Composition for rubber articles and rubber articles having low carbon footprint and high mechanical strength

Abstract

The present invention relates to a composition comprising a functionalized rubber, HTC lignin, and optionally a non-functionalized rubber. The present invention also relates to a rubber article obtained by vulcanizing the composition, a method for making a rubber article from the composition, and the use of the composition.

Description

Detailed Description of the Invention

[0001] Rubber compounds generally contain significant amounts of functional fillers, one reason being to reinforce the material to achieve the desired mechanical properties needed for the end use application.

[0002] Replacing traditional fillers such as carbon black in rubber compounds with renewable functional fillers (RFF) offers many benefits, including reduced compound weight, making the compound non-conductive, increasing the renewable content, and significantly reducing the carbon footprint.

[0003] However, replacing a large proportion of carbon black in rubber compounds, especially in non-polar rubbers such as ethylene propylene diene monomer rubber (EPDM), with RFF often leads to a deterioration in the compound's mechanical properties compared to a carbon black-based reference compound, which limits the amount of RFF that can be used in the composition and therefore the potential for reducing, for example, weight and CO2 footprint.

[0004] U.S. Patent Application Publication No. 2013 / 0150488 relates generally to the field of power transmission belts, and more particularly to rubber compositions reinforced with cellulosic fibers (kenaf) for use in belts. The application discloses that a compatibilizer, such as a maleated polymer, can improve adhesion of the fibers to the elastomer.

[0005] EP 2042346 discloses a lignin-containing rubber composition for tire treads, where lignin is used in small amounts as a lubricity-promoting material.

[0006] It has now been found that HTC lignin (HTC lignin is lignin that has undergone superheated steam carbonization) can significantly improve properties such as tensile strength, dynamic properties, and abrasion resistance when used with functionalized rubbers such as EPDM-g-MAH (EPDM rubber grafted with maleic anhydride) by itself, or in addition to non-functionalized rubbers such as olefin diene copolymers. The use of HTC lignin and functionalized rubbers allows for higher reinforcement levels, i.e., higher amounts of RFF in the composition, thereby enhancing the impact of other desirable characteristics of RFF on the compound.

[0007] This approach is applicable to all rubber processing molding techniques, such as extrusion, injection molding, compression molding, transfer molding, injection-compression molding, etc., and to all rubber articles containing olefin-diene copolymers, such as EPDM, bio-based EPDM, and other rubbers.

[0008] Accordingly, the present invention relates to compositions and rubber articles as defined in the claims. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 shows the vulcanization characteristics of Example 1. [Figure 2] FIG. 2 shows the stress-strain characteristics of Example 1. [Figure 3] FIG. 3 shows the vulcanization characteristics of Example 2. [Figure 4] FIG. 4 shows the stress-strain characteristics of Example 2. [Figure 5] FIG. 5 shows the vulcanization characteristics of Example 3. [Figure 6] FIG. 6 shows the stress-strain characteristics of Example 3.

[0010] The rubber may be selected from, inter alia, EPDM, EPR, butadiene rubber (BR), chloroprene rubber (CR), epoxidized natural rubber (ENR), hydrogenated nitrile rubber (HNBR), butyl rubber (IIR), isoprene rubber (IR), α-methylstyrene butadiene rubber (MSBR), acrylonitrile butadiene rubber (NBR), natural rubber (NR), styrene butadiene rubber (SBR), bromobutyl rubber (BIIR) and chlorobutyl rubber (CIIR). EPDM and EPM are preferred. These rubbers can be used as they are, as non-functionalized rubbers (component c)).

[0011] The functionalized rubber (component a)) can be derived from any one of the above rubbers by introducing functional groups. The functional groups can be introduced by grafting or other known methods. Suitable functional groups are carboxylic acid groups, epoxide groups, silane groups, chloro and / or bromo substituents. Carboxylic acid groups, such as maleic acid groups, are preferred.

[0012] Functional derivatives of EPDM and EPR are preferred, especially maleic acid grafted EPDM.

[0013] The filler is selected from HTC lignin (component b)) and blends comprising HTC lignin with other fillers such as carbon black, Neuburg diatomaceous earth, silica and additional white fillers (talc, chalk, kaolin).

