U.S. patent application number 11/849070 was filed with the patent office on 2008-10-30 for method of making medium density fiberboard.
Invention is credited to Masood Akhtar, Eric G. Horn, William R. Kenealy, Ross E. Swaney, Jerrold Winandy.
Application Number | 20080264588 11/849070 |
Document ID | / |
Family ID | 38951460 |
Filed Date | 2008-10-30 |
United States Patent
Application |
20080264588 |
Kind Code |
A1 |
Akhtar; Masood ; et
al. |
October 30, 2008 |
Method of Making Medium Density Fiberboard
Abstract
The present invention provides a method for producing an MDF
board from pulp from a fibrous lignocellulose material using a
treatment or pretreatment step which exposes the material to oxalic
acid or oxalic acid derivatives (particularly dialkyl ester
derivatives, particularly in the vapor phase). The treated wood is
then subjected to a sugar extraction wash and refined using any one
of the several pulping methods to produce a final pulp product.
Once this is done the pulp is used to make MDF boards having
improved water repellency properties.
Inventors: |
Akhtar; Masood; (Middleton,
WI) ; Kenealy; William R.; (Madison, WI) ;
Horn; Eric G.; (Madison, WI) ; Swaney; Ross E.;
(Madison, WI) ; Winandy; Jerrold; (Mazomanie,
WI) |
Correspondence
Address: |
QUARLES & BRADY LLP
33 E. MAIN ST, SUITE 900, P.O. BOX 2113
MADISON
WI
53701-2113
US
|
Family ID: |
38951460 |
Appl. No.: |
11/849070 |
Filed: |
August 31, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60824383 |
Sep 1, 2006 |
|
|
|
Current U.S.
Class: |
162/76 ;
162/164.1 |
Current CPC
Class: |
D21C 5/005 20130101;
D21C 1/04 20130101; D21C 3/04 20130101; Y10T 428/1303 20150115;
D21C 11/0007 20130101 |
Class at
Publication: |
162/76 ;
162/164.1 |
International
Class: |
D21C 3/04 20060101
D21C003/04; D21H 17/33 20060101 D21H017/33 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] This invention was made with United States government
support awarded by the following agency: DOE Grant # R530539 and
DOA # DE-FG45-02R530539. The United States has certain rights in
this invention.
Claims
1. A method of making Medium Density Fiberboard (MDF) having
improved moisture tolerance comprising: providing a fibrous
lignocellulose material; treating the material with a compound
having the formula ##STR00005## wherein R.sub.1 and R.sub.2 are
independently a member selected from the group consisting of --OH,
halide, substituted amine, unsubstituted amine, --OR.sub.3, and
##STR00006## wherein R.sub.3 and R.sub.4 are independently a
branched or unbranched, cyclic or linear, saturated or unsaturated,
substituted or unsubstituted C.sub.1-10 alkyl, at a temperature in
the range of 90-170.degree. C. generating a treated material;
extracting hemicellulose sugars from the treated material; refining
the treated material to generate a fibrous pulp, wherein the
refining step can be performed either before or after the
extraction step; adding a suitable resin to the fibrous pulp; and
forming the fibrous pulp into medium density fiberboard.
2. The method of claim 1, wherein the fibrous lignocellulose
material is reduced to a particle size in the range of 1-100 mm in
length.
3. The method of claim 2, wherein the reduced material is treated
with less than 6 dry wt % of the compound.
4. The method of claim 2, wherein the reduced material is treated
with 0.05-5 dry wt % of the compound.
5. The method of claim 2, wherein the reduced material is treated
with 1-3 dry wt % of the compound.
6. The method of any one of claims 2-5, wherein R.sub.1 and R.sub.2
are --OH.
7. The method of any one of claims 2-5, wherein R.sub.1 and R.sub.2
are --OR.sub.3, and wherein R.sub.3 is an ethyl.
8. The method of any one of claims 2-5, wherein R.sub.1 and R.sub.2
are --OR.sub.3, and wherein R.sub.3 is a methyl.
9. The method of claim 2, wherein the reduced material is treated
at a pressure less than 90 psig.
10. The method of claim 2, wherein the reduced material is treated
for a duration less than 4 hours.
11. The method of claim 2, wherein the reduced material is treated
for a duration in the range of 5 min. to 2 hours.
12. The method of claim 2, wherein the reduced material is treated
at a temperature in the range of 130-140.degree. C.
13. The method of claim 2, wherein the suitable resin is a
phenol-formaldehyde resin, and wherein a wax is further added to
the fibrous pulp.
14. The method of claim 13, wherein the medium density fiber board
comprises 93.5 wt % fiber, 6 wt % resin, and 0.5% wax.
15. The method of claim 2, wherein the reduced material is refined
by using a processing technique selected from the group consisting
of mechanical pulping, thermo-mechanical pulping, and chemical
treatment with mechanical pulping.
16. The method of claim 2, further comprising: mechanically
refining the treated reduced material one or more times to achieve
a predetermined level of freeness of the treated reduced material;
and dewatering the refined and treated reduced-material one or more
times.
17. The method of claim 16, wherein the treated reduced material is
mechanically refined 2-6 times, and wherein a freeness value of 100
ml CSF is achieved.
