Cellulose Chemistry and Technology - ACS Publications - American

12 Characterization of Cellulose and Synthetic Fibers by Static and Dynamic Thermoacoustical Techniques

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 20, 2017 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0048.ch012

PRONOY K. CHATTERJEE Personal Products Co., Subsidiary of Johnson & Johnson, Milltown,ΝJ08850

The c h a r a c t e r i z a t i o n of m a t e r i a l s by a c o u s t i c a l techniques i s an o l d a r t . Perhaps i t dates back hundreds of c e n t u r i e s . There i s no r e c o r d i n h i s t o r y when man f i r s t l e a r n e d t o d i f f e r e n t i a t e between a rock and a metal by s t r i k i n g them w i t h another object and l i s t e n i n g t o the c h a r a c t e r i s t i c frequency and amplitude of the r e s u l t i n g sound waves. The technique, however, emerged as a science when the s u b j e c t i v e l i s t e n i n g was changed i n t o the objec t i v e measurements by modern instrumentations. The subject o f d i s c u s s i o n o f t h i s paper i s not the d i f f e r e n t i a t i o n between two d i s s i m i l a r macro o b j e c t s but the determina t i o n of the changes at a molecular l e v e l which takes p l a c e due t o the environmental changes of a polymeric m a t e r i a l , v i z , c e l l u l o s i c and s y n t h e t i c f i b e r s . More s p e c i f i c a l l y , three i n d i v i d u a l t o p i c s of the a c o u s t i c a l techniques have been b r i e f l y discussed, v i z . c h a r a c t e r i z a t i o n o f i n t e r f i b e r bonding i n c e l l u l o s e sheets, water a b s o r p t i o n i n a paper l i k e non-woven s t r u c t u r e , and dynamic thermal a n a l y s i s o f t e x t i l e f i b e r s i n c l u d i n g cotton, rayon, and v a r i e t i e s of s y n t h e t i c f i b e r s . In d e s c r i b i n g the p r i n c i p l e s of the technique, mathematical d e r i v a t i o n s have been avoided as much as p o s s i b l e . The v e r s a t i l i t y of t h i s n o v e l a c o u s t i c a l technique has been c l e a r l y demonstrated by the f o l l o w i n g examples. Sonic Pulse Propagation i n a Paper L i k e S t r u c t u r e and the C h a r a c t e r i z a t i o n of I n t e r f i b e r Bonding Technique. A number o f handsheets were made according t o TAPPI standard T205m-58 u s i n g f u l l y bleached commercial k r a f t pulps as l i s t e d i n Table I. The s o n i c v e l o c i t y i n the sheets was determined with a pulse propagation meter, PPM-5R, manufactured by Η. M. Morgan and Co. The p r i n c i p l e o f the procedure i s de s c r i b e d elsewhere (1^). The other p h y s i c a l p r o p e r t i e s o f the sheets were measured" according t o the standard techniques ( £ ) .

173

Arthur; Cellulose Chemistry and Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

174

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Table I Pulp Samples ( K r a f t , f u l l y bleached

Description

Sample I d e n t i f i c a t i o n


pulp)

80% Cedar, 20% Hemlock Southern Pine Southern Pine Southern Pine Douglas F i r Douglas F i r 50% Douglas F i r , 50% Sawdust Southern Pine, Mercerized Southern Pine, Mercerized

A Β C D Ε F G H I

R e s u l t s and D i s c u s s i o n . The s t r u c t u r e o f a pulp handsheet ( o r paper) could be d e f i n e d as a heterogeneous system c o n s i s t i n g i n p a r t o f c e l l u l o s e unbonded f i b e r s and i n p a r t o f bonded regions with pores c o n t a i n i n g a i r . When a p u l s e propagates through the sheet ( F i g u r e 1), an a d i a b a t i c compression takes p l a c e i n a l l the c o n s t i t u e n t s of the sheet. However, according to T a y l o r and Craver (3), the a c o u s t i c a l mismatch o f a f i b e r / a i r surface i s too great t o permit d i r e c t t r a n s m i s s i o n o f the sound through f i b e r and v o i d space i n s e r i e s . L e t i t be assumed that the v e l o c i t y o f sound c, i s c o n t r o l l e d by only two s t r u c t u r a l c o n s t i t u e n t s : the bonded and the unbonded f i b e r regions. I t i s a l s o considered that ( l ) handsheets are made o f randomly o r i e n t e d f i b e r s which are interconnected by numerous i n t e r f i b e r bonds, and that ( 2 ) the bonded regions, the porous spaces, and the unbonded p o r t i o n s o f f i b e r s are uniformly d i s t r i b u t e d i n the sheet s t r u c t u r e . The bonded r e g i o n i s d e f i n e d here as the area o f i n t i m a t e contact between two f i b e r s . A p u l s e , as i t propagates, t r a v e l s through a s e r i e s o f two d i f f e r e n t s t r u c t u r a l c o n s t i t u e n t s as c i t e d above. Based on the above hypothesis, C h a t t e r j e e (2) d e r i v e d the f o l l o w i n g equation · (1) P IBE 1

