Rubber composition comprising calcium carbonate particles

Abstract

The invention provides a rubber composition comprising calcium carbonate and carbon black, wherein the calcium carbonate is in the form of circular calcium carbonate particles, that are prepared by pyrolysis of a waste stream comprising calcium carbonate as filler, wherein the circular calcium carbonate particles comprise a core of calcium carbonate covered by a shell of at least 0.01 to 50 %w carbon, hereinafter "CCC-cc particles", and wherein the ratio of CCC-cc particles to carbon black is at least 1: 2.

Description

[0001] Title: Rubber composition comprising calcium carbonate particles

[0002] Technical Field

[0003] The present invention relates to rubber compositions comprising calcium carbonate as filler.

[0004] Background

[0005] Fillers have been widely used in the rubber industry for many applications. Calcium carbonate (CaCCh) is one of the important inorganic powders and it is widely used as filler in order to reduce the cost in rubber industry. Calcium carbonate is a common substance found in rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skeletons and pearls. The vast majority of calcium carbonate used in industry is extracted by mining or quarrying. Ground calcium carbonate is used in a wide variety of rubber applications as both an extender and detackifying agent. It can also add stiffness or provide abrasion resistance.

[0006] A recent study of rubber / calcium carbonate compositions was performed by N Phuhiangpa et al 2020 IOP Conf. Ser.: Mater. Sci. Eng. 773 012013, DOI 10.1088 / 1757- 899X / 773 / 1 / 012013).

[0007] There are limits as to the amount of ground calcium carbonate (GCC) that may be added to rubber compositions. Moreover, GCC, despite its abundancy, is still a linear use of resources. Alternatively precipitated calcium carbonate (PCC) may also be used, but this is very expensive.

[0008] The current applicant has developed a technology to treat industrial waste streams like paper mill sludge (PMS), sewage sludge and other industrial waste. This technology allows filler content to be recovered from waste streams, in the form of circular calcium carbonate (CCC). The expression “circular” refers to the reuse of calcium carbonate that has been in use before. CCC has been used in rubber applications and found to add important sustainable benefits. Applying CCC enables rubber producers to cost effectively increase the circular content in their products, which in turn minimises their carbon footprint and reduces their use of primary resources.

[0009] Fillers such as carbon black may have an effect on the stress-strain behaviour of rubber. This is called the Payne effect. Payne, A. R. (1962). "The Dynamic Properties of Carbon Black- Loaded Natural Rubber Vulcanizates. Part I". J. Appl. Polym. Sci. 6 (19): 57-63. doi: 10.1002 / app.1962.070061906.

[0010] The Payne effect is the difference between the storage moduli at 0.56% and 100% of strain. It is usually used as an indication of the micro dispersion (degree of a filler distribution at a scale smaller than 2 pm) of the filler in the rubber. This parameter, which is defined as the difference between the storage modulus at low and high strains, is generally associated with the filler-filler interactions (filler-filler network) but also with the micro-dispersion of the filler in rubber compounds. A higher Payne effect value is commonly an indication of a worse microdispersion of fillers. Ideally, the Payne effect is relatively low.

[0011] The current inventors have investigated the use of circular calcium carbonate in rubber compositions. This has led to some surprising observations.

[0012] In LIS2018162645 a rubber composition is provided having excellent adhesiveness with particularly reinforcing members in environmental degradation, and capable of bringing high peel operability therewith. The rubber composition of this disclosure is obtainable by compounding a rubber component containing a diene based rubber, a wet silica, a carbon black and a calcium carbonate, wherein: a compounding amount of the wet silica is 3 parts by mass or more per 100 parts by mass of the diene based rubber; and a compounding amount of the calcium carbonate is 10 parts by mass or more and 120 parts by mass or less per 100 parts by mass of the diene based rubber. There is no information on using circular calcium carbonate. Moreover, whereas this reference suggests that the calcium carbonate used in the rubber composition may have been subjected to a surface treatment to bring excellent dispersity in the rubber composition, there is no information on the organic material to be used.

[0013] In JP2017171514 a spherical calcium carbonate particle is provided in which, in the production process of calcium carbonate, carbon is uniformly introduced into the inside of the particle thereof. Also provided is a method for producing a calcium carbonate particle produced by a spray pyrolysis method. There is no mention of a rubber composition comprising calcium carbonate particles and carbon black.

[0014] JP4793394 describes a method for recovering calcium carbonate from paper sludge waste. No rubber composition is disclosed.

