CA1122508A - Wood composites with foliage adhesive - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Wood can be hot-pressed into various composites using as adhesive subdivided plant foliage. Considerable bond strength is achieved, the bonds having water resistance adequate for many uses. The foliage is the primary adhesive i.e., is greater than 95% wt. of the active adhesive com-ponents present. The foliage can be used either in the form of a powder or as a dispersion in an aqueous liquid carrier. The foliage-wood system is hot-pressed to achieve the desired bonding, the pressing temperature being above the softening temperature of the foliage. The softening temperature of the foliage varies depending on the moisture content. The foliage proportions in the composite can range from about 1% to about 60% by wt. or more in some cases. Increased bond strengths have been achieved using form-aldehyde crosslinking agents or alkaline additives.

Description

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Related Application This application is related to my earlier application number 246,732 filed February 27, 1976 (now B Canadian Patent /, ~sl, 1 Field of the Invention This invention deals with wood adhesives and the preparation of wood composites by hot pressing. Foliage in finely divided form has been found to be an effective adhe-sive for wood where hot pressing is carried out. The foliage lG adhesive is suita~le for e.g., panel products such as par-ticle board, waferboard and plywood, and other laminates.
~he foliage may ~e any plant foliage, with evergreen and deciduous tree foliage usually most suitable.

D cription of the Prior Art Wood adhesive formulations are usually based on synthetic resins such as phenol-aldehyde, urea-aldehyde, urea-melamina-aldehyde condensation products and polyvinyl acetate glues. These resins and glues are extended with additives which control the viscosity or other rheological ~0 ~roperties, and which conserve moisture in the adhesive d~lring assembly. In addition to the extender, a filler is normallv incorporated in such formulations primarily to increase the bulk without undul~ interfering wlth the curing and adhesion properties. In my copending application 246,732 mentioned above, I disclosed that finely divided foliage can function as extender or as extender-plus-filler in adhesive form~lLations. Amounts of foliage up to about 95% by ~7t~ of the total adhesive solicls were found operative in this ear-l;e~ appllcation.
3~ On con';inuincJ my work with foliage, I fo,und that the resin adhesi-ve or glue was not essential when bonding 3~'' 1~2~

wood with selected hea-t and pressure levels.

~ummar~ OL the Invention In accordance with -this invention, finely-divided foliage is used as wood adhesive in hot-pressed composite -~ood products. The invention provides a method of bonding wood to form composite products comprising (a) subdividing plant foliage to a fine particle s~ze;
(b) uniformly contacting the finely-divided foli-G age with the wood to be bonded, the foliage being greater than 95% of the active adhesive components present by wt;
(c) subjecting the crude composite to bonding ?res.sure at a selected temperature above the softening tem-~rat~lre o~ the foliage, the selected temperature being high eno~gh to give the desired bond strength;
and (d) recovering the hot-pressed composite wood p~cduc~
The invention includes the resultin~ ho-t-pressed com~sit~ wood product comprising wood and wood adhesive, ~tre~r than 95~ of the active wood adhesive being sub-~ivided ~oli~ge which has been heat-sotened and bonded .ln~er pressure.
T~e invention also includes an adhesive composition ~or ~onding wood comprising (a~ subdivided foliage and ~b~ one of (i) an aqueous alkaline liquid, and ~i) a ormcldehyde crosslinking agent.
The composites of the invention are probabiy most sui~able rcr uses such as particleboard, waferboard, hard-b~;ard ~riberboard), wall panels or ceiling tilesl insulation Fanels, com~osite hardwood flooring, furniture components etc.

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In the accompanying drawing, Figure 1 is a graph showing the heat softening behaviour for wood, bark and fo-liage at three moisture levels.

_tailed Vescription and Examples Moisture Absorption One of the important parameters related to the use of each tree component for composite-product manufacture is the moisture absorption. To examine the moisture a~sorp-~ion, wood, bark and foliage from the same tree of Douglas-fir (softwood) and red alder (hardwood) were obtained. The wood, bark and foliage were oven dried at 105C to reach 0%
moisture content, then ground to pass a 5D mesh screen.
The powder samples were spread on a Syracusewatch glass and stored in humidity chambers at 30F dry bulb, 40F Dew point (5.6% EMC Room~ and 70F dry bulb, 57 F Dew point (12~ EMC Room) for one week. The percent moisture contents of the samples were then determined and expressed on an oven-dry weight basis as shown in the ~ol-lowing table: (EMC; Equilibrium moisture content) 2Q TAB~E 1 Moisture Content (~) on Absorption -Tree Species5.6% EMC 12% EMC
Wood Bark Foliage Wood Bark Foliage Douglas-fir9.1 9.7 9.8 14.2 14.0 14.9 Red alder8.7 9.3 10.6 13.3 14.0 17.6 -Each value is the averase of 4 samples.
The moisture cor.tents of the three components of Douglas-fir ur.der th~ two humidity conditions were essentially the same. The red alâer foliage had a moisture content about

