Making a lightly oxidized starch additive by adding a cationic polymer to starch slurry prior to heating the slurry

Paper and other cellulose materials are sized with a cationic starch prepared by forming an aqueous slurry of a lightly oxidized starch, adding a cationizing agent to the slurry and then heating the slurry in a continuous cooker.

BACKGROUND OF THE INVENTION 
Field of the Invention 
Various types of modified starches have been used in treating paper in 
order to improve its strength and surface characteristics. For example, 
modified starch additives are commonly coated onto formed cellulosic 
sheets in size presses and other types of coating apparatus. 
In these times of increasing awareness of the environmental aspects of 
manufacturing processes, it has been noted that cationic starches reduce 
BOD pollution problems. Cationic starches help retain fiber fines. They 
exhibit superior absorbancy onto anionic cellulosic fibers and onto common 
pigments. This improved absorbance and attendant superior pigment binding 
efficiency means that lesser amounts of cationic starch can be used to 
meet sheet specifications. Since lesser amounts of starch are used and a 
greater percentage of the starch used is bound onto the cellulose fiber, 
lesser amounts of BOD-producing starch will be present in effluents 
produced during paper manufacture. 
These important BOD-related properties of cationic starches are believed to 
be due to attraction between the starch and both anionically charged 
pigment and fiber resulting in improved chemical anchoring of coatings to 
the cellulose. When cationic starch is used as a surface size, more starch 
is retained on or near the surface of the sheet than is retained with 
conventional starches. Thus, less starch is needed to maintain surface 
strength and quality. Since the cationic starch is tightly bound to the 
paper fiber, it is not removed during the repulping of broke. Hence, 
starch from the broke is recovered in the papermaking operation rather 
than being lost in the mill effluent. This attachment to the fiber coupled 
with the fact that reduced amounts of cationic starch are needed at the 
size press results in significant reductions in mill effluent BOD. 
In addition, cationic surface sizing results in improved printing 
properties. These improved properties are believed to be due to a 
combination of fiber bonding and surface orientation resulting in more 
uniform starch concentration on the paper surface, and hence more uniform 
ink receptivity and improved ink hold-out. The improved fiber bonding 
provides a strong paper surface. Among the various improved printing 
characteristics experienced with the use of cationic starches are: better 
printing uniformity, better print definition, greater depth of color, 
reduced ink show-through, fewer pick-outs on offset press and reduced 
dusting. 
Cationic starches are generally manufactured in an approximately 12 hour 
process by reacting the granular starch in an alkaline medium with 
appropriate tertiary or quaternary amines, followed by neutralizing, 
washing and drying. The alkaline agent serves to promote reaction of the 
amine with the starch. Thus, in production of such commercial dry cationic 
starches, a special manufacturing process is required, increasong cost and 
offerring potential stream pollution hazards. 
U.S. Pat. No. 4,029,885 describes a means for avoiding problems associated 
with the use of the alkaline agent which entails the treatment of 
gelatinous anionic starches with a cationizing agent. The anionic starches 
employed in U.S. Pat. No. 4,029,885 include commercially available 
oxidized starches and ammonium persulfate process pearl starches. 
A method for producing cationic starches which has the important advantages 
of the U.S. Pat. No. 4,029,885 starches and also exhibit significantly 
enhanced retention on the paper fiber has now been discovered. As 
elaborated further below, this method requires the use of a limited group 
of anionic starches and the use of a very specific cationizing procedure. 
SUMMARY OF THE INVENTION 
The invention comprises an improved process for making cationic starch 
useful in surface sizing and coating of cellulosic materials. The 
invention contemplates that an aqueous slurry of a lightly oxidized starch 
will be formed, from 1-25% and preferably from 3-15% by weight of a 
cationizing agent will be added to the slurry and then the slurry will be 
heated in a continuous cooker to form an improved gelatinous cationic 
starch. 
The invention is directed primarily to "in-mill" continuous cooker 
applications. Certain anionic starches described below must be utilized in 
the practice of the invention. It is key to the practice of the invention 
that the cationizing agent be added prior to heating the starch slurry in 
the continuous cooker. 
