Industrial or technical carbon black (TCB) is primarily manufactured via incomplete combustion of hydrocarbons, although thermal decomposition in oxygen-deprived conditions can also yield it. The industrial-scale production of TCB involves meticulously controlled processes, employing precise techniques and measurements to ensure distinct properties that differentiate it from soot a contaminated byproduct (Donnet, 2017; Khodabakhshi
The significance of natural rubber for humans has increased steadily over the past century (Fan
Over 90% of TCB is composed of pure elemental carbon, where tine and spherical carbon atoms combine to form aggregates. To achieve various property balances, TCBs come in a variety of grades with a wide range of particle sizes, based on surface areas, aggregate morphologies with nanostructures, amount of ash and other compounds (Contec; Robertson and Hardman, 2021). The classification of rubber-grade carbon black (CB) follows the ASTM number system and the four-character nomenclature system. The first character ‘N’ indicates the influence of TCB on the curing rate of typical rubber. The second character indicates the average surface area of the TCB, while the last two characters are arbitrary (ASTM:D1765-17). The most typical TCB with a mean particle surface size is referenced in (Fan
Globally, approximately 15 million metric tonnes of TCB are produced annually, with about 93% directed to rubber industries. Of this, around 73% is used for tire production, and the remaining 20% in various other rubber appliances. The residual 7% is used for the production of coatings, inks, plastics and paints (Robertson and Hardman, 2021). According to Pehlken and Essadiqi (2005), tires are a complex mixture with a reinforcing agent of CB with silica (ca. 25%) and about 32% of CB can be recovered by tire pyrolysis.
The production of TCB is classified as unsustainable as it utilises non-renewable feedstock, also the production contributes significantly to CO2 emission and energy consumption. As a result, research on green fillers has gained increasing attention, especially for by-products from industrial or agricultural waste and recyclable materials (Fan
According to Intharapat
Radiocarbon analysis can distinguish between fossil and biobased carbon by detecting the 14C/12C isotope ratio within the sample (Haverly
There are currently no applicable standards specifying the requirements for a specific amount of biocomponents in TCB. However, the determination of the content of bio-based carbon in various materials can be carried out in accordance with the ASTM D6866 or EN 16640 standard. The EN16640 2017 standard applies in Poland and the measurements were carried out in accordance with it. The samples were analysed by two radiocarbon techniques, liquid scintillation counting (LSC) and accelerator mass spectrometry (AMS), at the Gliwice 14C and Mass Spectrometry Laboratory. Isotope ratio mass spectrometry (IRMS) measurements were used for the isotope fractionation correction.
In this study, four TCB samples of varying grades underwent examination. Currently, there are no existing standards specific to TCB samples. Nonetheless, the establishment of such standards is anticipated in the near future given the growing focus on environmental preservation. Manufacturers of CB typically do not disclose information regarding the presence of bioactive materials. However, exploring the viability of using the 14C method to ascertain the modern carbon content holds significance. The samples were sourced from Contec Inc. in Warsaw, Poland, and the details pertaining to each sample are outlined in
Details of the TCB samples (Contec; Fan et al., 2020).
