U.S. patent application number 10/463346 was filed with the patent office on 2004-12-23 for method for producing corn stalk pulp and paper products from corn stalk pulp.
Invention is credited to Ahmed, Aziz, Ryu, Haiil, Won, Jong-Myoung.
Application Number | 20040256065 10/463346 |
Document ID | / |
Family ID | 33517088 |
Filed Date | 2004-12-23 |
United States Patent
Application |
20040256065 |
Kind Code |
A1 |
Ahmed, Aziz ; et
al. |
December 23, 2004 |
Method for producing corn stalk pulp and paper products from corn
stalk pulp
Abstract
A new method for making pulp out of agricultural residue
includes harvesting certain portion of plant stalk. The harvested
plant stalk is bailed, transported and stored. At the mill, the
plant stalk is chopped and goes through pulping process. The pulp
is used to make varieties of papers with or without blending other
wood based pulp.
Inventors: |
Ahmed, Aziz; (Middleton,
WI) ; Won, Jong-Myoung; (Chuncheon, KR) ; Ryu,
Haiil; (Daejeon-Si, KR) |
Correspondence
Address: |
McGuire Woods LLP
Suite 1800
1750 Tysons Boulevard
McLean
VA
22102
US
|
Family ID: |
33517088 |
Appl. No.: |
10/463346 |
Filed: |
June 18, 2003 |
Current U.S.
Class: |
162/26 ; 162/76;
162/83; 162/90; 162/96; 162/97; 162/98; 162/99 |
Current CPC
Class: |
D21B 1/00 20130101; D21C
3/02 20130101; D21C 5/00 20130101; D21C 9/10 20130101; D21H 11/12
20130101 |
Class at
Publication: |
162/026 ;
162/076; 162/083; 162/090; 162/096; 162/097; 162/098; 162/099 |
International
Class: |
D21B 001/04; D21C
003/02 |
Claims
What is claimed is:
1. A method for producing pulp from agricultural residues,
comprising: harvesting a portion of a cornstalk plant, wherein the
harvesting includes removing a portion of the cornstalk below about
at least one of a ear on the cornstalk plant; drying the cornstalk
portions; chopping the cornstalk portions; washing of the chopped
cornstalk portions; compacting the washed cornstalk portions in a
screw feeder to remove water; extracting pulp from the compacted
cornstalk portions with an alkaline pulping solution at
predetermined conditions; fiberizing the pulp; washing the pulp;
and treating of the fiberized and washed pulp with a bleaching
solution, wherein the bleaching solution removes residual lignin
and color for increasing the brightness to greater than about 70%
ISO.
2. The method of claim 1, wherein batch processes of at least one
of trembling, stationary digester, and super batch digester is
utilized.
3. The method of claim 1, wherein continuous processing of at least
one of Pandia digester and Kymer digester are utilized.
4. The method of claim 1, wherein the cooking of cornstalk in the
alkaline solution is done at a temperature ranging from about 120
to 160.degree. C. for about 30 min to 120 min.
5. The method of claim 4, wherein the alkaline solution comprises
an alkaline hydroxide solution including at least one of sodium
hydroxide, potassium hydroxide, ammonium hydroxide, and calcium
hydroxide.
6. The method of claim 4, wherein the alkaline solution further
includes at least one of sodium carbonate and sodium
bicarbonate.
7. The method of claim 6, wherein the alkaline solution further
includes sodium hydroxide.
8. The method of claim 7, wherein the alkaline solution further
includes anthraquinone.
9. The method of claim 7, wherein the sodium hydroxide has a
concentration in the range from about 2% to 18% active alkali and
the anthraquinone has a concentration in the range from about 0.0%
to 0.5%.
10. The method of claim 7, wherein a pretreatment step involving
compacted cornstalk material with cellulose protecting agents such
as MgCl.sub.2, CaCO.sub.3 at a temperature between about 60 to
about 100.degree. C. for about 30 to about 60 minutes might be used
in order to protect the hemicellulose during alkaline digestion of
cornstalk.
11. The method of claim 1, wherein the bleaching solution comprises
chlorine dioxide.
12. The method of claim 1, wherein the treating of the fiberized
and washed pulp with a bleaching solution is performed at a
temperature ranging from about 50 to 100.degree. C. for about 30 to
120 minutes.
13. The method of claim 1, wherein the alkaline pulping solution
includes a concentration ranging from about 1% to 3% sodium
hydroxide.
14. The method of claim 1, wherein a chlorine dioxide-alkaline
extraction-chlorine dioxide (DED) bleaching sequence raises the
pulp brightness to about 80-85% ISO.
15. The method of claim 14, wherein after the DED sequence one of a
hydrogen peroxide bleaching solution (P), ozone solution (Z) and
oxygen solution (O) is used for raising the pulp brightness to
about 86 to 95% ISO.
16. The method of claim 15, wherein the chlorine dioxide bleaching
solution comprises a dosage of chlorine dioxide equivalent to
pulps' kappa factor ranging from about 0.01 to 0.5.
17. The method of claim 16, wherein the hydrogen peroxide bleaching
solution comprises: hydrogen peroxide of about 1 to 3% of o. d.
pulp weight;sodium hydroxide of about 1 to 3% of o. d. pulp weight;
sodium silicate of about 1 to 3% of o. d. pulp weight; magnesium
sulfate of about 0.02 to 0.06% of o. d. pulp weight; and trace
amounts of chealant
18. The method of claim 17, further comprising: a bleaching stage
to improve the brightness of cornstalk pulp, wherein the bleaching
stage uses bleaching reagent, such as ozone of about 0.05 to 5% (of
o. d. pulp weight) and oxygen of about 0.1 to 2% (of o. d. pulp
weight).
19. A method for making paper out of pulp from agricultural
residue, comprising: refining pulp from agricultural residue;
blending the pulp from agricultural residue; cleaning; screening;
and rolling in the paper machine, wherein the pulp from
agricultural residue is cornstalk pulp.
20. The method of claim 19, wherein the cornstalk pulp has freeness
level of at least 250 ml or greater.
21. The method of claim 19, wherein the cornstalk pulp has a kappa
number in a range of about 7 to 80.
22. The method of claim 19, wherein the cornstalk pulp has a kappa
number in a range of about 2 to 7.
23. The method of claim 19, wherein the cornstalk pulp has a kappa
number below about 2.
24. The method of claim 19, wherein cornstalk pulp can be used
without refining and/or with refining to 250-500 ml CSF before
combining with wood pulp to provide the specific properties that
can meet the end-uses of paper products.
25. The method of claim 19, wherein cornstalk pulp can be
fractionated into long fiber and short fiber fractions and
reblended depending on the properties of end-uses to maximize the
performance of cornstalk pulp.
26. The method of claim 19, wherein writing and printing paper,
photocopy, specialty papers, and envelope papers can be produced
from bleached cornstalk pulp by the blending with one or more pulp
and/or additives from a group comprising: bleached softwood
chemical pulp; bleached hardwood chemical pulp: 0-20%; filler
(precipitated or grounded calcium carbonate, clay, kaolin, talc,
titanium dioxide, etc.): 0-30%; dry strength chemicals (starch or
other polymeric materials): 0-4%; sizing agent (rosin emulsion,
AKD, ASA or others): 0.05-5%; and cationic and/or anionic polymeric
retention aids (starch, poly acryl amide, poly ethylene imine,
colloidal silica, bentonite, organic micro-particles, etc):
0-5%.
