Biodegradable rubber articles and methods for producing rubber articles

Abstract

The present invention relates to a method for preparing a biodegradable rubber article, comprising the step of adding HTC lignin to a rubber composition containing at least one rubber component, the use of HTC lignin to promote the biodegradation of the rubber article, and each of the rubber articles.

Description

Detailed description of the invention

[0001] This invention relates to a method for producing biodegradable rubber articles, the use of HTC lignin to promote the biodegradation of rubber articles, and each of these rubber articles.

[0002] The biodegradation of rubber materials takes a very long time. At the same time, rubber wear particles generated from tires are one of the main sources of primary microplastics that unintentionally end up in the ocean, for example. Because polymer materials do not decompose easily, microplastics constantly accumulate, which is a serious environmental problem for flora and fauna.

[0003] Extensive research on rubber biodegradation has shown that both natural and synthetic rubbers are broken down by microorganisms, bacteria, and fungi ubiquitous in the environment, particularly in soil. However, rubber degradation is a considerably slow process, and vulcanized rubber degrades even more slowly due to the interconnectedness of its polymer chains.

[0004] Surprisingly, soil degradation tests have found that the biodegradability of rubber can be significantly improved when the rubber contains some HTC lignin. Therefore, HTC lignin can be used to accelerate the biodegradation of rubber articles, thereby reducing the environmental impact of such articles.

[0005] The present invention therefore relates to the use of HTC lignin to promote the biodegradation of rubber articles. The rubber articles are obtained by the method of the present invention. In this method, HTC lignin is added to a rubber composition, and the resulting mixture is further treated according to conventional procedures.

[0006] The rubber composition contains at least one rubber component. The rubber component may be, for example: - Natural rubber (NR) - Epoxy rubber (ENR) -Butadiene rubber (BR) - Styrene-butadiene rubber (SBR) - Isoprene rubber (IR) - Epoxy-modified natural rubber (ENR) -Butyl rubber (IIR) - Bromobutyl rubber (BIIR) - Chlorobutyl rubber (CIIR) - Ethylene propylene diene monomer rubber (EPDM) - Ethylene propylene rubber (EPR) - Acrylonitrile butadiene rubber (NBR) - Hydrogenated nitrile rubber (HNBR) - Chloroprene rubber (CR) - Epichlorohydrin gum (ECO) - Silicone rubber (VMQ) -Fluororubber (FKM) Any one of them is acceptable.

[0007] These rubber mixtures can also be used. All rubber used in the rubber composition may be of fossil origin or bio-derived origin.

[0008] Preferred rubbers for tires include natural rubber (NR), butadiene rubber (BR), styrene-butadiene rubber (SBR), isoprene rubber (IR), epoxidized natural rubber (ENR), bromobutyl rubber (BIIR), chlorobutyl rubber (CIIR), and mixtures thereof.

[0009] HTC lignin is obtained by superheated steam carbonization of lignin, in which biomass is treated under pressure in the presence of hot water and / or steam. In contrast to pyrolysis, biomass decomposes incompletely during superheated steam carbonization, and the products are a carbon-rich solid material, a gaseous phase mainly composed of CO2, water, and water-soluble compounds.

[0010] HTC lignin can be prepared from any type of lignin-containing starting material, such as lignin-containing waste, as well as lignin in solid or soluble form, and mixtures thereof. A high lignin content of 60% by weight or more, preferably 80% by weight or more, and more preferably 90% by weight or more, is preferred in the starting material.

[0011] Preferred lignin-containing starting materials include black liquor derived from the digestion of woody biomass or a solid prepared therefrom, a solid derived from enzymatic hydrolysis of woody biomass, black liquor derived from the digestion of woody biomass using sulfites (lignosulfonates), or a solid or liquid prepared from the digestion of woody biomass using a solvent (e.g., organosorb lignin). In a preferred embodiment of the present invention, lignin is derived as a by-stream in the enzymatic hydrolysis of lignocellulose raw materials. This preferred starting material is also known as EH-lignin.

