[Technical Field]
[0001] The present invention relates to a method of improving the sound-absorbing performance
of wood as a sound-absorbing material, and more particularly to a method of improving
the ability of wood to absorb sound waves incident in the fiber direction of the wood
in a given frequency range by delignifying it.
[0002] An object of the present invention is to provide a sound-absorbing board having sound-absorbing
properties superior to that of unmodified wood by chemically treating wood.
[Background Art]
[0003] Currently, glass fiber, rock wool, gypsum board and the like, which are used as internal
or external sound-absorbing materials, are frequently used as building materials,
because they have excellent sound-absorbing capacity and insulation properties. However,
when exposed in air during use, they will have a harmful effect on human health due
to dust, etc., so that their use has gradually been restricted. Also, these materials
have low intrinsic strength, and so require a supporting frame.
[0004] Wood, with the potential to replace non-eco-friendly materials, is a recyclable natural
material and has a beautiful appearance and good processability, as well as excellent
strength compared to other materials. However, wood resources in Korea mainly consist
of small-diameter logs, curved logs and the like, and thus, there is a need to maximize
the utility of the small-diameter logs or curved logs, having low added value.
[0005] The present inventor has delignified wood materials, using small-diameter logs or
curved logs, by chemical treatment, and discovered that delignification resulted in
substantial improvement in the sound-absorbing capacity of the wood materials thereby
completing the present invention.
[0006] Wood is a sound reflective material having a sound absorption of about 5% in a frequency
range that human beings mainly use during their life. Thus, there have been many creative
inventions to improve the sound-absorbing performance of wood. Korean Patent Application
No.
99-38842 (entitled "a sound-absorbing wood material and a preparation method thereof") filed
by the applicant discloses a wood board having improved sound-absorbing performance
and low density and, at the same time, requisite strength, which is prepared by a
method comprising the steps of: adding a synthetic resin adhesive to wood particles
in an amount of about 5-30% by weight and stirring the mixture; forming the stirred
mixture into a mat; placing the mat into a mold having a plurality of discharge holes
form in the circumferential surface thereof; interposing the mold between upper and
lower cowls each having a plurality of core pins, which have different diameters and
are arranged on the same axis; and pressing the upper and lower cowls, in which the
pressing step is performed at a temperature of about 140-240 °C and a pressure of
about 20-40 kg/cm 2 for at least 5 minutes. Also, Korean Patent Laid-Open Publication
No.
2003-30645 (entitled "a wood floor structure having a sound-absorbing elastic material") discloses
a wood floor structure comprising: a sound-absorbing elastic material having perforated
adhesive holes to be filled with an elasticity-reinforcing adhesive; and a wood floor
panel placed on the sound-absorbing elastic material after being filled with the elasticity-reinforcing
adhesive.
[0007] Because the above-published wood materials comprise, in addition to wood, a separate
material for improving sound-absorbing performance, these materials are difficult
to realize and do not meet the eco-friendly trend. For this reason, the present inventor
developed a method capable of improving the sound-absorbing performance of wood using
wood anatomical approach and based on his through study of wood structure, thereby
completing the present invention. The sound-absorbing performance will now be described
in order to fully understand the present invention.
[0008] The absorption of sound is a process for removing or reducing the energy of sound.
Sound absorption is achieved by contact with a sound-absorbing material having many
pores, or by the vibration of a thin plate disposed on the wall surface with an air
layer interposed therebetween, or by a sound-absorbing device including a single resonator.
Although the absorbance of sound by the porous material varies depending on the thickness
of the porous material, it shows an excellent effect in a wide frequency range, but
the porous material needs structural support. Also, the plate vibration shows good
sound absorbance only in low frequency range. In addition, the absorbance of sound
by the single resonator shows high sound-absorbing effects only in a narrow frequency
range.
