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This paper describes the first in-depth attempt to characterize thermally induced aging of polypropylene (PP) samples by near infrared (NIR) spectroscopy. Significant levels of variation in NIR bands associated with short (amorphous-dominated) and long (crystalline-dominated) helices was readily captured when PP samples were subjected to thermal aging treatment. Partial least squares (PLS) regression models derived from the NIR spectra indicated significant level of correlation between the actual and predicted elongations of the samples. Analysis of PLS scores and two-dimensional (2D) correlation spectra derived from the aged PP samples revealed inner working mechanism of the regression model. Namely, the aging treatment essentially induces compositional change in crystalline and amorphous structures of the PP samples, which eventually affect the variation of the PLS scores. Thus, by utilizing the scores, it becomes possible to predict the change in the elongation property of the aged PP sample.

A technique for analyzing infrared imaging data based on two-trace two-dimensional (2T2D) correlation analysis is presented to extract pertinent information underlying spectroscopic imaging data. In 2T2D correlation mapping, each spectrum in hyperspectral data is individually compared with a reference spectrum to generate 2T2D asynchronous correlation intensity at the x- and y-coordinates on a 2T2D correlation map. Asynchronous correlation intensity develops only when the signal contribution from a certain species becomes even more significant in the sample spectrum compared with the reference spectrum. This feature can be advantageously utilized to examine molecular interaction or an intermediate form of the component present in a system of interest. 2T2D correlation mapping is examined using Fourier transform infrared imaging data of polymer composites based on polypropylene grafted with maleic anhydride melt-mixed with silica spheres. Infrared images derived by using conventional visualization based on a single wavenumber (i.e., 1713 cm−1) are dominated with the overwhelming infrared absorbance induced by the normal maleic anhydride species, making the identification of subtle but pertinent changes in the composite system difficult. A 2T2D correlation map derived from the maleic anhydride/silica spheres composite developed a significant asynchronous correlation intensity between the infrared bands at 1695 and 1713 cm−1 around a specific region on the map where the maleic anhydride and silica spheres coexist. On the other hand, such a correlation pattern becomes less acute when the silica spheres is modified with the octadecyldimethyl group to prevent the hydrogen bonding with the maleic anhydride. It thus revealed that the silanol groups on the surface of the silica spheres substantially interact with the maleic anhydride via the development of the hydrogen bonding.

Exposing polymers to high-pressure and supercritical CO2 is a useful approach in polymer processing. Consequently, the mechanisms of polymer–polymer interaction under such conditions are worthy of further investigation. Two-dimensional correlation analysis and two-dimensional disrelation mapping were applied to datasets of polycaprolactone –poly(lactic acid) blend with or without high-pressure CO2 obtained using in situ attenuated total reflection Fourier transform spectroscopic imaging. The relatively weak dipole–dipole intermolecular interactions between polymer molecules were visualized through the disrelation maps for the first time. Because of the specially designed polymer interface, the interactions between the same type of polymer molecules and different types of polymer molecules were differentiated. Under exposure to high-pressure CO2, all three types of interactions: interaction between polycaprolactone molecules and poly(lactic acid) molecules, interaction between polycaprolactone molecules and interaction between poly(lactic acid) molecules become weaker than those in the polymer interface without high-pressure CO2. The resulting increase in the Flory interaction parameter is the main cause of phase separation in the PCL–PLA blend under high-pressure CO2. The findings from this study will be of benefit for polymer processing with high-pressure and supercritical CO2.

We have developed a novel in situ Fourier transform infrared (FTIR) spectroscopic imaging technique that can probe the changes in the chemical structures around the matrix–filler interface of polym...

We have developed a novel rheo-optical Fourier-transform infrared (FTIR) imaging technique that can probe the molecular-scale deformation behavior of a polymer matrix in composite materials. This rheo-optical FTIR imaging is based on in situ-polarized FTIR imaging of a polymer sample while it is being deformed by mechanical force. This imaging technique readily captures the orientation of the polymer molecules resulting from the applied strain. Analysis of the resulting FTIR imaging data by disrelation mapping makes it possible to further elucidate subtle but pertinent spectral variations arising from changes in the state of molecules within the spectroscopic images. In this study, the rheo-optical FTIR imaging is applied to analysis of the deformation behaviors of a composite composed of polypropylene containing hydroxyl groups (PPOH) and silica spheres (SS) to investigate matrix-filler adhesion of the composite. Our rheo-optical FTIR imaging analysis revealed selective inhibition of PPOH orientation at the matrix-filler interface during tensile deformation due to high matrix-filler adhesion via hydrogen bonding. The strong link between the PPOH matrix and SS filler efficiently restricts mobility of the matrix, resulting in the reinforcement of PPOH by addition of SS. Rheo-optical FTIR imaging is an effective tool for probing localized deformation behavior at the matrix-filler interface as well as achieving a better understanding of the correlation between matrix-filler adhesion and the effective reinforcement of composites.