1. | TCB-N330 | 76–80 | Medium-high reinforcement. Used as tread, carcass and sidewall compounds for tires and rubber goods. |
2. | TCB-N550 | 39–41 | Medium-high reinforcement. Used in inner liners, carcass and sidewalls for passenger tires and rubber goods. |
3. | TCB-N660 | 34–36 | Medium reinforcement. Used in inner liners, sidewalls, sealing rings, cable jackets, rubber moulding and extruded items. |
4. | TCB-N772 | 31–32 | Semi-reinforcement. Used as inner liners of tires and rubber goods. |
The samples were prepared and analysed at the Gliwice 14C and Mass Spectrometry Laboratory in the frame of the Institute of Physics – Center for Science and Education, SUT, Poland (Pawlyta
Quantulus 1220TM liquid scintillation β spectrometer, was used for LSC measurements to determine the 14C isotope concentration (Pazdur
Liquid scintillation spectrometry is used for the β-emitting isotopes such as 14C. In general, for LSC measurements, the sample preparation method passed through sample combustion (organic matter is transformed into CO2) followed by benzene formation with the CO2 and then mixing with a scintillation cocktail (Gill
TCB samples were directly reacted with lithium metal, in a proportion of 1:1, to obtain lithium carbide (Li2C2) at 700°C of temperature. This reaction took place in a metal reactor for about an hour under controlled pressure conditions. In the next step, Li2C2 is hydrolysed by deionised water to produce acetylene (C2H2), which is purified by a highly hygroscopic mixture of potassium dichromate (K2Cr2O7) and sulphuric acid (H2SO4). C2H2 is trimerised to benzene using a preheated chromium catalyst (at 600°C ~0.5 h). The water molecules from the benzene samples were removed by keeping the sample in sodium metal for 24 h, followed by sublimation. Atmospheric radon was removed by keeping the benzene samples in the refrigerator (at −15°C) for a month, since the half-life of radon is 3.8 days. The complete process for preparing benzene is detailed in (Gill
IRMS method is applied to calculate the standardised isotope fractionation correction (Stuiver and Polach, 1977; Multiflow, 2012; Agnihotri
The uncertainty for δ13C values were calculated as a standard deviation of the mean value of the samples multiplied by the Student-Fisher coefficient.
The VarioMicroCube Elemental Analyzer coupled with an automated graphitisation equipment (AGE-3) system by IonPlus AG was used for the determination of total carbon content in samples and graphitisation (Němec
AMS measures the ratios of 14C/12C and 13C/12C precisely. No chemical pretreatments were used for AMS measurements. Approximately 1 mg of the sample was placed in tin boat capsules. The samples underwent combustion in an elemental analyser to generate CO2 gas. This gas was subsequently graphitised using AGE in the presence of H2 and Fe powder (Wacker
The results for the 14C isotope concentration alongside bio-based carbon content according to (EN16640, 2017) from LSC (lab code GdS) and AMS (lab code GdA) laboratories are listed in
The 14C isotope concentrations are mentioned in pMC for the four different classification categories of TCB samples. δ13C obtained by IRMS (*) and from the AMS measurements (**). The results were corrected for isotope fractionation. The critical χ2 values for confidence level α = 0.01 and four measurements = 11.34, for three measurements = 9.21 and for confidence level α = 0.05 and four measurements = 7.81, for three measurements = 5.99. Bio-based carbon content was calculated according to (EN16640. 2017; CIO, 2022), 100 REF is used for the year 2022 (CIO, 2022).
1. | TCB-N330 | GdS-4543 | 6.08 g | - | −32.44 ± 0.11* | 0.589 ± 0.084 | 6.66 | 0.589 ± 0.084 |
2. | GdA-7138.1.1 | 1.81 mg | 99.75 ± 0.93 | −29.20** | 0.436 ± 0.033 | Without GdS-4543 | 0.436 ± 0.033 | |
3. | GdA-7138.1.2 | 0.99 mg | −30.60** | 0.410 ± 0.038 | 0.28 | 0.410 ± 0.038 | ||
