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Description  |
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German Laid-Open application DOS No. 1,720,737 discloses a process for the
preparation of basic polymers in which poly-N-vinyl-N-methylcarboxylic
acid amides are subjected to acid hydrolysis at elevated temperature to
give basic polymers with secondary amino groups. It is true that
hydrolysis of the formyl compounds proceeds sufficiently rapidly at from
100.degree. to 110.degree. C., but, as described in Example 2,
stoichiometric amounts of hydrochloric acid at about 100.degree. C. result
in a degree of hydrolysis of only 62 mole %. As described in Example 1,
2.6 moles of hydrochloric acid per mole of formyl group equivalent at from
108.degree. to 109.degree. C. are required to achieve a degree of
hydrolysis of 93 mole %. The polymers are thereby in some cases modified
to an undesirable extent.
German Laid-Open application DOS No. 1,692,854 discloses the addition of
polymers of N-vinyl-N-methylcarboxylic acid amides to stock as drainage
assistants to improve the drainage rate in papermaking. However, the
effectiveness of these drainage assistants is still in need of
improvement.
It is an object of the present invention to provide linear basic polymers
which contain, as the characteristic component, copolymerized units of the
formula
##STR3##
and which are better than conventional basic polymers when used as
retention agents, drainage assistants and flocculants in papermaking.
We have found that this object is achieved, according to the invention,
with linear basic polymers which contain from 90 to 10 mole % of units of
the formula
##STR4##
and from 10 to 90 mole % of units of the formula
##STR5##
and have a Fikentscher K value of from 10 to 200 (measured in 0.5%
strength aqueous sodium chloride solution at 25.degree. C.).
The preparation of the compound of the formula CH.sub.2 .dbd.CH--NH--CHO
(N-vinylformamide) was first disclosed in German Published application DAS
No. 1,224,304. Homopolymerization of N-vinylformamide has not yet been
disclosed. We have found that N-vinylformamide can be polymerized using
free radical polymerization initiators, e.g. peroxides, hydroperoxides,
redox catalysts, or azo compounds which dissociate into free radicals,
preferably those azo compounds described for this purpose in German
Laid-Open application DOS No. 1,495,692. The polymerization is carried out
in a solvent or diluent at from 30.degree. to 140.degree. C. The molecular
weight of the polymers varies, depending on the polymerization conditions,
and is characterized in the text which follows by means of the Fikentscher
K value. The K value can vary within wide limits, for example from 10 to
200. Polymers having a high K value, e.g. above 80, are preferably
prepared by polymerizing N-vinylformamide in water. Polymers having a
lower K value, e.g. below 80, are obtained by carrying out the
polymerization in the presence of known regulators or in a solvent which
regulates the polymerization, e.g. an alcohol, such as methanol, ethanol
or n- or iso-propanol, or acetone or methyl ethyl ketone. Examples of
other polymerization regulators are hydroxylammonium salts, chlorinated
hydrocarbons and thio compounds, e.g. dodecylmercaptan. Polymers having a
lower K value can be prepared by, for example, polymerizing
N-vinylformamide in isopropanol using an isopropanol-soluble
polymerization initiator based on an azo compound.
2,2'-Azo-bis-(isobutyronitrile) is an example of a particularly suitable
azo compound for the polymerization in isopropanol. High molecular weight
polymers of N-vinylformamide are prepared using water-soluble azo
compounds, e.g. 2,2'-azo-bis-(2-amidinopropane) hydrochloride or
4,4'-azo-bis-(4'-cyano-pentanoic acid), the reaction being carried out in
aqueous solution. As well as by solution polymerization in water, a
water-soluble solvent or a mixture of water and a water-soluble solvent,
the polymerization can also be carried out as a water-in-oil emulsion
polymerization in a water-immiscible solvent. The reverse suspension
polymerization can also be used for the preparation of finely divided
polymers. If an aqueous medium is used, the pH during polymerization is
from 4 to 9, preferably from 5 to 7. In the case of solution
polymerization, polymer solutions having a solids content of from 5 to 50%
by weight, preferably from 3 to 30% by weight, are predominantly
prepared.
Poly-(1-aminoethylenes) are prepared from the polymerization product by
solvolysis in the presence of acids or bases at from 20.degree. to
200.degree. C., preferably from 40.degree. to 180.degree. C. and
particularly preferably from 70.degree. to 90.degree. C., the formyl group
being split off. From about 0.05 to 1.5 equivalents (for the purposes of
this invention, one equivalent is 1 gram equivalent) of an acid, e.g.
hydrochloric acid, hydrobromic acid, phosphoric acid or sulfuric acid, are
required per formyl group equivalent in the poly-N-vinylformamide. The pH
in the case of acid hydrolysisis from 5 to 0, preferably from 3 to 0, and
can be established by addition of a carboxylic acid, e.g. formic acid,
acetic acid or propionic acid, a sulfonic acid, e.g. benzenesulfonic acid
or toluene-solfonic acid, or an inorganic acid, e.g. hydrochloric acid,
sulfuric acid, phosphoric acid or hydrobromic acid. The hydrolysis
proceeds substantially more rapidly than that of N-methyl-N-vinylformamide
polymers and can therefore be carried out under milder conditions, i.e. at
lower temperatures and without an excess of acid.
