Historic Textile and Paper Materials II - American Chemical Society

Chapter 11

Heat-Induced Aging of Linen Howard L. Needles and Kimberly Claudia J. Nowak

Downloaded by COLUMBIA UNIV on September 5, 2012 | http://pubs.acs.org Publication Date: September 28, 1989 | doi: 10.1021/bk-1989-0410.ch011

Division of Textiles and Clothing, University of California, Davis, CA 95616

Linen made from flax fibers was aged by heating at 180°c in air for periods of up to ten hours. The heat-treated linen became progressively darker and more red and yellow (brown) in color and showed progressive losses in tensile and abrasion properties. Wide angle X-ray scattering suggested that the heat-aged linen was somewhat less crystalline than untreated linen. Scanning electron microscopy showed that heat aging caused long crevices longitudinal to the fiber axis and passing through nodes in the flax increasing the acces sibility and surface area of the fibers. Heat-aged linen dyed to lighter and slightly different shades and had fewer dyeing sites available for direct dyes than untreated linen. Therefore, flax oxidation during heating apparently led to some breakdown of crystalline regions in the cellulose, but did not provide additional dyeing sites. The loss in dyeing sites is thought to be due to heat-induced crosslinking of the amorphous regions in the flax. Linen t e x t i l e s made from f l a x f i b e r s have been known and used by mankind since antiquity (1). Flax has been used i n many t e x t i l e constructions including f i n e linen f a b r i c s , laces, embroideries, and b r i d a l fashions, and many h i s t o r i c l i n e n t e x t i l e s have become part of permanent museum c o l l e c t i o n s . Older linen f a b r i c s and laces are prized f o r t h e i r natural creamy color and l u s t e r and often have been recycled and reused. However, l i t t l e i s known about natural aging of l i n e n . Most aging studies f o r c e l l u l o s i c s such as l i n e n have involved accelerated heat-induced aging. Kleinert (2) observed that ancient linens exhibited low degrees of polymerization, loss of strength, severe f i b e r deterioration, high o v e r a l l c r y s t a l l i n i t y but short c r y s t a l l i t e s and a high degree of oxidation. Hackney and Hedley (3.) examined the aging of l i n e n 0097--6156789/041(M)159$06.(X)A) ο 1989 American Chemical Society

In Historic Textile and Paper Materials II; Zeronian, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


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HISTORIC TEXTILE AND PAPER MATERIALS Π

canvas kept i n the Tate Gallery under various conditions for 24 years. They found that l i g h t exposure during this period caused s i g n i f i c a n t changes i n the linen including losses i n t e n s i l e strength and s l i g h t d i s c o l o r a t i o n . Sulfur dioxide present i n the a i r was shown to contribute to this deterioration i n properties. Continuous changes i n temperature and humidity during the exposure of the linen were also implicated. Peacock (4) studied moist heat aging of linen at 70°c and 50% RH for 21 days. The heat-aged linen samples l o s t weight, discolored to a l i g h t grey brown, became more f l e x i b l e and l o s t t e n s i l e strength. Deterioration and d i s c o l o r a t i o n of other fabrics made from c e l l u l o s i c fibers can be accelerated by heating at elevated temperatures (5-13). These studies have shown that heat aging of c e l l u l o s i c s causes accelerated d i s c o l o r a t i o n , loss i n t e n s i l e properties, increased f i b e r breakage, reduction i n the degree of polymerization, reduction i n the degree of swelling, in some instances increases i n c r y s t a l l i n i t y , increases i n the carbonyl and carboxyl group content, decreases i n moisture content, and reduced the dye uptake of the f i b e r . These property changes are similar to changes i n natural-aged linens. Since so l i t t l e i s known about heat aging of l i n e n , we examined the dry heat-induced aging of linen at 180°C from 1 h r . to 10 h r s . We have studied the effect of heating on the c o l o r , on the dry and wet t e n s i l e properties, on the abrasion c h a r a c t e r i s t i c s , and on the dyeing and resultant color properties of the l i n e n . We also examined the effect of heat treatment on the c r y s t a l l i n i t y of flax by wide angle X-ray scattering (WAXS) and on the surface morphology of flax fibers by scanning electron microscopy (SEM). Experimental Materials. The linen was a bleached handkerchief linen (IL-61) with a thread count of 60 χ 50 p i c k s / i n c h from T e s t f a b r i c s , Inc. A l l direct dyes were commercial grade from Aldrich Chemical C o . , while sodium sulfate was reagent grade from Mallinckrodt Chemical Co. Heat-Induced Aging. Linen samples (12 χ 4") were washed i n deionized water containing 0.1% Triton X-100 surfactant, rinsed, and a i r d r i e d . The samples were aged at 180c i n a forced draft laboratory oven for 1, 3, 5 or 10 h r s . The samples were removed from the oven and conditioned at 2!OQ and 65% RH p r i o r to t e s t i n g . Test Methods. Color differences were measured on a MacBeth MS 2000 Color Spectrophotometer using the CIELAB color system and the yellowness index ( Y I ) . Three color readings were made and averaged for each sample. Color changes are the differences between heataged and untreated linen samples and are expressed as A L * , A a * , A b * , Δ Ε , and A Y I color differences (Table I ) . Dry and wet t e n s i l e properties of yarns (measurement of f i f t y yarns for each sample) were measured using an Instron t e x t i l e tester using ASTM Method D2256 and a three inch gauge length. The r e l a t i v e changes in t e n s i l e properties for the heat aged samples compared to untreated linen are given i n Table I I . M u l t i d i r e c t i o n a l abrasion tests (five specimens for each sample) were carried out on a Universal Wear