[0009] Particularly, glass wool or rock wool is frequently used in buildings, owing to the
advantages of good insulation properties in addition to sound-absorbing effects, but
when exposed to air, during use, it can have a harmful effect on the human health
due to dust. Also, this material has poor strength, and thus requires a supporting
frame. Accordingly, the present inventor believes that there is a need to develop
new materials, which have suitable levels of sound-absorbing and insulation properties
and, at the same time, are not harmful to the humans, one of these materials being
a wood material.
[Disclosure]
[Technical Problem]
[0010] The main objective of the present invention is to provide an eco-friendly, sound-absorbing
material.
[0011] Another objective is to provide a method for improving the sound-absorbing properties
of wood by removing substances from wood cell walls through a wood anatomical approach.
[Technical Solution]
[0012] To achieve the above objects, the present invention provides a use of a deliguified
wood as a material with improved sound absorbance. The deliguified wood is obtained
by the following steps of processing normal wood into a wood disc; removing lignin
from the wood disc; and drying the delignified wood disc under reduced pressure.
[0013] The kind of tree from which the wood used in the present invention is to be obtained
is not specifically limited. Wood mainly consists of cellulose, hemicellulose and
lignin, in which the lignin to be removed according to the present invention is a
polymer having a molecular weight of more than 50,000 and including a phenylpropane-type
carbon framework deposited between the cellulose microfibrillar structures of wood.
Lignin accounts for 20-30% of the dry weight of wood.
[0014] The delignification step can be performed using a known method, such as the chlorine-monoethanolamine
method, comprising chlorinating the wood discs, which renders wood discs brighter,
or the peracetic acid method. It is preferable in the present invention to use the
sodium chlorite method for oxidizing, degrading and dissolving out the lignin.
[0015] In order to minimize cracking of wood, the delignified wood discs are dried under
reduced pressure conditions (pressure: 70-90 cmHg; and temperature: 30-50 °C) to a
water content of 10-15%, which results in fine cracks on the surface of the wood discs.
Although the present invention is described with respect to the improvement of sound-absorbing
performance only for the wood discs, the inventive idea of improving sound absorbance
by increasing the wood pores can likewise be applied to plywood, particle board and
fiber board. Hereinafter, the present invention will be described in detail with examples,
but it is to be noted that these examples are for illustrative purpose only and are
not construed to limit the scope of the present invention.
[Advantageous Effects]
[0016] According to the inventive method for improving the sound absorbance of wood, a sound
reflective wood material having a sound absorbance of about 5% can be significantly
improved with respect to sound-absorbing performance in a frequency of 2 KHz-4 KHz,
in which the human hearing sense is generally most sensitive. Also, rock wool, glass
fiber and the like, which have been used as sound-absorbing internal materials, can
be substituted with inexpensive wood. Furthermore, the sound-absorbing wood material
according to the present invention is eco-friendly, and so can be used without fear
of health hazard or damage to environment. In addition, the inventive material is
recyclable so that it is superior to other materials in the efficiency of resource
utilization, whereby it can contribute to the efficient utilization of resources and
to an increase in the value of wood products.
[Description of Drawings]
[0017]
FIG. 1 is a photograph showing the result of visual observation for a wood disc treated
with the inventive method of improving sound-absorbing properties.
FIG. 2 is an electron micrograph showing a portion of the cross section of the wood
disc shown in FIG. 1.
FIG. 3 shows the sound-absorbing properties of a wood disc treated with the inventive
method and an untreated wood disc. In FIG. 3, specimen 1 is a result for the wood
disc treated with the inventive method, and specimen 2 is a result for the untreated
wood disc.
[Mode for Invention]
Example
[0018] Larch wood was processed in the transverse direction (to a 100-mm diameter for a
middle and low frequency specimen and a 29.9-mm diameter for a high frequency range
specimen, and a 30-mm thickness), to prepare wood discs. Each of the wood discs was
degreased with a mixture of alcohol and benzene and kept in a water bath with 1.21
of water containing 8 g of sodium chlorite and 1.6 ml of glacial acetic acid at 80
°C for 120 hours. Each of the delignified wood discs was dried to a moisture content
of 12% in a vacuum dryer at a pressure of 76 cmHg and a temperature of 40 °C. Then,
the structural features of the cross-sectional surface of each of the wood discs was
observed and at the same time, the sound absorbance thereof was measured in a frequency
range of 50-6400 Hz. The sound absorbance was measured using a two-microphone tube
and pulse analyzer.