[0014] HTC lignin is obtained by superheated steam carbonization of lignin, in which biomass is treated under pressure and in the presence of hot water and / or steam. In contrast to pyrolysis, during superheated steam carbonization the biomass is incompletely decomposed and the products are a carbon-rich solid material, a gas phase composed mainly of CO2, water, and water-soluble compounds.

[0015] 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 dissolved 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.

[0016] Preferred lignin-containing starting materials are black liquor from the digestion of woody biomass or solids prepared therefrom, solids from the enzymatic hydrolysis of woody biomass, black liquor (lignosulfonates) from the digestion of woody biomass with sulfites, or solids or liquids prepared from the digestion of woody biomass with solvents (e.g., organosolv lignin). In a preferred embodiment of the invention, the lignin is derived as a side stream in the enzymatic hydrolysis of lignocellulosic feedstock. This preferred starting material is also known as EH-lignin.

[0017] The lignin-containing starting material can be selected from the group consisting of kraft lignin, steam-exploded lignin, biorefinery lignin, supercritically separated lignin, hydrolyzed lignin, flash precipitated lignin, biomass-derived lignin, alkaline cooking lignin, soda process lignin, organosolv cooking lignin, alkali-treated lignin, enzymatic hydrolysis lignin, and any combination thereof. In one embodiment, the lignin is lignin. The lignin can be derived from softwood, hardwood, annual plants, or any combination thereof.

[0018] "Kraft lignin" is lignin derived from kraft black liquor, an alkaline aqueous solution of lignin residues, hemicellulose, and inorganic chemicals used in the kraft pulping process. Black liquor from this pulping process contains components derived from different softwood and hardwood species in varying proportions. Kraft lignin can be separated from black liquor by various techniques, including, for example, precipitation and filtration.

[0019] The term "flash precipitated lignin" should be understood to mean lignin precipitated from black liquor by using a carbon dioxide-based acidifying agent, preferably carbon dioxide, under the influence of an overpressure of 200-1000 kPa to lower the pH of the black liquor stream to a lignin precipitation level in a continuous process, and then suddenly releasing the pressure to precipitate the lignin. Flash precipitated lignin particles have a particle size of less than 2 μm and form agglomerates that can be separated from the black liquor using, for example, filtration.

[0020] The lignin may be derived from organosolv, a pulping technique that uses organic solvents to solubilize the lignin and hemicellulose.

[0021] The lignin may be slurried or dissolved for superheated steam conversion. Preferably, the lignin is dissolved in an alkaline solution such as NaOH. Dissolution may be accomplished by heating the lignin and alkaline solution mixture to about 80°C, adjusting the pH to above 7, e.g., 9-11, and mixing the lignin and alkaline solution mixture for a predetermined period of time. The mixing period may last about 2-3 hours. The exact pH value is determined based on the product grade target.

[0022] The slurry may be subjected directly to superheated steam treatment or may be fed to a separation unit to separate the precipitated lignin from the slurry.

[0023] The superheated steam carbonization process can be carried out in a reactor (HTC reactor) or, if necessary, in multiple parallel reactors operating in batch mode. 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. The lignin may be carbonized in the HTC reactor, thereby precipitating a stabilized lignin derivative with a high specific surface area. The formed slurry contains carbonized lignin particles. The HTC particles are separated from the slurry (e.g., by filtration), followed by drying the filter cake and grinding it to a suitable particle size.

[0024] The lignin-containing starting material, preferably in the form of a lignin solution, is subjected to a superheated steam carbonization (HTC) process. For example, HTC lignin can be obtained by heating the lignin-containing starting material in the presence of water to a temperature between 150 and 350°C, preferably between 150 and 250°C, typically under an autogenous pressure of 10 to 40 bar. The heat treatment may last from 30 minutes to 8 hours or more. Preferably, the treatment is completed within 1 to 6 hours, or more preferably within 2 to 4 hours.

[0025] For superheated steam carbonization of lignin-containing feedstock, it is preferred that at least a portion of the lignin is dissolved. Such partial or complete 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 HTC treatment favorably influences the particle size distribution of the HTC lignin depending on the application of the present invention. In a preferred embodiment, the lignin for superheated steam treatment is in solution.

