Durable Antistatic Agents: Structure-Property Correlations

---~-

Indian Journal of Textile Research Vol. 5, September 1980, pp. 77-87

Durable Antistatic Agents: Structure-Property Correlations

G M VENKATESH, T K DAS & S PAL

Ahmedabad Textile Industry's Research Association, Ahmedabad 380015 Received 20July 1979;accepted 14January 1980

The static charge build-up and the rate of decay of charge accumulated on polyester fabric treated with four commercial durable antistatic agents were studied. The treated fabrics at comparable add-on levels differ widely in static charge build-up, decay time, wash fastness and hydrophilicity. While some antistats improve soil removal, others increase soiling and soil retention. The gross structural features have been deduced from IR and NMR spectra of the antistats and structure-property correlations have been attempted.

The desirable fabric properties possessed by polyester and polyester/cellulosic blends have enabled them to achieve a large share of the textile market. The hydrophobic nature of synthetic fibres, such as polyester, is not conducive to the formation of an electrically conducting water film on their surface.

Consequently, static charge is generated and accumulated on these synthetic materials causing many problems during spinning, weaving and chemical processing, such as drying, heat setting and folding of the dried fabricsl-4. During actual wear, garments from synthetic fabrics are uncomfortable to the wearer, especially in hot and/or dry weather. The charge accumulated on the fabric or garment attracts and retains dust particles from the atmosphere. These problems can be overcome to a large extent by the use of antistatic agents. Two types of finishes are available:

(1) durable, and (2) non-durable. Spin finishes (non- durable antistats), which are non-substantive, are applied mainly at the manufacturing stage or on loose fibres in mills for facilitating mechanical processing under ambient humidity conditions and are removed during scouring. Durable antistatic agents, on the other hand, have a distinct affinity for textile fibres.

Commercially available antistatic agents differ widely in their efficiency in reducing static charge build-up.

Further, the durable finishes may differ in wash fastness and in their response to soiling and soil removal. Hence, a study was undertaken to assess the effectiveness of four commercially available antistats in reducing static charge build-up and promoting soil removal on polyester fabric and to correlate their structural groups with their performance as antistatic agents.

Materials and Methods

Polyester/cotton blend (67/33) fabric carbonized in 70% sulphuric acid was used. Four commercially

available antistats were dried to find out their solid contents.

Fabric treatment-Fabrics were padded with aqueous solutions containing different amounts of antistats and squeezed through a pair of rollers to obtain 75% wet pick-up. These samples were dried at 110°C for 10min and cured at 150°Cfsamples B, C and D) and at 190-200°C for about 40 sec (sample A), as recommended by the manufacturers.

Measurement of static charge-The static charge is generated on the fabric either through friction or on the application of an external electric field. The measurement of friction-induced charges has been shown to beunreliable1,2.5.6 because of the uncertainty in the surface area of contact, the rise in surface temperature and surface contamination during rubbing. Each one of these factors has considerable influence on the charge accumulated and charge decay.

Hence, a static Honestometer (Shishido

&

The fabric sample folded four times was mounted in the sample holder on the disc with a test area of 32 x 32 mm. The disc was set in rotation at 1250 rpm. An electric potential of^RkV was applied through a needle electrode. The static charge developed on the sample (measured in multi volts) and its attenuation after the electric field was switched off were detected by an electrometer type detector mounted on the opposite side of the needle electrode and recorded on chart paper. The needle electrode and the detector were separated from the sample surface by about 15 mm.

The measurements were carried out in a room conditioned at 26°C and 55% RH. The reported values are the means of three independent measurements.

