Use of UV rays for lignin removal in cellulosic textile materials

Abstract

The invention relates to a method comprising the use of UV rays which can be used in areas where the lignin removal from natural fibers is required. The invention especially relates to a method in which delignification is provided by using only UV rays without the need for post-treatment, use of chemicals and additional process steps in lignin removal in cellulosic textile materials.

Description

[0001] USE OF UV RAYS FOR LIGNIN REMOVAL IN CELLULOSIC TEXTILE MATERIALS

[0002] Technical Field

[0003] The invention relates to a method comprising the use of UV rays which can be used in areas where the lignin removal from natural fibers is required.

[0004] The invention especially relates to a method in which delignification is provided by using only UV rays of a certain wavelength, without the need for post-treatment, use of chemicals and similar additional process steps in lignin removal in cellulosic textile materials.

[0005] State of the Art

[0006] Lignin is the most abundant natural amorphous polymer in plant structures after cellulose. Its chemical structure varies depending on the plant species and morphological characteristics, primarily consisting of phenylpropane unit. Hemp fiber, which is one of the cellulose fibers with high lignin content, and surfaces derived from hemp can be used in the production of natural fiber-reinforced composites in composite manufacturing. Natural fiber-reinforced composites are preferred in high value-added industries such as automotive and aviation industries for their high strength and low weight. However, the lignin present in the fiber structure increases the reactivity of fibers and at the same time provides a rigid texture to the fibers. Therefore, it makes the fiber more breakable and reduces the flexibility of the fiber, which is a critical parameter in composite production. In order to prevent the negative effects of lignin in the use of cellulosic fibers, etc., the lignin removal process is applied.

[0007] Delignification refers to the process of removing lignin from cellulose fibers. There are several conventional methods applied for delignification. In the present embodiments, concentrated chemicals are used at high temperatures and pressures to remove the lignin component. This process, also known as alkaline process (alkaline treatment) in literature, can be performed by using chemicals such as sodium hydroxide (NaOH), sodium chlorite (NaCIO2), calcium carbonate (CaCO3), etc. Among these chemicals, sodium hydroxide (NaOH) is widely used. The reason for this is that the mercerization effect is provided in the fiber structure along with the delignification process. NaOH reacts with the hydroxyl groups in cellulose and removes lignin, pectin and hemicelluloses. While the removal of these components reduces density, it is also known that it increases the strength and the mobility of fibrils within the structure. While the process provides better fiber matrix adhesion due to the increased purity of the fibers, it also forms additional places for mechanical interlocking through fibrillation. Also, the axial separation of primary fibers leads to decreasing in fiber diameter, increasing of length-to-width ratio, and enhances the wettability of the fiber by providing a larger effective surface area. However, after this process, cellulose fibers become shorter (by depolymerization) and exposure to high temperature, pressure or alkali concentration can result in degraded fibers that cannot support effective load transfer. Additionally, conventional methods are performed by using high-volume machines (such as jets) that consume substantial amounts of water and energy.

[0008] Ultraviolet technology, along with various physical and chemical processes, continues to be researched for its use in various stages within the textile industry, as in many other sectors.

[0009] The component responsible for UV absorption in cellulose fibers is the lignin component due to its chromophore groups. Lignin behaves as an absorbing material that aids absorption with its both aliphatic and phenolic hydroxyl groups, as well as carboxyl groups. Lignin absorbs 85- 90% of rays. UV radiation also increases crystallinity, thus causing cracks on the surface. This increases the penetration of the chemicals used, resulting in more effective results. In the delignification process used in art, it is observed that treatment occurs at high temperatures and pressures along with a specific chemical concentration.

[0010] Literature comprises various delignification methods. Some of these methods are grouped and listed below:

[0011] 1 - Chemical Methods:

[0012] • Alkaline Process (Alkaline Treatment - Mercerization)

[0013] • Acetylation / Propionylation

[0014] • Silane Treatment (Silanization)

[0015] • Maleic Anhydride (Maleation)

[0016] • Graft Copolymerization

[0017] 2- Other Chemical Methods:

[0018] • Oxidation

[0019] • Benzoylation

[0020] • Treatment with Peroxide

[0021] • Treatment with Sodium Chlorite • Treatment with Isocyanates

[0022] • T reatment with Stearic Acid

[0023] • Treatment with Liquid Ammonia

[0024] • Etherification

[0025] • Treatment with Permanganate

[0026] • Sol-Gel Method

[0027] • Salicylic Acid

[0028] 3- Physical Methods a. Physical Modification Methods:

[0029] • Steam Explosion Process (STEX)

