Biocide Treatments for Composite Panels
H. M. BarnesJ. Kirkpatrick
Mississippi State UniversityForest Products Laboratory
Forest & Wildlife Research CenterStarkville, Mississippi
39th International Wood Composites Symposium
This research was sponsored, in part,by USDA CSREES Special Research Grant Program No. 2004-34158-14682 and the
Wood-Based Composites Center(University of Minnesota, Mississippi State University, Oregon State University, Virginia Tech)
Let’s reflect on:• Where have we been?
• Where are we now?
• What does the future hold?
When did we begin to engineer wood panels for added durability?
• Use of Douglas Fir veneer with some natural durability-1900s?
• Advent of “waterproof” glues (PF & PRF)-1930s
• Pressure treatment of plywood in the late 1940s-early 1950s
• Compreg
• Improved hygroscopic properties-since inception
• Fire retardant additives
The push for more durable panels...
• Opportunity for expanded end uses
• Needed; required in high risk areas
• Just to keep up with competitors
Challenges Opportunities• Decay
• Native termite(s)
• Formosan termite
• Mold issues
Formosan Termite
• In affected areas, high demand for treated wood
• $2+ billion problem
• Borate-treatments would seem to offer a solution
C. formosanus known infestations and projected northern migration
35° N Latitude
Mold Issues• Emotional—no scientific proof that
Stachybotrys caused health problems (CDC)
• “The mold issue has only become a problem because the public now perceives it as a health threat and attorneys are bringing the issue before juries to seek large judgments.”
• Cure the moisture problem!
Methods of Biocidal Addition:
• Pre-treatments
• In-process treatments
• Post-process treatments
• Non-conventional treatments
Preservatives applied to OSB/waferboard
• Borates– Zinc Borate– Calcium borate– Boric acid/ DOT– SBX– Vapor boron
• Copper Naphthenate • TBTO • Copper-8-quinolinolate• Copper + flourine
• Azaconazole• Tebuconazole +
propiconazole + IPBC• IPBC • CCA • Copper complex• ACA• PCP• PXTS• Others
Investigation of 5 preservative systems for use on wood composites
• Waterborne copper naphthenate• Powdered copper naphthenate• Zinc borate • Betaine [didecylpolyoxethylammoniumborate]• Copper (CO3:OH, 1:1) betaine (102) - <5%• Copper betaine (111) - 10-25%
Project Design
• Use randomly oriented strandboard model• Initial investigation at or above threshold
retentions for Reticulitermes• Single, fixed levels for: adhesive, wax,
pressing variables• Evaluated mechanical, physical properties
to ascertain effects
Statistical Layout
• Randomized Complete Block Design• Blocking Factor: group of strands (two)• Treatment: preservative (seven)• Replicates: panel (four) [two per block per
treatment]• Sub-samples (per panel): 4 static bending,
8 IB, 2 water soak
Blocking LayoutStrand group A (2 panels per treatment)
Zinc Borate
Powdered CuNap
BetaineControl
Vacuum Impreg WbCuNap
Waterborne CuNap
Cu + Betaine
Copper + Betaine
Strand group B (2 panels per treatment)
Zinc Borate
Powdered CuNap
BetaineControl
Vacuum Impreg WbCuNap
Waterborne CuNap
Cu + Betaine
Copper + Betaine
Panel Materials• SYP strands + < 5% mixed HW strands• Commercial OSB PF resin• Commercial particleboard emulsion wax• Preservative Systems
– Waterborne Copper Naphthenate– Powdered Copper Naphthenate– Powdered Zinc Borate– Betaine– Copper + Betaine
Waterborne Copper Naphthenate
• Developmental Sample– Naphthenic Acid + Copper Salt– Proprietary dispersant– Deep blue tint
Wb CuN + PF Resin
Powdered Copper Naphthenate
• 10% Calcium Silicate• 11.4 % Copper• Large particles-
refined to pass 100 mesh Ro-tap sieve shaker
Powdered Zinc Borate• Zinc borate