27. The method, of claim 19, wherein top white liner can be
produced from bleached cornstalk pulp by blending with one or more
additives from a group comprising: bleached softwood chemical pulp:
0-30%; bleached hardwood chemical pulp: 0-30%; filler (precipitated
or ground calcium carbonate, clay or kaolin): 0-20%; dry strength
agent (starch or other polymeric materials): 0-4%; sizing agent
(rosin emulsion, AKD, ASA or others): 0.05-2%; and retention aid
(starch, poly acryl amide, poly ethylene imine, colloidal silica,
bentonite, organic micro-particles, etc): 0-5%.
28. The method of claim 19, wherein carton package for milk, juice,
and other beverages can be produced from bleached cornstalk pulp by
blending with one or more additives from a group comprising:
bleached softwood chemical pulp: 0-20%; sizing agents (rosin
emulsion, AKD, ASA or others): 0.01-5%; and retention aid (starch,
poly acryl amide, poly ethylene imine, colloidal silica, bentonite,
organic micro-particles, etc): 0-5.5%.
29. The method of claim 19, wherein linerboard can be produced from
unbleached cornstalk chemical or semi-chemical pulp without or with
unbleached softwood chemical or semi-chemical pulp.
30. The method of claim 19, wherein corrugating medium can be
produced from high yield cornstalk pulp mixed with high yield
hardwood pulp.
31. The method of claim 19, wherein tissue papers, wet strength
papers, and industrial papers can be produced from bleached
cornstalk pulp by blending with one or more additives from a group
comprising: bleached softwood chemical pulp: 0-30%; bleached
hardwood chemical pulp: 0-20%; sizing agents (rosin emulsion, AKD,
ASA or others): 0.01-5%; and retention aid (starch, poly acryl
amide, poly ethylene imine, colloidal silica, bentonite, organic
micro-particles, etc): 0-5.5%.
32. The method of claim 19, wherein photocopy papers, specialty
papers, and envelope papers can be produced from bleached cornstalk
pulp by blending with one or more additives from a group
comprising: bleached softwood chemical pulp: 0-30%; bleached
hardwood chemical pulp: 0-20%; filler (precipitated or ground
calcium carbonate, clay or kaolin): 0-40%; dry strength agent
(starch or other polymeric materials): 0-5%; sizing agents (rosin
emulsion, AKD, ASA or others): 0.01-5%; and retention aid (starch,
poly acryl amide, poly ethylene imine, colloidal silica, bentonite,
organic micro-particles, etc): 0-5.5%.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a process for separating a
portion of a corn plants and producing pulp from the plant for
making paper products. More specifically, the present invention
relates to a method for harvesting portions of corn plants, that
is, harvesting portions from the ground up to about the ears of the
corn plant. Additionally, the present invention relates to a
versatile pulping process including at least one of mechanical,
semi-chemical, and chemical process in order to produce pulp
suitable for various paper products and producing various paper
products from the pulp.
[0003] 2. Discussion of the Related Art
[0004] Trees provide a major source of the fiber supply for paper
and paperboard products industries. Softwood is a very suitable
species for mechanical pulping. Chemical pulps of softwood are used
where the strength of the paper product is important. Hardwood has
a much shorter fiber than softwood and typically is not suitable
for mechanical pulping, but suitable for chemical and semi-chemical
pulping. Hardwood chemical pulp is used in paper products where
surface smoothness and optical properties are important. Wood based
fiber is expensive as it incurs a high chemical charge for pulping,
high energy input for cooking and refining, and high cost chemical
recovery systems. Additionally, the environmental impact of wood
based fiber is disadvantageous.
[0005] Agricultural residues such as cornstalks offer a promising
alternative source of fiber. In particular, they can serve as
important raw materials for making paper products, including
products for printing, writing, top linerboard, liner, tissue paper
and other specialty grade paper. Additionally, environmental
concerns have heightened the interest in using agricultural fibers.
Exploitation of agro-based resources for making paper products is
important to improve farm profitability and reduce environmental
pollution from burning and land disposal. Currently, the use of
agricultural plants for making paper products is negligible. This
is especially true in the United States where nearly 284 million
tons of total agricultural residues, including 150 million tons of
cornstalks are available annually. Cornstalk as a fiber source for
papermaking is not popular in major pulp and paper producing
countries as there are abundant and secure supplies of pulpwood
meeting the raw material requirements for large-scale
capital-intensive pulp mills. A large-scale pulp mill based on
agricultural residues needs a large supply of bulky raw materials,
thereby creating transportation problems. Additionally,
agricultural residues are seasonal, thereby creating storage
problems. Separation of appropriate parts of cornstalk residue
during harvesting will reduce transportation and storage problems.
A pulp mill based on cornstalk should be small scale and community
based. Optionally, a large-scale mill may be used depending on the
availability of cornstalk and supply logistic.
[0006] The related art covering non-wood pulping and papermaking
include U.S. Pat. No. 6,302,997 issued to Hurter et al. This
describes methods of non-wood pulping for papermaking. Cornstover
(stalks, leaves and husks) are used in this process and contain low
quality fiber and a high quantity of debris. Accordingly, transport
and storage problems in the farm as well as in the mill are present
in the related art. Additionally, pith, leaves, and husk contain a
small quantity of good fibers. Therefore, tube grinders, conveyers,
hydrapulpers, pumps, magnetic separators, and dewatering screens
have to handle huge volumes of unnecessary materials.
[0007] Accordingly, there is a pulp yield of 39.6%, which is
substantially low due to the presence of large quantity of low
quality fiber that are mostly removed during downstream processing.
This low quality fiber consumes chemicals without giving any
benefit to the pulp qualitatively and quantitatively and the mill
faces huge disposal problems due to large quantity of rejects. The
related art uses the traditional alkaline digestion process. The
addition of an acid treatment step, ozone bleaching step and a
peroxide-bleaching step makes this process expensive and
complicated. The process also includes high doses of chemicals
during hydrogen peroxide bleaching. Despite the disclosure of
interesting process steps in the foregoing U.S. patent, the
invention has a number of drawbacks, for example: 1) dealing with
cornstover having materials such as pith, leaves and husk that have
very little fiber value; 2) carrying the unnecessary mass to the
mill creates transportation and storage and disposal problems of
the large supply of reject materials; 3) low pulp yield; 4) high
chemical consumption in acid stage, bleaching stage and in
adjustments of pH; 5) the process involves extra steps that
increases capital costs and operating expenses; and 6) the process
saves energy during alkaline cooking but consumes more energy
through refining.
[0008] The present invention focuses on non-wood paper making
having an advantageous approach. By establishing harvesting,
pressing and bailing processes on the farm and allowing for
gathering places of goods and storage. Alternatively, it is to
establish a mini mill at the center of the corn growing area where
farmers will have their own storage facility and will transport the
materials to the mill at a schedule set by the mill. Ideally, mill
storage should not be more than about 15 days in order to optimize
the mill spatially. The mill should use a simple and
environmentally benign process with low capital and operating costs
to compete with the larger wood based mills. These processes are
not currently available in the art.
SUMMARY OF THE INVENTION
[0009] Accordingly, the present invention is directed to a process
for producing pulp and paper products from pulp that substantially
obviates one or more of the problems due to limitations and
disadvantages of the related art. For example, a process for
producing pulps suitable for use in papermaking, top white liner
making, liner making and other specialty papermaking. The process
includes a harvesting process for separating portions of the
cornstalk that are most suitable as fiber source in the field,
digesting the selected cornstalk portions with an alkaline pulping
solution with or without the presence of anthraquinone and/or other
catalysts, and treating the pulp with elemental chlorine free
bleaching solution in order to produce bleached pulp suitable for
papermaking. An advantage of the present invention is to provide a
cornstalk harvesting process that will take the bottom portion of
the cornstalk plant below about the ears of the plant, which
contains mostly the good fiber and less pith and leaving behind the
rest of the plant in the field for traditional farm use.
