New applications for carbon black. Mass colouring of viscose fibre

Transcription

1 Kauchuk i Rezina, No. 4, 2013, pp New applications for carbon black. Mass colouring of viscose fibre G.I. Razd yakonova Institute of Hydrocarbon Processing Problems, Siberian Section, Russian Academy of Sciences, Omsk Selected from International Polymer Science and Technology, 41, No. 2, 2014, reference KR 13/04/36; transl. serial no Translated by P. Curtis Chemical fibres a broad class of polymer products are widely used in different areas both in everyday life (clothing, footwear, household goods) and in engineering as reinforcing materials (cord, fabrics, etc.). Among chemical fibres, an important place in their volume of production (about 15%) is occupied by viscose fibres obtained from cellulose according to GOST They are used in the production of yarn used for the manufacture of cloth and knitted fabric of different designation, non-woven materials, artificial fur, floor coverings, and so on. At present, the production of viscose fibres worldwide amounts to 2.6 million t/year. Its distribution in the United States, Europe, and Asia is 1:4:9 [1], and its production is being developed not only because of a reduction in the rates of production of synthetic fibres (on account of increase in their manufacturing cost in connection with the growth in oil and gas prices and the limited nature of the world resources of these types of raw material) but also because of the considerable modernisation of production, with elimination of adverse ecological effects on the environment. On the world market, 83% of viscose fibres are used in the production of viscose cord, 12% in the production of mechanical rubber goods, and 5% in the production of viscose fabrics [2]. The prospects for production of viscose fibres worldwide are based on the availability and renewability of the natural raw material - wood cellulose - and on their good functional characteristics, especially their hygienic characteristics (non-electrifiability and moisture retention) [1, 3, 4]. The viscose process, invented 120 years ago, based on the treatment of cellulose with carbon disulphide in the presence of an aqueous solution of alkali with the production of an alkaline solution of cellulose xanthate (viscose) [5], is made attractive by the possibility of the mass colouring of viscose fibres with disperse dyes. One such dye is carbon black, a pigment absolutely unchanging over time and resistant to high temperatures, solvents, and corrosive media that ensures the deepest and strongest colouring of the fibre. When viscose is coloured in mass, its suspension form is used, designated by the letter V (for viscose in mass), stabilised by a surface-active agent, normally dispersing agent NF [6]. The pigment concentration in the suspension, like its degree of dispersion, is one of the main characteristics of the commercial product. It affects the rheological properties of the dye suspension and the ability to retain sedimentation resistance during storage. Highly dispersed suspensions of dye are produced in a bead mill by forcing an aqueous suspension of the pigment with dispersing agent NF through a bed of rapidly moving (over 6 m/s) grinding bodies in a spiral horizontal direction and at the same in a back-and-forth vertical direction from the central axis of movement of the bed [7]. During eddy motion in the closed space of the grinder, the grinding bodies (glass spheres) collide with each other, and the mechanical work of different types of force (centrifugal, impact, friction) ensures disaggregation of the agglomerates of compacted carbon black powder. The carbon black suspension that is produced in this way consists of particles or groups of particles of less than 1 µm size. In the production of a suspension of the first disperse black dye in Russia (1997), use was made of K354 channel black [8]. However, for a number of reasons (low product yield, adverse ecological impact, increase in the demand 2014 Smithers Information Ltd. T/15