18. The method of claim 1, wherein the ratio of water:fibrous
lignocellulose is in the range of 4:1 to 8:1.
19. The method of claim 2, wherein the fibrous lignocellulose
includes one or more members selected from the group consisting of
southern yellow pine, red pine, spruce, western hemlock, aspen,
loblolly pine and recovered paper.
20. The method of claim 19, wherein the particle size is in the
range of 6-14 mm in length.
21. The method of claim 2, wherein the step of treating the reduced
material includes cooking the material at a temperature in the
range of 90-170.degree. C.
22. The method of claim 2, wherein the reduced material is further
treated with one or more suitable enzymes and/or acetic acid.
23. The method of claim 1, wherein the refining step can be
performed either before or after the sugar extraction step.
24. A medium density fiber board made by any one of the methods of
claims 2-5.
25. A medium density fiber board made by claim 6.
26. A medium density fiber board made by claim 7.
27. A medium density fiber board made by claim 8.
28. A medium density fiber board made by any one of claims 9-23.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application Ser. No. 60/824,383 filed on Sep. 1, 2006
BACKGROUND OF THE INVENTION
[0003] Lignocellulosic materials are sources for the generation of
a variety of products. Some of the products retain significant
structural components of the lignocellulose such as mechanical pulp
Fibers from wood chips. Other compounds such as sugars derived from
the carbohydrate in lignocellulose are made into products by
fermentation or chemical conversion. The lignocellulose can be made
into products that represent a continuum of structured to molecular
products. The continuum of products is generated by a variety of
physical, chemical, biological and thermal processes.
[0004] Medium-density fiberboard (MDF) is an engineered wood
product formed by lignocellulosic fibers glued under heat, pressure
and a small amount of resin. In manufacturing MDF from wood, the
wood is first reduced to an intermediate stage in which the fibers
in the wood are separated from their natural environment and
transformed into a pulp like suspension. One of the components of
wood is lignocellulose. The most abundant component of
lignocellulose is the cellulose polymers. These are the most
desired polymers in the final product. The second most abundant
polymer is lignin. Lignin is useful as a material which allows
fibers to adhere in MDF.
[0005] The third major component of lignocellulose is the
hemicellulose. Hemicelluloses are polymers of sugars that are more
heterogeneous than cellulose. The hemicelluloses are comprised of
oligomeric sugars derived from arabinose, galactose, xylose and
mannose in addition to glucose. The hemicellulose and the lignin
are intermixed with the cellulose in lignocellulose and serve to
protect the cellulose from damage by organisms, enzymes or
chemicals. Removal of the hemicellulose and lignin is often a
portion of lignocellulose processing.
[0006] Pulp suitable for MDF production may be produced from
various types of lignocellulose using any one of several
techniques. The simplest of these techniques is the refiner
mechanical pulping (RMP) method in which a mechanical milling
operation grinds or abrades wood in water until a desired state of
freeness (an arbitrary measure of water drainage) is achieved
between its fibers. The RMP method is high yield, typically
converting approximately 95% of the dry weight of the wood into
pulp. The RMP method leaves most of the lignin and hemicellulose in
the pulp.
[0007] Other mechanical pulping methodologies include
thermo-mechanical pulping (TMP), chemical treatment with
thermo-mechanical pulping (CTMP), and chemi-mechanical pulping
(CMP). Alternatively there are also chemical pulping methods,
wherein a chemical/water solution is generally used to dissolve the
lignin and hemicellulose to promote the separation of the
fibers.
[0008] In thermo-mechanical processes (e.g. TMP and CTMP), high
temperatures are used to help separate the fibers during refining.
These processes generally require the refining to be carried out in
one or more steps. The first step is usually a pressurized step
with refining being performed at temperatures above 100.degree. C.
and immediately below or at the softening temperature of lignin.
During this step, the pulp is typically mechanically processed
using the TMP method. In subsequent steps, the pressure and
temperature is usually modulated to achieve the desired state of
freeness between the fibers.
[0009] Relatively high total electric energy amounts or high
quantities of input lignocellulose are required to produce pulps
using the above mentioned mechanical pulping techniques. In
particular, high energy inputs are generally required to obtain
fiber separation in woods rich in lignin as such woods typically
call for extended refining periods and higher refining temperatures
or pressures. Recent studies have also suggested that even thermal
or chemical softening treatments of such woods do not guarantee a
lower total energy consumption. This is because unprocessed fibers
which are only mildly separated by the thermal or chemical
treatments are difficult to fibrillate during the mechanical
refining process.
[0010] Fibrillation is necessary to increase the flexibility of the
fibers and bring about the fine material characteristics of quality
processed pulp. In fact, it has been suggested that a decrease in
the energy consumption from an established level in various TMP and
CTMP processes has been associated with the deterioration of
certain pulp properties, including a reduction in the long fiber
content of the pulp (See U.S. Pat. No. 5,853,534, which is
incorporated by reference here in its entirety). As a result, high
energy consumption in TMP and CTMP processes has been generally
necessary in today's pulping practices.
[0011] Along with the problems of the high energy cost of pulping.
MDF has the problem of generally having low moisture tolerance.