Nanodiamond/polyamide (ND/PA) nanocomposite was examined with infrared (IR) microscopy and time-domain nuclear magnetic resonance (TD-NMR) to elucidate in detail the interphase between amino functionalized ND (ND-NH

An optical coherence tomography (OCT) system combined with near-infrared spectroscopy (NIRS) was developed to carry out simultaneously the cross-sectional observation and spectral measurement of a specific area inside a polymer sample. This OCT-NIRS system consists of a fiber-optic-based spectrometer combined with an OCT system and enables non-invasive imaging up to a depth of several millimeters and the recording of the NIR spectrum in the observed area. A subsequent analysis of the collected data will provide key information revealing the way in which the microscopic structure of the polymer is affected by the chemical composition around it. A structural defect inside a molded polyamide (PA) 66 sample was examined with the OCT-NIRS system to demonstrate how this technique can be utilized to characterize chemical composition as well as the morphological features inside the sample. A specific void was detected by OCT when the PA sample was molded without any drying treatment. The NIR spectrum collected around the void area of the undried PA was then compared with that of vacuum-dried PA by two-trace two-dimensional (2T2D) correlation analysis to identify a subtle but pertinent difference in the spectral features. The appearance of several correlation peaks in the 2T2D asynchronous correlation spectrum revealed that the OH group represented by the NIR band at 1446 nm is found in relative abundance around the void, which clearly reveals that the development of the void in the molded PA results from inadequate sample pretreatment.

A binary amorphous polymer blend consisting of polyvinyl chloride (PVC) and polymethyl methacrylate (PMMA) was studied with a rheo-optical characterization technique based on the combination of a near-infrared (NIR) spectrometer and a tensile testing machine. In rheo-optical NIR spectroscopy, tensile deformations were applied to polymers to induce the displacement of molecular chains while being probed by NIR light. The application of this technique was extended to a partially miscible amorphous polymer blend consisting of PVC and PMMA to demonstrate how it can be utilized to detect subtle but important deformation behavior. A change in the NIR spectral feature revealed that the initial deformation of the blend induces the reorientation of the PVC chains. A part of the PMMA connected to the PVC was tagged during the PVC deformation. Further deformation of the sample eventually resulted in necking propagation to the surrounding area.

Disrelation mapping was applied to Raman imaging data for the first time to investigate submolecular-level variations that occurred at the interface between glass fiber (GF) and polypropylene (PP). Disrelation maps constructed with Raman spectra provided spatial as well as spectral information, which are not readily accessible from hypercubic data. For example, patterns that appeared in the disrelation maps showed the predominant development of a long helix band (1002 cm

Exposing polymers to high-pressure and supercritical CO2 is a useful approach in polymer processing. Consequently, the mechanisms of polymer–polymer interaction under such conditions are worthy of further investigation. Two-dimensional correlation analysis and two-dimensional disrelation mapping were applied to datasets of polycaprolactone –poly(lactic acid) blend with or without high-pressure CO2 obtained using in situ attenuated total reflection Fourier transform spectroscopic imaging. The relatively weak dipole–dipole intermolecular interactions between polymer molecules were visualized through the disrelation maps for the first time. Because of the specially designed polymer interface, the interactions between the same type of polymer molecules and different types of polymer molecules were differentiated. Under exposure to high-pressure CO2, all three types of interactions: interaction between polycaprolactone molecules and poly(lactic acid) molecules, interaction between polycaprolactone molecules and interaction between poly(lactic acid) molecules become weaker than those in the polymer interface without high-pressure CO2. The resulting increase in the Flory interaction parameter is the main cause of phase separation in the PCL–PLA blend under high-pressure CO2. The findings from this study will be of benefit for polymer processing with high-pressure and supercritical CO2.

