U.S. patent application number 11/285452 was filed with the patent office on 2007-05-24 for panel containing bamboo.
Invention is credited to Brian Christopher Gerello, Nian-hua Ou.
Application Number | 20070116940 11/285452 |
Document ID | / |
Family ID | 38053898 |
Filed Date | 2007-05-24 |
United States Patent
Application |
20070116940 |
Kind Code |
A1 |
Ou; Nian-hua ; et
al. |
May 24, 2007 |
Panel containing bamboo
Abstract
Disclosed is a panel comprising bamboo strands and wood
strands.
Inventors: |
Ou; Nian-hua; (Dacula,
GA) ; Gerello; Brian Christopher; (Statham,
GA) |
Correspondence
Address: |
Carlos Nieves, Esq.;J. M. Huber Corporation
333 Thornall Street
Edison
NJ
08837-2220
US
|
Family ID: |
38053898 |
Appl. No.: |
11/285452 |
Filed: |
November 22, 2005 |
Current U.S.
Class: |
428/292.1 |
Current CPC
Class: |
Y10T 428/249924
20150401; B27N 1/00 20130101; B27N 3/04 20130101 |
Class at
Publication: |
428/292.1 |
International
Class: |
D04H 1/00 20060101
D04H001/00 |
Claims
1. A panel comprising bamboo strands and wood strands.
2. The panel according to claim 1, wherein the panel contains about
25% to about 75% bamboo strands, and about 75% to about 25% wood
strands.
3. The panel according to claim 1, wherein the panel includes an
upper surface layer, a lower surface layer and a core layer,
wherein the bamboo strands are located exclusively in the upper
surface layer and a surface layer.
4. The panel according to claim 1, wherein the panel includes an
upper surface layer, a lower surface layer and a core layer,
wherein the upper surface layer, and the lower surface layer
consist essentially of bamboo strands and wood strands, and the
core layer consists essentially of wood strands.
5. The panel according to claim 1, wherein the wood strands are
selected from the group comprising cedar, pine, fir, aspen, oak,
and maple.
6. The panel according to claim 1, wherein the wood strands are
pine strands.
7. The panel according to claim 1, wherein the panel is in the form
of OSB.
8. A panel comprising: (1) about 25% to about 75% bamboo strands,
(2) about 75% to about 25% pine strands, and (3) a binder
resin.
9. The panel according to claim 8, wherein the binder resin is an
isocyanate resin.
10. The panel according to claim 1, wherein the panel contains
about 25% to about 75% bamboo strands, and about 75% to about 25%
wood strands, and wherein the panel includes an upper surface
layer, a lower surface layer and a core layer, wherein the upper
surface layer, and the lower surface layer consist essentially of
bamboo strands and wood strands, and the core layer consists
essentially of wood strands.
Description
BACKGROUND OF THE INVENTION
[0001] Bamboo is a lignocellulosic material widely used throughout
Asia as a building material because of its high strength,
durability and excellent dimensional stability, as well as its
ready supply and rapid replenishment-bamboo grows very rapidly,
reaching full maturity within 2 to 6 years, while even the fastest
growing wood tree species take as long as 15 to 30 years to grow to
full maturity.
[0002] However, in addition to these advantages, bamboo also has a
number of disadvantages. Since bamboo is hollow it cannot be
processed into solid lumber board or planks; nor can it be easily
process by conventional techniques used to make wood composite
materials. Processed bamboo also has a tendency to swell
excessively in the presence of moisture, a significant drawback for
a material to be used for structural purposes.
[0003] Furthermore, although bamboo's high strength is due in part
to its high density which means that bamboo-based material can
often be very heavy.
[0004] Despite these disadvantages, because of bamboo's ready
supply and excellent performance characteristics, manufacturers
have developed techniques to make wood composite materials out of
bamboo. For example, composite bamboo structural panels may be made
by hand-cutting bamboo strands from the outer part or surface of a
bamboo culm, and then weaving (again typically by hand) the strands
into mats. These hand-cut, hand-woven bamboo mats are then stacked
together along with several other similar mats and the mats then
pressed together under high temperature.