1

+

( E

2

-

G

E

2

)

J

where (1-3) = p r o p o r t i o n (by surface area) o f unbonded f i b e r regions, Ρχ = the d e n s i t y o f f i b e r , and Εχ and E 2 = i n v e r s e o f c o m p r e s s i b i l i t y o r modulus of unbonded p o r t i o n o f f i b e r s and i n t e r f i b e r bonded regions, r e s p e c t i v e l y . In the case o f unbeaten pulp handsheets, the sheet has an a p p r e c i a b l e p r o p o r t i o n o f unbonded r e g i o n s , and the modulus o f i n t e r f i b e r bonded regions i s very low compared to the modulus o f a


12.

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Thermoacousticàl

175

Techniques

s i n g l e f i b e r . By t a k i n g i n t o account t h e equations f o r mechanical p r o p e r t i e s of a sheet, equation ( l ) can be reduced t o the f o l l o w i n g form: dc

2

= k T 6

(2)

g

where, k^ = φ(λ,d,k' ,ν, ρ) and λ = r a t i o of the t e n s i l e modulus t o the modulus a t break, d = apparent d e n s i t y of the sheet, k = a constant f o r the b a s i s w e i g h t - d e n s i t y r e l a t i o n s h i p , ν = r a t e of t e n s i l e l o a d i n g f a c t o r , ρ = t r u e d e n s i t y o f f i b e r , and Tg = t e n s i l e breaking s t r e n g t h measured by i n s t r o n t e s t e r . A p l o t o f d c versus Tg i s shown i n F i g u r e 2 along w i t h the p l o t of u l t i m a t e t e n s i l e s t r e s s and M a l i e n b u r s t . As expected from equation ( 2 ) , d c and Τ β have a l i n e a r r e l a t i o n s h i p . The theory and the experimental r e s u l t s i n d i c a t e t h a t the t e n s i l e s t r e n g t h of a pulp sheet which i s p r i m a r i l y a f u n c t i o n o f i n t e r f i b e r bonding can be determined by a n o n d e s t r u c t i v e acous t i c a l technique. A s i m i l a r r e l a t i o n s h i p has a l s o been d e r i v e d f o r t h e modulus of the sheet and f o r d i f f e r e n t kinds o f paper s t r u c t u r e i n c l u d i n g r e s i n bonded papers (2). Among many a p p l i c a t i o n s , i t i s worthy o f mentioning t h a t the technique has been u n i q u e l y a p p l i e d i n c h a r a c t e r i z i n g the emboss i n g on f l u f f pad by C h a t t e r j e e ( 4 ) , o n - l i n e measurement o f s t r e n g t h c h a r a c t e r i s t i c s by Lu and i n determining i n t e r a c t i o n between f i b e r s and phenolTc r e s i n s by Marton and Crosby (6).


f

2

2

A b s o r p t i o n o f Water i n C e l l u l o s e Sheet by Sonic V e l o c i t y Response Technique. The wieking o f water i n a paper sheet i s conven t i o n a l l y done by a technique which i s known as the Klemm t e s t . According t o t h i s t e s t , a paper s t r i p i s hung v e r t i c a l l y above a trough f i l l e d w i t h water. The s t r i p i s lowered s l o w l y u n t i l the lower end o f i t i s touched by the water s u r f a c e . Simultaneously, a s e r i e s o f stopwatches i s a c t i v a t e d . The water f r o n t r i s e s through the paper and when i t reaches s p e c i f i e d marks, the times are recorded. A p l o t of w i c k i n g h e i g h t ( h ) versus time ( t ) p r o v i d e s t h e i n f o r m a t i o n concerning the r a t e of f l u i d w i c k i n g i n the paper. The r a t e constant i s c a l c u l a t e d by the LucasWashburn equation (7), which r e l a t e s the w i c k i n g r a t e and c a p i l l a r y s t r u c t u r e of the paper as f o l l o w s : h = kt