MDF, therefore, often swells when contacted with water and is
therefore of more limited use in outdoor settings and in
applications that encounter moisture such as furniture surfaces.
Absorption of moisture also often causes significant deterioration
in the mechanical integrity of the MDF.
[0012] In regards to reducing the energy costs of pulping,
applicants invented a method for producing pulp from fibrous
lignocellulose material using a treatment step which exposes the
material to oxalic acid, or oxalic acid and sodium bisulfite, prior
to pulping. Applicants discovered that pulping the resulting
product actually required less energy input and provided a pulp
with enhanced physical properties as compared to untreated fibrous
lignocellulose material (see, U.S. Patent Publication No.
20030041985). From this applicants determined that pretreatment
with oxalic acid or oxalic acid derivatives reduced energy
requirements in mechanical refining for making paper. This
technology is different from that which is described hereinbelow
for MDF, as the properties of fibers relevant to making paper
sheets are specific to paper products and are not related to the
properties that fibers will exhibit when formed into MDF. In
particular, the methods described below produce MDF that has,
in-part, improved water repellency, a resulting characteristic that
is not observable in the papermaking process.
[0013] Accordingly, an improved method is needed for producing pulp
which is energy efficient and is able to produce MDF having
improved water repellency properties.
SUMMARY OF THE INVENTION
[0014] Briefly, in one aspect, the present invention is a novel
method for producing an MDF board from pulp from a fibrous
lignocellulose material using a treatment or pretreatment step
which exposes the material to oxalic acid or oxalic acid
derivatives (particularly dialkyl ester derivatives, particularly
in the vapor phase). The treated wood is then subjected to a sugar
extraction wash and refined using any one of the several pulping
methods to produce a final pulp product. Once this is done the pulp
is used to make MDF boards having improved water repellency
properties.
[0015] In one embodiment, the method includes heating the fibrous
lignocellulose material (without reducing the material to a
specific particle size) at a temperature of between about
90.degree. C. and 170.degree. C., more suitably between 130.degree.
C. and 140.degree. C. in the presence of oxalic acid or oxalic acid
derivatives (optionally in the vapor phase), prior to refining the
material into a pulp. The dry weight amount of oxalic acid or
oxalic acid derivative employed may be less than about 6%, or
suitably less than about 5%, or more suitably between about 0.05%
and 5%, or most suitably between about 1% and 3%, of the dry weight
of the fibrous lignocellulose material. The treatment may be
conducted at ambient pressures or higher, and for a period of time
sufficient to allow the treated product to be later refined at
reduced energy input levels as compared to untreated materials,
typically less than about 4 hours.
[0016] Another aspect of the invention is a method of making medium
density fiberboard having improved moisture tolerance comprising
the steps or acts of providing a reduced material in water
comprising one or more fibrous lignocelluloses having particle
sizes in the range of 1-100 mm in length, treating the reduced
material with a compound having the formula
##STR00001##
wherein R.sub.1 and R.sub.2 are independently a member selected
from the group consisting of --OH, halide, substituted amine,
unsubstituted amine, --OR.sub.3, and
##STR00002##
wherein R.sub.3 and R.sub.4 are independently a branched or
unbranched, cyclic or linear, saturated or unsaturated, substituted
or unsubstituted C.sub.1-C.sub.10 alkyl, at a temperature in the
range of 90-170.degree. C. generating a treated reduced material,
extracting hemicellulose sugars from the treated reduced material
before or after refining it to a pulp, adding a suitable resin to
the fibrous pulp, and forming the fibrous pulp into medium density
fiber board. In an alternative embodiment, the compound includes
the proviso that at least one of R.sub.1 and R.sub.2 is other than
--OH.
[0017] In an exemplary embodiment of the method, the reduced
material is treated with less than 6 dry wt % of the compound.
[0018] In another exemplary embodiment of the method, the reduced
material is treated with 0.05-5 dry wt % of the compound.
[0019] In another exemplary embodiment of the method, the reduced
material is treated with 1-3 dry wt % of the compound.
[0020] In another exemplary embodiment of the method, R.sub.1 and
R.sub.2 are --OH.
[0021] In another exemplary embodiment of the method, R.sub.1 and
R.sub.2 are --OR.sub.3, and R.sub.3 is an ethyl.
[0022] In another exemplary embodiment of the method, R.sub.1 and
R.sub.2 are --OR.sub.3, and R.sub.3 is a methyl.
[0023] In another exemplary embodiment of the method, the reduced
material is treated at a pressure less than 90 psig.
[0024] In another exemplary embodiment of the method, the reduced
material is treated for a duration less than 4 hours.
[0025] In another exemplary embodiment of the method, the reduced
material is treated for a duration in the range of 5 min. to 2
hours.
[0026] In another exemplary embodiment of the method, the reduced
material is treated at a temperature in the range of
130-140.degree. C.
[0027] In another exemplary embodiment of the method, the suitable
resin is a phenol-formaldehyde resin, and a wax is further added to
the fibrous pulp.
[0028] In another exemplary embodiment of the method, the medium
density fiber board comprises 93.5 wt % fiber, 6 wt % resin, and
0.5% wax.