[0012] The lignin-containing starting material can be selected from the group consisting of Kraft lignin, steam-exploded lignin, biorefinery lignin, supercritical separation lignin, hydrolyzed lignin, flash-precipitated lignin, biomass-derived lignin, alkali-digested lignin, soda-process lignin, organosolve-digested lignin, alkali-treated lignin, enzymatic hydrolysis-processed lignin, and any combination thereof. In one embodiment, lignin is lignin. Lignin may be derived from conifers, broad-leaved trees, annual plants, or any combination thereof.

[0013] Kraft lignin is lignin derived from Kraft black liquor. Black liquor is an alkaline aqueous solution of lignin residue, hemicellulose, and inorganic chemicals used in the Kraft pulping process. This pulping-derived black liquor contains components derived from various coniferous and broadleaf tree species in different proportions. Kraft lignin can be separated from the black liquor by various techniques, including precipitation and filtration.

[0014] The term "flash-precipitated lignin" should be understood as lignin precipitated from black liquor in a continuous process under an overpressure of 200-1000 kPa, using a carbon dioxide-based acidifying agent, preferably carbon dioxide, to lower the pH of the black liquor stream to a lignin precipitation level, and then rapidly releasing the pressure to precipitate the lignin. Flash-precipitated lignin particles have a particle size of less than 2 μm and form aggregates. These aggregates can be separated from the black liquor, for example, by filtration.

[0015] The lignin may be derived from the organosolve process. Organosolve is a pulping technique that uses organic solvents to solubilize lignin and hemicellulose.

[0016] Lignin may be slurryed or dissolved for superheated steam conversion. Preferably, lignin is dissolved in an alkaline solution such as NaOH. Dissolution may be carried out by heating the mixture of lignin and alkaline solution to about 80°C, adjusting the pH to above 7, for example, 9-11, and mixing the mixture of lignin and alkaline solution for a predetermined time. The mixing time may be continued for about 2-3 hours. The exact pH value is determined based on the product grade target.

[0017] The slurry may be subjected directly to superheated steam treatment, or it may be supplied to a separation unit to separate the precipitated lignin from the slurry.

[0018] The hydrothermal carbonization treatment can be carried out in a reactor (HTC reactor) or, if necessary, in a plurality of parallel reactors operating batchwise. The dissolved lignin may be preheated before being introduced into the HTC reactor(s). The temperature in the HTC reactor(s) may be 150 - 250 °C and the pressure may be 20 - 30 bar. The residence time in the HTC reactor(s) may be about 3 - 6 hours. Lignin may be carbonized in the HTC reactor, whereby a stabilized lignin derivative having a high specific surface area may precipitate. The formed slurry contains carbonized lignin particles. The HTC lignin particles are separated from the slurry (e.g., by filtration), and subsequently the filter cake is dried and the cake is ground to a suitable particle size.

[0019] A lignin-containing starting material, preferably in the form of a lignin solution, is subjected to a hydrothermal carbonization (HTC) process. For example, HTC lignin can be obtained by heating a lignin-containing starting material in the presence of water to a temperature between 150 - 350 °C, preferably between 150 - 250 °C, usually under an autogenous pressure of 10 - 40 bar. The heat treatment may continue for 30 minutes to 8 hours or more. Preferably, this treatment is completed within 1 - 6 hours, or more preferably within 2 - 4 hours.

[0020] For the hydrothermal carbonization of a lignin-containing raw material, it is preferred that at least a part of the lignin is dissolved. Such partial or complete dissolution can be achieved by adjusting the pH to >7, preferably >9, most preferably >10. When the pH before the HTC treatment is between 10 - 12, preferably between 10 - 11, it preferably affects the particle size distribution of the HTC lignin according to the use of the present invention. In a preferred embodiment, the lignin for the hydrothermal treatment is in a solution state.

[0021] The temperature may be raised above 50°C, for example to 70 - 90°C, preferably 80°C, to facilitate dissolution. The dissolution conditions must be maintained for at least 5 minutes, more preferably at least 10 minutes, more preferably at least 15 minutes, particularly preferably at least 30 minutes, especially at least 45 minutes, but less than 300 minutes.

[0022] Regarding the present invention, it is not necessary for all of the lignin to dissolve in the liquid. However, it is advantageous for more than 50%, particularly preferably more than 60%, additionally preferably more than 70%, particularly preferably more than 80%, especially more than 90% of the lignin to be dissolved in the liquid.