[0019] FIG. 1 is a photograph showing the result of visual observation for a wood disc treated
with the inventive method for improving sound-absorbing properties, and FIG. 2 is
an electron micrograph showing a portion of the cross section of the wood disc shown
in FIG. 1.
[0020] As can be seen in FIG. 1, pluralities of fine cracks are distributed on the surface
of the disc after treatment according to the present invention. This indicates that,
on the surface having weak strength due to delignification, small splits were generated
even under reduced-pressure drying conditions, which cause low drying stress. As can
be seen from the electron micrograph of FIG. 1, intracellular substances between the
wood cell walls were dissolved and removed. As a result of this microstructural change,
the surface of the wood disc according to the present invention feels soft compared
to untreated conventional wood discs. Also, because the portion between the wood cell
walls, which has a high content of lignin, showing an elastic behavior in wood, was
removed, the wood has an increased porosity leading to a reduced reflectivity to sound
waves, thus showing improved sound-absorbing properties.
[0021] FIG. 3 shows the sound-absorbing properties of a wood disc treated with the inventive
method and an untreated wood disc. As shown in FIG. 3, the wood disc according to
the present invention showed improved sound-absorbing performance over the entire
measured frequency range, compared to the untreated wood disc. In a high frequency
range of more than 1 KHz, the difference in sound-absorbing performance between the
two wood discs was increased more, and in a frequency range around 4 KHz, the inventive
wood disc showed a 30% higher sound absorbance than that of the untreated wood disc.
In addition, in frequency ranges around 2 KHz and 6 KHz, the inventive wood disc was
almost twice as high in sound absorbance as the untreated disc.
1. Verwendung von delignifiziertem Holz als einen Stoff mit verbessertem Schallabsorbtionsgrad.
2. Verwendung gemäß Anspruch 1,
dadurch gekennzeichnet, dass
man das delignifizierte Holz durch die folgenden Schritte erhält: Verarbeitung von
normalem Holz zu einer Holzscheibe;
Entfernen von Lignin aus der Holzscheibe; und
Trocknen der delignifizierten Holzscheibe bei vermindertem Druck.
3. Verwendung gemäß Anspruch 1,
dadurch gekennzeichnet, dass
der Schritt der Ligninentfernung durch die Verwendung von Natriumchlorit ausgeführt
wird.
4. Verwendung gemäß Anspruch 2 oder 3,
dadurch gekennzeichnet, dass
vor der Delignifizierung der Schritt der Entfettung der Holzscheibe mit einem Gemisch
aus Alkohol und Benzol enthalten ist.
5. Verwendung gemäß einem der Ansprüche 1 bis 4,
dadurch gekennzeichnet, dass
der Stoff eine schallabsorbierende Platte ist.
1. Utilisation d'un bois délignifié en tant que matériau présentant une insonorisation
accrue.
2. Utilisation selon la revendication 1,
caractérisée par le fait que le bois délignifié est obtenu par les étapes suivantes consistant à :
- traiter du bois normal pour obtenir un disque de bois ;
- éliminer la lignine du disque de bois ; et
- sécher le disque de bois délignifié sous pression réduite.
3. Utilisation selon la revendication 1, caractérisée par le fait que l'étape d'élimination de la lignine est réalisée à l'aide de chlorite de sodium.
4. Utilisation selon l'une des revendications 2 ou 3, caractérisée par le fait qu'elle comprend l'étape de dégraissage du disque de bois par un mélange d'alcool et
de benzène avant la délignification.
5. Utilisation selon l'une quelconque des revendications 1 à 4, caractérisée par le fait que le matériau est un panneau insonorisant.