[0029] In another exemplary embodiment of the method, the reduced
material is provided by using a processing technique being
mechanical pulping, thermo-mechanical pulping, or chemical
treatment with mechanical pulping.
[0030] In another exemplary embodiment of the method, the method
further includes the steps or acts of mechanically refining the
treated reduced material one or more times to achieve a
predetermined level of freeness of the treated reduced material,
and, dewatering the refined and treated reduced material one or
more times. The treated reduced material may be mechanically
refined 2-6 times, whereby a freeness value of 100 ml CSF (Canadian
Standard Freeness) is achieved.
[0031] In another exemplary embodiment of the method, the ratio of
water:fibrous lignocellulose is in the range of 4:1 to 8:1.
[0032] In another exemplary embodiment of the method, the fibrous
lignocellulose includes one or more hardwoods or softwoods, such as
southern yellow pine, red pine, spruce, western hemlock, aspen,
loblolly pine and recovered paper.
[0033] In another exemplary embodiment of the method, the particle
size is in the range of 6-14 mm in length.
[0034] In another exemplary embodiment of the method, the reduced
material is further treated with one or more suitable enzymes
and/or acetic acid.
[0035] Another aspect of the invention is a medium density fiber
board made by any one of the methods set forth herein.
[0036] Before the embodiments of the invention are explained in
detail, it is to be understood that the invention is not limited in
its application to the details of construction and the arrangements
of the components set forth in the following description. The
invention is capable of other embodiments and of being practiced or
being carried out in various ways. Also, it is understood that the
phraseology and terminology used herein are for the purpose of
description and should not be regarded as limiting. The use of
"including", "having" and "comprising" and variations thereof
herein is meant to encompass the items listed thereafter and
equivalents thereof as well as additional items and equivalents
thereof.
[0037] It also is understood that any numerical value recited
herein includes all values from the lower value to the upper value.
For example, if a temperature range is stated as 100.degree. C. to
170.degree. C., it is intended that values such as 101.degree. C.
to 110.degree. C., 102.degree. C. to 105.degree. C., etc., are
expressly enumerated in this specification. These are only examples
of what is specifically intended, and all possible combinations of
numerical values between the lowest value and the highest value
enumerated are to be considered to be expressly stated in this
application.
[0038] Other objects, advantages and features of the present
invention will become apparent from the following specification and
claims.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0039] The present invention is a method for treating
lignocellulosic materials so as to produce pulp which is used to
make MDF boards. The present invention comprises a pretreatment
step which exposes the material to oxalic acid or oxalic acid
derivatives. In general, the step includes heat treating the
fibrous lignocellulosic material (e.g., wood) in combination with
oxalic acid or oxalic acid derivatives. The treated fibrous
material is then refined using any one of several pulping methods
to produce a pulp product. The treated material is subjected to a
sugar extraction process before or after refining, and the released
sugars may be recovered for other products.
[0040] The treatment method of the invention removes hemicellulose
from both hardwoods and softwoods. Since the method releases
hemicellulosic sugars it can be used in systems where hemicellulose
is present and might be available for recovery and may or may not
have to be removed to create another product from the material.
Thus hardwood, softwood chips and bark could be used as well as
pulp products and agricultural residues. The treatment of
lignocellulosic materials by this process provides a hemicellulosic
hydrolysate directly, but the saccharification of lignocellulose to
sugars can further be enhanced by enzymes or further acid
hydrolysis. The method also provides electrical energy savings in
the production of pulp. The subsequent pulp is used to produce MDF
boards having improved water repellency characteristics.
[0041] Fibrous lignocellulosic materials treated in accordance with
the present invention are defined to generally include materials
containing cellulose polymers, hemicellulose polymers and lignin.
Such materials may include, for example, hardwoods (i.e.,
broad-leafed species) and softwoods (i.e., conifers). More
specifically, these materials may include the Southern Yellow
Pines, Spruces, Western Hemlock, Aspens, and other smaller diameter
trees. The material may also originate from either round wood
(e.g., whole trees), residue (e.g., wood scraps left behind from
forest and sawmill operations), or recovered paper. Recovered paper
may include both pre-consumer recovered paper, such as trimmings
and scraps from printing, carton manufacturing, or other converting
processes which are reused to make pulp without reaching the final
consumer, or post-consumer paper, such as corrugated boxes,
newspapers, magazines, and office paper which has been
recycled.
[0042] Oxalic acid derivative or derivatives (used interchangeably)
as used herein is to be broadly construed. In the first instance
alkyl and dialkyl mono and diesters of oxalic acid are intended.
The alkyl moiety of the esters generally have from about 1 to about
10 carbon atoms, preferably about 1 to 6 and most preferably about
1 to 4 carbon atoms. The alkyl moiety may be substituted,
unsubstituted, cyclic, linear, branched or unbranched but is
predominantly hydrocarbon in character. Oxalic acid derivatives, in
one embodiment could include carboxylic acid derivatives other than
esters, e.g., amides, acid halides, and anhydrides. Preferred
oxalic acid derivative in the practice of this invention are the
methyl and ethyl diesters of oxalic acid. Generally, the oxalic
acid derivatives that can be used in the present invention, include
oxalic acid derivatives for formula (I)
##STR00003##
wherein R.sub.1 and R.sub.2 are independently hydroxyl, oxygen, a
halide, a substituted or unsubstituted amine, OR.sub.3 or a side
chain of formula (II):
##STR00004##
wherein R.sub.3 and R.sub.4 are independently a branched or
unbranched, cyclic or linear, saturated or unsaturated, substituted
or unsubstituted alkyl of from 1 to 10 carbon atoms; and wherein
R.sub.1 and R.sub.2 cannot both be hydroxyl.
