Optimised conditions The results given above underline the importance of sodium sulphite concentration. Optimum conditions thus established are as follows: sodium sulphite concentration 2.5 g/l, HTAB concentration 5.0 g/l, HERC concentration 1.0-2.5% o.w.f., time of treatment 30 min and tempera- ture 50°C. These experimental conditions are valid for the type of wool fabric used in this work. They may be applicable to other kinds of wool fabrics, but since the percentage area shrinkage depends on the characteristics of the fabric it would be necessary to check the effectiveness of the treatment for each type of fabric.

Influence of surfactant alkyl chain length To widen the applicability of the method to commercial cationic surfactants, the influence of the alkyl chain length

TABLE 3

Percentage area shrinkage of knitted wool fabrics treated with sodium sulphite and cationic surfact- ants of different alkyl chain lengths(")

Cationic HERC concn Area shrinkage surfactant "% 0.w.f.) W")

TTAB 2.0 2 HTAB 2.0 0 OTAB 2.0 18

Untreated sample 52

(a) Sodium sulphite concentrahon 2.5 g/l, surfactant concentration 5.0 g/l. time of treatment 1 h. temperature 50°C

on the effectiveness of these treatments was investigated. The area shrinkage values of wool samples treated with ?TAB, HTAB and OTAB are listed in Table 3.

The effectiveness of ?TAB in conferring shrink resist- ance to wool fabrics was similar to that of HTAB, but OTAB did not give worthwhile shrink resistance. These results show that the hydrophobic chain of the cationic surfactant plays an important role, as previously observed with sodium sulphite/cationic surfactant treatments [91.

CONCLUSIONS A new non-damaging treatment has been described for the shrink-resist finishing of wool fabrics, employing a reducing agent (sodium sulphite), a cationic surfactant and a cationic resin (Hercosett 125) in the same aqueous bath. The simultaneous presence in the treatment bath of the cationic surfactant and the cationic resin permits a decrease in both the concentration of the nucleophilic reagent and the temperature of the treatment.

REFERENCES 1. S Matsuoka et a]., Proc International Wool Text. Res. Conf., Paris, 2 (1965)

2. H Meichelbeck and H Knittel, Fette Seifen Anstrichmittel, 73 (1971) 25. 3. P Mir6 and J Garcia Dominguez, J.S D.C., 83 (1967) 91. 4. P Erra et al., Text. Research J., 53 (1983) 11, 666. 5. M R Julia et al., J.S.D.C., 101 (1985) 66. 6. E Jungermann, 'Cationic surfactants' (Surfactant Science Series, Vo1.4) (New

7. A G De Boos and E Finnimore, Tenside Detergents, 5 (1982) 262. 8. 'Method for the determination of the felting shrinkage in washing of wool and

9. P Erra et al., Proc. 7th International Wool Text Res. C o d . Tokyo, 4 (1985) 332.

233.

York: Marcel Dekker, 1970), 28.

wool containing fabrics and garments', IWS test method 185.

The desorbing action of polyvinylpyrrolidone

Kenzo Nishida, Yutaka Ando and Shingo Toriumi Dept of Industrial Chemisty, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184, Japan

r Work has been cam'ed out to obtain an understanding of the interaction between a cationic (basic) dye and polyvinylpyrrolidone, using visible absorption spectroscopy and viscomety. Changes in the enthalpy, entropy and number of binding sites on the polymer have been calculated.

INTRODUCTION Textile printing is still an industrial art, rather than a scientific technology [l]. Polyvinylpyrrolidone (subse- quently referred to as PVP) is used in textile printing as a stripping agent, as well as being a retarding agent in dyeing and a synthetic blood plasma for use in blood transfusion. It seems that PVP forms complexes with a large number of organic substances. The desorbing action can be ascribed to the binding action of part of the molecule. Its thermodynamic properties would be a useful starting point in investigating the nature of the desorbing action and should make it possible to elucidate the molecular interactions between the dye and the binding site of PVP. However, earlier studies have afforded very little knowledge about the dynamic behaviour of such a system.

The purpose of our research was to obtain an understanding of the binding forces which operate in these desorbing processes. Therefore the interaction of PVP with malachite green (subsequently referred to as MG) (C.I. Basic Green 4), as a model compound of cationic dyes in aqueous solution, has been studied.

EXPERIMENTAL

Materials PVP was obtained from C Holstein Co. Ltd (degree of polymerisation about 75000) and was used without further purification. MG was obtained from Eastman Kodak Co. Ltd (purity 99%).

Spectral method We studied the binding of PVP to MG in aqueous solution

96 JSDC Volume 104 February 1988

using spectroscopy and viscomet y. The rationale behind the spectroscopic technique is as follows. Unbound MG exhibits one set of absorption coefficients, and bound MG a different set, €5. We determined both sets, selecting for A (wavelength) a value at which E , + - E ~ has a large, easily measured value, after demonstrating that both and c',, obey Beer's law. The value of E A was determined in the absence of PVP, and €5 in a large enough excess of PVP to rnsure that virtually all the MG was bound. All of the work which uses this method was carried out in the visible rvgion of the spectrum. Details of the method and the representation of binding data have been described previously [2,3]. The concentration used was low enough to minimise PVP aggregation, and self-association of MG in aqueous solution was neglected.