2 to 4~ greater than the wood and bark. The resul~s ind~cate that foliage should have good moisture retention properties, desirable in ~he wood adhesive context.
Thermal Properties In addition to the above Douglas-fir and red alder materials, wood, bark and foliage of Western red cedar, western hemlock and big leaf maple were subjected to thermal softening analysis: a technique for examining the compressi~ility of materials under constant pressure (50 psi) and under a constant heating rate with observation of the flow or softening temperature of the material (Chow, S and K. J. Pickles. 1971. Thermal softening and degradation of wood and bark. Wood and Fiber, 3(3):166-178).
Great differences in the softening temperatures o wood, bark and foliage were observed, even though they had simi-lar moisture content. The responses are almost identical for softwood and hardwoods; therefore, only the results of Douglas-fir are presented in Figure 1.
- As shown in Figure 1, at a moisture content o 0%, wood and bark started to soften at 180C while the foliage showed an initial softening at 95C, a difference of almost 90C. As the moisture content of the material increased to the 9-10~ range, the softening temperatures of the wood, bark and foliage were lowered to 15sQ, 120 and 60C respectively. At a moisture content of 14-15%, the softening temperatures of wood, bark and foliage were 95 , 70 anc, 45C respectively. At temperatures greater than the initial softering ~emperature o foliage, the magnitude of foliage softening was several times greater than that of wood and bark.
These significant lower softening temperatures of foliage (in comparison to that of wood and bark~ even in the 0% moisture content condition suggest considerable 2~

potential plasticization or adhesive properties for foliage, for bonding wood or bark to form composite products. This knowledge of the thermal softening temperature variation as shown in Figure 1 provi.des the fundamental understanding of the necessary conditions for composite product pressing.
For example, at the absolute dry condition of the materials the use of foliage as adhesive for bonding should require a pressing temperature of greater than about 100C at a heating rate of about 18C/min; a decrease in the heating rate will lower the p.^essing temperature required slightly.
At a moisture content of about 10-15~, the minimum plasti-cization temperature for pressing is in the range of about 50C
to 70C.
Further, this research showed that the oliage alone when heated gave two exothermic peaks in the 120C
and 160C regions. These exothermic phenomena could be the result of complex reactions between the foliage che-micals which have relatively simple molecular structures i.e.l between phenolic and carbohydrate precursors (Forrest, G. I. 1975. Polyphenol Variation in Sitka spruce. Can.
J. Forest Res. 5. 26-37). With this knowledge of the ther-mal and chemical properties of foliage it appeared possible that foliage would have low enough plasticization tempe-ratures to develop good flow and contact with the bonding substrate under heat and pressure. The subsequent exothermic reactions of the foliage with a sufficiently high kinetic energy supply could accelerate the auto-adhesion of foliage and also the formation of .strong adhesion bonds in a foliage-wood system.
Tllis h~rpo~ilesis proved to be true according to the present invention; thus botanical foliage alone can be used as an adhesive, su table in the form of either foliage powder - ~12250~3 or mixed in an aqueous liquid carrier, especially for use in bonding wood products.
The starting foliage need not be dried out or "dead" but can be in green condition. The foliage can be dried and ground or otherwise subdivided, or can be wet-ground to a mulch or slurry. The foliage c~n be obtained from any available plant source. Usually the foliage is most suitably obtained from evergreen or deciduous trees.
Examples of trees with suitable foliage include pine, spruce, fir, hemlock, cedar, redwood, poplar, birch, maple, alder, elm and basswood.
The particle size of the ~oliage should be small enough to fill the interstices between the wood, i.e., be-tween the surfaces of layers, veneers, wafers, particles etc. A suitable foliage particle size is usnally ~rom about 10 to about 500 micrometers diameter, preferably about 50 to 400 micrometers. The particle size is not critical. Mix-tures of different foliages can be used and in some cases are desirable. Thus a desir~hle balance o~ properties can be achieved from folia~e combinations.
The foliage adhesive is mixed with or applied tc the wood similarly to other wood adhesives, either as a powder or in a liquid carrier. The liquid carrier may be water or any aqueous li~uid. The amount of foliage dis-persed in the liquid carrier would suitably be about 20 to 60% by wt. but this is not critical. This amount will be chosen to give a desirable viscosity for spreading or spraying.
The amount of foliage appli2d as adhesive can vary widely. Some bond strength between the wood is deve-'oped with amounts as low as 1% wt. foliage ~based on total wt. of composite). Since foliage itself i.s inexpensive, ~ 12;~