m

(3)

where k = constant = φ(τ,γ,θ,η) and r = average r a d i u s o f i n t e r f i b e r c a p i l l a r y , θ = constant angle, η,γ = v i s c o s i t y and s u r f a c e t e n s i o n o f water r e s p e c t i v e l y , m = constant (~0.5) and h = w i c k i n g height. A continuous m o n i t o r i n g device f o r the w i c k i n g measurement would h e l p t o develop an automatic instrument f o r t e s t i n g the r a t e



176

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Figure 1. Pulse propagation technique for the characterization of interfiber bond ing in pulp sheet (photomicrograph of Southern Fine handsheet, 125χ)

ULTIMATE TENSILE STRESS AND MULLEN BURST (dynes / c m ) Χ I0" 2

Figure 2. Relationship between the tensile strength properties and d c (c = sonic velocity in km/sec). (Plots corresponding to individual samples have the same ordinate value and are indicated by an arrow parallel to ab scissa.) 2

~

6

~

I

IOOO

2000

1000

2000

TENSILE BREAKING STRENGTH

3

3000

3000 (dynes/cm) X 10



12.

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Thermoacoustical

177

Techniques

of wicking i n paper. In view of t h i s c o n s i d e r a t i o n , the a c o u s t i c a l method f o r the measurement of wicking i n a paper l i k e s t r u c ture has been developed (8). For the present i n v e s t i g a t i o n , standard handsheets c o n s i s t i n g of bleached commercial pulps were used. The samples are b r i e f l y described i n Table I I . A set of p i e z o e l e c t r i c transducers of a p u l s e propagation meter i s p l a c e d a t a f i x e d d i s t a n c e on the sample sheet as r e p r e sented i n Figure 3. Water i s a p p l i e d by a c a p i l l a r y tubing at the midpoint between the transducers. The sonic pulse propagation time i n microseconds i s continuously measured during the a p p l i c a t i o n of the water. A t y p i c a l p l o t of s o n i c response before and during the wicking process i s shown i n Figure 4. New coordinates are drawn so as t o i n t e r s e c t a t the p o i n t corresponding to the commencement o f the a p p l i c a t i o n of water. The converted o r d i n a t e would represent the change of the r e c i p r o c a l v e l o c i t y of sound due t o wicking or ( l / c - l / c ) where c i s the sound v e l o c i t y at any time, t , during the wicking and c i s the sound v e l o c i t y b e f o r e the a p p l i c a t i o n o f water. The a b s c i s s a r e p r e s e n t i n g the wicking time i s c a l i b r a t e d i n seconds according to the speed of the chart paper. From the graph, the value of ( l / c - l/c ), is determined where c i s the sound v e l o c i t y at any time, t , during wicking and c i s the sound v e l o c i t y before the a p p l i c a t i o n of water. According t o an e a r l i e r p u b l i c a t i o n o f C h a t t e r j e e (8), the r a t e equation through a c o u s t i c a l measurement can be expressed as w

0

w

Q

w

Q

w

0

(l/c

w

- l/c ) = k't

(4)

m

0

where k' i s a constant and p r o p o r t i o n a l to k of equation

(3).

Results and D i s c u s s i o n . The t y p i c a l p l o t s of l o g ( l / c - l / c ) versus l o g t are shown i n Figure 5. The l i n e a r i t y of the p l o t s confirm equation ( 4 ) . The values of m, k, and k obtained from Klemm and s o n i c t e s t s are given i n Table I I I . The values of m obtained from both techniques are not too f a r apart from the t h e o r e t i c a l value of 0.5. Theoretically, k i s d e f i n e d as the height of the l i q u i d at one second wicking time whereas k i s defined as the r e d u c t i o n of sonic v e l o c i t y at one second wicking time. Hence, the absolute values of k and k' must not be compared. A f a i r l y good c o r r e l a t i o n between k and k i s evident from F i g u r e 6. Therefore, i t can be i n f e r r e d that k as obtained from the conventional Klemm t e s t and k as obtained from the s o n i c pulse propagation t e s t should represent the r a t e of wicking i n r e l a t i v e terms. The r e s u l t i n d i c a t e s t h a t the pulse propagation technique i s an e x c e l l e n t automatic method f o r the study of wicking i n a paper l i k e s t r u c t u r e . The technique i s a l s o very simple and quick. w

0

f

f

1

!