Drop absorbency and vertical rise tests-To determine the hydrophilicity of antistat-treated

77

INDIAN 1. TEXT. RES., VOL. 5, SEPTEMBER 1980

polyester fabrics, the drop absorbency test (AATee Test Method No. 79-1968) and the vertical wicking test were employed. In the first method, the time for complete sorption of a drop of distilled water applied on the sur;'ace at the centre of the fabric sample from a micro-burette was determined. In the second method described fully elsewhere9, the height of water level in a fabric of 100 x 13 mm size (cut warpwise), suspended above a large trough containing distilled water such that the lower end of the fabric strip just touched the water surface, was determined at the end of 10 min wicking time. Both these tests were carried out in a room maintained at 24°C and 60% RH.

Wash fastness of the applied finish-The antistat- treated fabric samples were washed at 50°C for 10 min with water containing 1 g/litre detergent in a tergotometer. The material to liquor ratio was 1: 65 and the samples were agitated at 50 rpm. The samples were rinsed in water and dried in an oven at 70°C. The treated fabrics were given up to 50 washes.

Selection of soils-Soil on textile materials comes from two different sources, namely (1) from the body of the wearer, and (2) from the environment 10,11.

Analytical studies on the nature and composition of the soil deposited on apparel and furnishing items during use ha ve shown that it is always a mixture which can be thought of to consist mainly of two components:

(I) a fluid component (lubricating oils, greases from machinery, secretions from the human skin, oils and fats from food and cosmetics), and (2) a solid component made up of clay minerals, metallic oxides, carbon with tarry substances derived from the combustion of coal and fuel oil in industrial areas.

Hence, two soils were chosen: (i) used motor oil, representing a particulate soil (a mxiture of soils) dispersion in an oleophilic soil, and (ii) ferric oxide, a polar particulate dry soil.

Selection of method of soiling-Soiling with oily soil was carried out according to the AA TCe Test Method No. 130-·1970. Fabric samples (size, 6 x 6 in) were mounted on an embroidery ring. Used motor oil (0.1 ml) of density 0.9 glml was placed on the surface at the centre of the fabric sample and the oil was allowed to wick for 18 hr. The Accelerotor method developed by Kissa 12 was used to soil the fabric with ferric oxide.

Ferric oxide (0.1 g) of about 2)1 size and fabric sample (2.5 g) were rotated at 1500 rpm for 1 min within the closed chamber of the Accelerotor. The loosely held soil was removed by mechanically shaking the soiled sample.

Washing of soiled sample--·The soiled fabric samples were washed in an aqueous. detergent in a

T ergotometer.

Evaluatio/l ofsoi/ed and washed samples-·lnstead of visually comparing soiled samples with photographic 78

standards, as in the AA Tee method, the reflectance spectra of the unsoiled, soiled and washed samples were measured with a visible spectrophotometer (Pretema Spectromat Model FS-3A) equipped with an integrating sphere.

Infrared spectroscopy-The infrared spectra of the antistatic agents were recorded using a double beam, high resolution, ratio recording Perkin-Elmer (Model 180) spectrophotometer. Samples. in the form ofKBr pellets (A, B and C), or a smear on a KBr crystal (D) were employed in this study.

N M R spectroscop y- The proton magnetic re- sonance spectra were recorded at 35°C with a 60 MHz Perkin-Elmer (Model R 12B) NMR spectrometer. The three solid samples were dissolved (20%) in chloroform-d, while the liquid sample was used as such.

The chemical shifts are expressed in (j units, i.e. ppm downfield from the tetramethylsilane (TMS) reference signal.

Electron microscopy-The unwashed and washed fabric samples treated with antistatic agents were mounted on SEM specimen stubs, coated with gold in a vacuum coating unit and observed employing a Cambridge Stereoscan (Model S4-1O) scanning electron microscope to detect changes in surface topography.

Results and Discussion

Structural information ]rom I Rand N

M

Durable antistatic finsihes for textiles are very few and most of them belong to one or other of the following classes 3: (1) nitrogen compounds such as long chain amines, amides and quaternary ammonium salts;

(2) esters of fatty acids and their derivatives;

(3) polyoxyethylene derivatives; and (4) polyglycols and their derivatives. However, exact structural information on these commercial products is not available. Based on the meagre information made available by the manufacturers, an attempt was made to ascertain the structural features of the durable antistats from their infrared and proton magnetic resonance spectra.

