Textile and Paper Chemistry and Technology

1 N e w Methods for Studying Particles in Viscose and

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Their Effects on Viscose Rayon Production JOHN DYER ITT Rayonier Inc., ERD, Whippany, NJ FREDERICK R. SMITH Avtex Fibers Inc., Front Royal, VA Cellulose is made into rayon through the viscose process outlined in Table I. In this process, wood pulp is steeped in aqueous sodium hydroxide to convert the cellulose to the more reactive sodium celluloseate. After steeping, the pulp is pressed to remove excess steeping liquor and then shredded into alkali cellulose crumbs. The crumbs are aged to reduce the cellulose DP before reacting with carbon disulfide to form sodium cellulose xanthate. The derivative is dissolved in dilute aqueous sodium hydroxide, yielding a viscous orange colored solution called viscose. The viscose is aged, during which time air is removed, and chemical and physical changes occur. Then, the solution is f i l tered before extruding through very small holes of a jet into an acid spin bath. There regeneration of the cellulose as filaments of rayon occurs. A normal jet for regular staple manufacture can contain more than 20,000 holes. Typical hole sizes are 1-3.5 mil or 25-90 microns. Particles or other discontinuities, even having size appreciably less than a jet hole, will interfere with viscose flow through the hole, changing the flow from laminar to plug over an area equal to the profile the particle presents to the hole. It is well established that many particles exist in viscose solutions. These originate from the raw materials used in the process - the pulp, caustic and water and from contaminants introduced with the raw materials or from line deposits. The normal practice to avoid interruption in fiber formation at the jet is to remove the particles by filtration. But it has been conclusively shown in several independent studies (1,2)that viscose cannot be completely freed of particles, even with repeated filtration. Rather, there is a distribution of particle sizes meeting some critical parameters of the filter media, filtration pressure and particle nature that will pass through the filters and reach the jet. The potential problems these particles can cause are jet hole plugging, either completely or partially, leading to high spinning 3

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

4

TEXTILE AND PAPER CHEMISTRY AND TECHNOLOGY

pressure and denier non-uniformity. I f the p a r t i c l e s pass through the j e t h o l e s , and most do, they would be expected to i n f l u e n c e f i b e r s t r u c t u r e formation. Adverse e f f e c t s of v i s cose p a r t i c l e s on f i b e r p r o p e r t i e s have been documented i n work by P h i l i p p , S c h l e i c h e r and Arnold (3) and by Zubakhina.j Serkov and Virezub ( 4 ) . Based on p a r t i c l e count measurements by conductometrie, microscopy and l i g h t s c a t t e r i n g methods, T r i e b e r (5) has sug gested a s i z e d i s t r i b u t i o n f o r v i s c o s e p a r t i c l e s which begins with molecules of c e l l u l o s e xanthate and extends to masses l a r g e r than 30 microns diameter. The m a j o r i t y of p a r t i c l e count s t u d i e s on v i s c o s e have been made by measuring the change i n c o n d u c t i v i t y as the p a r t i c l e s flow between e l e c t r o d e s . Vis cose c o n d u c t i v i t y i s p r i m a r i l y dependent on the c o n c e n t r a t i o n of f r e e NaOH and c e l l u l o s e . Conduction i n a g e l p a r t i c l e i s accomplished by movement of N a and OH" i o n s . An i n c r e a s i n g c o n c e n t r a t i o n of c e l l u l o s e i n a g e l decreases the l o c a l concen t r a t i o n of NaOH and the ease w i t h which ions move through i t . The C o u l t e r counter i s u s u a l l y c a l i b r a t e d using some uniformly s i z e d non-conducting p a r t i c l e s . I t i s then assumed that amy p a r t i c l e i n v i s c o s e , which has the same e f f e c t on c o n d u c t i v i t y , has the same dimensions. This i s obviously erroneous s i n c e c e l l u l o s e g e l s may have c o n d u c t i v i t y near that of the suspend ing f l u i d . I f the s p e c i f i c c o n d u c t i v i t y i s f o u r times that of the non-conducting c a l i b r a t i n g p a r t i c l e , the measured s i z e w i l l be 1/4 the a c t u a l s i z e . I f a s i g n i f i c a n t p o r t i o n of p a r t i c l e s c l a s s i f i e d 4-8μ are i n r e a l i t y gels 16-64y i n diameter, then the d i f f i c u l t i e s i n r e l a t i n g p a r t i c l e count to the e f f e c t on f i l t e r s and spinning becomes more i n t e l l i g i b l e . I t has been pointed out that i t i s v e r y important to d i l u t e v i s c o s e f o r conductometrie counting so t h a t the c o n c e n t r a t i o n of f r e e NaOH i s not changed. The e f f e c t of d i l u t i n g , which can cause changes i n the extent of s o l v a t i o n and mechanical degradation due to mixing on the p a r t i c l e s i z e and d i s t r i b u t i o n , had not been established. +