Solvolysis of the formyl groups in the poly-N-vinylformamide can also be
carried out in an alkaline medium, for example at a pH of from 9 to 14.
This pH is preferably established by addition of sodium hydroxide solution
or potassium hydroxide solution, but it is also possible to use ammonia,
an amine or an alkaline earth metal base, e.g. calcium hydroxide. From
0.05 to 1.5, preferably from 0.4 to 1.0, equivalents of a base are used
for the alkaline hydrolysis.
The formyl group can be split off in various solvents, e.g. in water, an
alcohol, ammonia or an amine, or a mixture of, for example, water and an
alcohol, or an aqueous solution of ammonia and/or an amine. In some cases,
it may be advantageous to carry out the solvolysis in an inert diluent,
e.g. in dioxane or an aliphatic or aromatic hydrocarbon.
Poly-(1-aminoethylenes) are obtained in all cases. In the case of
hydrolysis, the formyl group is split off from the poly-N-vinylformamide
by an acid or base in water, and formic acid or a salt of formic acid is
obtained as a by-product. In the case of solvolysis in an alcohol, also in
the presence of an acid or base, a formic acid ester is obtained as a
by-product, while formamide or a substituted formamide is obtained if the
solvolysis is carried out in ammonia or an amine. Particularly suitable
alcohols for the solvolysis are low-boiling alcohols, e.g. methanol,
ethanol, isopropanol, n-propanol, n-butanol and isobutanol.
The solvolysis by-products can be removed from the system either during or
after solvolysis. Thus, for example, if alcohol is used as the solvent, it
is possible to remove the resulting formic acid ester azeotropically from
the reaction mixture, in which case an entraining agent may be necessary.
The hydrolysis by-product (formic acid) can also be removed from the
system during or after hydrolysis. Preferably, the polyvinylformamide is
hydrolyzed with sodium hydroxide solution or hydrochloric acid at from
70.degree. to 90.degree. C. in aqueous solution. The K value of the
hydrolyzed polymer corresponds to that of the non-hydrolyzed
N-vinylformamide homopolymer.
The polyvinylformamides are thereby partially hydrolyzed, so that from 10
to 90%, preferably from 20 to 90%, of the formyl groups are split off. In
this manner, polymers are obtained which contain from 90 to 10 mole % of
units of the formula
##STR6##
and from 10 to 90 mole % of units of the formula
##STR7##
in random distribution and which can be defined, for example, by the
following formula:
##STR8##
where n is a number from 0.1 to 0.9, preferably from 0.2 to 0.9.
The hydrolysis depends on the reaction conditions, and can be carried out
under atmospheric, reduced or superatmospheric pressure. Aqueous or
alcoholic solutions are obtained, from which the polymer can be isolated
after the low molecular weight constituents have been separated off.
However, the aqueous or alcoholic solutions obtained during solvolysis can
also be used directly as retention agents, drainage assistants and
flocculants in papermaking. These polymers have an excellent action which
is superior to that of conventional commercial products, e.g.
polyethyleneimines, or polyamidoamines modified with ethyleneisimine. In
the case of hydrolysis with bases, polymers with free amino groups are
obtained, while hydrolysis with acids gives the corresponding polymer
salts, from which, however, polymers having free amino groups can likewise
be obtained after addition of a base, e.g. sodium hydroxide solution or
potassium hydroxide solution.
The linear basic polymers according to the invention are used to accelerate
drainage of the wet fiber web and to increase the retention of fines and
fillers by cellulose fibers during papermaking. Faster drainage of the
stock on the papermaking machine enables the speed of the machine and
hence production to be increased. Moreover, these compounds permit better
sheet formation and reduce the water content of the still moist paper, so
that less energy is required for drying the sheet than when conventional
drainage and retention agents are used.
Improved retention during papermaking saves raw materials, enables cheaper
fillers to be used instead of more expensive fibers, reduces the
circulation of water through the paper mill and, as a result of better and
more uniform fixing of fines and fillers, improves the printability of the
paper. It also means that less material passes into the effluent.
From 0.005 to 0.5% by weight, preferably from 0.01 to 0.1% by weight, based
on the dry fiber, of the poly-(1-aminoethylenes) obtained in the
solvolysis of poly-N-vinylformamides is added to the stock before sheet
formation for papermaking. Particularly advantageous effects are obtained
with basic polymers having a K value above 80.
