Elastomer composition and article comprising the composition

Abstract

The present invention relates to a composition comprising an elastomeric polymer and HTC lignin of 50 phr (parts per 100 parts of polymer) or more, wherein the HTC lignin has a particle size D90 of 5 μm or more determined by ISO 13320:2020 and a STSA surface area of 40 m 2 / g or less determined by ASTM D6556-14. The present invention also provides an article comprising the composition and the use of the composition in a gas barrier.

Description

Detailed Description of the Invention

[0001] The present invention relates to a composition comprising an elastomeric polymer and hydrothermally treated lignin, an article comprising the same, and the use of the composition in a gas barrier. [Background]

[0002] Carbon black is widely used as a filler for rubber articles such as tires. However, carbon black is generally manufactured from fossil materials and is therefore not a sustainable material. In order to manufacture rubber articles in a more sustainable and environmentally friendly manner, attempts have been made to replace carbon black with renewable materials such as lignin. However, to date, these attempts have not resulted in satisfactory rubber compositions, and each product has not been commercialized on a large scale.

[0003] WO 2016 / 185351 discloses a compound for a tire sealant comprising kraft lignin. Further uses of lignin in rubber blends are disclosed in WO 2020 / 140155 and Aini et al., Front. Mater. 6 (2020) 329.

[0004] EP 3243877 discloses a pneumatic tire comprising hydrothermally carbonized lignin. Hydrothermally treated lignin (also known as HTC lignin) is derived from lignin by thermochemical conversion in the presence of water (see, for example, Correa et al., Materials 11 (2018) 1568). The HTC lignin of EP 3243877 has a surface area of less than 150 m 2 / g. It is stated that HTC lignin can be used in an amount of 75% by weight of the total rubber composition. For an untreated sample containing 46 phr (parts per 100 parts of rubber), EP 3243877 suggests that the tanδ of the rubber composition containing HTC lignin is lower than that of the rubber composition containing carbon black. Further advantages are claimed in light of the tensile strength. No mention is made of air and gas permeability.

[0005] International Publication No. 2020 / 202125 discloses an inner liner containing HTC lignin as a partial substitute for carbon black. International Publication No. 2020 / 202125 preferably has a surface area of 30 to 55 m 2 / g, D 50 1 to 4 μm and D 90 5 to 8 μm, suggesting the use of 15 to 45 phr of HTC lignin. Compared with carbon black and combinations of carbon black and kraft lignin (see International Publication No. 2016 / 185351 above), a rubber mixture containing carbon black and 30 phr of HTC lignin is said to exhibit improved oxygen impermeability without changing M300%.

[0006] European Patent Application Publication No. 3974470 discloses a composition comprising a halobutyl rubber and 50 to 90 phr of a specific HTC lignin filler having an STSA surface area of 10 to 50 m 2 / g. The use of these fillers reduces gas permeability by 15% or less compared to carbon black. SUMMARY OF THE INVENTION

[0007] The present invention provides a composition having reduced gas permeability and further beneficial properties. The composition according to the present invention is particularly beneficial when used in articles requiring gas barrier properties such as gas barriers or hoses, membranes, hollow members, and tires. The composition is particularly useful in an inner liner for a pneumatic tire or for use as an inner liner for a pneumatic tire.

[0008] The composition according to the present invention comprises an elastomeric polymer and HTC lignin. The HTC lignin is present in an amount of 50 phr (parts per 100 parts of the polymer) or more. Preferably, the HTC lignin has a particle size D of 5 μm or more as determined by ISO 13320 90 and a surface area of 40 m 2 / g or less as determined by ASTM D6556-14.

[0009] Surprisingly, it has been found that the compositions according to the present invention can significantly improve several properties of elastomer-containing compositions, including gas permeability. [Detailed Description]

[0010] The polymers of the present invention are elastomers including rubbers, polymer-rubber mixtures and composites.