[0015] EP2058370 describes a rubber composition comprising carbon black and peroxide-treated aramid particles. No composition comprising calcium carbonate is disclosed. It has now been found how to facilitate the incorporation of calcium carbonate in rubber compositions, with greater sustainability, with less dependency on resources and even allowing for increased amounts of calcium carbonate as filler. Moreover, it has now been found that for the same amount of filler, a lower Payne effect may be achieved.

[0016] Summary of the Invention

[0017] Accordingly, the invention provides a rubber composition comprising calcium carbonate and carbon black, wherein the calcium carbonate is in the form of circular calcium carbonate particles, that are prepared by pyrolysis of a waste stream comprising calcium carbonate as a filler, wherein the circular calcium carbonate particles comprise a core of calcium carbonate covered by a shell of carbon, the particles comprising at least 0.01 to 50 % by weight of the carbon shell (based on the total weight of the particles), hereinafter “CCC-cc particles”, and wherein the ratio of CCC-cc particles to carbon black is at least 1 : 2.

[0018] Drawings

[0019] Fig. 1 and 2 show the cured Payne effect for the reference examples, the comparative examples and the examples according to the present invention.

[0020] Detailed description of the Invention

[0021] Circular calcium carbonate particles may be recovered from a post-consumer waste stream, in particular from waste streams containing at least 20 % by weight paper mill sludge as feedstock. Paper mill sludge (PMS) is the largest waste stream in the paper industry.

[0022] Generated in the water treatment facilities at paper mills, it consists of waste cellulose fibres (40-50%) and paper fillers like calcium carbonate and kaolin (50-60%). Pyrolysis of PMS is known and may provide CCC that can find use in paints, plastics, rubbers and paper.

[0023] The current inventors found that it is also possible when using pyrolysis of a waste stream comprising calcium carbonate to form CCC, but now with a shell of carbon (in the form of carbon black, also referred to as “biochar”) covering the CCC particles: CCC-cc. It has been found that the carbon shell covering the calcium carbonate particles facilitates the incorporation of the filler material into rubber compositions and allows higher loadings of calcium carbonate filler into the rubber compositions without loss of properties.

[0024] It is important to acknowledge that GCC, PCC and CCC are white, and may be used as whitener, whereas CCC-cc is not. The overall composition of CCC-cc is therefore different. The CCC-cc particles comprise a core of calcium carbonate covered by a shell of carbon. Preferably, the CCC-cc particles have a size in the range of 0.01 to 500 pm. More preferable, the CCC-cc particles have an average particle size dso in the range of 0.5 to 20 pm, preferably 0.7 to 4 pm and a particle size dgs in the range of 2 to 400 pm, preferably in the range of 3 to 10 pm. For instance, this may be extra fine material with a Dso of 1 pm and a Dgs of 5 pm, or a fine material with a Dso of 3 pm and a Dgs of 25 pm, or a base material with a Dso of 17 pm and a Dgs of 85 pm, or a coarse material with a Dso of 100 pm and a Dgs of 400 pm. Note in this respect that the CCC-cc may form aggregates that may be larger than the size limits mentioned above. However, such aggregates can easily revert to the particles that they are composed of during use.

[0025] The size determination may be performed by laser diffraction particle size analyzer e.g. Malvern 3000 or with gravitational sedimentation analysis, for instance, with the use of a SediGraph.

[0026] The shell content of the CCC-cc particles may vary widely. For instance, the carbon shell of the CCC-cc particles may be in the range of 2 to 25 % by weight, preferably in the range of 5 to 15 % by weight, more preferably in the range of 6 to 10 % by weight. This ratio is based on the weight of the CCC-cc particle.

[0027] The carbon content may be determined by any suitable means available to the person skilled in the art. A common method for assessing the presence of carbon covering a core of calcium carbonate is by way of thermogravimetric analysis, hereinafter TGA. The thermogravimetric data collected from the thermal reaction when the carbon in the shell is oxidized is compiled into a plot of mass or percentage of initial mass on the y axis versus either temperature or time on the x-axis. This plot, which is often smoothed, is referred to as a TGA curve and therefore provides information on the relative amount of carbon in the shell.

[0028] The CCC-cc particles may have an average shell thickness in the range of 10 to 100 nm, preferably in the range of 20 to 50 nm. The shell may entirely or only partly cover the core.

