Differential Scanning Calorimetry and NMR Studies on the Water

Chapter 20

Differential Scanning Calorimetry and N M R Studies on the Water—Sodium Lignosulfonate System Hyoe Hatakeyama , Shigeo Hirose , and Tatsuko Hatakeyama 1

1

2

Industrial Products Research Institute, 1-1-4 Higashi, Tsukuba, Ibaraki 305, Japan Research Institute for Polymers and Textiles, 1-1-4 Higashi, Tsukuba,

Downloaded by UNIV OF CINCINNATI on May 31, 2016 | http://pubs.acs.org Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch020

1

2

Ibaraki 305, Japan The phase transition and nuclear magnetic relaxation of the water-sodium lignosulfonate (NaLS) system with var ious water contents ranging from 0 to ca. 2.3 (grams of water per gram of sodium lignosulfonate) were evaluated by differential scanning calorimetry and nuclear magnetic resonance spectroscopy. It was found that at least two different kinds of water existed in the system: i.e., freez ing water and non-freezing bound water. The longitu dinal and transverse relaxation times of the water-NaLS system were measured as functions of water content and temperature. A minimum value for the H longitudi nal relaxation time (Τ ) was observed at a temperature around —25°C. A sudden decrease in H transverse re laxation time (T ) was also observed at a similar temper ature. The change of Τ and T of Na in the system corresponded well with the motion of H in water. 1

1

1

2

1

2

23

1

It is generally k n o w n t h a t polyelectrolytes are h i g h l y soluble i n water t h r o u g h h y d r a t i o n of ionic groups. However, a t t e n t i o n has not been p a i d to the p h y s i c o - c h e m i c a l properties of h i g h l y concentrated aqueous s o l u t i o n s of polyelectrolytes. W e have already reported that there are t w o k i n d s of w a t e r , i.e. freezing water a n d non-freezing water, a r o u n d the ionic groups i n the w a t e r - s o d i u m poly(styrenesulfonate) ( N a P S S ) , the w a t e r - s o d i u m cel lulose sulfate ( N a C S ) , a n d the w a t e r - c a t i o n salts of c a r b o x y m e t h y l c e l l u l o s e ( M e C M C ) systems (1-3). J u d g i n g f r o m the e x p e r i m e n t a l results o b t a i n e d b y differential s c a n n i n g c a l o r i m e t r y ( D S C ) a n d b y nuclear m a g n e t i c res onance ( N M R ) spectroscopy, water molecules are s t r o n g l y b o n d e d to the i o n i c groups a n d f o r m a h y d r a t i o n shell. In this study, we chose the w a t e r - s o d i u m lignosulfonate ( N a L S ) s y s t e m , w i t h various water contents r a n g i n g f r o m 0 to ca. 2.3 g r a m s of water per 0097-6156/89A)397-0274$06.00A) Ο 1989 American Chemical Society

Glasser and Sarkanen; Lignin ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

20.

HATAKEYAMA ET AL.

Water-Sodium Lignosulfonate System

275

g r a m o f N a L S . T h e t h e r m a l properties a n d H a n d N a nuclear m a g n e t i c r e l a x a t i o n times o f the s y s t e m were investigated. T h e phase t r a n s i t i o n t e m peratures o f the w a t e r - N a L S s y s t e m were measured as a f u n c t i o n o f water content. A t the same t i m e , the b o u n d water content was d e t e r m i n e d f r o m the e n t h a l p y o f t r a n s i t i o n . F u r t h e r m o r e , a d e t a i l e d s t u d y o f the l o n g i t u d i n a l a n d transverse r e l a x a t i o n times ( T i a n d T 2 ) was c a r r i e d o u t , a n d the m o l e c u l a r c o r r e l a t i o n times ( r ) a n d a c t i v a t i o n energies (E ) o f water i n the s y s t e m were e s t i m a t e d . 1