[0011] The compositions of the present invention can include many types of elastomers such as styrene-butadiene polymers and block copolymers, polyisoprene, natural rubber, polybutadiene, ethylene propylene rubber, silicone elastomers, fluoro-elastomers, polyurethane elastomers and nitrile rubber. Styrene butadiene (SBR) and butadiene (BR) are the most common rubber polymers in the tire industry. The compositions of the present invention can include one or more elastomers.

[0012] The elastomers of the present invention can be any elastomers including natural and synthetic rubbers. The rubbers used herein are diene polymers or diene-containing copolymers derived from butadiene, isobutylene and isoprene. Particularly preferred are isobutylene and isoprene copolymers (also known as butyl rubber) and their respective halogenated rubbers also known as halobutyl rubber.

[0013] Butyl rubber is a synthetic copolymer of isobutylene (typically 98 - 99% by weight) and isoprene (typically 1 - 2% by weight). Butyl rubber is characterized by its very low unsaturation content and has unique chemical and physical properties. Butyl rubber exhibits low gas permeability and high chemical resistance.

[0014] Butyl rubber is typically produced by cationic copolymerization of isobutylene and isoprene at low temperature, for example approximately -100°C or -90°C, in the presence of a Friedel-Crafts catalyst. Subsequently, halogenated butyl rubber can be produced, for example, by reacting a hexane solution of butyl rubber with elemental bromine or chlorine.

[0015] Halogenated butyl rubber can be obtained by halogenating butyl rubber during or after polymerization. Chloro- and bromo-butyl rubbers exhibit improved compatibility with other polymers and a higher curing rate than butyl rubber. Allylic C-Br or C-Cl bonds promote vulcanization and enable a fundamentally different curing chemistry compared to other elastomers based on the reactivity of allylic C-H bonds. Halobutyl rubber can be cured, for example, with only ZnO, giving a vulcanizate in the absence of sulfur. This unique curing chemistry can promote co-vulcanization with other rubbers such as natural rubber (NR) and styrene-butadiene rubber.

[0016] The halogenated butyl rubber for use in this formulation may contain a copolymer of isobutylene (e.g., 95 - 99.5 wt%, or preferably 98 - 99 wt%) and isoprene (e.g., 0.5 - 5 wt%, 0.3 - 6 wt% or 1 - 2 wt% based on the total weight of the monomers). Chlorobutyl rubber may contain chlorine in an amount of, for example, about 0.1 - about 6 wt%, or about 0.8 - about 15 wt% (based on the weight of the polymer). Bromobutyl rubber may contain bromine in an amount of, for example, about 0.1 - about 15 wt%, or about 1 - about 6 wt% (based on the weight of the polymer). In halogenated butyl rubber, the halogen content is limited by the isoprene content and further limited by the fact that only some of the double bonds are halogenated. In typical halobutyl rubber, 60% of the double bonds can have an allylic halogen substituent.

[0017] In a preferred embodiment, the rubber mixture comprises a halogenated butyl rubber, which may contain at least one further diene rubber. In a particularly preferred embodiment, the rubber mixture comprises from 31 to 100 phr of at least one halogenated butyl rubber and from 0 to 69 phr of at least one further diene rubber. In the case of the inner liner, a polymer derived from isobutene and para-bromomethylstyrene is preferred. In such a polymer, a high bromomethylstyrene concentration (e.g., 40 to 60 mol%, in particular 50 mol%) is particularly preferred. A commercially available polymer of this type is Exxon Mobile's Exxpro™ 3563.

[0018] The further diene rubber may be selected from the group consisting of natural rubber, butyl rubber, polybutadiene rubber, styrene-butadiene copolymer, synthetic polyisoprene, natural polyisoprene, styrene-isoprene copolymer, styrene-isoprene-butadiene terpolymer, solution-polymerized styrene-butadiene rubber, and emulsion-polymerized styrene-butadiene rubber, and / or ethylene-propylene-diene rubber.

[0019] The rubber component can be functionalized. This functionalization uses a further functionalization system that can enter into chemical bonding with a hydroxy group and / or an epoxy group and / or a siloxane group and / or an amino group and / or a phthalocyanine group and / or an aminosiloxane group and / or a carboxy group and / or the light-colored filler used.