Infrared absorption spectra of the four antistatic agents are shown in Fig.!. The salient features of the IR and NMR (not shown) spectra, necessary for structure-property correlations, are highlighted separately for each antistat (Tabi.:: 1).

Antistat A-The O-H stretching vibration appears as a broad band centred around 3460 cm - 1(Fig. Ic).

The most intense, broad band at 1100 em-1(Fig. la) is due to the characteristic vibrations of the aliphatic

... 0,

C C group. The bands in the regions 2800-3000 cm-1 and 1240-1460 cm-! correspond to the

, I' 11"11' 'II II' I! I II I~r!I'II~"I ' I III ^1'1IIIi~II' I ^I

VENKATESH et al.: DURABLE ANTISTATIC AGENTS: STRUCTURE-PROPERlY CORRELATIONS

o

o

ioOOO 3500 • 3000 2500 2000

WAVENUMBER. em1

Fig. I-Infrared spectra of antistatic agents [(a and b) spectral region, 1800-600 em-I, and (c) spectral region, 400()..2000cm-I]

20 4

(C)

ring stretching vibrations. This is supported by the NMR spectrum, which shows a signal at 8.06 {)due to aromatic protons. The strong band at 720 cm -1is due to the out-of-plane bending of the aromatic ring. A very weak signal due to methylene protons in the NMR spectrum suggests the absence of any aliphatic chain. A comparison ofthe spectra ofthe two antistats A and B suggests that the antistat Bcontains an aromatic ring with an ester group which is highly oxyethylated.

Antistat C- The IR spectrum shows an N-H stretching band at 3300 cm-1,amide I band at 1640 cm-1(Fig. Ib), amide II band at 1550em-1and amide III band at 1290 em-1. The medium intensity absorption band at 1100cm -¹shows that the extent of oxyethylation is much less than that in antistats A and B. The NMR integration curve supports this conclusion. The strong NMR signals in the region 0.89- 1.22{)due to methyl/methylene protons and the strong IR band at 715 cm -^I due to CH² rocking vibration suggest that it is probably a condensation product of a fatty acid amide with ethylene oxide, and the extent of oxyethylation is not much.

Antistat D-In IR, strong absorption centered at 3320 cm -^I, which appears as a broad band, is due to OH and NH stretching. Strong absorption at 1050 em -

I

groups. The absence of strong absorption at 1100

600 800 600

800

1400 1200 1000

WAVENUMBER, em'

Cb>

1800 1600

1800 1600

;!'"

zo

inIII

~III Z~

a:

•...

;!..z

QIII

'"

i

z~

a:~

1-'00 1200 1000

WAVENUMBER ,em'

stretching and deformation vibrations of the methyl!

methylene groups. Thus, the only positive in- terpretation of the infrared spectrum is that the molecule contains C-O-C linkages of the type present in polyoxyethylene. The absence of a doublet at 1.22 b in the NMR spectrum suggests that the C-O-C linkage present in the molecule is of polyoxyethylene type and not of polyoxypropylene type. The sharp peak at 3.58c)is due to the multiple CH20 groups of polyoxyethylene units. The resonance signal due to the terminal OH groups occurs in the region 3.1-3.4^C). The NMR integration curve for antistat A shows that the product is highly oxyethylated. This is in comparison to the resonance signal at 1.22^c) due to methylene protons.

Antistat B- The product shows strong absorption bands at 171Sand 1270cm-1 duetoC=OandC-O stretching vibrations of the ester group. The weak bands at 1600, 1570 and IS00cm-1 are due to aromatic

79

INDIAN J. TEXT. RES., VOL. 5, SEPTEMBER 1980

Table l-IR and NMR Data for Antistatic Agents Antistat IR (em-I)

A 3460 (b)

1100 (b, VS) 2800-3000, 1240-1460

B 3460 (b) .

