Historic Textile and Paper Materials - American Chemical Society

23 Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on June 17, 2016 | http://pubs.acs.org Publication Date: February 1, 1986 | doi: 10.1021/ba-1986-0212.ch023

Accelerated Aging of Cellulosic Textiles at Different Temperatures The Effect of Tetrahydridoborate Reduction Ira Block and Hye Kyung Kim Department of Textiles and Consumer Economics, University of Maryland, College Park, MD 20742 Measurements of tear strength and color change were made on a set of cotton cloths to study the rates of degradation under accelerated aging in a dry oven at temperatures ranging from 100 to 150 °C. Fabrics treated with either sodium or tetramethylammonium tetrahydridoborates were degraded at rates about one-half that of untreated controls. These results were consistent over the temperature range. Calculation of the activation energy (E ) by different methods showed E = 25.5 ± 1.5 kcal, in keeping with measurements made by others at lower temperatures. a

a

DIUM TETRAHYDRIDOBORATE, first used as a reducing agent for carbonyl species by Chaikin and Brown (I ) in 1949, was shown to be effec tive as a reducing agent for the aldehyde groups in polysaccharides in 1952 (2) and was reported to be effective in stabilizing oxycellulose in 1953 (3). Head (4), in 1955, studied the use of NaBHLt on both oxycellu lose and hydrocellulose and showed that a dilute, unbuffered solution was highly effective in removing aldehydes and stabilizing the materials. In 1965, Varshney and Luner (5) reviewed the literature on the use of NaBHi and other tetrahydridoborates in the manufacture of paper and discussed their use as bleaching agents and their ability to stabilize pulps against both alkaline and acidic treatments. In 1980, Tang et al. (6) and in 1982, Burgess (7) reported results of investigations on the use of tetra hydridoborates for paper conservation. Only very recently, however, has tetrahydridoborate reduction been considered to be more than just a bleaching method in the conservation of cellulosic textiles and paper. To some extent, the delay in studying the 0065-2393/86/0212-0411$06.00/0 © 1986 American Chemical Society

Needles and Zeronian; Historic Textile and Paper Materials Advances in Chemistry; American Chemical Society: Washington, DC, 1986.

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on June 17, 2016 | http://pubs.acs.org Publication Date: February 1, 1986 | doi: 10.1021/ba-1986-0212.ch023

412

HISTORIC T E X T I L E A N D PAPER MATERIALS

use of the reduction process was due to the belief that carboxylic acids, formed during the oxidation of cellulose, were the major cause of its decay. Block (8, 9), however, demonstrated that although deacidifica tion and buffering with an alkaline material were useful in extending the lifetime of new cellulosic textiles, the treatment was no more effective than rinsing in deionized water for protecting aged textiles. That carboxylic acid groups on the cellulosic chain play a minor role in the decay of the material is not surprising. As Davidson and Standing (10) and Davidson and Nevell (11) showed, acidic oxycelluloses are unstable because the carboxylic acids are converted to water-soluble, low molecular weight species. Thus, in old cellulosic textiles, the acidic species are removed from the fabric upon washing, and deacidification is not necessary. Kerr et al. (12) and more recently Hackney and Hedley (13) have provided independent evidence of the correctness of this view. Paper that has been subjected to sulfite pulping or that contains alum or rosin, which may form acids, responds well to deacidification because the additives are being neutralized. If the carboxylic acids on the cellulosic chain are not the major cause of the thermooxidative decay of old cellulosic textiles, one must consider the carbonyl species, particularly the aldehydes on the C and Qj carbons. Nikitin (14) noted that "the primary autoxidation process is a reaction of molecular oxygen with aldehyde groups, which initiates a chain reaction resulting in more profound changes and decomposition of the molecule". Thus, reduction of the aldehyde groups should lead to improved stability of degraded cellulose. In aqueous solution, tetrahydridoborates decompose as follows: 2

MBH4 + 2 H 0 — M B 0 + 4H 2

2

S

(1)

whereas the carbonyl species in cellulose are reduced according to the following reaction: C(=0)R + H - ^ H C ( O H ) R 2

(2)

In this chapter, we report the results of a study on the use of tetrahydridoborate reduction in improving both the color and strength reten tion of cotton fabric artificially aged at temperatures ranging from 100 to 150 °C.

