Ladies and gentlemen, welcome to the presentation Inhalable Aerosols
from Carbon Fibers.
My name is Sonja Mühlhaupt.
I am from the Karlsruhe Institute of Technology, Institute for
Technical Chemistry.
The work I will present is part of the project Carbon Fiber Cycle,
which is funded by the Federal Ministry of Education and Research,
Germany.
It is a joint project of the following three KIT institutes, the
Institute for Technical Chemistry, the Institute for Biological and
Chemical Processing and the Institute for Applied Biosciences.
Also participating are the Unit of Technologies of Juhls from the RVTH
Aachen University, the Institute for Composite Materials
Kaiserslautern and the companies Vitrocell Systems and Palas.
Carbon fiber reinforced polymers are used in high-performance
applications as aviation and aerospace, automotive engineering or wind
power.
However, these modern materials are used more and more in modern
consumer products as sports equipment and lifestyle.
While the processing and when reaching end of life, the carbon fibers
or rather the carbon fiber reinforced polymers are stressed by
processes like cutting, sawing and grinding.
Additionally, during the recycling process, most materials go through
a pyrolysis, resulting also in thermal stress.
Especially due to the thermal stress, the properties may change and
fibers and fiber fragments may be released into workplaces and
environment.
This is an example for two different carbon fibers, both treated in a
muffle furnace in 800 degrees hot air.
Both show changes on the surfaces.
The left one, which is a polyacrylonitrile-based carbon fiber,
exhibits pitting corrosion that can act as predominated breaking
points.
The right one was manufactured from pitch as precursor.
This one desqueezes along the fiber, developing tips like needles,
which are a critical geometry under the aspect of inhalation
toxicology.
To clarify such questions and possible risk for workers, the joint
project carbon fiber cycle is analyzing release scenarios for
inhalable carbon fibers.
The thermal and mechanical behavior of carbon fibers while treatment
is investigated and delivers the input to supply the toxicological
experiments with a defined and characterized material from inhalable
carbon fibers.
The fibers are tested for lung toxicity under submerged as well as
under air-liquid interface conditions, exposing the cell cultures
directly to aerosols containing inhalable carbon fiber fragments.
The results build the base to formulate recommendations of action
regarding the handling of carbon fibers and carbon fiber reinforced
polymers while their life cycle.
Let's have a closer view on inhalable fibers.
Under which conditions are fibers inhalable?
The World Health Organization has defined three geometric criteria to
classify critical fibers.
The so-called VHO fiber is at least 5 micrometer long, has a diameter
of maximum of 3 micrometer and an aspect ratio from length to diameter
of minimum 1 to 3.
Fibers fulfilling these criteria can cause typical disease patterns
related to fibers.
The asbestosis, which is a lung fibrosis, lung cancer and
mesotheliomas, that is a fiber-related form of lung cancer.
A typical mechanism causing these diseases is the frustrated
phagocytosis.
If fibers are too long, the macrophages, immune cells normally
cleaning the lung, are not able to phagocytize the foreign matter and
become overstrained.
This danger is greater the more rigid and biologically resistant the
fiber are and as a consequence this can lead to inflammation and
further on to cancer.
To investigate the toxic potential of carbon fibers, we will perform
air -liquid interface studies with airborne carbon fibers.
We established a triple culture from lung epithelial cells with
macrophages on the upper side and fibroblasts on the lower side of the
membrane insert in which the cells are cultivated.
While the exposure experiment, the lower side of the membrane insert
is located in the medium, whereas the upper side with the epithelium
and macrophages is not covered with medium and exposed to the aerosol
containing inhalable carbon fibers.
In pre-tests under submerged conditions, with the well-established
human A5 for lung cells, milt carbon fibers with a length of about 150
micrometer were compared to two types of quartz, which shows a typical
cancer risk when inhaled.
The carbon fibers were used as delivered by the manufacturer, the
pristine ones, and thermally treated in the Maffel oven at 800
degrees.