A rheo-optical near-infrared (NIR) spectroscopy, based on the combination of NIR spectroscopy and mechanical analysis, was applied to polyamide (PA) 6 samples consisting of bundled amorphous chains. Sets of strain-dependent NIR spectra as well as tensile stress of dried and wet treated PA 6 samples were collected during the mechanical elongation of the samples. The spectra were then subjected to two-dimensional (2D) correlation analysis to elucidate fine features of the spectral changes. An asynchronous correlation peak develops between the bands at 2355 and 2300 nm due to the combination modes of CH 2 groups arising from the rubbery amorphous chain and rigid crystalline lamella of the dried PA 6, respectively. It therefore indicates that during the tensile deformation, the orientation of the amorphous chain is induced first to cause the elastic deformation. Further elongation results in the rotation of the crystalline lamella connected with the amorphous chain. This correlation intensity apparently increases by the wet treatment, suggesting that water molecule in the PA 6 disrupts the H-bonding interaction between the adjacent polymer chains and thus makes the polymer more flexible. Accordingly, it is likely the H-bonding between the polymer chains works in a manner somewhat similar to cross-linked polymers, which substantially effects on the mechanical property of the PA 6.

Thermal degradation of crosslinking moiety in fluorinated rubbers was studied with a new method using spatial-dependent infrared (IR) microscopy and two-dimensional (2D) IR correlation spectroscopy. Upon heating the fluorinated rubber, initially the amount of crosslinker decreased followed by generating another chemical species with carbonyl substituent with IR absorption at around 1730 cm–1, implying generation of carboxylic acids forming intermolecular hydrogen bonding. Furthermore, projection 2D IR correlation analysis revealed that another chemical species with IR absorption at around 1755 cm–1 generates, indicating that further degradation progresses upon heating and intermolecular hydrogen bonding were broken. As a result, the multi-step degradation process of the crosslinker in the fluorinated rubber could be detected by combination of spatial-dependent IR microscopy and projection 2D IR correlation spectroscopy.

When near-infrared (NIR) spectroscopy is employed to determine the concentrations of inorganic acids in etchant solutions, the perturbation of the water bands resulting from the interactions with these acids is the only information available for analysis, since inorganic acids do not directly absorb NIR radiation. The water bands perturbed by dissociated hydronium ions and respective anions of the acids are not highly component-specific; therefore, characterization of their different interactions with water is necessary to understand the results of the multivariate quantitative analysis. For this purpose, the variations in the water bands that occurred with the inclusion of HCl, H2SO4, H3PO4, and HNO3 were initially examined with the aid of a two-dimensional (2D) correlation analysis. According to this analysis, components with higher acidity, such as HCl, perturbed the water hydrogen bonding network more strongly. Also, the interactions between each dissociated ionic species and water molecules were somewhat dissimilar. This dissimilarity enabled differentiation between the four acids, although the spectral specificity was not high owing to the absence of direct NIR absorption. The accuracy in the determination of concentrations was better for components with lower pKas, such as HCl and H2SO4, owing to their stronger perturbation of the water bands. When multicomponent samples were measured, the resulting accuracies deteriorated due to the further degradation in component specificity. Acquisition of reproducible spectra and avoidance of model over-fitting are critical for reliable NIR analysis of these types of samples, as the analyte-induced spectral features are broad and rather specificity-insufficient.

Hydrogen/deuterium (H/D) exchange of gelatinized starch was probed by in-situ near-infrared (NIR) monitoring coupled with two-dimensional (2D) correlation spectroscopy. Gelatinized starch undergoes spontaneous H/D exchange in D2O. During the substitution, the exchange rate essentially becomes different depending on solvent accessibility of various parts of the molecule. Thus, by analyzing the change in the NIR feature observed during the substitution, it becomes possible to sort out local structure and dynamics of the system. 2D correlation analysis of the time-dependent NIR spectra reveals the presence of different local structure of the starch, each having different solvent accessibility. For example, during the H/D exchange, the D2O is first absorbed by starch molecules especially around the surface area between the starch and water, where the water molecules are weakly interacted with the starch molecules. This absorption is quickly followed by the development of HDO species. Further absorption of the D2O results in the penetration of the molecules inside the starch and eventually develops the relatively strong interaction between the HDO and starch molecules because of the presence of dominant starch molecules.