amounts as high as 60% or 80% have been used and may be feasible in some cases. The usual range is from about 15 to about 50% foliage, preferably about 20-40%.
The pressing temperatures for such composites will usually be within about 120C and 250C but higher or lower temperatures can be used in cer~ain cases. As dis-cussed above, temperatures as low as 45-50C can be used at moisture contents near 15~. Pressures during pressing are desirably within the range from about 100 to about 600 psi.
There is usually no advantage in exceeding about 600 psi and pressures as low as about 50 psi will give densities and strengths adequate for some applications. The moisture content of both the foliage and the wood should preferably be within the range about 5-15% by wt. at pressing. The moisture is transferable between the wood and foliage and either one can be dryer than about 5%. Thus, dxy foliage powder will give good results with ~ood of 10~ mo~sture content. Allowances can be made for a wide variation in moisture content of each component so that moisture con-tent is not critical.
As illustrated below, the dimensional stabili-ty and water resistance of the folia~e wood composite can be considerable especially when suitable pressing conditions are chosen. As shown in Exam~les 1 and a, composites can be prepared which will stand up reasonably well to 2 hours in boiling water. This water resistance approaches that needed for exterior-grade boards. If desired, the water-resistance can be improved by incorporating before pressing water-resistan~ additives suc'n as fatty acids or w~x materials.
It is possible to treat tne foliage or the foliage wood mixture to enhance the adhesion (see Example 8~ on sub-sequent hot pressin~g. The addition of formaldehyde ~in any 2~Q~3 form able to react and crosslink), has been found to increase the strength of the Einal composite. A suitable concentration range for formaldehyde is from about 1% to about 20~6 by wt.
of the adhesive.
The natural pH of foliage is acidic, usually within the range 3.7 to 5.7. Increased internal bond strengths have been observed when the adhesive pH is raised to neutral and especially to alkaline valuesr e.~., of 10-12. Alkali metal or alkaline earth metal hydroxides are very suitable for this purpose. The addi-tion of from about 1% to about 5% by wt. sodium hydroxide (based on the weight of the composite) or the equivalent, is preferred.
The following examples are illustrative.
Example 1 Folia~e Adhesive Potential This experiment was designed to demonstrate the adhesive potential of foliage alone without the addition of a synthetic ad`nesive as in application 246,732. Dry Douglas-fir wood meal, moisture content about 6~, was used as the particleboard substrate for bonding. The board was prepared with the white spruce foliaye contents of 0, 20, 40, 60, 80 and 100~. A to-tal of a 1000 g of furnish (15.5 x 15.5 x 0.25 in) was pressed at 425 psi and 150C
for 3 mins. The press temperature was then shut off and the board allowed to cool to about 52C with pressure being allowed to reduce on its own for about 4 hours before remo-val from the press. This was done to avoid the blis-ter phenomena and allow a more representa~ive examination of the adhesive ~otential of the foliage. Two boards were made for each foliage concentration. Three internal bond speci-mens (2 x 2 in), two bending s~rength specimens (2 x 10 in) and three specimens (3 x 2 in) for dimensional stability and moisture absorption test were prepared. The results are shown in Table 2.

T~BLE ~

Foliage Internal 48_hours soak Concentrationbond str. L T M.C.
(~) (psi) MOR (%) (~