Experimental Fabric. The fabric used in this work was a plain weave, 80 X 80 cotton print cloth weighing about 100 g/m (Testfabrics, No. 400). The fabric was twice laundered and dried according to the American Association of Textile Chemists and Colorists (AATCC) Test Method No. 124-1978. 2



23.

BLOCK A N D KIM

Accelerated Aging of Cellulosic Textiles

413

Tetrahydridoborate Treatment. Both 98%-pure NaBH4 and 95%-pure tetramethylammonium tetrahydridoborate (TMA) were supplied by Alfa Products. Solutions (0.03 M) were prepared by adding weighed amounts of the solid to deionized water and diluting the solution to 1 L in a volumetric flask. After dissolution, the liquid was transferred to a shallow glass tray maintained at 25 °C in a water bath. Nine specimens of cloth cut to 10 X 10 cm and weighing about 9 g in toto were placed in the tray and allowed tofloatin the solution. Preliminary experiments showed that the results of the testing were not changed by soaking for periods longer than 20 min, nor was prewetting in water necessary. All samples were treated for 20 min. Control samples were soaked in deionized water at 25 °C for 20 min. Following soaking, samples were rinsed with deionized water, squeezed gently, and allowed to air dry overnight on glass-fiber screens. All samples were stored in desiccators over silica gel prior to accelerated aging. Accelerated Aging. Samples were removed from the desiccators and placed on glass-fiber screens in a forced-draft oven at the required temperature. Upon removal from the oven, samples were collected in a desiccator and then were transferred to a conditioned laboratory for testing. Mechanical Testing. Tensile strength tests were performed with an Instron tensile tester as per the American Society for Testing and Materials (ASTM) D-1682, and tear testing was done with an Elmendorf apparatus as per ASTM D-1424 at 21 °C and 65% rh, after conditioning the specimens for at least 24 h. Results reported are the average of three tests. Color Measurements. Color measurements were made on the samples with a Hunterlab model D25D2 color difference meter after conditioning. A white standard plate was used as a backing. Both fronts and backs of the cloths were measured three times, and the results were averaged. Color differences are reported in the LAB system.

Results and Discussion Initial measurements of tensile strength and extension at break were erratic, as were calculations of energy to break. This problem led to an investigation of the correlation between tensile and tear testing; the results are shown in Figure 1. This figure demonstrates that the tensile strength of the cloth is not sensitive to baking time until tear strength has dropped below about 70% of the initial value. For cloths degraded beyond this point, a linear relationship exists between tensile and tear strengths. These results are analogous to those reported by Graminski et al. (15) for the tensile strength and folding endurance of paper. Their results showed that folding endurance was a more accurate measure of the degradation of the material. Furthermore, as noted by Taylor (16), . . in contrast to the role of tensile strength, tearing strength is directly involved in the assessment of serviceability" of cotton fabrics. Thus, because tear strength is more closely related to the performance of the cloth in actual use, and because it proved to be more sensitive to treat-



414


o

1 ο

ι

I 20

1

ι 40

I

1 60

i

1 80

1

ί 100

PERCENT TEAR STRENGTH RETAINED

Figure 1. Comparison of strength retention by tear and tensile methods. Numbers in parentheses refer to baking time at ISO °C. ment of the fabric than tensile strength, mechanical testing is reported in terms of this parameter. Because changes in the relative humidity of the oven could affect the results, a study of the change in degradation rate as a function of relative humidity was conducted. Moisture was added to the air in the oven by permitting deionized water to seep through eight tubes perfo rated by 1-mm diameter holes along their length into a large shallow reservoir at the bottom of the oven. By adjusting the rate of water flow, the relative humidity could be controlled. The relative humidity was measured by use of wet-and dry-bulb thermometers and a psychrometric chart. The results, which are shown in Figure 2, indicate that the effect of relative humidity at 150 ° C is small. (For further discussion of temperature and humidity effects in accelerated aging, see Reference 19). A typical degradation curve for new and aged cloth is shown in Figure 3. This figure demonstrates that a T M A treatment is effective in slowing the rate of strength loss, even for cloth that has been artificially degraded to less than 60% strength retention. In addition, as shown in



23.