11.

Heat-Induced Aging ofLinen

NEEDLES & NOWAK

Table I.


Heating Time (hr.) AL* 1 -6.0 3 -8.8 5 -9.5 10 -16.4 Control L* « 94.8

Table I I .

Heating Time (hr.) 1 3 5 10

161

Heat-Induced Color Changes

Aa* -1.6 -0.7 -0.1 1.9 a* - 1.75

Ab* 20.4 24.7 25.7 31.6 b* - -7.1

ΔΕ

ΔΥΙ

21.3 26.3 27.4 35.7

20.9 34.0 34.3 47.8

Relative Changes in Tensile and Abrasion Characteristics of Heat-Aged Linen

Breaking Strength Dry Wet 0.75 0.64 0.54 0.36 0.49 0.31 0.39 0.17

Elongation at Break Wet Dry 0.62 0.94 0.58 0.76 0.82 0.66 0.54 0.41

Energy to Break Wet Dry 0.50 0.65 0.21 0.38 0.18 0.35 0.07 0.27

Abrasion Dry 0.77 0.71 0.58 0.41

Abrasion Tester from Custom S c i e n t i f i c Instruments using ASTM Method D3886 (Table I I ) . Scanning electron microscopy (SEM) was performed on gold-coated samples on a ISI DS-130 Scanning Electron Microscope using a Lab 6 filament at 10 kV (Figure 1). Wide angle X-ray scattering (WAXS) of untreated and heat-aged linen was carried out on a DIAN-XRD 800 diffractometer giving 50 kV Cuk radiation at 15 raA with scanning performed from 8 to 30° at 1.6 deg/min (Figure 2). a

Dyeing Procedure. Untreated and heat-treated 1 g samples were dyed from i n f i n i t e dyebaths containing Direct Red 2, Direct V i o l e t 51, or Direct Blue 7 (Figure 3) and 20% (owf) sodium s u l f a t e . The liquor r a t i o f o r each dyeing was 100:1, and the dyeings were carried out for 1 hr. at 100°C After dyeing, the samples were thoroughly rinsed with hot water, followed by deionized water, and allowed to a i r dry prior to measurement of color differences between untreated and heat-aged samples by the method described above (Tables I I I , IV, V). Results and Discussion Color and Tensile Property Changes i n Heat-Aged Linen. On heating at 180°C from 1 to 10 hrs, the linen f a b r i c became progressively darker (-AL*), s l i g h t l y more red (+Aa*) and progressively more yellow (+Ab*) i n character. The o v e r a l l color difference (ΔΕ) and yellowness index (ΔΥΙ) progressively increased with heating time (Table I ) . The combined e f f e c t was a progressive darkening and browning of the l i n e n . Such heat-induced color changes have been observed before for linen (4) and cotton (13), at lower temperatures or shorter heating times, but f u l l characterization of the color




Figure 1. Untreated linen: a, χ 5160; and b. χ 6930. Continued on next page.


NEEDLES & NOWAK

Heat-Induced Aging of Linen


11.

Figure 1. Continued. Linen heat-treated 10 h: c, χ 6990; and d, χ 9570.


163


164


DIFFRACTION ANGLE 2 θ Figure 2.

wide angle X-ray scattering (WAXS) diffractograms - untreated l i n e n , linen heattreated f o r 10 hrs.

Figure 3.

