Nanoparticle release from surface coatings due to

Faculty of Mechanical Engineering

Institute of Process Engineering and Environmental Technology

Research Group Mechanical Process Engineering

Nanoparticle release from surface coatings due to sanding D. Göhler, M. Vorbau, L. Hillemann and M. Stintz

1 Motivation 1. Nanoparticles are used in industrial and domestic applications to control customized product properties. For instance, in the field of surface coatings nanoparticle based additives (NPA) improve scratch resistance, ultra-violet-light-resistance or transparency for visible light. But there are several uncertainties concerning possible hazard to health, safety and environment. Up to now there are no standardized methods for the characterization of the nanoparticle release from surfaces in dependency on certain treatment processes. Relevant abrasion process parameters (contact pressure and peripheral speed), based on a survey of commercial sanding machines, were used to design a sanding test setup in laboratory scale.

2. Experimental setup and procedure Figure 1 shows the experimental apparatus. apparatus The sander (Model Dremel 400 Series Digital, Digital Dremel Europe, Netherlands) is mounted on a vertical shiftable carriage to adjust several contact pressures (1.0·104 Pa – 5.0·104 Pa). The sample is fixed on a translation unit that moves horizontally beneath the abrasion tool. The sanding process has been carried out at a sanding area of 10.4 cm2, a contact pressure of 10 kPa and a relative peripheral speed of 1.83 m·s-1 by using an abrasive paper with a graining of 600. The sample feed rate was set to 0.3 m·min-1. The experimental setup, shown in Figure 2, excluded the entrance of nanoparticles from the electrical motor and the environment to the swarf aerosol sample by operating in a laminar flow box and directing the sander exhaust flow to the laminar flow box exit. The sanding test apparatus was combined with an Engine Exhaust Particle Sizer (EEPS) and a Laser Aerosol Particle Size Spectrometer (LAP) to investigate a particle size range between 5.6 5 6 nm and 20 μm, μm whereas a Condensation Particle Counter (CPC) was employed to analyze the total particle number concentration. Both, coatings with and without NPA were analyzed. Samples of the generated particles were deposited on a grid in an electrostatic precipitator (ESP) for subsequent analysis by scanning electron microscope (SEM) and transmission electron microscope (TEM). Each sanding process was analyzed for 80 s with a lead time of 30 s (for knowing the background) and a lag time of 34 s (for collecting nearly all dust particles). At first the laminar flow box and the ESP were started, running the whole time. The CPC measurement was started after 15 s for a measurement time of 65 s, while the EEPS and the LAP measurement were started after 20 s. The abrasion process (duration 16 s) was started after another 10 s (timestamp 30 s). For the characterization of the particle release due to the discussed sanding process three different coatings with two different NPA were analyzed (see Table 1). Furthermore, the influence of aging was analyzed. Therefore, the PU and the UV coatings were exposed to UV-A radiation (wavelength 340 nm) for a time of 500 h at a temperature of 60°C. In addition to the dry aging, the AC coatings were exposed for another 500 h to a wet cycle at 50°C. The dry and wet cycles were alternated every 4 h.

Experimental apparatus and translation unit (Göhler et al., 2010)

Figure 1:

k 3.0 L min-1

1.0 L min-1 filter f2

filter f1

LAP 321

flowmeter

ESP

2.7 L min

Kr85

1:9

EEPS 3090 H

DIL 556

DIL 556

1:10

1:100

Schematic diagram of the experimental setup

Table 1:

Analyzed surface coatings

surface coating

sample carrier

two -pack polyurethane coating

oak plate

For more detailed information about the nanoparticle release of surface coatings containing NPA due to defined treatment processes see: Vorbau, M.; Hillemann, L.; Stintz, M. (2009). Method for the characterization of the abrasion induced nanoparticle release into air from surface coatings. coatings J. J Aerosol Sci., Sci 40 (3), (3) 209 209–217 217. Göhler, D.; Stintz, M.; Vorbau, M.; Hillemann, L. (2010). Characterization of nanoparticle release from surface coatings by the simulation of a sanding process. Ann. Occup. Hyg., 54 (6), 615-624.

