Water in Polymers - American Chemical Society

31 Glass Transition Temperature of Wet Fibers Its Measurement and Significance

Downloaded by UNIV OF MICHIGAN ANN ARBOR on February 18, 2015 | http://pubs.acs.org Publication Date: August 19, 1980 | doi: 10.1021/bk-1980-0127.ch031

JOHN F. FUZEK Tennessee Eastman Co., Kingsport, T N 37662

When a polymer i s heated t o a temperature above i t s m e l t i n g p o i n t (T ) , the c r y s t a l l i t e s of the polymer melt, and an abrupt change i n volume occurs. Since m e l t i n g i n v o l v e s a d i s c o n t i n u i t y i n a primary thermodynamic v a r i a b l e (volume) , m e l t i n g can be considered a f i r s t - o r d e r t r a n s i t i o n . At temperatures above i t s m e l t i n g p o i n t , the polymer i s a l i q u i d , and the slope of the l i n e AB shown i n F i g u r e 1 i s the c o e f f i c i e n t of thermal expansion f o r the melt. When a molten amorphous polymer cools t o a temperature below i t s m e l t i n g p o i n t , the polymer behaves as a rubber (BE) u n t i l the g l a s s t r a n s i t i o n temperature (T ) i s reached. Below t h i s temperature, the polymer behaves as I g l a s s (EF). I f a polymer c r y s t a l l i z e s , the path BCD i s followed. The c r y s t a l l i z a t i o n i s not sharp, however, and both s o l i d and l i q u i d phases are present between Β and C; so the m e l t i n g p o i n t must be d e f i n e d as a break i n the curve. For a t r u l y c r y s t a l l i n e s o l i d , the path ABGCD i s followed. For p r a c t i c a l polymers, the c r y s t a l l i z a t i o n i s u s u a l l y f a r from complete, and a t r a n s i t i o n r e g i o n BE F' i s observed as a temperature range s i m i l a r t o that f o r the amorphous polymer (BEF). The evident i n t e r p r e t a t i o n of t h i s phenomenon i s that a g l a s s t r a n s i t i o n has occurred i n the amorphous p o r t i o n of a s e m i c r y s t a l l i n e polymer ( 1 ) . The g l a s s t r a n s i t i o n i s a second-order t r a n s i t i o n caused by r e l a x a t i o n of the chain segments i n the amorphous p o r t i o n of the polymer. I t i s a t that temperature, Τ , that a n o n c r y s t a l l i n e polymer changes from a g l a s s y s o l i d t o ^ a rubbery l i q u i d . In terms of s t r u c t u r e , Τ i s g e n e r a l l y considered to represent the beginning of motion i 8 the major segments of the backbone mole c u l a r chain of a polymer. The temperature at which t h i s t r a n s i t i o n occurs i s of great p r a c t i c a l importance, s i n c e i t determines the s p e c i f i c u t i l i t y of a polymer. The wide use made of the term g l a s s t r a n s i t i o n temperature to c h a r a c t e r i z e polymer g l a s s e s i m p l i e s that there i s a w e l l d e f i n e d temperature that r e l a t e s to a f r e e z i n g p o i n t and at which a substance transforms d i s c o n t i n u o u s l y from l i q u i d to rubber to g l a s s . A c t u a l l y , the v a l u e found f o r Τ depends not only on the nature of the substance but a l s o on the method of determination, f

g

0-8412-0559-0/ 80/47-127-515505.00/ 0 © 1980 A m e r i c a n Chemical Society

In Water in Polymers; Rowland, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.