4. | TCB-N550 | GdS-4552 | 4.02 g | - | −30.417 ± 0.072* | 0.189 ± 0.063 | 30.76 | 0.189 ± 0.063 |
5. | GdA-7137.1.2 | 0.98 mg | 97.5 ± 2.3 | −25.70** | 0.508 ± 0.033 | Without GdS-4552 | 0.508 ± 0.033 | |
6. | GdA-7137.1.3 | 2.05 mg | −28.80** | 0.500 ± 0.035 | 0.03 | 0.500 ± 0.035 | ||
7. | TCB-N660 | GdS-4554 | 3.91 g | - | −31.82 ± 0.44* | 0.908 ± 0.092 | 51.09 | 0.908 ± 0.092 |
8. | GdA-7139.1.1 | 2.19 mg | 98.1 ± 1.9 | −28.80** | 0.489 ± 0.033 | Without GdS-4554 | 0.489 ± 0.033 | |
9. | GdA-7139.1.2 | 1.90 mg | −36.60** | 0.350 ± 0.043 | 24.17 | 0.350 ± 0.043 | ||
10. | GdA-7139.1.5 | 1.09 mg | −29.30** | 0.600 ± 0.031 | 0.600 ± 0.031 | |||
11. | TCB-N772 | GdS-4555 | 3.89 g | - | −31.453 ± 0.020* | 0.124 ± 0.091 | 22.45 | 0.124 ± 0.091 |
12. | GdA-7140.1.2 | 2.03 mg | 98.9 ± 1.0 | −33.00** | 0.380 ± 0.043 | Without GdS-4555 | 0.380 ± 0.043 | |
13. | GdA-7140.1.3 | 2.03 mg | −32.90** | 0.350 ± 0.043 | 0.350 ± 0.043 | |||
14. | GdA-7140.1.4 | 1.01 mg | −28.90** | 0.470 ± 0.035 | 5.58 | 0.470 ± 0.035 |
The 14C isotope concentrations of TCB samples, categorised into four different grades, were measured by LSC and AMS spectrometry.
For the TCB-N330 sample, the 14C concentration was measured at 0.436 ± 0.033 pMC and 0.410 ± 0.038 pMC via AMS and 0.589 ± 0.084 pMC via LSC. The AMS and LSC measurements demonstrate agreement.
In the case of the TCB-N550 sample, the 14C concentrations were 0.508 ± 0.033 pMC and 0.500 ± 0.035 pMC from AMS, and 0.189 ± 0.063 pMC from LSC. These results indicate a statistical inconsistency between AMS and LSC measurements.
For the TCB-N660 sample, the 14C concentrations were 0.489 ± 0.033 pMC, 0.350 ± 0.043 pMC and 0.600 ± 0.031 pMC by AMS, and 0.908 ± 0.092 pMC by LSC. The AMS and LSC measurements present statistical inconsistency. The AMS results for this sample demonstrate considerable scatter and do not pass the consistency test.
Regarding the TCB-N772 sample, the 14C concentrations were determined as 0.380 ± 0.043 pMC, 0.350 ± 0.043 pMC and 0.470 ± 0.035 pMC using AMS, and 0.124 ± 0.091 pMC using LSC. Similar to previous cases, the AMS and LSC measurements are statistically inconsistent.
To explain the disparities in measurement results between LSC and AMS, the authors are inclined to support the hypothesis suggesting sample inhomogeneity, which could be because of the ash contamination, the presence of hydrogen atom (provided by the original hydrocarbon feedstock), four-general oxygen-containing chemical groups and sulphur (Contec; Fan
The results obtained from measurements using two techniques (AMS and LSC) indicate a very low (<1 pMC) concentration of 14C in the tested samples. This suggests a substantial presence of fossil components in samples, indicating their production before the use of biogenic material. The Reference Value (REF) for the year of biomass formation is required to calculate the content of bio-based carbon in the sample (EN16640, 2017). This value corresponds to the 14C activity of pure biomass. The highest bio-based carbon content is determined using the REF value corresponding to the year 2022, set at 100 pMC. Therefore, the bio-based carbon content ratio corresponds to the 14C concentration within the sample. In our previous research (Gill
TCB samples underwent analysis in this study. The 14C isotope concentrations were measured in the samples using LSC and AMS radiocarbon techniques at the Gliwice 14C and Mass Spectrometry Laboratory. These TCB samples were sourced from the Contec Inc. Company. According to previous research, the TCB samples were expected to contain a higher concentration of modern carbon. However, all samples exhibited only a minute amount of 14C isotope concentration <1 pMC. The bio-based carbon content mirrors the 14C isotope concentrations of each sample. This study indicates that the four differently graded TCB samples were either not produced from renewable resources or were produced with a minimal share of them.