A rheo-optical characterization technique based on the combination of a near-infrared (NIR) spectrometer and a tensile testing machine is presented here. In the rheo-optical NIR spectroscopy, tensile deformations are applied to polymers to induce displacement of ordered or disordered molecular chains. The molecular-level variation of the sample occurring on short time scales is readily captured as a form of strain-dependent NIR spectra by taking an advantage of an acousto-optic tunable filter (AOTF) equipped with the NIR spectrometer. In addition, the utilization of NIR with much less intense absorption makes it possible to measure transmittance spectra of relatively thick samples which are often required for conventional tensile testing. An illustrative example of the rheo-optical technique is given with annealed and quenched Nylon 6 samples to show how this technique can be utilized to derive more penetrating insight even from the seemingly simple polymers. The analysis of the sets of strain-dependent NIR spectra suggests the presence of polymer structures undergoing different variations during the tensile elongation. For instance, the tensile deformation of the semi-crystalline Nylon 6 involves a separate step of elongation of the rubbery amorphous chains and subsequent disintegration of the rigid crystalline structure. Excess amount of crystalline phase in Nylon 6, however, results in the retardation of the elastic deformation mainly achieved by the amorphous structure, which eventually leads to the simultaneous orientation of both amorphous and crystalline structures.

Tensile deformations of a partially miscible blend of polymethyl methacrylate (PMMA) and polyethylene glycol (PEG) is studied by a rheo-optical characterization near-infrared (NIR) technique to probe deformation behavior during tensile deformation. Sets of NIR spectra of the polymer samples were collected by using an acousto-optic tunable filter (AOTF) NIR spectrometer coupled with a tensile testing machine as an excitation device. While deformations of the samples were readily captured as strain-dependent NIR spectra, the entire feature of the spectra was overwhelmed with the baseline fluctuation induced by the decrease in the sample thickness and subsequent change in the light scattering. Several pretreatment techniques, including multiplicative scatter collection (MSC) and null-space projection, are subjected to the NIR spectra prior to the determination of the sequential order of the spectral intensity changes by two-dimensional (2D) correlation analysis. The comparison of the MSC and null-space projection provided an interesting insight into the system, especially deformation-induced variation of light scattering observed during the tensile testing of the polymer sample. In addition, the sequential order determined with the 2D correlation spectra revealed that orientation of a specific part of PMMA chain occurs before that of the others because of the interaction between CO group of PMMA and terminal OH group of PEG.

We have developed a three-way evolved gas analysis-mass spectrometry technique combined with principal component analysis (EGA-MS-PCA) to probe the interfacial state between matrix and filler in poly(styrene-b-butadiene-b-styrene) (SBS) nanocomposites containing graphene nanoplatelets (GNPs). Although the peaks arising from the polystyrene and polybutadiene components present in the system were readily captured, the different patterns of peak intensities, which vary according to the applied temperature and GNP content, make interpretation of the data difficult. The data sets are thus subjected to mathematical decomposition based on principal component analysis (PCA) to selectively derive essential information. The EGA-MS-PCA process reveals that the inclusion of GNPs essentially works to restrict the decomposition of the polystyrene component in the SBS sample, mostly indicating the formation of a π–π stacking interaction between the SBS and GNPs. This observation, in turn, provides in-depth understanding that is likely to lead to stiffness of SBS by incorporation of GNPs.

Functionalized polypropylene with hydroxyl group (PPOH) nanocomposites with varying chemical structures in filler-matrix interfaces were examined by rheo-optical near-infrared measurements combined with two-dimensional correlation spectroscopy, to provide a better understanding of the reinforcement mechanism of nanocomposites. PPOH nanocomposites were fabricated by melt-mixing (i) silica nanospheres (SNS) and (ii) SNS modified with surfactant (mSNS). The decrease in the asynchronous correlation intensity from PPOH to SNS/PPOH indicated that the tensile deformation of amorphous and crystalline occurred simultaneously. These observations implied that the high interfacial adhesion between filler and matrix restricted the deformation of amorphous. This mechanism seems to contribute to the improvement in mechanical strength of the composite. The asynchronous correlation intensity of mSNS/PPOH was higher than that of SNS/PPOH, indicating that a certain level of deformation of the amorphous was allowed. It is therefore likely that the surface modification of SNS prevented filler-matrix interactions, leading to relatively low tensile strength of mSNS/PPOH. Thus, the techniques based on NIR spectroscopy clarify the effects of the filler-matrix interfacial adhesion of nanocomposites on the behavior of the crystalline and amorphous components during tensile testing, and may be generally applicable to evaluate filler-matrix adhesion behavior of a wide range of polymer nanocomposite systems.