516

WATER

IN P O L Y M E R S

s i n c e the measured value i s r a t e dependent (2). F o r a t y p i c a l d i l a t o m e t r i c t e s t , the time i n v o l v e d (hours) i s long enough t o g i v e a v i r t u a l l y s t a t i c value; that i s , i n c r e a s i n g the time s c a l e by an order of magnitude has l i t t l e e f f e c t on the measured Τ value. Other methods, such as c a l o r i m e t r i c and dynamic meth§ds, are c a r r i e d out a t much f a s t e r r a t e s and can give Τ values s i g n i f i c a n t l y d i f f e r e n t from those obtained i n a d i l a t o m e t r i c test. Many f a c t o r s are known t o i n f l u e n c e Τ v a l u e s : pressure, c r y s t a l l i n i t y , molecular weight, m o l e c u l a r b r a n c h i n g , c r o s s l i n k ing, copolymerization, the presence of monomer, and the presence of a low-molecular-weight l i q u i d or p l a s t i c i z e r (3-11). Almost a l l f i b e r s are composed of polymeric m a t e r i a l s . However, the c r y s t a l l i n i t y and the molecular o r i e n t a t i o n of the polymeric m a t e r i a l i n a f i b e r d i f f e r from those of the bulk polymer from which the f i b e r i s made. Hence the Τ of a f i b e r may be s i g n i f i c a n t l y d i f f e r e n t from that of a bulk polymer. An i n c r e a s e i n c r y s t a l l i n i t y g e n e r a l l y i n c r e a s e s Τ by 5 t o 15°C, and an i n c r e a s e i n molecular o r i e n t a t i o n g e n e r a l l y Increases Τ by 3 to 12 C. However, these i n c r e a s e a r e not d i r e c t l y a d d i t i v e . For example, a h i g h l y c r y s t a l l i n e and o r i e n t e d p o l y e s t e r f i b e r made from p o l y ( e t h y l e n e t e r e p h t h a l a t e ) , PET, w i l l have a Τ about 15°C higher than that of the amorphous bulk polymer. In c o n t r a s t t o bulk polymers, which g e n e r a l l y contain l i t t l e or no water, almost a l l f i b e r s absorb some water when conditioned at normal atmospheric temperature and humidity. The presence of t h i s moisture can r e s u l t i n a s u b s t a n t i a l lowering of the Τ . For example, p o l y ( v i n y l a l c o h o l ) f i b e r has a bone-dry Τ of 85°C, but the Τ of the f i b e r a t i t s e q u i l i b r i u m moisture r e g l i n of 6% i s about § l C ( 1 2 ) . Hence, 6% water reduces the Τ by 64°C. Very l i t t l e work has been reported on the Τ of wet f i b l r s (13-18). g

e

g

g

e

Experimental Samples of s e v e r a l f i b e r s were obtained f o r t h i s i n v e s t i g a t i o n . P o l y ( e t h y l e n e t e r e p h t h a l a t e ) and p o l y ( c y c l o h e x y l e n e d i methylene terephthalate) (PCHDMT) were commercial Kodel p o l y e s t e r f i b e r s ; the PET f i b e r s were filament p o l y e s t e r , whereas the PCHDMT f i b e r s were taken from tow before i t was cut i n t o s t a p l e . The p o l y ( l , 4 - b u t y l e n e terephthalate) (PBT) f i b e r s were experimentally spun. The nylon 6,6, Oiana nylon, and Otflon a c r y l i c were Du Pont commercial f i b e r s . The nylon 6 was A l l i e d Chemical commercial f i b e r . The V e r e l modacrylic and Estron acetate f i b e r s were Eastman commerical m a t e r i a l s . The Rhovyl v i n y l was Rhodiaceta commercial f i b e r . The s i l k was a commercial, degummed yarn. For the determination of wet Τ s , the f i b e r s were allowed to soak i n d i s t i l l e d water f o r 24 h? before t e s t i n g . T e n s i l e t e s t i n g was c a r r i e d out on an I n s t r o n t e s t e r w i t h the f i b e r s t o t a l l y immersed i n water a t the s p e c i f i e d temperature. T e s t i n g was c a r r i e d out a t 0, 10, 23, 30, 40, 50, 60, 70, 80, 90, f


31.