[0010] Another advantage of the present invention is to chop the
selected cornstalk section using a modified wood chipper.
[0011] Another advantage of the present invention is to separate
the chopped leaves and piths from the chopped stem
pneumatically.
[0012] Another advantage of the present invention is to reduce the
cornstalk processing steps from harvesting to digestion.
[0013] Another advantage of the present invention is to accept up
to 15% of pith in the digester to simplify the separation
process.
[0014] Another advantage of the present invention is to provide a
cornstalk pulping process that requires a minimum number of
processing steps. Another advantage of the present invention is to
provide a cornstalk pulping process that is cost effective and
environmentally benign at small- to medium-scale level.
[0015] Another advantage of the present invention is to provide a
cornstalk harvesting and pulping process that uses a minimal amount
of readily available and inexpensive equipment.
[0016] Another advantage of the present invention is to provide a
cornstalk processing system during harvesting to separate the
bottom portion of the cornstalk plant, below about the ears of the
cornstalk plant, from the rest of the plant, which is still
available to the farmer for traditional farm use.
[0017] Another advantage of the present invention is to make
compact square bales of dried cornstalk during the harvesting
process to reduce bulk to avoid transport and storage problem.
[0018] Another advantage of the present invention is to develop a
management system for transportation and storage of selected
cornstalk
[0019] Another advantage of present invention is to transport
cornstalk from the collecting point to the mill.
[0020] Another advantage of the present invention is to leave
portions of the cornstalk plant rejected during harvesting in the
field for soil conditioning and other traditional farm uses.
[0021] Another advantage of the present invention is to reduce the
contaminants in cornstalk during harvesting and compact baling
processes in order to reduce hot water requirements in washing
stage before chemical impregnation and digestion steps.
[0022] Another advantage of the present invention is to chop the
cornstalk followed by hot water washing and compression in screw
feeder where impregnated with cooking chemical before entering into
the digester.
[0023] In yet another advantage of the present invention is to
apply a compression step to eliminate water and hot water-soluble
extractive from the materials, and also to increase the digester
intake.
[0024] A further advantage of the present invention is to add
cooking chemicals just after the compression step for better
chemical impregnation of de-structured raw materials in a
continuous digester.
[0025] Another advantage of the present invention is to apply a
compression step to increase the digester input and to increase the
liquor impregnation into the material.
[0026] Another advantage of the present invention is to use the
standard paper mill equipment to process the cooked fiber.
[0027] Another advantage of the present invention is to digest the
raw materials at low temperatures in the range of about 110 to
160.degree. C. with a retention time of about 30 to 180
minutes.
[0028] Another advantage of the present invention is to add a
pretreatment step just after the washing and compression step,
where cellulose protecting agents such as MgCl.sub.2 or MgCO.sub.3,
and the like, will be impregnated at a temperature in the range of
about 60 to 100.degree. C. for a period of time in the range of
about 30 to 60 minutes.
[0029] Another advantage of present invention is to maximize the
hemicelluloses content of cornstalk chemical pulp by introducing a
pre-impregnation stage using cellulose protecting agents.
[0030] Another advantage of present invention is to take benefit of
hemicelluloses content in cornstalk pulp in papermaking process by
blending with softwood kraft pulp and using wet end chemistry.
[0031] Another advantage of present invention is to find the
synergic effect of cornstalk pulp in a typical
papermaking/boardmaking furnish.
[0032] Another advantage of the present invention is to use less
chemicals, for example, 8 to 20% active alkali with or without the
presence of catalyst such as anthraquinone and the like.
[0033] Another advantage of the present invention is to use less
chemicals in the elemental chlorine-free bleaching process.
[0034] Another advantage of the present invention is to apply
chlorine dioxide, alkaline extraction, peroxide, ozone, and oxygen
bleaching stages to obtain about 80 to 95% of brightness.
[0035] Another advantage of the present invention is to avoid
sulfur based chemicals in cooking liquor or in bleaching liquor to
remain committed to environmentally benign pulping and bleaching
processes.
[0036] Another advantage of the present invention is to fractionate
the fiber after bleaching into long fibers (mainly from cornstalk
skin) and into short fibers (mostly from pith). Another advantage
of the present invention is to use the cornstalk pulp to produce
various grades of paper without even fiber fractionation into long
and short fiber fraction.
[0037] Another advantage of the present invention is the
flexibility of using chemical pulp in a blend with bleached soft
wood kraft pulp (with or without prior refining) and filler.
[0038] Another advantage of the present invention is that the long
fiber fractions will be refined to approximately 250-500 ml CSF and
then added to the short fiber fraction before papermaking step.
[0039] Another advantage of the present invention is a cornstalk
pulping process that minimizes water use by reducing the number of
washing stages and by minimizing the number of dilution and
thickening stages, by recycling the internal water as much as
possible.
[0040] Another advantage of the present invention is to improve the
paper quality made from the bleached cornstalk pulp by adding
bleached softwood kraft pulp approximately 5 to 20%, inorganic
filler approximately 5 to 60%, starch approximately 0.25 to 4%,
sizing agent approximately 0.025 to 0.5%, cationic, anionic and/or
amphoteric retention aids, and the like.
[0041] Another advantage of the present invention is to use
cornstalk chemical pulp with or without refining in a blend with
bleached softwood kraft (with or without prior refining) and
filler.
[0042] Another advantage of the present invention is to use the
bleached cornstalk chemical pulp in a blend with bleached softwood
kraft pulp, bleached hardwood chemical pulp and filler.
[0043] Another advantage of the present invention is to use the
bleached cornstalk chemical pulp in a blend with hardwood CTMP
(chemi-thermo mechanical pulp) and/or BCTMP (bleached chemi-thermo
mechanical pulp) and filler.
[0044] Another advantage of the present invention is to use the
bleached cornstalk chemical pulp in a blend with bleached cornstalk
chemi-thermo mechanical pulp (CTMP/BCTMP), bleached hardwood
mechanical pulp, bleached softwood kraft pulp and filler.
[0045] Another advantage of the present invention is to use the
bleached cornstalk mechanical pulp in a blend with hardwood
chemical pulp and/or bleached hardwood mechanical pulp, bleached
softwood kraft pulp and filler.
[0046] Another advantage of the present invention is to use
unbleached cornstalk chemical and/or semi-chemical pulp in a blend
with unbleached softwood kraft pulp and/or unbleached softwood
semi-chemical (kraft) pulp to prepare packaging grade paper.
[0047] Another advantage of the present invention is to apply the
bleached cornstalk chemical pulp in a blend with bleached softwood
kraft pulp (0 to 10%) and filler (10 to 60%) in the outer layer of
the multi layer papers. The inner layer of the paper may contain
inferior quality fibers, such as recycled fiber, inferior virgin
fiber, pulp having extractives and pulp unsuitable for exposure on
paper surface.
[0048] Another advantage of the present invention is to use the
bleached cornstalk chemical pulp in top liner by blending with
bleached softwood kraft pulp (0 to 10%) and filler (0 to 60%) along
with very small quantities of starch, sizing agents and retention
aid.
[0049] Another advantage of the present invention is to use the
bleached cornstalk chemical pulp in an existing mill using the
furnish consisted of hardwood and softwood pulp and filler in order
to enhance the paper strength properties through superior fiber
bonding capability of cornstalk pulp.
[0050] Another advantage of the present invention is to use the
bleached cornstalk chemical pulp to increase the filler retention
in the paper without compromising strength properties.