BLOCK A N D KIM


415

Figure 2. Percent strength retained vs. baking time for cotton fabric at 150 °C and varying relative humidity. Key: •, 1% rh (0.02 g/g);0> 2% rh (0.08g/g);0,10%rh(0.5 g/g). Figure 4, the cloth is significantly whitened by the reduction treatment, and the more degraded it is, the greater the improvement in color. Treatment with NaBHi shows a similar pattern. The rates of degra dation of new cloth at temperatures ranging from 150 to 100 ° C are shown in Figures 5-8. The plots are based on a statistical model that assumes first-order kinetics for depolymerization (17). They show that, in all cases, the treated fabric has been protected against thermooxidative degradation. Furthermore, the fact that the curves exhibit a linear portion indicates that strength loss is following first-order kinetics and may mean that changes in the mechanical properties are directly propor tional to changes in the chemical state of the system. Examination of Figure 5 shows that degradation in the early stages is linear with time but occurs at a rate somewhat higher than the rate of degradation found at later times. This phenomenon is observed at temperatures down to 120 °C. Apparently we are observing at least two phenomena, one in which the cellulosic chains are readily broken, and one in which the chains are more resistant to thermooxidative attack. It is not necessarily true that these results indicate different chemical mechanisms at work. Consider the model described by Rowland et al. (18) in which cellulose is a somewhat defective crystal composed of



416


30

|~~ ι Μ ι ι I ι Μ ι ι 1 ι ι I 0

20

40

60

80

100

Baking Time at 150 C (hr)

Figure 3. Strength retention vs. baking time for water-washed and TMAtreated cotton. Key: O, new (untreated); Δ, baked 8 h (TMA treated); •, baked 48 h (TMA treated).

many disordered regions. We can postulate that the same chemical mechanisms are at work, but that they proceed at a much faster pace in the disordered regions than in the well-ordered regions. If this hypothe sis is true, then as cellulosic fabrics age, their rate of degradation should continually decrease as less and less disordered material is available for reaction. Thus, we should find that cellulosic fabrics degrade to some point, and in the absence of mechanical forces, such as handling and rapid changes in humidity, they should hardly seem to degrade further. This situation may account for the longevity of ancient cloths, such as Egyptian burial garments, and may also indicate that very ancient cello-



23.


BLOCK A N D KIM

0

J

l_J_l 20

1

I

40

LU

1

60

I

I

80

I

417

LU 100

Baking Time at 150 C (hr)

Figure 4. Color change vs. baking time for water-washed and TMAtreated cotton. Key: O, new (untreated); Δ, baked 8 h (TMA treated); •, baked 48 h (TMA treated). losic textiles do not require chemical treatment. A second consequence of this model—that old cellulosic textiles should be more crystalline than new ones—is well documented. In Figure 8 we see another phenomenon occuring that was not evi dent in the work done at higher temperatures. The time scale here is much extended. In the beginning, the fabric seems to increase in tear strength before undergoing any losses. Once again the NaBHrtreated material performs better than the water-washed material. We are likely observing a slow rearrangement of the morphology of the cellulosic


418



0.08H

θ

80

40

60

100

8 6

BAKING T H E

180

140

IN HOURS

Figure 5. Aging of cotton fabric at 150 °C. Key: •, untreated; O, treated with 0.05% NaBH . 4

0 . 0 8 H 0 . 0 ? i

ς•tocH I

0.060.05"

0

8 0

4 0

6 0

8 0

1 0 0

1 2 0 1 4 0

BAKING TINE IN HOURS

Figure 6. Aging of cotton fabric at 140 °C. Key: 0, untreated; O, treated with 0.05% NaBH . 4



23.