2 3

a

c


Experimental Sample Preparation. A s the N a L S s a m p l e , W A F E X , w h i c h was s u p p l i e d b y H o l m e n A B , Sweden, was used after p u r i f i c a t i o n a c c o r d i n g t o t h e m e t h o d r e p o r t e d by L e o p o l d (4). T h e a m o u n t o f sulfonic a c i d groups was deter m i n e d b y t i t r a t i n g a n aqueous s o l u t i o n o f purified lignosulfonic a c i d w i t h 1/5 Ν s o d i u m h y d r o x i d e . T h e lignosulfonic a c i d was o b t a i n e d f r o m N a L S b y passing i t t h r o u g h a n a m b e r l i t e I R - 1 2 0 B ( H ) c o l u m n . T h e sulfonate group content o f the N a L S was 1.6 m e q / g . T h e water content (W ) o f each s a m p l e was defined b y +

c

W (g/g) e

where W sample.

w

(1)

= W {g)IW,(g) w

is the weight o f added water a n d W

s

is the d r y weight o f each

Differential Scanning Calorimetry (DSC). T h e phase t r a n s i t i o n o f t h e w a t e r - p o l y e l e c t r o l y t e systems was measured u s i n g a P e r k i n - E l m e r differ e n t i a l s c a n n i n g calorimeter, D S C - I I , a n d a D u P o n t m o d e l 910 differential s c a n n i n g c a l o r i m e t e r . T h e s c a n n i n g rate for h e a t i n g a n d c o o l i n g e x p e r i ments was 1 0 ° C / m i n . D S C curves were o b t a i n e d i n the t e m p e r a t u r e range f r o m 50 t o — 120°C. A l u m i n u m sample pans for v o l a t i l e samples were p r e treated b y h e a t i n g w i t h water t o 120°C i n a n autoclave i n order t o a v o i d any r e a c t i o n between a l u m i n u m a n d water d u r i n g h e a t i n g a n d c o o l i n g r u n s . A f t e r the D S C measurement, the s a m p l e was weighed a g a i n t o c o n f i r m t h a t no weight loss h a d t a k e n place. T h e t e m p e r a t u r e a n d e n t h a l p y o f c r y s t a l l i z a t i o n o f sorbed water were c a l i b r a t e d u s i n g pure water as the s t a n d a r d . T h e b o u n d water content was c a l c u l a t e d b y the m e t h o d r e p o r t e d p r e v i o u s l y (1)· Nuclear Magnetic Resonance (NMR) Spectroscopy. Longitudinal and transverse r e l a x a t i o n times ( T i a n d T 2 ) o f H a n d N a i n t h e w a t e r polyelectrolytes systems were measured u s i n g a N i c o l e t F T - N M R , m o d e l N T - 2 0 0 W B . T 2 was measured b y the M e i b o o m - G i l l v a r i a n t o f the C a r r P u r c e l l m e t h o d (5). However, i n the case o f very r a p i d r e l a x a t i o n , t h e free i n d u c t i o n decay ( F I D ) m e t h o d w a s a p p l i e d . T h e s a m p l e t e m p e r a t u r e w a s changed f r o m 30 t o —70°C w i t h the assistance o f t h e 1180 s y s t e m . T h e accuracy o f the t e m p e r a t u r e c o n t r o l was ± 0 . 5 ° C . 1