[0051] Another advantage of the present invention is to use the
unbleached cornstalk chemical pulp with unbleached chemical or semi
chemical softwood kraft pulp to enhance strength properties of
papers such as sack paper, packaging paper etc.
[0052] Additional features and advantages of the invention will be
set forth in the description which follows, and in part will be
apparent from the description, or may be learned by practice of the
invention. The objectives and other advantages of the invention
will be realized and attained by the structure particularly pointed
out in the written description and claims hereof as well as the
appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0053] The accompanying drawings, which are included to provide a
further understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and together with the description serve to explain
the principles of the invention.
[0054] FIG. 1 is a flow chart describing a chemical pulping process
for corn stalk pulp.
[0055] FIG. 2 is a flow chart describing a mechanical pulping and
high yield pulping process for corn stalk pulp.
[0056] FIG. 3 is a flow chart describing a paper making process
from corn stalk pulp.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0057] Today the paper industry in the United States is in the same
situation as steel industry was a few decades ago. Small-scale
modern steel industries are more efficient than large-scale
facilities. Accordingly, it is time to look for technology for the
development of small-scale efficient pulp and paper industry. It is
also time to look for inexpensive fiber sources to face the
competition from high yield plantation trees such as eucalyptus,
acacia, and the like. Agricultural residue such as cornstover can
compete with eucalyptus and acacia as an inexpensive source of
fiber. The potential worldwide supply of cornstover is
approximately over 750 million tons per year, and the United States
alone can provide approximately 150 million tons annually.
[0058] The present invention emphasizes the need of the paper
industry to move to mini mill processes and to use agricultural
residues, such as corn stalks, and the like as fiber sources. The
process is a combination of compression impregnation and chemical
processes to produce high quality pulps.
[0059] The term agricultural residue is used to identify the
material remaining at the farm after separating the main crop from
the plant. For example, cornstalk is an agricultural residue, as it
remains in the field after harvesting the main product corn. The
residual cornstalk has very little or no commercial value at
present. Of course, other agricultural residues may also be
utilized and have been contemplated.
[0060] The present invention provides a cost effective and
environmentally benign process. For example, one stage of
compression impregnation and pulping and three to seven subsequent
stages of bleaching convert the selected part of cornstalk into
high quality, bright papermaking pulps of excellent strength,
cleanliness, and drainage rate. The process utilizes a portion of
the cornstalk plant below about the ears, for example,
approximately the bottom 2 to 3 ft of cornstalk plant (without
leaves and husk). These portions contain up to approximately 15%
pith without using any type of mechanical or chemical de-pithing,
thereby producing pulps having strength properties that are similar
and/or superior to the properties of hardwood pulps in lab-scale
trial. Additionally, a total pulp yield of about 46-50% may be
achieved on selected cornstalk portions, which is equal to or
better than the total yield value of hardwood pulps. The hardwood
pulp process utilizes harsher pulping conditions and more costly
pulping and bleaching processes. The processing of the present
invention establishes a high yield using low chemical charges,
temperature, and pressure.
[0061] Cornstalk Process Stages
[0062] The process of the present invention includes a unique
harvesting process that separates portions of the cornstalk plant,
that is portions from the ground up to about the ears of the plant.
For example, the portion separated may be approximately the bottom
2 to 3 ft of cornstalk plant. Of course, this depends on the
characteristics of the plant. The separated cornstalk portions are
compacted into a bale. For example, they are compacted into a
square or rectangular bales and stored at the farm until a
predetermined time, when it is then transported to the mill.
[0063] The use of whole cornstalks including leaves and husk in
pulping gives low yield and consumes more chemicals without any
real benefit.
[0064] A compression impregnation step that is common in
chemi-thermo-mechanical pulp, but never used in chemical pulping
has been used for different purposes.
[0065] The alkaline pulping step used in the present invention in
pulping is milder than that used in hard wood pulping process. The
pulping step uses both batch and continuous processes. For example,
a Pandia type continuous digester is suitable for alkaline pulping
of cornstalk. Pulp from the digester contains low lignin, for
example, kappa 8 to 10. Additionally, the pulp can be bleached to a
high brightness by using fewer steps than hardwood pulp process and
obtaining a similar yield.
[0066] The processes of the present invention may be done in the
following order; however, variations from the order have also been
contemplated.
[0067] Cornstalk Harvesting, Storage, and Transportation
[0068] In this process, the harvester removes a portion of the
cornstalk plant. For example, the harvester cuts the cornstalk just
below the ears. The first cut may be used for soil conditioning,
animal bedding and other traditional farm uses. The second cut
removes a portion of the cornstalk plant below about the ears of
the cornstalk plant. This portion has moisture content of about 10
to 20% and is compacted into a bale. Typically, it is compacted
into a rectangular bale or square bale, which is then transported
to a storage facility. The bale is stored in a dry atmosphere in
order to avoid fungi and the like.
[0069] Each farmer in approximately 50 mile radius relative to the
pulp mill stores the compact bales on the farm until a
predetermined time for delivering the materials to the mill. This
allows the mill to keep an inventory of compact bales for a reduced
time, for example, about 2 weeks. Of course the time of storage of
the bales may be longer or shorter. This type of management will
reduce storage requirements at the mill site. The mill may pay the
farmers for storage time or some other form of contractual
relationship may be established with the farmers.
[0070] Processing of Raw Materials
[0071] The next step in the process is to arrange the raw materials
into a digester. In this process the compacted bales of cornstalk
portions will be loosened and chopped to approximately 25 to 40 mm
size. The chopped material is arranged, for example dumped, onto a
lower part of an inclined conveyer belt. The conveyer belt may be
fitted in a steel housing filled with hot water under constant
circulation. The conveyer will transport the cornstalk within the
liquid from one end of the conveyer to the other end of the
conveyer. This is the process of wetting the cornstalk. In this
process dirt and/or other foreign materials attached to cornstalk
portions are loosened and separated via hot water soluble materials
into the water media. The upper end of the conveyer may be slightly
inclined and another conveyer may be fitted in a steel housing and
having an incline of about 30 degrees. The conveyor belt leads to a
hopper. However, the configuration of the belt may be in any
suitable configuration leading to the hopper. For example, the
incline may be less than or greater than 30 degrees. In-situ
cleaning process is performed on the cornstalk as it is transported
along the conveyor belt. For example, continuous hot water is
sprayed onto the material being transported along the conveyor belt
to clean off the residual dirt and any other foreign material. At
the opposite end of the conveyor belt the cleaned material, which
may be saturated with hot water, is arranged into the hopper. The
material may be fed into the hopper with a plug screw feeder or any
other suitable technique.
[0072] Pulping Process
[0073] The plug screw feeder compresses the cornstalk coming from
the feeder and removes the excess water and hot water soluble
extracts. At the end of the screw feeder, the compressed cornstalk
comes in contact with cooking liquor, thereby providing better
penetration of cooking liquor as it enters into the digester. In
this zone the cooking liquor flow is controlled in order to have
liquor to cornstalk ratio of about 3:1 to 7:1.
[0074] In case of pretreatment with cellulose protecting agents, an
additional step before the addition of cooking liquor should be
added to the pulping process.
[0075] A variety of different digesters may be used, for example, a
Pandia digester and the like. The Pandia digester is a horizontal
continuous digester that is well suited for the production of pulp
from all different non-wood fiber raw materials and provides
excellent results for high yield processing.