FUZEK

Glass Transportation

517

Temperatures

and 97°C f o r the wet determination and f o r the c o n d i t i o n e d determination a t -40°C i n a d d i t i o n t o these temperatures. Samples were conditioned f o r 24 h r a t 70°F + 2°F and 65% RH + 2% a f t e r the samples had been oven d r i e d f o r 1 hr a t 110°C. For determination of wet Τ by s p e c i f i c volume, d e n s i t i e s were determined p y c n o m e t r i c a l l y ^ w i t h water as the d i s p l a c i n g liquid. The f i b e r s were allowed to remain i n the water f o r 24 hr before weighing. Measurements were made a t 10°C i n t e r v a l s from 20 t o 90°C and a t 97 C. For determination of dry T 's, a lowv i s c o s i t y m i n e r a l o i l was used as the d i s p l a c i n g li§uid. For determination of Τ by d i f f e r e n t i a l scanning c a l o r i m e t r y (DSC), samples were w e i g h e d i n the sample c o n t a i n e r , and the temp erature was scanned a t a r a t e of 20 C/min. For wet determination, the f i b e r s were wet out f o r 24 hr before t e s t i n g . For thermomechanical a n a l y s i s (TMA), a p p l i c a b l e only t o dry f i b e r s , a load of 0.005 g/den. was a p p l i e d t o the f i b e r and a scan r a t e of 20°C/min was used. An X-Y recorder was used t o record f i b e r length as a f u n c t i o n of temperature. For determination of Τ from shrinkage measurements, f i b e r s were allowed t o s h r i n k a t tSe s p e c i f i e d temperature, and l e n g t h measurements were made manually.


e

8

e

D i s c u s s i o n of R e s u l t s Some of the methods that have been used t o measure Τ of polymers i n c l u d e : 1. Dilatometry ( s p e c i f i c volume). 2. Thermal a n a l y s i s . S p e c i f i c heat (DTA, DSC) Thermal expansion (TMA) Thermal c o n d u c t i v i t y 3. Dynamic methods. Mechanical Free o s c i l l a t i o n Resonance Forced o s c i l l a t i o n Wave propagation Dielectric Nuclear magnetic resonance 4. S t r e s s r e l a x a t i o n and creep. 5. T e n s i l e behavior. E l a s t i c modulus Stiffness S t r e s s decay Resilience 6. Others. P e n e t r a t i o n (TMA) B r i t t l e point Compressibility R e f r a c t i v e index g


WATER IN P O L Y M E R S


SPECIFIC V O L U M E

Contemporary Physics

Figure 1.

Melting and glass transitions in a polymer (1)

3

SPECIFIC V O L U M E , C M / G

T E M P E R A T U R E , °C

Figure 2.

Effect of temperature on the specific volume of polyesters


31.