[0043] In general, prior to beginning the pretreatment process, the
fibrous lignocellulose material is first reduced to a size
appropriate for pulping. Methods of reducing fibrous
lignocellulosic material to appropriate sizes for pulping are
conventional in the art. Reducing the size of the fibrous
lignocellulose material aids in having the material sufficiently
treated with the oxalic acid or oxalic acid derivative. In one
embodiment, the material to be treated is reduced to wood chips.
Generally acceptable size for wood chips include chips in a size
range of 1 mm to 100 mm in length. It is anticipated, however, that
the present method may also be effective with materials not reduced
to wood chips, such as those materials derived from recovered paper
or wood residues or logs themselves. It is also anticipated that
the present method may be effective in treating pulp itself.
[0044] The reduced fibrous lignocelluosic material is then treated
with an amount of oxalic acid or an oxalic acid derivative. The
level of oxalic acid or oxalic acid derivative used is empirically
derived for the species of wood and the end use of the fiber.
Higher concentrations may be used to recover hemicelluloses from
wood chips destined for chemical pulps or total saccharification
(enzymatic or second acid hydrolysis) than can be used for those to
be used for mechanical and thermomechanical pulps. Generally, the
amount of oxalic acid or oxalic acid derivative employed, as
expressed in dry weight percentage, may be less than about 6%, or
suitably less than about 5%, or more suitably between about 0.05%
and 5%, or even more suitably between about 1% and 3%, of the dry
weight of the fibrous lignocellulosic material.
[0045] In one embodiment, the method comprises adding oxalic acid,
dimethyloxalate or diethyloxalate oxalic acid esters in the
presence of heated wood chips, pulp or any lignocellulosic source
that has some water of hydration. Suitably the wood chips are first
heated in a digester, using direct atmospheric steam injection to
exclude air from the digester and bring the chips up to a
temperature required for reaction. The digester is then suitably
brought up to around 30 psig steam pressure (although 0 to 90 psig
steam can be used) by a combination of steam injection and jacket
pressure. This is continued until a stable temperature and pressure
are obtained. The temperature used is generally greater than
100.degree. C., typically between 130.degree. C. and 140.degree. C.
No upper limit has been established and temperatures of 170.degree.
C. have been used to extract sugars.
[0046] Oxalic acid or oxalic acid derivatives of low volatility are
suitably applied by impregnating the steamed wood chips with a
liquid solution. Volatile oxalic acid derivatives such as
dimethyloxalate or diethyloxalate may alternatively be applied by
injecting into the digester by gas pressure, suitably using carbon
dioxide or nitrogen. Generally, the pressure of the reaction
increases slightly due to the vaporization of the chemical and
diminishes within 2-3 minutes. The diethyloxalate or
dimethyloxalate oxalic acid esters rapidly vaporize allowing for
the delivery of the chemical into wood chips. The vaporized
chemical contacts water present within the wood chips and at least
one ester hydrolyzes to liberate acid which acidifies the water.
Since the water is kept to a minimum the acid concentration is high
and proportional to the amount of chemical injected. The elevated
temperature and localized acidity combine to hydrolyze the
hemicellulosic sugars present in the wood chips. Other reactions
such as esterification and transesterification are also possible
during this incubation. The delivery of the reactants via the vapor
phase provides a high concentration of acid at the water surface
layer in the chips.
[0047] The oxalate ester will generate a vapor concentration of the
chemical that is dependant on the volume of the vessel and amount
of chemical used. Increasing the concentration of the oxalate ester
in the vessel will increase the amount of carbohydrate liberated
from a given weight of wood chips. A threshold value of oxalate
ester has been observed, under a set time and temperature, in pine
and spruce where the increase in sugars liberated decreases
relative to the increase of oxalate ester used. This threshold
value has not been observed for liberation of hemicellulosic sugars
from aspen and maple. In one embodiment, a range of 0 to 100 ml of
oxalic acid or diethyl oxalate has been used for the treatment of
aspen, oak, maple, southern yellow pine, red pine and spruce in a
reactor with a total volume of 21.4 liters. In this embodiment,
increasing the wood chips (from 1.25 kg to 2.5 kg oven dry basis)
increased the amount of hemicellulosic sugars liberated from the
wood chips.
[0048] Suitably, the treated wood chips are maintained at a steady
temperature for a time period of between 5 minutes and 2 hours.
Maintaining the wood chips in the digester for a more extended time
will release more hemicellulosic sugars. Increasing the temperature
of reaction or chemical loading will also release more
hemicellulosic sugars. A temperature systematically increasing
and/or decreasing in time may also be employed.
