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Development of a new engineered wood product for structural

applications made from trembling aspen and paper birch

Katherina Beck

Alain CloutierAlexander Salenikovich

Robert Beauregard

Annual meeting of IAWS 2011 - StockholmAugust 31, 2011

Context

Engineered Wood Product

Utilization of existing

installations

Use of under-utilized species

Oriented Strand Lumber

• A structural composite lumber that combines parallel aligned wood strands with structural adhesive to form lumber-like structural products

• Can be produced in OSB mills• Using paper birch and trembling aspen

Four Problems

1. Conventional hot platen pressing results in a pronounced vertical density profile.

2. OSB production parameters are adapted to low density species.

3. Adequate bending strength to compete with engineered wood products on the market must be achieved.

4. Panel thickness limited by press opening.

Step1

Step 2

Step 3

Step 1: Develop a Pressing Procedure and Evaluate the Effect of Species

- Background -

• Problem: Conventional hot platen pressing results in a pronounced vertical density profile (VDP).

• Step-closure pressing significantly changes the traditional shape of the VDP (Wang et al. 2000).

conventional step-closure

VDP

Step 1: Develop a Pressing Procedure and Evaluate the Effect of Species

- Background –

• Problem: OSB production parameters are adapted to low density species.

• Panels produced from higher density species tend to have inferior bending properties compared to aspen panels (Blankenhorn et al. 1989, Brunette 1992).

• Thinner strands improve mechanical properties of birch panels (Au and Gertjejansen 1989, Yong et al. 1992).

• Specific surface:

SS =e · ρ

2Particle Mass

Particle Surface=~

e = strand thicknessρ = oven-dry wood density

Thin, slender particles

Step 1: Developing a Pressing Procedure and Evaluating the Effect of Species

- Materials and Methods -

• Trembling aspen (benchmark) and paper birch

• Similar specific surfaces for both species

• Three adhesive contents (3.5%, 5%, 7%)

• Unidirectional strand alignment

• Three-step-closing pressing procedure

Step 1: Production Parameters

Oven-Dry Wood

Density ρ [kg/m3]

Strand Thickness

e [mm]

Strand Length

ℓ [mm]

Target Panel

Density [m3/kg]

Specific Surface

SS1

[m2/kg]

Adhesive Content²

Powder PF

Liquid PF Total

Aspen 451 0.69 105 650 6.4

1.0% 2.5% 3.5%

1.43% 3.57% 5.0%

2.0% 5.0% 7.0%

Birch 617 0.51 105 650 6.4

1.0% 2.5% 3.5%

1.43% 3.57% 5.0%

2.0% 5.0% 7.0%

¹

² Percent per oven-dry wood weightPF = Phenol formaldehyde

ρ⋅=

eSS

2

+ =

Vertical Density Profiles

low adhesive content (3.5%)medium adhesive content (5%)high adhesive content (7%)

0

250

500

750

1000

1250

0 2 4 6 8 10 12 14 16Position (mm)

Den

sity

(kg/

m³)

Aspen

0

250

500

750

1000

1250

0 2 4 6 8 10 12 14 16Position (mm)

Birch

Den

sity

(kg/

m³)

- Results -

0.345 MPa

Internal Bond

• Internal bond (IB):- Adhesive content:

significant effect- Species:

no significant effect

AspenN = 230.63

(14.9)B

BirchN = 180.68

(39.6)B

7.0%

AspenN = 210.47

(14.1)A

AspenN = 220.55

(19.0)AB

BirchN = 160.45

(21.8)A

BirchN = 190.67

(33.1)B

0

0.2

0.4

0.6

0.8

1.0

3.5% 5.0%Adhesive Content

IB (M

Pa)

OSB O-2 (CSA-O437): 0.345 MPa

- Results -

Flatwise Bending

• Modulus of Rupture (MOR):- Adhesive content: no

significant effect- Species: no significant

effect

• Modulus of Elasticity (MOE):- Adhesive content: no

significant effect- Species: significant effect

360180180

[mm]

TimberStrand®

Aspen11.8(8.2)

A

Aspen72.2

(12.6)A

Birch10.6

(13.1)

B

Birch64.4

(27.5)A

0

25

50

75

0

4

8

12

100 16

MOR

(MPa

)

MOE

(GPa

)

Modulus of Elasticity

Modulus of Rupture

TimberStrand®

- Results -

• Modulus of Rupture:Means adjusted for short term loading; COV of 15%; thicknesses up to 89 mm; marketed in Canada

• TimberStrand® LSL40.2 MPa

• Modulus of Elasticity:• TimberStrand® LSL

9 700 MPa

• Modulus of Rupture (MOR):- Adhesive content: no


effect

• Modulus of Elasticity(MOE):- Adhesive content: no


effect

• Modulus of Rupture:Means adjusted for short termloading and 30 mm depth; COV of 15%; marketed in Canada

