U. S. DEPARTMENT OF COMMERCE

DANIEL C. ROPER, Secretary NATIONAL BUREAU OF STANDARDS

LYMAN J. BRIGGS, Director

NATIONAL BUREAU OF STANDARDS MISCELLANEOUS PUBLICATION M150

SUITABILITY OF SWEETPOTATO STARCH

FOR THE BEATER SIZING OF PAPER

By

CHARLES G. WEBER

MERLE B. SHAW

MARTIN J. O'LEARY

Issued June 15, 1935

UNITED STATES

GOVERNMENT PRINTING OFFICE

WASHINGTON : 1935

For sale by the Superintendent of Documents, Washington, D. C Price 5 cents

SUITABILITY OF SWEETPOTATO STARCH FOR THE

BEATER SIZING OF PAPER

By Charles G. Weber, Merle B. Shaw, and Martin J. O'Leary

ABSTRACT

In order to obtain information on the value of starch made from cull sweetpotatoes, a waste farm product, as beater sizing for paper, 26 paper-machine

runs were made in the Bureau's semicommercial mill. In this work, sweetpotato

starch was used in comparison with high-grade commercial starches made from

corn and cassava. The relative merits of the different starches used were deter- mined by comparing the results obtained with respect to retention of starch, retention of mineral filler, and properties of the finished papers. In general, the

use of beater starch improved the retention of mineral filler and increased the

bursting strength of the papers. Starch aided materially in filling the pores of the sulphite-soda papers, as indicated by decreased air permeability. No apparent

effects on the degree of sizing were noted, and the opacity was generally slightly decreased where starch was used. The papers containing sweetpotato starch were not inferior in any respect to those containing corn and cassava starches,

and superior results with respect to retention of mineral filler, and "closing of the sheet", were obtained with the sweetpotato starch. Apparently the starch made from the waste farm product is excellent for beater sizing, being at least as good as the corn and cassava starches commonly used for this purpose. CONTENTS

Page

L Introduction 1

II. Preparation and use of starches 2

III. Manufacture of experimental papers 3

IV. Discussion of results obtained with starch sizings 6

1. Sulphite-soda book papers 6

2. Rag-sulphite book papers 6

3. All-rag book papers 6

4. Effects of starches on stability of paper 7

V. Summary and conclusions 7

I. INTRODUCTION

A method of producing high-grade starch from cull sweetpotatoes, a waste farm product, has been developed by the Carbohydrate Division

of the Bureau of Chemistry and Soils of the United States Department of Agriculture. 1 In order to assist in appraising the potential

uses of this starch, its comparative quality as beater sizing for paper was studied at the National Bureau of Standards. Starch is widely

used as beater sizing in book papers and other printing papers,

mainly for its adhesive property which helps bind the fibers together,

increases the bursting strength, and improves the retention of mineral

filler. Starch improves the printing quality of some papers by closing

the sheet without excessive mechanical beating, and by laying surface

fuzz. Corn and cassava starches are now used almost exclusively in

this country for the purpose; hence the commercial use of sweetpotato starch in this field depends on its utility relative to those

starches.

» Ind. Eng. Chem. 25, 919 (1933). 134732—35 1
2 Miscellaneous Publications, National Bureau of Standards

The chemical and physical properties of the three different kinds

of starches had been shown by Thurber;2 however, no information was available on the value of sweetpotato starch for use in the manufacture of paper. Such information was obtained by making, on the

semicommercial equipment at the Bureau, a series of papers using

sweetpotato starch in comparison with representative commercial

starches made from corn and cassava. The papermaking equipment used in the study consisted of a 50-

pound copper-lined wood-tub beater with manganese-bronze bars

and plate; a Jordan refiner; a 4-plate screen; and a 29-inch fourdrinier

papermaking machine with a wire 33 feet in length, 2 presses, nine

15-inch dryers, a 7-roll machine-calender stack, and a reel. Detailed

descriptions of this equipment have been given in previous articles.3 4

II. PREPARATION AND USE OF STARCHES

Starch is useful as a sizing in paper only when added as a gelatinous,

colloidal solution, with adhesive strength. Natural, or unmodified,

starch is not affected by cold water, hence it must be gelatinized

before adding to the fiber furnish, if it is to be of value. When a water suspension of starch is heated, the starch granules absorb

water, and swell to many times their original size, to form a gelatinous paste, which is added to the beater furnish. The swelling

begins at 60 to 83° C and the paste thickens with increased temperature until a maximum viscosity is reached, after which the vis- cosity rapidly decreases if the temperature is maintained. The

temperatures at which gelatinization begins and the maximum

viscosity is reached vary according to the origin of the starch; also,

different kinds of starch vary greatly with respect to the viscosity

of pastes made from them. Data on the gelatinization temperatures

and viscosities of unmodified starches made from corn, cassava, and sweetpotatoes are given in an article by Thurber.6 Some of the starches employed for beater sizing are used in a

modified form. The starch may be modified by acid -hydrolysis or by oxidation, and the principal effect of either method is a reduction

in the viscosity of the paste which the starch will make when heated

with water. Starch is also marketed in a gelatinized form for use by

adding to the beater without swelling. The preparation of gelatinized starch consists essentially in swelling the starch in water,

drying the paste, and grinding.