[0029] The size, size distribution, carbon content and shell thickness are related to the pyrolysis feedstock as well as the pyrolysis conditions. Preferably waste streams containing at least 20 % by weight paper mill sludge are used as feedstock, with the remainder comprising postconsumer and industrial waste streams. Moreover, biomass may be added to increase the carbon content to the desired amount. Greater amounts of at least 40 w% PMS are preferred. The pyrolysis is typically performed at a temperature in the range of 500 to 800°C, depending on the quality of the feedstock. For instance, for feedstock comprising plastics, higher temperatures in the range of 800-1300°C may be used. Another condition that is relevant for the formation of the desired CCC-cc particles is the residence time, which may vary from a few minutes (at temperatures in the higher range) to hours (at temperatures in the lower range). Fast pyrolysis is preferred. The person skilled in the art may determine the optimum conditions within these ranges empirically.

[0030] The amount of CCC-cc may vary broadly. For instance, it may be used up to 200 parts per hundred rubber (phr), although for most applications an amount in the range of 2 to 100 phr, preferably 5 to 50 phr will be more typical. A higher amount may be applied, for instance to form a masterbatch that can then be used as additive in rubber composites.

[0031] With the higher amount of CCC-cc particles, a reduced amount of carbon black will be needed. This can be easily determined by the person skilled in the art. For instance, if a filler composition comprising carbon black and calcium carbonate is used, in an amount of from 10 to 200 phr, then the ratio by weight of CCC-cc to carbon black is preferably at least 1 :2, more preferably at least 2:3, still more preferably at least 3:4, still more preferably at least 1:1 , still more preferably at least 4:3, still more preferably at least 3:2.

[0032] The presence of some carbon black may still have benefits. Accordingly the ratio of CCC-cc to carbon black is preferably at most 100:1, more preferably at most 50:1, still more preferably at most 30:1, still more preferably at most 10:1, still more preferably at most 7:1.

[0033] The addition of CCC-cc to rubber is typically performed by mixing the CCC-cc particles with the appropriate equipment. For instance a two-roll mill may be used. Moreover, mixing may be done in a closed internal mixer followed by a two-roll mill to sheet out the compounds. Rubber processing generally consists of four basic steps: (1) mastication, to give easier flow,

[0034] (2) mixing, usually carried out immediately after mastication, when additives are incorporated,

[0035] (3) shaping of the viscous mass, for example, by extrusion or moulding, and (4) curing, when the rubber molecules become interlinked and the shape is fixed. The CCC-cc particles may be added to the rubber together with additional components, if any. As indicated above, the CCC-cc particles may also be added to the rubber in the form of a masterbatch, again comprising other rubber additives, if any.

[0036] Common rubber additives that may be used in addition to CCC-cc particles include processing aids, cure packages, plasticizers and (biobased) oils. In addition, the composite may comprise silica or other filler materials. Additional filler materials, however, will be used in lesser amounts than usually applied, in view of the presence of CCC-cc particles. For instance, in addition to CCC-cc particles, also conventional GCC, or PCC or CCC may be used, but at reduced amounts. Conveniently, the composite may also contain protective chemicals, to confer resistance to heat, sunlight, oxygen and ozone. Preferably additives are used that are biobased or circular, such as biobased oils and recycled carbon black.

[0037] The rubber component of the composite may be a natural or synthetic rubber, or a combination of rubbers. Suitable examples of common rubber materials include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), butyl rubber (HR), nitrile rubber (NBR), neoprene rubber (CR), Ethylene Propylene Diene Monomer (EPDM), polyurethane rubber (PUR or PU), fluorine rubber monomer (FKM or FPM) and silicone rubber (Q). Also blends may be used, e.g., NR 60 parts; BR 40 parts.

[0038] The rubber composition may be cured with common vulcanizing systems, e.g., with sulphur and an accelerator.

[0039] To allow coupling of the CCC-cc particles and the polymer, a coupling agent may be used. For instance alpha-lipoic acid by Sigma Aldrich and titanate Ken-React® CAPOW L 12 / H, titanium IV 2,2(bis 2-propenolatomethyl)butanolato, tris(dioctyl)phosphate with CAS No. 110438-25-0, from Kenrich Petrochemicals, Inc. may be added to the calcium carbonate. The amount can be optimised by the person skilled in the art, if used. For instance, the amount of added alpha lipoic acid may be in the range of 0.2-4 phr, whereas the amount of titanate may be in the range of 0.1 to 1.0 phr.

[0040] The invention is illustrated by the following examples.

[0041] Examples

[0042] A first series of experiments were performed using the following recipes, wherein experiments 5 and 6 are according to the present invention: Table 1

[0043] In the examples, it can be seen that the filler composition was varied, with 70 phr of Carbon Black (N550) on the one hand, various reference examples with a combination of CB and GCC; various comparative examples with a combination of CB and CCC, and a series of examples with CB and CCC-cc on the other hand. See Table 1.

