8 Characterization of Insoluble Cellulose Acetate Residues W. B. RUSSO Fiber Industries, Inc., Charlotte, N.C. 28237 G. A. SERAD Celanese Fibers Co., Charlotte, N.C. 28232
C o m m e r c i a l cellulose acetate is normally manufactured using a very high purity wood pulp because its applications have very c r i t i c a l processing and product requirements. Cellulose acetate films must be c l e a r and free of imperfections that could be caused by undissolved particles during solvent film castings. The preparation of cellulose acetate fibers requires the polymer solution to flow unobstructed through spinneret c a p i l l a r i e s that have extremely s m a l l diameters. A n y undissolved particulate matter that would cause disruptions i n fiber extrusion cannot be tolerated. Since cellulose derived f r o m wood pulp contains im purities which do not f o r m acetate esters soluble i n c o m m e r c i a l cellulose acetate solvents ( e . g . , acetone), these impurities must be reduced to an acceptable l e v e l . Consequently, wood pulps used to manufacture cellulose acetate contain 94 to 99 per cent alpha-cellulose, the remainder being hemicelluloses. This α - c e l l u l o s e level is higher than that required for the preparation of rayon, cellulose nitrate, or cellulose ethers. Of course, the increased purity results i n an increased cost. Hence, it has long been a goal to develop means to reduce the wood pulp purity requirements for the c o m m e r c i a l preparation of cellulose ace tate. This is desirable for the acetate manufacturer, the pulp manufacturer, and the ecology since the higher purity comes at a sacrifice i n wood y i e l d and increased pulp mill effluent treat ment requirements. It is well known that insoluble residues obtained f r o m the dissolution of cellulose acetate in acetone are enriched i n hemi cellulose acetates (1-4). However, our p r o g r a m to investigate the use of lower purity wood pulps to prepare cellulose acetate by either modifying the pulps or the process required quanti96
8.
RUSSO AND SERAD
tative characterizations. isolate,
quantify,
fractions
Hence,
this study was undertaken
and characterize
to
both soluble and insoluble
of c e l l u l o s e a c e t a t e i n a c e t o n e .
F o u r g e n e r a l c l a s s e s of p u l p ,
representing
nations of w o o d f u r n i s h a n d p u l p i n g p r o c e s s , These included a softwood kraft, kraft,
97
Insoluble Cellulose Acetate Residues
and hardwood sulfite.
various
were
combi-
examined.
softwood sulfite,
hardwood
T h e p u r i t y of the v a r i o u s p u l p s ,
along with typical acetylation grade pulps, are given in Table
T A B L E I:
I.
P u r i t y of A c e t y l a t i o n G r a d e a n d " L o w P u r i t y " W o o d Pulps Alkali S u g a r A n a l y s i s (%)
Solubility
Glucose Mannose Xylose
Purity-RjQ%
" L o w Purity" Grades Softwood K r a f t
85. 6
6.1
8.3
84
Softwood Sulfite
91.2 83. 5
6.9 0.6
1.9
85
91.5
2.4
15.9 6.1
89 87
98. 1
1.4
0.5
96
97.5
0.3
1.2
97
Hardwood Kraft Hardwood Sulfite Typical Acetylation Grade Softwood Sulfite Hardwood Prehydrolyzed Kraft
Fractionation Acetone,
Sequence the c o n v e n t i o n a l s o l v e n t u s e d to
manufacture
c e l l u l o s e a c e t a t e f i b e r s a n d f i l m s , w a s u s e d to p r e p a r e starting solutions.
(wt/wt) a c e t o n e / w a t e r .
the s o l v e n t a n d the c e l l u l o s e a c e t a t e f l a k e . i n the f r a c t i o n a t i o n ( F i g u r e
A 6 g/100
c a l l e d the a c e t o n e / w a t e r s o l u b l e s
saved for analysis.
a
The
(AWS),
combined were
The residue was weighed and likewise c c s o l u t i o n i n 91/9
methylene
000
fresh
and u l t r a -
A p o r t i o n of the r e s i d u e w a s s u b s e q u e n t l y
p a r e d a s a 6 g/100
solution
1) w a s u l t r a c e n t r i f u g a t i o n a t 1 5 ,
centrifugation repeated under s i m i l a r conditions.
for analysis.
cc
T h e f i r s t step
A f t e r d e c a n t i n g o f f the s u p e r n a t e ,
a c e t o n e / w a t e r s o l u t i o n w a s a d d e d to t h e r e s i d u e s supernates,
95/5
T h e w a t e r i n c l u d e s that c o n t a i n e d i n both
o f the c e l l u l o s e a c e t a t e (bone d r y b a s i s ) w a s u s e d . r p m for four hours.