Information contained in the literature and obtained from starch

manufacturers indicated that the practice with respect to the preparation of starch pastes for beater sizing varies greatly. Hence, it was necessary to determine, by trial, the best method of preparing

the sweetpotato starch for use in the beater. Four different methods

were used in preparing the pastes used in the first series of papers.

For machine run 1052, (see table 1) a 1:25 suspension of starch in

water was heated to 70° C, cooled, and added to the beater at the

start of the beating cycle; for machine run 1057, the temperature of

the starch suspension was raised to 68° C and the solution added to the beater % hour before the end of the beating cycle, after the clay,

2 Ind. Ens. Chem. 25, 565 (1933).

3 Tech. Pap. BS 21, 323 (1925) T340.

* Paper Trade J. [89] 19, 60 (Nov. 7, 1929).

s See footnote 2.
Weber, Shaw,

O'Leary Sweetpotato Beater Starch 3

rosin sizing, and alum had been added; the same procedure was

followed in machine run 1058 as in the preceding, except that the

temperature of the starch was raised to 80° C; and the conditions were the same for machine run 1060, except that the temperature

of the starch suspension was raised to only 61° C.

These preliminary runs indicated that the best results were obtained with sweetpotato starch when the gelatinization was stopped

before the maximum viscosity was reached, so that further swelling

might take place in the paper when in contact with the hot driers. The preparation for subsequent runs consisted in heating a suspension

of 1 part of starch in 25 parts of water to 68° C, with constant agitation, then cooling the paste to prevent further swelling, and adding

it to the beater furnish. The starch undergoes no further swelling

after being cooled to the temperature of the beater furnish, and is unaffected under normal conditions by the alum used to precipitate

the rosin sizing; therefore, the time at which it was added to the beater was apparently not important, provided thorough mixing with the

fibers was accomplished. Id the preliminary experiments with sweet- potato starch, the time of adding had no apparent effect, and this starch was added % hour before the completion of the beating cycle n subsequent runs. The commercial starches were prepared and used in accordance

with the manufacturers' directions, on the assumption that each

manufacturer has determined the method that gives the best results

with his particular product.6

III. MANUFACTURE OF EXPERIMENTAL PAPERS

It was not a purpose of the investigation to determine the effects of different amounts of starch in paper. Hence, in order to have comparable data on the results obtained with different starches, the same amount was used in each experiment. The amount used, 2 percent, was selected because it represented common commercial practice.

The papers made were all book papers. The following fiber combinations were used: 50 percent of sulphite, 50 percent of soda; 7 50

percent of rag, 50 percent of sulphite; and all-rag fiber made from

60 percent of new rags. Papers of each type were made without

starch, with sweetpotato starch, with the commercial starches, and

with and without clay filler. All papers of each type were made the

same, except with respect to the use of starch and filler, as indicated

by the data in table 1. Different papers of the same type containing

the same kind of starch were made the same, except with respect to the preparation of or time of adding the starch paste.

Manufacturers' directions were not followed in preparing the starches for machine runs 1062 and 1061. These were repeat runs for 1051 and 1053, respectively, and methods of preparation were altered in an effort to obtain better results.

7 Sulphite is a term used to designate wood fibers prepared by the acid-sulphite process; soda is a term

used to designate wood fibers prepared by the alkaline-soda process; and rag fibers are obtained from rags, principally cotton.
4 Miscellaneous Publications, National Bureau oj Standards

•9"S 11

ill

I

Hi I

f

Jli

5|J1

111

m

v-OOOHMiOCltOCINNNOO

^.CO 00 CO OS (M to "5 CO OS OS r-l

Is'

11

I

I

£3 oa b

Ijllllillllli

4!

• •_; •_; •

•

Ji 1

>C<I!M<M<N<M(M<M<M(M<M 4

iiiiiiiiilii

co co co co co"

linn

88S2SS

assess

SSS22S
Weber, Shaw,~\ O'Leary J Sweetpotato Beater Starch

Sooc e»W>OMO*N OOOOOOOOOOOOt^t^

NtOOOtOOOOO*

ei cn cn eo N <n <n n eo oo oo — oi «3

Tji tjJ Tii "5 pi «5 co

t»oo«ot»oo>o»ot>- §§§§§§§§

»h eo to »o eo o> >Q totd»o»dtdto»ot^ iqiqiO'O'QiQiQ'O

in © to oo ga c» © ' ' ' 'tHNfi © 00 ^

><N©

^ 3 o « te,5 fe o OHNMT)lif5!ON

OOOOOOOO

CN © ^ ®

p.° 5 s

GOO

•

s .9 e- ©1 II

S A©

2

* 1*3 s is

OT > O

.9 M

"o 5*3 —1 2

to M 2 © «&sa

855

• P5

S'a-gS £a

£ © £ W <N 1

.o © ©go g'G P 512

"8

>»;$ c3 to N'9 c! ^ lilt-IP

32 o^s ^S-o

2 t3 ^ 5 9 =7 '5

03 —. !3

pq 2 g-g pa .9 2 S?j-§Slr <§.a,a A " © 9 g

~ « °» ~ t»"

a "

