WO2024177598A1

WO2024177598A1 - Modification of wood cell wall with hydrophobic polylactic acid

Info

Publication number: WO2024177598A1
Application number: PCT/TR2024/050100
Authority: WO
Inventors: Mahmut Ali ERMEYDAN; Eylem DİZMAN TOMAK; Ahmet Can
Original assignee: Bursa Teknik Universitesi
Current assignee: Bursa Teknik Universitesi
Priority date: 2023-02-23
Filing date: 2024-02-07
Publication date: 2024-08-29
Anticipated expiration: 2025-08-23

Abstract

The invention is a wood modification method consists of methodologic steps as impregnating wood samples with monomer solution under vacuum to cause the cell walls (1) to swell, keeping the impregnated samples for at least 1 day for diffusion, and heating the treated wood to a temperature between 105-120°C in a closed system to carry out the polymerization process; aims to increase the water repellency and dimensional stabilization properties of wood as well as to reduce wood's water absorption and void content which is required for wood-rotting fungi.

Description

Modification of Wood Cell Wall with Hydrophobic Polylactic Acid

TECHNICAL FIELD

The invention relates to the grafting of lactide monomer, obtained from lactic acid obtained by fermentation of carbohydrate resources such as corn, into the wood cell wall by ring-opening reaction, thus modifying the cell walls by filling them with hydrophobic polylactic acid (PLA).

BACKGROUND ART

Wood is one of the oldest building materials used in buildings and is used in many areas, but the fact that this material is hydrophilic, can be degraded by biological organisms, can change its dimensions by being affected by the humidity of the environmental conditions, and can be affected by ultraviolet (UV) light and undergo photo-degradation limits its utilization. There are many wood modification methods developed to eliminate the disadvantages of wooden materials. One of these wood modification methods is heat treatment of wood material. Heat treatment of wooden material attracts great attention as it is an environmentally friendly wood preservation method. After being subjected to heat treatment, the water absorption of wood material may decrease and it may become more resistant to biological attacks. Additionally, it becomes more dimensionally stable compared to non-heat-treated material. However, there is a decrease in the mechanical properties of wood. Heat treatment has different effects on wood obtained from different species.

Sustainable wood modification, in other words, new generation modification systems, can be achieved by using energy efficient processes, non-toxic, bio-based and biodegradable chemicals that can be disposed of without polluting the environment at the end of their useful life. In recent innovative wood modification techniques, researchers have used biodegradable or natural compounds such as PCL, ACPC, low molecular weight PLA, PGA, PBS and PBA, polyglycerol succinate, sorbitol, citric acid, extractives, vegetable oils, waxes, natural resins, chitin and chitosan, as well as biobased renewable and/or biodegradable polymers. Bio-polyesters such as PLA, PGA, PBS, PBA, PCL may enter the wood cell wall and block the hydroxyl groups of the wood. They can provide a hydrophobic effect by reducing cell voids. Among these methods, PCL modification, which is a biodegradable polymer that undergoes in-situ modification of wood through a ring-opening reaction like lactide, provides wood with a dimensional stability of up to 60% and a water repellency effect of up to 50%. It was determined that the sample surfaces retained their color better after UV aging compared to the reference samples. A very good resistance has been achieved against white and brown rot fungi that degrade wood. The need for further studies has been expressed in terms of making the modification conditions under lower temperature conditions, preventing the formation of cracks in the sample cross-sections and improving the conditions of repeated use of the solution. As can be seen from the studies, new modification methods that are cheap and feasible are constantly being developed in order to improve the properties of wood and obtain a more durable material. There are wood plastic composite studies made with oligomeric lactic acid in the literature. Oligomeric lactic acid was used in these studies, and the penetration and adhesion of hydrophobic oligomers to the cell wall was partially limited at low temperatures. In leaching tests, PLA oligomers were washed about 80% from wood. Since oligomers are large molecules with low molecular weight, they cannot enter the wood cell wall. Later, an attempt was made to improve the oligomeric lactic acid method. It has been reported that esterification of lactic acid oligomers with hydroxyl groups on wood polymers is achieved at high temperatures such as 160-180 °C and for 48 hours. Dimensional stability increased with approximately 70% weight increase in the method. Dimensional stability achieved at 95% humidity was found to be approximately 70%. Among the experimental groups, the best biological resistance against C.versicolor fungus is achieved in the process applied at 160°C for 48 hours. In the method, high temperature application such as 160-180°C causes thermal degradation of the wood and a decrease in its mechanical resistance properties.

