Effect of Ionic Liquid Modiﬁed Synthetic Layered Silicates on Thermal and Mechanical Properties of High Density Polyethylene Nanocomposites Sébastien Livi, 1,2,3 Jannick Duchet-Rumeau,* 1,2,3 Jean-François Gérard 1,2,3 Abstract: In this work, synthetic layered silicates denoted Somasif ME-100 and Laponite 1 RD were modiﬁed with dialkyl imidazolium and alkyl phosphonium ionic liquids by cationic exchange reaction. In both cases, the phosphonium (P-ME, P-RD) or imidazolium ion (I-ME, I-RD)-treated micas and laponites display an excellent thermal stability compared to commonly used quaternary ammonium salts. To highlight the effect of these ionic liquids, the modiﬁed layered silicates were introduced in a high density polyethylene (HDPE). Thus, polyethylene nano- composites ﬁlled with a low amount of nanoparticles (2 wt%) were prepared by twin screw extrusion. Then, transmission electronic microscopy (TEM) analysis has been used to investigate the effect of ILs on the different morphologies of these nanocomposites. In addition, the use or not of compatibilizer such as PEgMA (20% by weight) has been also studied on the mechanical behaviour of these polymer nanocomposites. Even though the thermal stability of polyethylene matrix remains unchanged, a good stiffness-thoughness compromise has been observed. Keywords: cationic exchange; ionic liquid; mechanical properties; nanocomposite; polyeth- ylene; synthetic layered silicates Introduction Although the clays are well known for a long time, academic and industrial research were recently focused on the use of organically modiﬁed clays as reinforcing agents in polymeric materials. [1–3] In fact, due to their nanometric dimensions, their high speciﬁc surface and their high aspect ratios, the addition of layered silicates in polymer matrices can lead to signiﬁcant effects on the mechanical properties, [4,5] barrier performances [6,7] and ﬂammability resistance. [8] Generally, montmorillonite or synthetic layered silicates (Somasif ME- 100) are commonly used. [9,10] However, to obtain a good compatibility between poly- mer and clays during the preparation of nanocomposites, a surface treatment of pristine nanoclays is required. For years, the alkyl ammonium salts are commonly used [11–13] but nevertheless, their low thermal stability results in a degradation of these salts at 180  C due to the Hofmann elimination which limits their use in the nanocomposites processing at higher temperatures. [14,15] Thus, to increase the thermal stability of organically modi ﬁed clays, the use of thermally stable ionic liquids (ILs) such as imidazolium and phosphonium cations can offer a new alternative to ammonium salts. [16–20] According to the literature, imida- zolium and phosphonium ILs are known to have an excellent thermal stability thanks to aromatic ring and phosphore, respectively. However, few studies report the inﬂuence of the chemical nature of these surfactant agents on the ﬁnal properties of the nanocomposites. In this paper, the use of synthesized ionic liquids as intercalating agents of synthetic 1 Université de Lyon, F-69003, Lyon, France 2 INSA Lyon, F-69621, Villeurbanne, France 3 CNRS, UMR 5223, Ingénierie des matériaux poly- mères, France Fax: þ33 4 72438527; E-mail: jannik.duchet-rumeau@insa-lyon.fr Macromol. Symp. 2014, 342, 46–55 DOI: 10.1002/masy.201300228 46 | ß 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com