Near infrared (NIR) imaging data of poly(lactic) acid (PLA) nanocomposite were analysed by disrelation mapping to prove the possible interaction between PLA matrix and montmorillonite-based nanoclay. The basic concept of disrelation mapping can be viewed as a spatial filter based on two-dimensional (2D) correlation function to elucidate specific areas where disrelated variation between intensities occurs. Correlation intensity develops on disrelation map only if spectral intensities at v1 and v2 within the local spatial area vary in a dissimilar manner. This feature is especially suitable for identifying the area where interaction between components occurs, which is not fully detected by the conventional visualizations based on a single wavenumber. Disrelation maps constructed with NIR bands arising from the crystalline and amorphous components of the PLA. The pattern appearing on the disrelation map indicated different distributions of the crystalline and amorphous components of the nanocomposite sample. In addition, the development of disrelation intensity becomes acute especially at the area adjacent to the clay, revealing that the clay essentially works as nucleating agent to cause the additional development of crystalline structure of PLA by lowering the surface energy barrier.

Non-equilibrium behavior of liquid mixture of polyethylene glycol (PEG) and polypropylene glycol (PPG) is studied. During the phase variation of PEG/PPG mixture, time-resolved Fourier transform infrared (FTIR) spectra were collected by attenuated total reflection (ATR) technique to selectively capture the development and subsequent variation of PEG-rich phase, appearing within a layer of the sample adjacent to the measuring surface of the ATR diamond prism. The FTIR spectra were then subjected to a two-dimensional (2D) correlation method to elucidate subtle but important changes in the absorbance of spectral bands. 2D correlation spectra revealed fine details of the non-equilibrium system. During the phase variation, dissociation between PEG and PPG generates free PEG molecules first. The emergence of the free PEG molecules triggers the subsequent self-assembly via the development of intermolecular H-bonding between PEG molecules, which eventually generates bigger PEG aggregates.

In order to improve the mechanical properties of Polyhydroxyalkanoate (PHA), the polycaprolactone (PCL) pellet was blended with a PHA-based pellet. The effects of the mixing ratio on the tensile properties, Young's modulus, tensile strength and elongation at break, were examined using a universal testing machine. When the mixing ration of PCL increased to 50%, the elongation at break of the polymer blend increased and the gauge area of tensile test specimens whitened and became porous. In order to understand this behavior, a rheo-optical characterization technique based on near-infrared (NIR) spectroscopy was applied to the mechanical deformation of the polymer blends during static tensile tests. Two-dimensional (2D) correlation of NIR spectra was then examined. It was found from peaks of ethyl group or methyl group that PCL was preferentially deformed. The difference in the deformation behavior is thought to be the cause of the porous structure.

Application of the two-dimensional (2D) correlation spectroscopy is extended to Chemiluminescence (CL) spectra of isotactic polypropylene (iPP) under thermally induced oxidation. Upon heating, the polymer chains of the iPP undergoes scissoring and fragmentation to develop several intermediates. While different chemical species provides the emission at different wavelength regions, entire feature of the time-dependent CL spectra of the iPP samples were complicated by the presence of overlapped contributions from singlet oxygen (1O2) and carbonyl species within sample. 2D correlation spectra showed notable enhancement of the spectral resolution to provide penetrating insight into the thermodynamics of the polymer system. For example, the, oxidation induce scissoring and fragmentation of the polymer chains to develop the carbonyl group. Further reaction results in the consumption of the carbonyl species and subsequent production of different 1O2 species each developed in different manner. Consequently, key information on the thermal oxidation can be extracted in a surprisingly simple manner without any analytical expression for the actual response curves of spectral intensity signals during the reaction.

Evolutionary change in supermolecular structure of Nylon 6 during its melt-quenched process was studied by Near-infrared (NIR) spectroscopy. Time-resolved NIR spectra was measured by taking the advantage of high-speed NIR monitoring based on an acousto-optic tunable filter (AOTF). Fine spectral features associated with the variation of crystalline and amorphous structure occurring in relatively short time scale were readily captured. For example, synchronous and asynchronous 2D correlation spectra reveal the initial decrease in the contribution of the NIR band at 1485 nm due to the amorphous structure, predominantly existing in the melt Nylon 6. This is then followed by the emerging contribution of the band intensity at 1535 nm associated with the crystalline structure. Consequently, the results clearly demonstrate a definite advantage of the high-speed NIR monitoring for analyzing fleeting phenomena.

Bioplastics have attracted attention over the years from a perspective of environmental protection. Recently, attention is focused on bioplastics derived from inedible objects. Polyhydroxyalkanoates (PHAs) are known as a microbial origin plastic and expected to deal effectively with the food security issue. In this study, in order to use PHA for industrial and machinery parts and products, polycaprolactone (PCL) was blended with a PHA-based pellet to improve ductility and tensile strength. The effects of additives on tensile strength and elongation at break, dynamic tensile tests of the polymer blends were examined using split Hopkinson bar (SHPB) method at high strain rates.

