EP4720183A1

EP4720183A1 - Method for making biodegradable rubber articles and rubber articles

Info

Publication number: EP4720183A1
Application number: EP23729734.6A
Authority: EP
Inventors: Florian Diehl; Suvi Pietarinen; Barbara Gall; Christian Hübsch
Original assignee: UPM Kymmene Oy
Current assignee: UPM Kymmene Oy
Priority date: 2023-05-30
Filing date: 2023-05-30
Publication date: 2026-04-08
Also published as: KR20260014654A; AU2023450952A1; CN121487996A; WO2024245535A1; MX2025014313A

Abstract

The invention is concerned with a method for preparing biodegradable rubber articles comprising the step of adding HTC lignin to a rubber composition comprising at least one rubber component, the use of HTC lignin to facilitate biodegradation of rubber articles and respective rubber articles.

Description

Method for making Biodegradable Rubber Articles and Rubber Articles

The present invention relates to a method of making biodegradable rubber articles, the use of HTC lignin to facilitate the biodegradation of rubber articles and to respective rubber articles.

The biodegradation of rubber articles takes a very long time. At the same time, rubber wear particles from tires are one of the major sources of primary microplastics ending up unintentionally in e.g. the ocean. Since polymeric materials do not decompose easily, microplastics are constantly accumulating which is of serious environmental concern for flora and fauna.

Widespread studies on the biodegradation of rubbers have shown that both natural and synthetic rubbers are degraded by microbes, bacteria and fungi which are ubiquitous in the environment - especially soil. However, rubber degradation is a rather slow process and vulcanized rubber degrades even more slowly due to the interlinking of polymer chains.

Surprisingly it has been found by soil degradation testing that biodegradability of rubber can be significantly improved when it contains some HTC lignin. Thus, HTC lignin can be used to facilitate the biodegradation of rubber articles and thereby reduce the environmental burden provided by such articles.

The present invention thus relates to the use of HTC lignin to facilitate the biodegradation of rubber articles. The rubber articles are obtained by the method of the invention. In this method, HTC lignin is added to a rubber composition and the resulting mixture is the processed further according to conventional procedures.

The rubber composition comprises at least one rubber component. The rubber component may for example be one the following: natural rubber (NR) epoxidized rubber (ENR) butadiene rubber (BR) styrene-butadiene rubber (SBR) isoprene rubber (IR) epoxidized natural rubber (ENR) butyl rubber (HR) bromobutyl rubber (BUR) chlorobutyl rubber (CIIR) ethylene propylene diene monomer rubber (EPDM) ethylene propylene rubber (EPR) acrylonitrile-butadiene rubber (NBR) hydrogenated nitrile rubber (HNBR) chloroprene rubber (CR) epichlorhydrin rubber (ECO) silicone rubber (VMQ) fluoro rubber (FKM)

Mixtures of these rubbers may also be used. All of the rubbers used in the rubber composition may be derived either from a fossil source or from a biobased source.

Tire rubbers such as natural rubber (NR), butadiene rubber (BR), styrene-butadiene rubber (SBR), isoprene rubber (IR), epoxidized natural rubber (ENR), bromobutyl rubber (BUR), chlorobutyl rubber (CIIR) and mixtures thereof are preferred.

The HTC lignin is obtained by hydrothermal carbonisation of lignin, whereby biomass is treated under pressure and in the presence of hot water and/or steam. As opposed to pyrolysis, biomass decomposes incompletely during hydrothermal carbonisation and the products are a solid carbon-rich material, a gas phase composed mainly of CO2, water and water-soluble compounds.

HTC lignin can be prepared from any kind of lignin-containing starting material such as lignincontaining waste materials as well as lignin in solid or dissolved form and mixtures thereof. A high lignin content of 60 wt.-% or more, preferably 80 wt.-% or more or better still more than 90 wt.-% in the starting material is preferred.

Preferred lignin-containing starting materials are black liquor from the digestion of woody biomass or solids prepared from it, solids from the enzymatic hydrolysis of woody biomass, black liquor from the digestion of woody biomass with sulphites (lignosulfonates) or solids or liquids prepared from the digestion of woody biomass with solvents (e.g. organosolv lignin). In a preferred embodiment of the present invention, the lignin is derived as a side stream in the enzymatic hydrolysis of a lignocellulosic feedstock. This preferred starting material is also known as EH-lignin.

The lignin-containing starting material may be selected from a group consisting of kraft lignin, steam explosion lignin, biorefinery lignin, supercritical separation lignin, hydrolysis lignin, flash precipitated lignin, biomass originating lignin, lignin from alkaline pulping process, lignin from soda process, lignin from organosolv pulping, lignin from alkali process, lignin from enzymatic hydrolysis process, and any combination thereof. In one embodiment, the lignin is wood based lignin. The lignin can originate from softwood, hardwood, annual plants or from any combination thereof.