• TimberStrand® LSL40.2 to 55.1 MPa

• SolidStart® LSL43.6 to 59.4 MPa


9 000 to 10 700 MPa• SolidStart® LSL

9 300 to 10 700 MPa

Edgewise Bending180 180 180

540

[mm]

Birch10.3

(15.4)

A

Aspen10.6(8.4)

A

Aspen43.4

(16.0)

A

Birch43.0

(41.6)A0

20

40

60

80

100

MOR

(MPa

)

0

3

6

9

12

15

MOE

(GPa

)


Modulus of Rupture

MOR:40 to 60

MPa

MOE:9 000

to 10 700

MPa

- Results -

Step 2: Evaluate Interaction Between Slenderness Ratio, Specific Surface, Species,

and Performance

- Background -

• Problem: Adequate bending strength to compete with engineered wood products on the market.

• Particle geometry: - Strand length ↑ → bending properties ↑

(Barnes 2001, and others).- Slenderness ratio (length-to-thickness ratio) ↑

→ bending properties ↑ (Post 1958, Barnes 1988, and others).

Step 2: Evaluate Interaction Between Slenderness Ratio, Specific Surface, Species,

and Performance- Materials and Methods -

• Trembling aspen and paper birch

• Three strand lengths

• Two strand thicknesses

• 7% adhesive content

• Unidirectional strand alignment

• Three-step-closing pressing procedure

Step 2: Production Parameters

Oven-Dry Wood Density ρ [kg/m3]

Strand Thickness e

[mm]

Strand Lengthℓ [mm]

Specific SurfaceSS [m2/kg]

Slenderness Ratio SR¹

Trembling Aspen 459

0.49 77.6 8.8 1580.53 105.0 8.3 2000.45 142.1 9.8 3180.75 77.6 5.8 1030.71 105.0 6.2 1490.66 142.1 6.6 217

Paper Birch 624

0.46 77.6 7.0 1700.47 105.0 6.8 2230.43 142.1 7.4 3300.75 77.6 4.3 1040.71 105.0 4.5 1490.71 142.1 4.5 199

e

=RS¹

Internal Bond

• Internal Bond (IB):- Species:

no significant effect- Strand thickness:

no significant effect- Strand length:

no significant effectOSB O-2

OSB O-2 (CSA-O437): 0.345 MPa

N = 910.68

(21.0)A

N = 1160.76

(26.2)A0

0.4

0.8

1.2

IB (M

Pa)

Aspen Birch

- Results -

Flatwise Bending360

180180

[mm]

Flatwise Bending

• Species, thickness, and length: significant effect

• Slenderness ratio: significant effect

• Specific surface: significant effect

360180180

[mm]

S = shortM = mediumL = long

40.3(19.3)

48.9(19.3)

53.5(26.8)

66.0(15.3)

54.5(21.1)

65.5(15.7)

65.4(24.3)

77.6(15.9)

62.0(26.2)

85.1(20.2)

90.1(16.4)

99.2(19.5)0

30

60

90

120

MOR

(MPa

)MO

E (M

Pa)

TimberStrand®

S M LS M L S M L S M L

8943(7.1)

8189(7.9)

7766(18.6)

6395(15.1)

11642(9.4)

10391(11.7)

9647(11.9)

8218(11.5)

13581(14.9)

12624(13.4)

12107(7.0)

10002(11.0)0

4000

8000

1200016000 Modulus of Elasticity

Aspen Birchthin thick thin thick

Modulus of Rupture

TimberStrand®

• Modulus of Rupture:Means adjusted for short term loading; COV of 15%; thicknesses up to 89 mm; marketed in Canada

• TimberStrand® LSL40.2 MPa


9 700 MPa

- Results -

• Species, thickness, and length: significant effect

• Slenderness ratio: significant effect

• Specific surface: significant effect

• Modulus of Rupture:Means adjusted for short term loading and 30 mm depth; COV of 15%; marketed in Canada• TimberStrand® LSL

40.2 to 55.1 MPa• SolidStart® LSL

43.6 to 59.4 MPa



9 300 to 10 700 MPa

Edgewise Bending180 180 180

540

[mm]

MOR

(MPa

)MO

E (M

Pa)

42.7 (9.7)

35.0 (15.0)

38.8 (26.8)

28.8 (19.2)

51.4 (18.3)

45.3 (18.3)

41.8 (24.9)

29.1 (22.1)

66.3 (21.3)

55.4 (22.0)

65.7 (14.9)

40.3 (29.0)0

30

60

90

8371(6.7)

6971(6.7)

