Volumen II - SAM

inhibitory water soluble sugars, while alkaline hydrolysis degrades hemicelluloses and sugars to noninhibitory
substances. In the retention treatment, a coating is formed on the wood surface and inhibitory
substances are not released to the setting medium. On the other hand, it has been proved that the nature of the
extractives also has an influence on this inhibitory effect [11]. In general, the grade of setting inhibition
depends on the amount and type of sugars. For example, fructose does not affect cement setting up to
concentrations of 0.50 %, while glucose inhibits completely this process with concentrations of 0.25 %.
Conversely, wood treatments have the disadvantage that they can diminish in some cases the final
mechanical properties of resulting materials. Another very used strategy is the addition of inorganic
chemicals, known as accelerators, in order to accelerate the curing of the cement [10,12]. Cement chemicals
accelerators usually improve the properties of WCB [11].
In the present contribution, the influence of different wood treatments is evaluated on mechanical properties
of wood wool (WW) and final wood wool-cement boards (WWCB). Water conventional extraction,
degradation by alkaline hydrolysis and retention of inhibitory substances were selected as technological
strategies. Tensile tests of individual WW and compression tests of WWCB were performed for evaluation
of the mechanical behaviour. Resulting data were analyzed using experimental designs based on response
surface methods. Tensile elasticity modulus (T MOE) of WW, compressive elasticity modulus (C MOE) and
compressive strength (CS) of WWCB, were evaluated for a precise selection of the most convenient wood
treatment to be applied to the full scale process in future trials.
2. EXPERIMENTAL PROCEDURE
Wood wool of Populus X Euroamericana CV, provided from residues of local wood industry, was treated
according to three different methods as mentioned above: water extraction, alkaline hydrolysis and retention
of inhibitory substances by coating. In the first method, the WW was immersed into a water bath at 25, 62.5
and 100ºC during 5, 25 and 45 min. In the second method, alkaline hydrolysis was performed at room
temperature immersing WW into a calcium hydroxide solution during 4, 24 and 72 h with concentrations
between 5.6 and 22.2 g/l. In the last method, an organic polymer (acrylic styrene) was used as a coating
agent (CA) to form a film on the WW surface and thus, inhibiting the pass of undesirable substances to the
setting medium. Water-wood (H2O/W) ratios were 20, 30 and 40 g/g for extraction and hydrolysis methods.
For each treatment, ten different samples were prepared according to a combination of the cited variables.
This was based on experimental design methods. All the test conditions are summarized in Table 1.
Individual wood strands were then tested in an Instron 3344 (USA) machine for T MOE determination.
Thirty specimens per condition, ten conditions per treatment and three different treatments totalized 900 T
MOE measurements. Treated wood strands were compared against non-treated samples.
Nº
Table 1. Experimental conditions for wood treatments.
Extraction Hydrolysis Coating
H2O/W T t [Ca(OH)2] t H2O/W [CA] t Uses
(g/g) (ºC) (min) (g/l) (h) (g/g) (l/l) (min) (nº)
1 20 25 5 22.2 4 20 0,333 5 1
2 20 25 45 22.2 4 40 0,333 5 2
3 20 100 5 22.2 72 20 0,333 180 1
4 20 100 45 22.2 72 40 0,333 180 2
5 40 25 5 5.6 4 20 0,083 5 1
6 40 25 45 5.6 4 40 0,083 5 2
7 40 100 5 5.6 72 20 0,083 180 1
8 40 100 45 5.6 72 40 0,083 180 2
9 30 62.5 25 11.1 24 30 0,167 60 1
10 30 62.5 25 11.1 24 30 0,167 60 2
In a second step, thirty laboratory boards were obtained using the WW treated according to Table 1.
Preliminary trials were first done to adjust the cement paste composition using commercially available
Portland. The cement paste was then mixed with the WW and placed into a mould during 72 h to obtain
WWCB of 30x30x7 cm 3 after cement setting. After moulding, the samples were cut in cubes of 7 cm side,
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