1715, 1270 (S)

1600, 1570, 1500, 720 (S) 1100 (b, VS)

2800-3000, 1240-1460

C 3450

3300

1640, 1550, 1290 1100

715 (S) D 3320 (Vb)

1050 1610, 1550 715

NMR(c5) 3.1-3.4

3.58 1.22

8.06 3.6 1.25

3.59 0.89-1.22

2.85 3.65

0.89-1.22

Interpretation Terminal OH gr.

Multiple CHzO grs. of polyoxyethylene units Methyl/methylene protons Terminal OH gr.

Ester gr.

Aromatic protons Multiple CHzO gr.

Methyl/methylene protons OH group

N-H stretching Amide I, amide II and

amide III bands CHO gr. (Very weak) Methyl/methylene protons

(VS)

OH and NH 'stretching Primary 0 H gr.

Amide I, and amide II bands Methyl/methylene protons -C-CH2 protons

9

Remarks Highly ethoxylated

copolymer

Highly ethoxylated compound containing aromatic ring with ester linkage Condensation product of a

fatty acid amide with ethylene oxide

Alkanol amide type R-~NHCHzCH20H

o

where R is a medium chain alkyl gr.

b, broad; V, very; S, strong; and gr., group

Fig. 2-Static charge build-up and decay on cotton and polyester fabrics

polyester l'abric behaves more and more cotton-like with increasing add-on.

The charge decays logarithmically with time. The dissipation of charge from a conducting system can be represented as

V VI

1= Vae-IIRe or log Vo = -0.434

where Vais the initial voltage developed on the system;

VI'the voltage at time t(see);R,the surface or volume resistivity; and C, the capacitance. By measuring the decay time constant, T,defined as the time taken for the charge to decay to Ije of its original value, for a number of untreated and antistat-treated natural and synthetic em-I, which is present in other antistats, suggests that

a polyoxyethylene chain is not present in this sample.

The strong absorptions at 1610 and 1550 cm-1are due to amide I and amide II bands. The absorption at 715 cm-1 is due to multiple CH2 rocking. In the NMR spectrum, the methyl signal occurs at 0.87b. The methylene protons appear at 1.22tJ. The multiplate

o

centered at 3.65/jis due to CH2-OH protons. -C-CH2 protons appear at 2.52 tJ.N-CHz protons appear as a multi plate at 2.85J. It may be concluded that the product is probably alkanol amide type having the

o

structure R-C-NH-CHz-CH20H, where R is a medium chain alkyl group (from the results of nitrogen analysis).

Static behaviour-The magnitude of the charge built up on the fabric and the rate at which the charge decays decide the performance of a durable antistatic finish.

The smaller the charge accumulated in a given constant potential field, and the smaller the time required to decay, the better is the performance of the finish during actual wear. Fig. 2 shows the charge build-up and decay patterns for cotton fabric and polyester fabric, as well as polyester fabric with varying amounts of a commercial antistat (spin finish). There is a vast difference b~tween cotton and polyester fabrics as regards the magnitude of charge and time of decay.

The antistat has significantly modified the electrostatic characteristics of polyester even at low add-on and the 80

~"

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VENKATESH et a/.: DURABLE ANTISTATIC AGENTS: STRUCTURE-PROPERTY CORRELATIONS

w

~ 4

«

u

01,.8,

..

o 10 20 30 40 50

WASH CYCLES

Fig. 3-Static charge build-up on.antistat-treated fabrics as a function of wash cycles

,;1

c

A

u120fA I: 100'..

>-

~ 801

jg

~ 6' c(

~

the increase in decay time is almost negligible. Antistat B is very satisfactory up to 25 washes, but its performance seems to deteriorate with further washings. In the case of antistat ~ the decay time increases fairly rapidly with successive washes. These observations suggest that antis tat A is very durable at least up to 50 washes, while antistat D is only semi- durable.