[0044] SBR is a styrene-butadiene rubber extended with 37.5 parts of an oil (Buna VSL 2438-2 (OE), Lanxess, Cologne, Germany). 6PPD stands for the antioxidant N-(1,3-dimethylbutyl)-N'- phenyl-p-phenylenediamine. (Vulkanox® 4020 , Lanxess, Cologne, Germany). The crosslinker is sulphur. The accelerator is CBS (N-cyclohexyl-2- benzothiazole sulfenamide, Vulkacit® CZ , Lanxess, Cologne, Germany). The secondary accelerator is TBzTD (N- cyclohexyl-2- benzothiazole sulfenamide, Caldic B.V., Rotterdam, The Netherlands). Treated distillate aromatic extracts (TDAE) is a rubber processing oil (Hansen & Rosenthal, Hamburg, Germany).

[0045] The properties of the formulations were tested. Payne effect measurements were conducted to evaluate filler-filler and polymer-filler interactions. A RPA Elite Rubber Process Analyzer (TA Instruments) was utilized for these measurements at a temperature of 60°C. Samples were cured before performing the measurement. The storage modulus (G1) values were recorded during shear deformation, employing a strain sweep range of 0.84-100% at a frequency of 1 Hz. The results are shown in Fig 1 and 2.

[0046] 04 (comparative) has a cured Payne effect greater than that of C1, wherein circular calcium carbonate is used, or that of R2, wherein ground calcium carbonate is used. Surprisingly, in 05 and 06 a lower cured Payne effect is found as compared to R3, 02 and 03.

[0047] A second series of experiments were performed using the following recipes, wherein the SBS is replaced with Natural Rubber, in this case a TSR10 grade that has relatively low dirt contamination and ash content (NR-TSRIO).The experiments were performed with 000 particles comprising a core of calcium carbonate covered by a shell of carbon, the particles comprising at least 0.01 to 50 % by weight of the carbon shell (Carbonate B, CCC-cc). The amount of carbon in Carbonate B was analyzed by way of thermoqravimetric analysis as discussed hereafter.

[0048] For the preparation of the rubber compounds, Zinc oxide (ZnO) and stearic acid were used as activators (Millipore Sigma, Hamburg, Germany); sulfur, N-tert-butyl-benzothiazole sulfonamide (TBBS) and TetraBenzylThiuram Disulphide (TBzTD) (Caldic B.V., Rotterdam, The Netherlands) as curatives, and treated distillate aromatic extracted (TDAE) (Hansen & Rosenthal, Hamburg, Germany) as oil. 6PPD (6-Phenyl-1 ,3-dihydro-2H-benzimidazole-2- thione) was used prevent degradation caused by ozone and heat. Paraffinic wax was employed to prevent degradation caused by oxygen. In addition alpha-lipoic acid (Sigma Aldrich, The Netherlands), and the titanate Ken-React® CAPOW L 12 / H (Kenrich Petrochemicals Inc, USA) were reviewed as in-situ coupling agents for the calcium carbonate filled compounds. The experiments are according to the present invention: Table 2

[0049] Ingredients CB B-10 B-LA10 B-Ti10 B-20 B-LA20 B-Ti20

[0050] NR - TSR10 100 100 100 100 100 100 100

[0051] TDAE 10 10 10 10 10 10 10

[0052] Zinc oxide 4 4 4 4 4 4 4

[0053] Stearic acid 2 2 2 2 2 2 2

[0054] 6PPD 2 2 2 2 2 2 2

[0055] Paraffin wax 1.5 1.5 1.5 1.5 1.5 1.5 1.5

[0056] Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5

[0057] TBBS 1 1 1 1 1 1 1

[0058] TBzTD 0.2 0.2 0.2 0.2 0.2 0.2 0.2

[0059] Carbon Black N550 60 50 50 50 40 40 40

[0060] CCC-cc - 10 10 10 20 20 20

[0061] Alpha Lipoic Acid - - 0.7 - - 1.4

[0062] Titanate - - - 0.5 - - 0.5

[0063] The curing curves of the studied compounds are shown in Figure 3. The maximum cure torque (MH) gives an indication of the physical properties of the rubber compounds and is related to its crosslink density and internal interactions present such as the filler-filler and polymer-filler interactions. In Figure 4, it is shown that the coupling agents have a significant influence on the curing curves. Introduction of both coupling agents results in higher maximum cure torque values. The addition of the coupling agent alpha lipoic acid showed a higher impact on the curing behavior than the titanate.