[0020] Fillers are used to improve the mechanical properties of elastomers as well as vulcanized or crosslinked elastomers and rubbers. Typical examples are carbon black and silica. In tire manufacturing and the rubber industry, carbon black and silica are used on a large scale as fillers. Approximately 93% of carbon black is used in rubber compounding, which is often classified into two main segments: mechanical rubber goods (i.e., hoses and automotive belts) and tires.

[0021] The filler of the present invention contains hydrothermally carbonized lignin, also known as HTC lignin. Lignin is the second most abundant natural resource. It is an aromatic polymer that holds both cellulose and hemicellulose in plants, strengthening cell walls and protecting plants from parasites and diseases. The complex structure of amorphous lignin is formed by the bonding of different functional groups such as methoxyl, phenol, hydroxyl, and carbonyl groups. A large amount of lignin by-products are produced in the pulp and paper industry, and about 98% of it is usually incinerated to generate energy or simply discarded in landfills.

[0022] Hydrothermal carbonization is a thermochemical process in which biomass is treated under pressure in the presence of hot water and / or steam. Different from pyrolysis, biomass is incompletely decomposed during HTC, and the products are carbon-rich solid materials, a gas phase mainly composed of CO2, water, and water-soluble compounds.

[0023] HTC lignin can be prepared from any type of lignin-containing starting material such as lignin-containing waste materials, 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, or even better, more than 90% by weight in the starting material is preferred.

[0024] Preferred lignin-containing raw materials are black liquor obtained from the digestion of lignocellulosic biomass or solids prepared therefrom, solids obtained from the enzymatic hydrolysis of lignocellulosic biomass, black liquor (lignosulfonate) obtained from the digestion of lignocellulosic biomass with sulfite, or solids or liquids obtained from the digestion of lignocellulosic biomass with solvents (e.g., organosolv lignin). In a preferred embodiment of the present invention, lignin is derived as a side stream in the enzymatic hydrolysis of lignocellulosic raw materials. This preferred starting material is also known as EH-lignin.

[0025] The lignin-containing biomass can be selected from the group consisting of kraft lignin, steam-exploded lignin, biorefinery lignin, supercritical-separated lignin, hydrolyzed lignin, flash precipitated lignin, biomass-derived lignin, lignin obtained from an alkaline pulping process, lignin obtained from a soda process, lignin obtained from organosolv pulping, lignin obtained from an alkali process, lignin obtained from an enzymatic hydrolysis process, and any combination thereof. In one embodiment, the lignin is wood lignin. The lignin can originate from softwood, hardwood, annual plants, or any combination thereof.

[0026] "Kraft lignin" is lignin derived from kraft black liquor. The black liquor is an alkaline aqueous solution of lignin residues, hemicellulose, and inorganic chemicals used in the kraft pulping process. The black liquor obtained from the pulping process contains components from different softwood and hardwood species in various ratios. Kraft lignin can be separated from the black liquor by different techniques including, for example, precipitation and filtration.

[0027] The term "flash precipitated lignin" should be understood to be lignin precipitated from black liquor in a continuous process by reducing the pH of the black liquor stream to the precipitation level of lignin using a carbon dioxide-based acidifying agent, preferably carbon dioxide, under the influence of an overpressure of 200 - 1000 kPa and then suddenly releasing the pressure to precipitate the lignin. Flash precipitated lignin particles having a particle diameter of less than 2 μm form aggregates, which can be separated from the black liquor using, for example, filtration.

[0028] Lignin can result from an organosolv process. Organosolv is a pulping technique that solubilizes lignin and hemicellulose using an organic solvent.

[0029] Lignin can be slurried or dissolved for hydrothermal conversion. Preferably, lignin is dissolved in an alkaline solution such as NaOH. Dissolution can be achieved by heating a mixture of lignin and the 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 the alkaline solution for a predetermined time. The mixing time can last about 2 - 3 hours. The exact pH value is determined based on the product grade target.