2 for gas), the channel process was phased out in the middle of the last century in the United States, and at the beginning of this century in Russia [9]. A peculiar feature of channel black is the small size of its primary aggregates (about 200 nm) and its ability readily to be wetted by water on account of the functional groups of oxygen that are formed as a result of oxidation of the carbon particles in diffuse flames with free access of air in the process of its synthesis [10]. The search for technological solutions with respect to replacing channel black with furnace black obtained from liquid raw material has been directed primarily towards lowering the degree of structure of the furnace carbon black. For this, methods have been developed for suppressing the coagulation of globular particles during synthesis by their electrostatic stabilisation by ions of alkali and alkaline earth metals in the reactor. By this method, furnace carbon black Termoks P161 with a high specific surface, which is promising as a pigment for the colouring of fibre-forming polymers, was obtained [11, 12]. Other developed replacements of channel carbon black K354 in rubber compounds [13] for the colouring of polymers have not been used because of their low (by comparison with K354) specific adsorption surface. Meanwhile, Termoks P161 carbon black has been used as a deeply black pigment in the colouring of plastics [11]. The aim of this work is to compare the properties of viscose fibres coloured in mass by suspensions of K354 and Termoks P161 carbon black. Two specimens K354 carbon black manufactured by the Khazar Chemical Plant and Termoks P161 produced on a pilot unit at the Institute of Hydrocarbon Processing Problems (IPPU) of the Siberian Section of the Russian Academy of Sciences were compared. Their physicochemical properties are presented in Table 1. The screen diameter D w of the primary aggregates of disperse carbon was determined by the method described by Stacy et al. [14] using a Nuclepore membrane. The error of D w measurements was 7.4%. A characteristic feature of carbon black Termoks P161 is the mainly linear form of its aggregates according to the classification set out by Herd et al. [15], and therefore it is ideally suited to the forming of fibres through spinnerets. Another of its features is the high degree of dispersion of its globules and primary aggregates. Suspensions of K354 and Termoks P161 carbon blacks were obtained in a two-rotor bead grinder with a pigment concentration of 20% and a degree of dispersion of 4-5 ratings [8, 16]. Their addition to viscose did not cause any difficulties in the process of viscose fibre manufacture. Comparison of the optical properties of viscose fibre containing different concentrations (0.7, 1.8, and 2.2%) of the compared pigments K354 and Termoks P161 was conducted on a Spectro Eye spectrophotometer (GretagMacbeth) with a function for measuring CIE L*a*b* with a D65 standard light source using an observer for small specimens at an angle of 2. The standard white surface reference was barium sulphate in pellet form. Specimens were illuminated at an angle of 45, and the colour spectral characteristics were calculated using the GretagMacbeth program. The optical indices were calculated from ten measurements. The error of measurements amounted to no more than 0.2%. Data on the colour brightness L* of the compared specimens are given in Table 2, and values of the colour tone coordinates a* and b* in Figure 1. From the colorimetric data it can be concluded that, with an identical concentration of the compared pigments, viscose fibres coloured with a dye containing pigment Table 1. The physicochemical properties of carbon black specimens Termoks P161 Standard according to TU Value of property K354 Standard according to GOST Value of property Specific geometric surface (m 2 /g) Specific adsorption surface (m 2 /g) Specific external surface (m 2 /g) Iodine number (g/kg) Absorption of dibutyl phthalate (cm 3 /100 g) ph of aqueous suspension Mass fraction of losses at 105 C (%) Ash content (%) Mass fraction of residue after screening through sieve with a mesh cell size of mm Arithmetic mean diameter of globules d (nm) Average screen diameter D w (nm) T/16 International Polymer Science and Technology, Vol. 41, No. 4, 2014

3 Table 2. The properties of viscose fibre (tex 0.301, cut 65 mm) coloured with dyes based on Termoks P161 and K354 carbon black in identical concentration (1.8%) Carbon black grade Termoks P161 K354 Specific breaking load f t (mn/tex) Elongation at break ε (%) Hue Blue Red Colour brightness L* (kd/m 2 ) Figure 1. The positioning on the colour diagram of colour tone coordinates a* and b* of specimens of viscose threads coloured with carbon black K354 (2, 4, 6) and Termoks P161 (3, 5, 7) with a concentration in relation to α-cellulose of 0.7% (2, 3), 1.8% (4, 5), and 2.2% (6, 7), relative to uncoloured strands (1) carbon black Termoks P161 have a greater brightness L*, which is due to the greater amount of black colour, than viscose fibres with K354 carbon black. In Figure 1 it can be seen that, with the same concentration in the fibre, Termoks P161 gives a dark-blue hue to strands, which improves its colour perception by users. Carbon black Termoks P161 in the range of investigated concentrations gives the fibre increased tensile strength (Figure 2a), which is due to higher orientation of the fibre-forming polymers on the surface of its linear primary aggregates. In accordance with the increased orientation of the polymers, the elongation at break of fibre coloured with Termoks P161 is higher (Figure 2b). To explain the differences in the optical properties of viscose fibres coloured with K354 and Termoks P161 carbon black, the influence of the size of the globules and primary aggregates on the colouring power of carbon black was compared. Figure 2. The dependence of the physicomechanical properties of viscose fibre on the concentration of K354 (1) and Termoks P161 (2) We made use of specimens of carbon black (Table 3) with a wide range of dispersion of globules and aggregates. The dyeing power of the carbon black was determined from the change in colour of a whitener finely dispersed zinc oxide powder. Mixtures of zinc oxide and carbon black were prepared in a mass ratio of 3.75:1, stabilised by anionic surfactant SAS-1019 (sodium salt of di-2-ethylhexyl ester of sulphosuccinic acid), and were deposited on the glossy surface of an MFA-MA N1 cellulose acetate membrane in an ultrafiltration funnel. The homogeneity of the suspension was maintained by continuous 44 khz ultrasound cavitation in the funnel. The thickness of the layer deposited on the surface of the membrane was 0.2 mm according to the condition of optical homogeneity of the light-scattering layer. The coefficients of reflection of membranes with a deposited layer were measured on an SF-18 diffuse 2014 Smithers Information Ltd. T/17