[0064] Analysis of the carbon content by Thermoqravimetric analysis (TGA)

[0065] Thermogravimetric analysis (TGA) on Carbonate B and a carbonate without carbon shell (Carbonate A) was performed using a TGA 550 from TA Instruments. The TGA measurements involved subjecting samples to a controlled temperature ramp in order to determine their thermal stability and decomposition behavior. TGA was conducted under air atmosphere. A temperature ramp of 20°C / min'1was used with an end temperature of 800°C. The calcium carbonates exhibited decomposition above 600°C, which is the breakdown of the inorganic CaCOs into CaO (solid) and CO2 (gas), resulting in weight loss. However, for Carbonate B, weight loss was also observed above 350°C. This weight loss is an indication of the decomposition of organic matter, i.e. the carbon shell.

[0066] The thermal decomposition curve in Figure 3 illustrates a maximum calcium carbonate content of 91% with carbon-based residues being about 8% or less.

[0067] Two further compositions were prepared as in Table 3, wherein C7 is according to the invention, and R4 is a reference example. Table 3

[0068] These compositions were tested according to ASTM D 7723. The results are shown in Table 4.

[0069] The X-value is a 1-10 rating assigned by the software by comparing the sample to an image reference bank. A higher number relates to a better dispersion (similar to a Philips dispersion rating).

[0070] The Y-value is a 1-10 rating based on a count of large agglomerates. A higher number corresponds to fewer large agglomerates which equates to a better dispersion.

[0071] The Z-value is a % dispersion rating that is not based on filler loading.

[0072] It can be seen that overall, C7 outperforms R4.

[0073] Table 4

[0074] Conclusion

[0075] As follows from the experiments and the results in Tables 1 and 4, the CCC-cc particles of the present invention could be easily compounded with the rubber component. They could be included in greater amounts, without deterioration of their properties. The results therefore illustrate the advantages of using CCC-cc particles over CCC or GCC, even if combined with CB. Moreover, a surprising reduction in Payne effect is seen by selecting CCC-cc particles over CCC or GCC, provided the amount of CCC-cc particles is at least half of the amount of CB. Greater amounts of CCC-cc particles show even further reduced Payne effect.

[0076] Addition of a coupling agent further enhances the properties. io

Claims

CLAIMS1. A rubber composition comprising calcium carbonate and carbon black, wherein the calcium carbonate is in the form of circular calcium carbonate particles, that are prepared by pyrolysis of a waste stream comprising calcium carbonate as filler, wherein the circular calcium carbonate particles comprise a core of calcium carbonate covered by a shell of carbon, the particles comprising at least 0.01 to 50 % by weight of the carbon shell, hereinafter “CCC-cc particles”, and wherein the ratio of CCC-cc particles to carbon black is at least 1: 2.

2. The rubber composition of claim 1 , wherein the CCC-cc particles comprise the carbon shell in an amount of 2-25% by weight, preferably 5-15% by weight, more preferably 6-10% by weight.

3. The rubber composition of claim 1 or 2, wherein the CCC-cc particles are prepared by pyrolysis of a waste stream comprising or preferably composed of paper mill sludge.

4. The rubber composition of any one of claims 1 to 3, wherein the CCC-cc particles have a size in the range of 0.01 to 500 pm, preferable an average particle size dso in the range of 0.5 to 20 pm, preferably 0.7 to 4 pm and a particle size dgs in the range of 2 to 400 pm, preferably in the range of 3 to 10 pm, wherein the particle size is determined by laser diffraction particle size analyzer.

5. The rubber composition of any one of claims 1 to 4, wherein the composition comprises up to 200 parts per hundred rubber (phr), more preferably from 2 to 100 phr CCC- cc particles, more preferably from 5 to 50 phr CCC-cc particles.

6. The rubber composition of any one of claims 1 to 5, wherein the ratio of CCC-cc particles to carbon black is at least 2:3, preferably at least 3:4, more preferably at least 1 :1, still more preferably at least 4:3, still more preferably at least 3:2.

7. The rubber composition of any one of claims 1 to 6, wherein the ratio of CCC-cc particles to carbon black is at most 100:1, preferably at most 50:1 , more preferably at most 30:1, still more preferably at most 10:1 , still more preferably at most 7:1.

8. The rubber composition of any one of claims 1 to 7, wherein the composition comprises natural or synthetic rubber, preferably an oil extended styrene butadiene rubber.

9. The rubber composition of any one of claims 1 to 8, cured with sulphur and an accelerator.

10. The rubber composition of any one of claims 1 to 9 enhanced with a coupling agent.

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