EP3398189B1 - Device for improving the acoustic properties of spruce tone wood - Google Patents

Description

Technical area

The invention relates to a method for improving the acoustic properties of spruce tonewood for musical instruments.

State of the art

Sound wood for musical instruments (so-called resonance wood) should be as light as possible, but at the same time have a high modulus of elasticity (modulus of elasticity or Young's modulus) and a high speed of sound. It should also be free of knots and have narrow, homogeneous tree rings and a low proportion of latewood (<20%). Only a few, carefully selected wood assortments meet these strict quality criteria.

Musical instruments built during the late 17th and early 18th centuries have much better quality characteristics than contemporary instruments. One of the hypotheses to explain this difference attributes the special wood quality of these instruments to the climate situation known as the Maunder minimum, which prevailed between 1645 and 1715 and in which the longer winters and cooler summers evidently resulted in a slower and more uniform wood formation and thus a lower proportion of latewood , The famous violin maker Antonio Stradivari used in the last decades of his work (the so-called "golden era") mainly spruce wood of trees that had grown during the Maunder minimum. These instruments have long been regarded as a sound ideal that has only rarely been achieved again.

The (acoustic) material quality of sound wood is generally defined by the quotient c / p, where c is the speed of sound and p is the density of the sound wood (Ono & Norimoto, 1983; 1984; Spycher, 2008; Spycher et al., 2008; 4). The speed of sound is the square root of the ratio of modulus of elasticity (for bending longitudinally to the fiber) to density. The modulus of elasticity is a material-independent material value; the product of modulus of elasticity and area moment of inertia gives the flexural rigidity of the workpiece (Ono & Norimoto, 1983; 1984; Spycher, 2008; Spycher et al., 2008). The speed of sound, eg of spruce wood, in the longitudinal direction is 4800 to 6200 m / s, the average bulk density 320 to 420 kg / m ³ . Both parameters, like many other wood properties, are dependent on the moisture content of the wood, which increases the precision and infrastructure requirements for the experiments as well as the evaluation of the test results. Of particular interest in all measures to improve material quality is the impact relative changes in modulus and bulk density have on the speed of sound. If, in a certain measure, the modulus of elasticity (in%) changes approximately in proportion to the change in the bulk density (in%), the speed of sound remains approximately the same (the material quality then increases approximately inversely proportional to a reduction in the apparent density); such a ratio of relative changes in modulus of elasticity and bulk density is said to be "narrow" (Ono & Norimoto, 1983; 1984; Spycher, 2008; Spycher et al., 2008). On the other hand, if the modulus of elasticity (in%) decreases significantly less than the bulk density (in%), the speed of sound is increased (the quality of the material increases more than inversely proportional to a reduction in bulk density). Such a ratio of relative changes in modulus of elasticity and bulk density is termed "wide" or "large" and is highly desirable for achieving high material quality of tonewood (Schleske, 1998; Wegst, 2006). However, sound wood with a broad modulus of bulk density is rare in nature and therefore expensive (Bond, 1976, Bucur, 2006).

Various methods have been tried to improve the acoustic properties of tone wood. In particular, in the EP 1734504 A1 proposed to suspend the tonewood during a limited treatment time of the action of a wood-decomposing fungus species. In this case, the type of fungus and the duration of treatment should be chosen such that, on the one hand, an increase in the ratio of the speed of sound of the wood to the gross density of the wood is achieved and, on the other hand, the predetermined minimum strength values of the sound wood are not undershot. As fungus species Asco and Basidiomycetes from the family of Leotiaceae, Polyporaceae, Schizophyllaceae, Trichlomataceae and Xylariaceae were used. To perform the method, a feedboard method was used in which the sound wood to be treated is placed between two fungi of the same size.

As a result, extensive investigations revealed that one compared to the method EP 1734504 A1 more pronounced improvement of the acoustic properties of tonewood would be desirable. In particular, it was found that none of the proposed species of fungus is able to increase the damping factor of the sound wood. An increase in the damping factor while improving the quality of the acoustic material reduces the high tones of the instrument, which often sound painful to the listener.

In this regard, it has surprisingly been found that treatment with Physisporinus vitreus achieves an improvement in the above-mentioned acoustic material quality values while increasing the attenuation factor , thus achieving an overall improvement in the acoustic properties ( Black, FWMR, Spycher, M., Fink, S. (2008) Superior wood for violin - wood decay fungi a substitute for cold climate. New Phytologist 179, 1095-1104 ).

A disadvantage of the methods described so far is that a uniform colonization of the wood can not be guaranteed by the selected mushrooms. An irregular settlement has the consequence that the acoustic material quality is improved only inconsistently or even not at all. In addition, it entails the risk of undesirable strength losses, cracks and crevices in the wood. In addition, it has been found that Physisporinus vitreus has low levels of competition against other species of fungi and is therefore very susceptible to contamination by other species.

The article Lehringer, C. et al. (2010) Anatomy of bioincised Norway spruce wood. International Biodeterioration & Biodegradation , describes a similar process whereby the soundwood blank is immersed in a water-sawdust-mushroom-mycelium emulsion.

In the article Fuhr, MJ et al. (2012) Automated quantification of the impact of the wood-decay fungus Physisporinus vitreus on the cell wall structure of Norway spruce by tomographic microscopy. Wood Sci Technol 46,769-779 A method for the automatic visualization and quantification of microscopic cell wall elements of spruce wood is described, which is also able to show the changes caused by Physisporinus vitreus .

The WO2012 / 056109 A2 describes the use of plant-derived nanofibrillated cellulose in the form of a hydrogel or a membrane as a carrier material for various types of cell cultures.