the
The exact solvent composition used was
saved
pre-
chloride/
S O L V E N T SPUN R A Y O N , MODIFIED C E L L U L O S E FIBERS
Acetone Water Soluble Acetone/ Water
Acetone Water Insoluble
Methyle Chloride/ Methanol
Methylene Chloride/ Methanol Soluble
Methylene C h l o r i d e / M e t h a n o l Insoluble
D r y residue P r e p a r e 6% (wt/vol) s o l u t i o n in methylene chloride/methanol U l t r a c e n t r i f u g a t i o n (151.000 r p m f o r 2 h r s ) Decant s u p e r n a t e A d d 150 c c of f r e s h M e C l / M e O r > Repeat steps 3 and 4 C o l l e c t l i q u i d , weigh s o l i d s
6 g m s of bone d r y f l a k e " p e r 100 cc U l t r a c e n t r i f u g a t i o n (1 5,000 r p m f o - 4 h r s ) Decant s u p c r n a t e A d d 150 cc of f r e s h a c e t o n e / w a t e r Repeat steps 2 and 3 C o l l e c t l i q u i d , weigh s o l i d s
2
Figure 1. Fractionation sequence
1.0
1.2
1.4
1.6
Intrinsic V i s c o s i t y
Figure 2. Relationship of cellulose acetate intrinsic viscosity and 6% solution viscosity
8.
RUSSO AND SERAD
methanol.
99
Insoluble Cellulose Acetate Residues
T h e s o l u t i o n w a s u l t r a c e n t r i f u g e d at 15, 000 r p m f o r
two h o u r s .
The supernate was decanted,
fresh methylene
i d e / m e t h a n o l a d d e d , a n d the c e n t r i f u g a t i o n r e p e a t e d . bined supernate, (MCMS),
was saved for analysis.
methylene and
designated methylene
chlor-
The
com-
chloride/methanol
The final residue,
chloride/methanol insolubles (MCMI),
soluble
designated
was weighed
saved.
Analytical
Procedures
A c e t y l V a l u e (defined as percent
combined acetic acid).
A five wt. percent
s o l u t i o n of the c e l l u l o s e a c e t a t e f l a k e
was
p r e p a r e d i n a 91/9
(wt/wt) m e t h y l e n e
solvent.
chloride/methanol
A f i l m a p p r o x i m a t e l y 0. 001 i n c h t h i c k w a s c a s t f r o m the s o l u t i o n a n d a l l o w e d to a i r d r y .
It w a s p l a c e d i n a c u r v e d f i l m h o l d e r ,
h e a t e d to r e m o v e r e s i d u a l w a t e r , spectrophotometer
and scanned i n an infrared
o v e r t h e 2 . 5 to 4 . 5 m i c r o n r a n g e .
The
ratio
of the O H a b s o r b e n c e at 2. 9 m i c r o n s a n d the C - H a b s o r b e n c e 2.4
microns was calculated.
T h i s r a t i o w a s c o r r e l a t e d to
at
acetyl
value by m e a n s of a c a l i b r a t i o n p r o c e d u r e u s i n g a k n o w n standard.
F o r a c e l l u l o s e a c e t a t e of 5 5 . 07 a c e t y l v a l u e ,
the
sample
s t a n d a r d d e v i a t i o n (ten a n a l y s e s ) w a s 0. 0 2 . Filtration Value.
M o i s t u r e c o n t e n t of c e l l u l o s e
samples was determined by oven drying.
A 6 g/100
o f t h e s a m p l e w a s p r e p a r e d u s i n g e i t h e r a 95/5 tone/water vent.
acetate
cc
solution
(wt b a s i s ) a c e -
s o l v e n t o r a 91/9 m e t h y l e n e c h l o r i d e / m e t h a n o l s o l -
T h i s w a s s h a k e n f o r t w o h o u r s to a s s u r e d i s s o l u t i o n .
The
solution was filtered through 30-ply K i m p a k and Canton flannel at 200 p s i g n i t r o g e n p r e s s u r e plugged.
u n t i l the f i l t e r w a s
completely
A f i l t r a t i o n v a l u e w a s d e f i n e d as the g r a m s o f d r y
c e l l u l o s e a c e t a t e p e r c m ^ of f i l t e r a r e a w h i c h c a n be before blockage
filtered
occurs.
Cation Analysis.
Calcium,
magnesium,
and sodium were
determined by atomic absorption using conventional Intrinsic Viscosity.
techniques.
I n t r i n s i c v i s c o s i t y of c e l l u l o s e
acetate
f l a k e s w a s d e t e r m i n e d b y m e a s u r i n g the v i s c o s i t y of a 6 g/100
cc
s o l u t i o n of the f l a k e i n a c e t o n e / w a t e r a n d u s i n g the c o r r e l a t i o n of F i g u r e 2.
Solution viscosity was determined using a
d i r e c t r e a d o u t v i s c o m e t e r ( M o d e l 7-006) at
25°C.