[0026] Dissolution may be assisted by raising the temperature above 50° C., for example to 70-90° C., preferably 80° C. Dissolution conditions should be maintained for at least 5 minutes, more preferably at least 10 minutes, more preferably at least 15 minutes, especially at least 30 minutes, and especially at least 45 minutes but less than 300 minutes.

[0027] In the context of the present invention, it is not necessary for the lignin to be completely dissolved in the liquid, but it is advantageous if more than 50%, particularly preferably more than 60%, further preferably more than 70%, particularly preferably more than 80%, in particular more than 90% of the lignin is dissolved in the liquid.

[0028] In a particularly preferred embodiment, the at least partially dissolved lignin mixture also contains at least one crosslinker capable of reacting with the functional groups of the lignin. Such crosslinker compounds can have aldehyde, carboxylic acid, epoxide, hydroxy, isocyanate, or other functional groups. The functional groups of the crosslinker must be capable of reacting twice with the functional groups of the lignin. If the functional groups can only react once, the crosslinker must contain at least two such functional groups. Aldehydes, and especially formaldehyde, are preferred. The crosslinker may be added during the dissolution stage and / or during the HTC stage. The reaction of the crosslinker with the lignin may occur intermediately between the dissolution and HTC stages and may require pH adjustment to effect the reaction.

[0029] The cross-linking 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 times. Typical amounts are less than 40%, less than 35%, or preferably less than 25% by weight based on the weight of the lignin.

[0030] The amount and type of cross-linker helps to control the surface area of ​​the product obtained in the HTC stage. The use of a cross-linker increases the surface area of ​​the HTC lignin particles, so that increasing the amount of cross-linker generally increases the surface area.

[0031] The particle shape can be influenced by certain 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 advantageously does not exceed 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 advantageously 7 or higher, for example 8.5 or higher, or even 11 or higher. The inorganic ion concentration, 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 a PCE-PHD1 measuring probe at 20-25°C). The temperature of the superheated steam treatment may be limited to a maximum of 250°C, preferably between 150 and 250°C. Residence times of between 1 minute and 6 hours, for example between 30 minutes and 4 hours or between 1 and 3 hours, are also useful. The above measures may also be employed in combination.

[0032] If necessary, the particle size can also be adjusted by separation or by mixing different HTC lignin materials. Gravity separation in a liquid or gas medium is a suitable method. Equipment for separation is well known to those skilled in the art. Examples include cyclones, especially in the case of liquids, hydrocyclones, centrifuges or classifiers (air classifiers). However, the invention is not limited to the use of specific equipment. Any equipment that allows separation can be used, such as fluidized bed equipment, sieves, etc. Different types of separation can also be combined.

[0033] The resulting HTC lignin is preferably 180 ml 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, e.g., 25, 20, 15, or 10 m 2 / g or less. STSA specific surface area is determined in accordance with ASTM D6556-21. STSA (Statistical Thickness Surface Area) is a measure of the outer surface of an HTC lignin particle.

[0034] Advantageously, the BET surface area of ​​the HTC lignins deviates from the STSA surface area by no more than 20%, preferably no more than 15%, and more preferably no more than 10%. The BET surface area is determined by nitrogen adsorption by the particle as the total surface area of ​​the external and internal surfaces according to Brunauer, Emmett, and Teller. The method for determining BET surface area is also disclosed in ASTM D6556-21.

[0035] The weight ratio of total functionalized rubber to HTC lignin is in the range of 1:5 to 50:1, such as 1:20 to 20:1. Preferably, the ratio is in the range of 1:10 to 10:1, such as 1:7 to 7:1, more preferably 1:5 to 5:1.

[0036] The weight ratio of the sum of all functionalized rubbers and all non-functionalized rubbers to HTC lignin is in the range of 1:5 to 50:1, for example, 1:2 to 20:1, preferably 1:10 to 10:1, more preferably 1:5 to 5:1, and most preferably 1:2 to 2:1.

[0037] The functionalized rubber can be used as the sole rubber component or in a blend with non-functionalized rubber. In the case of a mixture of functionalized and non-functionalized rubber, the weight ratio of total functionalized rubber to total non-functionalized rubber can be up to 100:1, such as 1:100 to 100:1, preferably 1:50 to 50:1, more preferably 1:20 to 20:1 or 1:10 to 10:1, and most preferably 1:5 to 5:1, such as 1:3 to 3:1.

