The CLH classification of Multi-Walled Carbon Tubes was proposed by Germany .
The ECHA's RAC (Committee for Risk Assessment) has been discussing the CLH classification of Multi-Walled
Carbon Tubes.
We can submit comments until September 4, 2022.
On August 17,2022, the NBCI submitted comments on the German proposal that the carcinogenicity classificationis "1B".

Possibilities and Challenges of CNTs
August 17, 2022
CNT Subcommittee
Executive Summary
For a safer innovation approach using carbon nanotubes (CNTs), the socioeconomic impact of the emerging
technologies enabled by CNTs is an intrinsic motivation in research and development.
As we have already reported, there are various methodologies for CNTs‘ production, and the CNTs have diverse
morphology and physicochemical properties depending on the methodologies even if the names are the same as“Carbon Nanotubes”. This diversity of CNTs characteristics is a competence of the emerging technologies, in themeantime, the diversity makes the management of CNTs difficult.
In this paper, we indicate the scientific and economic impacts in our daily life enabled by using of CNTs. For instance,
CNTs have already been used widely as the key component of lithium-ion rechargeable batteries (LIBs) making themefficient and durable. CNTs are essential for reinforcement and electric conductivity of resines as well.
CNTs are being studied intensively as the key material for realizing the space elevator in future. The socioeconomic
impacts of these emerging technologies enabled by the use of CNTs should be recognized correctly prior to thediscussion on the regulartory framework of nanomaterials.
1. Introduction
Carbon Nanotubes (CNTs) have been known since 1976[1] [2].
Since the start of strategic investment in the “Nanotechnology andMaterials” in the 2nd Science and Technology Basic Plan of Japan enforced
in FY2001, CNTs have been a key material in the research anddevelopment of emerging technologies to realize a sustainable society.
CNTs are excellent in electrical and mechanical properties and are highly
durable materials. Those properties bring a drastic change into theproperties of various industrial materials by forming the composite evenwith a minimal amount such as weight and volume of CNTs.
In fact, the number of scientific papers and patents on CNTs hasremained at a high level up to the present day as shown in Fig.1.

Fig.1 Number of papers and patents on the topic of CNTs

We recognize that scientific and industrial expectation for CNTs is still high and the research targets of CNTs
applications are also wide-ranging as electronics and energy devices, industrial materials and so on[3].
Basically, CNTs for industrial usage are produced by Chemical Vapor Deposition (CVD) on a large-scale by thermal
pyrolysis of hydrocarbons gas, CxHy at 500 ~ 1000 degrees C. This CVD method has an almost infinite combinationsof catalyst source gases, catalysts, reaction temperatures, pressures, a flow rate of feeding gases, etc. By properly
adapting the process parameters, we could obtain various types of CNTs having diverse morphologies and properties.
For such diverse CNTs, it’s difficult to define the hazard levels univocally as we have published in2022[4]However, the diversity of morphology and properties of CNTs results in the diverse applications as shown
below.

2. Present Typical Applications of CNTs
2.1 Additives for Lithium Ion Battery (LIB)
Since the lithium-ion rechargeable battery (LIB) was launched on to
the market in 1991, the performance of LIB has been improved
significantly year by year. In particular, LIBs have been supporting the
IT/AI society, and now LIB is adopted as the main power source for
HEVs and EVs. It is no exaggeration to say that a sustainable futuresociety would not be complete without LIBs. This is because LIBs
have the highest energy density compared to existing batteries such as
lead-acid batteries (Pb), nickel-cadmium (Ni-Cd), and nickelhydrogen batteries (NiMH), and provide safer and lighter compact
rechargeable batteries.
And it has been found that the addition of CNTs increases theperformance

of

LIBs,

since

the

early

stagesof

LIBdevelopment.(Fig.2) [5]
It is now believed that this tremendous effect of CNTs as additives isdue to the following factors.
1) Improvement of energy density:

Fig.2 SEM pictures of (a) the carbon anode sheet containing

Fibrous CNTs connect active materials and increase the number of

CNTs in a commercial cell and (b) enlarged one.

active materials.
2)Reduction of electrical resistance between the active material and external circuit:
CNTs act as a good conductor of electrons and ions, reducing energy loss.
3)Suppression of heat generation in devices:
CNTs having high thermal conductivity thanks to phonon transferring nature reduce heat production between active
materials.
Originally, the suitable diameter of CNTs for this application was large such as 100nm or more, but recent reportsuggests hybrid additives including smaller diameter of CNTs such as 10-50nm and larger diameter of CNTs show
the best performance [6].
These excellent effects are achieved through the wonderful properties of CNTs themselves.
(a)the small diameter of CNTs
The small diameter of the CNTs makes it possible to distribute the CNTs homogeneously in the thin electrode material
and to introduce a larger surface area to react with the electrolyte.
(b)electrical conductivity
The improved electrical conductivity of the electrode is related to the high electrical conductivity of the fiber itself,
and the conductive network formation of the fibers with the graphite particles in the anode to form a fiber-mat.
(c)high intercalation ability
As compared with that of conventional whiskers, the relatively high intercalation ability of CNTs did not lower thecapacity of anode materials during charge-discharge cycles.

