Effect of POSS-grafted titanium dioxide on the electrical and thermal properties of LDPE/TiO 2 polymer nanocomposite Tung Tran Anh , 1 Michel Fr  echette, 2  Eric David, 3 Ren  e Veillette, 2 Patricia Moraille 4 1 Electric Power University, Hanoi, Vietnam 2 Hydro’s Qu ebec research institute, Varennes Qu ebec J3X 1S1, Canada 3 Ecole de Technologie Sup erieure, Montr eal Qu ebec H3C 1K3, Canada 4 University of Montr eal, Montr eal Qu ebec H3T 1J4, Canada Correspondence to: T. T. Anh (E - mail: tungta@epu.edu.vn) ABSTRACT: Two types of nanocomposites have been fabricated by a ball-milling technique. The first type consists of untreated tita- nium dioxide (TiO 2 ) incorporated into low-density polyethylene (LDPE). For the second one, TiO 2 filler chemically treated with trisi- lanol phenyl–polyhedral oligomeric silsesquioxane (TP–POSS) as compatibilizing agent was ball-milled with LDPE. All specimens were tested by microstructure analysis and thermal, dielectric characterization techniques. Microstructure analysis by atomic force microscopy and scanning electron microscopy show clearly an increased dispersion in presence of POSS. Scanning electron micros- copy even shows the formation of a particular structure due possibly to interactions between functionalization. It was observed that the modification of the surface of TiO 2 by the POSS decreased the dielectric loss. All nanocomposites containing treated TiO 2 revealed an improvement in thermal conductivity, with the most distinct value of 19% in case of LDPE containing 5 wt % treated TiO 2 . The incorporation of TiO 2 fillers seems to reduce the dielectric breakdown strength of the nanocomposites. However, nanocom- posites containing 3 and 5 wt % treated TiO 2 have exhibited a slightly enhancement in dielectric breakdown strength up to 5%. The improvement in surface resistance to partial discharge was found in all nanocomposites specimens, especially for both types of com- posite containing 7 wt % untreated and treated TiO 2 . V C 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46095. KEYWORDS: compatibilization; composites; dielectric properties; thermal properties; thermoplastics Received 10 September 2017; accepted 28 November 2017 DOI: 10.1002/app.46095 INTRODUCTION Low-density polyethylene (LDPE) is widely used in the cable industry because of its good characteristic, such as high dielec- tric breakdown (BD) strength and low dielectric loss. 1–4 How- ever, as many other polymeric materials, LDPE can be subjected to electrical degradation during operation leading to a reduction of the expected lifetime. In addition, the low thermal conductiv- ity of polymeric materials prevents significant heat dissipation which limits the performance of insulating system under high electrothermal stresses. In order to improve the dielectric and thermal properties of polymeric material, the incorporation of inorganic nanofillers into polymer matrix to form polymer nanocomposites or nano- dielectrics has been found to be an interesting possibility. 5–7 Indeed, this class of dielectric materials 6 has shown significantly enhanced performances compared to the neat polymer such as higher dielectric BD strength, thermal conductivity, or surface resistance to partial discharge (PD). 8–11 Titanium dioxide or titania (TiO 2 ) is a promising material for a large number of applications in different fields such as catalysis, dielectric ceramics, solar cells, and electronic devices. 12,13 TiO 2 - based composites compounded with different host polymers such as conducting polyaniline, 14,15 poly(phenylenevinylene), 16 or poly(methylmethacrylate) 17 have been studied in the last few years. High dielectric constant of TiO 2 is useful for development of small-scale electronic devices with improved BD strength. TiO 2 is also used as semiconductor because of wide bandgap (3.2 eV) in anatase phase. 18 Several investigations on nanocomposites incorporating TiO 2 for high voltage insulation applications, many focusing on the dielectric properties of these composites, have been reported. 19–22 It was found that the associated Maxwell-Wagner polarization due to the contrast of conductivity between the fil- ler and the host matrix, can significantly increase dielectric losses at power frequency. This phenomena is strongly affected by the dispersion degree of TiO 2 nanoparticles into the polymer matrix and the nature of the polymer-particles interface. In a V C 2017 Wiley Periodicals, Inc. J. APPL. POLYM. SCI. 2018, DOI: 10.1002/APP.46095 46095 (1 of 9)