2 3


LIGNIN: PROPERTIES AND MATERIALS

276 Results and Discussion

DSC. F i g u r e 1 shows D S C c o o l i n g curves of the w a t e r - N a L S s y s t e m h a v i n g various W 's f r o m 0.46 to 2.31 g / g . W h e n a s a m p l e w i t h water is cooled f r o m 50°C at the rate o f 1 0 ° C / m i n , a b r o a d peak ( P * ) is observed i n i t i a l l y , followed by a s h a r p peak representing c r y s t a l l i z a t i o n of water ( P j ) . H o w ever, as s h o w n i n F i g u r e 1, o n l y P * is observed i f W is lower t h a n ca. 0.5 g / g . T h e t e m p e r a t u r e for P j increases w i t h increasing W , w h i l e , o n the other h a n d , the t e m p e r a t u r e for P * decreases w i t h i n c r e a s i n g W . This feature of P * is different f r o m t h a t of the b r o a d peak representing freezi n g b o u n d w a t e r , P / / , w h i c h is observed w h e n water is b o u n d to the h y d r o x y l groups of p o l y m e r s such as l i g n i n , cellulose a n d p o l y ( h y d r o x y s t y r e n e ) derivatives h a v i n g no i o n i c groups (6-9). P / j appeared at a t e m p e r a t u r e lower t h a n t h a t of the c r y s t a l l i z a t i o n peak of water ( P / ) . O n the other h a n d , P * appears at a t e m p e r a t u r e higher t h a n t h a t o f Pj. A n e x o t h e r m i c peak s i m i l a r to P * was also observed i n the case of h i g h l y concentrated aqueous s o l u t i o n s of N a C S a n d N a P S S (1,2). T h e r e fore, i t is supposed t h a t P * is observed w h e n the molecules i n the waterp o l y e l e c t r o l y t e systems rearrange to a stable state h a v i n g lower energy t h a n the n o r m a l state of water. T h i s suggests t h a t the molecules i n the waterN a L S s y s t e m assume a loosely ordered state i n the range between the t e m peratures where P * a n d P / appear. T h e t e x t u r e of the s a m p l e was observed u s i n g a p o l a r i z e d l i g h t m i croscope e q u i p p e d w i t h a t e m p e r a t u r e controller. A l t h o u g h the W o f the s a m p l e c o u l d not be kept e n t i r e l y constant o w i n g to the s t r u c t u r e of the s a m p l e cell, a t e x t u r e s h o w i n g a n e m a t i c t y p e of m o l e c u l a r a r r a n g e m e n t was observed at a t e m p e r a t u r e c o r r e s p o n d i n g to t h a t between P * a n d P j . H o w e v e r , the t e x t u r e observed i n the w a t e r - N a L S s y s t e m was not as clear as those observed i n the w a t e r - N a P S S a n d the w a t e r - N a C S systems. T h i s unclear t e x t u r e observed i n the w a t e r - N a L S s y s t e m m a y be a t t r i b u t e d to the inhomogeneous c h e m i c a l s t r u c t u r e of N a L S . F i g u r e 2 shows the phase d i a g r a m of the w a t e r - N a L S s y s t e m . T h i s d i a g r a m was o b t a i n e d b y c o o l i n g the s y s t e m at a rate o f 1 0 ° C / m i n , i n d i c a t i n g t h a t the s y s t e m changes f r o m the i s o t r o p i c l i q u i d phase t h r o u g h the m e s o m o r p h i c phase to the c r y s t a l l i n e phase. T h e t e m p e r a t u r e o f c r y s t a l l i z a t i o n ( T ) increases w i t h increasing W a n d levels off at W ca. 1.5 g / g . T h e t e m p e r a t u r e ( T * ) c o r r e s p o n d i n g to the appearance o f P * decreases w i t h i n c r e a s i n g W a n d becomes difficult to observe i f W increases above ca. 2.3 g / g . T h e a m o u n t of freezing water i n the w a t e r - N a L S s y s t e m can be c a l c u l a t e d f r o m the enthalpy, a s s u m i n g the c r y s t a l l i z a t i o n e n t h a l p y of water to be 333 J / g (7). T h u s , c

c

c


c

c

c

c

c

c

c

W

f

(2)

= (AHj/myW,

where Wf is the a m o u n t of freezing water a n d AHj e n t h a l p y of the s y s t e m .

is the c r y s t a l l i z a t i o n



20.

HATAKEYAMA ET AL.


277

F i g u r e 1. D S C c o o l i n g curves of the w a t e r - N a L S s y s t e m w i t h v a r i o u s water contents, W (g/g). c



278

However, the value of Wj is less t h a n the t o t a l a m o u n t of water i n the s y s t e m , since water w h i c h is t i g h t l y b o u n d to the h y d r o p h i l i c groups of a p o l y electrolyte cannot be frozen (1,2). T h e r e f o r e , the t o t a l a m o u n t of water i n the s y s t e m is given b y W

(3)

