characterization of pacific northwest softwoods for wood composites production

Wood Materials & Engineering Laboratory

Characterization of Pacific Northwest Characterization of Pacific Northwest Softwoods for Wood Composites Softwoods for Wood Composites ProductionProduction

Chris Langum & Vikram YadamaDepartment of Civil and Environmental Engineering

Wood Materials and Engineering Laboratory

Washington State University

Eini Lowell

USDA FS PNW Res. Station, Portland, OR

April 26th, 2007


Presentation OutlinePresentation Outline

• Background & Justification

• Objectives & Tasks

• Methodology

• Results

• Conclusions


IntroductionIntroduction


Changing ResourcesChanging Resources

• Increasing environmental pressures have caused a change in available timber resources


Juvenile LumberJuvenile Lumber

• Young trees are composed of primarily juvenile timber

• Undesirable qualities of juvenile timber include:• Reduced mechanical

properties• Increased longitudinal

shrinkage• Lower density

• Leads to low-value lumber• Composites negate some

of these effects


Wood CompositesWood Composites

Lumber Veneers Strands Particles Fiber bundles Flour Fibers Cellulose

Incr

easi

ng E

nerg

y

Decr

easi

ng

Siz

eLess Labor but increasing capital

Increasing FormabilityIncrease in surface area per pound of wood

Decrease in Strength/wt. ratioIncreasing homogeneity

Lower quality raw material acceptableEngineered for specific properties & applications


Literature ReviewLiterature Review

• Juvenile/Mature timber transition age• Jozsa, Middleton, DeBell (western hemlock) – Age 25-40 yrs.• Abdel-Gadir, Krahmer (Douglas-fir) – Age 30 yrs.

• Juvenile timber properties• Studied by many; however, not much focus on tensile properties

• Olson (1996)• Studied density, pH, and furnish characteristics of lodgepole pine, western larch,

and Douglas-fir• Found species had an effect on panel properties; however, all species were

suitable for wood composites

• Strand properties• Price, Mahoney, Jahan-Latibari, Yadama• Strands have significantly lower mechanical properties (up to 50%)

Due to processing induced damage


Project ParametersProject Parameters

• 12 Douglas-Fir (Pseudotsuga menziesii)• Diameter ranged from 7.5” – 11.5”

• 12 Western Hemlock (Tsuga heterophylla)• Diameter ranged from 6.3” – 11.2”

• Trees selected from American Mill Site near Aberdeen, WA (Installation No. 727)

• Harvested logs were processed at Wood Materials and Engineering Laboratory, WSU


ObjectivesObjectives


Research ObjectiveResearch Objective

• Characterize variation in physical and mechanical properties of small diameter, fast-grown Douglas-fir and western hemlock clear specimens and wood furnish, for wood-based composites, as a function of location within the trees


Small Clear SpecimensSmall Clear Specimens• Task 1: Determine density profiles of specimens through

X-ray densitometry to establish zones where changes in mechanical properties may be encountered.

• Task 2: Test small clear specimens in tension parallel to grain, compression parallel to grain, and flexure by location to determine the extent of variation in mechanical properties with respect to height and diameter.


Wood Furnish For CompositesWood Furnish For Composites• Task 1: Investigate differences in particle size distributions

relative to tree height and radius when converted into wood flour.

• Task 2: Examine pH and buffering capacities of wood and their variation as a function of location within a tree.

• Task 3: Evaluate mechanical properties of strands produced from different locations within a tree and correlate these properties with previously discussed small clear specimen properties.


MethodologyMethodology


Sample PreparationSample Preparation

Tension

Bending

Compression

Density profiles

Moisture content


Small Clear SpecimensSmall Clear Specimens

Static Bending

0.05

Laser

Extensometer

Modulus of Elasticity

Modulus of Rupture

Compression Parallel to Grain

0.012

2” Epsilon Axial Extensometer

Young’s Modulus

Rupture Stress

Tension Parallel to Grain

0.05

2” Epsilon Axial

Extensometer

Young’s Modulus

Rupture Stress

Crosshead Speed

(in./min.)