[0023] In a particularly preferred embodiment, the mixture of at least partially dissolved lignin also contains at least one crosslinking agent capable of reacting with the functional groups of the lignin. Such crosslinking agent compounds can have aldehyde groups, carboxylic acid groups, epoxide groups, hydroxy groups, isocyanate groups, or other functional groups. The functional groups of the crosslinking agent must be able to react twice with the functional groups of the lignin. If the functional group can only react once, the crosslinking agent must contain at least two such functional groups. Aldehydes and particularly formaldehyde are preferred. The crosslinking agent may be added during the dissolution stage and / or during the HTC stage. The reaction between the crosslinking agent and the lignin may be at an intermediate stage between the dissolution stage and the HTC stage, and pH adjustment may be required to cause the reaction.

[0024] The crosslinking agent should be used in excess relative to the crosslinkable groups of the lignin. Such an excess can be 1.5 times, 2 times, or even 4 times. A typical amount is less than 40 wt%, less than 35 wt%, or preferably less than 25 wt% based on the weight of the lignin.

[0025] The amount and type of the crosslinking agent helps to adjust the surface area of the product obtained in the HTC stage. Using the crosslinking agent increases the surface area of the HTC lignin particles, and generally, increasing the amount of the crosslinking agent also increases the surface area.

[0026] Particle shape may be affected by specific process parameters, such as the dry matter content of the starting material mixture, the pH of the starting material mixture, the inorganic ion concentration of the starting material mixture, and the temperature and residence time during the superheated steam treatment. The dry matter concentration of the starting material mixture is preferably not more than 40% by weight (based on the starting material mixture), preferably 20% by weight or less, and most preferably 10% by weight or more. The pH is preferably 7 or higher, for example 8.5 or higher, and even more preferably 11 or higher. The inorganic ion value measured by conductivity is between 10 and 200 mS / cm, preferably between 10 and 150 mS / cm, more preferably between 10 and 50 mS / cm, even more preferably between 10 and 40 mS / cm, and particularly preferably between 10 and 25 mS / cm (determined by the conductivity of the PCE-PHD1 measuring probe at 20 to 25°C). The temperature of the superheated steam treatment may be limited to a maximum of 250°C or less, preferably between 150 and 250°C. Dwell time between 1 minute and 6 hours, for example between 30 minutes and 4 hours or between 1 and 3 hours, is also useful. The above methods may be used in combination.

[0027] If necessary, particle size can be adjusted by separation or by mixing different HTC lignin materials. Gravity separation in a liquid or gaseous medium is a preferred method. Equipment for separation is well known to those skilled in the art. Examples include cyclones, especially hydrocyclones in the case of liquids, centrifuges, or classifiers (air classifiers). However, the present invention is not limited to the use of specific equipment. Any equipment that enables separation, such as fluidized beds or sieves, can be used. Different types of separation can also be combined.

[0028] The resulting HTC lignin is preferably 180m 2 / g or less, preferably 120m 2 / g, 90m 2 / g, 60m 2 / g or 40m 2 / g or less, more preferably 30m 2 / g or less, for example 25 m 2 / g, 20 m 2 / g, 15 m 2 / g or 10 m 2 It has an STSA of / or less. The STSA specific surface area is determined according to ASTM D6556-21. The STSA (statistical thickness specific surface area) is an indicator of the outer surface of the HTC lignin particles.

[0029] The particles preferably have a particle size of D90 ≤ 30 μm, more preferably D95 ≤ 30 μm, and most preferably D99 ≤ 30 μm. It is most preferred that the particle size is D99 < 20 μm. The particle size is determined according to ISO13320.

[0030] Advantageously, the BET specific surface area of this HTC lignin deviates from the STSA specific surface area by at most 20%, preferably at most 15%, and more preferably at most 10%. The BET surface area is determined by nitrogen adsorption by the particles as the total surface area of the outer and inner surfaces according to Brunauer, Emmett, and Teller. The method for determining the BET surface area is also disclosed in ASTM D6556-21.

[0031] The HTC lignin can be used in any amount relative to the weight of the rubber article. Preferably, the HTC lignin is used in the range of 5 to 200 phr, 10 to 150 phr, 15 to 125 phr, 20 to 100 phr, and most preferably 25 to 75 phr (phr means the number of parts per 100 parts of rubber on a weight basis).