[0005] The problem with this method of manufacture of the bamboo
boards is that it is time consuming; the steps of cutting the
bamboo strips and then weaving the bamboo strips into the form of a
mat take a significant amount of time. And not only are these
processes time consuming, but they can lead to significant defects
in the final board product. Yet another disadvantage of the
aforementioned processes is that because they are composed of large
numbers of bamboo layers, they are require very high doses of resin
per layer, which adds greatly to the price of the product during
periods of high petroleum prices. Moreover, this process does
nothing to reduce the weight of the bamboo material.
[0006] Given the foregoing there is a need in the art for
structural panels that incorporate bamboo but have fewer defects,
are relatively light in weight than 100% bamboo panels, are less
susceptible to swelling when exposed to water and consume a smaller
amount of petroleum-based products.
BRIEF SUMMARY OF THE INVENTION
[0007] The present invention relates to a panel comprising bamboo
strands and wood strands.
DETAILED DESCRIPTION OF THE INVENTION
[0008] All parts, percentages and ratios used herein are expressed
by weight unless otherwise specified. All documents cited herein
are incorporated by reference.
[0009] As used herein, "lignocellulosic material" is intended to
mean a cellular structure, having cell walls composed of cellulose
and hemicellulose fibers bonded together by lignin polymer. Wood
and bamboo are both lignocellulosic materials.
[0010] By "wood composite material" or "wood composite component"
it is meant a composite material that comprises lignocellulosic
material and one or more other additives, such as adhesives or
waxes. Non-limiting examples of wood composite materials include
structural composite lumber ("SCL"), waferboard, particle board,
chipboard, medium-density fiberboard, plywood, and boards that are
a composite of strands and ply veneers. As used herein, "flakes",
"strands", and "wafers" are considered equivalent to one another
and are used interchangeably. A non-exclusive description of wood
composite materials may be found in the Supplement Volume to the
Kirk-Othmer Encyclopedia of Chemical Technology, pp 765-810,
6.sup.th Edition, which is hereby incorporated by reference.
[0011] The following describes preferred embodiments of the present
invention, which provides a composite panel comprising a mixture of
bamboo strands and strands from one or more wood materials. The
composite panel is prepared by mixing bamboo strands with the
conventional wood strands. As discussed in greater detail below,
the bamboo strands may be intermixed throughout the layers of the
wood composite material or alternatively the strands may be
concentrated only in the surface layers where they make a more
direct contribution to the strength of the material. Thus, the
composite material of the present invention has many advantages of
the bamboo material, such as strength, while also being lighter and
more resistant to water damage and water-caused swelling.
[0012] Like wood materials, bamboo's basic components are cellulose
fibers bonded together by lignin polymer, but bamboo differs from
other wood materials in the organization and morphology of its
constituent cells. Generally, most strength characteristics of
bamboo (tensile strength, flexural strength and rigidity) are
greatest in the longitudinal direction of the bamboo and the bamboo
fibers. This is due to the relatively small micro-fibrillar angle
of the cellulose fibers in the longitudinal direction. The hardness
of the bamboo culm itself is dependent on the density of bamboo
fibers bundles and their manner of separation. The percentage of
fibers does not consist either in the longitudinal direction of the
bamboo culm or in a cross section of the culm. In the longitudinal
direction, the density of fibers increases from the bottom of the
culm to its top, while the density of fibers in the bamboo culm
cross-section is highest closer to the outer surface and decreases
going deeper into the core of the material.
[0013] In the present invention the bamboo strands are preferably
cut into thicknesses of less than about 0.2 inch, such as less than
0.15 inches, such as in the range of about 0.01 inches to about
0.15 inches; and cut into widths of preferably greater than about
0.1 inches, such as more than about 0.15 inches, such as more than
about 0.5 inches. This cutting may be done either manually or with
mechanized clipping equipment. For purposes of improved strength
the bamboo strands should be cut along the longitudinal axis into
strands preferably longer than about 2 inches, such as about 3
inches, such as about 5 inches. While not intending to be limited
by theory, it is believed that the longer strip length will result
in more closely aligned strands when the strands are oriented using
a disk strand orienter, and without being limited by theory, it is
believed that more closely aligned strands will result in a final
wood composite board product that has an improved modulus of
elasticity along the longitudinal axis.