I n recent years, equipment f o r p a r t i c l e count measurement, based on changes i n l i g h t transmission, has been developed (6)· This equipment can be used with u n d i l u t e d v i s c o s e , the measure ments thus being more r e p r e s e n t a t i v e of the v i s c o s e s o l u t i o n at the various process stages from which samples may be taken. The equipment i s i l l u s t r a t e d i n Figure 1. I t c o n s i s t s of two b a s i c u n i t s , the sensor and the counter. A constant volume pump was used to feed v i s c o s e through the sensor. For l e s s v i s c o u s l i q u i d s , constant flow rates were obtained w i t h a b o t t l e sampling device using p r e s s u r i z e d a i r or n i t r o g e n . The b a s i c operation of t h i s equipment i s s t r a i g h t f o r w a r d (Figure 2) examination of a sample taking two minutes once the sensor has been flushed w i t h the sample. The sample flows through a small rectangular f l u i d passage past a window.


1.

DYER

AND SMITH

Studying

Particles

in

5

Viscose

TABLE I AN OUTLINE OF THE VISCOSE PROCESS PUjLP

ISTEEPI

[PRESSχaSHRÊD] I AGE XANTHATE

X MIX

HZ AGE FILTER

X

recovery of cellulose as fiber or film by decomposing the derivative.

[SPIN |VuASHaFINISH|

RAYON

Pacific Scientific Co. Figure 1.

The HI AC automatic

particle counter

(11)


6


P a r t i c l e s i n the f l u i d pass by the window one by one as long as s p e c i f i e d l i m i t s of p a r t i c l e c o n c e n t r a t i o n a r e not exceeded. L i g h t from a tungsten lamp i s formed by the window t o a p a r a l l e l beam of exact s i z e and d i r e c t e d onto a photodetector. Using the l i g h t i n t e n s i t y a d j u s t , the operator e s t a b l i s h e s the proper base v o l t a g e from the photodetector as i n d i c a t e d on the p a n e l base output meter. Each p a r t i c l e , as i t passes the window, i n t e r rupts a p o r t i o n of the l i g h t beam according to i t s s i z e . This causes a s p e c i f i c r e d u c t i o n ( o r p u l s e ) i n the v o l t a g e which i s p r o p o r t i o n a l t o the s i z e o f the p a r t i c l e . F i v e counting c i r c u i t s (channels) with p r e s e t thresholds t a l l y the p a r t i c l e s by s i z e . A s i z e range adjustment i s provided f o r each channel t o permit the operator t o s e l e c t any d e s i r e d s i z e ranges. A b u i l t i n c a l i b r a t i o n p u l s e generator provides the operator with r e f erence pulses t o simulate any p a r t i c l e s i z e f o r a d j u s t i n g and v e r i f y i n g the s i z e ranges. The p a r t i c l e count i s r e g i s t e r e d i n each channel as e i t h e r t o t a l - the t o t a l number l a r g e r than the s i z e f o r which the channel i s s e t or D e l t a - the number l a r g e r than the s e t t i n g of that channel but s m a l l e r than the s e t t i n g of the next h i g h e r channel. For the s t u d i e s d e s c r i b e d i n t h i s paper, the D e l t a mode was used. Various s i z e d sensors are a v a i l a b l e . One convenient f o r use with v i s c o s e i s a 5-150D sensor. Sensor dimensions f o r the c o n s t r i c t e d passage through the l i g h t beam shown i n F i g u r e 2 are 150μ square by 2450μ deep. P a r t i c l e s are s i z e d according to the extent t o which they i n t e r r u p t the l i g h t beam. The d i f ferent o r i e n t a t i o n s of an i r r e g u l a r p a r t i c l e passing through the sensor produces an output more c l o s e l y r e l a t e d to the a c t u a l s i z e of the p a r t i c l e than would a m i c r o s c o p i c examination i n a static field. A l l p a r t i c l e s i n the l i g h t beam a t any one time are counted as one p a r t i c l e of s i z e p r o p o r t i o n a l to the excluded l i g h t beam. A l a r g e number of s m a l l p a r t i c l e s : w i l l appear as a s i n g l e l a r g e p a r t i c l e . This phenomena of " c o i n c i d e n c e " i s avoided by s p e c i f y i n g that there should be no more than one p a r t i c l e i n t e n sen sor volumes. For the 5-150D sensor, there are 17000 sensor volumes per c . c , e s t a b l i s h i n g a l i m i t o f 1700 p a r t i c l e s p e r c.c. of sample. The 5-150D sensor i s s u i t a b l e f o r use w i t h v i s c o s e s having v i s c o s i t y of up to about 300 p o i s e s . Higher v i s c o s i t y s o l u t i o n s can be examined - t h e sensor w i l l withstand pressures of 2000 p s i but problems with blockage and c l e a n i n g of the sensor increase substantially at high v i s c o s i t y . The flow rate used f o r v i s c o s e was 36.5 g/m; the p a r t i c l e counts have been reported on a per gram b a s i s c a l c u l a t e d from the counts determined over a t o t a l time p e r i o d of two minutes. The r e p r o d u c i b i l i t y of the count data i s good; r e s u l t s f o r t e n consecutive counts each of twelve seconds on a s i n g l e v i s c o s e are given with averages and standard d e v i a t i o n s of the measure-