It should be noted at this point that the U.S. Pat. No. 4,029,885 referred 
to earlier states at column 4, lines 59-63, that the cationizing agent may 
be added at any time during the gelatinization and preferably that it 
should be added very late in the cook or after gelatinization is complete. 
The present invention thus differs significantly from the teaching of the 
U.S. Pat. No. 4,029,885 since Applicants' method requires that the 
cationizing agent be added substantially before the gelatinization process 
commences. 
The Anionic Starches 
The anionic starches used in the practice of the present invention are of a 
commercially available "partially oxidized" nature. These starches are 
sometimes referred to as "touch-modified." 
One common method of manufacture of oxidized starches entails the addition 
of a predetermined quantity of sodium hypochlorite to an aqueous starch 
slurry. Alkali is added to maintain the pH at 8-10 throughout the reaction 
and cooling is used to maintain the temperature in the range 
21.degree.-38.degree. C. The amount of hypochlorite added is usually 
equivalent to between 0.5 and 6.0% available chlorine, based on starch. 
Since the viscosity of the starch is inversely related to the degree of 
oxidation, the amount of hypochlorite is chosen based on the desired 
viscosity of the starch to be made. Following a reaction period of 5-24 
hours, the slurry is neutralized and free chlorine is destroyed with 
sodium bisulfite. Soluble by-products are then removed by washing and the 
starch is collected on vacuum filters and dried. 
Since, as noted earlier, the degree of oxidation of starch is inversely 
related to viscosity, the "partially oxidized" starches useful in the 
practice of the invention can be delineated in terms of the viscosity of 
an aqueous starch slurry. The partially oxidized starches useful in the 
practice of the invention thus should have a viscosity of from 100-500 
centipoises and preferably from 200-300 centipoises at a 6% concentration 
by weight and 150.degree. F. A typical commercially available 
touch-modified starch useful in the practice of the invention is D-210, a 
product of Grain Processing Corporation. The viscosity of this starch at 
6% by weight and 150.degree. F. is 250 centipoises. 
The Cationizing Agents 
The preferred cationizing agent is epichlorohydrin-dimethylamine 
condensate. However, other cationizing agents which would be useful in the 
practice of this invention would include diallyl dimethyl ammonium 
chloride polymer, quaternized ethylene dichloride-ammonia reaction 
product, quaternized polyethyleneimine and quaternized 
polyepichlorohydrin. 
THE EPICHLOROHYDRIN-DIMETHYLAMINE CONDENSATE 
The epichlorohydrin-dimethylamine (EPI-DMA) condensate which is used to 
react with the starch may be prepared by admixing EPI with DMA in 
approximately equimolar proportions utilizing reaction condensate 
conditions of temperatures about 60.degree.-80.degree. C. for one hour 
under alkaline pH conditions, as for example using 5% NaCl or a preferred 
range of 5-8% alkali metal hydroxide. The product is subsequently 
acidified with a mineral acid such as HCl to a pH of about 3.0, thus 
producing an amine salt or a quaternary ammonium anion site on the 
nitrogen of the DMA moiety. The basic condensate is a one-to-one reaction 
of EPI wherein the epoxy ring is attached or opened by DMA or ammonia to 
form the basic condensate which may further condense in irregular linear 
fashion. 
With reference to the term epichlorohydrin, it is understood for purposes 
of this invention that the brom analog, epibromhydrin, may be utilized in 
place of the preferred EPI. The variation of reaction conditions to 
produce the ternary compositions of the present invention e.g., 
EPI-DMA-ammonia, may be achieved by adding to the mix up to 30% molar of 
ammonium hydroxide utilized as concentrated ammonium hydroxide (26.degree. 
Be). The ternary compositions embodying 10% ammonia and 20% ammonia are 
preferred in this invention, and the efficacy of these compositions is 
believed due to the high proportion of quaternary ammonium groups which is 
effective for starch cationization at higher pH levels than a composition 
derived entirely from ammonia and EPI. The present condensates thus show 
particular advantages over starches modified with tertiary amines or 
tertiary amine polymers. 