Measurement

Instrumentation

Properties

Calculated

Tests according to ASTM D143-94: Standard Test Methods for Small Clear Specimens of Timber


Wood FurnishWood Furnish• Particle Size Distribution

• RoTap sieve shaker and screen of 20, 40, 60, 80, 100, and 120 mesh along with pan used to create distribution profiles

• Tensile Properties of Strands• Crosshead speed of 0.015 in./min.• ½” gage length Epsilon axial extensometer• Method according to Yadama (2002)

• pH and Buffering Capacity• 25 g wood flour and 250 g water refluxed for 20 minutes, aspirator

filtered, and allowed to cool to room temperature.• Sulfuric acid (H2SO4) used to titrate to pH of 3.0

• Sodium hydroxide (NaOH) used to titrate to pH of 7.0• Method according to Johns and Niazi (1980)

Twelve trees combined based on location


ResultsResults


Density ProfilesDensity Profiles

Courtesy of Wood and Fiber Science

Density profiles for Douglas-Fir match closely those published in Wood and Fiber Science


Clear Specimen PropertiesClear Specimen Properties

Douglas-fir Western Hemlock

Property Testing Wood Hndbk

% Diff Testing Wood Hndbk

% Diff

Density 0.46 0.48 -- 0.49 0.45 --

Flexural MOE (106 psi) 1.33 1.95 32 1.06 1.63 35

Flexural MOR (psi) 9,570 12,400 23 8,500 11,300 25

Comp. Young’s Mod. (106 psi) 1.42 2.15 34 1.04 1.79 42

Comp. Rupture Stress (psi) 4,840 7,230 33 4,010 7,200 44

Tens. Young’s Mod. (106 psi) 1.51 -- -- 1.11 -- --

Tens. Rupture Stress (psi) 9,890 17,630 44 9,380 14,690 36


MOE and MOR Variation – D-firMOE and MOR Variation – D-fir

• Comparison of means by Duncan’s T-test

MeanCOV

(%)

Mean

(psi)

COV

(%)

Mean

(psi)

COV

(%)

By Elevation

Top 0.47 8.6 1219807 14.0 • 8780 8.4 • 23

Middle 0.47 6.5 1368515 13.8 • 9476 8.4 • 27

Bottom 0.50 5.0 1334923 19.1 • 10080 8.9 • 28

By Radial Distance

Pith 0.48 6.1 1188325 13.1 • 9271 8.2 • 36

Intermediate 0.48 8.2 1413796 13.6 • 9626 9.7 • • 34

Bark 0.49 8.1 1441815 18.8 • 9878 16.6 • 8

Trees

Testedt Grouping

Douglas-firRelative Density MORMOE

t Grouping


MOR & MOE Variation – W. HemlockMOR & MOE Variation – W. Hemlock

MeanCOV (%)

Mean (psi)

COV (%)

Mean (psi)

COV (%)

By Elevation

Top 0.45 8.7 999626 11.8 • 7945 10.7 • 18

Middle 0.46 7.0 1085032 14.2 • 8396 7.5 • 23

Bottom 0.48 8.8 1084017 9.8 • 9082 10.8 • 29

By Radial Distance

Pith 0.48 7.5 982009 11.8 • 8567 8.8 • 35

Intermediate 0.45 8.4 1120443 15.0 • 8422 12.5 • 28

Bark 0.45 8.6 1234687 16.2 • 9120 15.0 • 7

Trees Testedt Grouping t Grouping

Western hemlock

Relative Density MOE MOR


Particle Size DistributionParticle Size Distribution

Douglas-Fir Western HemlockDouglas-Fir Particle Size Distribution by Location

1%

14%

35%

19%

7%

5%

19%

6%

26%

31%

16%

7%

5%

9%

1%

11%

30%

18%

8%

6%

26%

3%

18%

31%

16%

7%

5%

20%

0%

10%

34%

21%

8%

7%

20%

1%

14%

33%

19%

7%

6%

20%

0%

10%

20%

30%

40%

0.0328 0.0165 0.0098 0.0070 0.0059 0.0049 <0.0049Sieve Size

Per

cent

Pas

sing

Bottom - Pith Middle - Pith

Top - Pith Bottom - Intermediate

Middle - Intermediate Top - Intermediate

Western Hemlock Particle Size Distribution by Location

12%

31%

26%

12%

4%

3%

12%

16%

34%

23%

10%

4%

3%

10%

11%

28%

27%

13%

5%

4%

13%

2%

23%

33%

16%

6%

4%

15%

8%

28%

27%

13%

5%

4%

15%

5%

30%

30%

14%

5%

4%

11%

0%

10%

20%

30%

40%

0.0328 0.0165 0.0098 0.0070 0.0059 0.0049 <0.0049Sieve Size

Per

cent

Pas

sing

Bottom - Pith Middle - Pith

Top - Pith Bottom - Intermediate

Middle - Intermediate Top - Intermediate

• Douglas-fir wood flour contained a greater overall percent of fines.