Direct dye structures



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165

changes that occurred has not been made. The browning of the f a b r i c represents oxidation of the linen to form conjugated unsaturated structures that absorb l i g h t i n the v i o l e t and blue regions of the v i s i b l e spectra. Because of the high temperature ( 1 8 0 ° c ) and extended heating time involved (up to 10 h r s . ) i n t h i s study, i t was expected that the linen would undergo extensive degradation. This i s reflected i n the extensive loss in t e n s i l e and abrasion properties of the linen with wet t e n s i l e properties being much more severely affected than dry t e n s i l e properties (Table I I ) . Even after 1 h r . of heating, a s i g n i f i c a n t drop i n t e n s i l e properties was found with wet energy to break values being the most s e n s i t i v e - i n d i c a t o r of t e n s i l e property d e t e r i o r a t i o n . Although the heat-treated linen i s progressively more r e a d i l y abraded, the change in abrasion c h a r a c t e r i s t i c s seems to be a less sensitive indicator of l i n e n d e t e r i o r a t i o n . In summary, as the heating time increased, linen progressively decreased i n breaking strength, broke at shorter elongations, and exhibited lower energy at break and fewer cycles to abrasive f a i l u r e due to degradation. Wet t e n s i l e properties were much more affected than dry t e n s i l e properties. Losses i n the t e n s i l e strength of heat-aged linen (4) and cotton (5,10,13) were observed previously, but generally not at these levels of degradation with the exception of the work of Berry, Hersh, Tucker, and Walsh (10). Back and coworkers (6 7) using lower temperatures of heating have observed an increase in the wet t e n s i l e strength of c e l l u l o s e , a finding contrary to our study presented here for high temperature aging of linen. f

Scanning Electron Microscopy and Wide Angle X-Ray Scattering. Heataged (10 h r . ) and untreated linen samples were examined by scanning electron microscopy (SEM) (Figure 1) and wide angle X-ray scattering (WAXS) (Figure 2). Scanning electron microscopy showed that flax fibers from the untreated linen were c h a r a c t e r i s t i c of flax with periodic nodes and subtle f i b r i l l a r structure running longitudinally along the f i b e r axis (Figure l a , l b ) . Flax fibers from heat-treated (10 h r . ) linen have similar surface morphology compared to untreated linen (Figure l c , Id), but also have long and deep periodic cracks running p a r a l l e l to the f i b e r a x i s . These heat-induced cracks might be expected to increase the a c c e s s i b i l i t y of the flax fibers to dyes. WAXS diffractograms of untreated and 10 h r . heat-aged linen were the same except that the intensity of the diffractograun of heat-aged linen was less than that for untreated l i n e n . This suggests that heat aging does not p a r t i c u l a r l y affect the size and shape of c r y s t a l l i t e s i n the l i n e n , but that heating s l i g h t l y reduced the t o t a l c r y s t a l l i n i t y and s l i g h t l y increased the amorphous areas contained i n the l i n e n . Segal and coworkers (14) have shown a similar drop i n intensity of x-ray diffractograms as cotton was p a r t i a l l y d e c r y s t a l l i z e d . This i s contrary to the findings of other workers using other techniques that suggest that heating increased the c r y s t a l l i n i t y , decreased the degree of polymerization (DP), and introduced crosslinks into the cellulose (9,10,12).



166


Dyeing Properties of Heat-Aged Linen. The dyeing and resultant color properties of heat-aged linen were compared to these properties f o r untreated linen using three d i r e c t dyes of d i f f e r i n g structures (Figure 3 and Tables I I I , IV, V). Heat-treated and untreated linen dyed to medium shades with these d i r e c t dyes. However, the heat-treated l i n e n samples dyed to progressively l i g h t e r (AL*) and s l i g h t l y d i f f e r e n t shades (Aa*, Ab*) than found for untreated l i n e n . Perceptible color differences were observed (ΔΕ). Dyeing at these depths of shade e f f e c t i v e l y covered heatinduced darkening (AL*) and browning (Aa*, Ab*) of the l i n e n . Other workers have observed that heat-aged c e l l u l o s i c s dye to l i g h t e r shades than untreated c e l l u l o s i c s (5,8,13). This reduction i n dye adsorption by the heat-aged c e l l u l o s i c s has been attributed to heatinduced changes i n the a c c e s s i b i l i t y of the amorphous regions through processes such as c r o s s l i n k i n g or through actual loss of some of the amorphous regions through c r y s t a l l i z a t i o n . Table I I I .

Heating Time (hr.) 1 3 5 10 Dyed Control

AL*

1.9 2.4 3.6 4.4 L* - 35.9

Table IV.