[0076] When using a continuous Pandia digester it may contain two
to three horizontal tubes. The temperature may be raised to about
120 to 170.degree. C. at the end of first tube and about 120 to
170.degree. C. in the second tube for continuing the cooking, and
in the third tube to about 100 to 110.degree. C. for cooling down,
before letting it blow to the blow tank. The ramp time in the first
horizontal tube may vary from about 20 to 40 minutes, the cooking
time at the second tube may vary from about 20 to 90 minutes, and
cooling time in the third horizontal tube may vary from about 10 to
15 minutes. Optionally, the blow tank may include an agitator
fitted to defibrate the cooked fiber in a hot spent liquor
media.
[0077] In a batch process, a plug screw feeder compacts the bulky
cornstalk to allow for a maximum load. The load fills a rotating
and/or stationary digester with a liquor to solid content of about
3:1 to 7:1. The cooking temperature varies from about 120 to
170.degree. C. for a period between about 30 to 120 minutes. The
ramp time for raising the temperature from feed temperature to
cooking temperature varies from about 15 to 60 minutes. After the
cooking, the temperature of the digester is lowered to about 100 to
110.degree. C. and the pulp is released to a blow tank. In the blow
tank, an agitator is fitted to defibrate the cooked fiber in hot
spent liquor media.
[0078] The cooking liquor includes about 2 to 20% active alkali.
About 12 to 15% active alkali (on oven dry cornstalk basis) cooking
solution may be used to obtain a bleachable grade cornstalk pulp of
yield range of about 45 to 50%. To obtain liner pulp at the yield
range of about 60 to 70%, the active alkalinity may be in the range
of about 6 to 10%, and to obtain corrugating medium at the yield
range of about 80 to 95%, the active alkalinity may be in the range
of about 2 to 4%. The cooking liquor may contain any combination of
catalytic anthraquinone, and/or other similar reagents.
[0079] Fiber Processing Step
[0080] For chemical pulps the agitator that may be fitted at the
bottom accomplishes defibration in the presence of hot liquor.
Defibrating separates the fiber for thorough pulp washing and the
fibers might need to be further refined for papermaking. The
chemical pulps especially for high yield chemical pulp, that is
yields of about 60 to 70%, are refined after the cooking process to
liberate the individual fibers. For ultra-high yield pulp of about
80 to 95% obtained for corrugating medium, the pulps are refined to
separate the individual fibers.
[0081] Screening, Washing and Cleaning Stage
[0082] After disintegration in a blow tank, pulps will be sent
through a coarse screen to remove uncooked and/or semi-cooked
and/or fiber lumps before sending the pulp to washing stage. Black
liquor will be separated at screening and washing stages and sent
to a chemical recovery boiler for recycling. The chemical pulps
require thorough washing in order to recover processing chemicals
and to clean the pulp. The brown stock can be washed by the
existing commercial washer. Screening and cleaning of cornstalk
pulp are preferably done before bleaching. This will save bleaching
chemicals and improve the bleachability of the pulp.
[0083] Bleaching
[0084] A moderate application of bleaching solution, for example,
chlorine dioxide, alkaline hydrogen peroxide, and alkaline
extraction solutions may be used to remove the residual lignin and
to increase the pulp brightness to a predetermined level. Bleaching
conditions such as temperature, time, and bleaching liquor
concentration, typically depends on lignin content of the pulp and
on the optimum conditions for particular bleaching agents.
[0085] For example, temperatures ranging from about 60 to about
90.degree. C. are used when using chlorine dioxide or alkaline
peroxide as a bleaching agent in a closed system. Typically, the
bleaching processes last about 30 to 120 minutes, which includes
the time required to adjust the pulp temperature to the desired
temperature level. The bleaching temperature is maintained for
about 30 to 120 minutes. A three step bleaching sequence
(hereinafter "DED") can raise the cornstalk pulps' brightness to
about 80 to 85% ISO level and addition of one of more bleaching
stages such as peroxide, ozone, or oxygen bleaching stage can raise
the brightness to about 86 to 95% ISO.
[0086] Papermaking
[0087] The bleached pulp is a mixture of long fiber mainly derived
from cornstalk skin and short fiber derived mainly from pith.
Refining of this mixture before papermaking will create more fines
resulting in a water drainage problem because the fines hold more
water than the fiber.
[0088] Short fiber does not need refining, whereas the long fibers
might or might not need refining in order to develop bonding
properties. The bleached fiber should be fractionated into long and
short fiber fractions. The long fiber fraction will be refined and
then mixed with the short fiber fraction before papermaking.
[0089] In an alternative way, when the bleached cornstalk pulp is
mixed with bleached softwood kraft and/or bleached hardwood kraft
pulp for papermaking, the fractionation is not necessary. Since the
cornstalk pulp is softer, slender and require less energy to
refine, mechanical action during mixing with softwood kraft pulp
and/or hardwood kraft pulp lead to refining in some extent and
develop fiber-fiber bonding properties. Depending on the end
products, cornstalk pulp (bleached or unbleached) can be mixed with
softwood kraft pulp (bleached or unbleached with or without
refining) to various extent.
[0090] The bleached pulp is used to prepare paper, for example,
printing and writing paper, photocopy paper, top white linerboard,
tissue paper, base paper, wood free papers, coated paper,
multiplayer paper/paper board, specialty papers, and the like. CTMP
and BCTMP of cornstalk can be used to prepare newsprint by blending
with softwood kraft pulp (5 to 20%). Bleached cornstalk CTMP can be
blended with cornstalk bleached chemical pulp for preparing writing
& printing grade paper. The high yield semi-chemical cornstalk
paper can be blended with high yield softwood kraft pulp to produce
sack paper, wrapping paper, packaging board, carton board etc.
Dissolving pulp and useful by-products derived from hemicellulose
can be produced from cornstalk.
[0091] Printing and writing paper, photocopy paper, and top white
linerboard may contain approximately 5 to 20% bleached softwood
Kraft pulp, having approximately 5 to 60% filler content. The
filler may include any combination of calcium carbonate, clay,
talc, kaolin, titanium dioxide, and the like. In addition to
filler, any combination of sizing agents, dry strength agents, wet
strength resins, and retention aids may be applied during the paper
making. The sizing agents may include any combination of rosin
emulsion, alkenyl succinic anhydride (ASA), alkyl ketene dimmer
(AKD), and the like. The dry strength agents may include any
combination of starch, gums, soluble cellulose derivatives, and the
like. The wet strength resins may include any combination of
polyvinyl alcohol, latex, and the like. The retention aid may
include any combination of polyacrylamide, polyethylene amine, and
the like.
EXAMPLES
[0092] The examples presented below illustrate cornstalk pulp and
paper quality compared to hardwood pulp. Certain aspects of the
examples are described in terms of techniques and procedures found
by the inventors to work well in the practice of invention. The
examples are created through the use of standard laboratory
practices of inventors. The examples presented are not meant to be
limiting, and numerous changes, modifications or alterations may be
applied without departing from the scope of the invention.
Example 1
[0093] The cornstalk portions were separated manually from the
leaves and other unwanted materials. The cornstalk stems were then
broken into small pieces mechanically. The mechanical separation
was accomplished with two oppositely rotating devil teeth plates.
The system separates the skin, however, a substantial quantity of
pith remains with the skin. It is noted that any other suitable
mechanical separating tool may be utilized.
[0094] Pulping experiments were conducted using the pith and skin
as received from the process. The quantity of pith was about 23% of
total cornstalk except leaves, cones and ears. In a few laboratory
scale experiments, the cornstalk skin was separated completely, and
in some cases 15% pith was added to the skin to verify the effects
of pith on handsheet properties. In the experiments, the cornstalk
pieces were cleaned in a pulper by using hot water and dried in air
to obtain the desired cornstalk consistency. The consistency of the
cleaned cornstalk is beneficial in order to adjust the quantity of
cooking chemicals, liquor to cornstalk ratio, and to know the pulp
yield.