1.

DYER A N D SMITH

Studying Particles

in Viscose

7

ment i n Table I I . Since p a r t i c l e s should not be removed from the sample during the counting, samples can be r e c y c l e d o r used i n f u r t h e r experiments but care must be taken to avoid contaminat i o n with a i r . Results given i n Table I I I were f o r a f i l t e r e d v i s c o s e with and without a i r and with two r e c y c l e s on each sample. The i n c l u s i o n of only a s m a l l q u a n t i t y of a i r (about 0.5 cc/100 g) i n the v i s c o s e had a pronounced e f f e c t on the p a r t i c l e count. The change i n the p a r t i c l e count on r e c y c l i n g i n d i c a t e s that s m a l l amounts of a i r were trapped i n the v i s c o s e with each c y c l e ; the number of l a r g e p a r t i c l e s apparently i n c r e a s e d and the number o f s m a l l p a r t i c l e s decreased. When there was an a p p r e c i a b l e amount of a i r i n the v i s c o s e , some deaeration occurred during the part i c l e count measurement and the count on the r e c y c l e d sample shows a decrease i n l a r g e p a r t i c l e s with an i n c r e a s e i n the number of s m a l l p a r t i c l e s . In the e a r l y stages of e v a l u a t i n g the HIAC p a r t i c l e counter, a t t e n t i o n was d i r e c t e d toward r e s o l v i n g the q u e s t i o n of what changes occur on d i l u t i n g v i s c o s e . A comparison was made of part i c l e counts on v i s c o s e s using the C o u l t e r counter and HIAG counter. Both d i l u t e d and u n d i l u t e d v i s c o s e s were examined with the l a t t e r equipment. The number of p a r t i c l e s counted i n v i s c o s e by the C o u l t e r counter and HIAC counter was very d i f f e r e n t , being much g r e a t e r f o r the HIAC as seen i n Table IV. T h i s was p r e d i c t e d because one method counts changes i n an e l e c t r i c f i e l d while the other counts changes i n l i g h t t r a n s m i s s i o n . F o r the Coulter count the v i s c o s e was d i l u t e d 1:6 using 6% NaOH. The sample i s changed by d i l u t i o n . The HIAC shows the number of s m a l l p a r t i c l e s i s g r e a t l y increased i n the d i l u t e d samples. A c l o s e r examination of the e f f e c t of d i l u t i n g v i s c o s e was made. A standard v i s c o s e was mixed i n v a r i o u s p r o p o r t i o n s with 6.45% NaOH. HIAC p a r t i c l e counts per gram of sample measured on the v i s c o s e , the d i l u t e d samples and the d i l u e n t are g i v e n i n Table V. The p a r t i c l e d i s t r i b u t i o n was a l s o c a l c u l a t e d from the measured d i s t r i b u t i o n i n the u n d i l u t e d v i s c o s e and c a u s t i c . G e n e r a l l y , the number of l a r g e p a r t i c l e s decreased i n p r o p o r t i o n to the d i l u t i o n but the s m a l l p a r t i c l e count was r e l a t i v e l y una f f e c t e d . S i m i l a r c a l c u l a t e d and measured p a r t i c l e d i s t r i b u t i o n s have been observed f o r other v i s c o s e d i l u t e d 1:10 with c a u s t i c or water. To a c e r t a i n extent, t h i s observation i s the r e s u l t of coi n c i d e n c e . But, a t 1:4 and 1:10 d i l u t i o n , the t o t a l number of p a r t i c l e s c a l c u l a t e d i s a p p r e c i a b l y l e s s than the 1:10 c o i n c i dence l i m i t of 1700 p a r t i c l e s per c.c. or one p a r t i c l e i n every 10 sensor volumes. As w i l l be shown l a t e r , there have been r e a l changes i n the nature and number of p a r t i c l e s on d i l u t i n g v i s cose, many more of the p a r t i c l e s can be removed by f i l t e r i n g the d i l u t e d v i s c o s e than when the u n d i l u t e d v i s c o s e i s f i l t e r e d .