Dipl.-Ing. Daniel Göhler, TU Dresden, Inst. of Process Engineering and Environmental Technology Research Group Mechanical Process Engineering, D-01062 Dresden Phone: +49 351 463 32051 Fax: +49 351 463 37058 Email: [email protected] Web: http://www.mvt-tu-dresden.de

ID

-

PU

oak plate

ZnO

oak plate

Fe2O3


PU-ZnO

aluminum plate

-


aluminum plate

ZnO

UV curable clearcoat

oak plate

-

UV curable clearcoat

oak plate

ZnO

white pigmented architectural coating

fiber cement plate

-


fiber cement plate

ZnO


fiber cement plate

Fe2O3

1.0E+06

PU-Al-ZnO

UV-ZnO AC AC-ZnO AC-Fe2O3

t = 10 s t = 15 s t = 20 s t = 25 s t = 30 s t = 35 s t = 40 s t = 45 s t = 50 s

1 6E 02 1.6E-02 1.2E-02 8.0E-03

5.0E+05

4.0E-03

0.0E+00

0.0E+00 1

PU-Al

UV

2.0E-02

density distributiion, weighted by num mber -1 q0 [nm ]a

1.5E+06

PU-Fe PU Fe2O3

2.4E-02

t = 10 s t = 15 s t = 20 s t = 25 s t = 30 s t = 35 s t = 40 s t = 45 s t = 50 s

2.0E+06

10

100

0

1000

electrical mobility diameter x [nm]

100

200

300

400

500

600

electrical mobility diameter x [nm]

Figure 3: Evolution of dN/dlog(x) of the PU swarf particles, measured by EEPS

Figure 4: Evolution of q0 of the PU swarf particles, measured by EEPS 1.0E+12

25.00

-

swarf m mass [mg g]

Fe2O3

15.00

10.00

5.00

number of rele eased particles x < 100 0 nm [-]

1.0E+11

ZnO

20.00

ZnO

1.0E+10

Fe2O3

1.0E+09 1.0E+08 1.0E+07 1 0E 06 1.0E+06 1.0E+05 1.0E+04 1.0E+03 1.0E+02 1.0E+01 1.0E+00

0.00 PU

PU*

PU*-AL

UV

UV*

AC

AC*

PU

Figure 6:

Figure 5: Swarf mass, *aged samples

PU*

PU*-Al

UV

UV*

AC

AC*

Number of released particles x < 100 nm, *aged samples

7.5

transformed density distribution weighted by number, w dQ0/dlog(x) [-]

Investigations on aged surface coatings show an increase of the nanoparticle release. In accordance to the unaged samples, no free NPA were found during the analysis with SEM and TEM.

0.3 L min-1

NPA

two -pack pack polyurethane coating

-

No significant difference could be observed between the coatings with and without NPA. TEMimages of precipitated swarf particles (Figure 8) show that the generated particles come from the matrix material, which contains the embedded NPA.

CPC 3022A


transformed density distrib bution of the number concentra ation -3 dN/dlog(x) [cm ]

For the given stress of the sanding process the swarf mass (Figure 5), the particle size distribution (e.g. Figure 4) of the released aerosol and consequently the number of released particles depend primarily on the used surface coating (Figure 6). The results show a considerable generation of nanoparticles during the sanding process.

filter f3

10 L min-1

Figure 2:

2.5E+06

Preliminary investigation have shown that the particle release due to sanding processes depends on the contact pressure, the peripheral speed, the sample feed and the graining of the abrasive paper.

valve

Q

valve

T

valve

Q -1 1

Q

3. Experimental setup

4. Results

valve

-3 kV / +13 kV

ZnO additive Fe2O3 additive

6.0 4.5 3.0 1.5 0.0 10

100

1000

particle diameter [nm]

Figure 7: Particle size distributions of the NPA, based on photon cross correlation

Figure 8: TEM-image of a precipitated PU-ZnO swarf particle

The authors wish to thank: • German Paint Industry Association (VdL), Frankfurt a.M., Germany, - financial support • Bayer Technology Services, Leverkusen, Germany, TEM-investigations • Institut für Lacke und Farben e.V., Magdeburg, Germany, sample preparation.