## 3 Results
### Results of the Nano-Release Study  
After the abrasion test was performed on the LDPE and EPDM nanocomposites (without pre-conditioning) the areas that were abraded with sand showed a dull, scratched surface (Figure 6). This indicated a gentle and homogeneous abrasion of the surface. After transferring the abraded material and the sand into 96% ethanol, AF4/MALLS measurements were performed to detect potential CB nano-particulates. The relevant AF4 elution times for CB were between t = 17 to 32 min, but no signal other than that obtained from the sand blank (without contact to a nanocomposite) was recorded (Figure 7).  
Prior to the abrasion test, the specimens of the LDPE and EPDM samples were subjected to pre-stressing under various conditions. After the heat treatment (24 h at 100 \({}^{\circ}\)C), all materials showed a significantly higher plasticity but no deformation or change in surface integrity was observed. Once cooled down to room temperature no differences to the original nanocomposites were perceived. Storing the nanocomposites at low temperatures (24 h at \(-\)50 \({}^{\circ}\)C) resulted in no obvious changes of the LDPE compounds, whilst the EPDM specimens showed increased stiffness, though still flexible and not brittle. Once warmed up to room temperature in a desiccator preventing condensate formation, all  
Figure 5: AF4/MALLS fractograms of reference dispersions (dark grey) with no contact to sand and recovery dispersions with contact to sand (bright grey) of 75 ng/mL. PX 80 (**a**) and PX 85 (**b**), as well as 125 ng/mL N550 (**c**) and N772 (**d**).  
samples returned to their original flexibility. The swelling of the nanocomposites with solvents did not cause apparent differences with the original LDPE nanocomposites. The EPDM specimens did however swell while in contact with toluene and shrunk after being desiccated in the oven (Figure 8). Furthermore, the EPDM samples ended up being significantly less flexible after this chemical treatment.  
Figure 8: N550-EPDM compound before (left) and after (right) immersion in toluene for 24 h at 40 \({}^{\circ}\)C.  
Figure 6: Surface texture of (**a**) unstressed and (**b**) stressed low density polyethylene (LDPE) carbon black (CB)-nanocomposites. (**c**) shows the transition region between abraded (lower left region) and unstressed (upper right region) polymer surface at which the cell closure was placed (images taken at hundredfold magnification with an optical light microscope).  
Figure 7: AF4 fractograms of the nanocomposites that were abraded for 30 min with quartz sand compared to blank quartz sand.  
Mechanical stressing seemed to affect only the LDPE samples. Once detached from the clamps, the LDPE strips were found slightly elongated with a significant reduction in thickness at their center (by approximately 1 mm out of 3 mm). On the contrary, the EPDM strips retained their original shape with no visible changes.  
Although preconditioning seemed to influence the integrity of the nanocomposites in some cases, the AF4 measurements on the dispersants from the subsequent abrasion test showed no signal for CB (Figure 9), thus indicating the absence of CB release. These findings were validated by fortification of the re-dispersed abrasion/sand samples with a known amount of CB-dispersion (25 \(\upmu\)L of a 1 mg/L PX 80/PX 85 stock dispersion were added to 5 mL supernatant for a resulting 5 ng/mL CB content; due to lower signal intensities, the N550 and N772 supernatants were spiked to 25 ng/mL). Examples for PX 80 are shown in Figure 9. The CB signal demonstrates that the sand matrix did not influence the detectability of CB. In other words, CB would have been detected if released as uncoated CB particles from the nanocomposites through abrasion with or without preconditioning.