"Kraft lignin" is lignin that originates from kraft black liquor. Black liquor is an alkaline aqueous solution of lignin residues, hemicellulose, and inorganic chemicals used in a kraft pulping process. The black liquor from the pulping process comprises components originating from different softwood and hardwood species in various proportions. Kraft-lignin can be separated from the black liquor by different, techniques including e.g. precipitation and filtration.

The term "flash precipitated lignin" should be understood as lignin that has been precipitated from black liquor in a continuous process by decreasing the pH of a black liquor flow, under the influence of an over pressure of 200 - 1000 kPa, down to the precipitation level of lignin using a carbon dioxide based acidifying agent, preferably carbon dioxide, and by suddenly releasing the pressure for precipitating lignin. The flash precipitated lignin particles, having a particle diameter of less than 2 pm form agglomerates, which can be separated from black liquor using e.g. filtration.

The lignin may originate from an organosolv process. Organosolv is a pulping technique that uses an organic solvent to solubilize lignin and hemicellulose.

The lignin may be slurried or dissolved for the hydrothermal conversion. Preferably, the lignin is dissolved in alkaline solution, such as NaOH. The dissolution may be accomplished by heating the mixture of lignin and alkaline solution to about 80 °C, adjusting the pH to a value above 7, such as 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 grade target of the product.

The slurry may directly be subjected to hydrothermal treatment or fed to a separation unit, wherein the precipitated lignin may be separated from the slurry.

The hydrothermal carbonization treatment may take place in a reactor (HTC reactor), or if needed, in several parallel reactors, working in a batchwise manner. The dissolved lignin may be pre-heated before being entered in 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 three to six hours. In the HTC reactor, the lignin is carbonized, whereby a stabilized lignin derivative with a high specific surface area may be precipitated. The formed slurry comprises the carbonized lignin particles. The HTC lignin particles are separated from the slurry (e.g. by filtration), followed by drying the filter cake, and crushing the cake to a suitable particle size.

The lignin-containing starting material, preferably in the form of a lignin solution, is subjected to a hydrothermal carbonization (HTC) process. For instance, the HTC lignin can be obtained by heating a lignin-containing starting material in the presence of water to temperatures between 150 and 350°C, preferably between 150°C and 250°C under autogenic pressure, typically 10 to 40 bar. The heat treatment can be maintained for 30 minutes and up to 8 or more hours. Preferably, the treatment is completed within 1 to 6 hours or more preferably within 2 to 4 hours.

For the hydrothermal carbonisation of the lignin-containing raw materials it is preferred that at least a part of the lignin is dissolved. Such partial or full dissolution can be achieved by adjusting the pH to >7, preferably >9 and most preferably >10. A pH between 10 and 12, preferably between 10 and 11 before the HTC treatment favorably impacts the particle size distribution of the HTC lignin for the use according to the present invention. In a preferred embodiment, the lignin for the hydrothermal treatment is in solution.

The dissolution may also be assisted by raising the temperature to more than 50°C, for instance 70 to 90°C and preferably 80°C. The dissolution conditions should 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, in particular at least 45 minutes but less than 300 minutes.

For the present invention, it is not necessary that the entire lignin is dissolved in the liquid. Advantageously, however, more than 50%, particularly preferably more than 60%, in addition preferably more than 70%, particularly preferably more than 80% in particular more than 90% of the lignin dissolved in the liquid.

In a particularly preferred embodiment, the mixture of the at least partially dissolved lignin also comprises at least one crosslinking agent capable of reacting with the functional groups of the lignin. Such crosslinking compounds may have aldehyde, carboxylic acid, epoxy, hydroxyl, isocyanate or other functional groups. The functional group of the crosslinking agent should be capable of reacting twice with the functional groups of the lignin. If the functional group can only react once, the crosslinking agent should contain at least two such groups. Aldehydes and especially formaldehyde are preferred. The crosslinking agent may be added in the dissolution step and/or the HTC step. The reaction of the crosslinking agent with the lignin may also be an intermediate step between the dissolution and the HTC steps and it may require a pH adjustment to effect the reaction.

The crosslinking agent should be used in excess relative to the cross-linkable groups of the lignin. Such excess can be 1.5, 2 or even 4-fold. Typical amounts are less than 40, less than 35 or preferably less than 25 wt.-% based on the lignin weight.

The amount and type of the crosslinking agent helps to adjust the surface area of the product obtained in the HTC step. The use of the crosslinking agent increases the surface area of the HTC lignin particles, whereby generally the surface area also increases with an increase in the amount of crosslinker.