The spectral measurements were conducted with a Hitachi model 124 recording spectrophotometer, equip- ped with cells of 1 cm path length. A cooling block was installed to permit control of temperature within +O.l"C. No attempt was made to adjust pH.

The aqueous solution of MG was added to the aqueous PVP in a volumetric flask and the concentration of MG was finally measured as 4.5X lo6 mol/l.

The binding data may be represented by Eqn 1 (Klotz plots):

_- 1 1 1 r X+; -

where r- number of moles of bound MG per mole of polymer

A = concentration of free MG n= number of binding sites on one polymer unit K= binding constant.

Viscometry An Ubbelohde viscometer was used, the flow time for water at 20°C being about 330s. The kinetic energy correction under these conditions is small and was therefore neglected.

RESULTS AND DISCUSSION The effect of PVP on the visible absorption spectrum of an aqueous MG solution is shown in Figure 1. Addition of va ying amounts of PVP to a constant concentration of MG in aqueous solution greatly affects the shape of the spectra f:or comparison, the absorption spectra of an aqueous solution of MG at the same concentration is also shown in Figure 1. The addition of PW to MG in aqueous solution causes an increase in the absorbance at A,,, (about 617nm). The spectral change may be attributed to binding trlking place between MG and PVP in aqueous solution.

We found that the formation of such a complex takes place over a period of time, complete equilibrium in aqueous soluhon being attained after about 30min. This fact is significant when studying desorption processes in dyeing.

The ptl of the solution after mixing MG and PVP directly i n aqueous solution was in the range 4 .44.8.

Figure 2 shows Klotz plots of l / r against 1/A at 20°C. The intercept on the ordinate gives the value of lln. The binding constant K can be obtained from Eqn 1. The numerical values for the enthalpy, W , and entropy, AS",

0 . 4 8 4 0 . 1 9 4

L . 570 610 650

Wavelength, nm

Figure 1 - Effect of the addition of PVP on the visible absorbance spectrum of MG in aqueous solution at 20°C; concn of MG 4.5~1WmoI4 concn of P W (% by weight) indicated next to curves

changes for these complex-forming reactions were esti- mated from the temperature-dependent equilibrium con- stant in aqueous solution (Table 1). The binding was found to be endothermic and the values of W and AS" were both positive. It should be noted that, even assuming straight lines were obtained, all the data presented are subject to about 10% uncertainty.

10

I I 1 I I 1

10 20 f 1m I x 105

30

figure 2 - Klotz plot to determine the binding constant K and the number of binding sites according to Eqn 1 for the MG-PW complex in aqueous solution at 20, 30 and 40°C

TABLE 1

Values for binding constant and thermodynamic quantities for the binding of malachite green and polyvinylpyrrolidone in aqueous solution

Temp. K A C w AS' (K) n ( X lo5) (kJ/mol) (kJ/rnol) (J/(mol K))

293 2.05 1.56 -29.1 303 0.691 5.87 -33.4 40 236 313 0.793 4.47 -33.8

JSDC Volume 104 February 1988 97

The measured thermodynamic parameters provide an insight into molecular interactions, such as hydrogen bonding, hydrophobic bonding, van der Waals interac- tions and electrostatic interactions, between the bound MG molecules and the PVP binding sites in aqueous solution [4]. They also clarify the nature of the con- formational changes in both the PVP and the MG molecule on binding [5].

The enthalpy and entropy changes for the formation of the complex show unexpectedly large positive values [5]. This may be due to the release of water, which is ordered around the MG and the PVP [61.

Binding of MG is accompanied by a release of the counter ion in form of an oxalate ion, although this has a negligible contribution to enthalpy. Hydrophobic bond forces may be the main factor in the formation of a complex between MG and PVP. It seems that the mechanism of the desorbing action can be generally ascribed as an entropy-driven reaction.

Our numerical values of W = 4 0 k J / m o l and AS’= 236 J/(mol K) are both positive, as are the values found for non-intercalating drugs. For example, the AH” values of complex formation in the binding of the non- intercalating diaminosteroid pregn-5-ene-3P,17a-di- amine (common name irehdiamine-A) to DNA has been found to be 92 kJ/mol (M luteus) and 50 kJ/mol (calf thymus). Hence the complex has a large positive enthalpy and is stabilised by a positive standard entropy change of about 236 J/(mol K) (M luteus) and 397 J/(mol K) (calf thymus) 171.

However, the results of Chaires et al. have shown that the binding of the drug daunomycin to calf thymus DNA is exothermic, with AH”=-53.5 kJ/mol (at 25°C) and A F = -67.7 J/(mol K) [3]. The data from this equilibrium study are consistent with an intercalative binding of daunomy- cin. On the other hand the steroid can also exhibit positive A t P and AS’, and so is not intercalating with DNA. We therefore conclude that the desorbing action is not strong, but cationic dyes such as MG bind to the crystal surface of a fibre to form aggregates.

