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

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

• Adya Singh, Tatjana Smolic, Elizabeth Dunningham

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Introduction

• 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

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Objectives

• To enhance dimensional stability and stiffness
• To launch high value product in the market
• Possible applications furniture, joineries...

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Process development

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

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Materials and Methods

• Rotary peeled veneer
• Dry sapwood
• Veneer samples conditioned at 20?C and 50 RH

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Zirconyl chloride treatment

• 30 min soak in ZrOCl2x8H20 solution
• Range of salt concentrations used (0.01-3.5)

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• Veneers saturated and radially pressed to 40
  compression
• Pressing temperature 130C
• Pressing time 15 min

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Weverk press
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• 3 point bend test (before and after compression)
• Tensile test (compressed samples only)

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Veneer sample cut up for testing
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• Treated and compressed veneer was also tested
• For dimensional stability (humidity cycling, and
  24 hr water soak)
• Surface hardness
• Microscopically and
• Chemically

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Scanning Electron Microscopy

• Control uncompressed
• Control compressed
• Zr treated compressed

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Chemical testing

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

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Compression and thickness reduction
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Changes in density
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Density before and after compression

• Error bars represent one standard deviation

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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 , MOE8.23GPa and MOR85.8MPa

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Stiffness improvement

• Overall improvement by bend test

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Specific 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

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Stiffness and strength in tension
Measured 12 months after initial MOE
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Humidity cycling conditions

• 20C 65RH
• 25 C 90-96RH
• 25 C 30-40RH
• Thickness recovery (spring back) measured after
  humidity cycling

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Thickness recovery after humidity cycling
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Thickness recovery after 24 hours water soak
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SEM images

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

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

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• 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

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• 3 ZrOCl2x8H2O treated and compressed veneer
• The pattern of cell deformation is irregular,
  some cells are radially flattened but others
  deformed unevenly

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• 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

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• 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

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Chemical analysis

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

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GC analysis of monosacharides

• could be compression wood

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Surface Hardness test

• Error bars represent one standard deviation

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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

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