The following documents were encountered during the preliminary patent search.

CN1 15212985A The patent document with application number discloses a polylactic acid modified plastic preparation device comprising a polylactic acid preparation technology area including a soaking tank. It is explained that lactic acid is produced through fermentation of corn.

CN1 15216129A The technical field of environmentally friendly biodegradable materials is explained in the patent document with application number. A heat-resistant bio-based degradable composite material and its preparation method are described. CN1 15109336A The patent document with application number describes the modified bauxite washing mud reinforced wood-plastic composite material and its preparation method.

CN1 15093716A The patent document belongs to the field of wood-plastic composite technology. Specifically, it includes a bio-based wood-plastic composite material and its preparation method.

CN1 15073902A The patent document describes an environmentally friendly method for the preparation of a lightweight thermal insulating polylactic acid foam material.

CN1 1501 1 158A Wood paint coatings are included in the patent document. It includes a particularly anti-corrosion environmental protection wood paint coating and its preparation method.

CN1 14939917A Artificial fiber board technology is explained in the patent document. Particularly wet resistant wood was described as a three-layer board. Moisture-resistant three-layer wooden board is formed out of moisture-resistant magnesium sulfur cementitious material as an inorganic adhesive.

As a result, all the problems mentioned above have made it necessary to make an innovation in the relevant field.

PURPOSE OF THE INVENTION

The present invention aims to eliminate the above-mentioned problems and make a technical innovation in the relevant field.

The main purpose of the invention is to graft the lactide monomer, which is generally obtained from lactic acid by fermentation of corn, into the wood cell wall through a ringopening reaction, thus modifying the cell wall by filling the voids with hydrophobic polylactic acid (PLA).

Another purpose of the invention is to provide a solution to the problem of swelling/shrinking cycle according to the humidity conditions of the environment in which it is located, which is attributed as the most important disadvantage of wood. Another aim of the invention is to present an effective and permanent production method that provides resistance against fungi that cause rotting in wood and does not have any leaching problems.

Another purpose of the invention is to increase the service life of the wooden product in areas of use above flood level.

Another purpose of the invention is to offer an environmentally friendly approach to ensure more rational and efficient use of decreasing forest resources by extending the lifespan of wood.

BRIEF DESCRIPTION OF THE INVENTION

In order to achieve all the purposes mentioned above and to emerge from the detailed explanation below, the present invention aims to increase the water repellency and dimensional stabilization properties of wood; It is a wood modification method that aims to reduce water absorption and void ratio of wood in order to reduce the amount of moisture required for fungi that rot wood. According to this; a) impregnating wood samples with monomer solution under vacuum to cause the cell walls to swell, b) keeping the impregnated samples for at least 1 day for diffusion, c) heating the treated wood to a temperature in the range of 105-120°C in a closed system to carry out the polymerization process,

The production steps are determined by including the method steps above.

A preferred embodiment of the invention is to use lactide monomers dissolved in a polar solvent as the monomer solution mentioned in the process step 'a'.

Another preferred embodiment of the invention is the use of catalyst in process step 'a'.

A preferred embodiment of the invention is to characterize the catalyst as tin(ll)2- ethylhexanoate (Sn(Oct)2).

Another preferred embodiment of the invention is to swell the wood up to 15% in a polar solvent before the 'a' process step. A preferred embodiment of the invention is to use dimethylformamide (DMF) as said polar solvent.

Another preferred embodiment of the invention is to characterize the polymerization process mentioned in process step 'c' as a lactide polymerization process.

BRIEF DESCRIPTION OF THE FIGURES

Lactide modification of wood is shown in Figure 1 .

Figure 2 shows the Fourier transform infrared spectroscopy (FTIR) results according to the lactide percentages of modified wood.