Presentation of the invention

The object of the invention is to provide an improved method for the production of spruce sound wood for musical instruments, which ensures in particular an improvement in the acoustic properties, a shorter process time and a more homogeneous product. Other objects of the invention are to provide an improved sound wood for musical instruments, as well as musical instruments made thereof.

These objects are achieved according to the invention by the method specified in claim 1.

According to the invention, in order to improve the acoustic properties of spruce tonewood for musical instruments, a wood tone blank is subjected to Physisporin vitreus treatment under controlled, sterile conditions. In this case, the previously sterilized soundwood blank is dipped in a liquid medium enriched with fungus mycelium and kept therein with exclusion of light during a contact time and finally sterilized. The liquid medium contains nanofibrillated cellulose (NFC) in a proportion of 200 to 300 g per liter. "Controlled, sterile conditions" in the present context means an environment in which at least the temperature and the relative humidity are kept within a predefined range and contamination with foreign fungal species is prevented. According to the invention, a temperature of 18 to 26 ° C and a relative humidity of about 60 to about 80% are set.

The initial sterilization and subsequent treatment with Physisporinus vitreus under sterile conditions in a suitable incubation container ensures that the process is not affected by contamination. With the final sterilization the effect of Physisporinus vitreus is stopped in a controlled way. The fact that the liquid medium contains nanofibrillated cellulose (NFC) in a proportion of 200 to 300 g per liter, a significantly improved efficiency of the process is achieved, which thus runs much faster and more homogeneous.

The measures according to the invention ensure a reproducible, uniform improvement of the acoustic properties of the sound wood that is free from local defects.

As a sound wood blank is generally a plate-shaped portion of a suitable sound wood to understand, which is intended in particular for the production of the ceiling or the bottom of a string or plucked instrument. In the present context, it is without exception spruce wood.

As incubation container for the process control under sterile conditions, a closable medium-tight container made of sterilizable materials, for example, from an autoclavable plastic is generally suitable. Furthermore, the container must be equipped so that inside a controlled atmosphere of predetermined humidity is adjustable. For the controlled supply of air at least one designed with a sterile microfilter valve is provided.

A liquid medium enriched with fungal mycelium is understood in a manner known per se to be a buffered aqueous solution with nutrients, which has been mixed with mycelium samples of a pure culture of Physisporinus vitreus and then grown for a suitable time.

According to the invention, the liquid medium contains a proportion of 200 to 300 g of nanofibrillated cellulose (NFC) per liter of liquid medium. As used herein, the term "nanofibrillated cellulose", also abbreviated "NFC", includes cellulose fibers having a diameter of about 3 nm to about 200 nm and a length of at least 500 nm and an aspect ratio (length: diameter) of at least 100 μm understand. Typically, the NFC fibers have a diameter of 10 to 100 nm, an average of 50 nm and a length of at least a few microns, and the aspect ratio may also be 1,000 or more. NFC is generally obtained by a mechanical comminution process of wood and other vegetable fibers; first descriptions go to Herrick et al. ( Herrick, FW; Casebier, RL; Hamilton, JK; Sandberg, KR Microfibrillated cellulose: Morphology and accessibility. J. Appl. Polym. Sci. Appl. Polym. Symp. 1983, 37, 797-813 ) as well as Turback et al. ( Turbak, AF; Snyder, FW; Sandberg, KR Microfibrillated cellulose, a new cellulose product: Properties, uses, and commercial potential. J. Appl. Polym. Sci. Appl. Polym. Symp. 1983, 37, 815-827 ) in 1983. The new material was initially called microfibrillated cellulose (MFC). Today, however, besides the term MFC, different terms such as cellulose nanofibers (CNF), nanofibrillated cellulose (NFC) and cellulose nano- or microfibrils are commonly used. It is a semi-crystalline cellulosic material made of cellulosic fibers with a high aspect ratio (= ratio of length to diameter), lower degree of polymerization compared with intact plant fibers and correspondingly increased surface area, which is obtained for example by a homogenization or grinding process ( Andresen, M .; Johansson, LS; Tanem, BS; Stenius, P. Properties and characterization of hydrophobized microfibrillated cellulose. Cellulose 2006, 13, 665-677 ). In contrast to the straightforward "cellulose whiskers", which are also referred to as "cellulose nanocrystals" and have a rod-shaped shape with a length of usually 100 to 500 nm (depending on the cellulose source, there are also up to 1 micron long crystals) , cellulose nanofibers are long and flexible. The NFC formed therefrom usually contains crystalline and amorphous domains and has a network structure due to strong hydrogen bonds (see eg Lu, J .; Askeland, P .; Drzal, LT Surface modification of microfibrillated cellulose for epoxy composite applications. Polymer 2008, 49, 1285-1298 ; Zimmermann, T .; Pöhler, E .; Geiger, T. Cellulose fibrils for polymer reinforcement. Adv. Eng. Mat. 2004, 6, 754-761 . Iwamoto, S .; Kai, W .; Isogai, A .; Iwata, T. Elastic modulus of single cellulose microfibrils from tunicate measured by atomic force microscopy. Biomacromolecules 2009, 10, 2571-2576 ).

It goes without saying that the method according to the invention can in principle be carried out with a single sound wood blank. As a rule, however, for the sake of efficiency alone, several chopped wood blanks are treated simultaneously. For this purpose, the incubation container is expediently equipped with corresponding recesses and support elements. Conveniently, the method can be carried out in particular with two sound wood blanks, which together form a cover for a violin.

Preferred embodiments of the method are defined in the dependent claims.