[0030] • Thermo-Mechanical Processes

[0031] 4- Physico-Chemical Methods

[0032] • Plasma Treatment

[0033] • Corona Discharge Treatment

[0034] • Dielectric Barrier Discharges

[0035] • High-Energy Radiation Methods

[0036] • Ultrasonication

[0037] 5- Enzymatic Treatment

[0038] • Oxidative Enzymes

[0039] • Hydrolytic Enzymes

[0040] • Mixed Enzyme Systems

[0041] 6- Treatment with Fungi

[0042] • White Rot Fungi

[0043] 7- Biological Methods

[0044] • Microbial Delignification

[0045] The methods mentioned above are especially applied to improve the properties of fibers by modifying them before natural fiber-reinforced composite applications. However, among the methods mentioned above, the most used is the alkaline process. Figure 1 shows the cellulose structure before alkaline treatment (left side) which is one of the applications in the art, and the change in the crystalline cellulose structure (right side) after treatment.

[0001] The chemical reaction between the fiber cell and NaOH occurs as the equation given below.

[0046] Fiber cell- OH + NaOH Fiber cell- O' Na++ H2O + impurities

[0047] Conventional alkaline delignification basically involves solution preparation, delignification of the process with NaOH using the exhaust method, detergent washing, cold rinsing and drying processes. Beside the negative aspects of the present art such as the use of chemicals and water and the generation of waste at the end of the process, there is also a loss of time due to the long process time. Nowadays, the severe impact of global warming and the depletion of clean water resources have formed a need for more environmentally friendly and sustainable methods.

[0048] As a result of the research carried out in the literature, patents that may be relevant to the subject were found.

[0049] The application numbered US20110263836 relates to a method for treating lignin-containing fibrous material to reduce its susceptibility against turning yellow. The said document generally involves enzymatically stabilizing the lignin of the material with an oxidizing agent that can oxidize phenolic or similar groups capable of reacting that leads to the formation of colored regions on the fibers and treating the material with a fluorescent whitening agent. However, the document does not mention the use of UV rays alone in lignin removal.

[0050] The application numbered EP3386697A1 in the art relates to a method fortreating the material structure of lignocellulosic material (preferably wood). The said method comprises the following steps: (1) wetting the lignocellulosic material structure with at least one organic liquid to dissolve at least 40% and at most 85% by weight of the lignin present in the material; (2) washing the structure obtained from step (1) with at least one organic liquid to remove the dissolved lignin obtained from the wetting step (1 ), thereby producing a partially delignified structure; (3) filling the partially delignified structure obtained from the washing step (2) with at least one filling compound and thereby obtaining a filled partially delignified structure and (4) obtaining the filled partially delignified structure resulting from the filling step (3) to obtain a composite material structure consisting of a three-dimensional transformed filler compound network included in the network of cellulose and lignin. However, there is no method in the document that involves using UV rays alone to remove lignin.

[0051] Another application in the art is the document numbered TR2012 / 00217. The said document relates to a UV-curable transfer film and a method for preparing the UV-curable transfer film and the application of the UV-curable transfer film in the field of finishing materials. In the said patent UV curing is used to provide a colored transfer film that is rich in color and pattern and exhibits high decorative and protection performance, and its use for lignin removal is not described.

[0052] In conclusion, it is necessary to make a development in the relevant technical field due to the negativities described above and the inadequacy of existing solutions about the subject,.

[0053] Object of the Invention

[0054] The present invention relates to a method used in lignin removal in cellulosic textile materials that meets the above-mentioned requirements, eliminates all disadvantages and brings some additional advantages.

[0055] The primary object of the invention is to introduce an environmentally friendly and sustainable method enabling the lignin removal in cellulosic fibers, especially cellulosic textile materials, without the need for additional chemicals or water use or post-processing.

[0056] The object of the invention is to provide delignification process in cellulosic textile materials by exposing them to UV radiating power sources in the UV environment.

[0057] An object of the invention is to provide a method that prevents loss of time by exposing fiber / fabric / materials to UV radiation in the UV environment for short periods of time without any processing.

[0058] Another object of the invention is to provide the delignification process to be performed without the need to adjust parameters such as temperature or pressure.

[0059] In order to achieve the objects described above, the invention is an environmentally friendly and sustainable method for the lignin removal in cellulosic textile materials and comprises the delignification process by exposing the materials to power sources emitting UV rays in the UV environment.

[0060] In order to achieve the objects described above, the invention relates to the use of UV rays for the removal of lignin, wherein the use of UV rays from power sources emitting UV rays for the removal of lignin from cellulosic textile materials. The structural and characteristic features and all the advantages of the invention will be more clearly understood by means of the drawing given below and the detailed description written with reference to this drawing, and therefore the evaluation needs be made by taking this drawing and detailed description into consideration.