FUZEK


Temperatures

519


X-Ray d i f f r a c t i o n Small-molecule d i f f u s i o n 3-Radiation absorption V i s c o s i t y - a c t i v a t i o n energy Many of these methods a r e not s u i t a b l e f o r use with f i b e r s because of t h e i r p h y s i c a l nature. For example, many of the dynamic methods i n v o l v i n g l o s s modulus are not s u i t a b l e f o r f i b e r Τ measurements because two of the f i b e r dimensions a r e very s S a l l . Monofilaments can be t e s t e d , but they are not r e p r e s e n t a t i v e of the m a j o r i t y of t e x t i l e f i b e r s i n use today. Obviously, measure ment of p e n e t r a t i o n , c o m p r e s s i b i l i t y , small-molecule d i f f u s i o n , and a c t i v a t i o n energy i n v i s c o s i t y methods i s not p o s s i b l e f o r fibers. Of the methods that can be used f o r f i b e r s , the most common i n v o l v e s s p e c i f i c volume. The use of s p e c i f i c volume f o r determining the Τ of two p o l y e s t e r f i b e r s i s shown i n F i g u r e 2. These data were o f t a i n e d p y c n o m e t r i c a l l y with water as the d i s p l a c i n g l i q u i d . The f i b e r s were steeped i n water f o r 24 hr before t e s t i n g t o o b t a i n wet Τ s f o r these f i b e r s . To o b t a i n T 's of dry f i b e r s by t h i s meth§d, a l o w - v i s c o s i t y m i n e r a l o i l caS be used as the d i s p l a c i n g l i q u i d . Another common method used f o r measuring Τ i s thermal a n a l y s i s . The g l a s s t r a n s i t i o n i s a s s o c i a t e d with changes i n s p e c i f i c heat, not with l a t e n t heat. Thus the t r a n s i t i o n occurs as a b a s e - l i n e s h i f t r a t h e r than as d i s t i n c t endotherms i n DSC or d i f f e r e n t i a l thermal a n a l y s i s (DTA). As shown i n F i g u r e 3, wet determinations a r e more d i f f i c u l t than d r y determinations, s i n c e the wet f i b e r s must be sealed i n DSC capsules t o prevent moisture vapor from escaping during the determination. F u r t h e r , the base l i n e s h i f t i s u s u a l l y very s m a l l , and an accurate measure i s d i f f i c u l t to accomplish. A thermal method that allows measurement of f i b e r - l e n g t h change as a f u n c t i o n of temperature can be used t o determine the Τ of a f i b e r i f the length change i s great enough. T h i s c r i t e r i§n i s e a s i l y met by undrawn and p a r t i a l l y o r i e n t e d p o l y e s t e r f i b e r s as w e l l as by other f i b e r s that e x h i b i t moderate shrinkage at temperatures above t h e i r Τ s . The method used can i n v o l v e simple shrinkage measurements (Figure 4) or the more e l a b o r a t e d i f f e r e n t i a l technique, TMA (Figure 5 ) . The Τ i s taken as the abrupt length change from the base l i n e . BecaSse of experimental d i f f i c u l t i e s , the TMA method i s a p p l i c a b l e only t o dry or conditioned f i b e r s . T e n s i l e p r o p e r t i e s that are r e l a t e d t o f i b e r s t i f f n e s s can be used t o measure the Τ of almost a l l f i b e r s . The e l a s t i c modulus, that i s , the sl§pe of the Hookean r e g i o n of the f i b e r s t r e s s - s t r a i n curve, i s a measure of the f i b e r s t i f f n e s s and can be used f o r Τ determination s i n c e , by d e f i n i t i o n , a g l a s s i s s t i f f e r than § rubber (Figure 6). Since the t r a n s i t i o n from a g l a s s y t o a rubbery s t a t e i n v o l v e s a r e d u c t i o n i n s t i f f n e s s , the temperature a t which the modulus i s a b r u p t l y lowered i s taken as f

f

8




HEAT


Figure 3.

Differential scanning calorimetry curves for undrawn PET fibers

SHRINKAGE, % 40 r-

Figure 4.

Effect of temperature on shrinkage of undrawn PET fibers



FUZEK


Temperatures

DIMENSIONAL C H A N G E , %

-6 r

Figure 5.

Thermomechanical analysis (TMA ) of fibers

Figure 6.

Effect of temperature on modulus of elasticity



522


TIME, MIN

0

20

40

60

80

100


Figure 8.

Effect of temperature on stress decay time for wet fibers


31.

FUZEK


523

Temperatures

the Τ . Other t e n s i l e p r o p e r t i e s , such as break t e n a c i t y and b r e a k e l o n g a t i o n show no i n f l e c t i o n i n property-temperature curves. A few f i b e r s , n o t a b l y the modacrylics and the a c r y l i c s , show a r a p i d i n c r e a s e i n e l o n g a t i o n j u s t above t h e i r Τ s . For determination of wet Τ by t h i s method, a c t u a l t e n s i l e n t e s t i n g was c a r r i e d out with f i b e r t o t a l l y immersed during the t e s t . T e n s i l e work recovery can be considered a dynamic-loss modu l u s obtained a t very low c y c l i n g r a t e s . A f i b e r i s s t r e s s e d t o 3 g/den. and immediately allowed t o recover. The work recovered e x h i b i t s a marked r e d u c t i o n a t the g l a s s t r a n s i t i o n temperature (Figure 7 ) . S t r e s s r e l a x a t i o n , or s t r e s s decay, occurs when a f i b e r i s extended i n l e n g t h t o a predetermined s t r e s s l e v e l and h e l d at that length. We a r b i t r a r i l y s t r e s s e d f i b e r s t o 0.5 g/den., per mitted the decay t o occur, and measured the time r e q u i r e d f o r the s t r e s s t o decay t o 0.4 g/den. T h i s time i s p l o t t e d against temp e r a t u r e (Figure 8). For wet nylon 6,6 and wet PET f i b e r s , the time f o r the s t r e s s t o decay increased r a p i d l y when the T 's had been reached. As i n d i c a t e d e a r l i e r , Τ i s not a f i x e d temperature f o r a p a r t i c u l a r substance; i t i s § value that i s i n f l u e n c e d by the method used f o r i t s determination. A comparison of the r e s u l t s from s i x methods used to measure the Τ of PET f i b e r s i s given i n Table I . g