Advantageously, the treatment with Physisporinus vitreus EMPA 642 performed (claim 2).

Advantageously, during the exposure time a temperature of about 22 ° C, in particular in the range of 21 ° C to 23 ° C, and a relative humidity of about 70%, in particular in the range of 65 to about 75% set (claim 3).

• Modul für Biegung längs zur Faser mindestens 7 GPa, vorzugsweise mindestens 10 GPa;
• Druckfestigkeit längs zur Faser mindestens 24 N/mm², vorzugsweise mindestens 34 N/mm²; und
• Druckfestigkeit quer zur Faser mindestens 3 N/mm², vorzugsweise mindestens 4.2 N/mm².

In the implementation of the method, the exposure time is preferably selected such that the following strength values of the sound wood are met (claim 4):

• Module for bending longitudinally to the fiber at least 7 GPa, preferably at least 10 GPa;
• Compressive strength along the fiber at least 24 N / mm ² , preferably at least 34 N / mm ² ; and
• Compressive strength across the fiber at least 3 N / mm ² , preferably at least 4.2 N / mm ² .

The measures according to the invention make it possible to produce tonewood having outstanding properties using a comparatively short exposure time of 4 to 6 months (claim 5).

The liquid medium used for the process according to the invention is preferably obtained by incubation of an NFC-containing nutrient medium inoculated with Physisporinus vitreus under controlled pH conditions (claim 6). Advantageously, an aqueous nutrient medium with spruce wood extract and nanofibrillated cellulose is initially introduced and inoculated with a mushroom-containing liquid medium culture or with mushroom-covered sawdust particles.

The sterilization of the sound wood blank to be carried out after the exposure time of several months can in principle be carried out in a known manner. Preferably, ethylene oxide is used for this purpose (claim 7).

As a result of the inventive method, there is an increase in the color index of the treated chopped wood blanks. Preferably, the color space (L *, a *, b *) defined color index E * increased by at least 14 (claim 8). In addition, a change in color of the wood is advantageously effected, which is characterized by a defined in the color space (L *, a *, b *) color difference .DELTA.E * of at least 11 (claim 9).

The spruce sounding wood for musical instruments produced by the method according to the invention is characterized in that the sound radiation in the longitudinal direction is increased by at least 20%, preferably by at least 24%, compared to untreated sound wood and the attenuation in the longitudinal direction by at least 25%, preferably by at least 29% is increased. As is generally the case with wood, a distinction is also made in this case between longitudinal, radial and tangential directions. The longitudinal direction corresponds to the direction of tree growth, while the radial and tangential directions refer to the approximately circular tree rings. When Klangholz the properties in the longitudinal direction for its acoustic properties, especially for the sound of a violin, are particularly important.

An advantageous musical instrument, in particular a stringed instrument, can be constructed with at least one soundboard made from tonewood which has been improved according to the invention. In the present context, "musical instrument" is to be understood in the widest sense; In particular, such resonant plates can also be used for wooden membranes in loudspeakers.

Brief description of the drawings

Fig. 1

gelelektrophoretische Auftrennung der RAPD-Fragmente unter Verwendung des Primers 08/9328; die Proben sind mit Untersuchunsgnummern gekennzeichnet (Tabelle 1), die Negativkontrolle (kein Templat-DNA) ist mit N bezeichnet; als DNA-Molekulargewichtsmarker wurde eine 100bp-Leiter (M) verwendet;

Fig. 2

Massenverluste in Holzproben nach 12-monatiger Inkubationszeit mit Physisporinus vitreus: Rohdichte ρ_R (Balken) und Massenverlust Δm (Linie mit Quadraten) für drei verschiedene Holzarten;

Fig. 3

(a) Beispiel für die Relaxation der Spannung (Stress) σ im Holz in Abhängigkeit von der Zeit; (b) Aufnahme einer Holzprobe vor und nach der Mikro-Biegebelastung;

Fig. 4

Spannungsrelaxation in Abhängigkeit zur Verformung unter Last in frisch geschlagenem Holz (Kontrolle), in pilzbehandeltem Fichtenholz und in alten Holzproben (Testore, Rougemont);

Fig. 5

Zunahme der Klangabstrahlung in longitudinaler Richtung in Holzproben nach 12-monatiger Inkubationszeit mit Physisporinus vitreus;

Fig. 6

Zunahme der Dämpfung in longitudinaler Richtung in Holzproben nach 12-monatiger Inkubationszeit mit Physisporinus vitreus;

Fig. 7

Veränderung der Gesamtfarbe (grün) und der Helligkeit (grau) von Klangholz (a) und Bauholz (b) nach unterschiedlicher Dauer (4-12 Monate) der Pilzbehandlung oder Lagerzeit; (c) frischgeschlagenes Holz (oben), 12 Monate pilzbehandelte Proben(mitte), alte Holzproben aus Rougemont (unten);

Fig. 8

Farbabstand ΔE* von Klangholz (offene Kreise) und Bauholz (gefüllte Kreise) nach unterschiedlicher Dauer (4-12 Monate) der Pilzbehandlung gegenüber dem unbehandelten Zustand; die gestrichelte Linie zeigt den Farbabstand einer alten Holzprobe (Rougemont) gegenüber einer frischgeschnittenen Probe derselben Holzart; und

Fig. 9

Qualitativer Vergleich der FT-IR Spektralabsorption für unbehandeltes Holz (Kontrolle), 12 Monate pilzbehandeltes Holz und altes Holz (Testore und Rougemont) bei verschiedenen Wellenzahlen. Bei einer Wellenzahl von 1508 und 1738 cm^-1 wurden Spitzenwerte gemessen (gestrichelte Linien).