BLOCK A N D KIM

" Ί '

80

419


" Ί '

1

40

I"" 60

I 80

τγτ

1

100

120

"-ΗΓ

"•1"' 140

160


Figure 7. Aging of cotton fabric at 120 °C. Key: ·, untreated; O, treated with 0.05% NaBH . 4

'"»"••

100

300

ι

»

300

400

'

•" ι· ·

1

500

600

700

800


Figure 8. Aging of cotton fabric at 100 °C. Key: •, untreated; •, treated with 0.05% NaBH . 4



420


chains within the fiber that leads to a reduction in internal stress and a concomitant increase in tear strength, although a restructuring of the yarns during thermal treatment is not impossible. This stress reduction occurs along with degradation, and in the early life of the fabric it leads to some improvement in mechanical properties. It is, however, soon sur passed by the deteriorating effects of depolymerization, so only at the lower temperatures is the phenomenon observed. At ambient conditions the molecular rearrangement is likely to be so slow that depolymeriza tion is the overwhelming process. Figure 9 is an Arrhenius plot of the results of the accelerated aging of new fabric at different temperatures. Regardless of the properties measured, long-term strength retention and short-term strength retention or color change (the slopes) for both treated and untreated cloth fell within the range of 25.5 ± 1 . 5 kcal/mol; no statistically significant differ ence between the highest and lowest values at the 0.05 or the 0.1 confi dence levels was found. These results are in excellent agreement with the literature (19) and show that the reaction mechanisms do not change over the temperature range from 100 to 150 °C. Tables U V summarize the preceding results in terms of the ratios of tetrahydridoborate-treated to water-washed cloth for color change and strength retention. Table I shows that the T M A treatment does little to affect the change in color of new or slightly degraded cloth, but it is quite effective for those cloths that have been aged significantly. Table II yields similar conclusions for NaBHt, although NaBHt does not appear to do as well as T M A . This result indicates that extremely long

0.002300

0.002375

0.002450

0.002525

0.002600

0.002675

1/T

Figure 9. Arrhenius plot for cotton fabric. Key: —, treated with NaBHé; , untreated; O , long-term strength retained; •, color change; Δ , short-term strength retained; O , 1/(percent strength retained).



— — —

-0.8 1.6

0.2

— — .— —

8

0

— —

-0.8 1.0 0.3

16

—

-3.7 1.0 2.5 3.6

24

—

-1.0 2.7 3.8

32

—

— 4.3 5.0

— —

-1.8

, 1.9 3.7

48

40

Total Baking Time (hours)

3.0

— —

-1.0

56

1.0

—

— 1.6

,

64

1.5 1.0

— .—

72

— 1.0

—

96

N O T E : Values are the differences in color change at 150 °C between new cloth that was washed with water and new cloth that was treated with TMA. Negative values mean that the water-washed cloth was less discolored than the treated cloth.

0 8 16 24 48

Prebake Time (hours)

Table I. Color Change: TMA-Treated Versus Water-Washed Cloths


422


Table II. Color Change: NaBH4-Reduced Versus Water-Washed Cloths Baking Baking Temperature ("C ) Time (hours)


150

4 10 16 24 48 8 16 24 48 96 144 16 24 96 144 200 400 800

140

120

100

Color-Change Difference" -5.6 -8.7 -6.9 -7.0 -11.0 0.0 -0.9 -1.3 -1.0 -2.4 -2.6 1.1 1.0 0.0 0.0 0.0 -0.1 -0.1

Values are the differences in color change between new cloth that was washed with water and new cloth that was treated with NaBFL}. Negative values mean that the water-washed cloth was less discolored than the treated cloth.

a

aging times are required at lower temperatures before the results manif est themselves. Table III shows that the reduction treatment does signif icantly improve strength retention for older fabrics and is also useful for new ones, whereas Table IV indicates that NaBKU may be more benefi cial than T M A .

Conclusions Tetrahydridoborate reduction of cellulosic textiles improves color and strength retention. N a B H appears to give better strength retention, whereas T M A seems superior in color retention. These results are inde pendent of baking temperatures over the range from 100 to 150 ° C , and humidity effects are small at elevated temperatures. 4

Acknowledgments We wish to acknowledge the help of R. V . Kuruppillai in performing some of the experiments, the enlightening conversations with B. F. Smith, and the generous financial support of the National Museum Act, administered by the Smithsonian Institution.