Figure 3 shows the swelling values obtained according to lactide percentages of modified wood with lactide.

Figure 4 shows the dimensional stability (%) values obtained according to lactide percentages of modified wood with lactide.

Figure 5 shows the mass loss (%) values obtained after the fungal rot test ( Coniophora puteana exposure) according to the lactide percentages of modified wood with lactide.

Figure 6 shows the scanning electron microscope (SEM) images of the cross-sectional surfaces of the wood material modified with 10% lactide before the fungal decay test.

Figure 7 shows the scanning electron microscope (SEM) images of the cross-sectional surfaces of the wood material modified with 20% lactide before the fungal decay test.

Figure 8 shows the scanning electron microscope (SEM) images of the cross-sectional surfaces of unleached 10% lactide-modified wood material after the fungal decay test.

Figure 9 shows the scanning electron microscope (SEM) images of the cross-sectional surfaces of unleached 20% lactide-modified wood material after the fungal decay test.

Figure 10 shows the scanning electron microscope (SEM) images of the cross-sectional surfaces of the leached 10% lactide-modified wood material after the fungal decay test.

Figure 1 1 shows the scanning electron microscope (SEM) images of the cross-sectional surfaces of leached wood material modified with 20% lactide after the fungal decay test. DESCRIPTION OF REFERENCE NUMBERS IN THE FIGURES

1. Cell wall

2. D,L- lactide

3. Organotin Catalyst

4. Dimethylformamide

5. Heat treatment

6. Polylactic acid FTIR spectrum

7. FTIR Spectrum of Degraded 20% Lactide Modified Wood

8. FTIR Spectrum of 20% Lactide Modified Wood

9. FTIR Spectrum of Degraded 10% Lactide Modified Wood

10. FTIR Spectrum of 10% Lactide Modified Wood

11. FTIR Spectrum of Degraded Control Spruce Wood

12. FTIR Spectrum of Control Spruce Wood

13. Swelling values of control samples in water

14. Swelling values of 10% Lactide modified samples in water

15. Swelling values of 20% Lactide modified samples in water

16. Dimensional stability of 10% Lactide modified samples

17. Dimensional stability of 20% Lactide modified samples

18. Mass loss of unleached control samples after fungal degradation

19. Mass loss of leached control samples after fungal degradation

20. Mass loss after fungal degradation of unleached 10% lactide modified samples

21. Mass loss after fungal degradation of leached 10% lactide modified samples

22. Mass loss after fungal degradation of unleached 20% lactide modified samples 23. Mass loss after fungal degradation of leached 20% lactide modified samples

24. Mass loss after fungal degradation of unleached positive control acetylated wood samples

25. Mass loss after fungal degradation of leached positive control acetylated wood samples

26. SEM image of samples modified with 10% lactide before fungal degradation test

27. SEM image of samples modified with 20% lactide before fungal degradation test

28. SEM image of unleached samples modified with 10% lactide after fungal degradation test

29. SEM image of unleached samples modified with 20% lactide after fungal degradation test

30. SEM image of leached samples modified with 10% lactide after fungal degradation test

31. SEM image of leached samples modified with 20% lactide after fungal degradation test

DETAILED DESCRIPTION OF THE INVENTION

In this detailed explanation, the subject of the invention "Bulking the voids of the wood cell wall (1 ) with hydrophobic polylactic acid and modifying the wall" is explained only with examples that will not create any limiting effect for a better understanding of the subject.

The subject of the invention relates to the grafting of lactide monomer, obtained from lactic acid obtained by the fermentation of corn, into the wood cell wall (1 ) through a ringopening reaction, thus modifying the voids in the cell wall (1 ) by filling them with hydrophobic polylactic acid (PLA).

The invention is a lactide modification process of wood and is implemented by introducing certain chemicals at certain stages. The lactide used in the invention is obtained by lactic acid fermentation of carbohydrate sources such as sugar cane, corn, sugar beet and cassava.

