MAK PAPER MCA ASPEN SEMICIIIMICAL
AND GPOUNDIVCCD PULPS
April 1948
No. 81709
UNITED STATES \ DEPARTMENT OF AGRICULTURE
FOREST SERVICE
FOREST PRODUCTS LABORATORY
Madison 5, Wisconsin
In Cooperation with the University of Wisconsin
BOOK PAPER FROM ASPEN SEMICHZMICAL AND GROUNDWOOD PULPS!
By G. E. LACKIN, Technologist
Abstract
Recent experiments made at the U. S. Forest Products Laboratory on the production of base stock for coated book paper showed that a total of as much
as 80 percent of aspen semichemical and groundwood pulps may be used without
significant sacrifice in quality of paper or materially changing the papermaking operations. It was found that the aspen semichemical pulp provided
the necessary strength, and when used with a free aspen groundwood, satisfactory stock freeness and absorbency in the sheet were obtained. Coating,
supercalendering, and printing trials were made with satisfactory results.
Introduction
Groundwood pulp containing high proportions of aspen is now commercially used
with spruce sulfite pulpin book papers. Previous experiments at the Forest
Products Laboratory showed that although quite satisfactory strength properties were obtained from furnishes containing high percentages of aspen
groundwood and semichemical pulps, the machine operating conditions and
coating characteristics were somewhat unsatisfactory. Low freeness, low wetweb strength, and "picking" at the press rolls and dryers were the major
operating difficulties previously experienced when somewhat more than 50 percent aspen was used. The surface of the paper did not present the best
receptivity to coating, which resulted in reducing the amount of coating that
could be applied to the sheet.
The objectives of the work reported hero were to improve the paper machine
operating conditions and obtain better sheet properties by combining a freer
aspen groundwood with the aspen semichemical pulp and softwood sulfite pulp.
It was believed that satisfactory strength could be obtained by using the
bleached aspen semichemical pulp, and that improved receptivity to coating and
higher freeness would be obtained by the use of the freer aspen groundwood.
-Presented at the Spring Meeting of the Northwestern Division of the American
Pulp & Paper Mill Superintendent's Association at King's Gateway Hotel,
Land 0' Lakes, Wis., June 6 and 7, 19474
?"Use of Bleached Aspen Semecchenical Pulp in Groundwood Book Paper," by
J. N. McGovern. Tech. Assoc. Papers, vol. 29, 472-478 (1946). Paper
Trade Jour., vol. 123, No, 20, 47-52 (November 14, 1946).
Roport g oo Ai1b9
444:
Descri tion of Ex erimental Pul s and Machine Runs
In this work a series of experimental paper machine runs was made in which the
total amount of aspen pulps used in the furnish was varied from 50 to 80 percent. Included in this series was a reference standard run using commercial
wet broke composed of 50 percent bleached spruce sulfite pulp and 50 percent
book-grade aspen groundwood pulp. The neutral sulfite semichemical pulp used
in the experimental runs was prepared by cooking aspen to a yield of about
75 percent, milling to a freeness of 555 cc. (Schopper-Riegler) to obtain
satisfactory fiberization, and bleach4ng in three-stages, namely, chlorine,
alkaline extraction, and hypochlorite2, The bleached aspen pulp had a bursting strength of one point per pound per ream and a tearing strength of 1.26
grams per pound Ter ream. The experimental free groundwood pulp used was
prepared by grinding aspen on a silicon carbide pulpstone with a medium
sharp surface to a Canadian Standard freeness of about 15 cc., or about twice
that of the commercial slow groundwood previously used, — which was 60 cc.
The energy consumption for this free groundwood was g 6 horsepower-days per
ton of wood (oven-dry basis) as compared to about 130 for the slow commercial
groundwood, which, if the pulp were otherwise suitable, would be a distinct
advantage. The softwood sulfite pulp was commercial book grade bleached
spruce and hemlock sulfite. The physical test data for these pulps are given
in table 1.
Base stock for magazine book paper of 40-pound basis weight (25 x 40 - 500)
was chosen for the experimental paper machine runs. which were made on the
Laboratory experimental Fourdrinier paper machine.• . The furnishes
for these runs were prepared without processing in the beater or jordans.
Two percent alum and 12 percent clay were added at the beater for all furnishes,
except the commercial wet-broke, which contained approximately the amount of
clay retained in the experimental papers. The data on the furnishes, headbox freeness, and sheet properties for the ' experimntal runs are given in
table 2.
Discussion of Results
The machine operating conditions and the sheet properties obtained for the .
reference standard run, containing 50 percent softwood sulfite pulp and
50 percent commercial aspen groundwood pulp, established a reference point
for comparison with the other experimental runs using higher percentages of
aspen pulp.
When aspen semichemical pulp was substituted for half of the sulfite
(machine run 2872), the stock freeness dropped about 20 percent and the porosity of the sheet was reduced by about one-fourth compared to the standard
'Bleaching of Semichemical Pulps," by F. A. Simmonds and R. M. Kingsbury.
Paper Trade Jour. 124 (No. 4) 53-60, (January 23, 1947).,
•n•n•
Report No. R1709
-2.
run (machine run 2871). Although, the strength .of the sheet was not appreciably affected, the reduced porosity adversely affected the receptivity of
the sheet to coating. In commercial production the reduction in machine
speed required by the low freeness of this furnish would be undesirable.
To raise the freeness of the stock and the porosity of the sheet, the experimental free aspen groundwood pulp was substituted for the slower one in machine
run 2873, and the remainder of the furnish was composed of 25 percent aspen
sendchemical pulp and 25 percent spruce sulfite pulp. This substitution
resulted in a much higher freeness of stock and increased porosity of sheet
compared to those obtained in the reference standard run, though a slightly
lower strength was obtained.
These results indicated that a still higher percentage of the aspen semichemical pulp might be used in a furnish containing free aspen groundwood.
So another trial was made using 20 percent spruce sulfite, 30 percent aspen
sanichemical, and - 50 percent free aspen groundwood pulps (machine run 2876).
In this run the freeness of the stock going to the machine and the properties
of the paper were virtually the same as those obtained in the reference
standard run. Coating, supercalendering, and printing trials were made on
sample rolls of this paper with results that were entirely satisfactory; no
difficulty was encountered in any of the converting operations.
Report No. R1709
-3-
Table 1.-•Fhysical test data on pulps used in experimental runs
Pulp properties
:Aspen groundwood: Bleached :Bleached
:aspen neu-:softwood
Slow, : Free,:tral sul-. :sulfite
:shipment:grinder:fite semi-:shipment
2512 :run 561: chemical : 2513
:digestions:
:
: 5234N
•
5235N
•
Bursting strength-pts. per lb. per
0.23
0.20 :
0•9g
:
..51
.55 :
1.26
: 1.96
lb. per in. width: 21.5
: 16.0 : 29,3
lb. per sq. in.: 1,484 : 1,098: 7,230 : 16.9
: 3,350
ringlA
Tearing resistance-gm. per lb. per rm.: Tensile strength Stretch percent: 2.6
Folding endurance double folds .
Density gm. per c.c.:
Ream weight (25 x 40 - 500) Freeness (Schopper-Riegler) (Canadian Standard) Report No. R1709
: 2.60 :
6.8
0052
: 3.2
:
•
313
:
27
.44 :
.41 :
.75
:
.60
lb.:
114 :
107 : 57.3
: 57.6
c.c.:
c.c.:
260 :
60 :
415 :
115 : :
:
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