Hydrophilicityoffirlisltes~Anantistat is known to form a film on the fibre surface. Hence, tbe drop absorbency time and the vertical rise are better measures of the hydrophilicity of the finish than the moisture regain, which is a bulk property. The drop

~bsorbency and the vertical rise both depend on the hydrophilicity of the finish and the distribution of the finish on the fibre surface. The drop absorbency results are shown in Fig. 5. It i~ seen that the unwashed samples of the antistat-treated fabrics behave abnormally compared to the washed samples.

Particularly, the fabrics treated with antistats A andB exhibit large absorbency time before washing.

However, after washing, the general behaviour of different antistat-treated fabrics towards drop absorbency is more or less the same. But the drop

10 20 30 4fY 50

•••,,~ CVClES

Fig. 5-Drop abt.orbenc'Yti.me versus 'Wasnc'Yc\ell

1501

3

10 20 30 40 50

WASH CYCLES

Fig. 4-Decay time constant of antistat-treated fabrics versus wash cycles

A Q

B

C

E 10

"'

Q.

::> 8

o-'

=> 6

CD

fibres and blends, it has been shown that the log r- log R plot is linear16•17•A cotton fabric with surface resistivity of about l{)9 ohm at 65% RH haS a decay time constant of O.ot sec, i.e. the charge drops in O.ot sec to lie (37%) of its original value. On the other hand, a polyester fabric with a high reSistivity (about l{)15 ohm)'has a time constant of about 40 min. Wilson16•18 found the slope of 10gr-Iog.R plot to he 0.86 instead of unity expected from theoretical considerations. One of the main reasons for this discrepancy is the fact that the static charges decay not only by conduction, but also by radiations.6• The· radiation process is generally similar to the conduction process.· The voltage-time relationship should, therefore, be modified to include both the radiation and conduction constants.

The magnitudes of the charge developed on polyester fabric treated with the four antistats have been shown in Fig. 3. Very little charge is developed on the unwashed samples. Further, antistat A shows more charge than others. However, after one wash, the accumulated charges are somewhat large and different from one another. The fabric treated with antistat A shows the minimum charge, while the antistat D- treated fabric shows the maximum charge develop- ment. These treated fabrics have comparable antistat add-on. The removal ofloosely held antistat molecules during washing is mainly responsible for the increase in . charge development after washing and drying. Further, washing has practically no effect on charge development on fabrics treated with antistat A. In the case of other antistats, the charge build-up increases with repeated washing, suggesting perhaps progressive removal of the finishes.

The decay time constant increases with repeated washing (Fig. 4). The rate of increase of decay time is different for different antistats. In the case of antistat A,

81

INDIAN J. TEXT. RES., VOL. 5. SEPTEMBER 1980

o

400 500 600 700

WAVElENGTH,nm

Fig. 7-0ily soil removal from antistat-treated fabrics o

400 500 600 700

WAVELENGTH,om

Fig. 6-Removal of oily soil from polyester control fabric [I, soiled; 2 to 6, after 1 to 5 washes; and 7, unsoiled]

7 CONTROL.O

90

-:60w

~ 50'

<t '

•...

1J40

J"-

~ 30

Oily soil removal-Removal of oily soil from the control fabric after repeated washing is depicted in Fig. 6. The control fabric soils heavily and after one wash, a large percentage (about 65%)of soil is removed.

However, the rate of removal of the soil with further washing is not large. The fabrics treated with the four antistatic agents show more or less similar behaviour with repeated washing cycles. The soiling and the soil release properties after one and five washes for the control and the treated fabrics are compared in Fig. 7.

The control fabrics and fabrics treated with antistats A and B soil to more or less the same extent, while the antistat D-treated fabric soils to the maximum extent.