[0095] In this series of experiment, a ramp time of approximately
60 minutes was applied, the cooking time was approximately 60
minutes, and cooking temperature was about 150.degree. C. The
cooking was done using a soda process. The quantity of sodium
hydroxide expressed as active alkali was varied from about 12 to
15% to get acceptable pulps. Tables 1, 2, and 3 show the quantity
of active alkali in cooking liquor, screened pulp yield, pulp
freeness (CSF), and mechanical and optical properties of
handsheets.
1TABLE 1 Handsheet properties of screened pulp from cornstalk
without pith refined with PFI mill. Active Yield Tensile Tear Index
Burst index alkali Screen PFI CSF Density index (mN .multidot. (kPa
.multidot. Brightness Opacity Exp.. No. (%) (%) revolution (ml)
(kg/m.sup.3) (N-m/g) m.sup.2/g) m.sup.2/g) (%) (%) CT-3 B1 13 45
2000 360 817 96 5.9 6.5 38 85 CT-3 B2 14 46 1500 436 807 94 6.8 6.2
40 86 CT-3 B3 15 45 1500 370 830 96 6.2 6.5 40 86
[0096]
2TABLE 2 Handsheet properties of screened pulp from cornstalk
containing approximately 15% pith refined with PFI mill Active
Yield Tensile Tear index Burst index Scattering alkali Screen PFI
CSF Density Index (mN .multidot. (kPa .multidot. Brightness Opacity
Coeff. Expt. No. (%) (%) revolution (ml) (kg/m.sup.3) (N-m/g)
m.sup.2/g) m.sup.2/g) (%) (%) (m.sup.2/kg) CT-4 B1 13 44 1300 360
847 90 6.5 5.9 39 83 15.6 CT-4 B2 14 45 1300 360 865 91 5.8 6.1 39
84 16.4 CT-4 B3 15 44 1300 370 845 91 5.9 6.0 38 83 15.0
[0097]
3TABLE 3 Handsheet properties of screened pulp from cornstalk
containing approximately 23% pith unbeaten. Active Yield Tensile
Tear index Burst index Scattering alkali Screen PFI CSF Density
Index (mN .multidot. (kPa .multidot. Brightness Opacity Coeff.
Expt. No. (%) (%) revolution (ml) (kg/m.sup.3) (N-m/g) m.sup.2/g)
m.sup.2/g) (%) (%) (m.sup.2/kg) CT-2 B1 13 44 443 757 90 5.3 5.6 39
89 19.6 CT-2 B2 14 44 440 788 94 6.6 5.9 39 89 19.6 CT-2 B3 15 45
467 786 93 6.0 5.8 40 89 19.8
[0098] The properties of pulps from cornstalk containing
approximately 15% pith are of a slightly lower quality than pulp
properties obtained from cornstalk without pith. The handsheet
properties are close to that of hardwood pulp. These results
demonstrate that cornstalk containing certain amount of pith is
suitable to produce quality pulp. One can easily avoid the huge
task and cost associated with the mechanical separation of pith
from the skin.) The existing process that could be used to separate
skin from pith is hammer milling. This process generates lots of
fines and dust, which will create environmental pollution,
deteriorate the fiber quality and increase the loss of quality
fiber. The development of new machine that will effectively
separate the skin in an environmentally begnin way and without
cutting and losing of good fiber will be very expensive. This
separation of cornstalk skin from pith is not necessary at all, as
demonstrated in lab-scale experiments as shown in Table 1, 2 and 3.
The kappa number of the pulps measured using Tappi Standard methods
are between about 8 to 12, which is very low compared to kraft
softwood pulp (kappa number of about 27 to 30) and to hardwood pulp
(kappa number of about 18 to 22) with a similar pulp yield.
Accordingly, cornstalk pulp requires less bleaching chemicals than
half of those required for softwood and hardwood pulp.
Example 2
[0099] The raw cornstalk material, from the bottom portion of the
plant, comprises mostly skin and includes knots and pith. That
includes, the lower portion of the cornstalk plant below about the
ears of the plant, for example, about the bottom 2 to 3 ft of
cornstalk. This consists of thick skin and relatively low pith. The
leaves present in the lower part of cornstalk may be easily removed
after chopping. The removal or separation of the leaves may be done
by blowing air due to the difference in density of chopped
cornstalk and leaves. The fiber quality is not significantly
affected due to the presence of a small quantity of pith in the
lower part of the cornstalk as shown in example 1.
[0100] In this experiment, 1.27 kg (oven dry basis) of selected
cornstalk, as described above, was cooked using about 14% active
alkali. This was done with a liquor to cornstalk ratio of about
7:1, a cooking temperature of about 150.degree. C., a cooking time
of about 60 min, and ramp time of about 60 min in order to raise
the temperature from about 80 to 150.degree. C. The screened pulp
yield was about 46%. The pulp was screened on a slot type screen of
0.008 inches and dewatered on a 200 mesh screen to remove the fines
from the pulp. The pulp from this cook is shown as (CT-D1) and was
subjected to bleachability tests. Two of the bleached pulp samples
were processed to prepare handsheet in order to determine the
mechanical and optical properties.
[0101] Six samples, of about 10 g each represented in the Table 4
below as CT-d-1-1, CT-d-1-2, CT-d-1-3, CT-d-1-4, CT-d-1-5,
CT-d-1-6. These samples were bleached using a variety of chlorine
dioxide concentrations in the (D1) stage, followed by similar
concentrations of sodium hydroxide in an extraction stage (E), and
similar concentrations of chlorine dioxide in the (D2) stage.
Additionally, three of the six samples were further bleached using
a hydrogen peroxide (P) stage of similar chemical composition in
all three cases. The bleaching conditions, chemical concentrations,
and chemicals used in the different bleaching stages and the final
brightness are presented in Table 4.
4TABLE 4 Bleaching conditions and resultant final brightness Sample
No. CT-d-1-1 CT-d-1-2 CT-d-1-3 CT-d-1-4 CT-d-1-5 CT-d-1-6 D.sub.1
Stage Kappa factor 0.20 0.25 0.30 0.35 0.35 0.30 Chlorine
equivalent 1.6 2.0 2.4 2.8 2.8 2.4 Temperature (.degree. C.) 90 90
90 90 90 90 Time (min) 90 90 90 90 90 90 E.sub.1 Stage NaOH (%) 2 2
2 2 2 2 Temperature (.degree. C.) 90 90 90 90 90 90 Time (min) 90
90 90 90 90 90 D.sub.2 Stage Kappa factor 0.25 0.25 0.25 0.25 0.25
0.25 Chlorine equivalent 2.0 2.0 2.0 2.0 2.0 2.0 Temperature
(.degree. C.) 90 90 90 90 90 90 Time (min) 90 90 90 90 90 90 P
stage H.sub.2O.sub.2 (%) 2 -- 2 2 -- -- NaOH (%) 1.5 -- 1.5 1.5 --
-- Na.sub.2SiO.sub.3 (%) 1.5 -- 1.5 1.5 -- -- MgSO.sub.4 (%) 0.05
-- 0.05 0.05 -- -- Final Brightness (%) 87.5 84 88 87 85 84
[0102] The results demonstrate that cornstalk pulp can obtain a
high brightness level while using low amounts of chemicals. The
results are due to lower lignin content of the pulp correspond to
one third of softwood and hardwood chemical pulps. The cornstalk
needs less cooking chemicals, lower cooking temperatures and less
cooking time compared to the wood. The cornstalk processing cost
will be similar to that wood when using a selected portion of the
lower part of cornstalk. Additionally, the cost of storage and
transportation will be minimized by low cost of cornstalk, and
ultimately the cost of cornstalk at the mill gate will be much
lower than that of wood.