[0030] The slurry can be subjected directly to hydrothermal treatment or fed to another unit where the precipitated lignin can be separated from the slurry.

[0031] The hydrothermal carbonization treatment can be carried out in one reactor (HTC reactor) or, if necessary, in several parallel reactors operating in batch mode. The dissolved lignin can be preheated and then fed into the HTC reactor(s). The temperature inside the HTC reactor(s) can be 150 - 250 °C and the pressure can be 20 - 30 bar. The residence time inside the HTC reactor(s) can be about 3 - 6 hours. Inside the HTC reactor, the lignin is carbonized, whereby a stabilized lignin derivative with a high specific surface area can precipitate. Then, the formed slurry containing the carbonized lignin can be removed and cooled.

[0032] Preferably, the lignin-containing starting material in the form of a lignin solution is subjected to a hydrothermal 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 of 150 - 350 °C, preferably 150 °C - 250 °C, under autogenous pressure, typically 10 - 40 bar. The heat treatment can be maintained from 30 minutes to 8 hours or more. Preferably, the treatment is completed within 1 - 6 hours or more preferably within 2 - 4 hours.

[0033] For the hydrothermal carbonization of lignin-containing raw materials, 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 higher than 7, preferably higher than 9, most preferably higher than 10. A pH of 10 to 12, preferably 10 to 11, before the HTC treatment has a favorable effect on the particle size distribution for use according to the present invention. In a preferred embodiment, the lignin for the hydrothermal treatment is dissolved.

[0034] Dissolution can also be assisted by raising the temperature to higher than 50 °C, for example 70 to 90 °C, 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, especially at least 45 minutes but less than 300 minutes.

[0035] For the present invention, it is not necessary for the entire lignin to be dissolved in the liquid. However, advantageously, more than 50%, particularly preferably more than 60%, more preferably more than 70%, particularly preferably more than 80%, especially more than 90% of the lignin is dissolved in the liquid.

[0036] In a particularly preferred embodiment, the mixture of at least partially dissolved lignin may also contain 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 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 groups. Aldehydes and particularly formaldehyde are preferred. The crosslinking agent can be added in the dissolution step and / or the HTC step. The reaction between the crosslinking agent and the lignin can also be an intermediate step between the dissolution step and the HTC step, which may require pH adjustment to carry out the reaction.

[0037] The crosslinking agent must be used in excess relative to the crosslinking groups of lignin. Such an excess can be 1.5, 2 or even 4 times. Amounts exceeding 4-fold excess are unnecessary and thus not economically recommended. Typical amounts are less than 40 wt%, less than 35 wt% or preferably less than 25 wt% relative to the lignin weight. Specifically, in the case of formaldehyde, the amount can be as little as less than 10 wt% or even less than 5 wt%.

[0038] The amount and type of crosslinking agent serve to adjust the surface area of the product obtained in the HTC process. The use of the crosslinking agent increases the surface area of the HTC lignin, and thus generally the surface area also increases with the increase in the amount of the crosslinking agent.

[0039] The HTC lignin for use in the present invention has a D 90 particle size of 5 μm or more as determined by laser diffraction in accordance with ISO 13320:2020. The particle size D 90 of the HTC lignin is preferably 8 μm or more such as 10 μm or more. Particularly preferred is a D 90 value of 20 μm or more or even 30 μm or more.

[0040] In measurements in accordance with ISO 13320:20, the HTC lignin is suspended in distilled water and the particle size distribution is measured by laser diffraction. Before and / or during the measurement of the particle size distribution, the sample to be measured is dispersed by ultrasound until a stable particle size distribution is obtained over several measurements.