After one washing, fabrics treated with antistats Band A and the control fabrics In that order appear cleaner than the fabrics treated with antistats D and C. After absorbency time in the case of antistat A remains more

or less constant even after several washes, while it increases slowly in the case of antistats Band D with repeated washing. In the case of antistat C, the drop absorbency time increases rapidly after about 10 washes and iCvelsoff beyond 25 washes. The vertical rise results are more or less similar. These results appear to be different from the conclusions drawn from static charge measurements. it is difficult to correlate static behaviour with hydrophilicity simply because of the differences in the experimental conditions in these two tests. While the static charge was measured below 60% RH, the treated fabric was in direct contact with water in the drop absorbency and vertical rise tests.

However, antistat A shows the best behaviour in all the cases. Although antistat C behaves somewhat better than D in static properties, its hydrophilicity is poorer.

Probable explanations for the observed differences can be put forward by considering the molecular structures of the antistats. As shown earlier, antistats A and Bare highly ethoxylated products. The highly ethoxylated chain in A is responsible for its good static and hydrophilic properties. Antistat B is slightly poorer than A mainly because of the distinct differences in hydrophobic chains. Antlstat D has a large number of polar groups, such as -~-NH2 and -OH, and, therefore,

o

it shows hydrophilicity comparable to that of antistat B. But its static properties are poor. Antistat Cshows better static properties than D, because it is a nitrogen- containing cationic product.

The differences in the hydrophilicities of the washed and unwashed samples can be explained as follows.

The films of the antistats on the fabric are highly discontinuous and full of crevices. In the absence of many hydroxyl groups, the treated fabrics remain in the anhydrous state after curing. The rate of hydration appears to be slow, especially in the case of fabrics treated with antistats A and B, probably because of the uncoiling of oxyethylene chains; consequently, the treated fabrics show poor absorbency before washing.

After washing, the oxyethylene chains orient themselves in the linear direction and the film becomes more continuous. This helps in rapid movement of water and increases hydration.

Soiling and soil release properties-The effect of non- ionic, anionic and cationic antistats, both durable and non-durable, on the soiling and soil release properties has been examined18-20. Some of the main conclusions are: (1) a very significant percentage of soiling of women's slips is due to static charge, (2) antistats have no effect on areas where contact sdiling occurs, and (3) a non-durable antistat facilitates soil removal, while the opposite seems to be the case with durable antistats.

82

''r'''''''''''''''''''f'''''''''''''''1

VENKATESH et aL: DURABLE ANTISTATIC AGENTS: STRUCTURE·l'ItOPBltfi' COltULAtIONS

SOIL-WASH-S01L {;YCLE

121-

.~~

8t

Al\ef ~ Soilif\Cil

--<;

4 _• ⁰¹₆₁

;-^'"

l&I

u

u

~ 16LL I

~

~---

41 ~ o·

...

• 01 . .

400

500700600 400SOO600700 WAVELENGTH.lnm

Fig. 8-Decrease of oily soil removal efficiency of treated fabrics with repeated soil-wash cycles

five washes, the fabrics treated with antistats A and B appear much cleaner than the control fabrics. It appears that antistats

e

The behaviour of the untreated and antistat-treated fabrics subjected to repeated soiling and washing cycles is shown in Fig. 8. With repeated cycles, the difference in soiling between the fabrics treated with the antistats narrows down considerably and all the samples soil very heavily and the residual soil build up increases significantly. The superiority of the fabrics treated with antistats A and B diminishes with repeated soil-wash cycles.

Particulate soil removal-The soil release behaviour with r~gardto particulate soiIis shown in Fig. 9. All the fabrics, control as well as the antistat-treated ones, soil more or less to the same degree. On washing, the control fabric and the fabric treated with antistat

e

On the other hand, the fabrics treated with antistats A, Band C (cured at 150DC)exhibit poor soil release properties. With successive washing, the performance of the antistat D-treated fabric improves, while that of the remaining treated fabrics continues to be poor in comparison to the control sample. After five successive washes, the fabrics, especially the control sample, contain very little residual particulate soil. This is in contrast with the behaviour of the oily soiled fabrics.