f

g

g

TABLE I Glass T r a n s i t i o n Temperature (T ) of Conditioned and Wet PET F i b e r s Determined by Various Methods

Method

T

S p e c i f i c volume DSC Shrinkage Modulus Work recovery Stress-decay

g

(Conditioned), *C

T

g

(Wet), °C

69 71 73 71 70 —

60 63 59 57 50 58

For conditioned PET, the Τ ranges from 69 t o 73°C and, f o r wet PET, from 50 t o 63 C. The wider range obtained with the wet f i b e r s probably r e s u l t s from increased experimental d i f f i c u l t y i n o b t a i n i n g some of the data on wet f i b e r s . In a l l cases, however, the wet Τ was 10 t o 20°C lower than the conditioned Τ f o r PET fibers. %f these methods, the use of f i b e r modulus i s p r e f e r r e d because i t i s a p p l i c a b l e to a l l f i b e r s , that e x h i b i t d i s t i n c t e

g




°l Ο

I

I 2

I

I

Ι

4

J

I

β

I 8

WATER C O N T E N T , % W/W

Figure 9.

Effect of moisture content on the T of PET fibers 9


31.

FUZEK


Temperatures

525

g l a s s t r a n s i t i o n s , and t h i s procedure can be c a r r i e d out more e a s i l y than the others, thus r e q u i r i n g l e s s time than many of the other methods. Conditioned and wet Τ s were determined from modulus data f o r a number of other fi§ers (Table I I ) . In each case, the wet Τ was s u b s t a n t i a l l y lower than the dry Τ . g 8 TABLE I I


f

Glass T r a n s i t i o n Temperatures of Various F i b e r s Wet and Conditioned

T

Fiber PET p o l y e s t e r PCHDMT p o l y e s t e r PBT p o l y e s t e r Nylon 6,6 Nylon 6 "Qiana" nylon "Orion" a c r y l i c " V e r e l " modacrylic Acetate "Rhovyl" v i n y l Silk

g

(Conditioned), °C 71 91 47 40 41 150 97 59 84 75 108

Τ

—

(Wet), *C

ΔΤ _ J

14 20 9 11 13 60 67 21 54 20 78

57 71 38 29 28 90 30 38 30 55 30

The lowering of the Τ by organic l i q u i d s , p l a e t i c i z e r s , and monomers has been weUndocumented, but the lowering of the Τ of polymers by water i s r e l a t i v e l y obscure. Most polymers are hydrophobic; hence they do not absorb much water. However, enough water i s taken up by most f i b e r s to lower the Τ substan t i a l l y . PET f i b e r regains about 0.4% moisture from an atmosphere (21*C) and 65% RH. This amount of water lowers the Τ by about 2 C. Soaking the f i b e r i n water can introduce as muc8 as 7% water i n t o the f i b e r over a 24-hr p e r i o d , and t h i s amount of water lowers the Τ by about 16*C. Further soaking i n water does not i n c r e a s e the w l t e r uptake. Intermediate l e v e l s of water up take can be obtained by soaking f o r periods of time up to 24 h r . The e f f e c t of water i n PET f i b e r on the Τ i s shown i n Figure 9. A s i m i l a r curve f o r nylon 6, which i s morl h y d r o p h i l i c than PET, was p r e v i o u s l y published (16). For nylon 6, the wet f i b e r ( a f t e r 24 hr i n water) contains about 6% water and has a Τ of about 28·C, whereas the conditioned f i b e r (70°F and 65% RS) with 4% water has a Τ of about 41*C. The bone-dry f i b e r has a Τ of over 100 C. Equations that r e l a t e Τ to the presence of p l a s t i c i z e r s , organic l i q u i d s , and monomerI i n polymers have been proposed by a number of i n v e s t i g a t o r s . Among the f i r s t was the equation p r o posed by Fox and F l o r y i n 1954 (19): 8

