Crystallization behavior and morphological development of isotactic polypropylene blended with nanostructured polyhedral oligomeric silsesquioxane molecules

Abstract

The thermal properties and morphological development of isothermally crystallized isotactic polypropylene (iPP) blended with nanostructured polyhedral oligomeric silsesquioxane (POSS) molecules at very small loading of POSS were studied with differential scanning calorimeter (DSC), thermal gravimetric analysis, dynamic mechanical analysis, polarized optical microscopy (POM), and wide-angle X-ray diffraction (WAXD). The result of DSC indicated that the crystallization rate of iPP increases with the increase in POSS contents during crystallization; moreover, the melting temperature of iPP/POSS nanocomposites slightly decreases, while the heat of fusion increases with the addition of POSS molecules at melting and remelting traces. The storage modulus and thermal stability, respectively, remarkably decrease, while the glass transition temperature of isothermally crystallized iPP/POSS nanocomposites increases slightly with the increase in POSS contents. The morphologies results of WAXD and POM show that the POSS molecules form about 35 nm sized nanocrystals and aggregate to form thread-like and network structure morphologies, respectively, in the molten state even when the POSS content is very small. These results, therefore, suggest that the interaction force between the POSS molecules should be larger than the force between POSS molecules and iPP matrix; however, those interactions depend on the chain length of functionalized substituents on the POSS cage. Therefore, the POSS molecules aggregate forming nanocrystals and act as an effective nucleating agent for iPP and influence the thermal properties of iPP/ POSS nanocomposites due to the shorter chain length of functionalized substituents, methyl, on the POSS cage.

Study of thermal properties of polyethylene and polypropylene nanocomposites with long alkyl chain-substituted POSS fillers

“…Moreover, the increasing POSS mass% contents in polyolefin/POSS nanocomposites caused a further increase in the X c values. These results indicate that POSS particles may act as nucleating agents for the crystallization process of polyethylene or polypropylene matrices [20,25,31].…”

“…Moreover, the presence of POSS nanofillers clearly improved thermal stability of those materials [20,23,24]. However, it should be mentioned that the papers published to date covered mainly the properties of polyolefin/POSS nanocomposites which contained POSS molecules with relatively short alkyl chain substituents (from methyl to iso-octyl) [20][21][22][25][26][27][28][29][30]. Only few papers related to nanocomposites with long alkyl chain substituents (from n-octyl to n-octadecyl) on the T 8 POSS core [31,32] and most of those studies focused on PP/POSS [20-22, 25, 28-30] and LDPE/POSS [26,27,31,32] nanocomposites, while studies on HDPE/POSS nanocomposites were limited [33].…”

Segmental dynamics in hybrid polymer/POSS nanomaterials

“…Methyl substituted POSS, melt blended in isotactic polypropylene [67] and ethylene/propylene copolymers [68], restrict mobility and increase T g by a few degrees.…”

Morphology and crystallization kinetics of polyethylene/long alkyl-chain substituted Polyhedral Oligomeric Silsesquioxanes (POSS) nanocomposite blends: A SAXS/WAXS study

“…Chen [19,20] also studied isothermal crystallization and morphology development in melt blended polyproplylene (PP)-octamethyl POSS nanocomposites. They found that the crystallization rate increased with increasing POSS content due to the aggregation of POSS nanocrystals.…”