The differences in the behaviours of oily and particulate soil release agents can be explained by considering the mechanism of soil release21. The removalof oily soil occurs mainly through the roll-up mechanism. The cellulosic fabric is hydrophilic and can

801

40

30

20

10

400 500 600 700o

WAVELENGTH"nm

Fig. 9-Particulate soil removal efficiency of treated fabrics as a function of wash cycles

release oily soil spontaneously as a result of the roll-up mechanism when hydrated. The polyester control fabric is hydrophobic and needs mechanical work to complete the roll-up of oily soil. However, when the fabric is treated with an antistatic agent, a film is formed on the fibre surface by co-crystallization and the agent becomes anchored to the fibre. This increased 83

INDIAN J.TEXT. RES., VOL. 5,SEPTEMBER 1980

u

S

••

III~

t=

5

o

5

Fig. lo-Decay times of treated fabrics concentration of antistats

as a function of

(a)

(c)

hydrophilicity facilitates diffusion of water to the soil- fibre. interface. Hence, the antistat-treated fabrics exhibit, in general, better oily soil release properties.

The particulate soiling, on the other hand, is caused by the adhesion of the soil particle to the fibre surface. The adhesion concept is supported by scanning electron micrographs of the particulate soiled samples+' .

The removal of particulate soil during laundering involves breaking the adhesive bond between the soil particle and the fibre. The strength of this bond and consequently the energy required to detach the particle depends on the contact mechanism, the size of the particle and the smoothness of the fibre surface. The surface of the fibres in the control fabric issmooth and consequently the particulate soil can be easily detached from the fibre surface during laundering. In the case of treated fabrics, the antistat forms a soft film on the fibre surface and this coating has a number of crevices in it

(b)

(d)

Fig. II-Scanning electron micrographs of the antistat-treated fabrics showing the surface topography. Antistat A treated before washing(a) and after washing (b),and antistat D-treated before washing (c) and after \1{ashing (d) ( x 85(0)

84

VENKATESH et aJ.:DURABLE ANTISTATIC AGENTS: STRUCTURE-PROPERTY CORRELATIONS

Condmion

8S

600 '100

500

WAVELENGTH #nm 400

washing should be different. The soil release behaviour ohhe fabrics treated with antistat A and C subjected to soiling with ferric oxide before and after washing is shown in Fig. 12. It is seen that the washed samples, especially the one treated with antistat A, exhibit much better soil release properties than the unwashed treated fabrics.

The data on the structure and properties of the four antistats are summarized in Tables 1-3. It is seen that antistat A is very efficient, both as an antistatic agent and as an oily soil release agent. It is also exceptionally durable. Antistat B is similar to A in static and oily soil release properties. However, it does not appear to be equally durable. Antistats C and D are effectiveonly as antistatic agents. They have poor oily soil release properties. All the antistats appear to have fairly good to poor particulate soil removal properties. However, very severe conditions of soiling with both oily and particulate soils almost to the saturation level. In actual wear, the garments are not normally subjected to such severe conditions of soiling. For obtaining ve,ry durable antistatic pl10perties in conjunction with good soil release, the product musthave aproper balance of ethoxylated chain length to hydrophobic chain length.

Fig. 12-Particulate soil release properties of antistat-treated fabrics subjected to soiling before and after one wash. The numbers denote

the number of washes given to the soiled fabrics

When the particulate soil is forced onto this film in an Accelerotor, the soil is held tenaciously in the fdm as well as in the crevices.^"£hough the fibre surface is more hydrophilic than the control, it is thus difficult to detach the soil.

