Photo‐oxidation and Stabilization of sPP and iPP/Boehmite‐Disperal Nanocomposites

Photo‐oxidation studies on polypropylene (PP)/organoclay nanocomposites were performed. Nanocomposites of isotactic (iPP) and syndiotactic (sPP) polypropylene were prepared by melt compounding. The nanofiller was Boehmite Disperal OS2–alumina hydrates (Al(OH)O) modified by C10–C13 alkylbenzene sulfonic acid. The nanofiller content was 1, 5, and 10 wt%. There is a clear pro‐degradation effect of filler for both types of polypropylene used. The extent of this effect depends on the amount of filler and type of polypropylene used. In the case of sPP samples, the pro‐degradation effect is proportional to the amount of filler in the whole concentration range of filler content used. In the case of iPP, there is a pro‐degradation plateau at 5 wt% content of filler and higher concentration of filler (10 wt%) does not increase the rate and the course of photo‐oxidation. Two long term stabilizers of HAS family were tested ‐ commercial oligomeric stabilizer Chimassorb 944 (CHIM) and synthesized combined HAS/phenol (TMP). Stabilizing efficiency depends on the filler content. CHIM is able to stabilize just the nanocomposites with the lowest content (1 wt%) of filler. There is no stabilizing effect of this HAS in the case of the higher amount of nanofiller (5 and 10 wt%) in both types of polypropylene. By contrast, the combined HAS/phenol‐TMP revealed some stabilizing efficiency over the whole range of filler content. The possible reasons for this difference are discussed. Interactions of filler with some HAS stabilizers were studied in cyclohexane as a model liquid for polypropylene by UV‐spectroscopy. Interaction resulted in the fixing of additive on filler. Much stronger interaction has been obtained for oligomeric CHIM in comparison with low molecular HAS.

Keywords:

• polypropylene nanocomposites
• photo‐oxidation
• stabilization
• hindered amine stabilizers–HAS
• stabilizer/filler interaction

5 Acknowledgements

The authors would like to thank the VEGA Grant Agency on the project VEGA 2/5108/26 for financial support.