0 0 175 board dissolved 9~ 121011.40 152 128 210 33340.29 33 27 205 28700.~5 45 37 ~0 201 12820.82 71 51 100 220 17650.01 1.2 7.
, MOR = Modulus of Rupturs L = Linear expansion T = Thickness swelling M.C. = Moisture content The 100% foliage content specimens after the 48 hours water soak were further subjected to 2 hours boiling in water. The moisture absorption of the specimens was 15.7% ~hile the linear expansion and the thickness swelling were 1.44 and 19.8~ xespectively. The specimens a~er boi-ling were air-dried for 2 weeks and their internal bond strength tested. The internal bond strength averaged 5~ psi.
The above results show that foliage alone without the addition of synthetic resin can develo~ strong adhesive properties. The adhesive bonding has water resistance.
As also shown by the 2 hours boiling in water of the 100%
foliage board, the foliage board demonstrated the property of boiling water-resistant bonding which is normally accep-ted as exterior-grade bonding. This will be further explored in Example 4.
Example 2 Foliage ~Content and Board Strength To further demonstrate the adhesive properties of _9_ foliage, western Led cedar, Douglas-fir, white spruce and lodgepole pine foliages were used. Fine Western hemlock sawdust which had been dried to a moisture conten-t about 2.5% ove~-dry weight, was prepared~ The foliage was first dried to about 0% moisture content and then ground in a Wiley mill to pass a 30 mesh screen. The foliage concentra-tion in-the particleboards ranged from 0 to 40% based on the total weight of the board. Each of the two 15 x 15 inch boards was pressed at 150C for 6 mins to a thickness of 0.25 inch giving a density of about 1. Six, 2 x 2 inch specimens for internal bond strength testing were cut from each board and tested. The average internal bond strengths of the boards are shown below:

.
Foliage Internal bond strength (psi) concentration (%) W red cedar D. fir O O O

` 20 105 ~9 -- . .

The boards with the foliages of white spruce and lodgepole pine were only made with 20% foliage content in the sawdust board. The internal bond strengths obtained were 62 and 54 psi respecLively for th2 white spruce and 30lodgepole pine boards.

\8 The experimental results demonstrate thak the ad-hesi~re property of foliage of different tree species and the ~oliage-wood bond can form in a short pressing -time with the foliage content as low as 1%.
Example 3 Improvement of Bond Strength by Increasiny the Pressing Energy Pressins temperatures of 150 and 200C were used with a pressing time of 6 mins to give a 0.25 inch thick board with a density of 0.9 to 1Ø Douglas-fir, whits spruce and lodgepole pine foliages were used. Twenty percent of dry powdered foliage was mixed in hemlock sawdust (6%
moisture content). Two, 15 x 15 inch boards were made for each experimental condition. Three specimens for internal ~ond strength test and two specimens for bending strength test were cut from each board.
The averaye bending and internal bond strengths are shown below:

-Foliage Internal bond ( si) Bendin~ stren~th (psi) Species 150~C 200~C 150C ~00C
_ ._ Dou~las-fi- 79 182 1787 3383 White spruce 62 126 1182 2501 Lodgepole pine 54 96 962 2555 The above results demonstrate that the strengths of foliage-wood boards increase with an increase in pressing temperature. This suggests that the foliage adhesive pro~erties improve with an increase in input pressing erergy.
Example 4 Durabilitv Tests of Foliage-Wood Board The durabili-ty nature of ~he foliage~wood boards was ex~m;ned ma~iny boards at a constant press temperature but using different press tiMes. Foliaye-wcod boards wer2 ~l~22~

pressed at 200C and 425 psi for 5, 10, 15, 20, 25, 30 and 60 mins. The white spruce fo~iage used had a powder content in the Douglas fir wood meal ~oard of 20%. Two boards were made for each pressing time. The densit~ of the boards was 0.9 to 1. Each board was cut so that 4 bending s-trength specimens and 6 specimens for internal bond tests were obtained.
The following tests were done:
1. Bending tests while the specimens were dry and also after 2 hours boiling in water.
2. Internal bond strength tests while specimens were dry and also dried at 60C overnight after 2 hours boiling in water.

3. Moisture content and dimensional change measure-ments were made on previously tested (1) dry bending test specimens after soaking i~ water for 24 hours at 20C.
The test results are given in Tables S and 6.
These results demonstrate that when suitable pres-sing schedu}es (ti~e-temperature combination) provide suE-ficient energy, a durable oliage-wood board can be prepared which will stand up to boiling water trea~ment.
Example 5 The Moisture Content of Wood Particles and the Temperature of Board Formation and the Internal Bond Strength This experiment was designed to examine the pres-sing schedule especially the temperature and pressure influence on foliage particleboard formation when Douglas-fir shavings which had a relatively high moisture content of about 19%
were used. The shavings were mixed with oven-dry Douglas-fir foliage powder ~passed 30 mesh size) at a 20~ oliage concen-tration. The press temperature was set for 300F (15 ac ~ and ~L2~Q~3 T~BLE 5 Board Strength .
Press time Internal bond (psi? MOR ~psi) (min) dry boiled dry boiled 48(31)* - 1011 92(28) - 2130 79 76(28) 2(1) 2246 219 ~0 175(46) 12(8) 26Q7 352 139(61) 6(2) 2570 261 134(46) 18(11) 2265 948 149(5) 47(16) 2110 903 *Standard deviation.