Aa*

1.0 0.7 0.9 0.6 a* - 48.6

Ab*

0.1 0.1 -0.3 -0.1 b* - 28.2

ΔΕ

2.1 2.5 3.7 3.5

Color Changes i n Heat-Aged Linen Dyed with Direct V i o l e t 51

AL*

0.4 1.5 0.8 1.5 L* - 20.4

Table V.


Color Changes i n Heat-Aged Linen Dyed with Direct Red 2

Aa*

Ab*

0.7 0.6 0.7 1.3 a* - 9.1

-0.5 -0.1 -0.2 -0.8 b* - -8.8

Ε

Δ 0.9 1.6 1.1 2.1

Color Changes i n Heat-Aged Linen Dyed with Direct Blue 71

AL*

1.6 2.8 3.3 5.0 L* - 21.9

Aa*

Ab*

0.3 0.6 0.6 0.7 a* - 0.1

-1.4 -2.4 -2.8 -3.5 b* - -9.4

ΔΕ

2.1 3.7 4.4 6.1

As heating time increased, the linens dyed with Direct Red 2 to progressively l i g h t e r shades (+AL*) and were s l i g h t l y more red (+Aa*) i n character compared to untreated linen (Table I I I ) . The heat-aged linens dyed with Direct V i o l e t 51 to progressively l i g h t e r (+AL*) and s l i g h t l y more red (+Aa*) and blue (-Ab*) shades compared


11.

NEEDLES & NOWAK


167

to untreated l i n e n . F i n a l l y heat-treated linen samples dyed with Direct Blue 71 to progressively l i g h t e r (+AL*) and red (+Aa*) and blue (-Ab*) shades than untreated l i n e n . Samples dyed with Direct Blue 71 exhibited the greatest color differences (ΔΕ) suggesting that heat-aging lowered the number or a c c e s s i b i l i t y of dyeing s i t e s most for t h i s larger t r i a z o d i r e c t dye. These findings are consistent with the proposal that although heat aging causes a s l i g h t increase i n the amorphous content of the f l a x , crosslinking also occurs lowering the a c c e s s i b i l i t y of these dyes.


Conclusions As expected, heat-aging caused the linen to darken and brown and to undergo a reduction i n t e n s i l e and abrasion properties. Heat aging led to formation of long deep crevices l o n g i t u d i n a l l y along the f i b e r axis and passing through the nodes i n the f l a x . Although these crevices appear to increase the a c c e s s i b i l i t y and surface area of the f i b e r s , dye uptake d i d not increase. Heat-aged linen was less dyeable than untreated linen with the largest of the three dyes having less access to dye s i t e s within the heat-aged l i n e n . Although wide angle x-ray d i f f r a c t i o n suggests that there i s an apparent net increase i n the amorphous regions present within the heat-aged c e l l u l o s e , there i s a net decrease i n dyeing s i t e s available. These findings suggest that the heat-induced crosslinking within the amorphous regions of the f l a x occurs lowering the number of accessible dyeing s i t e s .

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

11. 12. 13. 14.

Cook, J . G. Handbook of Textile Fibres. I. Natural Fibres; Merrow Publishing Co., Ltd., 1984; p 4. Kleinart, T. N. Holzforschung 1977, 21, 77. Hackney, S.; Hedley, G. Stud. Conserv. 1981, 26, 1. Peacock, Ε. E. Stud. Conserv. 1983, 28, 8. Hessler, L. E . ; Workman, H. Textile Res. J . 1959, 26, 487. Back, F. L . ; Klinga, L. O. Svensk Papperstiden. 1965, 66, 745. Back, F. L . ; Didriksen, Ε. I. Svensk Papperstiden. 1969, 72, 687. Rushnak, I.; Tanczos, I. Preprint, IUPAC Symposium on Macromolecules; Helsinki, 1972; V, 127. Zeronian, S. H. In Cellulose Chemistry and Technology; Arthur, Jr., J . C., Ed., ACS Symposium Series; 1977; 48, 189. Berry, G. M.; Hersh, S. P.; Tucker, P. Α.; Walsh, W. K. In Preservation of Paper and Textiles of Historic and Artistic Value; Williams, J . C., Ed., Advances in Chemistry Series; 1977, 164, 228. Shafizadeh, F.; Bradbury, A. G. W. J . Appl. Polym. Sci. 1979, 23, 1431. Lewin, M.; Guttmann, H.; Derfler, D. J . Appl. Polym. Sci. 1982, 27, 3199. Brushwood, D. E. Textile Res. J . 1988, 58, 309. Segal, L . , Creely, J . J., Martin, J r . , A. E . ; Conrad, C. M. Textile Res. J . 1959, 19, 786.

RECEIVED January 24,1989


Historic Textile and Paper Materials II - American Chemical Society

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