8

e

e

8

8


526

WATER IN

POLYMERS

W W JL - JSU + S τ τ τ g g g « weight fraction of polymer. p


W T

(i)

s

* weight fraction of solvent. « T of polymer. gp g Τ » Τ of solvent. g g S

s

This equation f i t s the data well for small amounts of these additives. It also f i t s the data for water i n most fibers, since the amount i s usually quite small. A more refined equation was proposed by DiMarzio and Gibbs i n 1963 (20). Δ Τ Δν Δ

Τ^

M-V

·Τ Ρ 2V

s s (polymer) — T

S

»

T

«

Difference i n solvent volume fraction,

Vp

«

Polymer molar volume.

V

*

Solvent molar volume,

«

Τ

Δγ

s

Τ

s

g M

»

g

g

(plasticized polymer).

of polymer, g Constant - 7.5 perfectly flexible solvent molecule. « 6.0 f l e x i b i l i t y * to polymer. - 4.8 r i g i d solvent molecule.

This equation f i t s fiber moisture-content data over a wider range than does Fox's equation. The T 's for conditioned and bone-dry fibers and fibers soaked in water fgr 24 hr as determined from modulus data are shown l n Table III for a number of fibers with normal moisture regains of 0.4 to 9.4%. The more-hydrophilic fibers show the greatest effect of water on Τ . Attempts have been made to correlate the reduction i n Τ causld by water to moisture-related fiber properties such as moisture regain, advancing contact angle, and water imbibition (Table IV). 8

Τ reduction due to water content cannot be predicted on the basis 8f these properties; but, generally, a fiber with a high moisture regain, a low advancing contact angle, and a high water imbibition shows a large reduction i n Τ . g


31.

FUZEK


527

Temperatures

TABLE I I I


Glass T r a n s i t i o n Temperature — Wet, Conditioned, and Dry F i b e r s

T

Fiber

Continued

PET p o l y e s t e r Nylon 6,6 "Qiana" nylon Silk Acetate

71 40 150 108 84

JL''

C

Dry

Water i n Moisture Wet F i b e r , % Regain, %

Wet

73 59 175 197 118

57 29 90 30 30

6.8 6.1 10.1 22.2 15.3

0.4 4.2 2.5 9.4 5.0

* At normal e q u i l i b r i u m r e g a i n

e

(70 F, 65%

RH).

** Bone dry — *** Wet

Τ

calculated. g out by soaking 24 hr i n water.

TABLE IV D i f f e r e n c e Between Wet

Τ

and

Conditioned Τ

g

Fiber

f o r Various F i b e r s g

g, Moisture Conditioned-Wet, °C Regain, %

PET p o l y e s t e r ΡCDT p o l y e s t e r PBT p o l y e s t e r Nylon 6,6 Nylon 6 "Qiana" nylon "Orion" a c r y l i c " V e r e l " modacrylic Acetate "Rhovyl" v i n y l Silk