Exemplary embodiments of the invention will be described in greater detail below with reference to the drawings, in which:

Fig. 1

gel electrophoretic separation of the RAPD fragments using primer 08/9328; the samples are labeled with assay numbers (Table 1), the negative control (no template DNA) is designated N; the DNA molecular weight marker used was a 100 bp ladder (M);

Fig. 2

Mass losses in wood specimens after 12 months of incubation with Physisporinus vitreus: bulk density ρ _R (bars) and mass loss Δm (line with squares) for three different species of wood;

Fig. 3

(a) Example of relaxation of stress (stress) σ in wood as a function of time; (b) taking a wood sample before and after the microbending load;

Fig. 4

Stress relaxation as a function of deformation under load in freshly felled wood (control), in mushroom treated spruce and in old wood samples (Testore, Rougemont);

Fig. 5

Increase in sound radiation in the longitudinal direction in wood specimens after 12 months incubation period with Physisporinus vitreus;

Fig. 6

Increase in attenuation in longitudinal direction in wood specimens after 12 months incubation with Physisporinus vitreus;

Fig. 7

Change in the overall color (green) and brightness (gray) of tone wood (a) and lumber (b) after different duration (4-12 months) of fungal treatment or storage time; (c) freshly cut wood (top), 12 months mushroom treated samples (middle), old wood samples from Rougemont (bottom);

Fig. 8

Color difference ΔE * of sound wood (open circles) and timber (filled circles) after different duration (4-12 months) of the fungus treatment compared to the untreated condition; the dashed line shows the color difference of an old wood sample (Rougemont) compared to a freshly cut sample of the same type of wood; and

Fig. 9

Qualitative comparison of FT-IR spectral absorption for untreated wood (control), 12 months of fungal treated wood and old wood (Testore and Rougemont) at different wavenumbers. At a wave number of 1508 and 1738 cm ^-1 peak values were measured (dashed lines).

Ways to carry out the invention Molecular biological fungal determination

For the molecular determination of Physisporinus vitreus , a clone-specific primer was designed and synthesized. As a result, a sensitivity of 10 ^-5 can be achieved in a real-time polymerase chain reaction (real-time PCR, real-time PCR). The detection of P. vitreus by the use of species-specific primers in combination with fungal DNA extraction techniques directly from wood is greatly simplified, since in the implementation of the identification a normal standard PCR followed by gel electrophoresis is sufficient. The time required for this process lasts a few hours and is therefore significantly faster and more effective compared with the conventional method, because it can be dispensed with the production of pure cultures. In addition, the risk of foreign contamination during the sampling is significantly minimized by the use of the specific primer pair.

In order to detect the presence and penetration depth of P. vitreus , small samples were taken from the interior of the wood under sterile conditions and transferred to nutrient media using the conventional method. Subsequently, the samples were incubated in the climate chamber for several days and examined for mycelial growth of the fungus. The determinants were macroscopic and microscopic characteristics of the mycelium. This procedure takes several days to weeks and involves risks of foreign contamination, which make (re) identification of P vitreus more difficult. As an alternative to this time-consuming process, molecular biology methods developed in the 1980s for the characterization of fungi can be used (Schmidt and Moreth, 2006).

To meet the above-mentioned quality criteria for a reliable identification method, strain-specific primers were constructed for the clear detection of the fungus P. vitreus . Table 1 lists the types of fungi used in these studies. DNA extraction for the molecular biological studies was carried out using the Extract-N-Amp ™ Plant PCR Kit from Sigma Aldrich according to the manufacturer's instructions. Table 1: Fungus species used mushrooms Isolate no. origin 1 Physisporinus lineatus CBS 701.94 Centraalbeureau voor Schimmelcultures 2 Physisporinus ulmarius CBS 186.60 Centraalbeureau voor Schimmelcultures 3 Physisporinus laetus CBS 101079 Centraalbeureau voor Schimmelcultures 4 Physisporinus sanguilentum CBS 193.76 Centraalbeureau voor Schimmelcultures 5 Physisporinus vinctus CBS 153.84 Centraalbeureau voor Schimmelcultures 6 Physisporinus rigidus CBS 160.64 Centraalbeureau voor Schimmelcultures 7 Physisporin vitreus EMPA 642 BFH Hamburg 8 Physisporin vitreus EMPA 643 Albert-Ludwigs-University Freiburg 9 Physisporin vitreus EMPA 674 BFH Hamburg 10 Physisporin vitreus EMPA 675 BFH Hamburg 11 Physisporin vitreus EMPA 676 Centraalbeureau voor Schimmelcultures

In the first step, RAPD (Randomly Amplified Polymorphic DNA) PCR was performed for strain differentiation of the fungi used. By using very short oligonucleotide primers, specific DNA band patterns are generated by PCR in this method and used for differentiation. These are some of the most common methods to perform a quick kinship analysis and to identify different isolates of a species (Schmidt and Moreth, 1998, Schmidt and Moreth, 2006). In total, DNA samples from 11 species of fungi (Table 1) were amplified with 10 random 10-mer primers, and the electrophoretically separated band patterns were evaluated ( Fig. 1 ).

For the development of a specific primer pair for P. vitreus, first the ITS 1 / ITS 4 primer combination of White et al. (1990) amplified the ITS1-5,8S-ITS2 region of the fungal species used with a thermocycler from the company Biometra. Target region of the primers used was the ribosomal DNA (rDNA). It consists, inter alia, of coding gene segments 18S, 5.8S and 28S rRNA (in fungi and other eukaryotes) that are conservative (Schmidt and Moreth, 2006). These three coding gene segments are separated by highly variable introns, the Internal Transcribed Spacers (ITS1 and ITS2).

