Page 18 - InnoRenew CoE International Conference 2023
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e behaviour of thermo-hydro-mechanical (THM) densified poplar
Ulises Rojas-Alva¹*, Nataša Knez², Lei Han3,4, Marica Mikuljan4, Andreja Kutnar3,4
1 Department for Fire-safe Sustainable Built Environment (FRISSBE), ZAG (Slovenian National Building and Civil Engineering Institute);
Obrtna cona Logatec 35, SI-1370 Logatec, Slovenia; ulises.rojas-alva@zag.si, grunde.jomaas@zag.si
2 Slovenian National Building and Civil Engineering Institute; Dimičeva 12, Ljubljana, Slovenia; natasa.knez@zag.si
3 Faculty of Mathematics, Natural Sciences and Information Technologies, University of Primorska, Glagoljaška 8, 6000 Koper, Slovenia;
lei.han@innorenew.eu, andreja.kutnar@innorenew.eu
4 InnoRenew CoE, Livade 6a, 6310 Izola, Slovenia; marica.mikuljan@innorenew.eu
* Corresponding author
Thermo-hydro-mechanical (THM) densification, which involves a combination of heat, moisture, and compressive
force in the transverse direction of the wood, is a method of increasing the density and thereby improving the
mechanical properties in the first place of fast-grown low-density wood species (Sandberg et al., 2021). However,
as with all cellulose products aimed at the built environment, the fire performance of the densified wood products
needs to be characterized. Therefore, cone calorimeter experiments, following the ISO 5660-1 standard (ISO,
2015), were carried out for a range of densified samples of Black poplar (Populus spp.) to investigate its fire
behaviour. Densification was performed by THM treatment in open system press at 170oC-200oC. Time to
ignition, critical heat flux, pyrolysis properties derived from thermogravimetric analysis, and the heat release
rate (HRR) were determined during the testing campaign. The test on poplar had five groups (1) unmodified
specimens, (2) THM-densified specimens (densified from 20 to 10 mm), (3) THM-densified specimens (densified
from 15 to 10 mm) (4) phenol-formaldehyde resin-impregnated and THM-densified specimens (densified from
20 to 10 mm), (5) phenol-formaldehyde resin-impregnated and THM-densified specimens (densified from 15 to
10 mm). The preliminary results showed that the time to ignition was increased 5 times after resin impregnation
(when exposed to 35 kW/m² heat flux), whereas the influence on time to ignition from densification alone is
weak-dependent. The heat release rate (HRR) of poplar was slightly decreased by densification, but the peak
HRR increased somewhat by densification. For the untreated poplar sample, the critical heat flux is around 16
kW/m2, while the densification increased the critical heat flux of poplar to 18 kW/m2. The poplar samples after
resin impregnation and densification achieved the highest critical heat flux at around 22 kW/m2. All in all, resin
impregnated and THM treated poplar are significantly less ignitable than untreated poplar.
Keywords: wood densification, time to ignition, heat release rate, black poplar, critical heat flux
Acknowledgement: The authors gratefully acknowledge receiving funding from ARRS and FWF, PROJECT
CODE: J4-3087
REFERENCES
ISO. (2015). ISO 5660-1:2015 Reaction-to-fire tests -- Heat release, smoke production and mass loss rate -- Part 1:
Heat release rate (cone calorimeter method) and smoke production rate (dynamic measurement).
Sandberg, D., Kutnar, A., Karlsson, O., & Jones, D. (2021). Wood Modification Technologies: Principles, Sustainability, and
the Need for Innovation. CRC Press.
18 1 3 – 1 4 S E PT E M B E R 2 0 2 3 I I Z O L A , S LOVE N I A
Ulises Rojas-Alva¹*, Nataša Knez², Lei Han3,4, Marica Mikuljan4, Andreja Kutnar3,4
1 Department for Fire-safe Sustainable Built Environment (FRISSBE), ZAG (Slovenian National Building and Civil Engineering Institute);
Obrtna cona Logatec 35, SI-1370 Logatec, Slovenia; ulises.rojas-alva@zag.si, grunde.jomaas@zag.si
2 Slovenian National Building and Civil Engineering Institute; Dimičeva 12, Ljubljana, Slovenia; natasa.knez@zag.si
3 Faculty of Mathematics, Natural Sciences and Information Technologies, University of Primorska, Glagoljaška 8, 6000 Koper, Slovenia;
lei.han@innorenew.eu, andreja.kutnar@innorenew.eu
4 InnoRenew CoE, Livade 6a, 6310 Izola, Slovenia; marica.mikuljan@innorenew.eu
* Corresponding author
Thermo-hydro-mechanical (THM) densification, which involves a combination of heat, moisture, and compressive
force in the transverse direction of the wood, is a method of increasing the density and thereby improving the
mechanical properties in the first place of fast-grown low-density wood species (Sandberg et al., 2021). However,
as with all cellulose products aimed at the built environment, the fire performance of the densified wood products
needs to be characterized. Therefore, cone calorimeter experiments, following the ISO 5660-1 standard (ISO,
2015), were carried out for a range of densified samples of Black poplar (Populus spp.) to investigate its fire
behaviour. Densification was performed by THM treatment in open system press at 170oC-200oC. Time to
ignition, critical heat flux, pyrolysis properties derived from thermogravimetric analysis, and the heat release
rate (HRR) were determined during the testing campaign. The test on poplar had five groups (1) unmodified
specimens, (2) THM-densified specimens (densified from 20 to 10 mm), (3) THM-densified specimens (densified
from 15 to 10 mm) (4) phenol-formaldehyde resin-impregnated and THM-densified specimens (densified from
20 to 10 mm), (5) phenol-formaldehyde resin-impregnated and THM-densified specimens (densified from 15 to
10 mm). The preliminary results showed that the time to ignition was increased 5 times after resin impregnation
(when exposed to 35 kW/m² heat flux), whereas the influence on time to ignition from densification alone is
weak-dependent. The heat release rate (HRR) of poplar was slightly decreased by densification, but the peak
HRR increased somewhat by densification. For the untreated poplar sample, the critical heat flux is around 16
kW/m2, while the densification increased the critical heat flux of poplar to 18 kW/m2. The poplar samples after
resin impregnation and densification achieved the highest critical heat flux at around 22 kW/m2. All in all, resin
impregnated and THM treated poplar are significantly less ignitable than untreated poplar.
Keywords: wood densification, time to ignition, heat release rate, black poplar, critical heat flux
Acknowledgement: The authors gratefully acknowledge receiving funding from ARRS and FWF, PROJECT
CODE: J4-3087
REFERENCES
ISO. (2015). ISO 5660-1:2015 Reaction-to-fire tests -- Heat release, smoke production and mass loss rate -- Part 1:
Heat release rate (cone calorimeter method) and smoke production rate (dynamic measurement).
Sandberg, D., Kutnar, A., Karlsson, O., & Jones, D. (2021). Wood Modification Technologies: Principles, Sustainability, and
the Need for Innovation. CRC Press.
18 1 3 – 1 4 S E PT E M B E R 2 0 2 3 I I Z O L A , S LOVE N I A