14 20 9 11 13 60 67 21 54 20 78

0.4 0.2 0.3 4.2 4.0 2.5 2.0 2.1 5.0 0.2 9.4

Contact Angle,

9

41.3 44.6 —

43.1 47.7 41.3 43.7 36.5 19.0 —

22.0

Water of Imbibition, 1.2 1.6 3.0 5.7 7.8 2.0 2.6 7.9 18.0 2.2 35.8


%



528

Τ has great s i g n i f i c a n c e i n the processing and use o f t e x t i l e fiBers. For a l l f i b e r s except the e l a s t o m e r i c s and the p o l y o l e f i n s , the Τ i s higher than ambient temperature. That i s , the amorphous polyfier of the f i b e r must e x i s t i n the g l a s s y s t a t e . Since f i b e r s are o f t e n processed under hot, wet c o n d i t i o n s (as during dyeing and f i n i s h i n g ) , the wet Τ may be of even greater importance than t h e dry Τ . Of p a r t i c u l a r importance i n the performance of wash-and-wëar f a b r i c s , the wet Τ of the f i b e r must be a t l e a s t as h i g h as the temperature the f a b r i c w i l l reach during laundering. I f the wash water temperature exceeds the wet Τ of the f i b e r , molecular motion w i l l permit changes that w i l l r e l u i t i n dimensional i n s t a b i l i t y and cause the f a b r i c to have poor wash-and-wear performance. In other words, w r i n k l i n g w i l l occur, and the f a b r i c w i l l r e q u i r e i r o n i n g . The wet Τ of a f i b e r that e x h i b i t s good wash-and-wear, or permanent-press? behavior should be a t l e a s t 60 t o 70°C, s i n c e the t y p i c a l home laundry uses water at temperatures up t o 65 C. The wet Τ of PET f i b e r i s s l i g h t l y below t h i s l e v e l ; consequently, t h i s f i b e r e x h i b i t s only marginal wash-and-wear performance. The f i b e r i s u s u a l l y blended with cotton and the c o t t o n i s c r o s s l i n k e d t o improve dimensional s t a b i l i t y . The a b i l i t y of PET f i b e r s t o f u n c t i o n reasonably w e l l i n wash-and-wear garments i s probably due t o the r e l a t i v e l y long time (compared with laundering time) r e q u i r e d f o r the Τ t o be lowered t o the e q u i l i b r i u m wet Τ v a l u e . A high wet Τ ^should ensure adequate dimensional s t a b i l i t y during l a u n d e r i n | . Dimen s i o n a l s t a b i l i t y can a l s o be obtained i n a f i b e r with a low wet Τ i f the f i b e r can be l i g h t l y c r o s s l i n k e d i n the f a b r i c o r , p i e f e r a b l y , i n the garment c o n f i g u r a t i o n . Durable-press r e s i n s and permanent-press f i n i s h e s on c e l l u l o s i c s , p a r t i c u l a r l y c o t t o n , f u n c t i o n i n t h i s manner because the wet Τ of cotton i s w e l l below 0 C. Untreated c o t t o n demonstrates^very poor wash-and-wear performance, but cotton with i t s wet Τ increased by c r o s s linking i s quite satisfactory. ^ e

e

Conclusions Methods f o r measuring the g l a s s t r a n s i t i o n temperature that are p a r t i c u l a r l y adaptable t o f i b e r s , both wet and dry, have been proposed. In p a r t i c u l a r , the use of the e l a s t i c modulus has been shown t o give r e l i a b l e estimates of the Τ of f i b e r s . The e f f e c t of the presence of water i n the f i b e r , bo£h at r e g a i n l e v e l and t o t a l l y wet out, on the f i b e r Τ and the s i g n i f i c a n c e of the wet Τ of f i b e r s on the s t a b i l i t y of f a b r i c s and garments made from fhera have been d i s c u s s e d .

Abstract The glass transition temperature (T ) of an amorphous polymer is the temperature at which motion occurs in the major segments of the backbone molecular chain of the polymer. However, the effect of water on the Τ of a hydrophobic polymer has generally g

g


31.


FUZEK

Temperatures

529

not been recognized. Almost all fibers are only partially crystal line; hence they exhibit glass transition phenomena. And all fibers have an equilibrium moisture content at 70°F and 65% RH. This moisture content has been shown to result in a marked lower ing of the Τ for many fibers. Further reductions in Τg occur when the fiber is allowed to wet out in water until equilibrium saturation is reached. These lowered Tg 's are of significance in the processing and care of textile products. Several methods particularly useful for measuring the wet and dry Τ of fibers have been explored.


g

g

Literature

Cited

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January 4, 1980.


Water in Polymers - American Chemical Society

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