The resulting PCR products were then commercially purified and sequenced (Synergene, Zurich). The sequence of the ITS region of P. vitreus 642 has been deposited in the international database EMBL (Accession No. FM202494). Due to the nature of the specificity of the ITS domain, the sequence of P. vitreus 642 was used to study using the Clustal X program and the Basic Local Alignment Search Tool (Primer-BLAST) of the National Center for Biotechnology Information (NCBI, http: // www.ncbi.nlm.nih.gov/tools/primer-blast/) to isolate short DNA sequences (20 bases), which occur exclusively in the fungus P. vitreus. These short DNA sequences were synthesized (Microsynth) and used as a P. vitreus-specific primer pair. Thus, P. vitreus is no longer distinguished solely by a band pattern, but by a species-specific PCR, in which only DNA of P. vitreus, for which the primer pair was constructed, allowing the generation of a PCR product of 426 base pairs. The evaluation or differentiation is unambiguous since it only gives either a positive or a negative result (Schmidt and Moreth, 2000, Schmidt and Moreth, 2006).

Deposit of biological material

A sample of the above-mentioned strain Physisporinus vitreus EMPA 642 has been successfully deposited with the Centraalbureau voor Schimmelcultures Fungal Biodiversity Center (CBS-KNAW), a recognized depository (International Depository Authority (IDA)) under the Budapest Treaty since 1981. The stored material has been assigned the accession number FM202494.

Examples 1. Mushroom pre-cultivation

For fungal cultivation, Physisporinus vitreus (EMPA strain No. 642 or 643) was pre-cultivated on a suitable, sterile malt agar medium in Petri dishes (Ø 9 cm). As soon as the culture medium was completely overgrown by the fungus mycelium of P. vitreus (after approx. 12-16 days), approx. 2g of sterile spruce sawdust (particle size <2mm) was placed in the middle of the medium in each Petri dish under sterile conditions. After a further 4 to 6 weeks, the sawdust substrate, completely mixed by P. vitreus, was used to inoculate the liquid medium.

1.1 nutrient composition

• Malt extract 40g / liter
• Agar (pure) 25g / liter

1.2 Incubation conditions

22 ° C and 70 ± 5% rel. Humidity (in the dark)

1.3 Preparation of liquid medium

A nanofibrillated cellulosic nutrient medium has proved to be a particularly suitable liquid medium for the cultivation of P. vitreus on the basis of preliminary experiments.

2. Nutrient medium composition

• 300 g Nano-fibrillierte Cellulose / Liter
• 5.0 g Malzextrakt / Liter
• 7.1 g KCl / Liter

¹⁾ Fichtenholzextrakt (ca. 200g Fichteholzsägemehl in 1 Liter Leitungswasser während 30 Minuten ausgekocht; 24 Std bei Raumtemperatur stehen gelassen und abfiltriert)In tap water with 10% spruce wood extract ¹⁾ :

• 300 g of nano-fibrillated cellulose / liter
• 5.0 g malt extract / liter
• 7.1 g KCl / liter

¹⁾ spruce wood extract (about 200g spruce sawdust in 1 liter of tap water boiled for 30 minutes, allowed to stand at room temperature for 24 hours and filtered off)

2.1 Inoculation of the liquid medium

1200 ml nanofibrillated cellulose-containing liquid medium was sterilized in a steam autoclave for 20-30 minutes at 121 ° C and with about 100 ml mushroom-containing (not more than 8 weeks old) liquid medium culture (with the same composition) or in the inoculation of a liquid medium with first culture fresh mushroom-covered sawdust particles (about 1 - 2 g) as described in paragraph 2 with P. vitreus inoculated.

2.2 incubation

The nanofibrillated cellulose-containing liquid medium was incubated under sterile conditions with P. vitreus in a bioreactor under controlled pH conditions (pH adjusted to 6.8 - 7.2 or optionally under controlled oxygen supply). The speed of the agitator was set low. Alternatively, the culture medium can also be used as a standing or shaking culture in suitable Erlenmeyer flasks with cotton stoppers on a horizontal shaker (50 rpm) for 4 to 8 weeks in a climatic chamber in the dark at 22 ° C. and 70 ± 5% rel. Humidity can be produced.

3. Mushroom treatment of spruce wood

The introduction of the mushroom-containing liquid medium and the actual exposure time or fungus treatment of the spruce (violin ceiling boards made of spruce wood) was carried out under sterile conditions in a specially prepared incubator.

3.1 Structure of the incubator

The incubator consists of a heat-resistant plastic container (PPC) with internal dimensions of 554 mm x 354 mm x 141 mm (source: WEZ Kunststoffwerk AG, CH-5036 Oberentfelden, item no. 6413.007) and a matching, modified lid with sight glass. In this incubator were two in their dimensions and shape of the treated sound wood blanks (violet corners) adapted stainless steel treatment tanks and fitting recessed holders (Auflagervorrichtungen), each with a corresponding filler pipe with 3 to 4 outlet openings, which within the incubator with a hose system ( made of heat-resistant material) and an inlet valve are connected. With this construction, the mushroom-containing liquid medium can be filled into the incubator under sterile conditions.

3.2 Preparations before introducing the liquid medium

The two tonewood blanks to be treated (for a violin corner) are placed in the appropriate support devices in stainless steel treatment tanks. The total amount of the mushroom-containing liquid medium required later for filling can be reduced by optionally filling a few glass beads as placeholders (volume displacer) in the lower area of the treatment tank.