8

tfPU FLUID

P

FLUID PASSAGE

A

m B k S i

OUTPUT METER

PHOTOOETECTOR

SIZE RANGE ADJUSTMENT

* LIGHT INTENSITY ADJUST

X Ο Ο Ο Ο ΟΟ ο ο ο ο ο ο CHANNELS ^

Pacific Scientific Co. Figure 2. The HIAC auto matic particle counter (11)

CALIBRATION PULSE GENERATOR

TABLE I I R e p r o d u c i b i l i t y of HIAC P a r t i c l e 12 Second Count # at 36.5 g/m i

5

Count

ί

P a r t i c l e s / g Viscose 3G 10 ί 15

Ι

975

734

128

? f

60μ î

I

1

1789

2

1717

954

731

137

11.8

3

1680

928

728

132

12.8

4

1770

978

749

126

7.6

5

1767

953

727

137

9.2

6

1746

934

735

124

9.9

7

1693

944

717

133

8.3

8

1818

972

734

126

8.9

9

1720

955

737

126

12.2

10

1706

925

740

141

12.2

Average

1741

952

734

131

10.1

45

19

8.5

5.9

1.9

Standard Deviation

8.6 i ι


1.

Studying

DYER A N D SMITH

Particles

in Viscose

TABLE I I I E f f e c t of A i r and R e c y c l i n g Sample

Sample

it Times Recycled

Viscose

0

3559

233

1

3402

2 Viscose + A i r

Particles/g 10 15

30

60μ

24

6

2.6

225

27

9

3.6

3142

203

34

15

6.4

0

41

57

200

383

453 \

1

64

67

223

408

368

2

90

83

255

443

266

5

I î

Λ

TABLE IV Comparison of HIAC and C o u l t e r Counts P a r t i c l e Count/g. HIAC Coultei (7-30μ) (8-32u) u d

Viscose Sample

Filtered

Ratio HIAC/Coulter d u

A

452

3771

2000

8.3

4.4

Β

78

1867

2297

23.9

29.5

C

262

: 3639

1978

13.9

7.6

ι

Unfiltered D

969

11911

2534

12.3

2.6

Ε

! 4333

\ 5334

6609

1.2

ι..

d:

diluted

u:

undiluted

;


10


This i s shown by the r e s u l t s given i n Table V I . The f i l t e r medium was g l a s s f i b e r paper. P a r t i c l e counts b e f o r e and a f t e r f i l t r a t i o n of the u n d i l u t e d v i s c o s e , the v i s c o s e d i l u t e d 1:10 with 6.2% NaOH and 1:10 with water and f o r the mixer charge and d i l u e n t s , show that only a few of the l a r g e r p a r t i c l e s were r e moved from u n d i l u t e d v i s c o s e . P a r t i c l e removal from the d i l u t e d v i s c o s e was much more e f f e c t i v e , the p a r t i c l e counts on the f i l t r a t e being s i m i l a r to those measured f o r the f i l t e r e d d i l u e n t s . Two f i l t e r a b i l i t y t e s t s have been widely used f o r e v a l u a t ing v i s c o s e q u a l i t y . One i s the t e s t based on v i s c o s e flow through a standard f i l t e r medium a t constant p r e s s u r e . The other t e s t uses a constant flow and the f i l t r a t i o n "T" value i s c a l c u l a t e d from t h e pressure b u i l d - u p . P a r t i c l e counts measured on v i s c o s e , a f t e r f i l t e r i n g o r passing through a j e t with 1500 χ 63.5 micron diameter holes under constant pressure and a t con s t a n t flow r a t e , are compared i n Table V I I . The f i l t e r element was that normally used i n f i l t r a t i o n "T" t e s t - a candle f i l t e r wound with four l a y e r s of cotton y a r n . Constant flow, 29 g/m, was obtained from a volumetric pump and constant pressure, 39 p s i , was obtained using compressed n i t r o g e n . At constant flow r a t e , the pressure build-up was i n s i g n i f i cant when about 500 g v i s c o s e was f i l t e r e d through the candle f i l t e r o r passed through the j e t . The candle f i l t e r removed the l a r g e p a r t i c l e s , causing an apparent i n c r e a s e i n the number of s m a l l p a r t i c l e s from 2200 t o 3200 due t o c o i n c i d e n c e . P a r t i c u l a t e m a t e r i a l s i z e d a t greater than the h o l e dimension (63.5u) was not removed by the j e t under s i m i l a r c o n d i t i o n s of flow. This observation suggests t h a t the l a r g e p a r t i c l e s a r e not s p h e r i c a l . A l l p a r t i c l e s i n the sensor at any one time are counted as one p a r t i c l e of s i z e p r o p o r t i o n a l t o the excluded l i g h t beam. I t i s p o s s i b l e that elongated p a r t i c l e s ( f i b e r s ) w i l l pass through the sensor i n s e v e r a l sensor volumes. The small p a r t i c l e s i n these volumes w i l l not be counted unless the l a r g e p a r t i c l e s a r e removed. A t constant pressure, 39 p s i , the candle f i l t e r again r e moved the l a r g e r p a r t i c l e s and i n c r e a s e d the s m a l l p a r t i c l e count. The same v i s c o s e f i l t e r e d through the j e t a t t h i s p r e s sure appeared t o have an increased number of l a r g e p a r t i c l e s with no change i n the number of s m a l l p a r t i c l e s . There i s some i n d i c a t i o n that p a r t i c l e s i z e i s increased by agglomeration p o s s i b l y o c c u r r i n g during a t r a n s i e n t holdup of the l a r g e r g e l p a r t i c l e s i n the j e t h o l e s . I t i s expected t h a t , i f t h i s does occur, the mechanism could be analogous to s i l t i n g and channel ing phenomena and w i l l be i n f l u e n c e d by p a r t i c l e d e f o r m a b i l i t y , the pressure i n the system and d e f e c t s i n the j e t h o l e s . There i s evidence t h a t , a t constant flow r a t e , p a r t i c l e s plugging j e t holes break away and a r e extruded as pressure i n c r e a s e s . Making c e r t a i n assumptions on the average p a r t i c l e s i z e , the t o t a l p a r t i c u l a t e volume i n one c.c. o f the v i s c o s e sample