[0032] For example, other components for compounding and processing may be present. For example, processing aids such as process oils (mainly paraffinic oils and bio-based oils), PEG, waxes, stearic acid, ZnO, desiccant CaO, sulfur vulcanizing agents, peroxide vulcanizing agents, etc., flame retardants, antioxidants, etc. may be present as long as they are not harmful to the properties of the composition.

[0033] The mixture can be obtained by mixing the components according to conventional procedures. In one method, the HTC lignin is added to the rubber composition.

[0034] The rubber article may contain further solids such as carbon black, settled silica, Neuburg siliceous earth, and additional white fillers (talc, chalk, kaolin). The further solids may be used in the range of 5-200 phr, 10-150 phr, 15-125 phr, 20-100 phr, most preferably 25-75 phr.

[0035] The composition may further contain one or more silane compounds, such as 3,3'-bis(triethoxysilylpropyl)tetrasulfide (TESPT), 3,3'-bis(triethoxysilylpropyl)disulfide (TESPD), 3-thiocyanatopropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, vinyltriethoxysilane, and chloropropyltriethoxysilane, of which TESPT and TESPD are preferred. The silane compound is in the range of 0.25-20 phr, 0.5-16 phr, 0.75-12 phr, 1.0-10 phr, 1.5-8 phr, 2.0-6 phr, and 2.5-5 phr (phr means parts per 100 parts of rubber).

[0036] The rubber articles according to the present invention can be used in a variety of fields. Their excellent biodegradability makes them most effective in rubber articles that would normally pose an environmental hazard, such as tires, especially vehicle tires.

[0037] The biodegradability of the rubber articles of the present invention can be determined according to ISO 17556. Preferably, the biodegradation after 150 days is >5%, after 360 days it is >10%, after 480 days it is >15%, and after 720 days it is >20%. The biodegradation of the rubber articles of the present invention is preferably more than 40% higher after 360 days and more than 50% higher after 720 days compared to carbon black. [Brief explanation of the drawing]

[0038] [Figure 1]This graph shows the biodegradation of comparative examples, the present invention, and pure HTC lignin, measured according to ISO 17556.

[0039] [Examples] Two samples were prepared by incorporating 50 phr of carbon black (N330) or 50 phr of HTC lignin into natural rubber. The compositions were as follows:

[0040] [Table 1]

[0041] Vulcanizable rubber compositions were prepared using a two-step mixing process in a closed-type mixer model TMI 0.6 manufactured by ERMAFA Sondermaschinen-und Anlagenbau GmbH, as shown in Table 2. Lamination of the rubber compositions was then carried out after each mixing step using a two-roll mill model LaboWalz W150 manufactured by Vogt Labormaschinen GmbH. The rubber laminates obtained by milling after the second mixing step were press-vulcanized at 150°C for 30 minutes in a hydraulic press model LP3000 600kN manufactured by MonTech Werkstoffprufmaschinen GmbH to obtain sheets, which were then evaluated for biodegradability.

[0042] [Table 2]

[0043] For comparison, HTC lignin was also examined independently.

[0044] Biodegradation was measured according to ISO 17556, and the results are shown in Figure 1.

[0045] [Table 3]

[0046] The HTC lignin-containing rubber articles were found to exhibit higher biodegradability compared to the carbon black-based comparative examples at all time points (see Table 3). The improvement in biodegradability of the compound of the present invention was 13.8% after 60 days, 25.5% after 150 days, 43.8% after 360 days, and 55.5% after 720 days.

[0047] The biodegradation of rubber compounds filled with HTC lignin according to ISO 17556 was over 5% after 150 days, over 10% after 360 days, over 15% after 480 days, and over 20% after 720 days. At the end of the study (720 days), the HTC lignin-containing rubber articles showed biodegradation more than 55% higher than the carbon black-containing rubber articles.

[0048] It is also noteworthy that the biodegradation of lignin-containing rubber articles did not follow the biodegradation rate of HTC lignin itself. This indicates that HTC lignin and the rubber material interact, resulting in the high biodegradation rate shown in Figure 1.

Claims

1. A method for preparing a biodegradable rubber article, comprising the step of adding HTC lignin to a rubber composition containing at least one rubber component, wherein the rubber article has more than 5% biodegradation after 150 days, preferably more than 10% biodegradation after 360 days and / or more than 20% biodegradation after 720 days, in accordance with ISO 17556.