[0041] The particle size distribution can be affected by specific process parameters. For example, particle size control can be achieved by adjusting the dry matter content of the feed, the pH of the feed, the inorganic ion concentration of the feed, and the temperature and residence time during the hydrothermal treatment. Advantageously, the dry matter concentration of the feed does not exceed 40% by weight (based on the feed), preferably is 20% by weight or less, and most preferably is 10% by weight or more. The pH is advantageously 7 or more, such as 8.5 or more or even 11 or more. The inorganic ions measured by conductivity are in the range of 10 mS / cm to 200 mS / cm, preferably 10 mS / cm to 150 mS / cm, more preferably 10 mS / cm to 50 mS / cm, still more preferably 10 mS / cm to 40 mS / cm, and particularly preferably 10 mS / cm to 25 mS / cm (determined as the conductance of the measuring probe of PCE-PHD1 at 20 °C to 25 °C). The temperature of the hydrothermal treatment can be limited to a maximum of 200 °C to 250 °C, preferably a maximum of 210 °C to 245 °C. A residence time of 1 minute to 6 hours, such as 30 minutes to 4 hours or 1 to 3 hours, is also useful. The above measurements can also be employed in combination.

[0042] 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. Devices for separation are well known to those skilled in the art. Examples include cyclones, particularly liquid cyclones in the case of liquids, centrifuges or classifiers (there is an air classifier. However, the present invention is not limited to the use of a specific device. All devices that enable separation, such as fluidized bed devices, sieves, etc., can be used. Different types of separation can also be combined.

[0043] The resulting HTC lignin has an STSA of 40 m 2 / g or less, such as 25, 20, 15 or 10 m 2 / g or less, more preferably 30 m 2 / g or less. The STSA surface area is determined in accordance with ASTM D6556-14. The STSA (statistical thickness specific surface area) indicates the outer surface of the HTC lignin particles.

[0044] Conveniently, the BET specific surface area of the present HTC lignin deviates from the STSA surface by at most 20%, preferably at most 15%, more preferably at most 10%. The BET surface area is determined as the total surface area of the outer and inner surfaces by nitrogen adsorption by the particles according to Brunauer, Emmett, and Teller. The method for determining the BET surface is also disclosed in ASTM D6556-14.

[0045] The composition according to the present invention may further comprise cure activators or dispersants such as stearic acid (as exemplified), and other processing aids such as naphthenic oil, for example. The processing aids, emulsifiers or dispersants can be ammonium, sodium or potassium salts of C12-C24 fatty acids, such as ammonium, sodium or potassium salts of oleic acid, palmitic acid, stearic acid or linoleic acid. Alternative dispersants include ammonium and alkali metal salts of polyethoxylated sulfates of C6-C20 alkyl alcohols, or polyethoxylated alkylphenoxyethanol and acid esters (for example, phthalic acid, adipic acid, phosphoric acid at loadings of 5-15 and 5-30 phr). The suitable amount of the emulsifier can be, for example, about 0.1 to about 15 phr, or about 0.1 to about 5 phr.

[0046] The HTC lignin and any optional additional components are incorporated into the elastomer according to known methods described, for example, in ASTM D3182-21b. The amount of HTC lignin is 50 phr or more, preferably 60-100 phr and most preferably 90 phr or more.

[0047] The composition according to the present invention comprises a vulcanization reactant, an activator, a catalyst or an accelerator, such as ZnO and / or sulfur and / or an accelerator activator and / or a sulfur donor / accelerator, such as: thiazole, sulfenamide, guanidine, dithiocarbamate and thiuram sulfide; for example, thiocarbamamyls, dithiocarbamyl, alkoxycarbonylthio, dialkylthiophosphoryl, diamino-2,4,6-triazinyl, thiuram xanthate, and / or can be formulated with the help of alkylphenol. A preferred thiazole is dibenzothiazyl disulfide (MBTS), and a preferred thiuram is tetramethylthiuram monosulfide (TMTM). A preferred alkylphenol is poly-tert-amylphenol disulfide. When used, a suitable accelerator can be added in an amount of, for example, about 0.1 to about 10 phr, or about 0.1 to about 5 phr.

[0048] The composition according to the present invention is useful for the manufacture of industrial rubber items such as belts, drive belts, and hoses. The composition according to the present invention is particularly useful in rubber products that require gas impermeability, such as hoses. Its unique properties are particularly beneficial in the inner liner.

