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

Abstract

A rheo-optical characterization technique based on the combination of near-infrared (NIR) spectroscopy and mechanical analysis was applied to the nanocomposite consisting of hydroxyl-functionalized polypropylene (PPOH) and mesoporous silica (MPS) to probe the deformation behavior. Substantial levels of spectral changes of NIR spectral features were captured when the polymer samples underwent tensile deformation. Sets of spectra were subjected to projection treatment to remove the effect of baseline fluctuations and thickness change inevitably caused by the tensile deformation of the sample. Then, two-trace two-dimensional (2T2D) correlation spectroscopy was applied to the pretreated spectra to elucidate spectroscopic signature associated with the difference between the initial and deformed samples. An asynchronous correlation peak appears between the bands at 1720 and 1700 nm respectively reflecting the contributions of predominantly amorphous and crystalline component of the PPOH, indicating the predominant variation of amorphous structure followed by that of crystalline structure. In addition, the predominant spectral change related to the amorphous band becomes even more acute by including the MPS with large pores. It is hence likely that the larger pore size of the MPS confines the more amorphous structure, which, in turn, causes simultaneous reorientation of the polymer chains in the amorphous region during the elastic deformation. Consequently, the incorporation of the MPS selectively restricts the deformation of the amorphous structure which eventually provides the obvious increase in the mechanical property of the PPOH polymer.

Aging of polypropylene probed by near infrared spectroscopy

“…This is also true for NIR bands. [19][20][21] The bands observed in Figure 3 are the s regularity bands, which are essential to crystal formation. The development of the multiple regularity bands in the NIR spectra indicates the fact that each band represents different number of helical turns in the PP system.…”

“…For example, the contribution from the peak observed around 1706 nm becomes even more acute for the well-crystalized PP. [19][20][21] While the detailed origin of these bands is not fully understood yet, this peak mostly represents the CH 2 group of PP arising from longer helix predominantly present in crystalline component. [19][20][21] On the other hand, intensity change at around 1724 nm may be associated with shorter helices which are often observed in the amorphous domain of PP.…”

“…14,15 Importantly, NIR spectroscopy readily captures so-called regularity bands associated with the helical structures of PP, although there is no clear appearance or disappearance of ''pure'' crystalline or amorphous band in the NIR as well as IR region. [16][17][18][19][20][21] The development of the multiple regularity bands in the NIR spectra represents different number of helical turns in the PP system. For example, the contribution from the peak observed around 1706 nm becomes even more sharp for the wellcrystalized PP.…”

“…[19][20][21] On the other hand, intensity change at around 1724 nm is associated with shorter helix which are often observed in the amorphous domain of PP. [19][20][21] It is thus likely that the spectral intensity variations of these NIR bands can be used as an empirical inference to determine the changes in the ordered and disordered polymer structures associated with aging of PP polymer. In fact, such spectral features of PP have been utilized for rheo-optical NIR characterization of nano composite polymers based on PP to reveal change in molecular-level deformations of crystalline and amorphous structures.…”

“…In fact, such spectral features of PP have been utilized for rheo-optical NIR characterization of nano composite polymers based on PP to reveal change in molecular-level deformations of crystalline and amorphous structures. [19][20][21] In this work, NIR analysis of PP polymer is further extended to the first in-depth attempt to elucidate the aging-induced variation of PP samples. Particular focus is made on the determination of the elongation property (i.e.…”