(d)high flexibility
The electrode is achieved due to the network formation of CNTs in a fiber-mat structure.
(e) high endurance
CNTs absorb the stress in the electrodes caused by the intercalation of Li-ions.
(f) Improvement of penetration of the electrolyte
This effect is due to the homogeneous distribution of CNTs surrounding the anode material.
Through vigorous research and development over 20 years, CNTs in anodes and even in cathodes now contributesignificantly to the ultra-long life of LIBs. Currently, the CNTs are inevitable for LIB as mentioned above.
2.2 Electrically Conductive VMQ (Methyl Vinyl Silicone Rubber)
Recently, CNT-filled conductive VMQ composites havebeen developed, a completely new material that offers
high conductivity due to the effective addition of CNTs
and can be applied in electrode pads for medical devices
for neuromodulation therapy. [6] Figure 3(a)(b).
Highly dispersed high-purity CNTs create a CNT-VMQ
composite material with extremely stable and highelectricalconductivity,

flexibility,

andFig.3(a)durability

compared to other conductive filler materials such as

Fig.3(b)Fig.3(a) Appearance of CNT dispersed VMQ sheet.
(b) Image of CNT-applied device that reduces body tremors

conventional carbon black.
In particular, the use of long CNTs eliminates the falling carbon tiny particle out of the rubber compared toconventional conductive carbon black, and the Biocompatibility test of CNT-filled conductive VMQ was passed andapproved by the US Food and Drug Administration(FDA), which was a major trigger for the adoption of CNTs.
This breakthrough material has been implemented in medical wearable devices to improve the quality of life of people
suffering from neurological diseases.
2.3 CNTs dispersed Paint system
Metal corrosion has huge economic and safety impacts on socialand economic infrastructure. From this viewpoint, the corrosionprotecting polymer coatings have been required, strongly.
Necessary factors for high-performance polymer coatings include
strong adhesion between the substrates and polymer layers andphysicochemical and mechanical properties of the polymer layer.
These factors depend on the choice of appropriate additives thatare CNTs as the strongest element for reinforcing. CNTs dispersed
coatings will make the lifetimes of metal products surprisingly long evenin chemically and/or mechanically severe environments, thereby greatly

Fig.4 Nuts & Bolts reinforced by CNT
paint in oil field in middle east country

reducing their life-cycle costs which means “the environmentally friendly products”.

The metallic fasteners such as nuts and bolts which are coated by CNTs dispersed paint are already being expanded
for use in chemical plants in middle east countries located under very harsh environments.[7] (Fig.4).
The suitable diameter of CNTs for this application is much larger such as 80 nm and these CNTs reinforce polymer
film for tremendous strength and durability against the harsh and severe environment.
3. Applications in the future
3.1 Development of CNT Synthesis Technology as a Strategy for Fixing Global Warming Gases
As mentioned before, CNTs are produced by thermal pyrolysis of hydrocarbons gas, CxHy. And scientists around theworld believe that greenhouse gases can be immobilized by using them as raw materials for CNTs and have been
vigorously investigating methods and conditions for this purpose [8].
The basic chemical formula for synthesizing CNTs from CO2 is as follows;
Dissolution: CO2(gas) + Li2O(soluble) →Li2CO3(molten)
Electrolysis: Li2CO3(molten) →C(solid)＋Li2O(soluble)+O2(gas)Net: CO2 (gas) →C(solid) +O2(gas)Meanwhile, when we think of greenhouse gases, CO2 gas
comes to mind, but methane (CH4), which has an even higher
global warming potential that has 21 times higher than CO2,
is already being used for CNTs synthesis [9].
In the future, it will contribute to a hydrogen society byrealizing low-cost hydrogen production as a byproduct, too.

Fig.5 Schematic diagram of H2 production system utilizing CNTs synthesis(Fig.5) The use of these warming gases will dramatically reducethe cost of CNTs, which will lead to a remarkable expansion of
CNT applications in the future.
3.2 Space Elevator
Half a century of space exploration has diversified the purposes
for which humans have ventured into space.
However, in order to further expand the possibilities, economical
and mass transportation of people and materials is essential.
The "space elevator," which connects Earth and space via cables
and allows people to travel to and from space as easily as taking©Obayashi Corporation

Fig.6(a) Conceptual drawing of a space elevator utilizing CNTs’ ropea train, is expected to be a more efficient, economical, andenvironmentally friendly means of transportation compared torockets [10]. (Fig.6(a))
As long as it is built on the earth, there is a limit point at which
the construction will break under its own weight. Although aspace elevator, a tower that extends into space, was theoreticallyfeasible, it was only a dream because there was no material with