[0103] Below is described about bleaching of cornstalk pulp on
mechanical and optical properties of handsheets.
5TABLE 5 Properties of bleached cornstalk pulp Tensile Tear index
Burst index Scatt. CSF Density Index (mN .multidot. (kPa .multidot.
Brightness Opacity Coeff. Sample (ml) (kg/m.sup.3) (N-m/g)
m.sup.2/g) m.sup.2/g) (%) (%) (m.sup.2/kg) CT-d1 (DED) 320 866 104
7.4 7.2 82.4 61 18.4 CT-d1 335 875 91 5.8 5.9 87.2 61 18.4
(DEDP)
[0104] The Canadian Standard freeness (CSF) of bleached cornstalk
pulps were in the range of about 540 ml. These CSF values came down
to about 330 ml by refining in PFI mill with only 1000 revolutions,
which is less than one-tenth of those required for bleached
eucalyptus (hardwood) chemical pulps. This indicates that cornstalk
pulp has great advantage in terms of reduced refining energy
consumption.
[0105] The addition of one peroxide step increased the brightness
of the pulp from about 82.4 to 87.2%, but the strength properties
of handsheets decrease significantly. As a result, it will be
necessary to evaluate the brightness requirement of final product
in order to select the bleaching sequence and number of stages. For
example, writing and printing papers contain about 15 to 25%
calcium carbonate as a filler to improve paper surface smoothness,
printing opacity, and brightness. Wet web strength and dry strength
of paper can be easily manipulated by using wet end chemistry.
Example 3
[0106] In pilot-scale cooking, about 21.56 kg chopped cornstalks
(oven dry basis) were packed in a rotating digester. A vacuum was
created in the digester allowing for better impregnation of the
liquor (cooking solution) into the cornstalk. The digester was
rotated for about 30 minutes, allowing the temperature to rise from
ambient to about 80.degree. C. for good impregnation. The ramp time
was about 30 minutes to allow the temperature to rise from about 80
to 150.degree. C. and cooking time was about 60 minutes at
approximately 150.degree. C. The cooking liquor includes about 14%
active alkali. At the end of the cooking period the pipeline
between the digester and blow tank was connected and the pressure
was slowly released to reduce the pressure corresponding to a
temperature of about 100 to 105.degree. C. At this point the valve
was opened completely to blow all of the pulp from the digester to
the blow tank via the pressure differential. The blow tank includes
a screen at the bottom to facilitate washing the pulp with hot
water after the transfer of the pulp to the blow tank. The pulp was
washed with hot water and then transferred to a large screen having
0.008 inches wide slots. The screen reject was less than about
0.07%. The pulp was then dewatered under pressure to about 30%
solid content. The dewatered pulp was then shredded and kept in a
cold room for future use. The screened pulp yield was around 46.5%,
which was similar to lab scale studies. Three samples, each of
about 30 g on oven dry basis, were refined at 400, 700, and 1000
revolutions in a PFI mill. Handsheets were prepared and tested
according to TAPPI standard methods. Table 6 shows the results from
the three samples refined at 400, 700, and 1000 revolutions in PFI
mill, respectively.
6TABLE 6 Physical, mechanical and optical properties of screened
unbleached pulp from pilot scale pulping. Tensile Tear index Burst
index Scatt. CSF Density Elongation Index (mN .multidot. (kPa
.multidot. Brightness Opacity Coeff. Sample (ml) (kg/m.sup.3) (%)
(N-m/g) m.sup.2/g) m.sup.2/g) (%) (%) (kg/m.sup.2) BD-2 (400) 380
674 3.00 83 4.2 5.7 27 95 BD-2 (700) 360 733 3.02 82 4.5 5.4 30 93
BD-2 (1000) 350 728 3.10 81 4.5 5.5 27 94
[0107] The handsheet demonstrates very good mechanical properties
with tensile index: 82 N-m/g, tear index 4.5 mN.m.sup.2/g, and
burst index 5.5 kPa.m.sup.2/g. It is important to note that during
lab-scale pulping, cornstalks were washed well with hot water and
pith contents were adjusted manually. However, during the pilot
scale trial we could not wash and adjust the pith content due to
large amount of materials involved. As a result, cornstalk used in
pilot scale cooking might contain higher percentage of dirt and
pith compared to cornstalk used in lab-scale cooking. This is one
of the reasons of getting slightly inferior pulp and low initial
brightness compared to lab-scale pulp. These problems can be solved
if pulp is produced at the pulp mill and incorporated with a full
set of washing, screening and cleaning systems.
Example 4
[0108] In this example, properties of bleached cornstalk pulp were
compared to equivalently bleached kraft hardwood pulps. Moreover,
two sets of copy paper with grammage of about 75 g/m.sup.2 were
prepared using filler, for example, precipitated calcium carbonate,
starch, sizing agent, retention aids, etc, to see the properties.
It is observed from the table that cornstalk pulp gives
significantly higher tensile and burst index values than eucalyptus
and aspen pulps. However, the tear values of eucalyptus are
significantly higher than that of cornstalk pulp. The results are
shown in Table 7.
7TABLE 7 Mechanical and optical properties of bleached cornstalk
pulp and bleached kraft eucalyptus pulp, and bleached kraft aspen
pulps. Tensile Tear index Burst index Scatt. CSF Density Elongation
index (mN .multidot. (kPa .multidot. Brightness Opacity Coeff.
Sample (ml) (kg/m.sup.3) (%) (N-m/g) m.sup.2/g) m.sup.2/g) (%) (%)
(kg/m.sup.2) BD-2 (DED) 350 680 3.2 81 4.5 5.7 82 61 BD-2 (DEDP)
355 820 2.58 82 4.36 4.93 82.9 65.2 21.1 BD-2(DEDP) 300 850 2.95
91.2 4.54 4.99 82.5 60.9 18.3 BD-2(DEDP), -- 719 4.92 76.1 5.35
5.52 82.6 81.2 34.5 Filler: 6.6% BD-2(DEDP) -- 640 3.24 62.6 5.66
4.08 85 86.8 48.1 Filler: 15.1% Eucalyptus 420 685 3.21 55.3 6.7
3.53 88 74 35.6 (bleached) Aspen 600 -- -- 35 4.4 1.93 82.5 78
(bleached) Note-1: BD-2 (DEDP); Filler 6.6%: Handsheets of grammage
75 g/m.sup.2, like copy paper, were prepared by using 86.6%
cornstalk, 6.6% bleached softwood kraft pulp and 6.6% precipitated
calcium carbonate as filler. 20 kg/ton (o.d. basis) of cationic
potato starch, 2 kg/ton of AKD sizing agents and cationic and
anionic retention aid were used during handsheet making. Note-2:
BD-2 (DEDP); Filler 15.1%: Handsheets of grammage 75 g/m.sup.2,
like copy paper, were prepared by using 77.4% cornstalk, 7.5%
bleached softwood kraft pulp and 15.1% precipitated calcium
carbonate as filler. 20 kg/ton (o.d. basis) of cationic potato
starch, 2 kg/ton of AKD sizing agents and cationic and anionic
retention aid were used during handsheet making.
[0109] These two experiments show that paper made from cornstalk
pulp can be improved significantly by judicial use of wet end
chemistry during papermaking. The opacity of handsheet, an
important requirement for printing and writing grade paper, was
improved largely due to filler (precipitated calcium carbonate)
integration in fiber matrix.
