Cellulosic particles and methods of making them

Details Cellulosic particles and methods of making them Cellulosic particles and methods of making them

2000-07-14

2002-09-17

Seidleck, James J. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C524S035000

Reexamination Certificate

active

06451884

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to cellulosic particles of the kind known as fibrids and to methods of making the same.
Cellulosic fibrids can be made by mixing together under turbulent conditions a spinning solution of cellulose and a coagulating liquor. One example of such a solution is viscose, which contains sodium cellulose xanthate. Examples of coagulating liquors for viscose include aqueous salt solutions and aqueous acid solutions. The fibrids so produced comprise, often predominantly, fine fibrous particles a few microns in diameter; of comparable size to the fibres in woodpulp. These fibrids may also comprise platelike or globular particles of similar size to those fibres and of more or less irregular shape. For example, in the familiar salt figure test for viscose ripeness, viscose is mixed with aqueous sodium chloride. If the sodium chloride concentration is too low, a solution is formed; if it is too high, a more or less coherent precipitated lump is formed; but at the correct concentration, fibrids are formed. The fibrids formed in the salt figure test contain residual xanthate groups. If such fibrids are acidified, or if an acidic coagulating liquor is used, then the xanthate groups are destroyed and cellulose is regenerated.
BACKGROUND ART
Modified cellulose particles have been proposed as additives in papermaking, in particular to assist in formation of the paper web (sheet) and in sludge dewatering. In a series of papers in Das Papier (1980, vol. 34, pp. 575-579; 1981, vol. 35, pp. V33-V38 and pp. 555-562; and 1983, vol. 37, pp. 181-185), Kaufer et al. disclose cationically modified cellulose particles prepared by the reaction of woodpulp with reagents such as 3-chloro-2-hydroxypropyltrimethylammonium chloride and the use of such particles as additives in papermaking.
Philipp and Lang (Faserforschung und Textiltechnik, 1966, vol. 17, pp. 299-304) disclose the addition of poly(ethyleneimine) to diluted viscose and titration of the resulting mixture with aqueous acid. A precipitate formed at mildly or moderately alkaline pH (8-11), depending upon the exact experimental conditions. The precipitate is described as a floc, indicating that it was composed of fibrids. The first formed precipitate was believed to comprise a salt of a polymeric cation (protonated poly(ethyleneimine)) and a polymeric anion (cellulose xanthate). The authors refer to such salts generically as “symplexes”. Titration was continued until the mixture became acid (pH 3), and at least partial regeneration of cellulose xanthate to cellulose occurred, thus yielding cationically modified cellulosic particles by a viscose process. Philipp and co-workers elsewhere propose the use of cationically modified cellulose particles and symplexes as additives for use in papermaking (Dawydoff et al., Acta Polymerica, 1987, vol. 38, pp. 307-313, and Philipp et al., Progress in Polymer Science, 1989, vol. 14, pp. 91-172).
WO-A-96/26220 discloses a process in which a cationic polyelectrolyte is added to diluted viscose and the resulting mixture is mixed with a coagulating and regenerating liquor such as dilute sulphuric acid to form cationic cellulosic fibrids useful as additives in papermaking. The viscose was added to the coagulating liquor, or vice versa. Such polyelectrolytes include polydialkyldiallylammonium salts, in particular polydialkyldiallylammonium chloride (polyDADMAC), dicyandiamide, dicyandiamide condensates, polyamines, polyimines such as poly(ethyleneimine), and ionenes. The viscose may contain about 30 percent by weight of the polyelectrolyte on cellulose.
DISCLOSURE OF THE INVENTION
We have found that, when viscose containing a cationic polymer such as a polymeric amine is coagulated and regenerated in an acid bath, a high proportion of the cationic polymer may dissolve in the acid bath instead of becoming incorporated (as is desired) in the precipitated and regenerated cellulose. Furthermore, some of the polymer may dissolve out of the regenerated cellulosic article during washing to remove impurities or during subsequent use. This is a significant problem, particularly in the manufacture and use of regenerated cellulosic articles which contain a high proportion of cationic polymer so as to exhibit high cationic activity and which have a high surface-to-volume ratio, for example cationic cellulosic fibrids.
According to the invention, there is provided a cationic cellulosic fibrid characterised in that it comprises from greater than 10 up to 50 percent by weight on cellulose of a polymeric amine of weight-average molecular weight in the range from 100,000 to 1,000,000 comprising monomeric units having the formula:
—XCR
3
((CH
2
)
N
NR
1
R
2
)(CH
2
)
m
—
where X is selected from the group consisting of a chemical bond, O and NR
4
; R
1
and R
2
are the same or different and are selected from the group consisting of H, C
1
-C
4
alkyl, phenyl, and phenyl substituted with one, two or three substituents selected from the group consisting of C
1
-C
4
alkyl, C
1
-C
4
alkoxy, F, Cl and Br; R
3
and R
4
are independently selected from the group consisting of H, methyl and ethyl; m is an integer in the range from 1 to 4; and n is an integer in the range from 0 to 4.
According to the invention, there is further provided a method for the manufacture of cationic cellulosic fibrids, including the steps of:
(a) combining viscose with an aqueous solution of a polymeric amine, thereby forming an amine-containing dope;
(b) mixing the amine-containing dope with a coagulating and regenerating liquor under turbulent conditions, thereby forming a slurry of cationic cellulosic fibrids in a spent liquor; and
(c) collecting the cationic cellulosic fibrids from the spent liquor,
characterised in that the amine-containing dope contains from greater than 10 up to 50 percent by weight on cellulose of a polymeric amine of weight-average molecular weight in the range from 100,000 to 1,000,000 comprising monomeric units having the formula:
—XCR
3
((CH
2
)
n
NR
1
R
2
)(CH
2
)
m
—
where X is selected from the group consisting of a chemical bond, O and NR
4
; R
1
and R
2
are the same or different and are selected from the group consisting of H, C
1
-C
4
alkyl, phenyl, and phenyl substituted with one, two or three substituents selected from the group consisting of C
1
-C
4
alkyl, C
1
-C
4
alkoxy, F, Cl and Br; R
3
and R
4
are independently selected from the group consisting of H, methyl and ethyl; m is an integer in the range from 1 to 4; and n is an integer in the range from 0 to 4. The expression “spent liquor” is used as a convenient name for the byproduct liquor produced in the method of the invention; it will be appreciated that this liquor often retains some coagulating and regenerating powers.
The weight-average molecular weight of the polymeric amine is preferably in the range from 200,000 to 500,000. The polymeric amine is preferably a poly(vinylamine), for example a partially-hydrolysed poly(N-vinylformamide) as disclosed by F Linhart and W.Auhorn (Das Papier, 1992, vol. 46(10A), pp. V38-V45). EP-A-0,692,599 discloses the manufacture of cellulosic fibres which contain polymeric amines, in particular by the viscose process. The polymeric amines of EP-A-0,692,599 comprise an aliphatic backbone with pendent amine groups as specified for use in the present invention, and they are of molecular weight above 1000. The amount of polymeric amine disclosed in EP-A-0,692,599 may be in the range from 0.1 to 10, preferably from 0.3 to 3, percent by weight on the cellulose in the spinning solution (e.g. viscose). The fibres of EP-A-0,692,599 exhibit improved dyeability and increased wet and dry tenacities.
We have found that the method of the invention permits the incorporation of polymeric amine into cationic cellulosic fibrids with a high degree of efficiency and that a high proportion of the polymeric amine remains within the fibrids of the invention during aqueous processing, for example when used as additives in papermaking to assist in web formation or sludge dewatering. We have found that 80 perce

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