All samples show no significant response regarding viability in
comparison to the negative control, not by the release of lactate
dehydrogenase LDH assay, which is an indicator of membrane damage, nor
by a decrease of the Alamar blue signal, which is an indicator of
metabolic activity.
The air-liquid interface exposure experiments take place in an
automated exposure station developed at KIT and manufactured by
Vitrocell Systems.
We follow two routes for supplying the system with carbon fiber
-containing aerosols.
We disperse pre-treated fibers into an air flow, or we take an aerosol
sample from a cutting device for carbon fiber reinforced polymers.
In both cases, the aerosol is led to the exposure system, passing the
PSI -selective inlet, which is a PM10 inlet.
At the different steps of the process, the aerosol will be
characterized as well as the deposited dose on the cell culture
surface.
To estimate a suitable fiber concentration for the air-liquid
interface studies, we have a look on typical concentration limits in
workplaces for hazardous materials, which is expected to act
comparable.
The corresponding regulations for materials like asbestos or mineral
wool define different concentrations, which are acceptable or
tolerable concentrations.
Starting from the tolerable concentration from asbestos of 10.000
fibers per cubic meter and assuming a safety factor of 10 to the no
-observable -effect level no-EL, which we want to detect, we can
estimate a useful mass concentration of around 10 mg per cubic meter.
To generate the aerosol of airborne carbon fibers, we used an aerosol
generator with a segmented belt to disperse carbon fibers.
The generator is located in a digestory equipped with HEPA13 filter
and has an additional housing to avoid fiber exposure of the operator.
Using a commercial polyacrylonitrile-based fiber as model material, we
found a configuration to generate an aerosol with a mass concentration
of 200 mg per cubic meter directly behind the generator, which is
stable for 4 hours.
It is operated with a nozzle pressure of 1.2 bar and a belt velocity
of 12% corresponding to 1 cm per minute.
After passing the tubing and the PM10 inlet, we expect the fiber
aerosol to reach reasonably concentrations of fibers.
This will be measured in the next weeks.
The World Health Organization has defined the image analysis of
micrographs as a standard method for measuring fibers at workplaces.
On this standard, we refer when establishing additional methods.
For fast testing while developing a fiber aerosol generation method,
we used the gravimetric analysis.
For an online detection while the aerosol exposure experiments, we
want to use an optical particle detector.
For this aim, first measurements of the fiber aerosol with the Palas
Velas Digital 2000 have been performed.
In parallel, we tested a planetary ball milled to generate smaller
fibers near to the geometric criteria of a VHO fiber.
Milling 5 minutes at 500 rounds per minute generates a carbon fiber
powder of around 10 micrometer in length.
As shown in the beginning, carbon fibers are increasingly used in
modern products.
While production of carbon fiber reinforced polymer products, their
use and the following recycling process, the carbon fibers are treated
in different ways.
A thermal treatment of them can cause changes in the surface like
pitting corrosion or degradation along the axis.
And in the following, the formation of inhalable carbon fiber
fragments can be observed.
Within our project carbon fiber cycle, we successfully tested an
aerosol generator with short carbon fibers.
We produced fibers with a mean length of 10 micrometer for the next
step, which is the generation of an aerosol containing VHO fibers.
The cell culture systems for fiber toxicity based on the triple
culture from epithelial cells, macrophages and fibroblasts is
developed for the exposure at the air-liquid interface.
In future, we will perform air-liquid interface exposures towards an
aerosol containing carbon fibers, matching the VHO criteria to
investigate the biological risk of inhalable carbon fiber fragments.
With this summary, I would like to thank all my co-authors and
partners within the carbon fiber cycle project.
Thank you for your interest in this work.
I would be happy to discuss any questions in the session AH4, Indoor
and Occupational Aerosols and Health, on Thursday afternoon at 2.30 p
.m. Goodbye!