2. The method according to claim 1, wherein the rubber is selected from natural rubber (NR), epoxidized rubber (ENR), butadiene rubber (BR), styrene-butadiene rubber (SBR), isoprene rubber (IR), epoxidized natural rubber (ENR), butyl rubber (IIR), bromobutyl rubber (BIIR), chlorobutyl rubber (CIIR), ethylene propylene diene monomer rubber (EPDM), ethylene propylene rubber (EPR), acrylonitrile butadiene rubber (NBR), hydrogenated nitrile rubber (HNBR), chloroprene rubber (CR), epichlorohydrin rubber (ECO), silicone rubber (VMQ), fluororubber (FKM), and mixtures thereof.

3. The method according to claim 1 or 2, wherein the rubber article comprises natural rubber (NR), butadiene rubber (BR), styrene-butadiene rubber (SBR), isoprene rubber (IR), epoxidized natural rubber (ENR), bromobutyl rubber (BIIR), chlorobutyl rubber (CIIR), and mixtures thereof.

4. The method according to any one of claims 1 to 3, wherein the HTC lignin is used in an amount of 5 to 200 phr, 10 to 150 phr, 15 to 125 phr, 20 to 100 phr, most preferably 25 to 75 phr.

5. The HTC lignin is 180 m ２ / g or less, preferably 120 m ２ / g or less, 90 m ２ / g or less, 60 m ２ / g or less or 40 m ２ / g or less, more preferably 30 m ２ / g or less, for example, 25 m ２ / g or less, 20 m ２ / g or less, 15 m ２ / g or less or 10 m ２ / g or less of ST-SA, and the method according to any one of claims 1 to 4.

6. The method according to any one of claims 1 to 5, wherein the rubber article comprises further solids such as carbon black, settled silica, Neuburg siliceous soil, and additional white fillers (talc, chalk, kaolin).

7. The method according to any one of claims 1 to 6, wherein the rubber article is a tire, in particular a vehicle tire.

8. Use of HTC lignin to promote the biodegradation of rubber articles.

9. The use according to claim 8, wherein the rubber is selected from natural rubber (NR), epoxidized rubber (ENR), butadiene rubber (BR), styrene-butadiene rubber (SBR), isoprene rubber (IR), epoxidized natural rubber (ENR), butyl rubber (IIR), bromobutyl rubber (BIIR), chlorobutyl rubber (CIIR), ethylene propylene diene monomer rubber (EPDM), ethylene propylene rubber (EPR), acrylonitrile butadiene rubber (NBR), hydrogenated nitrile rubber (HNBR), chloroprene rubber (CR), epichlorohydrin rubber (ECO), silicone rubber (VMQ), fluororubber (FKM), and mixtures thereof.

10. The use according to claim 8 or 9, wherein the rubber article comprises natural rubber (NR), butadiene rubber (BR), styrene-butadiene rubber (SBR), isoprene rubber (IR), epoxidized natural rubber (ENR), bromobutyl rubber (BIIR), chlorobutyl rubber (CIIR), and mixtures thereof.

11. The use according to any one of claims 8 to 10, wherein the HTC lignin is used in an amount of 5 to 200 phr, 10 to 150 phr, 15 to 125 phr, 20 to 100 phr, most preferably 25 to 75 phr.

12. The HTC lignin is prepared according to ASTM D6556-21, at a rate of 180 m ２ / g or less, preferably 120m ２ / g or less, 90m ２ / g or less, 60m ２ / g or less or 40m ２ / g or less, more preferably 30m ２ Less than or equal to 25mg, for example, 25mg ２ / g, 20m ２ / g, 15m ２ / g or 10m ２ The use according to any one of claims 8 to 11, having an STSA of less than or equal to / g.

13. The use according to any one of claims 8 to 12, wherein the rubber article comprises further solids such as carbon black, settled silica, Neuburg siliceous soil, and additional white fillers (talc, chalk, kaolin).

14. The use according to any one of claims 8 to 13, wherein the rubber article is a tire, in particular a vehicle tire.

15. A rubber article obtained according to any one of claims 1 to 14.

Images