17 Reaction of Formaldehyde Vapor with Water-Wetted Wool S. M. AL-KHAYATT , H. L. NEEDLES, S. A. SIDDIQUI, and S. H. ZERONIAN 1
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Division of Textiles and Clothing, University of California, Davis, CA 95616
Wool wetted with water at 80% wet pick up was reacted with gaseous formaldehyde f o r 0.25 to 2 hours, at 23, 60 and 80°C. In the absence of catalysts formaldehyde reacted rapidly with wool at all temperatures with the most rapid reaction occurring at 60°C. Although the reaction proceeded at a slower rate at 23°C, maximum improvement i n wet wrinkle recovery and f e l t i n g shrinkage with a minimum reduction i n t e n s i l e properties occurred at t h i s temperature. The color of the wool was unaffected by formaldehyde treatment. The formaldehydetreated wools were yellowed by a f i l t e r e d xenon plasma arc at the same rate as untreated wool and the face and back of the wool fabrics yellowed to similar degrees. Nevertheless, dyeing studies and scanning electron microscopy demonstrated that even b r i e f formaldehyde treatment protected the wool from light-induced weathering. The reaction of aqueous solutions of formaldehyde with wool keratin has been investigated by a number of workers (1-7). Introduction of crosslinks into wool by formaldehyde treatment was postulated i n these studies, but l i t t l e direct evidence f o r crosslinking was found. Mason (5) has presented physical e v i dence f o r formation of crosslinks as methylene groups i n wool. Such crosslinks would be expected to increase the i n t e r n a l v i s cosity within the f i b e r , thereby decreasing the rate at which setting i s l o s t i n hot water. This hypothesis was tested by Caldwell et a l . (8) who compared the crease recoveries of wool fabrics treated with aqueous formaldehyde or formaldehyde vapors with those of untreated f a b r i c s . They found that the treatments enhanced the set through introduction of crosslinks that i n h i b i ted the rearrangement of disulphide bonds i n the wool. Kann (9,10) noted that formaldedye treatment protected wool against a l k a l i 'Current address: Department of Mechanical Engineering, University of Baghdad, Iraq.
0097-6156/ 84/0260-0281 $06.00/ 0 © 1984 American Chemical Society
Arthur et al.; Polymers for Fibers and Elastomers ACS Symposium Series; American Chemical Society: Washington, DC, 1984.
Baghdad,
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damage. Such treatment subsequently was used i n scouring, bleaching and dyeing processes to protect wool against chemical attack. Reaction of wool with formaldehyde vapor rather than with aqueous formaldehyde would be preferred since treatment i n the vapor state would have less effect on the desirable properties of wool. Previous studies (8-13) have shown that formaldehyde vapor treatment improved selected properties of wool. Morris and Molvig (11) exposed wool yarns to formaldehyde vapor at 25 to 80°C under yarn extensions of 0 to 40% at moderate humidities. They found that maximum formalization occurred at 50°C with l i t t l e further e f f e c t occurring at temperatures higher than t h i s . Tension on the yarns had very l i t t l e e f f e c t on the rate or degree of formalization of the wool. The wool yarns treated with formaldehyde vapor showed s l i g h t l y decreased breaking strength, major decreases i n elongation at break, and greatly reduced a l k a l i s o l u b i l i t i e s compared to control wool yarns. T r e z l and coworkers (12,13) studied vapor phase formaldehyde treatment of wool under vacuum. Treatments were conducted at 60 to 100°C using no catalyst or formic acid, trimethylamine, triethylamine, 15-crown-5-ether and 18-crown-6-ether as catalysts. In their system, the presence of water vapor was found to i n h i b i t the rate of formaldehyde uptake. They found that more s i t e s were attacked by formaldehyde vapor than by aqueous formaldehyde. Optimum reaction rates were observed at 70 to 80°C, and formic acid was found to be the most e f f e c t i v e catalyst of those used. Scanning electron microscopy (SEM) did not reveal any scale damage to the wool. The treated wool was more thermally r e s i s t a n t , and no change i n hand or d y e a b i l i t y of the wool was found. The treated wool had improved t e n s i l e strength and i n i t i a l modulus with l i t t l e change i n elongation at break. In a comprehensive study (14), formaldehyde vapor treatment of wool was very c a r e f u l l y examined by c o n t r o l l i n g treatment temperature, water content of the wool, and formaldehyde vapor concentration. Even short periods of formaldehyde treatment produced large decreases i n a l k a l i s o l u b i l i t y and supercont r a c t i o n . Addition of acid or base catalysts or swelling agents and thorough drying of the wool reduced the e f f e c t , whereas treatment temperatures of 80-100°C, high humidities, and high formaldehyde concentration increased the rate of reaction. The amino groups were shown to be involved i n the crosslinking reaction with formaldehyde, whereas the tyrosine groups were not. Also the properties of reduced wool could be p a r t i a l l y restored through formaldehyde vapor-treatment. The t e n s i l e properties of formaldehyde vapor-treated wools were less affected than control wool by treatment with acids, a l k a l i s , or swelling agents. Prolonged formaldehyde treatment of the wool led to reduced abrasion resistance compared to untreated wool. Formaldehyde crosslinking of wool was e f f e c t i v e i n setting reduced or annealed wools, and a l k a l i , heat and sunlight-induced yellowing of wool was reduced by formaldehyde treatment, presumably through blocking of amino and tryptophan groups. The dyeing properties of the wools and the lightfastness of the dyed wools were only s l i g h t l y affected by formaldehyde treatment. There are no reports i n the
Arthur et al.; Polymers for Fibers and Elastomers ACS Symposium Series; American Chemical Society: Washington, DC, 1984.