The filling hoses were connected to the filling valves within the incubator container.

The incubator was tightly closed with the lids (with sight glass) and the entire container including the sound wood blanks placed therein under low heat, e.g. Sterilized with ionizing radiation.

3.3 Introduction of the mushroom-containing liquid medium

The incubator previously sterilized and equipped with the sound wood blanks (violin corners) to be treated under sterile conditions was subjected to a 10% negative pressure (approx. 100 mbar). Due to the negative pressure in the incubator, the mushroom-containing liquid medium can be supplied via the filling tube into the treatment container with the sound wood blanks under sterile conditions via the previously likewise sterilized plastic tubes and valves, which are directly connected to the bioreactor or a shaking culture.

As soon as the sound wood blanks (covered by the sight glass in the lid) are evenly covered by a layer of mushroom-containing liquid medium approx. 5 to 10 mm thick, the supply line was stopped and the supply hoses emptied. The incubator was then vented to normal pressure with a sterile microfiltered valve and incubated as a whole for the intended fungal treatment (exposure time) in a suitable air conditioning cabin.

3.4 Incubation of freshly beaten, fungus-treated and old spruce wood samples

Twins samples with dimensions of 12 x 2.5 x 150 mm (Radial x Tangential x Longitudinal) taken from a red spruce ( Picea abies L.). The tree was felled in autumn 2009 in the Sufers region. The gross density of the wood was 370 kg / m ³ with a relative wood moisture content of 65%. The wood samples had narrow annual rings and the sound wood could be assigned to the quality grading 'master fine'. Some wood samples were used as untreated controls, the others were incubated in the dark at 22 ° C and 70% relative humidity with P. vitreus . For comparative studies, old wood samples were taken from a cello (built in 1700, violin maker Catenes) and a beam from a historic house in Rougemont (dated 1756, Switzerland), which was used for the construction of a cello. At a relative humidity of 65%, the bulk density of the wood samples from Testore and Rougemont was 410 and 456 kg / m ³ . In addition, twin samples of small and wide-ringed wood were examined before and after fungal treatment. In addition, samples of wide and narrow wood were made.

Of all the wood specimens, specimens with a cutting thickness of 0.06 mm, 15 mm long and 1.5 mm wide were prepared with a rotation microscope before and after the treatment. The incubator with the wood samples surrounded therein by the fungus-containing, nanofibrillated cellulose-containing liquid medium was incubated for the required exposure time (fungus treatment) in a suitable air conditioning cabin at 22 ° C. (and 70 ± 5% relative humidity). F.) for 12 months. In the interval of 2 to 4 weeks, fresh, oxygen-rich air was supplied under sterile conditions through the valve with the sterile microfilter. After a 12-month incubation period, the wood samples were cleaned and then sterilized with ethylene oxide. From each sample variant, a minimum of 5 replicates were tested in a micromechanical instrument to determine stress relaxation. Subsequently, the samples were analyzed by Fourier Transform Infrared Spectrometer (FT-IR) and Dynamic Water Vapor Sorption (DVS).

4. Removal and aftertreatment of the modified wood

After the fungus treatment, the incubator is opened. The fungus-treated wood samples lying in the treatment tank were removed from the nanofibrillated cellulosic liquid medium completely grown by the fungus mycelium and carefully (with a metal spatula) carefully cleaned of superficially adherent mycelium.

4.1 Drying of spruce wood after fungus treatment

The freshly picked, mushroom-modified wood chippings (violin corners) have a relatively high water content of z.T. more than 150 to 250% and then have to be dried gently to avoid cracking (ring peeling).

For this purpose, the spruce boards store only in a climatic chamber (20 ° C) and 80% rel. Moisture (possibly previously in a container with a xylene-containing atmosphere to prevent mold growth) and are then over a period of several weeks gradually in a climatic chamber at 65% and later at 50% rel. Damp dried down.

4.2 Sterilization of the fungus-treated wood chippings

After drying and before processing the fungus-modified wood chippings for instrument making, these can optionally be sterilized with ionizing radiation (under low heat).

5. Mass losses in mushroom-treated wood

The bulk density ρ _{R of} the different wood samples before and after the fungal treatment is in Fig. 2 seen. The average mass loss Δm of the fungus-treated wood samples was 3.3% ± 0.9%. From the Fig. 2 It can be seen that with decreasing bulk density of the wood lower mass losses were recorded. In the high-quality sound wood (low bulk density) the highest, in the inferior wood (high bulk density), the lowest mass losses were recorded.

6. Stress relaxation in mushroom treated wood

wobei σ ₀ die Initialspannung und σ_t die Spannung nach 120 Sekunden Relaxation ist.Micromechanical investigations were carried out under bending load according to Burgert et al (2003). The thickness of the wood samples was determined in the middle and on the sides of the samples with a micrometer vernier caliper. Width and length (~10 mm) were measured under the transmitted light brightfield microscope. The samples were loaded with a maximum load of 50 N and the experiments were carried out at a speed of 1 μm / s ( Fig. 3 ). At certain load levels, the motor was turned off for 120 seconds to measure the stress relaxation. The relative stress relaxation was calculated as follows: $$\frac{{\sigma }_0-{\mathrm{<figure-callout\; id="0"\; label="\sigma \; t\; \sigma "\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">\sigma \; </figure-callout>}}_t}{{\sigma }_{}}$$

where σ _{0 is} the initial stress and σ _{t is} the stress after 120 seconds of relaxation.

