Title: Adding value to radiata pine wood: stiffness and dimensional stability enhancement by a novel process
1Adding value to radiata pine wood stiffness and
dimensional stability enhancement by a novel
process
- Adya Singh, Tatjana Smolic, Elizabeth Dunningham
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3Introduction
- Pinus radiata , New Zealands important natural
resource - But it lacks stability and stiffness required in
high value applications - High performance applications demand specific
property improvements
4Objectives
- To enhance dimensional stability and stiffness
- To launch high value product in the market
- Possible applications furniture, joineries...
5Process development
- A novel process developed to enhance stiffness
through chemical treatment in combination with
heat and compression
6Materials and Methods
- Rotary peeled veneer
- Dry sapwood
- Veneer samples conditioned at 20?C and 50 RH
7Zirconyl chloride treatment
- 30 min soak in ZrOCl2x8H20 solution
- Range of salt concentrations used (0.01-3.5)
8- Veneers saturated and radially pressed to 40
compression - Pressing temperature 130C
- Pressing time 15 min
9Weverk press
10- 3 point bend test (before and after compression)
- Tensile test (compressed samples only)
11Veneer sample cut up for testing
12- Treated and compressed veneer was also tested
- For dimensional stability (humidity cycling, and
24 hr water soak) - Surface hardness
- Microscopically and
- Chemically
13Scanning Electron Microscopy
- Control uncompressed
- Control compressed
- Zr treated compressed
14Chemical testing
- Zr content in treated veneer by ICP
- carbohydrate content (CHO) analysis
- NMR (not successful)
- SEM-EDAX (not successful)
- XPS (ESCA) (not successful)
15Compression and thickness reduction
16Changes in density
17Density before and after compression
- Error bars represent one standard deviation
18Properties of unmodified radiata pine
- Radiata pine is a medium density softwood
- Dry timber (from 30 years old trees) has average
density of 453kgm-3 , MOE8.23GPa and MOR85.8MPa
19Stiffness improvement
- Overall improvement by bend test
20Specific stiffness of Zr treated compressed veneer
- 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
- Error bars represent one standard deviation
21Stiffness and strength in tension
Measured 12 months after initial MOE
22Humidity cycling conditions
- 20C 65RH
- 25 C 90-96RH
- 25 C 30-40RH
- Thickness recovery (spring back) measured after
humidity cycling
23Thickness recovery after humidity cycling
24Thickness recovery after 24 hours water soak
25SEM images
- Uncompressed veneer showing normal appearance of
axial tracheids and rays and radial files of
axial tracheids
26- Untreated compressed veneer showing considerable
spring back of cells after water soak prior to
block preparation (for microscopy)
27- 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
28- 3 ZrOCl2x8H2O treated and compressed veneer
- The pattern of cell deformation is irregular,
some cells are radially flattened but others
deformed unevenly
29- 3 ZrOCl2x8H2O treated and compressed veneer
- Radial flattening of cells is evident in some
parts - Cell walls are highly deformed but are largely
intact with only minor cracks
30- 3 ZrOCl2x8H2O treated and compressed veneer
- Radial cell walls appear to be more deformed than
tangential walls, with pit borders showing a
range of deformities
31Chemical analysis
- Concentration of Zr in 3 ZrOCl2x8H2O treated and
compressed veneer was 0.278 on oven dried weight
basis measured by ICP
32GC analysis of monosacharides
- could be compression wood
33Surface Hardness test
- Error bars represent one standard deviation
34Conclusions
- 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
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