[0049] Conventional hot water extraction may be used for
hemicellulosic sugar extraction. Suitably, the wood chips may be
heated to 170.degree. C. for 30 minutes with hot water at a water
to wood ratio of 4:1. The water may be collected for extractives
including the sugars, etc. for fermentation or other uses.
[0050] The extracted, washed wood chips arc then ready for pulping.
Many pulping methods are suitable for the present invention
including mechanical and chemical pulping methods. Mechanical
pulping methods include mechanical pulping, thermo-mechanical
pulping (TMP), chemical treatment with thermo-mechanical pulping
(CTMP), and chemi-mechanical pulping (CMP). Chemical pulping
methods include chemical pulping, sulfate (kraft) and sulfite
processes. Suitably, the wood chips are used for thermomechanical
pulp generation. Thermomechanical pulp generation with treated
chips have been shown to provide energy savings from 25 to 50%.
[0051] In one embodiment, when the treated wood chips are subjected
to mechanical pulping, dilution water is added to the treated
material and the material is run through a mechanical refiner in a
number of sequential passes. The number of passes of the treated
material/pulp mixture will depend upon the freeness desired for the
particular MDF to be made. The treated material/pulp mixture is
repeatedly fed through refiners until the desired level of freeness
is achieved. The pulp may also be dewatered as necessary between
passes. Loblolly pine, treated using the procedures described
above, requires between about 2 to 6 repeated passes to obtain a
100 ml CSF value in a single rotating 300 mm diameter disk
atmospheric refiner.
[0052] The overall energy efficiency of the process can be compared
with that of a standard process by pulping untreated material in
the same apparatus while at the same time monitoring the energy
consumption of the refining mill. Generally speaking the treated
material requires significantly less energy input through the
refiner to achieve the same level of freeness in the resulting
pulps.
[0053] The pulps made through this procedure may then be made into
MDF boards using standard techniques.
[0054] The present invention is further explained by the following
examples which should not be construed by way of limiting the scope
of the present invention.
EXAMPLES
Example 1
[0055] Properties of MDF made from wood pretreated with OA and DEO.
Red pine logs were obtained from SENA. Logs were debarked and
chipped at FPL to a nominal size of 6-14 mm. Chips were placed in
barrels and frozen to prevent the growth of contaminating
microorganisms. Their moisture content was 42%.
[0056] Processing of control chips. Untreated (control) red pine
wood chips were placed in a large rotating digester and steam was
introduced to displace air and bring the chips to temperature
(135-140.degree. C.). External temperature measurement was used as
well as an internal probe as a secondary source of temperature
measurement. The chips were cooked for 30 minutes at 135.degree. C.
Following the cook, the wood chips were subjected to a sugar
extraction procedure consisting of atmospheric hot water washing
(.about.240 liters, a water to wood ratio of 8:1) at a temperature
of 80.degree. C. for 30 minutes to collect the extractives
including the sugars, etc. for fermentation. The wood chips were
then collected and stored at 4.degree. C. until TMP processing for
MDF fiber.
[0057] Processing of Hot Water Chips. Untreated (control) red pine
wood chips were placed in a large rotating digester along with
water (at a water to wood ratio of 4:1). The temperature was raised
to 170.degree. C. and then held at that temperature for 15 minutes.
External temperature measurement was used to monitor the
temperature. Following the cook, the wood chips were subjected to a
sugar extraction procedure consisting of atmospheric hot water
washing (increasing the water volume to 240 liters, in a final
water to wood ratio of 8:1) at a temperature of 80.degree. C. for
30 minutes to collect the extractives including the sugars, etc.
for fermentation. The wood chips were then collected and stored at
4.degree. C. until TMP processing for MDF fiber
[0058] Processing of oxalic acid (OA) treated chips. Oxalic acid
dihydrate from Sigma-Aldrich was used in a quantity of 35 grams
into 7500 ml. water at (0.33% wt. solution of oxalic acid) per
2.5-kilograms oven dried wood chips. Red pine wood chips were
placed in a large rotating digester and steam introduced to
displace air and bring the chips to temperature (100.degree. C.).
The steam was stopped and a vacuum drawn on the digester and the
oxalic acid solution was admitted and allowed to impregnate the
chips. The excess solution was drained and the temperature brought
to 135.degree. C. When at temperature the chips were cooked for 10
minutes. Following the cook, the wood chips were subjected to a
sugar extraction procedure consisting of atmospheric hot water
washing (.about.240 liters, a water to wood ratio of 8:1) at a
temperature of 80.degree. C. for 30 minutes to collect the
extractives including the sugars, etc. for fermentation. The wood
chips were (hen collected and stored at 4.degree. C. until TMP
processing for MDF fiber.
[0059] Processing of diethyloxalate (DEO) treated chips.
Diethyloxalate from Sigma Aldrich was used in a quantity of 20-ml.
per 1-kilogram oven dried wood chips. Red pine wood chips were
placed in a large rotating digester and steam introduced to
displace air and bring the chips to temperature (140.degree. C.).