'~

S3a
6 Miscellaneous Publications, National Bureau of Standards

IV. DISCUSSION OF RESULTS OBTAINED WITH STARCH

SIZINGS

1. SULPHITE-SODA BOOK PAPERS

It is obvious that in order to obtain benefits from starch and clayfiller, substantial quantities must remain in the finished paper. The

retention of starch was rather low in the sulphite-soda papers, the

average being 38 percent. However, the sweetpotato starch showed

up well in comparison with the other kinds, the average retention

for that starch being 46 percent as compared to 38 and 24 percent

for corn and cassava starches, respectively. In general, the retention

of clay filler was improved by the starches, the outstanding exception

being corn starch B, a modified starch, which apparently reduced

rather than increased the retention of filler. The best retention of

filler in this group was obtained with sweetpotato starch in machine

run no. 1057. Other properties affected by starch sizing were air

permeability, opacity, bursting strength, and tearing strength. Starch

aided in closing the sheet, as indicated by reduced air permeability,

and helped to lay surface fuzz, both of which aid the printing

quality. The data show that the lowest air permeability was obtained

with sweetpotato starch. In general, the bursting strength and

tensile strength of the sulphite-soda papers were increased somewhat

by starch, but some resistance to tear was sacrificed and the presence

of starch lowered the opacity.

2. RAG-SULPHITE^BOOK PAPERS

Some of the results obtained with starch were quite different for

this type of paper than for the sulphite-soda type. The retention of

starch was approximately the same as for the sulphite-soda papers,

and the effects on the retention of clay filler were also much the same;

however, while the effects on the properties of the papers were of the same order as for the sulphite-soda papers, except for air permeability,

they were less pronounced. In these papers, starch increased rather

than decreased air permeability. The only significant differences

between results obtained with the different kinds of starch were rela- tive to starch retention and air permeability. Very unsatisfactory

retention of clay filler was again obtained with corn starch B.

3. ALL-RAG BOOK PAPERS

Two series of all-rag papers were made. The first was made without clay filler, since many such papers contain little filler, and the

second with approximately 14 percent of filler added.

The retention of starch was much better in the all-rag type of

papers than in either of the preceding, the average being 59 percent.

The effects of the starch were much the same as for sulphite-soda

papers, except that no significant effects on the retention of clay filler or on air permeability were apparent. The bursting strength was

increased appreciably and the tearing strength and opacity were decreased. The best starch retention was obtained with sweetpotato

starch in machine run no. 1096.
Weber, Shaw,

O'Leary Sweetpotato Beater Starch 7

The effects of clay filler on the properties of paper may be seen by

comparing data for machine runs 1090 and 1095 of this group, also 1063 and 1064 of the rag-sulphite papers, and 1048 and 1049 of the

sulphite-soda papers. In each comparison, the two papers were made

the same, except that one contained approximately 14 percent of filler and the other none. In general, clay filler increased the air permeability, improved the opacity, and decreased the strength and water

resistance.

4. EFFECTS OF STARCH ON STABILITY OF PAPER

Since the stability of book papers is of importance in its relation to lasting quality, information on the resistance to deterioration of papers containing different kinds of starch was obtained. Sulphitesoda papers from machine runs 1050, 1060, and 1061, containing

corn, sweetpotato, and cassava starches, respectively, were subjected

to an accelerated-aging test 8 9 10 employed by the Bureau for testing

stability of papers. The retention of folding endurance after heating was 74, 74, and 68 percent, respectively, for the three papers, indicating no significant differences in the stability of papers sized with

the different kinds of starch.

V. SUMMARY AND CONCLUSIONS

The results of the comparative tests described indicate that sweet- potato starch is as satisfactory a beater sizing for paper as the commercial corn and cassava starches commonly used. Papers sized

with sweetpotato starch were equal to the best papers sized with the

other starches with respect to strength, opacity, and degree of sizing.

Superior retention of mineral filler, and closing the sheet, as indicated

by the air permeability, were obtained with the sweetpotato starch.

A limited number of tests indicated that the papers containing sweet- potato starch were as stable as those containing other starches.

Washington, March 23, 1935.

8 BS J. Research 7, 466 (1931) RP352.

» Paper Trade J. [95] 4, 28 (July 28, 1932).

"> BS J. Research 11, 727 (1933) RP620. O