In order for the hydrophobic lactide molecule to penetrate into the cell wall (1 ) successfully, the swelling of the wooden cell wall (1 ) is applied. Swelling the wood by 15% in a polar aprotic (4) solvent before modification increases the success of the modification. At this stage, wooden samples are first impregnated in polar solution under vacuum and then the diffusion stage is started. The samples are kept in the solution for 24 hours, thus ensuring full swelling of the cell wall (1 ). In the first stage, monomer impregnation is carried out in the cell wall (1 ) of the wood in the presence of organotin catalyst (3) and D,L-Lactide (2). Figure 1 shows the lactide modification of wood.

Lactide monomer solution is prepared with dimethylformamide (4) (DMF) and organotin catalyst (3), expressed as tin(ll) 2-ethylhexanoate Sn(Oct)2. Swelled wooden samples are impregnated with monomer solution under vacuum. Then the diffusion phase begins. Lactide impregnation is carried out by keeping the samples in solution for 24 hours and allowing the monomer to penetrate the cell wall (1 ).

Polymerization is carried out at high molecular weights by ring-opening reaction of lactide monomer in the ring structure in the presence of organotin catalyst (3). Polymerization is carried out at high molecular weights by the monomer ring opening reaction. The monomer is covalently bonded to the hydroxyl groups through the ring opening reaction. Since the organotin used for the polymerization of lactide initiates the polymerization reaction above 100°C, the wood impregnated with lactide monomer solution is left in a closed system at a temperature between 105-120°C (5). The polymerization process is carried out by lactide polymerization and PLA formation on the wood cell wall (1 ). Lactide modification can be applied to completely dry all wood species.

Figure 2 shows the chemical characterization result (FTIR) obtained according to lactide percentages in wood modified with lactide. The presence of polylactic acid in all wood samples, which is formed as a result of the polymerization of lactide, is shown of the polylactic acid FTIR spectrum (6), degraded 20% lactide modified wood FTIR spectrum (7), 20% lactide modified wood FTIR spectrum (8), degraded 10% lactide modified wood FTIR spectrum and 10% lactide modified wood FTIR spectrum (10). In the FTIR spectra of control samples exposed to the brown rot fungus Coniophora puteana, it is seen that hemicellulose (1730 cm^-1) and cellulose (1130 cm^-1) components are degraded, and the intensity of the characteristic peak of lignin, 1509 cm^-1, has increased. In modified samples no significant change due to degradation is observed.

As seen in Figure 2, there are control spruce group and modified wood of 10% and 20% lactide concentration. When the peaks on the control spruce spectrum (12) and the degraded control spruce spectrum (1 1 ) compared with the wood modified by polylactic acid, the strong FTIR peak at 1755 cm^-1 on 20% lactide modified wood spectrum (8) and the degraded 20% lactide modified wood spectrum (7) can be recognized easily. Similarly, if spruce samples are treated with polylactic acid, the peak at 1755 cm^-1 is seen on the 10% lactide modified wood spectrum (10) and the degraded 10% lactide modified wood spectrum (9). The 1755 cm^-1 peak is an FTIR peak belongs to the carbonyl group (C=O) vibration of polylactic acid polymer. When this situation is compared with the FTIR spectrum of control spruce (12) and degraded control spruce (1 1 ), polylactic acid in 10% lactide (10), 10% degraded lactide (9), 20% lactide (8) and 20% degraded lactide (7) samples, it has been observed spectroscopically that the polymer exists in modified samples. In summary, it has been proven by spectroscopic chemical analysis that polylactic acid modification of spruce samples has occurred.

In-situ polymerization is achieved by lactide polymerization of the lactide solution impregnated on the cell wall.

Figure 2 also proves that the modification is stable against the accelerated aging test, which includes 2 cycles and 4 steps of drying and soaking processes, and fungal degradation test, because the polylactic acid is still attached to the wood surface that indicates the method is permanent.

In Figure 3, swelling values of control samples in water (13), swelling values of 10% lactide modified samples in water (14) and swelling values of 20% lactide modified samples in water (15) are shown as the drying and soaking stages of the wood. In the swelling experiment consisting of 2 cycles (drying-soaking together, 1 cycle is repeated 2 times to complete 2 cycles) and 4 steps (soaking-drying-soaking-drying is a total of 4 steps), it is seen that the water uptake rate of modified wood decreases between 36% and 41 %.

