Polypropylene/layered double hydroxide nanocomposites

We report a novel synthesis method for the preparation of polypropylene/layered double hydroxide (PP/LDH) nanocomposites, in which LDH nanosheets, [Mg₂Al(OH)₆](DDS)·2H₂O (Mg-Al-DDS), were prepared using a one-step reverse microemulsion method. PP/LDH nanocomposites were prepared by direct mixing of the obtained LDH nanosheets with PP in xylene at 140 °C. Loadings of the LDH in PP of 0.5, 1.0, 1.5, 2.0, 4.0, 8.0 and 16.0 wt% were investigated. The results indicate that the LDH nanosheets were highly dispersed in PP and this dramatically improves the performance of the nanocomposites at very low LDH loadings (e.g. 1.0 wt%). In particular, the thermal stability, melting transition, recrystallisation behavior, and rheological properties of the PP/LDH nanocomposites were evaluated. The thermal stability (T_0.5) of the pure PP was increased from 336 to 384 °C by 1.0 wt% addition of the Mg-Al-DDS nanosheets. At 1.0 wt% loading the melting temperature (T_m) and the recrystallisation temperature (T_c) of PP were also increased by 2.5 and 6.7 °C respectively. The nanocomposites showed decreased G′ and G′′ when the LDH nanoplatetet loading is low (<2.0 wt%). With 0-2.0 wt% of LDHs, both G′ and G′′ decreased with the increase of LDH loading. While on increasing the LDH loading from 2.0 wt% to 16.0 wt% both the storage modulus (G′) and loss modulus (G′′) gradually increased. At a 16.0 wt% LDH loading, the rheological response changes and the elastic solid-like behavior is observed, with only a limited reduction in G′ at low frequency. For the PP/LDH nanocomposites containing 0.5-4.0 wt% LDH, tan δ decreases monotonously with increasing frequency (w). Above 8.0 wt% LDH loading, tan δ starts to show three different stages: rubbery, viscoelastic and a glassy state. These results demonstrate that the reverse microemulsion method is a simple and efficient approach for the one-step synthesis of LDH nanosheets for use in the synthesis of polymer/LDH nanocomposites with enhanced thermal, rheological and mechanical properties.