session 13 ic2011 bonigut

Bonigut, KrugForest Products Society 65th International Convention Portland, OR, June 2011

Properties of thermally modified oriented strandboards (OSB)

Juergen Bonigut, Dr. Detlef KrugInstitute of Wood Technology Dresden, Dresden, Germany


Outline

1. Current situation2. Research goals3. Material and method4. Selected results5. Summary


Current situation - TMT

Thermal modification of solid wood is at the centre of R & DDegree of modification depends on the parameters

temperature

ambient pressure

oxygen content

duration of modification


Advantages

reduced moisture uptake

increased biological durability

improved dimensional stability by reducing swelling and shrinking

Disadvantages

decreased density

reduced physical properties

increased brittleness

forming of cracks, halos (softwoods)

Current situation - TMT


Current situation - PF WBM

Phenol formaldehyde resin bonded wood-based materials:

industry: storage of PF-bonded wbm in a (hot-) stack

during hot-stacking further and complete adhesive curing takes place due to high temperatures of panels right after hot-press

results in enhanced mechanical strength properties and improved hygroscopic properties


OSB production

logs / solid wood stranding strands resination forming hot-pressingOSB panels


logs / solid wood stranding strands resination forming hot-pressingOSB panels

Treatment types


logs / solid wood stranding strands resination hot-pressingOSB panels

Treatment types


Goals

Thermal post-treatment of PF-bonded oriented strandboards (OSB)

reduction of equilibrium moisture content (EMC),

reduction of thickness swelling,

improvement of internal bond strength (IB) after 2 h boiling,

reduction of creep behaviour.

Exploratory investigations with MUF-bonded SWP and PF-bonded MDF showed promising results


Material

PF-bonded industrial OSB

type: OSB/3 (acc. to EN 300)

density: 620 kg/m3 (38.7 lbs/cu.ft),

thickness: 16 mm (0.63 in.),

adhesive content: 7 % PF (solids/oven-dry wood)

content hydrophobing agent: 1.5 % paraffin (solids/oven-dry wood)


Thermal post-treatment

Post-treatment of OSB took place according to Mühlböck- procedure in a partner company‘s treatment chamber

Heating up and cooling down of the chamber: 3 min/KMaximum temperatures:

160 °C (320 F)

170 °C (338 F)

180 °C (356 F)

Holding time: 4 h


In analogy to thermally modified solid wood (TMT), OSB showed darker colouration over whole cross-section

Thermal post-treatment


Testing of properties

Short-term properties

IB (dry & 2 h boiling) (EN 300, EN 319),

MOR & MOE (EN 310),

TS (EN 317),

WA,

EMC (EN 323).

Long-term property

creep behaviour testing climate: 20 °C (68 F) / 85 % humidity


IB

Requirements for load-bearing boards for use in humid conditions (type OSB/3) according to EN 300: 0.32 MPa and 0.13 Mpa, respectively


MOR & MOE (main axis)

Requirements for load-bearing boards for use in humid conditions (type OSB/3) according to EN 300 (main axis): 20 MPa (MOR) and 3,500 MPA (MOE), respect.


TS

Requirements for load-bearing boards for use in humid conditions (type OSB/3) according to EN 300: max. 15 % after 24 h immersion in water


WA


EMC

Climate: 20 °C (68 F) / 65 % humidity


Creep behaviour

Creep factor describes relation between time-dependent increase of deflection under load and elastic initial deflection

Tested in accordance with ENV 1156

Wood-based panels – Determination of duration of load and creep factors


Creep behaviour

Creep behaviour is dependent on:

duration

stress level

climate

Duration of testing: 105 days

Stress level: 25 % of Fmax

Test climate: 20 °C (68 F) / 85 % humidity


Creep behaviour


Summary

Influence of thermal post-treatment on PF-bonded OSB

Property strongly positive

slightly positive

hardly / minor

slightly negative

strongly negative

IB (dry & after 2h boiling)

X

MOR & MOE X TS & WA (2 h & 24 h) X

EMC X creep behaviour X


Summary

Conclusion: by thermally post-treating PF-bonded OSB very positive effects could be shown, i. e. improvemements of most physical properties

Research into thermal post-treatment of wbm will be continued


[email protected]