Structure−property relationships of polypropylene-based nanocomposites obtained by dispersing mesoporous silica into hydroxyl-functionalized polypropylene. Part 2: Matrix−filler interactions and pore filling of mesoporous silica characterized by evolved gas analysis

Abstract

Nanocomposites containing mesoporous silica (MPS) materials with various pore structures (SBA-15 and MCM-41 types) melt mixed into polypropylene (PP) or PP functionalized with hydroxyl groups (PPOH) were characterized by analytical pyrolysis techniques, such as evolved gas analysis (EGA)-mass spectrometry (MS) and heart-cut EGA-gas chromatography (GC)/MS, to evaluate the interactions between the polymer matrix and MPS and the pore filling of the MPS in the nanocomposite. The EGA-MS measurements revealed that nanocomposites with MPSs evolve specific degradation products, which can be attributed to strong interactions between the polymer molecules and the internal pores. The amount of these specific products increased upon increasing the pore size of the MPS and the hydroxyl content in the polymer matrix. Sufficiently large pores of MPS and high hydroxyl contents in the matrix appear to provide strong interactions because the MPS pores are well-filled with polymer molecules, which contributes to the improved physical properties of the nanocomposites.

Rheo-Optical Near-Infrared (NIR) Characterization of Hydroxyl-Functionalized Polypropylene (PPOH)-Mesoporous Silica Nanocomposites Using Two-Trace Two-Dimensional (2T2D) Correlation Analysis

“…This result agrees with the fact that the development of the folded crystalline structure of PP is essentially restricted by the confinement in the pores. 8,9 Another notable observation is that the elongations of the PP samples provide no obvious changes in the crystallinities. The lack of the changes in the crystallinities mostly indicates that such deformation does not cause significant level of disintegration of the crystalline structure.…”

“…It is believed that mechanical as well as optical properties of the PPOH nanocomposite system is closely associated with hydrogen bonding-based interaction between the –OH groups of the PPOH and internal pores. 8,9 For example, Fig. 2 represents a schematic diagram of PPOH polymers embedded in nanopores of MPS.…”

“…In the PPOH nanocomposite system, some polymer molecules readily penetrate into the nanopores of the MPS because of the hydrogen bonding between the –OH groups of the polymer and pore surface of the silica. 8,9 The development of such confined polymer structure mostly restricts the reorientation of the polymer chains when the system undergoes mechanical deformation. In addition, the molecules inside the pores remain as unfolded polymer chains, i.e., transparent amorphous structure, due to the small size nanopores (e.g., less than 10 nm) of the MPS.…”

“…Thus, by dispersing the MPS, it is possible to improve the mechanical property of the PPOH polymer without losing its optical transparency. 8,9

Figure 2.Schematic diagram of PPOH polymers embedded in the nanopores of MPS.

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Variation of Ultimate Properties in Extruded iPP-Mesoporous Silica Nanocomposites by Effect of iPP Confinement within the Mesostructures

“…Presence of larger or smaller pores along these mesoporous particles might involve important changes, mainly related to the capability of iPP chains to be included within those bare tubes by the shear forces applied during processing. By means of evolved gas analysis, pore filling was described to be different between MCM-41 and SBA-15 in materials based on mesoporous silicas with hydroxyl-functionalized polypropylene [31], being much smaller in the former. The existence of more iPP chains within SBA-15 particles [2][3][4] could lead to that important variation in those two rheological parameters.…”