An alternative baseline correction method for diffuse reflection near-infrared (NIR) spectra, searching region standard normal variate (SRSNV), was proposed. Standard normal variate (SNV) is an effective pretreatment method for baseline correction of diffuse reflection NIR spectra of powder and granular samples; however, its baseline correction performance depends on the NIR region used for SNV calculation. To search for an optimal NIR region for baseline correction using SNV, SRSNV employs moving window partial least squares regression (MWPLSR), and an optimal NIR region is identified based on the root mean square error (RMSE) of cross-validation of the partial least squares regression (PLSR) models with the first latent variable (LV). The performance of SRSNV was evaluated using diffuse reflection NIR spectra of mixture samples consisting of wheat flour and granular glucose (0–100% glucose at 5% intervals). From the obtained NIR spectra of the mixture in the 10 000–4000 cm−1 region at 4 cm intervals (1501 spectral channels), a series of spectral windows consisting of 80 spectral channels was constructed, and then SNV spectra were calculated for each spectral window. Using these SNV spectra, a series of PLSR models with the first LV for glucose concentration was built. A plot of RMSE versus the spectral window position obtained using the PLSR models revealed that the 8680–8364 cm−1 region was optimal for baseline correction using SNV. In the SNV spectra calculated using the 8680–8364 cm−1 region (SRSNV spectra), a remarkable relative intensity change between a band due to wheat flour at 8500 cm−1 and that due to glucose at 8364 cm−1 was observed owing to successful baseline correction using SNV. A PLSR model with the first LV based on the SRSNV spectra yielded a determination coefficient (R2) of 0.999 and an RMSE of 0.70%, while a PLSR model with three LVs based on SNV spectra calculated in the full spectral region gave an R2 of 0.995 and an RMSE of 2.29%. Additional evaluation of SRSNV was carried out using diffuse reflection NIR spectra of marzipan and corn samples, and PLSR models based on SRSNV spectra showed good prediction results. These evaluation results indicate that SRSNV is effective in baseline correction of diffuse reflection NIR spectra and provides regression models with good prediction accuracy.

Molecular-level interaction between poly(lactic acid) (PLA) and clay was probed by near-infrared (NIR) imaging based on disrelation mapping. Sets of NIR imaging data were measured under varying temperature. The spectra were subjected to null-space projection to remove overwhelming baseline changes arising from light scattering. Disrelation maps derived from baseline-corrected spectra revealed that the disrelation intensity between 5785 and 5825 cm−1 becomes especially significant around the boundary between the PLA and clay, suggesting the predominant development of crystalline structure in the region. Further disrelation intensities around the boundary appeared when additional heating was applied to the system. The emergence of such additional disrelation pattern reveals the growth of the PLA crystals and propagation of the crystalline region caused by the heating. Consequently, conclusive evidence on the nucleation induced by the clay is provided by the NIR imaging analysis of the PLA sample.

We propose a technique for evaluating the compatibilization effect of maleic anhydride-grafted polypropylene (MAPP) introduced into glass fiber reinforced polypropylene by probing chemical structures using Fourier transform infrared (FTIR) microscopy. The dispersion state of MAPP in the composites was investigated by FTIR imaging constructed with integrated spectral intensity arising from carbonyl groups. MAPP was predominantly distributed around the glass fibers, due to the formation of interactions between the carbonyl groups in MAPP and the surface silanol groups on the fibers. The effects of interfacial interactions on matrix-fiber adhesion of the fiber composite were confirmed by observation of a fracture surface, using FTIR imaging, after tensile testing. The presence of polymer adhered to the fiber was detected. This revealed cohesive failure to occur in the matrix portion, attributable to improved interfacial adhesion. The addition of MAPP is therefore essential to improve matrix-filler adhesion, which contributes to enhanced strength and ductility by efficient stress transfer and prevention of fracturing at the matrix-fiber interface. This characterization technique can be utilized as a generally applicable tool to reveal the mechanisms of compatibilization of polymer composites.