The K value of the polymers was measured in 0.5% strength aqueous sodium
chloride solution at 25.degree. C. by the method of H. Fikentscher,
Cellulosechemie 13 (1932), 58 to 64 and 71 to 74; K=k.10.sup.3.
1. Preparation of the Polymers
EXAMPLE 1.1
80 g (1,125 mmoles) of vinylformamide were dissolved in 385 g of water in a
flask provided with a stirrer, a thermometer and an apparatus for working
under nitrogen. 1.3 g (4.8 mmoles) of 2,2'-azo-bis-(2-amidinopropane)
hydrochloride were added, the oxygen was removed by passing in nitrogen
and the reaction mixture was heated to 60.degree. C. in the course of half
an hour and kept at this temperature for 5 hours. The conversion was then
99.3%.
450 g of 10% strength sodium hydroxide solution (1,125 mmoles) were then
added to the resulting viscous polymer solution, which had a K value of
81, and the mixture was heated at 80.degree. C. for 5 hours, to give a
polymer in which all the formyl groups had been split off (degree of
hydrolysis=90%). A total of 916 g of an aqueous polymer solution having a
Brookfield viscosity, measured at 25.degree. C., of 140 mPa.s were
obtained.
EXAMPLE 1.2
80 g of N-vinylformamide were dissolved in 385 g of water in the apparatus
described in Example 1.1, and were polymerized to a conversion of 98.1% in
the course of 5 hours at 55.degree. C. by addition of 0.65 g of
2,2'-azo-bis-(2-amidinopropane) hydrochloride. The resulting polymer,
which had a K value of 95, was heated at 80.degree. C. with 23 g of 36%
strength hydrochloric acid (227 mmoles) for 3 hours to give 489 g of a
polymer solution in which 20% of the formyl groups had been split off from
the polymer. The Brookfield viscosity of the solution, measured at
25.degree. C., was 16,000 mPa.s.
EXAMPLE 1.3
80 g of N-vinylformamide were dissolved in 385 g of water in the apparatus
described in Example 1.1, 0.65 g of the azo compound described in Example
1.1 was added, as a polymerization inhibitor, and the mixture was heated
to 55.degree. C. in the course of 1 hour. Polymerization was carried out
at 55.degree. C. in the course of 5 hours. After the polymerization, the
reaction mixture was heated for another half an hour at 60.degree. C. to
complete the conversion, which was then 100%. The resulting polymer, which
had a K value of 120, was then hydrolyzed with 68.5 g of 36% strength
hydrochloric acid (676 mmoles) at 90.degree. C. for 2 hours to give 534.5
g of an aqueous polymer solution having a Brookfield viscosity, measured
at 25.degree. C., of 10,500 mPa.s. 60% of the formyl groups of the polymer
employed in the hydrolysis had been split off.
2. Use of the polymers as retention agents, drainage assistants and
flocculants
The following polymers were used:
Polymer I:
A commercially available high molecular weight polyethyleneimine
Polymer II:
A polyamidoamine obtained from adipic acid and diethylenetriamine, onto
which ethyleneimine had been grafted and which had been crosslinked with
polyethylene glycol dichlorohydrin ether containing 9 ethylene oxide
units, cf. Example 3 of German Patent No. 2,434,816.
Polymer III:
The polymer according to Example 1.3
Polymer IV:
The polymer according to Example 1.2
Polymer V:
The polymer according to Example 1.1
Polymer VI:
The polymer according to Example 1.3, but polymerized only up to a K value
of 102 and with 82% of the formyl groups removed by hydrolysis with
hydrochloric acid.
Polymer VII:
A polymer obtained from N-methyl-N-vinylformamide, which had a K value of
106 and had been hydrolyzed to the extent of 75% with hydrochloric acid
(prepared according to Example 2 of German Laid-Open application DOS No.
1,692,854).
EXAMPLE 2.1
Various amounts of the polymers to be tested were added to 1 l of ligneous,
kaolin-containing newsprint stock having a consistency of 2 g/l and a pH
of 7.8, and a Schopper-Riegler apparatus was used to determine the SR
freeness and the drainage time, ie. the time taken for 700 ml of back
water to run out of the apparatus. The polymers used and the results
achieved therewith are shown in Table 1.
TABLE 1
______________________________________
Freeness (SR) and drainage time (sec)
with a polymer addition of
0.02% 0.06% 0.1% 0.02% 0.06% 0.1%
______________________________________
no addition
64 99.2
Polymer I 57 45 40 75.2 47.4 39.4
(comparative)
Polymer II 54 40 36 67.2 39.6 32.5
(comparative)
Polymer III
46 33 30 51.0 28.8 24.8
(according to
the invention)
______________________________________
EXAMPLE 2.2
The drainage-accelerating effect of polymer V was tested by the procedure
described in Example 2.1. Polymer II was used for comparison with the
prior art. The results are shown in Table 2.