[0014] After being cut, the bamboo strands are dried (as described
below) and coated with isocyanate polymeric resin. The binder
concentration of the isocyante resin is in the range of about 2 wt
% to about 12 wt %, based on the dry weight of the bamboo. One or
more isocyanate binder resins may be used, preferably the
isocyanates are selected from the diphenylmethane-p,p'-diisocyanate
group of polymers, which have NCO-- functional groups that can
react with other organic groups to form polymer groups such as
polyurea, --NCON--, and polyurethane, --NCOON--; a binder with
about 50 wt % 4,4-diphenyl-methane diisocyanate ("MDI") or in a
mixture with other isocyanate oligomers ("pMDI") is preferred. A
suitable commercial pMDI product is Rubinate 1840 available from
Huntsman, Salt Lake City, Utah, and Mondur 541 available from Bayer
Corporation, North America, of Pittsburgh, Pa. Also suitable for
use are phenol formaldehyde ("PF"), melamine formaldehyde, melamine
urea formaldehyde ("MUF"), urea-formaldehyde, polyvinyl acetate
("PVA"), and the co-polymers thereof. Suitable commercial MUF
binders are the LS 2358 and LS 2250 products from the Dynea
corporation.
[0015] A wax additive is commonly employed to enhance the
resistance of the bamboo strands to moisture penetration. Preferred
waxes are slack wax or an emulsion wax. The wax solids loading
level is preferably in the range of about 0.1 wt % to about 3.0 wt
% (based on the weight of the bamboo).
[0016] As used in the present invention, the bamboo is mixed with
strands cut from naturally occurring hard or soft woods, singularly
or mixed, whether such wood is dry (having a moisture content of
between 2 wt % and 12 wt %) or green (having a moisture content of
between 30 wt % and 200 wt %). Suitable soft and hard wood species
include cedar, pine, fir, aspen, oak, maple, and other species as
well. Typically, the raw wood starting materials, either virgin or
reclaimed, are cut into strands, wafers or flakes of desired size
and shape, which are well known to one of ordinary skill in the
art. The bamboo strands and the hard/soft wood strands are each
separately dried and coated with polymer resin binder, and then
after the separate coating stages the coated hard/soft wood strands
and coated bamboo strands are admixed together.
[0017] The binder resin and the other various additives that are
applied to the wood materials are referred to herein as a coating,
even though the binder and additives may be in the form of small
particles, such as atomized particles or solid particles, which do
not form a continuous coating upon the wood material.
Conventionally, the binder, wax, and other additives are applied to
the wood materials by one or more spraying, blending or mixing
techniques, a preferred technique is to spray the wax, resin,
fungicide and other additives upon the wood strands as the strands
are tumbled in a drum blender.
[0018] After being coated and treated with the desired coating and
treatment chemicals, these coated strands are used to form a
multi-layered mat, preferably a three layered mat which is then
pressed to form a composite wood component. This layering may be
done in the following fashion. The coated flakes are spread on a
conveyor belt to provide a first ply or layer having flakes
oriented substantially in line, or parallel, to the conveyor belt,
then a second ply is deposited on the first ply, with the flakes of
the second ply oriented substantially perpendicular to the conveyor
belt. Finally, a third ply having flakes oriented substantially in
line with the conveyor belt, similar to the first ply, is deposited
on the second ply such that plies built-up in this manner have
flakes oriented generally perpendicular to a neighboring ply.
Alternatively, but less preferably, all plies can have strands
oriented in random directions. The multiple plies or layers can be
deposited using generally known multi-pass techniques and strand
orienter equipment. In the case of a three ply or three layered
mat, the first and third plys are surface layers, while the second
ply is a core layer. The surface layers each have an exterior
face.
[0019] The above example may also be done in different relative
directions, so that the first ply has flakes oriented substantially
perpendicular to conveyor belt, then a second ply is deposited on
the first ply, with the flakes of the second ply oriented
substantially parallel to the conveyor belt. In the present
invention, the longitudinal edge of the board is formed parallel to
the conveyor belt, so that flakes oriented substantially parallel
to the conveyor belt will be oriented substantially arranged
substantially parallel to the conveyor belt, will end up being
substantially parallel to the longitudinal edge of the final wood
panel product. Finally, a third ply having flakes oriented
substantially perpendicular with the conveyor belt, similar to the
first ply, is deposited on the second ply.