The molecular architecture changes of crosslinked urethane during photo-oxidation was investigated by Fourier transform infrared spectroscopy (FTIR) in combination with two-dimensional (2D) correlation analysis. The 2D correlation FTIR spectroscopy provided insight into molecular architectural dynamics during photo-aging, where the sequential order of peak changes was determined upon perturbation with photo-aging. Photo-oxidation was monitored from the decrease in the peak intensity at 1537 cm−1 (attributed to the urethane group) and the generation of the hydrogen bonded C =O groups at 1698 cm−1 immediately after urethane decomposition. Several notable peaks appeared (1712, 1650, and 1750 cm−1) in the later stages, which were attributed to the free photo-oxidative product. In summary, photo-oxidation involved a cleavage of urethane crosslink and generation of end groups that formed hydrogen bonds with surrounding hydrogen bonding sites. Further degradation of the free photo-products was observed likely because of the small number of accessible hydrogen bonding sites due to the increasing heterogeneity of the internal structure.

Degradations of polyester (-COO-) and polyether (-O-) polyurethane (PU) samples in KOH aqueous solution were examined by microscopic infrared (IR) spectroscopy coupled with two-dimensional (2D) correlation analysis. The PU sample were subjected to degradation treatment in the KOH aqueous solution. Sets of IR spectra were collected as a function of distance under varying the distance to the sample surface where the degradation predominantly occurs. The spatial changes in the IR spectra were sorted out by 2D correlation spectroscopy. Namely, the hydrolysis of the polyester and polyether PU initially occurs in hard segment by dissociating weak intermolecular hydrogen bonding between the urethane groups of adjacent PU chains. Further degradation eventually induces the hydrolysis of C=O groups present in the soft segment domain.

Thermally induced variation of an ABA type block copolymer including microlamellar and liquid crystal (LC) structures was probed monitored by two-dimensional (2D) small-angle X-ray scattering (SAXS). By taking an advantage of strong X-ray light source of a synchrotron radiation facility, i.e. Spring-8, time-resolved SAXS spectra of the block copolymer sample based on PEMA and BB-5(3-Me) was collected during heat treatment well below isotropization temperature of the LC structure. A substantial level of change in the spectral feature are observed when the sample is subjected to the applied temperature. Fine features of the spectral changes are readily analyzed by 2D correlation method, including conventional and hetero-spectral correlation analysis. Hetero-spectral 2D correlation analysis of the spectra collected along and perpendicular to the fiber axis elucidated details of the thermally induced variation of the microdomain structure of the copolymer. Namely, it was revealed that the heating of the copolymer sample first induces the decrease in the diffraction peak intensity at 0.32 nm−1 and 0.42 nm−1 in the spectra collected along the direction perpendicular to the fiber axis. Further heating eventually leads to the development of the peak at 0.27 nm−1 in the spectra measured along the direction parallel to the fiber axis. Above observation suggests that the applied temperature first result in the rotation of the periodical lamellar structure initially aligned to the direction perpendicular to the fiber axis. This rotation eventually leads to the appearance of the periodical lamellar structure along the direction parallel to the fiber axis.

Submolecular-level variation of polypropylene (PP) caused by aging treatment is studied by two-dimensional (2D) small-angle X-ray scattering (SAXS) in conjunction with 2D correlation spectroscopy. PP samples were prepared by a T-die extrusion method and then probed by 2D SAXS. Direction-depending SAXS profile data were obtained by extrusion the SAXS intensities along the direction from 90° (i.e. direction of extrusion) to 120° on the 2D SAXS image. 2D correlation spectra derived from the SAXS profiles of the PP samples revealed the detailed orientations of the lamellae in the polymer system. For example, the development of asynchronous correlation peaks indicates that significant portion of the lamellae in the initial PP sample aligns to the direction of the extrusion. These lamellae tend to go through subsequent crystallization to increase the thickness during the cooling process, while the polymer chain inclined to the direction of the extrusion does not undergo such sufficient level of crystallization. It was also revealed that the aging treatment based on the heating well above glass transition temperature of the PP (ca. 0 °C) essentially provides additional crystalline growth especially to the inclined lamellae.

We demonstrate a Fourier transform infrared (FTIR) spectroscopic imaging combined with two-dimensional (2D) correlation analysis to elucidate matrix-filler interaction of polymer composites. Composite of maleic anhydride grafted polypropylene (MAPP) and silica sphere (SS) was fabricated. The FTIR image and disrelation map derived from sets of FTIR spectra suggest that the maleic anhydride groups in MAPP surround the SS surface and interact with the silanol on the surfaces of SS via hydrogen bonding. This clear link between MAPP and SS indicates that MAPP can be utilized as a suitable amphiphilic compatibilizer for an SS filler when it is mixed with hydrophobic polymer. FTIR imaging analysis was then further extended to categorize the interfacial states of more complicated polymer composites consisting of polypropylene (PP)/SS containing MAPP as a compatibilizer. Probing the interfacial chemical state using FTIR imaging revealed the interaction between MAPP and SS to contribute to improved elastic modulus of PP/MAPP/SS.