Static charge and hydrophilicity properties as a function of antistat add-on- The full decay time as a function of antistat add-on for antistats A and D is shown in Fig. 10. Prior to washing, all the samples show satisfactory static properties irrespectiwof add- on. After washing, the treated fabrics show a decrease in decay time with increasing antistat content on the fabric as expected. It has been indicated earlier that one end of the antistat gets anchored to the fibre surface, while the hydrophilic group is attached to atmospheric water molecule through hydrogen bonding. In theory, a continuous monolayer of the antistat should give maximum static protection. But in practice it is difficult to achieve such a distribution and hence one talks in terms of an optimum or limiting concentration. It is clear from Fig. 10that the optimum concentration is in the region 3-5% on the weight of the fabric. Lower add- ons may tend to give poor improvement, while higher add-ons give little or no improvement. The static protection gained, when the fabric is treated with the optimum concentration of the antistat, depends on the efficiency of theantistat, and no useful purpose will be served by increasing the antistat concentration.

In actual use, the static charge accumulated on a fabric and its rate of dissipation, and hence the undesirable effectscaused, vary widely according to the relative humidity and temperature of the ambient atmosphere. The differences in static behaviour for different antistats tend to narrow down at higher humidities and increase with decreasing relative humidity. It can also vary under the same humidity conditions with different wearers.

Electron micrographs-The surface topographx of the fibres from the antistat-treated fabrics before and after washing is shown in Fig. II. The films on fabrics (unwashed) treated with antistats A and

0

However, after washing, the film on the antistat A- treated fabric becomes smoother and more or less continuous (Fig. 11b). In contrast, the surface topography of the film on the antistat D-treated fabric changes very little after washing (Fig. lid). The surface structure of the fabrics treated with antistats Band C resembles that of the fabrics treated with antistats A and

0

If the above interpretation is correct and the adhesion mechanism of particulate soiling is also correct, the soil release properties of the antistat- treated fabrics (especially the ones treated with antistats A and B) subjected to soiling before and after

INDIAN 1. TEXT. RES., VOL. 5, SEPTEMBER 1980

Table 2-Physical Characteristicsof Antistatic Agents

....•..'",,

Antistat SolubilityCuringHand of the fabricIonicPhysical formSolid

content

character temperature

As supplied

After drying% °C Before washAfter wash

A

White mobileWhite powder14.4 Soluble inSoft and smooth190-200Non-ionicHarsh dispersion

cold water B

Pale colouredWhite powder26.1 Soluble in150-160Non-ionicSoftdo liquid

cold water C

Light brownBrown powder21.4 Soluble inllO-l20Cataionicdod9 coloured

cold and liquid

hot water D

ColourlessHigh viscous26.1 Soluble in150-160Non-ionicdodo liquid

light yellowcold water liquid

Table 3-Characteristics of Antistatic Agents Antistat

Nitrogen Comparative ranking

content %

Wash fastnessHydrophilicStatic charge propertySoiling and soil release properties

nature Charge

Decay

Oily soil (usedParticulate soil build-up

motor oil) (ferric oxide)·time A

1 (very satis-1 after one0

I

(minimum)wash (minimum)control)control

50 washes) B

2 (very satis-2 after one02 2 2 (better than do factory up to

wash control)

25 washes) ^C

2.0

3 3 3 2

3 (worse than do control)

D

4 (semi-durable)9.94 2 3 4 (worse than do control)

·See text for after-wash soil release properties.

Acknowledgement

The authors wish to express their thanks to Dr N.E.

Dweltz, Assistant Director and Dr H.C. Srivastava, Deputy Director, both of ATIRA, for useful discussions. Their thanks are also due to Dr P.c.

Mehta, Director, ATIRA, for permission to publish this paper. Technical assistance of Mrs M.M. Shah in recording NMR and visible spectra, of Miss R.V. Shah in recording IR spectra and of Shri R.S. Chauhan in SEM observations is gratefully acknowledged. The manufacturers of the antistats used in this study are also thanked for supply of free samples.

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86

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,"

~ 'III'II I'· I II 111111"" I III; '11"11'I I'111111l~h~111IilIIII, II I H II IIll ~ ;:11·11;!II.,I1'1I

VENKATESH et oJ.:DURABLE ANTISTATIC AGENTS: STRUCTURE-PROPER.TY CORRELATIONS

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