In Figure 4, in the experiment carried out in 2 cycles and 4 steps consisting of drying and soaking steps of the wood according to the amount of monomer in the lactide modification, the dimensional stability of the test result was calculated based on the swelling values of the wood compared to the control wood and it was seen that it was between 18% and 56%.

In Figure 5, even in the 10% lactide modified samples subjected to accelerated aging test, the biological activity against the brown rot fungus Coniophora puteana is equivalent to the positive control sample (acetylated wood), and the mass loss after fungal degradation of the unleached positive control acetylated wood samples (24) is compared to that of the mass loss of the leached positive control acetylated wood samples after fungal degradation (25) is shown. The modified product meets the requirements for protection in EN 1 13-1 standards. The mass loss after fungal degradation of unleached samples modified with 10% lactide (20), mass loss of leached samples modified with 10% lactide (21 ), mass loss of unleached samples modified with 20% lactide (22), mass loss of leached 20% lactide modified samples (23) compared to the mass loss of unleached control samples (18) and the mass loss leached control samples (19), and it was found that the biological resistance of unleached and leached samples are 92%, 99%, 72% and 86% respectively.

The critical factor for wood-rotting fungi is the presence of 30% moisture in the wood, and thanks to the method within the scope of the protection of the invention, as the moisture and void ratio in the wood decreases, there is no suitable environment for the development of fungi, and thus the wood gains resistance against fungi that cause wood rot.

Figure 6, Figure 7, Figure 8, Figure 9, Figure 10 and Figure 1 1 show SEM images after the treatments applied on wooden surfaces following the method within the protection scope of the invention. Accordingly, SEM image of samples modified with 10% lactide (26) and SEM image of samples modified with 20% lactide before fungal degradation test (27), SEM image of unleached samples modified with 10% lactide (28) and SEM image of unleached 20% lactide modified samples after fungal degradation test (29), SEM image of leached 10% lactide modified samples (30) and SEM image of leached 20% lactide modified samples after the fungal degradation test (31 ) support the FTIR findings that indicates the presence of the polymer in wood structure. In addition to the cell wall, the polymer was also seen in small amounts in the lumen region on the surface of the cell wall. Although no degradation of the cell wall is observed in the samples after the fungal degradation test, the presence of the polymer continues in the cell lumens (27-31). The presence of fungal cells can also be seen in the cell lumens, but when combined with the result of no mass loss, it was revealed that the fungi were unable to degrade the modified wood.

The scope of protection of the invention is specified in the attached claims and cannot be limited to what is explained in this detailed description for exemplary purposes. Because a person skilled in the art can produce similar structures in the light of what is explained above, without deviating from the main theme of the invention.

Claims

1. The invention is a wood modification method to increase the water repellency and dimensional stabilization properties, wherein; reduces the amount of moisture required for fungi that rot wood by reducing its water absorption and void ratio and the method is characterized in that; a) impregnating wood samples with monomer solution under vacuum to cause the cell walls (1 ) to swell, b) keeping the impregnated samples for at least 24 hours for diffusion, c) heating the impregnated wood to a temperature between 105-120°C in a closed system to carry out the polymerization process.

2. The invention is a wood modification method in accordance with 1 wherein; the use of lactide monomers dissolved in a polar solvent as the monomer solution mentioned in the process step a).

3. It is a wood modification method in accordance with claim 2, wherein; the use of catalyst in the process step a).

4. It is a wood modification method in accordance with claim 3, wherein; The catalyst is characterized as tin(ll) 2-ethylhexanoate (Sn(Oct)2).

5. The invention is a wood modification method according to claim 1 wherein; step a) is swelling of the wood in a polar solvent to 15% before processing step.

6. It is a wood modification method according to claim 2 or 5 wherein; The mentioned polar solvent is the use of dimethylformamide (DMF).

7. It is a wood modification method in accordance with claim 1 , wherein; The polymerization process mentioned in process step c is characterized as lactide polymerization process.