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Table I I PULP SAMPLES Apparent D e n s i t y


Sample Identification

of handsheet g/cc

Description of Pulp

0.35

Ground Wood, P a r t i a l l y Bleached

0.65

80% Cedar-20$ Hemlock, Kraft

C

0.59

Northern P i n e , S u l f i t e

D

0.59

Hemlock, S u l f i t e

Ε

0.60

Southern P i n e , K r a f t

F

0.56

Redwood, K r a f t

G

0.52

50$ Douglas Fir-50% Sawdust, K r a f t

0.54

Douglas F i r , K r a f t (sample 1)

0.50


0.50

Southern P i n e , K r a f t (sample 2)

0.49

Southern P i n e , K r a f t Semibleached

0.50




CHATTERJEE

Thermoacousticol

Techniques

Figure 3. Fulse propagation technique for the measurement of fluid wicking in pulp sheet (photomicrograph of Southern Pine hanasheet, 100X).

CHART SPEED : J

inches/min.

Figure 4. Typical sonic response during wicking. Width of the strip: 15 mm. t' = pulse propagation time for 10cm distance, Φ = [1/c — l/c ], t = wicking time; sonic response: be, before wicking; c, application of water; cd, during wicking; d, termination of test. w

0




50 Γ

ΙΟ

50

100

WICKING TIME t(sec) Figure 5.

Relationship between sonic velocity and wicking in handsheets. Logarithmic plots of Equation 4.

Figure 6. Correlation between the rate constants (k 6k'j determined by Klemm and sonic tests respectively. Correlation coefficient is 0.976.


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Thermoacoustical

Techniques

181


Table I I I EQUATION CONSTANT AND RATE PARAMETERS DETERMINED BY KLEMM AND SONIC TESTS Equation Constant and Rate