The particle morphology can be influenced by certain process parameters. For instance, by adjusting 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 hydrothermal treatment. Advantageously, the dry matter concentration of the starting material mixture does not exceed 40 wt.-% (based on the starting material mixture), preferably not more than 20 wt.-% and most preferably not below 10 wt.-%. The pH is advantageously 7 or higher such as 8.5 or more or even 11 or higher. Inorganic ions as measured by conductivity to a value between 10 mS/cm and 200 mS/cm, preferably between 10 mS/cm and 150 mS/cm, more preferably between 10 mS/cm and 50 mS/cm, moreover preferably between 10 mS/cm and 40 mS/cm, in particular preferably between 10 mS/cm and 25 mS/cm (determined as conductance of the measuring probe of the PCE-PHD1 at 20°C to 25°C). The temperature of the hydrothermal treatment can be limited to maximum value of 250°C or less, preferably between 150°C and 250°C. Residence times between 1 minute and 6 hours such as between 30 minutes and 4 hours or 1 and 3 hours are also useful. The above measures may also be adopted in combination.

If need be, the particle size can also be adjusted by separation or by mixing different HTC lignin materials. Gravity separation in liquid or gaseous media is a suitable method. Devices for separation are well known to those skilled in the art. Examples include cyclones, esp. hydrocyclones in case of liquids, centrifuges or classifiers (air classifiers). However, the present invention is not limited to the use of specific devices. All devices that allow separation can be used, e.g. fluidized bed devices, sieves etc. Different types of separation can also be combined.

The resulting HTC lignin preferably has an STSA of 180 m²/g or less, preferably 120 m²/g, 90 m²/g, 60 m²/g or 40 m²/g or less, more preferably 30 m²/g or less, such as 25 m²/g, 20 m²/g, 15 m²/g or 10 m²/or less. The STSA surface area is determined according to ASTM D 6556-21. STSA (statistical thickness surface area) is an indication of the outer surface of the HTC lignin particles.

The particles preferably have a particle size of D90 < 30pm, more preferably D95 < 30pm, and most preferably D99 < 30pm. It is most preferred that the particle size is D99 < 20pm. The particle size can be determined according to ISO 13320

Advantageously, the BET specific surface area of the present HTC lignin deviates only by a maximum of 20% preferably by a maximum of 15% more preferably by a maximum of 10% from the STSA surface. The BET surface area is determined as the total surface area of outer and inner surface by means of nitrogen adsorption by the particles according to Brunauer, Emmett and Teller. A method for determining the BET surface is also disclosed in ASTM D 6556-21.

The HTC lignin may be used in any amount based on the weight of the rubber article. Preferably, it is used within the range of 5 - 200 phr, 10 - 150 phr, 15 - 125 phr, 20 - 100 phr and most preferably 25 - 75 phr (phr means parts per 100 parts rubber on a weight basis).

Other components, e.g. for compounding and processing can be present. For examples process oil (mainly paraffinic oils, and bio-based oils), process aids such as PEG, waxes, stearic acid, ZnO, drying agent CaO, sulfur cure, peroxide cure; flame retardants, antioxidants and the like may be present as long as they are not detrimental to the properties of the composition.

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.

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

The composition may further comprise one or more silane compound such as 3,3'-bis- (triethoxysilylpropyl)-tetrasulfide (TESPT), 3,3'-bis-(triethoxysilylpropyl)-disulfide (TESPD), 3- thiocyanato-propyltriethoxysilane, y-mercaptopropyl-trimethoxysilane, vinyltriethoxysilane, chlorpropyltriethoxy-silane or he like, whereby TESPT and TESPD are preferred. The silane compounds range from 0.25 - 20 phr, 0.5 phr- 16 phr, 0.75 phr - 12 phr, 1.0 phr- 10 phr, 1.5 phr- 8 phr, 2.0 phr - 6 phr and 2.5 - 5 phr (phr means parts per hundred parts rubber). The rubber article according to the present invention can be used in various fields. Its superior biodegradation properties are most effectively used in rubber articles which may otherwise present an environmental hazard such as tires and especially vehicle tires.

The biodegradability of the rubber articles of the invention can be determined according to ISO 17556. It is preferable that the biodegradation after 150 days is > 5%, after 360 days > 10%, after 480 days > 15%, and after 720 days > 20%. The biodegradation of the rubber articles according to the present invention compared to carbon black is preferably more than 40% higher after 360 days and more than 50% higher after 720 days.