[0020] An important aspect of the present invention is the
distribution of the bamboo strands throughout the wood panel. The
bamboo strands may be evenly distributed throughout the wood panel,
located in all three plies. Alternatively, the bamboo strands may
be instead be located only in the surface layers. When the bamboo
strands are located solely in the surface layers, they are there in
order to affect the basic and novel properties of the surface
layers such as strength and material weight. [This sentence is for
legal purposes]
[0021] After the multi-layered mats are formed according to the
process discussed above, they are compressed under a hot press
machine that fuses and binds together the wood materials, binder,
and other additives to form consolidated OSB panels of various
thickness and sizes. The high temperature also acts to cure the
binder material. Preferably, the panels of the invention are
pressed for 2-15 minutes at a temperature of about 175.degree. C.
to about 240.degree. C. The thickness of the OSB panels will be
from about 0.6 cm (about 1/4'') to about 5 cm (about 2''), such as
about 1.25 cm to about 6 cm, such as about 2.8 cm to about 3.8
cm.
EXAMPLES
[0022] Composite panels were made according to the prior art and
the present invention as follows. Bamboo strands were cut on a CAE
disk flaker to an approximate size of 0.032 inch by 3 inches by 6
inches. Pine flakes were made under normal stranding conditions to
a size of 0.032 inch by 3 inches by 5 inches. The strands were then
mixed together in ratios of 75:25, 50:50, and 25:75 of pine to
bamboo (see Table I, below). In the tables below it is noted as to
whether the bamboos is distributed throughout the material, or
whether the bamboo strands are found in the surface layers only. In
all cases, the core constituted 40% of the weight of the composite
panel, while the surface layers constituted 60%. A resin
concentration of 5% MDI was used along with the wax concentration
being 1.5%. The panels were pressed at 400.degree. F. for 175
seconds at 200+ PSI to a target density of 44 pcf and a target
thickness of 3/4 inch thick.
[0023] The panels were then tested for several different wood
composite performance characteristics according to the protocol
specified in ASTM D1037. These performance characteristics included
Modulus of Elasticity ("MOE", a measure of panel stiffness) in both
the parallel and the perpendicular directions (with the results
then averaged); Modulus of Rupture ("MOR", a measure of panel
strength) in both the parallel and the perpendicular directions
(again, the results were then averaged); 1 inch thickness swell,
and edge swell.
[0024] The results were as follows. TABLE-US-00001 TABLE I Ratio:
Thickness Edge Pine/Bamboo Swell (at 1'') Swell 100/0 5.2 9.2 75/25
5.4 9.8 50/50 4.1 8.4 25/75 3.8 7.3 0/100 8.3 11.3 100/0 5.2
9.2
[0025] As can be seen in table I, the addition of pine greatly
reduced the amount of swelling that an all-bamboo panel showed. In
fact, the best performance was obtained when an even mixture of
pine and bamboo strands was used. The measurements obtained were
somewhat different depending on whether they were made at the edge
or at a distance of 1 inch from the edge, toward the interior of
the sample as required by ASTM D1037, but for both measurement
methods the overall trend was exactly identical. TABLE-US-00002
TABLE II Average MOE of Samples Ratio: Bamboo strands distributed
Bamboo only in Pine/Bamboo throughout material surface layers 100/0
848307 848307 75/25 896859 876046 50/50 935900 917397 25/75 1109851
1034548 0/100 1117454 --
[0026] TABLE-US-00003 TABLE III Average MOR of Samples Ratio:
Bamboo strands distributed Bamboo only in Pine/Bamboo throughout
material surface layers 100/0 5625 5625 75/25 3990 4351 50/50 6070
6503 25/75 6891 6538 0/100 7923 --
[0027] As can be seen in tables II and III, the addition of bamboo
to form a panel made of a blend of bamboo and pine strands
significantly improves the strength of the panel compared to the
strength of a panel that is 100% pine. This was true when strength
was measured both by MOE and MOR.
[0028] It will be appreciated by those skilled in the art that
changes could be made to the embodiments described above without
departing from the broad inventive concept thereof. It is
understood, therefore, that this invention is not limited to the
particular embodiments disclosed, but it is intended to cover
modifications within the spirit and scope of the present invention
as defined by the appended claims.
* * * * *