Sample .fication

Klemm Test ( E q u a t i o n 3) k m

Parameters

Sonic Test (Equation 4) k m

A

0.54

0.10

0.55

0.22

Β

0.48

0.29

0.52

0.54

C

0.49

0.29

0.54

0.63

D

0.48

0.38

0.49

0.90

Ε

0.48

0.56

0.54

1.20

F

0.44

0.61

0.50

1.20

G

0.46

0.54

0.54

1.30

H

0.49

0.66

0.55

1.40

I

0.46

0.62

0.56

1.70 1.70

J

0.45

0.76

0.56

Κ

0.47

0.79

0.51

1.80

L

0.44

0.85

0.52

2.00



182 Qynamic Thermoacoustical

Technique


This s e c t i o n presents an a c o u s t i c a l technique which can be used to determine the changes i n r e l a x a t i o n a s s o c i a t e d w i t h polymers ( f i b e r s ) under dynamic h e a t i n g c o n d i t i o n s . The p r i n c i p l e of the technique w i t h i t s t h e o r e t i c a l d e r i v a t i o n s was d e s c r i b e d e a r l i e r (9,10). Technique and Theory. In p r i n c i p l e , the method c o n s i s t s of a continuous measurement of the propagation time of sonic pulses of constant frequency (7kc) through the t e s t sample which i s being h e l d under l i g h t t e n s i o n and heated at programmed temperature ( F i g u r e 7). The experimental setup i s shown i n Figure 8. In the f i g u r e , A represents the h e a t i n g b l o c k of a DuPont 900 DTA where H r e p r e sents the h e a t i n g element and T 2 and T 3 represent the reference and sample w e l l s , r e s p e c t i v e l y . Two a d d i t i o n a l holes ( Τχ and T4 ) were d r i l l e d a l l the way from one end t o the other through the h e a t i n g b l o c k . The h e a t i n g b l o c k was thoroughly i n s u l a t e d by p u t t i n g asbestos caps on both ends and c o v e r i n g the r e s t w i t h asbestos tape. M e l t i n g p o i n t tubes, open on both ends, were i n s e r t e d i n t o h o l e s Τχ and T 4 . The h e a t i n g b l o c k was mounted h o r i z o n t a l l y and thermocouples were i n s e r t e d i n Τχ, T2> and T 3 . These thermocouples were connected t o d i f f e r e n t t e r m i n a l s of the DuPont DTA c e l l as shown i n Figure 8. The f i b e r sample was t i e d w i t h one end t o a clamp S, passed under a p u l l e y Ρχ and on a notched ceramic p i e z o e l e c t r i c c r y s t a l transducer Ζχ, through hole T 4 and supported by another i d e n t i c a l p i e z o e l e c t r i c c r y s t a l Z 2 and a s e t o f p u l l e y s P 2 and f i n a l l y terminated at a suspended weight of 5g. The p i e z o e l e c t r i c c r y s t a l s were connected to an e l e c t r i c a l pulse generating and r e c o r d i n g device, R. The d i s t a n c e between Ζχ and Z 2 was 3.6 cm which was kept constant throughout the experiment. The sound pulses are t r a n s m i t t e d through the f i b e r sample and the time r e q u i r e d f o r p u l s e s t o propagate from Ζχ t o Z 2 i s recorded. Knowing t h i s propagation time and the d i s t a n c e between Ζχ and Z 2 , one can c a l c u l a t e the v e l o c i t y of sound through the sample. However, i n the present technique, i t i s necessary t o r e c o r d the p u l s e propagation time o n l y ; the v e l o c i t y conversion i s not r e q u i r e d . The sample i s heated i n a i r atmosphere at a programmed r a t e of 20°C per minute. The system temperature i s c o n t i n u o u s l y recorded on a DTA chart whereas the s o n i c response i s simultane o u s l y recorded on a time base r e c o r d e r provided w i t h the p u l s e propagation device. The a b s c i s s a of the o r i g i n a l s o n i c c h a r t i s l a t e r converted t o a temperature s c a l e . I n the case of a simultaneous d i f f e r e n t i a l thermal a n a l y s i s and dynamic t h e r m o a c o u s t i c a l a n a l y s i s ( 9 ) , the f i b e r s are cut i n t o s m a l l p i e c e s by u s i n g a Wiley m i l l with~~60 mesh screen, and 5 mg of t h i s sample was poured i n t o a m e l t i n g p o i n t tube. The tube i s



CHATTERJEE

Thermoacoustical

Techniques

Figure 7. Dynamic thermoacoustical technique for the characterization of textile fibers (photomicrograph of partially drawn polyester fiber, 1000X)

AdjuMtobiê

Figure 8.

Mount

A schematic of dynamic thermoacoustical system


184

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TECHNOLOGY

then p l a c e d i n t o the sample c a v i t y T2> and a thermocouple, as shown i n F i g u r e 8, i s i n s e r t e d i n t o the sample. S i m i l a r l y , i n r e f e r e n c e c a v i t y T 3 , a m e l t i n g p o i n t tube c o n t a i n i n g reference g l a s s beads i s i n s e r t e d . The reference thermocouple i s then embedded i n t o the g l a s s beads. For t h e r m o a c o u s t i c a l a n a l y s i s , the setup i s the same as t h a t d e s c r i b e d i n the preceding s e c t i o n . On h e a t i n g the metal b l o c k A , the DTA curve of the sample i s obtained on the X-Y recorder of the DTA instrument and a thermo a c o u s t i c a l curve of the sample i s obtained on the time base recorder. A sketch of a h y p o t h e t i c a l dynamic thermoacoustical curve i s shown i n F i g u r e 9. The p u l s e propagation time f o r a d i s t a n c e of χ cm of the sample at room temperature i s represented by the h o r i z o n t a l p o r t i o n o f the curve AB. As long as the d i s t a n c e χ i s kept constant, AB remains p a r a l l e l to the a b s c i s s a . The v e l o c i t y of sound through the m a t e r i a l at 25°C i s equal t o (χ/120) χ 106 km/sec. The temperature programming of the DTA apparatus i s i n i t i a t e d at B. As long as the sample remains p h y s i c a l l y and c h e m i c a l l y unchanged, the curve continues to i n d i c a t e the h o r i z o n t a l l i n e . At C the sample begins to transform t o a d i f f e r e n t phase and the curve d e v i a t e s from the base l i n e . A change towards the upward d i r e c t i o n i n d i c a t e s the lowering of the sound v e l o c i t y . I t i s known t h a t the v e l o c i t y of sound i s h i g h e s t i n s o l i d , lowest i n gas, and i n t e r m e d i a t e i n l i q u i d . Therefore, one may assume t h a t the upward t r e n d of the curve would i n d i c a t e the change of polymer from compact form t o r e l a t i v e l y f l u i d form o r , i n other words, an i n c r e a s e of molecular motion of polymers. An opposite phenomenon i s i n d i c a t e d by the downward t r e n d of the curve FG. The sample at G i s c e r t a i n l y i n a l e s s f l u i d s t a t e than at F. Again G t o H shows no p h y s i c a l or chemical change i n the sample. At H the sample r e v e a l s the p r e m e l t i n g behavior. As the m e l t i n g s t a r t s , there i s a sharp upward t r e n d of the curve u n t i l the sample breaks a t I due t o the a c t u a l m e l t i n g . The r e c o r d e r pen drops immediately t o zero, i n d i c a t i n g thereby a d i s c o n t i n u i t y of the pulse propagation path. I t has been shown e a r l i e r (9) t h a t the pulse propagation time (μ) i n a f i b e r ( o r polymer f i l m ) can be expressed by the f o l l o w i n g equation: f