The proposed process of desorption is as follows. It is suggested that the reduction in viscosity of the MG-PVP complex in aqueous solution is due to the MG molecules becoming enclosed within the PVP chain. Therefore binding of MG is accompanied by a release of water, which is ordered around the MG and the PVP. This behaviour of the MG-PVP complex in solution may be mainly explained in terms of its volume depression (Figure 3). Consequently the change of conformation shows the increase in the number of binding sites per unit volume in a random coil (Figure 4). It is possible that similar results would be obtained with other cationic dyes, and the technique described could be used to cany out further investigations in this area.

CONCLUSION Changes in the absorption spectra of malachite green (MG) brought about by addition of polyvinylpyrrolidone (PVP) are evidence of binding between these compounds in aqueous solution.

Measurements of enthalpy and entropy changes for these binding reactions show positive values. From comparison with two other systems, it is concluded that

1.1

I (a)

l.O t 0.8

a * 0

1

0 LI]

> m

I 1 I 1 i

In 0.1 0.2 0.3 0.4 0.5 I ._

.-

> .- + m m n -

1.1 I

1 (b) 1 .o

0 0

0 0.8

111111 0.5 0.1 0.2 0.3 0.4

Concentration of PVP, wt%

O.gl a PVP i) PVPtMG

Figure 3 - Reduction in V J S C O S ~ ~ ~ caused by the fonnatrori of MG-PW complex in aqueous solution at (a) 20°C and (b) 3 0 Y , concentration of MG 9 OX lo4 mol/l

Hydration

Release of hydration water and dye packed within

the polymer chain

Figure 4 - Schematic representation o f the formation of complex between PVP and MG molecules (0) during desorptioi7

98 JSDC Volume 104 February 198

the bindiriq forces between MG and PVP are not as strons REFERENCES Y -

as expect,>d. The rcduced viscosity of the MG-PVP complex,

compare(! with that of PVP alone, may be explained by the MC; snolecules being enclosed by the PVP chain, accompaiiied by a release of water.

* * *

This u/( rk was partially supported by the Tokyo Ink Mfg c o . Ltd

1. W Clarke and L W C Miles, Rev. Prog Coloration, 13 (1983) 27 2 J Steinhardt and J A Reynolds, ‘Multiple equilibria in proteins’ (New York.

Academic Press, 1969) 60, 101 3 J B Chaires. N Dattagupta and D M Crothers, Biochemistry, 21 (1982) 3933. 4 I M Klotz and F M Walker, J . Amer. Chem. Soc . 68 (1946) 1486. 5 J B Chaires, Biopolymers, 24 (1985) 403. 6. A Bein-Naim, ‘Hydrophobic interactions’ (New York: Plenum Press, 1980) 69.

204. 7. N Dattagupta. M Hogan and D M Crothers, Proc. Nat. Acad Sci USA, 75

(1978) 4286.

The measurement of fluid flow Peter Croft

Allied Colloids plc, Low Moor, Bradford. West Yorkshire BD12 OJZ

INTRODl JCTION The most rudimentary process control system requires a means of measuring physical variables of the material streams insolved. The important parameters are tempera- ture, prvs-,ure. flow, level, density and viscosity. This article prt.psents the operating principles involved in commerc,iCilly available liquid flowmeters and offers guidelines t o the parameters to be considered for their suitability lor particular applications.

DIFFERENTIAL PRESSURE (DP) METERS The most 1:ommon flow measurement devices are those in which i: restnction or constriction is placed in the fluid flow path The flow velocity is thereby increased and hence the Kinetic energy, with a corresponding change in the pressur t. difference across the restriction. The pressure difference *nay be measured by a manometer, a differen- tial pressnit. (DP) cell or by a pressure transducer.

Fundarnt?ntal calculations are based upon derivatives of the Bernoi~lli equation, but basically it can be shown that the flow r.ite is proportional to the square root of the pressure tlifferential. The principle finds application in orifice plattis (Figure l), venturi meters (Figure 2) and Pitot tubes (Figlire 3) . (In Figures 1 and 2 Az is the differential pressure 1

i’ocition 1 Position 2 1 I

r:iow -

Figure I )dice meter

?his publicatioi is sponsored by the Society's lndustnal Resources Committee

Position 1 Position 2

figure 2 - Ventud meter

Static holes

F l o ~

Static uresture

Total pres5ure

Figure 3 - Pitot tube

The basic meters are of simple construction with no moving parts, resulting in low capital and maintenance costs. They may be fabricated in corrosion-resistant materials and operate over a wide range of temperatures, pressures and pipe diameters. Measuring devices do not normally show a straight-line relationship between flow rate and differential pressure. They have low turn-down ratios (i.e. the ratio of change in flow rate), typically 4:1, and all are intrusive, i.e. there is a mechanism that ‘intrudes’ into the flow path.

JSDC Volume 104 February 1988 99