In Fig. 4 The stress relaxation of freshly beaten (control), fungus-treated and old wood is compared. The stress relaxation was calculated from the reduction between the initial and the effective tension after 2 minutes. Although a certain scatter of the measured data was recorded (determination index: R = 0.6-0.82), it is clear that the fungus-treated wood has a higher stress relaxation than freshly cut wood.

The time-dependent mechanical behavior of a material, such as stress relaxation, allows conclusions to be drawn about the size and reorientation of important cell elements at different temporal and spatial levels (Cosgrove 1993). In the micromechanical stress relaxation tests, a gradual reduction was observed, presumably due to the reorientation of various cell wall components in the wood is due. We suspect that there is a reorientation of the wood fibers interconnected by the middle lamella, the delay being due to the incorporation of the cellulosic fibrils into the amorphous matrix of hemicellulose and lignin. The differences in the relaxation behavior between freshly cut wood, wood treated with fungus and old wood suggest that the material is degraded at the submicroscopic level, which is primarily due to the degradation of lignin and hemicelluose. This results in stress relaxation in the wood (Köhler et al, 2002, Sedighi Gilani and Navi 2007). The degradation of the cell wall matrix (hemicellulose and lignin) around the embedded cellulose fibrils in turn has an influence on the vibration properties or changes the damping properties of the wood (Noguchi et al., 2012).

7. Sound emission and attenuation

The most important acoustic properties that are used for the selection of sound wood for musical instruments are the damping (tanδ) and the sound radiation (R). High-quality sound wood has a high sound radiation (R). R describes how strongly the vibrations of a body are damped due to the sound radiation. The attenuation of sound, on the other hand, refers to any kind of reduction of the sound intensity that does not necessarily have to do with a reduction of the sound energy, for example by divergence, ie by distributing the sound energy over a larger area. Both properties were examined on untreated controls and on fungal treated wood. The vibration characteristics of wood samples were measured before and after fungal treatment (as described under 5.4) at a relative moisture content of 65%. The results show that both the sound radiation and the attenuation in the fungus-treated wood increase significantly ( Fig. 5-6 ).

8. Color measurements

Wobei L* die Helligkeit von 0 (schwarz) bis 100 (weiss) definiert während a* das Verhältnis von rot (+60) zu grün (-60) und b* das Verhältnis von gelb (+60) zu blau (-60) angeben.The color measurements were made on wood samples with a tristimulus colorimeter (Konica Minolta) at wavelengths between 360-740 nm. The device allows the non-contact measurement of brightness and color at a measuring angle of 1 °. The color coordinates were determined for fungus-treated and freshly beaten wood and the color index was calculated as follows: $${\mathrm{e}}^{*}=\sqrt{{\left({\mathrm{L}}^{*}\right)}^2+{\left({\mathrm{a}}^{*}\right)}^2+{\left({\mathrm{b}}^{*}\right)}^2}$$

Where L * defines the brightness from 0 (black) to 100 (white) while a * defines the ratio of red (+60) to green (-60) and b * the ratio of yellow (+60) to blue (-60) specify.

Out Fig. 7 For example, the color index E * _ab and the brightness L * for freshly felled and mushroom treated tone wood (a) and lumber (b) can be taken after 4 to 12 months. As the duration of the fungal treatment increases, the color index increases while the brightness decreases. In the original state, an E * index of 29.9 (± 0.8) was found for freshly sounded wood (a) and lumber (b) ( Fig. 7a-b ). After a 12-month fungal treatment, an increase in the E * index of 44.5 (± 1.2) for mushroom-treated Fig. 7a ) and of 41.6 (± 0.6) for mushroom treated timber ( Fig. 7b ).

From an aesthetic point of view, a high color index (E *) is advantageous in violin making, since the wood has an older color appearance after the fungus treatment. Comparative studies with color measurements on old wood samples (Rougemont from 1756, Switzerland) gave a color index E * = 37.2 and a brightness index L * = 73.7.

However, the color changes of interest here are usually described not only by changing the value of E *, which by definition is the length of a vector in the color space spanned by L *, a * and b * Change vector ΔE *, which connects the color point (L ₀ *, a ₀ *, b ₀ *) before color change with the color point (L ₁ *, a ₁ *, b ₁ *) after color change: $${\mathrm{AE}}^{*}=\sqrt{{\left({\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">L</figure-callout>}}_1^{*}-{\mathrm{<figure-callout\; id="0"\; label="L"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">L</figure-callout>}}_0^{*}\right)}^2+{\left({\mathrm{a}}_1^{*}-{\mathrm{a}}_0^{*}\right)}^2+{\left({\mathrm{<figure-callout\; id="1"\; label="b"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">b</figure-callout>}}_1^{*}-{\mathrm{<figure-callout\; id="0"\; label="b"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">b</figure-callout>}}_0^{*}\right)}^2}$$

The size ΔE * is also called the color difference. In the Fig. 8 the time course of the color difference ΔE * of sound wood (open circles) and lumber (filled circles) after different duration (4-12 months) of the fungus treatment compared to the untreated state is shown. For comparison, the dashed line is the color difference an old wood sample (Rougemont) compared to a freshly cut sample of the same wood species shown.