CHEMISTRY

μ = 0.82χ k ε

f

(5)

3

where ε i s d e f i n e d as the s o n i c v i s c o e l a s t i c f u n c t i o n o f the polymer at a constant s o n i c frequency, k i s the molecular o r i e n t a t i o n f a c t o r , and χ i s the d i s t a n c e between transducers. There f o r e , according t o equation ( 5 ) , the dynamic t h e r m o a c o u s t i c a l curves which w i l l be discussed here represent e as a f u n c t i o n o f temperature. 3

s

R e s u l t and D i s c u s s i o n . Thermoacoustical curves of a v a r i e t y of s y n t h e t i c f i b e r s are shown i n F i g u r e 10. These curves are a l l


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obtained under the same c o n d i t i o n and at the same s c a l e s e n s i t i v i t y . The f i r s t curve i s f o r n y l o n 6,10. The curve shows a d i s t i n c t upward d e v i a t i o n from the base l i n e at 45°C. This d e v i a t i o n i s a t t r i b u t e d t o the g l a s s t r a n s i t i o n temperature of n y l o n 6,10. Premelting behavior of the polymer i s r e v e a l e d by the change of slope of the curve above 150°C. The m e l t i n g i s i n d i c a t e d by the sharp upward t r e n d of the curve and then an instantaneous drop to the zero l i n e (not shown i n the c h a r t ) . I t i s important t o note t h a t above the g l a s s t r a n s i t i o n temperature, the pulse propagation time i n c r e a s e d c o n t i n u o u s l y w i t h the r i s e of temperature. Prior t o m e l t i n g , however, the propagation time i n c r e a s e d a t an a c c e l erating rate. The curves of d i f f e r e n t f i b e r s a l l show d i f f e r e n t charact e r i s t i c natures. However, as expected, the t h e r m o a c o u s t i c a l behavior of a g l a s s f i b e r i n d i c a t e s no s i g n i f i c a n t change i n the temperature range shown. The dynamic t h e r m o a c o u s t i c a l curves of c o t t o n and rayon are shown i n F i g u r e 11. They are d i s t i n c t l y d i f f e r e n t , p a r t i c u l a r l y above 250°C. Rayon shows a d i s t i n c t peak a t about 340°C, whereas c o t t o n shows a s e r i e s of o v e r l a p p i n g peaks at higher temperatures. These peaks can be a t t r i b u t e d t o the decomposition of c e l l u l o s e f i b e r s . Because of a v a r i e t y of chemical changes at the decompos i t i o n temperature, such as polymer s c i s s i o n , end-group u n z i p p i n g ( 1 1 ) , e t c . , the v e l o c i t y of pulses was slowed down r e s u l t i n g i n a peak. The right-hand s i d e of the peak i n d i c a t e s the resumption of the o r i g i n a l speed as the chemical changes were over and the c e l l u l o s e molecule was converted to a s t a b l e carbonized form. Again, the curve of g l a s s f i b e r has been i n c l u d e d as a r e f e r e n c e . A simultaneous t h e r m o a c o u s t i c a l curve and d i f f e r e n t i a l thermal a n a l y s i s curve were obtained w i t h n y l o n 6,10 by the t e c h nique d e s c r i b e d e a r l i e r . For the t h e r m o a c o u s t i c a l curve, the sample was mounted as shown i n Figure 8 and f o r DTA the sample was cut i n t o s m a l l p i e c e s . Both curves were obtained simultaneo u s l y as shown i n F i g u r e 12. The dynamic t h e r m o a c o u s t i c a l technique o f f e r s an o p p o r t u n i t y t o develop a new i n s t r u m e n t a t i o n i n the f i e l d of thermal a n a l y s i s . However, f u r t h e r refinement i s r e q u i r e d i n the experimental t e c h nique. More p r e c i s e measurements can be done by i n s e r t i n g the e n t i r e f i b e r mounting setup and both p i e z o e l e c t r i c transducers i n s i d e the h e a t i n g chamber. Atmospheric c o n t r o l and an a b i l i t y t o c o o l the furnace below room temperature are a l s o e s s e n t i a l . I n b r i e f , t o b u i l d a standard instrument, the experimental design shown here would r e q u i r e f u r t h e r m o d i f i c a t i o n . Concluding Remarks The s o n i c pulse propagation technique i s shown to be an e x c e l l e n t n o n d e s t r u c t i v e method f o r e s t i m a t i n g i n t e r f i b e r bonding i n c e l l u l o s e sheet. The technique a l s o has a unique a p p l i c a t i o n f o r studying the l i q u i d w i c k i n g i n c e l l u l o s e sheets. The dynamic