Example 5
[0110] In this example, physical, optical and mechanical properties
of papers prepared in pilot scale paper machine from bleached
cornstalk pulp and bleached mixed hardwood kraft pulp has been
illustrated for comparison. Pulping of cornstalk was carried out in
pilot scale digester and was subjected to washing, screening,
dewatering and bleaching. The brightness of corn stalk pulp ranged
from 88 to 90% as illustrated in example 2.
[0111] The furnish for the preparation of cornstalk paper is as
follows: Bleached cornstalk chemical pulp: 60%, Bleached northern
softwood kraft pulp (commercial grade): 20%, filler (precipitated
calcium carbonate): 20%; starch: 0.5% (based on o.d. fiber basis);
Hercon size 79 AKD (0.5%): 0.2% (o.d fiber basis) and Nalco 7520
Retention aid (0.1%): 0.05% (o.d. fiber basis). Bleached cornstalk
pulp (never dried) is blended with softwood kraft pulp in a
hydrapulper. No refining was required, as just agitation of
hydrapulper dropped the freeness to about 400 ml. Filler and starch
are added to the machine chest. The sizing agent and retention aid
are metered into the machine chest.
[0112] The furnish for the preparation of hardwood paper is as
follows: bleached mixed hardwood pulp (commercial grade): 60%,
bleached northern softwood kraft pulp (commercial grade): 20%;
filler (precipitated calcium carbonate): 20%; starch: 0.5%; Hercon
size 79AKD (0.5%): 0.2%, and Nalco 7520 retention aid (0.1%):
0.05%.
[0113] Hardwood and softwood kraft pulp laps are mixed in a
hydrapulper and refined at 3.71% consistency to 470 ml CSF level.
Filler and starch are added to machine chest. The Sizing agent and
retention aid are metered into the machine chest.
[0114] The results are presented in Tables 8, 9, 10, and 11.
8TABLE 8 Test results of paper made in pilot paper machine.
Printing Scattering Absorption Gurley Sample Grammage Density
Brightness Opacity coefficient coefficient porosity ID (g/m.sup.2)
(kg/m.sup.3) (%) (%) (kg/m.sup.2) (kg/m.sup.2) (sec/100 ml) wood
80.4 698 87.4 89.8 67.6 0.17 7.1 pulp cornstalk 76.9 784 88.7 87.2
59.5 0.14 171 pulp
[0115] Table 8 shows that the density of cornstalk pulp was higher
than those of wood pulp. Brightness of cornstalk pulp is nearly 1
point higher than wood pulp, but the printing opacity is more than
2 points lower. Both scattering coefficient and absorption
coefficient for wood pulp were slightly higher than cornstalk pulp.
Scattering coefficient is inversely related to paper bonding
property. Porosity for cornstalk pulp is 171 sec/100 ml compared to
7.1 sec/100 ml for wood pulp. That means wood pulp result in much
more porous structure than cornstalk pulp.
9TABLE 9 Test results of paper made in pilot paper machine
Scattering Absorption Sample Brightness Opacity coefficient
coefficient CIE ID (%) (%) (kg/m.sup.2) (kg/m.sup.2) L A b L* a* b*
Whiteness CIE Tint wood 87.35 91.14 64.16 0.17 95.21 0.11 2.96
96.26 0.05 3.00 77.27 -1.96 pulp cornstalk 88.63 88.95 58.01 0.15
95.29 0.25 2.09 96.33 0.19 2.14 81.35 -1.66 pulp
[0116] Table-9 shows that CIE Whiteness of cornstalk pulp was about
4 points higher than wood pulp and CIE Tint was lower than wood
pulp. Brightness, opacity, scattering coefficient, absorption
coefficient of cornstalk pulp and wood pulp were similar. LL* that
represents lightness increasing from zero for black to 100 for
perfect white, is similar for both cornstalk pulp and wood pulp;
a,a* that represents redness when plus, is higher for cornstalk
pulp than wood pulp; b,b* that represents yellowness when plus, is
higher for wood pulp than cornstalk pulp.
10TABLE 10 Test results of paper made in pilot paper machine
Tensile Tensile Tearing Tearing Filler strength index Stretch TEA
strength Index Context Sample ID (kN/m) (kN-m/g) (%) (J/m.sup.2)
(mN) (mN-m.sup.2) (%) wood MD 2.15 0.0267 0.74 9.53 308 3.8 17%
pulp CD 0.87 0.0120 1.73 11.56 379 4.7 Cornstalk MD 3.25 0.0423
1.10 21.84 451 5.9 22% pulp CD 1.94 0.0255 2.65 37.02 494 6.4
[0117] Table-10 shows the comparison of strength properties of wood
pulp and cornstalk pulp both in machine-direction (MD) and
cross-direction (CD). All of the strength properties of cornstalk
pulp are 40% to 300% higher than that of wood pulp. Tensile
strength properties of cornstalk pulp in machine direction was
about 50% higher, and in cross-direction is 122% higher than those
of wood pulp. Stretch value of cornstalk pulp in MD and CD
directions were respectively 50% and 100% higher than those of
hardwood pulp. TEA (tensile energy absorption) value of cornstalk
pulp in MD direction is 130% and in CD direction is 200% higher
than those of hardwood pulp. Similarly tear index of cornstalk pulp
in MD direction is 55% higher and CD direction is 36% higher than
those of hardwood pulp. Filler, in general, are responsible for
weak bonding properties of paper. Although cornstalk pulp retained
22% filler compared to 17% filler in wood pulp, cornstalk pulp was
much stronger than wood pulp. Pilot paper machine trial has further
demonstrated that cornstalk pulp can hold the filler in the fiber
matrix more efficiently than does wood pulp.
11TABLE 11 Test results of paper made in Pilot paper machine
Sheffield Burst Burst Taber Log 10 Smoothness Strength Index
Stiffness Number of MIT Folding Sample ID (SU) (kPa)
(kPa-m.sup.2/g) (g-cm) Double Folds Endurance wood pulp MD 1.70 23*
1.34* CD 0.71 8* 0.88* Felt 155 64.5 0.80 Wire 160 63.4 0.79
Cornstalk pulp MD 1.63 41 1.60 CD 0.91 19 1.27 Felt 157 134 1.74
Wire 143 134 1.74 Note: *a 0.5 kg weight was used in MIT Fold
instead of the 1 kg weight.
[0118] Table 11 shows the Sheffield smoothness, burst index, Taber
stiffness and number of double folds of both cornstalk and hardwood
pulp. Sheffield smoothness of cornstalk pulp and hardwood pulp were
similar in the felt direction, whereas in wire direction cornstalk
pulp was more smooth than hardwood pulp. Burst strength of
cornstalk pulp was more than 100% stronger than hardwood pulp.
Number of double folds for cornstalk pulp in MD and CD directions
are respectively 41 and 19 compared to 23* and 8* for wood pulp.
Since wood pulp is too weak to fold under 1 kg tension, 0.5 kg
tension was applied. 8* is actually equivalent to 1 number of fold
and 23* is equivalent to only 8 number of fold, if measured under 1
kg tension.
[0119] Paper machine trial has clearly demonstrated that cornstalk
paper prepared under identical condition as hardwood paper, is much
superior in terms of strength properties than that of hardwood
paper, and similar to each other in terms of optical
properties.
[0120] It is understandable that various details of the invention
might be changed without deviating from the scope of this
invention. Moreover, the above-mentioned descriptions in various
examples are for the purpose of illustration only, not for the
purpose of limitation. Various modifications can be made in the
present invention without departing from the spirit or scope of the
invention. Thus, it is intended that the present invention cover
the modifications and variations of this invention provided they
come within the scope of the appended claims and their
equivalents.
* * * * *