When at temperature the DEO was introduced by an injector pipe
attached to the top of the digester and forced into the digester
using carbon dioxide or nitrogen gas pressure. External temperature
measurement and an internal temperature measurement probe were
used. Chips were cooked for 30 minutes at 140.degree. C. Following
the cook, the wood chips were subjected to a sugar extraction
procedure consisting of atmospheric hot water washing (.about.240
liters, a water to wood ratio of 8:1) at a temperature of
80.degree. C. for 30 minutes to collect the extractives including
the sugars, etc. for fermentation. The wood chips were then
collected and stored at 4.degree. C. until TMP processing for MDF
fiber.
[0060] TMP Production. The cooked wood chips prepared as indicated
above were fiberized in a Laboratory Pressurized Refiner (TMP). The
TMP is a 12-inch single disc pressurized mechanical Sprout-Bauer,
model #12-1CP. Energy consumption was measured using an Ohio
Semitronic Model WH 30-11195 Integrating Wattmeter attached to the
power supply side of the 44.8 kW electric motor. The feed rate
through the refiner was 1 kg/min. Energy was reported in Wh/kg. The
refiner plate gap settings were approximately 0.005 inch.
[0061] MDF production. The fiberized wood as made into 19 mm thick
panels, made at 5% moisture content using a commercial
phenol-formaldehyde resin. After preparation the boards were cut
and physical properties of the boards determined using the standard
testing techniques found in the (ASTM D 1037-78, 2005) American
Society for Testing and Materials. 2005. Annual book of ASTM
Standards. Vol. 04.10 Wood. ASTM International, West Conshohocken,
Pa., which is incorporated by reference here in its entirety. The
study shows that hemicellulosic sugars can be removed and recovered
prior to MDF production and the MDF has enhanced properties
compared to the control. The results for the study arc shown in
Table 1.
TABLE-US-00001 TABLE 1 Water soak (24 hour) Carbohydrate Swell
Absorption released, % or wood Wood treatment (%) (%) chip Control
9.1 30.6 1.1 Oxalic acid 4.0 16.0 4.4 DEO 3.8 13.5 5.3 Hot water
12.0 93.9 7.6 Table 1 Red pine medium density fiberboard tests and
extent of carbohydrate removal. MDF properties from boards
containing 93.5% fiber, 6% resin and 0.5% wax.
[0062] It was not evident that the samples would have increased
water repellency as a result of the OA and DEO pretreatments and
subsequent extraction. The normal extraction procedures that are
done with hot water have not been shown to have this benefit to the
MDF production.
Example 2
[0063] Materials and Methods. Wood chips. Red pine logs were
obtained from SENA. Logs were debarked and chipped at FPL to a
nominal size of 6-14 mm. Chips were placed in barrels and frozen to
prevent the growth of contaminating microorganisms. Moisture
content was 42%. After the experimental cooking procedures, the
wood chips were collected and stored at 4.degree. C. until TMP
processing for MDF fiber.
[0064] Experimental cooks. Control red pine wood chips were
subjected to time and temperature and extraction protocols, but
without chemical cook (positive control). Following the cook, the
wood chips were subjected to the extraction procedure consisting of
atmospheric hot water washing (.about.240 liters) to collect the
extractives including the sugars, etc. for fermentation.
[0065] Oxalic acid dihydrate obtained from Sigma-Aldrich was used
in a quantity of 35 grams into 7500 ml. water at 70.degree. C.
(0.33% solution of oxalic acid) per 2.5-kilograms oven dried wood
chips. A rotating digester was used to cook the wood chips to the
desired temperature and time. External temperature measurement and
an internal temperature measurement probe were used. The chips were
cooked for 10 minutes at 135.degree. C. Following the cook, the
wood chips were subjected to the extraction procedure consisting of
atmospheric hot water washing (.about.240 liters) to collect the
extractives including the sugars, etc. for fermentation.
[0066] Diethyloxalate (DEO) obtained from Sigma Aldrich was used in
a quantity of 20-ml. per 1-kilogram oven dried wood chips. A
rotating digester was used to cook the wood chips to the desired
temperature and time. External temperature measurement and an
internal temperature measurement probe were used. Chips were cooked
for 30 minutes at 135.degree. C. Following the cook, the wood chips
were subjected to the extraction procedure consisting of
atmospheric hot water washing (.about.240 liters) to collect the
extractives including the sugars, etc. for fermentation.
[0067] Pine wood chips were subjected to hot water extraction. The
wood chips were heated to 170.degree. C. for 30 minutes with hot
water, where the water to wood ratio was 4:1. Following the cook,
the water was collected for extractives including the sugars, etc.
for fermentation.
[0068] Fiber production for the TMP process. Cooked wood chips were
fiberized in a Laboratory Pressurized Refiner (TMP). The TMP was a
12-inch single disc pressurized mechanical Sprout-Bauer, Model
#12-1CP. Energy consumption was measured using an Ohio Semitronic
Model WH 30-11195 integrating a Wattmeter attached to the power
supply side of the 44.8 kW electric motor. Feed rate through the
refiner was 1 kg/min. Energy is reported in Wh/kg. Refiner plate
gap settings were approximately 0.005 inch.