1.

DYER

Studying

AND SMITH

Particles

in Viscose

TABLE V E f f e c t of D i l u t i n g •

Sample

11

Viscose

P a r t i c l e s / g Sam]pie 30 10 15

5

60μ

Undiluted Viscose m.

2849

1059

346

28

5.3

D i l u t e d Viscose 2:3 c.

2055

715

237

22

3.8

m.

2999

866

266

22

3.2

1:2 c.

1659

543

182

19

3.1

m.

3162

828

234

19

2.2

1:4 c .

1063

285

100

14

2

m.

2316

390

133

19

1.9

706

130

51

11

1.3

m.

2300

397

129

11

.5

m.

468

27 ι ,,

18

9

1:10 c.

6.45% NaOH m. measured

!

·* 1

c. c a l c u l a t e d

TABLE VI E f f e c t of D i l u t i n g ι Sample

5

Viscose P a r t i c l e s / g Sample 30 10 15

60y

Γ ί Viscose

U

1944

855

507

84

6.7

i

F

1945

792

463

72

5.6

1781

250

94

15

1.5

51

15

1

.2

' 2476

302

101

10

.8

i

\ Viscose D i l .

U

1

•i

1:10 w 6.2% NaOH

F

Viscose D i l .

U

1:10 w H2O

F

; 266

46

21

1

.3

6.2% NaOH

F

250

46

23

2

.1

H0

F

ί 410

37

23

2

0

2

U:

