4.6 M EASURING SURFACE WETTABILITY
5.1.1 Influence of raw material, type of adhesive and climatic conditions on the surface
5.1.1.1 Influence of raw material and climatic conditions on the surface roughness of uncoated
For all uncoated UF-bonded particleboards (PB) the equilibrium moisture content (E.M.C.) was measured after storage under different climatic conditions (20°C / 30 % relative humidity (r.h.), 20°C / 65 % relative humidity and 20°C / 85 % relative humidity). The results are shown in Figure 19.
Figure 19: Equilibrium moisture content (E.M.C.) (%) of uncoated UF-bonded particleboards, made using with different raw materials in the surface layers (fresh particles, recycled particles and cork particles) after storage under different climatic conditions (20°C / 30% relative humidity, 20°C / 65%
relative humidity and 20°C / 85% relative humidity)
As can be seen from Figure 19 the moisture content of all UF-bonded particleboards increased with increasing relative humidity irrespective of the lignocellulosic raw material used in the manufacture of the boards. UF-bonded particleboards made with fresh and recycled particles in the surface layers showed more or less the same rise in moisture content with increasing relative humidity during storage.
For UF-bonded particleboards made with fresh and recycled particles the equilibrium moisture content after storage at 20°C / 30 % r.h. was 5.6 %. After storage at 20°C / 65 % r.h.
the moisture content of both types of boards increased to 8.7 % (UF-bonded PB with fresh particles) and 8.3 % (UF-bonded PB with recycled particles) respectively. The highest moisture contents (12.3 % and 12.2 %) were reached, when the particleboards were stored under a climate of 85 % relative humidity. Boards with recycled chips in the surface showed slightly lower equilibrium moisture content.
The equilibrium moisture content of the uncoated UF-bonded particleboards with cork particles in the surface layer was lower than that of UF-particleboards made with fresh and recycled particles. The equilibrium moisture content of uncoated UF-bonded PB with cork
8.7
12.3
5.6 8.3
12.2
4.1 7.5
10.7
5.6
0 5 10 15 20
20 / 30 20 / 65 20 / 85 20 / 30 20 / 65 20 / 85 20 / 30 20 / 65 20 / 85 Climate conditions [temperature (°C) / relative humidity (%)]
Moisture content after storage under different climate conditions [%]
Fresh particles Recycling particles Cork particles
particles in the surface layer increased with increasing relative humidity from 4.1 % E.M.C.
(20°C / 30% r.h.) over 7.5 % E.M.C. (20°C / 65% r.h.) to 10.7 % E.M.C. (20°C / 85% r.h.).
Figure 20 shows an individual measurement of a roughness profile of an uncoated UF-bonded particleboard, made using fresh particles in the surface layer after reaching equilibrium moisture content (8.7 %) at climate 20°C / 65% relative humidity (variant 1). The profile gives information which describes the surface characteristics, e.g., average roughness (Ra), the mean peak-to-valley height (Rz), maximum-peak-to-valley height (Rmax). The measured profile parameters help in the interpretation of the surfaces. In case of this work Ra was chosen as the main parameter to describe the surfaces.
PB-Measurement-no.: 124 Ra 5.5 µm Rz 33.2 µm Rmax 50.7 µm
Figure 20: Individual measurement of a roughness profile of a uncoated UF-bonded particleboard, made using fresh particles in the surface layer after reaching equilibrium moisture content (8.7 %) at climate 20°C / 65% relative humidity (variant 1)
In Figure 21 the influence of the raw material and the moisture content on the roughness of UF-bonded particleboards is presented. Figure 21 shows on the one hand that UF-bonded particleboards with recycled particles are of higher roughness irrespective of the moisture content (Ra = 10.5 µm at 20ºC / 65% r.h.) in comparison to fresh particles (Ra = 5.5 µm at 20ºC / 65% r.h). On the other hand UF-bonded PB with cork particles on surface layers do have the smoothest surfaces (Ra = 2.7 µm at 20ºC / 65% r.h.).
Moreover, Figure 21 shows the general influence of different climatic conditions on the roughness of UF-bonded particleboards. Independent of the raw material used the roughness of UF-bonded particleboards increased with increasing moisture content. The Ra-value increased with raising relative humidity in the region of 30% r.h. over 65% r.h. to 85% r.h.
from 4.3 µm over 5.5 µm to 5.7 µm. In case of recycled particles Ra increased in the same region from 10.5 µm up to 12 µm.
GS R-Profil
VER 10,00 µm/Skt LC 0,80 mm
As the results indicate cork particles showed a quite different behaviour; there was no detectable increase in the roughness of the boards due to increase in the moisture content of the boards.
Figure 21: Average roughness Ra (µm) of uncoated UF-bonded particleboards, made using different raw materials in the surface layers (fresh particles, recycled particles and cork particles) after storage under different climatic conditions (20°C / 30% relative humidity, 20°C / 65% relative humidity and 20°C / 85% relative humidity)
5.1.1.2 Influence of raw material and climatic conditions on the surface roughness of uncoated TF-bonded particleboards as assessed by the contact method
For all uncoated TF-bonded particleboards (PB) the equilibrium moisture content was measured after storage under different climatic conditions (20°C / 30 % r.h., 20°C / 65 % r.h.
and 20°C / 85 % r.h.). It can be seen from Figure 22 that the moisture content of all TF-bonded particleboards increased with higher relative humidity irrespective of the lignocellulosic raw material used for making the boards. TF-bonded particleboards made with fresh and recycled particles in the surface layers showed more or less the same rise in moisture content with increasing relative humidity during storage. For TF-bonded particleboards made with fresh and recycled particles the equilibrium moisture content after
4.3
5.5 5.7
10.5 10.5 12.8
3.9
2.7 2.8
0 5 10 15 20
5.6 8.7 12.3 5.6 8.3 12.2 4.1 7.5 10.7
Moisture content (%) after storage under different climate conditions
Average roughness Ra [µm]
Fresh particles Recycling particles Cork particles
storage at 20°C / 30 % r.h. was about 6.3 %. After storage at 20°C / 65 % r.h. moisture content of both types of boards went higher to 10 %. The highest moisture contents (14.5 % and 14.7 %) were reached, when the particleboards were stored under a climate of 85 % relative humidity.