= Wf + W f

c

n

where Wf is the a m o u n t of freezing water a n d W f is t h a t of non-freezing water. F i g u r e 3 shows the r e l a t i o n s h i p between W Wf a n d W f. T h e value of Wf increases i n p r o p o r t i o n to W at water contents higher t h a n the specific c r i t i c a l a m o u n t w h i c h is o b t a i n e d b y the e x t r a p o l a t i o n of the l i n e a r Wf vs. W plots to the h o r i z o n t a l a x i s . T h e c r i t i c a l value o b t a i n e d is 0.56 g / g . T h i s a m o u n t corresponds to a n a m o u n t less t h a n the p o i n t at w h i c h the water i n the w a t e r - N a L S s y s t e m can no longer be c r y s t a l l i z e d . A s s h o w n i n F i g u r e 3, W f does not change a p p r e c i a b l y w i t h i n c r e a s i n g W. n

C1

n


c

c

n

c

H NMR. F i g u r e 4 shows the change of T i values for * H of water i n the w a t e r - N a L S s y s t e m w i t h the inverse absolute t e m p e r a t u r e ( K " * ) . T h e T i value decreases w i t h decreasing W a n d w i t h decreasing t e m p e r a t u r e i n the t e m p e r a t u r e range above — 2 5 ° C , where a m i n i m u m value for T i is o b served. T h e Τχ m i n i m u m occurs at a t e m p e r a t u r e lower t h a n t h a t at w h i c h water molecules i n the s y s t e m become r i g i d . In the t e m p e r a t u r e range be low —25°C, a steep increase i n the T i value is observed w i t h decreasing temperature. F i g u r e 5 shows the change of T 2 values for * H of water w i t h the inverse absolute t e m p e r a t u r e . A sudden decrease i n T 2 values is seen at almost the same temperatures at w h i c h the m i n i m u m i n T i is observed. The T 2 values give a n average representation of the m o t i o n of water molecules i n the s y s t e m . Therefore, i f we consider the m o l e c u l a r m o t i o n of water i n the w a t e r - N a L S s y s t e m h a v i n g a c e r t a i n W , the T 2 values at higher t e m p e r a t u r e s are characteristic of more m o b i l e w a t e r , w h i l e the T 2 values at lower t e m p e r a t u r e s are characteristic of more r e s t r i c t e d w a t e r . It is u s u a l l y not possible to d i s t i n g u i s h various p e r t u r b e d sites i n a n N M R e x p e r i m e n t . Therefore, i t is c u s t o m a r y to l i m i t the n u m b e r o f sites to two representing the free (Pf) a n d b o u n d (Pi,) fractions w i t h Pf + Pb = 1. If we assume = 1/7*, (i = 1, 2), t h e n l

1

c

c

Ri = PfRif

(4)

+ PR h

ih

In the case of free water, the extreme n a r r o w i n g c o n d i t i o n is fulfilled a n d t h u s Rif = R f = Rf. T h u s , f r o m E q u a t i o n 4, we can w r i t e 2

(R

x

- PfRf)l(R

A c c o r d i n g to Woessner et al. water can be expressed as

2

- PfRf)

= Rn/R2b

(5)

(10,11), the r e l a x a t i o n rates of the b o u n d


20.

HATAKEYAMA ET AL.


279

NaLS-HzO 2.0

"5 W.

/


1.0

ι y*^

0 C)

ι

ι

ι

1.0

w

c

2.0

/ g/g

F i g u r e 3. R e l a t i o n s h i p between water content (W ), (Wf) a n d non-freezing water content (W f). c

freezing water content

n

Figure 4. Temperature dependence of the H longitudinal relaxation time of water i n the water-NaLS system.

Figure 5. Temperature dependence of the H transverse relaxation time of water i n the water-NaLS system.