[0061] Drawings Assisting the Description of the Invention

[0062] Figure 1: The cellulose structure before alkaline application (left side), which is one of the applications in the present art and the view of the change in the crystalline cellulose structure (right side).

[0063] Figure 2: The view of the example applications in which the UV radiating power sources used in the inventive method can be used in the production process (First application and Second application regions).

[0064] Reference Numbers

[0065] 1. First application region

[0066] 2. Second application region

[0067] A: Cellulosic product

[0068] S: Cellulose

[0069] L: Lignin

[0070] Y: Fats-waxes

[0071] Detailed Description of the Invention

[0072] In this detailed description, the preferred embodiments of the invention are described solely for the purpose of a better understanding of the subject and in a way that does not form any limiting effect.

[0073] The invention relates to an environmentally friendly and sustainable method for the lignin removal in cellulosic textile materials. The method, which is subject of the invention comprises performing the delignification process by exposing material to UV rays in a UV environment.

[0074] The invention relates to the use of UV rays in the lignin removal in cellulose textile materials. In the invention, power sources that emitting UV rays in the UV environment are used in an open manner and the material is located in the middle of the UV environment so that it can receive rays from all directions. The sample is exposed to power sources emitting UV rays in the UV environment for a determined period of time. This period is determined according to the parameters given below, and the sample is preferably exposed to power sources emitting UV rays in the UV environment for a period of 10-90 minutes, more preferably for 60 minutes.

[0075] The duration of impact of UV rays on lignin depends on various factors. Therefore, optimizing the duration before the process needs to be performed for efficient operation. Intensity of UV Rays: The intensity of UV rays determines how long it takes to have an impact on lignin. Higher intensity UV ray may have an impact faster. Wavelength of UV Rays: UV rays with different wavelengths may affect lignin differently. Some UV rays may penetrate deeper. Amount and Type of Lignin: Plant species and cellular structures vary in terms of lignin content and type. These factors may affect the duration of impact of UV rays. Other Environmental Conditions: The duration of impact of UV rays may vary depending on environmental conditions (such as humidity, temperature, wind, etc.)

[0076] A sample study was performed for lignin removal with the method, which is subject of the invention. In the study, the raw fabric was used as a reference for comparison. In order to numerically express that delignification occurs only with the UV process, conventional delignification was also performed on the raw fabric. In this process, delignification process (20% NaOH according to fabric weight, 1:100 flotte ratio and 60 minutes at 98<C) was performed. UV treatment was applied by exposing the fabric to power sources which emitting only UV rays for 60 minutes. The process applied with the invention does not use water or chemicals. The preliminary measurement results are given in table 1 below.

[0077] Table 1 Residual lignin determination values of samples When Table 1 is analysed, it is seen that the lignin detected on the raw fabric is 8.62. While this rate decreased by 8.25 to 4.29% after the conventional delignification process, it was observed that there was a decrease of 8.16 to 5.33% by applying only UV treatment. Therefore, it is observed that the fabrics treated with UV for the same duration without any use of water and chemicals yielded more advantageous and better results in terms of lignin values compared to the conventional lignin removal process. In the conventional delignification process, the use of water, chemicals, and temperature (98‘C) are essential parameters. However, in the UV treatment applied with our method, which is subject of the invention, none of these parameters are required.

[0078] UV rays used in the method, which is subject of the invention can be used with different modifications according to their usage areas in the production process. For instance, it can be applied in a cabin, or it can be modified in front of / inside a ram or fulard where the surfaces of cellulosic-containing textile materials / materials pass. In Figure 2, it is given the view of sample applications where these UV rays in the production process can be used.

[0079] With the inventive method, the process steps and duration forthe removal of lignin are reduced compared to the conventional delignification process. The method does not require the use of additional chemicals or water or post-processing, and there is no need for chemical oxygen.

[0080] References

[0081] [1] Sunny, T., & Pickering, K. L. (2021). An Overview of Alkali Treatments of Hemp Fibres and

[0082] Their Effects on the Performance of Polymer Matrix Composites. Alkaline Chemistry and Applications.

Claims

CLAIMS1. An environmentally friendly and sustainable method for lignin removal in cellulosic textile materials, characterized by comprising; performing the delignification process by exposing materials to power sources emitting UV rays in a UV environment.

2. The method according to claim 1 , characterized in that; the delignification process is performed by exposing the materials to UV rays for an application period of 10 to 90 minutes.

3. The use of UV rays in lignin removal, wherein the use of UV rays from power sources emitting UV rays for the removal of lignin from cellulosic textile materials.

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