[0049] The inner liner is a rubber inner layer used in tubeless pneumatic tires, i.e., pneumatic tires without an air chamber, to ensure its seal under the pressure of the air contained in the cavity of the pneumatic tire. The inner liner must ensure that as much oxygen as possible remains in the air filling trapped in the cavity and does not spread to the parts of the pneumatic tire to cause deterioration. Therefore, the material for the inner liner must exhibit exceptional gas barrier properties. Furthermore, increasing the thickness is associated with a series of disadvantages related to weight gain and a compromise in rolling resistance, so the material for the inner liner must exhibit such properties at a minimum thickness.

[0050] Preferably, the composition of the present invention is an inner liner containing HTC lignin and halobutyl rubber.

Examples

[0051] Samples A, B, D, and F (for comparison) and Samples C, E, and G (of the present invention) were prepared based on the compositions in Table 1. The powder and oil components were added to the polymer, followed by mixing for 7 minutes (ramp down) in a 1,600 ccm chamber volume Banbury internal mixer set at 40 °C and 60 rpm (70% fill factor). Thereafter, curatives were added and mixing was continued for 4 minutes. A 0.5 mm thick sheet was formed and subjected to curing at 170 °C for 35 minutes. The sheet was subjected to the tests described below.

[0052] The air permeability was evaluated in accordance with ASTM D1434 - 82(09)e1 using a LabThink VAC - V1 gas permeability tester. The nitrogen transmission rate was determined at 23 °C with a sample test area of 38.48 cm2.

[0053] The tensile properties were determined in accordance with ASTM D412 - 16 at 23 °C and 100 °C. Prior to the test, the 100 °C sample was conditioned in an artificial climate chamber maintained at 100 °C for 30 minutes.

[0054] The compression set was measured at 70 °C after 24 hours in accordance with ISO 815 - 1. The density was measured in accordance with ASTM D297.

[0055]

Table 1

[0056] The data shows that the composition according to the present invention results in a lower gas permeability compared to carbon black of comparative surface area. Specifically, at a loading of 60 phr, the air permeability decreases by 8 and 26% respectively. At a loading of 90 phr, the decrease is 30%. This is unexpected as the prior art suggests much lower loadings (less than 45 phr) and either requires carbon black as a co - filler or reports more modest decreases. Further, it is noted that the effect on air permeability is particularly beneficial when the surface area is low and the loading is high. It is even more remarkable that the composition of the present invention exhibits improved M100% and M300% properties, especially at high temperatures. A further beneficial property of the composition of the present invention is the reduced compression set. Yet another advantageous result is the formation of a reduced density, which enables a product with reduced gas permeability at a lower weight.

Claims

1. A composition comprising an elastomeric polymer and HTC lignin of 50 phr (parts per 100 parts of the polymer) or more, wherein the HTC lignin has a particle size D of 5 μm or more determined by ISO 13320:2020 ９０ and a composition having a STSA surface area of 40 m ２ / g or less determined by ASTM D6556-14.

2. The composition according to claim 1, wherein the elastomeric polymer is halobutyl rubber.

3. The composition according to claim 1 or 2, wherein the HTC lignin is present in an amount of 60 to 100 phr, preferably 90 phr or more.

4. The HTC lignin has an STSA surface area of less than 30, preferably less than 25, more preferably less than 20, even more preferably less than 15, and most preferably less than 10 m ２ / g or less as determined by ASTM D6556-14, and the composition according to any one of claims 1 to 3.

5. The HTC lignin is present in an amount of 90 phr or more and has a surface area of 10 m ２ / g or less, the composition according to any one of claims 1 to 4.

6. The above-mentioned D ９０ The composition according to any one of claims 1 to 5, wherein D is 15 μm or more.

7. An article comprising the composition according to any one of claims 1 to 6.

8. The article according to claim 7, which is a tire, a tire sealant or an inner liner.

9. Use of the composition according to any one of claims 1 to 6 in a gas barrier.

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