TABLE 2
______________________________________
Freeness (SR) and drainage time (sec)
with a polymer addition of
0.06% 0.1% 0.06% 0.1%
______________________________________
no addition
66 107.5
Polymer II
50 41 56.8 41.4
(comparative)
Polymer V
47 38 51.0 36.3
______________________________________
EXAMPLE 2.3
Various amounts of the polymers shown in Table 3 were added to 1 l of stock
comprising 80% of bleached sulfite pulp and 20% of kaolin and having an
alum content of 0.5% and a pH of 6, and sheets of paper were then produced
with the aid of a Rapid-Kothen sheet-forming apparatus. The weight per
unit area of the sheets of paper and their filler content, which was
determined by ashing, are criteria for the effectiveness of the polymer.
The higher the weight per unit area and the filler content of the sheets
of paper, the more effective the retention agent.
TABLE 3
______________________________________
Weight per unit area (g/cm.sup.2)
and ash content (%)
with a polymer addition of
0.02% 0.04% 0.06% 0.02% 0.04% 0.06%
______________________________________
no addition
58.0 4.2
Polymer I
61.3 62.1 62.6 7.7 9.1 9.7
(comparative)
Polymer II
62.3 64.1 64.5 9.6 11.7 12.0
(comparative)
Polymer III
67.6 69.9 70.8 12.0 14.7 14.7
______________________________________
EXAMPLE 2.4
The filler retention was determined as described in Example 2.3, using a
stock comprising 80% of bleached sulfite pulp and 20% of kaolin and having
an alum content of 1.5% and a pH of 4.8. The effectiveness of polymer IV
was compared with the conventional retention agents I and II, and the
results are summarized in Table 4.
TABLE 4
______________________________________
Ash content
with a polymer addition of
0.02% 0.04% 0.06%
______________________________________
no addition 3.7
Polymer I (comparative)
5.8 6.3 7.0
Polymer II (comparative)
8.8 9.5 9.9
Polymer IV 10.9 11.9 12.6
______________________________________
EXAMPLE 2.5
To determine the flocculating effect and the purification effect on waste
water of the polymers according to the invention, various amounts of the
polymers shown in Table 5 were added to a stock rich in fines and
containing, per liter, 1 g of sulfite pulp and 0.25 g of kaolin. The
suspension was stirred and allowed to settle, and the transparency of the
supernatant purified water was in each case determined photometrically.
The results are summarized in Table 5.
TABLE 5
______________________________________
Transparency (%)
with a polymer addition of
0.02% 0.04%
______________________________________
no addition 19.0
Polymer I (comparative)
42.0 60.8
Polymer II (comparative)
41.9 52.1
Polymer III 57.5 77.8
______________________________________
EXAMPLE 2.6
Various amounts of the polymers to be tested were added to 1 l of a
ligneous, kaolin-containing newsprint stock having a consistency of 2 g/l
and a pH of 7.8, and a Schopper-Riegler apparatus was used to determine
the SR freeness and the drainage time, i.e. the time taken for 700 ml of
back water to run out of the apparatus. The polymers used and the results
achieved therewith are shown in Table 6.
TABLE 6
______________________________________
Freeness (SR) and drainage time (sec)
with a polymer addition of
0.02% 0.06% 0.1% 0.02% 0.06% 0.1%
______________________________________
no addition
62 99.3
61 101.0
Polymer II
51 38 34 68.0 40.1 34.0
(comparative)
51 39 34 68.2 40.2 34.0
Polymer VII
50 50 50 66.8 64.6 66.0
(comparative)
50 49 50 66.5 63.8 67.0
Polymer VI
49 34 31 61.4 33.4 29.3
49 33 31 62.0 32.3 29.5
______________________________________
The effectiveness of the polymer VI used according to the invention has
been improved, compared with that of the closest prior art (Polymer VII),
in a manner which could not be predicted.
EXAMPLE 2.7
The filler retention was determined on a stock comprising 80% of bleached
sulfite pulp and 20% of kaolin and having an alum content of 0.5% and a pH
of 6.0. Various amounts of the polymers shown in Table 7 were added to 1 l
of this stock, and sheets of paper were then produced with the aid of a
Rapid-Kothen sheet-forming apparatus. The filler content of the sheets of
paper, which was determined by ashing, is a criterion of the effectiveness
of the polymer as a retention agent.
TABLE 7
______________________________________
Ash content
with a polymer addition of
0.02% 0.04% 0.06%
______________________________________
no addition 3.7
Polymer II (comparative)
9.3 10.6 11.5
Polymer VII (comparative)
10.0 9.8 9.9
Polymer VI 9.6 12.1 13.1
______________________________________
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