[0038] In a most preferred embodiment, the weight ratio of functionalized rubber to HTC lignin ranges from 1:5 to 5:1, the weight ratio of total functionalized rubber plus total non-functionalized rubber to HTC lignin ranges from 1:5 to 5:1, most preferably from 1:2 to 2:1, and the weight ratio of total functionalized rubber to total non-functionalized rubber is 1:3 to 3:1.

[0039] 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, with TESPT and TESPD being preferred. The silane compounds may be present in the ranges of 0.25 to 20 phr, 0.5 to 16 phr, 0.75 to 12 phr, 1.0 to 10 phr, 1.5 to 8 phr, 2.0 to 6 phr, and 2.5 to 5 phr (phr means parts per hundred parts of rubber).

[0040] Other ingredients may also be present, for example, for formulation and processing purposes, such as process oils (mainly paraffinic oils and bio-based oils), PEG, waxes, stearic acid, ZnO, drier CaO, processing aids such as sulfur vulcanizing agents, peroxide vulcanizing agents, flame retardants, antioxidants, etc., as long as they are not detrimental to the properties of the composition.

[0041] The mixture can be obtained by mixing the components according to conventional procedures. A rubber article can be obtained from the composition by mixing component a), component b) and optionally component c), compounding the mixture, and then vulcanizing the mixture.

[0042] The compositions of the present invention are suitable for the manufacture of a wide range of rubber products including profiles, hoses, seals, O-rings, weatherstrips, gaskets, tubes, membranes, insulators, cables, wiper blades, bushings, tapes, foils, linings, flooring, plugs, nipples, conveyor belts, seals, tires, and the like.

[0043] Example 1 The ingredients listed below were first mixed in two stages using a laboratory mixer (ERMAFA TMI 0.6 intermeshing internal mixer). In the first mixing stage, the rubber, HTC lignin, filler, plasticizer, silane, and processing agents were mixed together for 4 minutes, then mixed for an additional 5 minutes at 120°C. In the second mixing stage, the accelerator and sulfur were added to the base mix, and the whole was mixed for a total of 4.5 minutes. The mixture was then sheet molded and vulcanized at 170°C according to Table 2 below.

[0044] The vulcanization properties of the compositions are shown in Figure 1. The stress-strain properties are shown in Figure 2. In both figures, the reference curves show the properties of the same composition and identical processing without the silane.

[0045] The data show that silanizing EPDM reduces torque during vulcanization and results in a rubber with beneficial stress-strain properties.

[0046] Example 2 First, the ingredients listed below were mixed as in Example 1 above.

[0047] The ingredients listed below were first mixed in two stages using a laboratory mixer (ERMAFA TMI 0.6 intermeshing internal mixer). In the first mixing stage, the rubber (functionalized and non-functionalized), HTC lignin, filler, plasticizer, and processing agents were mixed together for 4 minutes, then mixed for an additional 2 minutes at 120°C. In the second mixing stage, the accelerator and sulfur were added to the base mixture, and the whole was mixed for a total of 4.5 minutes. The mixture was then sheet molded and vulcanized at 170°C according to Table 2 below.

[0048] The vulcanization characteristics of the compositions are shown in Figure 3. The stress-strain characteristics are shown in Figure 4. In both figures, the reference curves show the properties of the same composition and identical processing without grafting the EPDM.

[0049] Example 3 Example 2 above was repeated, but now 4.6 phr of TESPT was added. Mixing was performed as in Example 2 to combine the TESTP and EPDM-g-MAH. After 2 minutes at 120°C, the silane (TESPT) was added, and mixing was continued for an additional 2 minutes at 120°C.

[0050] The vulcanization properties of the compositions are shown in Figure 5. The stress-strain properties are shown in Figure 6. In both figures, the reference curves show the properties of the same composition and identical processing without the silane.

[0051] reference Example 1 was repeated with the compositions set out in Table 1 below.

