Confinement of iPP crystallites within mesoporous SBA-15 channels in extruded iPP-SBA-15 nanocomposites studied by Small Angle X-ray scattering

Abstract

The main objective of this research is the study of different nanocomposites based on isotactic polypropylene (iPP) and mesoporous SBA-15 silica prepared by melt extrusion, analyzing the possible effect of this filler on the polymorphic behavior of iPP and the eventual observation of confinement effects. Thus, simultaneous Small Angle X-ray Scattering/Wide Angle X-ray Diffraction (SAXS/WAXD) synchrotron experiments at variable temperature have been performed on several iPP nanocomposites with different contents of SBA-15 mesoporous particles. Real-time variable-temperature SAXS measurements turned out a very useful tool to analyze the confinement of iPP crystallites within SBA-15 channels, and also to determine the most probable long spacing of chains located outside the SBA-15 nanospaces. Importance of these structural features is assessed by changes in the mechanical response of the final materials, finding that the presence of mesoporous particles leads to a reinforcing effect and contribute to improve the final dimensional stability.

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

“…Confinement was deduced through the observation of a noticeable discontinuity in the intensity of the first order (100) diffraction of the SBA-15 related to its characteristic hexagonal arrangement. The upward step took place in the temperature interval ranging from 95 to 120 • C, which was fully in agreement with the one noticed for a small endotherm exhibited in the DSC experiments [2][3][4]. Earlier investigations on several SBA-15 composites [5][6][7] described that the intensity of the SBA-15 diffraction was dependent on the eventual scattering contrast between walls and inside of the mesopores.…”

“…These variations were ascribed to those changes in the electron density from iPP chains arranged inside the SBA-15 particles, which were semicrystalline at low temperatures or fully amorphous after the melting of these iPP crystallites existing within mesoporous channels. Moreover, the intensity of that first order reflection was strongly dependent on SBA-15 content [2,4]. These results confirmed the ones described in previous works performed at room temperature on in situ polymerized nanocomposites of poly(N-isopropylacrylamide)/SBA-15 [8] as well as on polyethylenimine (PEI)-based composites wet impregnated with either MCM-41 or 9].Regarding the existence of a small endothermic event in DSC, it should be said that this process was also observed for in situ polymerized materials based on ultra-high molecular weight polyethylene (UHMWPE) and 11] as well as in nanocomposites based on high density polyethylene (HDPE) and MCM-41.…”

“…From these measurements, precise information was also deduced on the influence of the MCM-41 on iPP long spacing since overlapping does not occur between most probable iPP long spacing peak with the characteristic diffractions from the MCM-41 hexagonal nanostructure in comparison with existing superposition in SBA-15-based materials.Polymers 2020, 12, 70 2 of 21 nanocomposites, can contribute to the enhancement of some of those excellent properties and to allow spreading out even more its applicability.Confinement of iPP chains within the ordered spaces present in SBA-15 mesoporous silica was proved recently by Small-angle X-ray scattering (SAXS) using synchrotron radiation, these measurements constituting a reliable and powerful tool [2]. The iPP macrochains filled out those nanometric channels when composites were obtained not only by in situ polymerization [3] but also, unexpectedly, by extrusion [2,4] of the two components, the molten iPP and the SBA-15 particles. Confinement was deduced through the observation of a noticeable discontinuity in the intensity of the first order (100) diffraction of the SBA-15 related to its characteristic hexagonal arrangement.…”

“…Confinement of iPP chains within the ordered spaces present in SBA-15 mesoporous silica was proved recently by Small-angle X-ray scattering (SAXS) using synchrotron radiation, these measurements constituting a reliable and powerful tool [2]. The iPP macrochains filled out those nanometric channels when composites were obtained not only by in situ polymerization [3] but also, unexpectedly, by extrusion [2,4] of the two components, the molten iPP and the SBA-15 particles. Confinement was deduced through the observation of a noticeable discontinuity in the intensity of the first order (100) diffraction of the SBA-15 related to its characteristic hexagonal arrangement.…”

Ordered mesoporous SBA‐15 functionalized with yttrium(III) and cerium(III) complexes: Towards active heterogeneous catalysts for oxidation of sulfides and preparation of 5‐substituted 1H‐tetrazoles

“…Among the supports mentioned above, mesostructured catalysts, due to their extremely high surface area and extreme efficiency, have attracted attention over homogeneous catalysts, and they have applications in various fields such as gas storage, catalysis, adsorption, sensing, light harvesting and so on . Among various mesostructured catalysts, ordered mesoporous SBA‐15 with a regular two‐dimensional hexagonal array of pores and long one‐dimensional channels has already garnered increasing regard due to its ease of preparation, large internal surface area, excellent thermal and chemical stability, thick silica walls (2–6 nm), low cost and great density of surface Si─ OH groups . Functionalization of SBA‐15 can be performed by the incorporation of various groups.…”