Comparison of the Properties of Ultrasonically and ... - ACS Publications

16 Comparison of the Properties of Ultrasonically and Mechanically Beaten Fibers JAAKKO E. L A I N E ☼and DAVID A. I. GORING

Downloaded by UNIV OF ARIZONA on April 19, 2017 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0058.ch016

Pulp and Paper Research Institute of Canada and Dept. of Chemistry, McGill University, Montreal, Que., Canada

Several authors have d e s c r i b e d the u l t r a s o n i c beating of cellulosic f i b e r s (1-4). These i n v e s t i g a t i o n s have shown t h a t stock c o n s i s t e n c y , sound frequency and i n t e n s i t y , time of t r e a t ment and extent of stirring i n f l u e n c e the final paper p r o p e r t i e s of the f i b e r s . These p r o p e r t i e s can differ c o n s i d e r a b l y from those of mechanically beaten f i b e r s , but the fundamental f a c t o r s r e s p o n s i b l e f o r such d i f f e r e n c e s are still not c l e a r . T h i s note describes some l i m i t e d observations made during experiments in which we s t u d i e d changes in f i b e r p h y s i c a l prop e r t i e s produced by s o n i c a t i o n ( 5 ) . The r e s u l t s , though not comprehensive, provide some e l u c i d a t i o n of the mechanism of ultrasonic b e a t i n g . Experimental. Bleached k r a f t pulp f i b e r s from b l a c k spruce were i r r a d i a t e d i n the p r e v i o u s l y d e s c r i b e d system (23 kHz, 10 W/cm ) (5) f o r 3 h at a consistency of 0.5%. Comparative mechanic a l b e a t i n g was done in a V a l l e y l a b o r a t o r y beater according to Tappi-standard Τ 200 ts-66. Both the u l t r a s o n i c and mechanical treatments were r e l a t i v e l y m i l d . Thus the i n c r e a s e i n the f i n e s content produced by b e a t i n g was considered to be n e g l i g i b l e . A l s o , at such low l e v e l of b e a t i n g , paper strength would be expected to be governed by i n t e r f i b e r bonding r a t h e r than by f i b e r s t r e n g t h . Paper p r o p e r t i e s were determined i n accordance with appro p r i a t e Tappi standards. Paper p r o p e r t i e s of the mechanically beaten sample corresponding to the same freeness and breaking length of the u l t r a s o n i c a l l y t r e a t e d sample were obtained by i n terpolation. F i b e r s a t u r a t i o n p o i n t s were measured by the s o l u t e e x c l u s i o n method as d e s c r i b e d elsewhere (5). 2

*Present

address:

Laboratory of Wood Chemistry, H e l s i n k i U n i v e r s i t y of Technology, Otaniemi, Finland. 245

Turbak; Solvent Spun Rayon, Modified Cellulose Fibers and Derivatives ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

SOLVENT

SPUN

RAYON,

MODIFIED CELLULOSE

FIBERS


246

Figure J . Comparison of scanning electron micrographs of mechanically beaten (A) and ultrasonically irradiated (B) fibers at a breaking length of 5.5 km


16.

LAINE

Beaten Fibers

A N D GORING

247

Results and Discussion. A comparison of the ultrasonically and mechanically beaten fibers i s shown i n Table I. At the same freeness ultrasonic irradiation produced higher tear, opacity and bulk than mechanical beating, but tensile and burst strengths were lower. However, comparison of the paper properties at the same tensile strength i n Table II shows that the two fiber samples were similar i n almost a l l respects. Freeness i s an exception; i t was considerably lower for the sonicated sample. Table I. Comparison of mechanically and ultrasonically beaten fibers at a freeness of 528 ml.


Property

Untreated control e

2

Tear index (mN m /g) Tappi opacity (%) Bulk (cm /g) Breaking length (km) Burst index (kPa-m /g) 3

2

19.6 76.7 1.75 3.1 2.0

Type of treatment: Mechanical Ultrasonic 11.7 69.1 1.51 8.6 6.6

20.8 74.4 1.60 5.5 4.1

Table II. Comparison of mechanically and ultrasonically beaten fibers at abreaking length of 5.5 km. Property

Untreated control

Freeness (ml) Tear index (mN*m/g) Tappi opacity (%) Bulk (cm /g) Burst index (kPa«m /g) Fiber saturation point (cm /g) 2

3

2

636 19.6 76.7 1.75 2.0 0.78

Type of treatment : Mechanical Ultrasonic 610 20.2 74.0 1.66 3.7 0.98

528 20.8 74.4 1.60 4.1 1.12

3

Fiber f l e x i b i l i t y i s an important parameter contributing to freeness. Stone, Scallan and Abrahamson (6) have shown that the fiber saturation point as measured by the solute exclusion technique correlates with fiber f l e x i b i l i t y . These authors found that the higher the fiber saturation point, the lower was the freeness and the higher was the f l e x i b i l i t y of both bleached kraft and sulphite fibers. From the results i n Table I I , i t i s evident that although both types of treatment increased the fiber saturation point, the effect was larger i n the case of the sonicated fibers. Therefore i t i s not surprising that the freeness i s lower i n the l a t t e r . Scanning electron micrographs of the mechanically and u l t r a sonically beaten fibers are shown i n Figure 1. Some surface rupture i s seen i n the case of the sonicated fibers confirming the results reported previously (5). However, the mechanical treatment also produced f i b r i l l a t i o n and, for the samples shown i n

American Chemical Society Library 1155 16th St. N. W. Turbak; Solvent Spun Rayon, Modified Cellulose Fibers and Derivatives Washington, C. 20036 ACS Symposium Series; American ChemicalD. Society: Washington, DC, 1977.

248

SOLVENT SPUN RAYON, MODIFIED CELLULOSE

FD3ERS

Figure 1, the effect was larger i n the case of the mechanically beaten fibers. The results therefore indicate that ultrasonic irradiation increases fiber swelling and thus f l e x i b i l i t y , thereby, providing a slow draining pulp. At equal tensile strength, mechanically beaten fibers have a higher freeness and are less swollen. Thus unusual fiber properties are produced by sonication as opposed to mechanical treatment. For conventional papermaking, a slow draining fiber i s usually a disadvantage. However, there may be applications i n which a swollen, flexible fiber i s desirable.


Literature Cited

1. Jayme, G. and Rosenfeld, Κ., Das Papier, (1955), 9, (13/14), 296; (17/18), 423. 2. Kocurek, M.J., "The Mechanisms and Effects of Ultrasonic Irradiation on Cellulose Fibers", MS-thesis, State University College of Forestry, Syracuse University, Syracuse, 1967. 3. Iwasaki, T., Nakano, J., Usuda, M. and Migita, N., J. Jap. Tappi, (1967), 21, (10), 557; A.B.I.P.C., 38, 7608. 4. Laine, J.Ε., MacLeod, J.M., Bolker, H.I. and Goring, D.A.I., Paperi Puu, (1977), 59, (4a), 235. 5. Laine, J.Ε. and Goring, D.A.I., Cellulose Chem. Technol., (1977), (4). 6. Stone, J.E., Scallan, A.M. and Abrahamson, B., Svensk Papperstidn., (1968), 71, (19), 687.


Comparison of the Properties of Ultrasonically and ... - ACS Publications

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