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l i t e r a t u r e examining the rapid reaction of high levels of formaldehyde vapor with water-wetted wool substrate. Recently we have treated prewetted wool f a b r i c s with formaldehyde vapor under nitrogen i n the temperature range from 23 to 80°C using very high concentrations of formaldehyde vapor. The effect of rapid reaction of high levels of formaldehyde with water-wetted wool on the properties of the treated wools were examined including t e n s i l e properties (dry and wet), wrinkle recovery (dry and wet), a l k a l i s o l u b i l i t y , f e l t i n g shrinkage, color, dyeing c h a r a c t e r i s t i c s , and weathering due to simulated sunlight.
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Experimental Materials and Reagents. The fabric used was a 1 x 1 p l a i n weave worsted wool f a b r i c (style #6561) i n the ready to dye state obtained from Burlington Industries. Other chemicals and dyes used i n the study were reagent grade materials from A l d r i c h Chemical Company and used without further p u r i f i c a t i o n . Formaldehyde Treatment. Wool samples (12 x 5 cm) were prewetted i n d i s t i l l e d water containing 0.1% sodium l a u r y l sulfate f o r 10 minutes. The samples were passed through a laboratory pad to remove excess water leaving 80% water uptake and then fixed to a fiberglass screen designed to conform to the inside contour of a 2 l i t e r resin k e t t l e with v e r t i c a l walls. After the mounted wool sample was placed i n the reaction v e s s e l , the top of the reaction vessel was covered with a f i t t e d glass top containing gas i n l e t and exit tubes and a humidity sensing device. Formaldehyde vapor was introduced into the reactor by passing nitrogen gas through a solution of 30% formaldehyde i n a bubbler heated at 70°C at a rate of 5 cc/sec and into the reactor f o r a period of 15 to 120 minutes. The reactor was maintained at 23°, 60° or 80°C. After formaldehyde treatment, nitrogen was passed through the reactor for 15 minutes to remove unreacted formaldehyde vapor. The f a b r i c s were removed from the apparatus and conditioned (21°C, 65 RH) p r i o r to testing and analysis. Testing Procedures. The t e n s i l e properties of dry and wet warp yarns from control and treated samples were measured by ASTM D2256-66T on an Instron Tensile Tester, Model TM using a gauge length of 3 inches and a rate of extension of 33% per minute (Table I ) . Wrinkle recovery (dry and wet) values were determined by AATCC test method 66-1978 (Table I I ) . The f e l t i n g shrinkage and a l k a l i s o l u b i l i t i e s were determined by the methods outlined by Haron (14) (Table I I ) . Weathering Procedures. Samples (7 x 12 cm) of untreated and formladehyde-treated wools were exposed to simulated sunlight weathering i n an Atlas Weather-ometer, Model Ci35W equipped with a f i l t e r e d xenon arc. The samples were i r r a d i a t e d continuously for 168 hours t o t a l with 18 minute water spray following every 102 minutes of i r r a d i a t i o n throughout the cycle. The f a b r i c surface received 0.67 w/m i r r a d i a t i o n at a black panel temperature of 63°C and 45% RH during the i r r a d i a t i o n .
Arthur et al.; Polymers for Fibers and Elastomers ACS Symposium Series; American Chemical Society: Washington, DC, 1984.
Arthur et al.; Polymers for Fibers and Elastomers ACS Symposium Series; American Chemical Society: Washington, DC, 1984.
15 30 60 120
15 30 60 120
15 30 60 120
23 23 23 23
60 60 60 60
80 80 80 80
Treatment Temp. (°C) Time (min)
0.82 0.75 0.74 0.74
0.80 0.73 0.73 0.77 0.80 0.83 0.77 0.77
0.77 0.70 0.70 0.67 0.82 0.78 0.72 0.74
0.97 0.95 0.98 1.03 1.02 1.03 1.05 0.98
0.89 0.82 0.74 0.81
0.86 0.84 0.84 0.88
0.83 0.83 0.83 0.87
Rel. Elong. at Break Dry Wet
0.77 0.81 0.76 0.81
1.01 0.99 1.01 0.97
Rel. Breaking Strength Dry Wet
0.79 0.86 0.78 0.72
0.73 0.64 0.68 0.70
0.81 0.75 0.84 0.72
0.78 0.73 0.66 0.70
0.73 0.62 0.63 0.59
0.73 0.77 0.71 0.79
Rel. Energy to Break Dry Wet
TABLE I. Relative Tensile Properties of Formaldehyde and Untreated Wool Warp Yarns
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Reaction of Formaldehyde with Wool
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