1. Effect of POSS as Compatibilizing Agent on Structure and Dielectric Response of LDPE/TiO2 Nanocomposites
Bouchaib Zazoum1,2*, Michel Fréchette1, Eric David2
1 Institut de Recherche d’Hydro-Québec (IREQ), Varennes, Qc, Canada
2 École de technologie supérieure (ÉTS), Montréal, Qc, Canada

2. ABSTRACT
Two types of nanocomposites were prepared. The first type was prepared by ball milling-blending of untreated titanium dioxide (TiO2) nanoparticles into low density polyethylene (LDPE). For the second type, a commercial chemically treated TiO2 with trisilanol phenyl polyhedral oligomeric silsesquioxane (TSP–POSS) as dispersant was ball milling-blended into LDPE. In this paper, titanium dioxide was selected as a model to show the effect of POSS on dispersion improvement of metal oxides nanoparticles and to understand the correlation between structure and dielectric response of LDPE/TiO2 nanocomposites. The microscopic observation by AFM showed that the TiO2 treated with the POSS were better dispersed in the polymer matrix as compared to untreated TiO2. Furthermore, the dielectric loss for the nanocomposites filled with treated TiO2 was significantly lower than that for nanocomposites filled with untreated TiO2 nanoparticles.

3. BACKGROUND
The main challenge in the preparation of nanocomposites materials is dispersion of the individual nanoparticle into the polymer matrix, due to the incompatibility of hydro-phobic matrix with hydrophilic filler. To overcome this problem and enhance the interfacial interaction between the nano-particles and the polymer matrix, TiO2 nano-powder was surface modified by trisilanol phenyl polyhedral oligomeric silsesquioxane (TSP–POSS).

4. This work
The objective of the present paper is to prepare nanocomposites by ball milling process and to examine the effect of surface mo-dification of TiO2 with TSP-POSS on dispersion of metal oxides nanoparticles, and dielectric response of polyethylene/TiO2 nanocompo-sites.

5. MATERIALS
Low density polyethylene LDPE (ALKATEQ XDS34P) with a density of g/cm3 and a melt flow index of 0.4 g/10 min was supplied by Marplex, Australia.
TiO2 nanopowder (Aeroxide Titanium Dioxide P25) was manufactured by Sigma-Aldrich, while a commercially available treated TiO2 nanoparticles was purchased from Hybrid Plastics.
Surface of TiO2 was modified with trisilanol phenyl polyhedral oligomeric silsesquioxane (TSP–POSS) and the titanium dioxide used in the treated TiO2 is the same as that of the untreated TiO2.

6. FABRICATION
LDPE/TiO2 nanocomposites were prepared by high-energy ball milling process.
3 wt% TiO2 nanoparticles, either untreated TiO2 (untr-TiO2) or treated TiO2 (tr-TiO2), were manually premixed into LDPE powder.
The mixture powder was then milled for 40 min of active milling using high-energy shaker mill (SPEX CertPrep 8000).
The obtained powder was press-molded using an electrically heated hydraulic press to form thin film with a thickness of 500 µm.

7. MORPHOLOGY
The silanol groups of POSS were bound to TiO2 surfaces by covalent bonding in order to improve the dispersion of TiO2 nanoparticles within the polyethylene matrix.

8. AFM micrographs of nanocomposites containing 3 wt% of TiO2 nanoparticles. Scale bar 200 nm.

9. DIELECTRIC RESPONSES

10. CONCLUSION
LDPE/TiO2 nanocomposites have been successfully prepared by high-energy ball milling process.
Surface modified TiO2 with POSS showed the enhancement in quality of dispersion in comparison to untreated TiO2. POSS breaks TiO2 agglomerates by functioning as a dispersing agent.
The results showed also that the dielectric response of these nanocomposites was affected by the surface modification of the TiO2 nanoparticles. It was found that the LDPE filled with the treated TiO2 nanoparticles exhibited lower dielectric loss com-pared to the LDPE filled with the untreated TiO2 nanoparticles.