The proportions of EPI and DMA which are used at a preferred equimolar 
ratio may vary within the range of about 0.8-3 mols of EPI to 1 mol of 
DMA. Condensates utilizing greater than 3 tend to crosslink the starch. On 
the other hand, condensates using less than 0.8 mols of EPI per mol of 
DMA lack sufficient reactive sites. Where utilized herein broadly the term 
"condensate" refers to both the binary EPI-DMA and the ternary 
EPI-DMA-NH.sub.3 condensates described and claimed herein. A typical 
procedure for preparing the EPI-DMA-NH.sub.3 condensate is described in 
Example 1 of the U.S. Pat. No. 4,029,885. 
Use in Paper Sizing 
As discussed earlier, the cationic starch described above is both useful 
and practical in the surface treatment of cellulosic materials. This 
modified starch constitutes an important surface sizing material. Usually, 
the amounts employed will be at least 30 pounds of the cationic starch per 
ton of cellulosic material, which corresponds to 1.5% by weight. 
Ordinarily, the dosage will be within the range of 1.5-12.5% by weight, 
and preferably it will be within the range of 3.0-7.5%. 
The cationic starch may be applied by any of the common surface treatment 
processes well known in the art, including processes utilizing a vertical 
or horizontal size press, tub sizing apparatus or calender sizing, etc. 
Among the improved paper properties attainable by using the cationic 
starch are increases in the surface strength and opacity, as well as 
increases in the density or reduction in the porosity of the cellulose 
fibers, increases in water repellancy and improved resistance to ink 
penetration. The invention is especially useful for the preparation of 
printing papers. It can also be used in making board grade paper used in 
making liners of single faced or double faced corrugated board, or in the 
corrugating medium itself. 
PREFERRED EMBODIMENT 
Although dosages will vary depending on the actual and desired 
characteristics of the cellulosic materials being treated, in a preferred 
embodiment, the dosage of cationic starch would be about 100 pounds per 
ton. This contemplates the use of D-210 which has been treated with 5% by 
weight of the EPI-DMA condensate described in the U.S. Pat. No. 4,029,885.

EXAMPLE 1 
The purpose of the experiments described below was to compare the amounts 
of soluble starch released upon repulping of paper stock coated with 
starch prepared according to the method of this invention to the amounts 
released of starches prepared by other commonly utilized methods. 
Sheets of a commercial 45 pound offset grade base paper made from hard wood 
and soft wood kraft pulp containing 1/4% rosin and 1/2% alum were sized on 
a coating machine (Keegan coater) and dried on a drum drier (Noble and 
Wood). The paper was then repulped and filtered and the filtrate was 
tested in order to determine starch retention on the paper. 
The measurement of relative starch retention entailed a colorimetric 
determination based upon the use of starch sensitive dyes. The starch 
content measured was that present in the filtrate of the repulped coated 
paper. The comparison entailed the use of: (1) paper coated with 
uncationized starch, (2) paper coated with "fully oxidized" starch (15 
centipoises at 6% and 150.degree. F.) cationized by addition of 
cationizing agent both before and after the cooker, and (3) 
"touch-modified" starch (250 centipoises at 6% and 150.degree. F.) 
cationized both before and after the cooker. The data obtained is set 
forth in Table I below. 
Examination of the data in Table I will show that while little difference 
was observed between fully oxidized starch cationized either before or 
after the cooker, touch-modified starch cationized by the addition of 
cationizing agent before the cooker showed significant improvements in 
starch retention. 
TABLE I 
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Soluble Starch 
Sample Description ppm % Reduction 
______________________________________ 
1. Base stock 0 -- 
2. Fully oxidized* starch 
cooked at 280.degree. F. 
55 -- 
3. Fully oxidized starch cooked as above, 
but Epi-DMA-NH.sub.3 polymer solution 
containing 4.7% active polymer on 
starch solids added after cook 
18 67.3 
4. As in 3, but polymer solution added to 
starch slurry before cook 
19.5 64.5 
5. Partially oxidized** D-210 starch 
cooked at 280.degree. F. 
61 -- 
6. Partially oxidized D-210 starch cooked 
as above, but Epi-DMA-NH.sub.3 polymer 
solution containing 4.7% active polymer 
on starch solids added after cook 
43 29.5 
7. As in 6, but polymer solution added to 
starch slurry before cook 
18 70.5 
______________________________________ 
*15 centipoise at 6% starch solids and 150.degree. F. 
**250 centipoise at 6% starch solids and 150.degree. F.