[0069] MDF production. 19 mm thick panels were made at 5% moisture
content using a commercial phenol-formaldehyde resin. After
preparation, the boards were cut and physical properties of the
boards determined using the standard testing techniques found in
ASTM D 1037-78, 2005. American Society for Testing and Materials
(2005), Annual book of ASTM Standards, Vol. 04.10, Wood, ASTM
International, West Conshohocken, Pa.
[0070] Results. After OA and DEO pretreatments, hemicellulosic
sugars can be removed and recovered prior to MDF production and the
MDF has enhanced properties compared to both the raw control and
the hot water control.
TABLE-US-00002 TABLE 2 Red pine medium density, fiberboard tests
and extent of carbohydrate removal. Bending Internal Water soak (24
hour) Carbohydrate Wood MOR MOE bond Swell Absorption released %
treatment (N/mm.sup.2) (N/mm.sup.2) (N/mm.sup.2) (%) (%) Wood chip
Control 16.8 1824.9 0.179 9.1 30.6 1.1 Oxalic acid 14.3 1457.3
0.241 4.0 16.0 4.4 DEO 14.3 1498.5 0.193 3.8 13.5 5.3 Hot water
16.2 1598.6 0.172 12.0 93.9 7.6 Note: MDF properties from boards
containing 93.5% fiber, 6% resin and 0.5% wax.
[0071] Unexpected superior results. It was not evident that the
samples would have increased water repellency as a result of the OA
and DEO pretreatments and subsequent sugar extractions. The normal
extraction procedures that are done with hot water have not been
shown to have this benefit to the MDF production. We were surprised
to see this result.
Example 3
[0072] Pilot scale data were generated at the Andritz Research and
Development Laboratory in Springfield, Ohio. The Andritz facility
is known to provide refining results similar to industrial scale
such that data obtained can be used for scaled up with confidence.
The procedures used to process both the red pine and the spruce
wood used in the refining tests at Andritz were the same procedures
as described above for materials and methods.
TABLE-US-00003 TABLE 3 Pilot-scale refining results from Andritz on
spruce. Bending Internal Water soak (24 hour) Carbohydrate Wood MOR
MOE bond Swell Absorption released % treatment (N/mm.sup.2)
(Nmm.sup.2) (N/mm.sup.2) (%) (%) Wood chip Spruce 13.5 1558 0.18
31.2 110.0 1.2 Control Spruce 14.8 1951 0.41 14.8 66.6 3.5 Oxalic
Acid Spruce DEO 19.3 1951 0.44 10.0 32.1 4.0 Note: MDF properties
from boards containing 93.5% fiber, 6% resin and 0.5% wax.
Carbohydrate is the total identified carbohydrate (mannose + xylose
+ arabinose + glucose + galactose, in decreasing order) released as
a percentage of the weight of the wood chips.
TABLE-US-00004 TABLE 4 Pilot-scale refining results from Andritz on
red pine. Bending Internal Water soak (24 hour) Carbohydrate Wood
MOR MOE bond Swell Absorption released % treatment (N/mm.sup.2)
(N/mm.sup.2) (N/mm.sup.2) (%) (%) Wood chip Red Pine 19.3 2124 0.31
19.6 72.6 1.0 Control RedPine 15.4 1579 0.32 15.2 39.2 5.5 Oxalic
Acid Note: MDF properties from boards containing 93.5% fiber, 6%
resin and 0.5% wax. Carbohydrate is the total identified
carbohydrate (mannose + xylose + arabinose + glucose + galactose,
in decreasing order) released as a percentage of the weight of the
wood chips.
[0073] For the treated red pine wood chips, the resulting MDF
strength was slightly lower than the control. However, the
unexpected water repellency was evident. For the treated spruce
wood chips, the water repellency was again unexpectedly increased
over the control, and the strength of the resulting MDF was also
surprisingly enhanced. The red pine species in Table 4 was very
similar to that shown in Table 2.
[0074] Utility of the Described Embodiments
[0075] MDF is widely used as a structural material in objects such
as buildings and furniture. In many of these uses the MDF may
become exposed to water. It is well known that exposure to water
causes deterioration of conventionally-produced MDF, resulting in
losses of mechanical integrity, dimensional stability, and asthetic
appearance. Because of this it is common to restrict the use of MDF
to applications free from moisture exposure, and/or to apply
protective paints, varnishes, or other coatings in an attempt to
ameliorate the negative effects of moisture on the material. These
applied coatings represent an additional cost and may not be fully
satisfactory for various uses.
[0076] Methods currently in use to improve the water repellency of
MDF involve the addition of water-repellent materials to the MDF.
Additional binding resin and/or specific water repellency materials
can be added to the MDF. A useful and distinguishing feature of
applicants' invention is that additional water repellent materials
need not be added to the MDF. This is because the improved water
repellency is achieved through an initial chemically-induced
modification to the lignocellulosic material itself before the MDF
is formed. The modified lignocellulosic fibers remain compatible
with the binding resin used to form the board.
[0077] While the present invention has now been described and
exemplified with some specificity, those skilled in the art will
appreciate the various modifications, including variations,
additions, and omissions that may be made in what has been
described. Accordingly, it is intended that these modifications
also be encompassed by the present invention and that the scope of
the present invention be limited solely by the broadest
interpretation that lawfully can be accorded the appended
claims.
* * * * *