Effect of extractives on vibrational properties of African Padauk (Pterocarpus soyauxii Taub.)

Abstract

Extractives can affect vibrational properties tan1 (damping coefficient) and E'/2 (specific Young's modulus) but this is highly dependent on species, compounds, and cellular locations. This paper investigates such effects for African Padauk (Pterocarpus soyauxii Taub.), a tropical hardwood with high extractives content and a preferred material for xylophones. 5 groups of 26 heartwood specimens with large, yet comparable, ranges in vibrational properties were extracted in different solvents. Changes in vibrational properties were set against yields of extracts and evaluation of their cellular location. Methanol (ME) reached most of compounds (13%), located about half in lumen and half in cell-wall. Water solubility was extremely low. tan1 and E'/2 were very strongly related (R 2 30.93), but native wood had abnormally low values of tan1, while extraction shifted this relation towards higher tan1 values. ME extracted heartwood became in agreement with the average of many species, and close to sapwood. Extractions increased tan1 as much as 60%, irrespective of minute moisture changes or of initial properties. Apparent E'/2 was barely changed (+2% to -4%) but, after correcting the mass contribution of extracts, was in fact slightly reduced (down to -10% for high E'/2), and increasingly so for specimens with low initial values of E'/2.

Radial variations of vibrational properties of three tropical woods

“…Therefore, we assume that extractives are responsible for the variations of viscoelastic properties between our specimens. The influence of extractives on damping coefficient was also revealed by other researchers Obataya et al, 2000;Brémaud et al, 2010a;Minato et al, 2010), by changing the extractive content either through extraction or impregnation.…”

“…A "standard relation" was established to describe the statistical relation between these properties (Ono and Norimoto, 1983), based on more than 1000 specimens taken from 20 softwood species. The validity of this relation has also been shown on hardwood species (Brémaud et al, 2010a). Recently, using selective extractions, Brémaud et al (Brémaud et al, 2010a;Brémaud et al, 2010b) showed that wood extractives modified this "standard relation" by changing the intercept of the line, not its slope.…”

“…The validity of this relation has also been shown on hardwood species (Brémaud et al, 2010a). Recently, using selective extractions, Brémaud et al (Brémaud et al, 2010a;Brémaud et al, 2010b) showed that wood extractives modified this "standard relation" by changing the intercept of the line, not its slope.…”

“…On the other hand, the intercept, which indicates how far the actual tanδ deviates from the MFA-prediction part, reflects the influence of chemistry, the extractives in our case. Proof can be found from the study of Brémaud et al (2010a), who performed extraction on African Padauk wood and compared the vibrational properties before and after the extraction. It turned out that only the intercept changed while the slope was identical.…”

“…These secondary constituents are determinant for some wood properties, such as color and durability. Additionally, they have been shown to influence wood viscoelastic behavior Brémaud et al, 2010a;Brémaud et al, 2010c;Minato et al, 2010), although this effect differs from case to case: some extractives induce a strong decrease of the damping coefficient, while some other slightly increase it (Obataya et al, 1999), and some have limited effect (Sakai et al, 1999).…”