Figure 22: Equilibrium moisture content (E.M.C.) (%) of uncoated TF-bonded particleboards, made using different raw materials in the surface layers (fresh particles, recycled particles and cork particles) after storage under different climatic conditions (20°C / 30% relative humidity, 20°C / 65%
relative humidity and 20°C / 85% relative humidity)
The equilibrium moisture content of the uncoated TF-bonded particleboards with cork particles in the surface layer was compared to TF-particleboards made with fresh and recycled particles in general on a lower level. The equilibrium moisture content of uncoated TF-bonded PB with cork particles in the surface layer increased during storage of the boards under higher humidity from 5.2 % E.M.C. (20°C / 30 % r.h.) over 8.1 % E.M.C. (20°C / 65 % r.h.) to 12.8 % E.M.C. (20°C / 85 % r.h.).
Figure 23 shows an individual measurement of a roughness profile of an uncoated TF-bonded particleboard, made using fresh particles in the surface layer after reaching equilibrium moisture content (10.0 %) at climate 20°C / 65% relative humidity (variant 2).
6.1
10.0 14.5
6.3
10.0 14.7
5.2 8.1
12.8
0 5 10 15 20
20 / 30 20 / 65 20 / 85 20 / 30 20 / 65 20 / 85 20 / 30 20 / 65 20 / 85 Climate conditions [temperature (°C) / relative humidity (%)]
Moisture content after storage under different climate conditions [%]
Fresh particles Recycling particles Cork particles
PB-Measurement-no.: 224 Ra 5.7 µm Rz 31.8 µm Rmax 45.2 µm
Figure 23: Individual measurement of a roughness profile of an uncoated TF-bonded particleboard, made using fresh particles in the surface layer after reaching equilibrium moisture content (10.0 %) at climate 20°C / 65% relative humidity (variant 2)
Figure 24 shows the influence of the raw material on the roughness of bonded PB. TF-bonded PB with recycled particles showed the highest roughness of the surface (Ra = 7.8 µm at 20ºC / 65% r.h.) in comparison with TF-bonded PB with fresh particles (Ra = 6.0 µm at 20ºC / 65% r.h.). On the other hand TF-bonded PB with cork in the surface layers are comparatively of smooth surfaces (Ra = 3.7 µm at 20ºC / 65% r.h.).
Figure 24 also shows that changes in climatic conditions impacts the roughness of the particleboards differently. The roughness value Ra of TF-bonded particleboards with recycled particles increased due to increase in the moisture content. In case of TF-bonded particleboards made from fresh chips and those with cork particles in the surface no increase in roughness was found, on the contrary the Ra-values decreased slightly when the moisture content of the boards increased.
GS R-Profil
VER 10,00 µm/Skt LC 0,80 mm
Figure 24: Average roughness Ra (µm) of uncoated TF-bonded particleboards, made using different raw materials in the surface layers (fresh particles, recycled particles and cork particles) after storage under different climatic conditions (20°C / 30% relative humidity, 20°C / 65% relative humidity and 20°C / 85% relative humidity)
5.1.1.3 Influence of raw material and climatic conditions on the surface roughness of uncoated UF- and TF-bonded particleboards as assessed by the contact method In the Figures 25 and 26 the results are summarized. As can be seen from Figure 25, in general, an increase in the equilibrium moisture content of the boards was measured, when the relative humidity increased from 30% r.h. over 65% r.h. to 85% r.h. Moreover, the influence of the type of adhesive on the moisture content of the manufactured particleboards was also obvious. TF-bonded PB showed higher equilibrium moisture content compared to UF-bonded PB.
As can be seen from Figure 26 particleboards made with recycled particles in the surface layer had the roughest surfaces (average roughness (Ra)) irrespective of the adhesive used.
6.5 6.0
4.3
5.6
7.8 7.5
4.8
3.7 4.5
0 5 10 15 20
6.1 10.0 14.5 6.3 10.0 14.7 5.2 8.1 12.8
Moisture content (%) after storage under different climate conditions
Average roughness Ra [µm] Fresh particles Recycling particles Cork particles
5.6
Moisture content after storage under different climate conditions [%]
Figure 25: Equilibrium moisture content (E.M.C.) (%) of uncoated UF- and TF-bonded particleboards, made using different raw materials in the surface layers (fresh particles, recycled particles and cork particles) after storage under different climatic conditions (20°C / 30% relative humidity, 20°C / 65% relative humidity and 20°C / 85% relative humidity)
4.3 5.5 5.7
Figure 26: Average roughness Ra (µm) of uncoated UF- and TF-bonded particleboards, made using different raw materials in the surface layers (fresh particles, recycled particles and cork particles) after storage under different climatic conditions (20°C / 30% relative humidity, 20°C / 65% relative humidity and 20°C / 85% relative humidity)