– 2ZnO 3B2O3 3.7H2O (Boric acid and Zn salt)– Fine, dry powder– White tint– Odorless– Can have clumps
• Powdered addition to panels
Betaine
• Clear liquid• Developed in Europe
Betaine + PFBetaine + waxBetaine
Copper + Betaine (111)
• Dark blue liquid• Developed in Europe
Copper + Betaine (102)
• Copper based formulation• Developed in Europe• Dark blue liquid
Target Loadings
• Zinc Borate: 1.0 % w/w
• All CuN formulations: 1.6 kg/m3 (0.10 pcf)
• Betaine: 32 kg/m3 (2 pcf)
• Copper + Betaine (102): 16 kg/m3 (1 pcf)
• Copper + Betaine(111): 8 kg/m3 (0.5 pcf)
Methods of Biocide Addition• As powder during blending: -Zinc Borate
-Powdered CuNap
• Mixed with adhesive: -Wb CuNap
• Vacuum impregnation (pretreatment): -Wb CuNap
• Mixed with emulsion wax:– Cu + Betaine (102)
– Cu + Betaine (111)
– Betaine
Control
Wb CuNap
Cu + Betaine (111)
(threshold)
Cu + Betaine (102)
Cu + Betaine
(111)
Betaine Zinc Borate
Powder CuNap
Vacuum Impregnated Wb CuNap
ControlZinc Borate
Vac Wb CuNapWb CuNapPowdered CuNap
BetaineCu + Betaine-111Cu + Betaine-102
Static Bending
• MOE, MOR, and Work to Max. Load calculated from three-point bending with center load (ASTM D1037)
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0MOE / 100,000 (psi)
R102
WbCuN
R111
Control
Betaine
P CuN
Vac WbCuN
ZB MOE
AB
AB
B
A
A
A
A
A
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
R102
R111
Control
WbCuN
Betaine
VacWbCuN
PCuN
ZB MOR
MOR / 1000 (psi)
A
A
AB
ABC
ABC
BC
CD
D
0.0 0.5 1.0 1.5 2.0 2.5Wml (in-lbf / in3)
R102
R111
Control
Betaine
WbCuN
Vac WbCuN
P CuN
ZB Work to Max. LoadC
BC
BC
BC
BC
AB
A
A
Bending Results• MOE: ZB significantly lower
• MOR: both powder systems significantly lower
• Wml: ZB significantly lower
• ZB shows greatest effects
Bending Results
• CuNap systems were equivalent• Betaine systems performed well (in
some cases better than controls, but not significantly).
• Betaine + Cu (102) showed the best performance.
Internal Bond
0 10 20 30 40 50 60psi
R111
Control
WbCuN
R102
Betaine
Vac WbCuN
P CuN
ZB Internal Bond
A
BC
AB
A
A
BC
D
C
Internal Bond Results
• Powdered systems inferior
• 3 systems met 50 psi minimum: Wb CuNap, Cu + Betaine (102), & Cu + Betaine (111).
Dimensional Stability• 2/24-hour water soak:
– Thickness swell– Linear expansion– Water absorption– Moisture content
Import Thickness swell chart
0 10 20 30 40 50 60 70 80 90 100% Increase
ZB
Betaine
P CuN
R102
WbCuN
R111
Control
V WbCuN
2 Hours24 Hours
Thickness SwellA
AB
ABC
ABC
ABC
BC
C
D
0 20 40 60 80 100 120% Weight Increase
ZB
Betaine
R102
P CuN
WbCuN
R111
Control
Vac WbCuN Water Absorption
2 Hours24 hours
A
B
A
AB
AB
AB
AB
C
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0% Increase
ZB
Betaine
P CuN
WbCuN
R102
VacWbCuN
R111
Control Linear Expansion
2 Hours
24 Hours
B
A
A
A
A
A
A
A
Physical properties: Results• Betaine and zinc borate gave poorest
performance
• Zinc borate specimens fell apart *
• Vacuum pretreated Wb CuNap had better performance than other CuNaps
• No improved performance by any biocide system, but no deleterious effects (excluding ZB & Betaine)
Conclusions• Zinc borate considerably worse than
other systems and controls *
• In most cases, all systems (except ZB) performed comparably with controls
• Powdered systems, overall had poorer performance than others.
Conclusions• Of Betaine systems, Cu + Betaine
biocides (102 & 111) performed better than Betaine only system
• Overall, CuNap systems as good as Cu + Betaine systems
• Of CuNap systems: Vacuum pretreated CuNap had better thickness swell than other CuNapsystems.
Future Research• Investigation of pyrethroids and
copper-boron systems
• Emulsion systems for powders
• Fungal decay resistance and termite resistance
• Leaching studies
Questions/Comments