unfiltered,

: 661

1—

F : filtered


12


was c a l c u l a t e d . The r e s u l t s a r e shown i n Table V I I I . In t h i s case, c o i n c i d e n c e has much l e s s impact on the d i s t r i b u t i o n s i n c e , although a much l a r g e r number of s m a l l p a r t i c l e s are counted a f t e r the l a r g e p a r t i c l e s have been removed, the i n crease i n p a r t i c u l a t e volume due to the s m a l l p a r t i c l e s i s a r e l a t i v e l y s m a l l f r a c t i o n o f the t o t a l p a r t i c u l a t e volume. These r e s u l t s show that p a r t i c u l a t e m a t e r i a l was removed by the candle f i l t e r but not by the j e t . T h i s i s not unexpected s i n c e the l a r g e r p a r t i c l e s are not s p h e r i c a l and w i l l be able to pass through the 63.5 micron diameter h o l e s . In the next experiment v i s c o s e was passed through a 325 mesh, s t a i n l e s s s t e e l s c r e e n i n which the openings were a p p r o x i mately 50 microns square. The p a r t i c l e counts and f i l t e r a b i l i t y measurements shown i n Table IX were made b e f o r e and a f t e r . A l though the screen was not an e f f i c i e n t f i l t e r , i t d i d remove h a l f of the p a r t i c l e s i n the 30 and 60y counts and the f i l t e r a b i l i t y improved (a low "T" v a l u e corresponds to improved f i l t e r a b i l i t y ) . A p o r t i o n of the r e s i d u e was removed from the s c r e e n there was i n s u f f i c i e n t f o r p a r t i c l e count - and mixed with the u n f i l t e r e d v i s c o s e . As expected, the number of l a r g e p a r t i c l e s i n c r e a s e d and the f i l t e r a b i l i t y was a d v e r s e l y a f f e c t e d . The e f f e c t of c o i n c i d e n c e on the s m a l l p a r t i c l e count i s e v i d e n t . Much e f f o r t has been expended to show c o r r e l a t i o n between f i l t e r a b i l i t y measurements and some f u n c t i o n of a p a r t i c l e count or d i s t r i b u t i o n . The very l i m i t e d success of those e f f o r t s has l e d to arguments of e x p l a n a t i o n . The statements of p a r t i c l e s i z e d i s t r i b u t i o n say l i t t l e , i f anything, about the nature of the p a r t i c l e s o r t h e i r shape. T r e i b e r (7) has r e c e n t l y s t u d i e d the shapes of p a r t i c l e s r e movable by f i l t r a t i o n ; a s i m i l a r study was a l s o suggested by Meskat ( 8 ) . Both have recognized the p o s s i b i l i t y that many of th.e p a r t i c l e s are deformable g e l s . The e l a b o r a t e v i s c o s e g e l f r a c t i o n a t i o n procedure used by Durso and Parks (9) i n v o l v e s d i l u t i o n and consequently cannot avoid changes i n p a r t i c l e number and s i z e . I t i s suggested that the e x i s t i n g data i s s u f f i c i e n t to conclude that w i t h i n a body o f v i s c o s e (e.g. 1 gX there e x i s t s thousands of p a r t i c l e s having a wide d i s t r i b u t i o n of s i z e s , shapes and v i s c o s i t i e s o r d e f o r m a b i l i t i e s . The range of v i s c o s i t i e s at the micro l e v e l i s probably from that of the s o l v e n t to the extremely h i g h v a l u e s o f p o o r l y s u b s t i t u t e d a l k a l i c e l l u l o s e f i b e r s . A l k a l i c e l l u l o s e does not flow at 40,000 p s i but, as seen on the macro s c a l e , even p o o r l y xanthated a l k a l i c e l l u lose flows at 1000 p s i . The problem of f i l t r a t i o n may then be i n t e r p r e t e d as a f u n c t i o n of the behavior of many d i f f e r e n t s m a l l volumes o r masses of v a r i o u s v i s c o s i t i e s . Those p a r t i c l e s having dimens i o n s s m a l l e r than the f i l t e r openings w i l l probably pass through r e a d i l y . As the s i z e of the p a r t i c l e approaches that of


1.

DYER A N D SMITH

Studying

Particles

in

13

Viscose

TABLE V I I E f f e c t of F i l t e r i n g

1 Unfiltered

Particles/g Viscose 30 j 15 10

5

Sample Condi t i o n

60y

2197

1785

1518

34

2.6

Filter

3262

1549

296

2.4

0.4

Jet

2152

1753

1484

34

2.5

Filter

3009

1761

610

7.2

1.4

Jet

2193

1755

1529

60

Constant Flow

Constant P r e s s u r e

-

5.4 ! 1

TABLE V I I I E f f e c t of F i l t e r i n g • • « 6" P a r t i c u l a t e Volume cm χ 10 60μ Ί 30 15 10 5

1

J

Sample C o n d i t i o n

Σ

.40

1.61

6.33

1.21

.78

10.33

Filter

.59

1.39

1.22

.08

.11

3.39

Jet

.39

1.58

6.19

1.21

.75

10.12

Filter

.54

1.58

2.55

.26

.40

5.34

Jet

.39

1.58

6.38

2.18

1.56

12.09

Unfiltered Constant Flow

Constant Pressure


14


the f i l t e r opening, i t w i l l pass through a t some speed d e t e r mined by i t s v i s c o s i t y and the pressure gradient or i t may b l o c k the passage i f i t i s not deformable by the f o r c e s around it. P a r t i c l e s l a r g e r than the passage, i f not deformable at the r e l a t i v e l y low pressure d i f f e r e n t i a l across t h e i r dimensions, w i l l simply b r i d g e across the f i l t e r openings and become p a r t of the f i l t e r . The l a r g e r p a r t i c l e s , which are deformable, w i l l , of course, pass through or b l o c k passages i n s i d e the f i l t e r as determined by v i s c o s i t y and p r e s s u r e . Hermans and Bredee (10) have shown that f i l t r a t i o n of v i s cous l i q u i d s follows one of four f i l t r a t i o n laws. These are, i n order of i n c r e a s i n g s e v e r i t y ; sludge, intermediate, standard and pure choking. Most v i s c o s e s f o l l o w the intermediate law when the blockage rate = K w

2.303 l o g P/P

0

= Kt

where Ρ = p r e s s u r e drop across the f i l t e r at any P

0

time

= i n i t i a l pressure drop

t

= time

Κ

= f i l t r a t i o n constant

w

= r e s i s t a n c e of f i l t e r a t time t .