NOTE:

— —

1.03 — —

0

:

:

— —

1.12 1.01 —

8

— —

1.21 1.23 1.05

16

—

1.18 1.18 1.09 1.10

24

—

— 1.26 1.12 1.16

32

—

— — 1.04 1.15

40 1.15 — — 1.20 1.07

48

— 1.02

— 1.33 —

56

Total Baking Time (hours)

— 0.94

— 1.24

64

— — — 1.35 1.19

72

— — — — 1.30

96

Values are the percent-strength-retained ratios at 150 °C of cotton cloth treated with TMA to cotton cloth washed with water.

0 8 16 24 48

Prebake Time (hours)

Table III. Percent Strength Retained; TMA-Treated Versus Water-Washed Cloths


424

HISTORIC T E X T I L E A N DPAPER MATERIALS

Table IV. Percent Strength Retained: NaBH -Reduced Versus Water-Washed Cloths 4

Baking Baking Temperature (°C) Time (hours)


150

140

120

100

4 10 16 24 48 8 16 24 48 96 144 16 24 96 144 200 400 800

Percent-StrengthRetained Ratio 0

0.90 0.94 1.67 2.05 2.12 1.11 1.29 1.33 1.41 1.76 1.93 1.40 1.55 1.89 2.14 1.07 1.49 1.89

Values are the percent-strength-retained ratios of cotton cloth treated with NaBÎLt to cotton cloth washed with water.

a

Literature Cited 1. Chaikin, S. W.; Brown, W. G. J. Am. Chem. Soc. 1949, 71, 122. 2. Abdel-Akher, M.; Hamilton, J. K.; Montgomery, R.; Smith, F. J. Am. Chem. Soc. 1952, 74, 4970. 3. Meller, A. TAPPI 1953, 36, 366. 4. Head, F. S. H. J. Text. Inst. Trans. 1955, 46, T400. J. Text. Inst. Trans. 1955, 46, T584. 5. Varshney, M. C.; Luner, P. TAPPI 1961, 44, (44), 285. 6. Tang, L.; Troyer, Μ. Α.; Williams, J. C. Prepr. of the Sixth Annu. Conf., IIC—Canadian Group, Ottawa, July 1980. 7. Burgess, H. D. Prepr. Tenth Annu. Meet. of the AIC, Milwaukee, May, 1982. 8. Block, I. J. Am. Inst. Conserv. 1982, 22, 25. 9. Block, I. Prep. of the Contributions to the Wash. Congr. of the IIC, Sep tember, 1982. 10. Davidson, G. F.; Standing, H. A. J. Text. Inst. Trans. 1951, 42, T141. 11. Davidson, G. F.; Nevell, T. P. J. Text. Inst. Trans. 1956, 46, T439. 12. Kerr, N.; Hersh, S. P.; Tucker, P. Α.; Berry, G. M. In "Durability of Macromolecular Materials"; Eby, R. K., Ed. ACS SYMPOSIUM SERIES No. 95; American Chemical Society: Washington, D.C., 1979; p. 25. 13. Hackney, S.; Hedley, G. Prepr. of the Seventh Triennial Meet, of the ICOM Comm. for Conserv. Copenhagen, September, 1984. 14. Nikitin, Ν. I., In "The Chemistry of Cellulose and Wood"; J. Schmorak, Trans., Israel Program for Scientific Translations: Jerusalem, 1979; p. 171.



23.

BLOCK A N D KIM


425

15. Graminski, E. L.; Parks, E. J.; Toth, Ε. E. In "Durability of Macromolecular Materials"; Eby, R. K., Ed.; ACS SYMPOSIUM SERIES No. 95, American Chemical Society: Washington, D.C., 1979. 16. Taylor, H. M. J. Text. Inst. Trans. 1959, 50, T161. 17. Jellinek, H. H. G. In "Aspects of Degradation and Stabilization of Poly mers"; Elsevier: New York, 1978; p. 2. 18. Rowland, S. P.; Nelson, M. L.; Welch, C. M.; Hebert, J. J. Text. Res. J. 1976, 46, 194. 19. Block, Ira Prepr. of the Seventh TriennialMeet.of the ICOM Comm. for Conserv., Copenhagen, September, 1984. RECEIVED

for review November 26, 1984.

ACCEPTED

March 13.


Historic Textile and Paper Materials - American Chemical Society

Recommend Documents