Nametre
S O L V E N T SPUN R A Y O N , MODIFIED C E L L U L O S E FD3ERS
100
C a r b o x y l Content. A n i o n exchange procedure was used f o r the d e t e r m i n a t i o n of the c a r b o x y l c o n t e n t . Flake was treated w i t h H C 1 to c o n v e r t t h e c a r b o x y l g r o u p s to t h e i r a c i d f o r m . C a r b o x y l protons w e r e then l i b e r a t e d by exchange w i t h c a l c i u m acetate and subsequently titrated. S u g a r A n a l y s i s . Q u a n t i f i c a t i o n of the c a r b o h y d r a t e c o n tent w a s a c c o m p l i s h e d b y gas c h r o m a t o g r a p h y of the t r i m e t h y l s i l a t e d s u g a r m o n o m e r s w h i c h w e r e o b t a i n e d b y h y d r o l y s i s of t h e c e l l u l o s e a c e t a t e o r w o o d p u l p (_5, 6 ) . S p e c i a l p r o c e d u r e s w e r e d e v e l o p e d to c h a r a c t e r i z e 7 0 - 1 0 0 m g s a m p l e s . A n accurate d r y sample weight and acetyl value w e r e f i r s t obtained and the f o l l o w i n g h y d r o l y s i s p r o c e d u r e u s e d : 1.
T h e s a m p l e w a s d r i e d at 15-20
f o r about two h o u r s ,
m m pressure and 65°C
cooled i n a dessicator
to r o o m
temperature,
then weighed. 2.
O n e m l o f 77 p e r c e n t s u l f u r i c a c i d w a s a d d e d f o r
v a t i o n a n d s h a k e n f o r o n e to t h r e e h o u r s .
sol-
Extremely discolored
samples were discarded. 3.
T h e s o l v a t e d s a m p l e w a s d i l u t e d w i t h 25 m l o f d i s t i l l e d
w a t e r a n d 5 m l of a 2. 0 m g / m l m y o - i n o s i t o l s o l u t i o n ( r e f e r e n c e sugar). 4.
The solution was then r e f l u x e d f o r four h o u r s .
N e x t , a n e u t r a l i z a t i o n step c o n s i s t e d of p l a c i n g . a 5 m l a l i q u o t of the h y d r o l y z e d s a m p l e i n a c e n t r i f u g e t u b e , a d d i n g 0. 7 g of b a r i u m c a r b o n a t e p o w d e r , a n d p l a c i n g the c o n t e n t s i n t o a v a c u u m o v e n at 6 5 ° C . A f t e r n e u t r a l i z a t i o n , c o i n c i d e n t w i t h the c e s s a t i o n of b u b b l e s , the m i x t u r e w a s c e n t r i f u g e d (2, 000 r p m f o r 10-15 m i n u t e s ) . T h e r e s u l t a n t s u p e r n a t e w a s p l a c e d i n t o a 10 m l p e a r - s h a p e d f l a s k a n d e v a p o r a t e d to d r y n e s s u n d e r r e d u c e d p r e s s u r e w i t h a r o t a r y e v a p o r a t o r (bath t e m p e r a t u r e 2 5 - 3 5 ° C ) . Trimethylsilation was accomplished by adding a 1 m l a m p u l e of T R I - S I L ( P i e r c e C h e m i c a l C o m p a n y ) i n t o the f l a s k a n d p e r m i t t i n g i t to r e a c t f o r o n e h o u r a t 5 0 ° C . The reaction vial w a s c e n t r i f u g e d to s e t t l e t h e p r e c i p i t a t e . A 1 - 2 m i c r o n s a m p l e of supernate w a s u s e d f o r gas c h r o m a t o g r a p h i c a n a l y s i s . Gas chromatograph conditions were: 1. A 4 0 - f o o t , 1/8 i n c h O . D . s t a i n l e s s s t e e l t u b e p a c k e d w i t h D e x s i l 3 0 0 G C (5 p e r c e n t ) o n C h r o m a s o r b W . 2.
Injection p o r t t e m p e r a t u r e of 2 5 0 ° C ,
p e r a t u r e of
detector
tem-
280°C.
3. P r o g r a m s e q u e n c e w a s to i n j e c t a t 1 6 0 ° C w i t h a 12 m i n u t e h o l d t i m e , f o l l o w e d b y a 1 ° C / m i n u t e p r o g r a m r a t e to 250°C.
8. RUSSO AND SERAD
Insoluble Cellulose Acetate Residues
R e s p o n s e f a c t o r s w e r e d e t e r m i n e d f o r a v a r i e t y of s u g a r s , shown i n T a b l e II· T A B L E II: R e s p o n s e F a c t o r s f o r G a s
as
Chromatography RF
Sugar α Glucose 3 Glucose Y Glucose
1.23 1. 22 1.22
ot, β X y l o s e