Some v i s c o s e s obey the standard

-±-

sT^

law:

- - L -

- Kt

v/Po"

3/2 In t h i s case, the blockage rate i s ' . The p a r t i c l e s i n the v i s c o s e form a l a y e r around the i n s i d e of the pores of the f i l t e r media, g r a d u a l l y plugging them. A problem i n e v a l u a t i n g v i s c o s e i s t h a t not only can the p a r t i c l e s deform but the f i l t e r media i s not r i g i d and there i s a broad spectrum of r a t e s f o r the plugging of i n d i v i d u a l pores. In the manufacture of rayon, there w i l l s t i l l be many par t i c l e s i n the v i s c o s e when i t i s extruded through the j e t , even though i t has been f i l t e r e d s e v e r a l times. The j e t contains r e l a t i v e l y few l a r g e h o l e s compared to the v e r y numerous s m a l l pores of the f i l t e r media. The passage of p a r t i c l e s through j e t holes i s a random event. I t was speculated, assuming uniform dimensions f o r the h o l e s , that j e t h o l e plugging a l s o would occur randomly. At constant flow r a t e , the plugging of some h o l e s w i l l cause i n creased flow through the other h o l e s . To study t h i s e f f e c t , two


1.

DYER AND SMITH

Studying

Particles in

Viscose

15

j e t s , one w i t h l a r g e h o l e s (980 χ 3.5 m i l diameter) and one w i t h 1500 s m a l l holes (2 m i l diameter) were connected to a common v i s cose supply from a volumetric pump or a p r e s s u r i z e d c o n t a i n e r . The setup i s o u t l i n e d i n Figure 3. The t e s t was made at con s t a n t flow r a t e or constant pressure, recording at convenient time i n t e r v a l s the amount of v i s c o s e d e l i v e r e d from each j e t . Large p a r t i c l e s , >3.5 m i l , b l o c k both j e t s randomly and, gen e r a l l y , to s i m i l a r extents. P a r t i c l e s 2-3.5 m i l w i l l not pass f r e e l y through j e t A but are expected to pass through the h o l e s of j e t Β though, perhaps, not without some e f f e c t . Small par t i c l e s , >2 m i l , w i l l pass through the holes i n both j e t s u n t i l t h e i r passage i s r e s t r i c t e d as the h o l e s p l u g . T h i s occurs f i r s t i n the small h o l e j e t as p a r t i c l e s are deposited by a f i l t r a t i o n mechanism. The o v e r a l l e f f e c t i s t o reduce the flow through the s m a l l h o l e j e t and i n c r e a s e i t through the o t h e r . Examples of measurements made a t constant flow and at constant pressure are given i n Table X. The change i n flow d i s t r i b u t i o n i s measured as the r a t i o of the flow through the two j e t s . Accompanying the change at constant t o t a l flow, pressure b u i l d s up and w i l l e v e n t u a l l y cause p a r t i c l e s to break loose and be ex truded and the flow p a t t e r n w i l l become e r r a t i c . This i s not seen i n t h i s example. The pressure at which t h i s occurs appears to be r e l a t e d to the d e f o r m a b i l i t y of the p a r t i c l e s plugging the h o l e s . At constant pressure, the t o t a l flow i s decreased as the j e t holes p l u g . Both streams are a f f e c t e d i n the same way with the flow from the s m a l l h o l e j e t being reduced to 25% and from the l a r g e h o l e j e t to 87% of t h e i r o r i g i n a l values over a 60 minute p e r i o d . At constant pressure, the flow w i l l e v e n t u a l l y stop when a l l the holes are completely plugged. The r e s u l t s i n t h i s t a b l e (Table X) were obtained using an u n f i l t e r e d v i s c o s e . They show the method - D i f f e r e n t i a l Flow appears to have s i g n i f i c a n t p o t e n t i a l f o r use i n e v a l u a t i n g v i s cose f i l t e r i n g q u a l i t y , perhaps even spinning q u a l i t y . In p r a c t i c e , v i s c o s e i s f i l t e r e d before s p i n n i n g . The j e t h o l e plugging c h a r a c t e r i s t i c of the f i l t e r e d v i s c o s e , although i t contains numerous p a r t i c l e s that have passed through the f i l t e r s f o r reasons of s i z e , shape or d e f o r m a b i l i t y p r o p e r t i e s , i s ex pected to be q u i t e d i f f e r e n t to that f o r an u n f i l t e r e d v i s c o s e . A comparison of r e s u l t s from the d i f f e r e n t i a l flow t e s t on f i l t e r e d and u n f i l t e r e d v i s c o s e at constant t o t a l f l o w i s g i v e n i n Table X I . S u b s t a n t i a l pressure build-up was observed with the u n f i l t e r e d v i s c o s e to the p o i n t where p a r t i c u l a t e m a t e r i a l was extruded from plugged h o l e s and the f l o w r a t i o became e r r a t i c . With the f i l t e r e d v i s c o s e , there was no pressure b u i l d up and no s i g n i f i c a n t change i n the flow r a t i o . F i l t e r i n g had removed the p a r t i c l e s causing j e t h o l e p l u g g i n g . In c o n c l u s i o n , the HIAC p a r t i c l e counter i s used w i t h un d i l u t e d v i s c o s e , a v o i d i n g changes caused when the sample i s