• Western hemlock wood flour produced larger particles through same

processing parameters. • Little variation occurred between locations with the exception of the middle-

pith location in both species.


pH and Buffering CapacitypH and Buffering Capacity

MILLILITERS OF0.01 N NaOH 0.01 N H2SO4

3

4

5

6

7

-18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8

pH

Bottom - Pith

Middle - Pith

Top - Pith

Bottom - Intermediate

Middle - Intermediate

Top - Intermediate

Average

0.01 N NaOH MILLILITERS OF 0.01 N H2SO4

3

4

5

6

7

-6 -4 -2 0 2 4 6 8 10

pH

Bottom - Pith

Middle - Pith

Top - Pith

Bottom - Intermediate

Middle - Intermediate

Top - Intermediate

Average

Douglas-Fir (pH = 4.38) Western Hemlock (pH = 4.98)

• Douglas-fir was more resistant to changes in pH from bases (Sodium Hydroxide)

• Limited variation between locations regardless of species


Strand PropertiesStrand PropertiesDouglas-Fir

• Ave. Ex = 934,410 psi vs. 1.51x106 psi

• Ave. rupture stress = 4,400 psi vs. 9,890 psi

Western Hemlock• Ave. Ex = 874.330 psi vs. 1.11x106 psi

• Ave. rupture stress = 4,100 psi vs. 9,380 psi

• No variation in strength or stiffness with respect to height; however, stiffness tends to increase as you go from bottom to top log contrary to strength

• Radial location had greatest affect on strength – mid region tends to yield better quality strands


Transformation EquationsTransformation EquationsEstimate other elastic constants

Douglas-Fir

• E1 = 1,117,332 psi

• n12 = 0.535

• G12 = 13,281 psi

• E2 = 25,521 psi

Western Hemlock

• E1 = 971,529 psi

• n12 = 0.518

• G12 = 32,965 psi

• E2 = 34,145 psi

2

422

1

12

12

4

1

sincossin

21cos

11

EEGEEx

4

2

12212

12

14

22

12

1

2

14412

sincossin2cos

cossin1)cos(sin

E

Ev

G

E

G

E

E

Ev

xyv


Strand Stiffness PropertiesStrand Stiffness PropertiesEstimating strand properties from clear specimen properties

(Douglas-Fir only)

• Strand Young’s Modulus = 934,410 psi• Flexural MOE = 1,330,000 psi• Tensile YM = 1,510,000 psi• Compressive YM = 1,420,000 psi

• Ratio of • Strand YM / Flex. MOE = 0.71• Strand YM / Tens. YM = 0.62• Strand YM / Comp. YM = 0.66

• W. Hemlock: 0.82, 0.79, 0.84


Strand Strength PropertiesStrand Strength PropertiesEstimating strand properties from clear specimen properties

(Douglas-Fir only)

• Strand Rupture Stress = 4,403 psi• Flexural MOR = 9,570 psi• Tensile Rupture Stress = 9,890 psi• Compressive Rupture Stress = 4,840 psi

• Ratio of • Strand RS / Flex. MOR = 0.46• Strand RS / Tens. RS = 0.45• Strand RS / Comp. RS = 0.91

• W. Hemlock: 0.48, 0.44, 1.02


ConclusionsConclusionsSmall Clear Specimens

• Flexure: • Significant decrease in strength and stiffness from bottom to top and pith to

bark of both species.

• Compression: • Both species strength unaffected by height (with exception of WH lower bolt,

which was significantly larger).• Both species strength unaffected by radial location. • Stiffness was significantly lower at pith for both species.• WH stiffness unaffected by height.

• Tension:• Both species possessed highest strength at bottom bolt and no significant

difference occurred beyond.• Strength increased in both species with distance from the pith.• Stiffness was unaffected by height in either species.• Stiffness increased with distance from pith in DF; however WH decreased

significantly from the middle to outer zone.


Conclusions (Cont.)Conclusions (Cont.)Strand Properties

• pH and Buffering Capacity: • Both species indicated little variation with respect to location with the exception

of the lower pith location.• DF – more acidic

• Particle Size Distribution: • DF – Most particles were retained by the #60 sieve and more fines were

produced when compared to western hemlock.• WH – Equal amounts were retained by #40 and #60 sieve which equates to

larger particles being produced under identical processing parameters

• Strands: • Little variation occurred in either species with respect to strength and even

less variation occurred with respect to stiffness as indicated by K-S test.• Reduction factors were calculated for estimation of strand properties with clear

specimen data. • Stiffness reduced by 30-40% in DF & 15-20% in WH• Strength reduced by 50-55% in both species


AcknowledgmentsAcknowledgments

• USDA FS PNW Research Station, Portland, Oregon

• Stand Management Cooperative for materials, field work in harvesting them, and transportation

characterization of pacific northwest softwoods for wood composites production

Documents

lower mechanical properties

panel properties

wood flour

woodbased composites

buffering capacities

test small clear specimens

krahmer douglasfir age

western larch