Dimens.ional Stability .
Press time 4 hours soak2 hours boil (min) L(%) T~%) MC(%)L(%) T(%) MC(%) 5.50 118 135 - - -1.06 33 ~0 3.36 107 1~0 0.92 30 35 2.73 ~6 105 0.78 24 34 1.96 63 80 0.56 20 22 2.22 59 88 1.32 37 42 1.20 ~0 55 0.53 12 21 1.01 30 4~

the initial pressure was 400 psi. A thermocouple was inserted in the center of the board and ihe board was pressed to the desired temperature. The pressure was then released in steps of 50 psi each minute un-til the pressure reached 0 and the press was then opened. The desired temperatures were 140, 120, 100, 80 and 60 C.
The results of this experiment are shown in the following Table 7.

Center board ~otal press In-ternal Modulus of tOmp. time bond rup-ture ( C) (min) (psi) (psi) 140 8.5 84 3129 ~00 7 61 2278 60* 4 26 1016 , *The pressure was dropped to 200 psi and the press was opened~
The results of this experiment showed that a stron~
foliage-wood board can be produced with a combination of pres-sing schedules. Even when the center temperature of the board is 60C, the wood shavings can form a board with modu-lus of rupture approaching 1000 psi.
The experimental results confirm the softening tem--perature data (e.g., Figure 1) which indicated that when the foliage moisture content is about 15~ or more, the folia~e can flow or become plas~ iæed at pressing temperatures as low as 45C. Since the wood particles used in E~ample 5 had a moisture content of 19%, tk~ energy can be easily transferred to the whol~ foliage-~ood systQm and thus at 60C, the foli-age adhesive properties -~ere well developed.
Example 6 .
In ano~her experiment, instead of 19~ moisture con-ten~ in the wood sha~ings, wood shavings with g~ moisture content were used. Tne Douglas-fir wood shavings were mixed with 20% Douglas-fir foliage and the mixture then was press~d to a density of about 1 and a thickness of 0.25 inch. The ~ressing conditions were: (a) the board was made at a pres-~ing temperature oE 175C ancl pressure of 400 psi for 1 min and then pressure was dropped 100 psi for 2 mins before press -i4-~1122~

opening; (b) the board was made at a pressing temp~rature of 175C and pressure of ~00 psi for 11 mins and then the pres-sure was dropped to 100 psi for 1~ mins beEore the press opening. In the above pressing conditions, the board cen-ter temperature after 1 min pressing was about 110C which is higher than the softening tempera-ture o~ foliage but below the initial softening temperature of bark and wood.
The resulting internal bond strength for the two pressing conditions were 45 and 56 psi, respectively for the condi-1~ tions of (a) and (b). The MOR for the boards were 1283 and 1319 psi, respectively for the (a) and tb) boards.
Example 7 Whole Tree Board Since the foliage adhesion principle was esta-blished, it was worthwhile to try to bond whole tree com-ponents without the use of syn-thetic resin. The whole tree components included foliage, bark and wood.
Five-year-old red alder trees which contain about 15 to 30% of foliage, were cut and dried in an oven at 105C
to have a moisture contant of about 1.5% based on oven-dry weight. This combined material was then ground in a Wiley mill. The wood and bark slivers produced had an average of 0.25 inch length and 0.06 inch width. The whole mass was then pressed at 150C, 180C and 200C, respectively for 6 mins. The board thickness was 0.5 inch and its density was 0~9 to 1Ø
Tests on the resulting boards showed that the in-ternal bond strengths were 63, 45 and 129 psi and the modulus of rupture in bending were 1664, 1562 and 1050 psi respeetive-ly for the pressing temperatures of 150 and 180 and 200C.
This experiment demonstrates that the use of foli-age as adhesive can extend to whole tree bonding including bark and wood.