280 J _

_

T

~ 2

2i

1

3r

ci

+

where Σ% = 1> d G is the i n t e r a c t i o n constant d e t e r m i n i n g the m a g n i t u d e of the r e l a x a t i o n , u>o the a n g u l a r resonance frequency, a n d r - the c o r r e l a t i o n t i m e . T h e above expressions allow for m u l t i p l e c o r r e l a t i o n t i m e s i n the systems. However, i f we assume t h a t the r e l a x a t i o n of b o u n d water i n the w a t e r N a L S s y s t e m is d e t e r m i n e d b y one average c o r r e l a t i o n t i m e r , we c a n combine E q u a t i o n s 5, 6, a n d 7, to give a

n

ct


c

w h i c h is a f u n c t i o n o n l y of u r . It m i g h t be a n o v e r s i m p l i f i c a t i o n to o n l y consider one type of average b o u n d water. However, for p r a c t i c a l purposes, i t seems reasonable to use t h i s c a l c u l a t i o n m e t h o d as a s t a r t i n g p o i n t for the e v a l u a t i o n of b o u n d water i n the w a t e r - N a L S s y s t e m . F i g u r e 6 shows the c a l c u l a t e d r values p l o t t e d vs. inverse absolute t e m p e r a t u r e . I n the t e m p e r a t u r e range below —15°C, i t is seen t h a t the r values are not dependent o n W b u t dependent o n t e m p e r a t u r e . T h e r value increases f r o m ca. 3 x 1 0 ~ sec at — 15°C to ca. 3 x 1 0 ~ sec at - 6 0 ° C . T h i s shows t h a t the b o u n d water i n the s y s t e m is i n the state between viscous l i q u i d a n d n o n - r i g i d s o l i d i n t h i s t e m p e r a t u r e range. A s seen f r o m the figure, the l n r vs. t e m p e r a t u r e " " (K" ) plots are a p p a r e n t l y l i n e a r . T h e t e m p e r a t u r e dependence of r m a y be expressed w i t h considerable accuracy b y the A r r h e n i u s e q u a t i o n i n the f o r m (12) 0

c

c

c

c

c

8

7

1

c

1

c

r

c

= r exp

(Ea/RT)

0

(9)

where E is the a c t i v a t i o n energy for the r e l a x a t i o n process of the b o u n d w a t e r . T h e value o f E was f o u n d to be c a . 24 k J / m o l . T h i s value cor responds w e l l w i t h the a c t i v a t i o n energy of the b o u n d water p r e v i o u s l y r e p o r t e d (2). a

a

Na NMR. F i g u r e 7 shows the change o f T i values for N a i n the w a t e r N a L S s y s t e m w i t h the inverse absolute t e m p e r a t u r e at various W ' s . T h e I n T i plots are linear i n the t e m p e r a t u r e range where T i values c o u l d be observed i n t h i s e x p e r i m e n t . A t temperatures lower t h a n — 2 0 ° C , i t was difficult to measure the Τχ value of N a b y the 180-T-90 degree pulse m e t h o d because of the extreme b r o a d e n i n g of the l i n e w i d t h of the N M R peaks. F r o m the slopes of the r e l a x a t i o n rate ( l n T ^ " ) vs. inverse absolute t e m p e r a t u r e , the apparent a c t i v a t i o n energy (E ) of the r e l a x a t i o n process was c a l c u l a t e d . T h e value o b t a i n e d was ca. 12 k J / m o l . T h i s value corre sponds w e l l w i t h the a c t i v a t i o n energy for N a i n persulfonate i o n o m e r s w i t h water (13). 2 3

23

c

2 3

1

a

2 3


20.

HATAKEYAMA ET A L


e/ c

281

e

0 ι

10"

-20 ι ι Wc 209 157 136 1· 21 1· 01 0-80 0 60

ο • _

δ Α

• • χ


u φ «ίο-

I

-40 I

-60 ι

ι

ί

7

êfn

Λ/Α

* * χ'* 1 Ε£

t i l ΙΟ"

8

i

1

ι

ι

ι

36

48 (1000/Τ)/Κ-'

F i g u r e β. T e m p e r a t u r e dependence of the average c o r r e l a t i o n t i m e of water i n the w a t e r - N a L S s y s t e m .

θ / °c 30

20

10

0

-10

—ι

u (Λ Ε

2

·

33

34 35

3-6 37 3·β

(1000/Ό/Κ -I

F i g u r e 7. T e m p e r a t u r e dependence of the i n the w a t e r - N a L S s y s t e m .

2 3

39

N a longitudinal relaxation time



282

θ


30 20

001

/

°C

10

0

-10

-20

3 3 3Λ 35 36 37 3-8 3 9 A O (1000/T)/K H

Wc

- O -

138

- · -

1.18

-Δ-

1.02

-*r

0.76

F i g u r e 8. T e m p e r a t u r e dependence of the i n the w a t e r - N a L S s y s t e m .