12.

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Figure 11.

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Dynamic thermoacoustical curves of cellulose fibers in air

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Figure 12.

Simultaneous DTA and dynamic thermoacoustical an alysis of Nylon 6,10 in air


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t h e r m o a c o u s t i c a l technique described i n t h i s paper f u r t h e r expands the t h e r m o a n a l y t i c a l f i e l d . Acknowledgment The author wishes t o acknowledge the management o f P e r s o n a l Products Company, a Johnson & Johnson Company f o r g i v i n g permis s i o n t o present t h i s paper t o the C e n t e n n i a l meeting of t h e American Chemical S o c i e t y .


Abstract The mechanism of sonic pulse propagation in cellulose sheets at isothermal condition and in cotton, rayon and synthetic fibers at dynamic heating conditions have been reviewed. The velocity of sonic pulse in a dry cellulose sheet is controlled by the proportion, modulus and density of two structural constituents of the sheet: the bonded and unbonded fiber regions. Use of this technique to characterize interfiber bonding and liquid absorption is discussed. Theory and application of Dynamic Thermoacoustical Analysis are described. The method consists of a continuous measurement of the propagation time of sonic pulses through the sample held under light tension and heated at programmed temperatures. Viscoelastic properties of a variety of synthetic and cellulosic fibers were examined by this technique. Literature Cited

1. Craver, J. K. and Taylor, D. L., Tappi (1965) 48(3), 142. 2. Chatterjee, P. Κ., Tappi (1969) 52(4), 699. 3. Taylor, D. L. and Craver, J. Κ., "Consolidation of the Paper Web", London, British Paper and Board Makers' Association, Trans. Cambridge Symposium, 852 (1965). 4. Chatterjee, P. K., unpublished work. 5. Lu, M. T., Tappi (1975) 58(6), 80. 6. Marton, R. and Crosby, C. Μ., Tappi (1971) 54(8), 1319. 7. Washburn, E. W., The Phys. Review (1921) 17, 273. 8. Chatterjee, P. K., Sevensk Papperstidning (l971) 74, 503. 9. Chatterjee, P. K., J. Macromol. Sci.-Chem. (1974) A8(1), 191. 10. Chatterjee, P. Κ., "Thermal Analysis", Vol. 3, Proceedings of the Fourth International Conference on Thermal Analysis, held in Budapest, Hungary, July 8-13, 1974; Akademiai Kiado, Budapest (1975) 835. 11. Chatterjee, P. K. and Conrad, C. M., J. Polymer Sci., Part A-1 (1968) 6, 3217.


Cellulose Chemistry and Technology - ACS Publications - American

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