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Example 8 Effec~ of Formaldehyde and Caustic on Foliage Adh _ ion Using the identical pressing conditions as in Example 2, particleboard having the following matexial con-stituents were made:
~a) 10% of dry cedar foliage powder in the hemlock sawdust board;
(b) 10% of a cedar foliage-paraformaldehyde mix-ture in the hemlock sawdust board. T~e foliage-formaldehyde mixture added had 10%
of paraformaldehyde content.
(c) 10~ of cedar foliage mixed in the same saw-dust and then the mixture sprayed with 10% of the weight of board of sodium hydroxide-water solution (10% caustic content).
(d) 10% cedar foliage mixed in the same hemlock sawdust and the mixture sprayed with 10% o~
the weight of board of sodium hydroxide solu-tion (30% caustic content).
The results showed that the internal bond strengths were 52, 92, 84 and 200 psi, respectively or boards of (a), (b), (c) and (d). Thi~ example de~onstrated that the adddition of formaldehyde and caustic water enhanced the folia~e ad-hesion on subsequent hot pressing.
Example 9 Folia~e Glue Adhesion in Plywood Ty~e ~amination To simulate a plywood-type glue, 400 g of Douglas-fir foliage powder ~assed 30 mesh) was mixed in water ~800 g) and sodium hydroxide (96 g) solution to give 8% sodium hy- ;~
droxide ~ontent. The pH of the adhesive mixture was 1~;
this glue was spread on white spruce veneers with 30 pounds per thousand square feed of double glueline. They were allowed to have an o~en assembly time of 5 mins and then ~IL22S0~3 were pressed at lS0C for 12 mins at 200 psi. The in-ternal bond strength of the 5-ply plywood laminations was tested according to particleboard specifications and was found to be an average internal bond strength of 70 psi (plywood density was about 0.45). This example demonstra-ted tha~ the foliage adhesive can be prepared as liquld glue for bonding.

Claims (18)

CLAIMS:

1. A method of bonding wood or bark to form composite products comprising:
a) subdividing plant foliage to a fine particle size;
b) uniformly contacting the wood or bark to be bonded with adhesive which consists essentially of one of (i) said subdivided foliage, (ii) said subdivided foliage with up to 20% formaldehyde by weight of the adhesive, and (iii) said subdivided foliage having its natural acid pH
raised to neutral or alkaline pH; said adhesive being present in sufficient amounts to bond the wood or bark; and preparing a crude composite thereof;
c) subjecting the crude composite to bonding pressure at a selected temperature above the softening temperature of the foliage, the selected temperature being high enough to give the desired bond strength; and d) recovering the hot-pressed composite wood or bark product.

2. The method of claim 1 wherein the hot-pressing temperature is selected from within the range of 45 to 250°C.

3. The method of claim 1 wherein the hot-pressing pressure is from about 50 to 600 psi.

4. The method of claims 1, 2 or 3 wherein the amount of the foliage is within about 15% to about 80% by wt. of the composite.

5. The method of claims 1, 2 or 3 wherein the amount of the foliage is from about 20% to about 40% of the composite.

6. The method of claims 1, 2 or 3 wherein the foliage in step (b) is in the form of dispersion in an aqueous liquid carrier.

CLAIMS:

7. The method of claims 1, 2 or 3 wherein the foliage in step (b) is in the form of a free-flowing powder.

8. The method of claims 1, 2 or 3 wherein the foliage is selected from evergreen foliage, deciduous tree foliage and mixture thereof.

9. The method of claims 1, 2 or 3 wherein the foliage or mixture of foliages is selected for a particular combi-nation of properties.

10. The method of claims 1, 2 or 3 wherein the foliage is bonded at neutral or alkaline pH.

11. The method of claims 1, 2 or 3 wherein a formalde-hyde cross-linking agent is incorporated before bonding.

12. A hot-pressed composite wood or bark product com-prising wood or bark and wood adhesive, greater than 95% by wt. of the active wood adhesive being subdivided foliage which has been heat-softened and bonded under pressure.

13. A hot-pressed composite wood or bark product com-prising wood or bark and wood adhesive, said wood adhesive consisting essentially of one of (i) subdivided foliage, (ii) said foliage with up to 20% formaldehyde by wt. of the adhesive, and (iii) said foliage having its natural acid pH raised to neutral or alkaline pH, said foliage being heat-softened and bonded under pressure.

14. The composite wood product of claim 12 wherein the foliage is selected from evergreen foliage, deciduous tree foliage and mixtures thereof.

CLAIMS:

15. The composite wood product of claim 12, 13 or 14 wherein the foliage is present in amounts within about 15 to about 80% by wt. of the composite.

16. The composite wood product or claims 12, 13 or 14 wherein the foliage is present in from 20% to about 40% by wt. of the composite.

17. The composite wood product of claims 12, 13 or 14 wherein the adhesive was bonded at alkaline pH.

18. The composite wood product of claims 12, 13 or 14 wherein the internal bond strength is increased by formalde-hyde cross-linking.