9. FT-IR analyzes

In Fig. 9 The FT-IR spectra of fungal treated wood, freshly cut wood and old wood (Testore and Rougemont) are shown in the 1800-800 cm ^-1 region with absorption at 1508 cm ^-1 , which depends on the aromatic ring vibration (C = C) was derived from lignin, normalized. In the old wood, there is a significant increase in the lignin polysaccharide ratio at 1738 cm ^-1 wavenumber due to hemicellulose degradation (Garcia Esteban et al., 2006, Nagyvary et al., 2006, Ganne-Chédeville et al 2012). Similar degradation processes were recorded by means of FT-IR also on the fungus-treated wood. The measurements showed that the absolute values of the wavenumbers 818, 589, 1051, which are representative of hemicellulose and lignin, were reduced. Although the degradation processes of the polysaccharides and lignin are not identical during the fungal treatment and the natural aging, it can be assumed that the physical properties and the sorption behavior and / or the swelling and shrinkage behavior are comparable in comparison to the freshly beaten wood.

Compared to freshly beaten wood, FTIR analyzes revealed significant changes in the ratio of lignin / polysaccharides in fungal and old wood (Lehringer et al., 2011; Sedighi Giliani et al., 2014a; Sedighi Gilani et al., 2014b). A significant difference was the lower proportion of hemicellulose in old wood. Qualitative studies confirm that both lignin and hemicellulose degrade at different levels during wood delignification (Lehringer et al., 2011). Although the degradation processes of lignin and hemicellulose are not identical after selective delignification and natural aging, it can be assumed that their composition differs markedly from that of freshly felled wood. Presumably, the different composition of freshly cut wood has an influence on the interaction with moisture, eg sorption dynamics, moisture capacity and dimensional stability of the material. These changes will also have an impact on the wood anatomy and supermolecular structure of the cell walls, which in turn have a significant impact on the vibromechanical properties of the wood. Studies show that increasing anatomical homogeneity of the wood structure can advantageously influence the vibration properties, bending stiffness and damping of the wood (Jakiela et al., 2008, Stoel and Borman, 2008).

As water molecules enter the woody cell wall, they are taken up by the surfaces of the cellulosic microfibrils and the matrix consisting of lignin and hemicellulose. The uptake of water molecules via the hydroxyl groups between the wood polymers results in a reduction in the flexural rigidity of hemicellulose and lignin in the cell wall, which affects the vibration and mechanical properties of the material. The attenuation of the wood is significantly increased with increasing relative humidity (Hunt and Gril 1996, Sedighi Gilani et al 2014b), which has a negative effect on the sound properties of the wood. The degradation of hemicellulosity in old and fungal treated wood reduces the influence of moisture absorption on vibration and mechanical properties of the material (mechano-sorptivity). This finding has recently been confirmed in wood incubated with P. vitreus (Sedighi Gilani et al 2014 b). Another consequence of lignin and hemicellulose degradation in the cell walls is the increased exposure of the crystalline cellulose and improved sorption stability of the wood. In comparison to newly felled wood, an accelerated diffusion process of water molecules could be recorded on old and fungal treated wood by means of dynamic sorption tests (Sedighi Gilani et al 2014 b).

It is likely that higher material stability during moisture vapor exchange with the atmosphere will ensure the reliability of the vibration properties and the time-dependent mechanical properties of the wood, e.g. Enhance stress relaxation and creep behavior (Hunt and Gril 1996).

The method of fungal wood modification described here leads to a temporal reduction of the stress relaxation of the material under various mechanical (eg tuning) and physical (eg air humidity fluctuations) boundary conditions, which is of crucial importance for the stability and sound quality of musical instruments made of wood. The striking similarities between naturally aged and fungus treated wood show that the fungus treatment is a valuable wood modification process for the accelerated aging of tonewood. The success A fungus-treated violin in a blind test at the Osnabrück Baumpflegetagen in 2009 is most likely due to the similarity of the mechanical and hygroscopic stability of mushroom-treated and old wood.

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Claims (9)

1. A method for improving the acoustic properties of spruce resonance wood for musical instruments, wherein at least one resonance wood blank is subjected to a treatment with Physisporinus vitreus under controlled, sterile conditions, wherein that the previously sterilized resonance wood blank is immersed into a liquid medium enriched with fungus mycelium and kept therein in the dark for an exposure time and finally sterilized, wherein during the exposure time a temperature of 18 to 26ºC and a relative humidity of approximately 60 to approximately 80% are maintained, characterized in that the liquid medium contains nanofibrillated cellulose (NFC) in an amount of 200 to 300 g per liter.
2. The method according to claim 1, wherein the treatment is carried out with Physisporinus vitreus EMPA 642.
3. The method according to claim 1 or 2, wherein during the exposure time a temperature of 21ºC to 23ºC and a relative humidity of approximately 65 to approximately 75% are maintained.
4. The method according to one of claims 1 to 3, wherein the exposure time is chosen in such manner that the resonance wood fulfils the following strength values:

   - a module for bending longitudinally to the fiber of at least 7 GPa, preferably 10 GPa;

   - a compressive strength longitudinally to the fiber of at least 24 N/mm², preferably 34 N/mm²; and

   - a compressive strength transversely to the fiber of at least 3 N/mm², preferably 4.2 N/mm².
5. The method according to one of claims 1 to 4, wherein the exposure time is 4 to 6 months.
6. The method according to one of claims 1 to 5, wherein the liquid medium has been obtained by incubation of an NFC-containing nutrient medium inoculated with Physisporinus vitreus under controlled pH conditions.
7. The method according to one of claims 1 to 6, wherein the sterilization of the resonance wood blank is carried out with ethylene oxide.
8. The method according to one of claims 1 to 7, wherein an increase in the color index E* defined in the color space (L*,a*,b*) by at least 14 is effected.
9. The method according to one of claims 1 to 8, wherein a color change of the wood is effected which is characterized by a color distance ΔE* defined in the color space (L*,a*,b*) of at least 11.

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