©Obayashi Corporation

Fig.6(b) Space Elevator Construction Schedulethe necessary "lightness" and "strength" for the cable connecting the earth and space.
However, CNTs, a light and strong material opened the gate to the realization of this wonderful space elevator.
The space elevator is planned to be built by the year 2050 with a capacity to carry 100-ton climbers as construction
schedule (Fig.6(b)).
It is composed of a 96,000-km CNTs cable, a 400-m diameter floating Earth Port and 12,500-ton counterweight.
Other facilities include Martian/Lunar Gravity Centers, Low Earth Orbit Gate, Geostationary Earth Orbit Station, aMars Gate and a Solar System Exploration Gate.
CNTs’ researchers have to develop continuous and defect-free CNTs having a tensile strength of 150 GPa by
2030 to realize space elevators.
The current technology levels are not yet sufficient to realize the concept, but this plan itself is realistic.
The breakthrough of the CNTs synthesis method is absolutely required to realize this mankind’s dream.
4. Conclusion
We have discussed several present applications and expected great applications.
Though the total worldwide production of CNTs is estimated to be about 5,000 tons per year, it is difficult to say that
“CNTs have been industrialized”, which leaves an undeniable imbalance compared to the number of active papers as
pointed out in Fig.1.
We recognize that there are several challenges that need to be addressed in order to make CNTs even more useful andwidespread for future grand usage.
(1) Inadequate performancesSize-derived strong aggregates, resulting in difficult dispersion, CNTs lattice defects, resulting in non-uniform quality,
fiber-derived orientation and alignment, resulting in anisotropic performance.
(2) Economical efficiency
CNTs are still staying at a high costs.
Economic "causality dilemma" Chicken and Egg Problem unique to new materials exists.
It is calculated that at least several thousand tons per year of demand and production are required to replace carbon
black.
(3) Applications
We have unexplored and undiscovered "applications
that can only be achieved only with CNTs."
If the current situation is (1) on the above, it is also
necessary to develop applications for "applications
with a wide range of acceptable performance.“(4) Social Implication
As defined by ISO/IEC GUIDE51, "Absolute safety
does not exist."
We, CNT Subcommittee take the position that "if
CNT is judged to be acceptable in consideration of

Fig.7 Risk evaluation

its hazard and convenience, risk management is possible by minimizing exposure to CNT, even if the hazard of CNT
cannot be quantified". (Fig.7[12])Risk = Hazard x Exposure (contact between nanoparticles and humans, Exposure)
Even if there is a CNT-specific hazard, if we can reduce and control the possibility of contact, we can minimize therisk to an "acceptable risk," i.e., "deemed safe" as defined by ISO.
LCA (Life Cycle Assessment) are needed, as well, for sustainable development and commercial readiness. LCA
should include energy consumption, performance lifetime, degradation or disposal of CNT-based products and theirsafety.
We hereby propose that the above critical issues be addressed in an international framework.
We believe that this would be a more useful endeavor for humanity than a one-sided and weakly grounded discussionof the dangers of CNTs.
ABOUT NBCI
NBCI (Nanotechnology Business Creation Initiative) is a Japanese institution established in 2003 to launch andexpand the nanotechnology business. NBCI is made up of more than 140 Japanese organizations interested in
nanotechnology, promoting the collection and sharing of the latest technical and environmental safety information,and networking with industry, academia and government. Furthermore, we are making recommendations on R &D strategies, environmental safety regulations, and standardization activities in the field of nanotechnology.
Website: https://www.nbci.jp/en/index.html

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Crystal Growth 32(1976)335-349[3] Engineering of oriented carbon nanotubes in composite materials, R.Beigmoradi, A.Samimi and D.MohebbiKalhori, Beilstein J.Nanotechnol.2018,9,415-435[4] Objective, fair and consistent hazard classification of MWC(N)T to facilitate the safer innovation, NBCI, July2022
https://www.nbci.jp/file/NBCI_Comment_on_CLH_report_20220708.pdf[5] Vaper-grown carbon fibers Basic properties and their battery applications, M.Endo, Y.A.Kim, T.Hayashi,
K.Nishimura, T.Matusita, K.Miyashita, M.S.Dresselhaus, Carbon 39, 2001, 1287-1297[6]Press Release(Japanese), National Institute of Advanced Industrial Science and Technology (AIST) and Zeon
Corporation, January 2021

https://www.aist.go.jp/aist_j/new_research/2021/nr20210517/nr20210517.html[7] Press Release, GSI Creos Corporation, CNT dispersed paint, Nanotect® is adopted by ADNOC, UAE nationaloil company
https://www.gsi.co.jp/en/business/technology/product02/main/013/teaserItems1/02/linkList/0/link/nanotechnology%20final.pdf[8]Thermodynamic assessment of CO2 to carbon nanofiber transformation for carbon sequestration in a combined
cycle gas or a coal power plant, J.Lau, G.Dey and S.Licht,, Vo.122, 400-410, 2016
https://www.sciencedirect.com/science/article/pii/S0196890416304861?via%3Dihub[9] Press Release (Japanese), Toda Kogyo Corporation
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https://www.obayashi.co.jp/chronicle/130th/en/story/space-elevator/[11]Nano Carbon FAQ, 2022, NBCI (Japanese)
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