7901(12.6)

6493(14.7)

10799(6.0)

9641(8.5)

9614(16.7)

8249(13.5)

13505(7.9)

12163(6.4)

13203(4.9)

10494(11.6)0

4000

8000

12000

16000

S M LS M L S M L S M L

Aspen Birchthin thick thin thick

Modulus of Rupture



MOR:40

to 60 MPa

MOE:9 000

to 10 700

MPa

- Results -

0

2000

4000

6000

8000

10000

12000

14000

16000

0 50 100 150 200 250 300 350 400Slenderness Ratio SR [mm/mm]

MOE

[MPa

]

MOE Values, AspenMOE Values, BirchMOE Regression, Aspen @ 725kg/m³MOE Regression, Birch @ 725 kg/m³

Edgewise Bending - Regression

Aspen:MOE = -1803 + 9.6 Density + 27.4 SR

R² = 0.81

Birch:MOE = -10403 + 20.4 Density + 24.4 SR

R² = 0.88

A B

M

Compression

• Species and strandlength: significanteffect

• Strand thickness: no significant effect

10.8(18.4)

14.5 (15.2)

9.1 (19.1)

11.1 (14.7)

9.7 (22.4)

10.4(15.3)

0

5

10

15

20

Stre

ngth

(MPa

)

2254(23.1)

2852 (15.2)

1318(24.6)

1418(20.9)

1101(31.4)

1219(22.7)

0

1000

2000

3000

4000

MO

E (M

Pa)

Aspen BirchCompressive Strength

S L S M L

Compressive MOE


- Results -

Step 3: Evaluate a Laminated OSL Prototype

- Background -

• Problem: Panel thickness limited by press opening in OSB mills.

• Face-lamination of thin panels allows to achieve adequate thickness.

Step 3: Evaluate a Laminated OSL Prototype

- Materials and Methods -

• Trembling aspen and paper birch panels- 0.55 mm thick, 142 mm long strands; 7% PF

content

• Industrial webstock OSB

• Phenol-resorcinol adhesive

• Small scale testing

• Larger scale testing

Edgewise Bending – Small Scale

« Birch, aspen OSL» « OSB »

9.9(3.0)

10.6(3.0)

5.2(6.4)

0

3

6

9

12

15

Aspen Birch OSB

MOE

(GPa

)

52.0 (4.7)

58.4 (11.4)

26.4(6.1)

0

30

60

90

Aspen Birch OSB

MOR

(MPa

)


Modulus of Rupture

- Results -






9 300 to 10 700 MPa

MOR:40 to 60

MPa

MOE:9 000

to 10 700

MPa

45

30

[mm]180 180 180

540

4515 15 15

30 30

[mm] 4611.5 11.5 11.5 11.5

Edgewise Bending – Larger Scale

[mm]

2160720 720 720

46120






9 300 to 10 700 MPa

Edgewise Bending – Larger Scale

26.8(3.8)

24.0(4.8)

0

10

20

30

40

smallbeams

large beams

MOR (

MPa)

10%

46.7 52.60

30

60

90

Aspen BirchMO

R (MP

a)9.9 10.6

0

3

6

9

12

15

Aspen Birch

MOE (

GPa)


Modulus of Rupture


Modulus of Rupture

¹ No size effect indicatedin literature → ignored.

- Results -

MOR:39 to 57

MPa

MOE:9 000

to 10 700

MPa

4.9(6.4)

5.2(2.6)

0

3

6

9

small beams

large beams

MOE (

GPa)

( )¹6%

Conclusions

• Step 1: Develop a Pressing Procedure and Evaluate the Effect of Species- Using a three-step closing schedule, a near-homogenous VDP

was achieved.- Respecting similar specific surface for both species, comparable

internal bond and bending properties were achieved.

• Step 2: Evaluate Interaction Between Slenderness Ratio, Specific Surface, Species, and Performance- Not only strand geometry and species had an effect on bending

properties; the slenderness ratio and specific surface also played a role.

- Strand length is a compromise between bending and compression performance.

Conclusions (2)

• Step 3: Evaluate a Laminated OSL Prototype- Average MOR and MOE values make laminated aspen and birch

OSL competitive with similar EWPs.

Engineered Wood Product

Utilization of existing

installations

Use of under-utilized species

Laminated Oriented Strand

Lumber

The properties of theselaminated OSL products

offer an affordable, viable alternative to similar

products on the market.

These laminated OSL products can be

manufactured in existingOSB mills, allowing them

to react to marketdemand by alternatingbetween OSB and OSL.

Paper birch, currently an underutiziled species,

can be given added value.

Three Advantages

In the Future…

• Other species

• Mill trials

• Full size testing

• Panel combinations

• Panel jointing

• Connections

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