[0052] [Table 1] a Keltan4465, manufactured by Alanxeo b Manufactured by UPMBiochemicals GmbH c Tudalen 1927, H&R, Klaus Dahleke made by KG d Si 69, manufactured by Evonik e ROYALTUF TM 485, 0.4-0.6 wt% maleic acid group, manufactured by SI Group f ZINKWEISS HANSA ULTRA, made by Lehmann & Voss & Co. KG g Palmera B 1805, manufactured by Avokal GmbH h Made by Avokal GmbH i Struktol SU95, manufactured by Schill+Seilacher "Struktol" GmbH j LUVOMAXXMBT, manufactured by Lehmann & Voss & Co. KG k LUVOMAXXZDTP DL 73, manufactured by Lehmann & Voss & Co. KG l LUVOMAXX TBzTD, manufactured by Lehmann & Voss & Co. KG

[0053] [Table 2] a ML = Minimum Torque b MH = Maximum torque c Delta = difference between the above d t s2 = induction time e t 90 = Optimal vulcanization time f For tensile testing g For hardness, rebound resilience, and DIN abrasion tests h RT means room temperature

[0054] Test Method: Moving Die Rheometer Test: ASTM D 5289-19a, a~e Mooney Viscosity (MU): ASTM D 1646-19a Tensile test: ASTM D 412-16(2021) Hardness: ASTM D 2240-15(2021) DIN Abrasion: DIN ISO4649:2021-06

[0055] The data shows that combining functionalized rubber with HTC lignin results in improved stress-strain properties in terms of higher modulus, higher tensile strength, higher rebound resilience levels, and lower DIN abrasion at comparable hardness and elongation at break.

Claims

1. a) functionalized rubber, b) HTC lignin, and c) optionally a non-functionalized rubber A composition comprising:

2. The composition of claim 1 comprising a functionalized rubber and a non-functionalized rubber.

3. 3. The composition according to claim 1 or 2, wherein the functionalized rubber is selected from functional derivatives of EPDM, EPR, butadiene rubber (BR), chloroprene rubber (CR), epoxidized natural rubber (ENR), hydrogenated nitrile rubber (HNBR), butyl rubber (IIR), isoprene rubber (IR), α-methylstyrene butadiene rubber (MSBR), acrylonitrile butadiene rubber (NBR), natural rubber (NR), styrene butadiene rubber (SBR), bromobutyl rubber (BIIR) and chlorobutyl rubber (CIIR), with functional derivatives of EPDM and EPR and especially maleic acid-grafted EPDM being preferred.

4. The composition of any one of claims 1 to 3, wherein the functionalized rubber has functional groups selected from carboxylic acid groups, epoxide groups, silane groups, chloro and / or bromo substituents.

5. 5. A composition according to any one of claims 1 to 4, wherein the weight ratio of total functionalised rubber to said HTC lignin is in the range of from 1:5 to 50:1, such as from 1:20 to 20:1, preferably from 1:10 to 10:1, such as from 1:7 to 7:1, more preferably from 1:5 to 5:

1.

6. 6. The composition of any one of claims 1 to 5, wherein the weight ratio of total functionalized rubber plus total non-functionalized rubber to the HTC lignin is in the range of 1:5 to 50:1, for example 1:2 to 20:1, preferably 1:10 to 10:1, more preferably 1:5 to 5:1, and most preferably 1:2 to 2:

1.

7. 7. A composition according to any one of claims 1 to 6, wherein the weight ratio of total functionalised rubber to total non-functionalised rubber is 100:1 or less, such as 1:100 to 100:1, preferably 1:50 to 50:1, more preferably 1:20 to 20:1 or 1:10 to 10:1, most preferably 1:5 to 5:1, such as 1:3 to 3:

1.

8. The composition of any one of claims 1 to 7, further comprising one or more silane compounds, of which TESPT and TESPD are preferred.

9. A rubber article obtainable by vulcanizing the composition according to any one of claims 1 to 8.

10. 10. The rubber article of claim 9, selected from profiles, hoses, seals, O-rings, weatherstrips, gaskets, tubes, membranes, insulators, cables, wiper blades, bushings, tapes, foils, linings, flooring, plugs, nipples, conveyor belts, seals and tires.

11. 1. A method of making a rubber article, comprising the steps of mixing component a), component b), and optionally component c), compounding the mixture, and then vulcanizing the compounded mixture.

12. Use of a composition according to any one of claims 1 to 8 in rubber articles, preferably profiles, hoses, seals, O-rings, weatherstrips, gaskets, tubes, membranes, insulators, cables, wiper blades, bushings, tapes, foils, linings, flooring, plugs, nipples, conveyor belts, seals and tires.

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