TABLE IX E f f e c t of F i l t e r i n g Particles/g 5 10

Sample

Viscose 15 30 I 60μ

Filterability

Unfiltered

3258

1394

440

37

9

14.8

Filtered

3278

1472

433

20

4

10.0

2610

1201

572

91

19

20.4

Unfiltered + Residue

Constant

Viscose

Pressure

Supply

Viscose Supply

Jet

2 mil

Figure S.

Jet

3.5 m i l

Differential flow test



8.66

7.17

5.04

3.70

2.98

0

15

30

45

60

Time (min. )

24.04

23.67

21.89

20.35

17.79

Constant Flow 27 g/m Jet A Jet Β 1500 Holes 980 Holes (2 m i l ) (3.5 m i l )

28

25

24

20

18

psi

8.07

6.40

4.34

2.84

2.05

B/A

....... ^ . , . . .

.....

1.92

2.42

3.49

5.02

7.83

...

13.13

13.53

13.82

14.43

15.05

15.05

15.95

17.31

19.45

22.88

g/m Constant Pressure 20 p s i Jet A Jet Β 1500 Holes 980 Holes (2 m i l ) (3.5 m i l ) Flow

V i s c o s e Flow

D i f f e r e n t i a l Flow T e s t a t Constant Flow Rate and Constant P r e s s u r e

TABLE Χ

6.84

5.59

3.96

2.87

1.92

B/A

18

T E X T I L E AND

VO

PAPER CHEMISTRY AND

CO

00 CO ι

rH•

rH•

rH•

rH•

eu CO o M 0> ν-/

h

m ON•

VO

•

•

m

•

st

•

;

CU

S

•H

0 -H g

Ο rH

0 CM

0 CO

0

Ο

m

0 vO


1. DYER AND SMITH

Studying Particles in Viscose

19

diluted for conduc tome t r i e counting. The measurements were thus more representative of the viscose solution at the various process stages from which the samples were taken. It is pro bable that a test to evaluate the deformability of viscose par t i c l e s can be developed using the particle count before and after f i l t e r i n g under different applied pressures. To detect the effect of particles i n filtered viscose, the pore dimensions must be much smaller than normal jet holes. As described i n this paper, the differential flow method was insensitive to particles i n f i l t e r e d viscose because the jet hole sizes used were too large. It i s suggested that useful i n formation about viscose particles could be obtained by using f i l t e r media of controlled pore size rather than the jets. Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

Samuelson, O., Svensk Papperstidn. 52 465 (1949). Treiber, E., J. Poly. Sci., 51, 297 (1961). Arnold, A., Philipp, B . , and Schleicher, Η . , Faser forsch u. Textiltech. 21 361 (1970). Zubakhina, N. L., Serkov, A. T . , and Virezub, A. I., Khim. Volokna, 14 33 (1972). Treiber, E., and Nadziakiewicz, H. C., J. Poly. S c i . Part C (2) 357 (1963). Krueger, E . O., B u l l . Parenteral Drug Assoc., 26, 2 (1972). Treiber, E., Lensinger Berichte, 18 5, 12 (1965). Treiber, E., Faserforsch u Textiltech. 15 618 (1964). Durso, D. F., and Parks, L. R . , Svensk Papperstidn. 64 853 (1961). Hermans, P. H., and Bredee, H. L., Rec. Trav. Chim. Pays-Bas 54 680 (1935). Figures 1 and 2 reproduced by kind permission of HIAC Instruments Division, Pacific Scientific Company, P.O. Box 3007, Montclair, California 91763.


Textile and Paper Chemistry and Technology

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