Example

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

Table 1

The curable rubber compositions were prepared in an internal mixer model TMI 0.6 from ERMAFA Sondermaschinen- und Anlagenbau GmbH applying a two-step mixing process as described in Table 2. Lamination of rubber compositions was done subsequently after each mixing step by a two-roll mill model LaboWalz W150 from Vogt Labormaschinen GmbH. The rubber laminates obtained from milling after the second mixing step were pressed and cured in a hydraulic press model LP3000 600kN from MonTech Werkstoffprufmaschinen GmbH at 150°C for 30 minutes to produce sheets, which were then evaluated for biodegradability.

Table 2:

By way of comparison, the HTC lignin was also considered in isolation.

The biodegradation was measured according to ISO 17556 and the results are shown in Figure 1.

Table 3

¹ (Invention - Comparative)/Comparative * 100%

It was found that the HTC lignin containing rubber article showed a higher biodegradation at all time points compared to the comparative example based on Carbon Black (see Table 3). The biodegradability improvement of the biodegradation of the inventive compound is 13.8% after 60 days, 25.5% after 150 days, 43.8% after 360 days, and 55.5% after 720 days.

The biodegradation of the rubber compound filled with HTC lignin according to ISO 17556 was greater than 5% after 150 days, greater than 10% after 360 days, greater than 15% after 480 days and greater than 20% after 720 days. At the end of the study (720 days) the HTC lignin containing rubber article showed a more than 55% higher biodegradation than the carbon black containing rubber article.

It is also noteworthy that the biodegradation of the lignin-containing rubber article did not follow the rate of the biodegradation of the HTC lignin as such. This goes to show that the HTC lignin and the rubber material interact to provide the high biodegradation rate shown in Figure 1.

Claims

1. Method for preparing biodegradable rubber articles comprising the step of adding HTC lignin to a rubber composition comprising at least one rubber component, whereby the rubber article has a biodegradation greater than 5% according to ISO 17556 after 150 days, and preferably a biodegradation greater than 10% after 360 days and/or a biodegradation greater than 20% after 720 days.

2. 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 (HR), bromobutyl rubber (BUR), chlorobutyl rubber (CIIR), ethylene propylene diene monomer rubber (EPDM), ethylene propylene rubber (EPR), acrylonitrile-butadiene rubber (NBR), hydrogenated nitrile rubber (HNBR), chloroprene rubber (CR). epichlorhydrin rubber (ECO), silicone rubber (VMQ), fluoro rubber (FKM), and mixtures thereof.

3. Method according to claim 1 or claim 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 (BUR), chlorobutyl rubber (CIIR) and mixtures thereof

4. Method according to any of the preceding claims, wherein the HTC lignin is used in an amount of of 5 - 200 phr, 10 - 150 phr, 15 - 125 phr, 20 - 100 phr and most preferably 25 - 75 phr.

5. Method according to any of the preceding claims, wherein the HTC lignin has an STSA according to ASTM D 6556-21 of 180 m²/g or less, preferably 120 m²/g or less, 90 m²/g or less, 60 m²/g or less or 40 m²/g or less, more preferably 30 m²/g or less, such as 25 m²/g or less, 20 m²/g or less, 15 m²/g or less or 10 m²/g or less.

6. Method according to any of the preceding claims, wherein the rubber article contains further solids such as carbon black, precipitated silica, neuburg siliceous earth, and additional white fillers (talc, chalk, kaolin).

7. Method according to any of the preceding claims, wherein the rubber article is a tire, especially a vehicle tire.

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

9. 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 (HR), bromobutyl rubber (BUR), chlorobutyl rubber (CIIR), ethylene propylene diene monomer rubber (EPDM), ethylene propylene rubber (EPR), acrylonitrile-butadiene rubber (NBR), hydrogenated nitrile rubber (HNBR), chloroprene rubber (CR), epichlorhydrin rubber (ECO), silicone rubber (VMQ), fluoro rubber (FKM), and mixtures thereof.

10. Use according to claim 8 or claim 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 (BUR), chlorobutyl rubber (CIIR) and mixtures thereof

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

12. Use according to any of claims 8 to 11, wherein the HTC lignin has an STSA according to ASTM D 6556-21of 180 m²/g or less, preferably 120 m²/g or less, 90 m²/g or less, 60 m²/g or less or 40 m²/g or less, more preferably 30 m²/g or less, such as 25 m²/g, 20 m²/g, 15 m²/g or 10 m²/g or less.

13. Use according to any of claims 8 to 12, wherein the rubber article contains further solids such as carbon black, precipitated silica, neuburg siliceous earth, and additional white fillers (talc, chalk, kaolin).

14. Use according to any of claims 8 to 13, wherein the rubber article is a tire, especially a vehicle tire.

15. Rubber article obtainable according to any of the preceding claims.