaking extension of the PES/MTF yarn is somewhat higher (12.6%).e incorporation of re resistant MAC bres in • the MAC/CO yarn decreases the elasticity modulus by about 10% (3.9 cN/tex), which means that the resistance of MAC/CO yarn in the eld of lower loads is lower than with the 100% CO yarn (4.3 cN/tex).On the other hand, the speci c stress in the yield • point of the MAC/CO yarn increases (7.83 cN/ tex) by about 45%, while the speci c stress in the yield point of the 100% CO yarn is 5.42 cN/tex, meaning that the eld of elastic deformations of the MAC/CO yarn is wider.e incorporation of conductive MTFs decreases • the elasticity modulus of the PES/MTF yarn by about 10% (8.6 cN/tex).e elasticity modulus of the 100% PES yarn amounts to 9.64 cN/tex.e incorporation of conductive MTFs also de-• creases the speci c stress in the yield point (4.33 cN/ tex) of the PES/MTF yarn, while the speci c stress in the yield point of the 100% PES yarn amounts to 4.81 cN/tex.e region of elastic deformations of the PES/MTF yarn is about 11% narrower.