Volumen II - SAM

and then tested for evaluation of mechanical properties. Compression tests were performed in a Instron 1137
(Illinois, USA) machine in the direction perpendicular to moulding.
Tensile strength determination of individual WW and compression tests of WWCB were both made under
controlled room conditions at 23 ºC and at 50 % of relative humidity.
3. RESULTS AND DISCUSSION
All WW treatments demonstrated a good performance for avoiding setting inhibition. However, they have
induced changes on mechanical properties of WW and WWCB. Table 2 shows the experimental average T
MOE of treated WW; and the experimental C MOE and CS for WWCB produced with treated WW.
In general, non-treated WW presented an average T MOE of about 1200 MPa. T MOE of treated samples
resulted significantly increased depending on test conditions. Average T MOE resulted about 1600 MPa for
extraction, 1800 MPa for hydrolysis and 2100 MPa for coating treatment (see Tables 1 and 2).
The maximum and minimum T MOE measured in 300 total specimens per treatment, were 7890-186 MPa
for extraction, 7287-268 MPa for hydrolysis and 7174-203 MPa for coating. In addition, the difference
between maximum and minimum T MOE measured within one sample of 30 specimens corresponding to a
given test condition, could be as high as 7419 MPa for extraction, 6660 MPa for hydrolysis and 6971 MPa
for coating treatment. As observed, highly dispersed values were obtained in T MOE determinations.
Therefore, a very high number of specimens had to be tested in order to get reliable information about the
influence of the process variables on mechanical properties of WW.
The normal dispersion on T MOE measurements was 13 % for extraction, 19 % for hydrolysis and 18 % for
coating treatment. Therefore, T MOE could be considered as affected by a given process parameter when its
influence resulted higher than the cited values. Based on this assumption, the increase of the H2O/W ratio
during extraction, the decrease of the immersion time during hydrolysis and the increase of CA concentration
during coating treatment could be considered as responsible for the T MOE increase. The rest of the
variables could not be taking into account since their effects were within the normal dispersion range.
Nº
Table 2. Experimental T MOE for WW, C MOE and CS for WWCB.
Extraction Hydrolysis Coating
T MOE C MOE CS T MOE C MOE CS T MOE C MOE CS
(MPa) (MPa) (MPa) (MPa) (MPa) (MPa) (MPa) (MPa) (MPa)
1 1120 1.03 0.11 2329 0.98 0.07 2488 0.89 0.09
2 1579 0.82 0.07 1945 0.98 0.07 2320 1.09 0.10
3 1311 1.09 0.10 1458 1.40 0.11 1883 0.70 0.06
4 1563 0.61 0.08 1684 0.75 0.07 2203 0.65 0.08
5 1808 1.31 0.10 1683 1.15 0.08 2357 1.09 0.13
6 1617 0.89 0.10 1981 1.09 0.09 1608 1.31 0.15
7 2135 1.23 0.10 1484 0.89 0.06 1637 0.89 0.08
8 1908 0.93 0.11 1828 1.03 0.10 1674 0.61 0.09
9 1692 0.98 0.11 1892 1.09 0.12 2322 0.70 0.07
10 1206 1.09 0.11 1339 1.23 0.11 2591 0.52 0.09
Additional information about the influence of the studied variables on treated WW, could be get from
compressive tests of WWCB. In this case, hundreds of wood strands were cement-bonded and formed a new
whole and more uniform material. The WW strands were then tested simultaneously contributing to a more
accurate determination of mechanical properties.
In general, CS of WWCB obtained with WW treated by extraction and coating was, in both cases, higher
than those obtained with WW treated by hydrolysis. This observation suggests a decrease of WW
mechanical properties caused by the aggressive alkaline medium which promotes disaggregation and
breaking of wood constitutive fibers. Extraction and coating treatments have not affected significantly the
integrity of wood strands, preserving their mechanical properties. Figures 1 to 3 present the model
functionality of C MOE with the corresponding treatment variables.
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