Adya Singh, Tatjana Smolic, Elizabeth Dunningham

Ensis Wood Processing

THE JOINT FORCES OF CSIRO & SCION


Adding value to radiata pine wood: stiffness and dimensional stability enhancement by a novel process

Adya Singh, Tatjana Smolic, Elizabeth Dunningham



Introduction Pinus radiata , New Zealand’s

important natural resource But it lacks stability and stiffness

required in high value applications High performance applications

demand specific property improvements


Objectives

To enhance dimensional stability and stiffness

To launch high value product in the market

Possible applications: furniture, joineries...


Process development

A novel process developed to enhance stiffness through chemical treatment in combination with heat and compression


Materials and Methods

Rotary peeled veneer Dry sapwood Veneer samples conditioned at 20C and

50% RH


Zirconyl chloride treatment

30 min soak in ZrOCl2x8H20 solution Range of salt concentrations used

(0.01-3.5%)


Veneers saturated and radially pressed to 40% compression

Pressing temperature 130°C Pressing time 15 min

200mm

100mm


Weverk press


3 point bend test (before and after compression)

Tensile test (compressed samples only)


Veneer sample cut up for testing

HT1

HT2WS1

WS2

TT15mm

40mm

100 mm


Treated and compressed veneer was also tested

For dimensional stability (humidity cycling, and 24 hr water soak)

Surface hardness Microscopically and Chemically

HT1

HT2WS1

WS2

TT15mm

40mm

100 mm


Scanning Electron Microscopy

Control uncompressed Control compressed Zr treated compressed


Chemical testing

Zr content in treated veneer by ICP carbohydrate content (CHO) analysis NMR (not successful) SEM-EDAX (not successful) XPS (ESCA) (not successful)


Compression and thickness reduction

Target Solution Initial Compressed Compression Compress.

strength /%thickness/mmthickness/mm % %control 2.63 1.58 40 400.01 2.64 1.71 35 400.1 2.68 1.61 40 401 2.64 1.51 43 40

2.5 2.68 1.52 43 402.7 2.64 1.59 40 403 2.59 1.38 47 40

3.4 2.69 1.56 42 403.5 2.51 1.51 40 40


Changes in density

Solution Initial Compressed Density strength density density increase

% g/cm3 g/cm3 %control 0.401 0.621 550.01 0.390 0.594 520.1 0.371 0.600 621 0.389 0.622 60

2.5 0.441 0.712 612.7 0.395 0.631 603 0.371 0.601 62

3.4 0.416 0.659 583.5 0.437 0.656 50


Density before and after compression

Error bars represent one standard deviation

0

0.2

0.4

0.6

0.8

1

350.01

400.1

431

432.5

402.7

473

423.4

403.5

40control

Dens

ity (g

cm-3

)

not compressed compressed

Comp. Strain%Soln. Conc%


Properties of unmodified radiata pine

Radiata pine is a medium density softwood Dry timber (from 30 years old trees) has

average density of 453kgm-3 , MOE=8.23GPa and MOR=85.8MPa


Stiffness improvement Overall improvement by bend test

Solution initial MOE 3pt bendstrength MOE after compressonMOE increase

% Gpa Gpa %control 6.30 13.77 1190.01 5.37 13.55 1520.1 6.14 13.46 1191.0 6.08 14.72 1422.5 5.02 9.90 972.7 6.11 15.60 1553.0 7.70 17.77 1313.4 5.45 11.31 1083.5 7.15 11.28 58



Specific stiffness of Zr treated compressed veneer

0

10

20

30

40

0.01 0.1 1 2.5 2.7 3 3.4 3.5

Soln conc.

MO

Es (G

pa)

Uncompressed Compressed

Modulus of Elasticity was normalised to specific value by dividing MOE with specific gravity

Stiffness improvement increased with increasing density

Salt concentrations did not increase stiffness


Stiffness and strength in tension

Solution bend tensile tensilestrength MOE MOE MOR

% Gpa Gpa Mpacontrol 12.5 13.24 53.55

0.1 11.09 12.66 50.261 15.25 17.52 47.02

2.5 10.15 13.09 19.762.7 13.56 12.60 25.283 19.24 14.24 33.24

3.5 14.88 13.56 24.71

Measured 12 months after initial MOE


Humidity cycling conditions

20°C& 65%RH 25 °C & 90-96%RH 25 °C & 30-40%RH Thickness recovery (spring back) measured

after humidity cycling


Thickness recovery after humidity cycling

21 2023

19

5

11

4 53

0

5

10

15

20

25

0 0.01 0.1 1 2.5 2.7 3 3.4 3.5

Soln conc.

Aver

age

thic

knes

s re

cove

ry%


Thickness recovery after 24 hours water soak

3128

3128

16 15 1411 12

0

5

10

15

20

25

30

35

0 0.01 0.1 1 2.5 2.7 3 3.4 3.5

Soln conc.

Aver

age

thic

knes

s re

cove

ry%


SEM images

Uncompressed veneer showing normal appearance of axial tracheids and rays and radial files of axial tracheids


Untreated compressed veneer showing considerable spring back of cells after water soak prior to block preparation (for microscopy)


3% ZrOCl2x8H2O treated and compressed veneer showing excellent compression retention after water soak prior to block preparation (for microscopy)

Note that compression extends throughout the entire thickness of veneer


3% ZrOCl2x8H2O treated and compressed veneer

The pattern of cell deformation is irregular, some cells are radially flattened but others deformed unevenly



Radial flattening of cells is evident in some parts

Cell walls are highly deformed but are largely intact with only minor cracks



Radial cell walls appear to be more deformed than tangential walls, with pit borders showing a range of deformities


Chemical analysis

Concentration of Zr in 3% ZrOCl2x8H2O treated and compressed veneer was 0.278% on oven dried weight basis measured by ICP


GC analysis of monosacharides

Sample Control Control Zr-chloride Zr-chloride SolidAverage % compressed replicate wood content (w/w) 3% 3%

Arabinose 1.44 1.53 1.27 1.01 1.44Xylose 6.3 6.1 5.9 5.7 4.8Mannose 12.2 13.3 11.8 9.2 12.1Galactose 1.7 1.6 1.6 5.3* 1.6Glucose 48.4 47.5 44 45.5 44.9Total 69.9 70 64.6 66.7 64.9

*could be compression wood


Surface Hardness test

1.351.12

1.04

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

ControlCompressed

Zr compressed Control

Dept

h of

pen

etra

tion/

mm



Conclusions Compression fixation improved with an increase in

the concentration of Zr (particularly at 3% and above)

Stiffness increased up to 150 % Stiffness enhancement followed density increase No loss in cell wall components Mechanical damage to cell walls may have

contributed to strength losses Future developments to consider environmental

issues and specific product applications Potential for use of low grade radiata wood, e.g.

juvenile wood


Documents

Adya Singh, Tatjana Smolic, Elizabeth Dunningham