4 Table 3. The properties of the carbon black specimens a Carbon black grade Diameter (nm) Optical characteristics of layer of carbon black with whitener, deposited on membrane Globules (d) Aggregates (D w ) R ρ α (%) P P P P N N K a R - measured coefficient of reflection; ρ - true coefficient of reflection; α - relative dyeing power reflection spectrophotometer. The true coefficient of reflection ρ was calculated from measured coefficients of reflection R by means of the formula: ρ = R (0.96 R) The Gurevich-Kubelka-Munk (GKM) function was calculated from the relation (1 - ρ) 2 /2; the relative dyeing power α was calculated from the ratio of the GKM function of the tested and control specimens of carbon black. As the control specimen, use was made of N330. Table 3 gives experimental results of the optical characteristics of layers deposited on a membrane, with different grades of carbon black. Comparison of the dependence of the optical properties on the degree of dispersion of the particles and aggregates of carbon black revealed two optically differing sections of the rectilinear dependence of the colouring power of the pigment on the size of its particles (Figure 3). The change in colouring power in bilogarithmic coordinates has a rectilinear form. The slope coefficients of the straight-line equations, characterising the intensity of colouring of pastes Figure 3. The dependence of the relative dyeing power on the average diameter of the particles (d) and aggregates (D w ) of carbon black by carbon black, differ twofold, which indicates the preferential influence of the size of the aggregates by comparison with the size of the globules. As carbon black Termoks P161 is more disperse than K354, the colour characteristics of viscose fibre with Termoks P161 are perceived to be appreciably better. Thus, the colouring power of pigment carbon black is determined more by the size of its aggregates and less by the size of the particles forming the aggregate. The advantage of carbon black Termoks P161 over channel black K354 as pigment in the mass colouring of viscose fibres has been established. Fibres coloured with Termoks P161 carbon black are stronger, with a better hue. REFERENCES 1. html 2. Ashpina O., Chem. J., (3):36 (2005). 3. Perepelkin K.E., Ross. Khim. Zh., 46(1):31 (2002). 4. Perepelkin K.E., Chemical Fibres: Development of Production, Methods of Production, Properties, Prospects. SPGUTD, St Petersburg, 354 pp. (2008) GOST Technical-grade dispersing agent NF. 7. Ermilov P.I., Dispersed Pigments. Khimiya, Leningrad, 420 pp. (1984). 8. TU uploads/2007/12/ pdf 10. Razd yakonova G.I. et al., Kauch. i Rezina, (5):6 (2011). 11. Russian Patent , MPK C 09 C 1/50 (1997). T/18 International Polymer Science and Technology, Vol. 41, No. 4, 2014

5 12. TU Pankratov V.A. et al., Proizvod. Shin Rezinotekh. Asbestotekh. Izdelii, (11):3 (1980). 14. Stacy C.J. et al., Rubber Chem. Technol., 48(2):538 (1975). 15. Herd C.R. et al., Rubber Chem. Technol., 65(1):107 (1992). 16. TU Received Smithers Information Ltd. T/19

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