2 3

" • -

0.62

N a transverse r e l a x a t i o n t i m e


20.

HATAKEYAMA ET A L


283

F i g u r e 8 shows the change o f T 2 values o f N a w i t h inverse absolute t e m p e r a t u r e . A s seen f r o m F i g u r e 8, t w o types o f transverse r e l a x a t i o n s are observed. O n e is "slow" a n d the other a "fast" r e l a x a t i o n . T h i s means t h a t t h e transverse r e l a x a t i o n decays i n a n o n - e x p o n e n t i a l m a n n e r . N o n e x p o n e n t i a l r e l a x a t i o n due t o q u a d r u p o l e r e l a x a t i o n was characterized b y H u b b a r d (14). A c c o r d i n g t o his c a l c u l a t i o n , the transverse r e l a x a t i o n s p r o duced b y a quadrupole i n t e r a c t i o n are t h e s u m o f two o r more d e c a y i n g e x p o n e n t i a l s . A s s h o w n i n F i g u r e 8, the longer transverse r e l a x a t i o n t i m e (T25) decreases w i t h decreasing t e m p e r a t u r e , a l t h o u g h t h e shorter t r a n s verse r e l a x a t i o n t i m e ( T 2 / ) does not change m u c h w i t h t e m p e r a t u r e . T h e s u d d e n decrease o f the T25 value a t a r o u n d — 15°C m a y reflect the i n f l u ence o f the c r y s t a l l i z a t i o n o f water i n the w a t e r - N a L S s y s t e m . T h i s result is quite reasonably e x p l a i n e d i f we assume t h a t the s o d i u m i o n is s u r r o u n d e d b y the non-freezing water a n d t h a t this non-freezing water is s u r r o u n d e d b y the free water. Therefore, t h e m o t i o n o f the free water i n the s y s t e m i n d i r e c t l y affects t h a t o f the s o d i u m i o n .


2 3

Literature Cited 1. Hatakeyama, T . ; Nakamura, K.; Yoshida, H . ; Hatakeyama, H . Thermochmica Acta 1985, 88, 223. 2. Hatakeyama, H.; Iwata, H.; Hatakeyama, T . In Wood and Cellulosics; Kennedy, J . F . , et al., Eds.; Ellis Horwood: Chichester, 1987; C h . 4. 3. Nakamura, K . ; Hatakeyama, T . ; Hatakeyama, H . In Wood and Cellulosics; Kennedy, J . F . , et al., Eds.; Ellis Horwood: Chichester, 1987; Ch. 10. 4. Leopold, B. Acta Chem. Scand. 1952, 6, 64. 5. Meiboom, S.; Gill, D. Rev. Sci. Inst. 1958, 29, 688. 6. Hatakeyama, T . ; Hirose, S.; Hatakeyama, H . Makromol. Chem. 1983, 184, 1265. 7. Nakamura, K . ; Hatakeyama, T . ; Hatakeyama, H . Textile Res. J. 1981, 51, 607. 8. Hatakeyama, T . ; Ikeda, Y . ; Hatakeyama, H . Makromol. Chem. 1987, 188, 1875. 9. Nakamura, K . ; Hatakeyama, T . ; Hatakeyama, H . Polymer 1983, 24, 871. 10. Woessner, D. E . ; Zimmerman, J. R. J. Chem. Phys. 1963, 67, 1590. 11. Woessner, D. E . ; Snowden, B. S. J. Colloid and Interface Sci. 1970, 34, 290. 12. Farrar, T . C . ; Becker, E . D. Pulse and Fourier Transform NMR; Aca demic: New York, 1971; p. 57. 13. Komoroski, R. A . In Ions in Polymers; Eisenberg, Α . , Ed.; American Chemical Society: Washington, D C , 1980; C h . 10. 14. Hubbard, P. S. J. Chem. Phys. 1970, 53, 985. RECEIVED March 17,1989


Differential Scanning Calorimetry and NMR Studies on the Water

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