Photo-Fries rearrangement of phenyl salicylate was examined by real-time infrared (IR) monitoring in conjunction with density functional theory (DFT) calculation. Changes in the spectral features were readily captured during the photo-induced chemical reaction of the phenyl salicylate by means of two-dimensional (2D) correlation spectroscopy. The obvious variations of spectral intensities due to the production of 2,2′-dihydroxybenzophenone and 2,4′-dihydroxybenzophenone are clearly identified to provide in-depth understanding to the photo-Fries rearrangement. Namely, when exposed to UV-irradiation, the majority of the phenyl salicylate undergoes photothermal degradation. Further irradiation to the rest of the phenyl salicylate then results in the production of 2,2′-dihydroxybenzophenone followed by the development 2,4′-dihydroxybenzo-phenome products. Such delay in the production of 2,4′-dihydroxybenzo-phenome implies the presence of some more pathways, which makes its reaction efficiency lower than that of 2,2′-dihydroxybenzophenone.

Tensile deformations of isotactic polypropylene (iPP) and its nanocomposite were examined by a rheo-optical characterization technique based on near-infrared (NIR) spectroscopy to derive the submolecular-level understanding of the deformation mechanism during a tensile test. Sets of NIR spectra of the iPP samples were collected by using an acousto-optic tunable filter (AOTF) NIR spectrometer coupled with a tensile testing machine as an excitation device. Mechanical deformation of the samples was readily captured as strain-dependent NIR spectra. However, the main feature of the NIR spectra was overwhelmed by the contribution from the baseline change due to the substantial decrease in the sample thickness and subsequent change in the NIR light scattering. The variation of the spectral feature suggests that the deformation of the iPP involves the elongation of the rubbery amorphous chains prior to the displacement of the crystalline lamellae, providing elastic and subsequent plastic deformations during the tensile testing. In addition, it is revealed that the nanoclay layers dispersed within the iPP matrix restrict the elongation of the amorphous chains. Such interaction makes iPP hard and brittle, so that it yields no obvious ductile fracture during the tensile deformation.

A simple and effective strategy for improving the accuracy of the multivariate determination of polyethylene (PE) density using Raman spectroscopy has been demonstrated. This strategy is based on the possibility that varied polymeric structures of the PE samples, especially at a sub-zero temperature range, would enhance their spectral selectivity, thereby potentially improving the multivariate correlation with their pre-determined physical properties such as density. For the evaluation, Raman spectra were collected at regular intervals during continuous increase of the PE temperature from cryogenic to near room temperature. Then, using partial least squares (PLS) regression, calibration models were developed to correlate the Raman spectral features collected at each time period with the reference PE density values. Interestingly, the accuracy was improved when the temperature of the PE pellets was -35 °C, near the glass transition temperature (Tg). To explain the improved accuracy, a two-dimensional (2D) correlation analysis was employed to detail the spectral variation induced by temperature change. Diverse segmental chain motions (so called micro-Brownian motion) predominantly occurring in the amorphous section of the PEs around Tg greatly enhanced the spectral selectivity among PE samples. In addition, minor β-relaxation occurring around this temperature was an additional source of the enhanced spectral selectivity. In parallel, differential scanning calorimetry (DSC) curves of the samples were also examined to check the existence of the phase transitions.

Multiple-perturbation two-dimensional (2D) correlation spectroscopy was applied to sets of near-infrared (NIR) imaging data of polylactic acid (PLA) nanocomposite samples undergoing UV degradation. Incorporation of clay nanoparticles substantially lowers the surface free energy barrier for the nucleation of PLA and eventually increases the frequency of the spontaneous nucleation of PLA crystals. Thus, when exposed to external stimuli such as UV light, PLA nanocomposite may show different structure alternation depending on the clay dispersion. Multiple-perturbation 2D correlation analysis of the PLA nanocomposite samples revealed different spatial variation between crystalline and amorphous structure of PLA, and the phenomenon especially becomes acute in the region where the clay particles are coagulated. The incorporation of the clay leads to the cleavage-induced crystallization of PLA when the sample is subjected to the UV light. The additional development of the ordered crystalline structure then works favorably to restrict the initial degradation of the polymer, providing the delay in the weight loss of the PLA.

Dynamic absorption behavior of oleic acid (OA) onto silica gel was probed by infrared (IR) spectroscopy. Once OA is injected into silica gel placed on a horizontal attenuated total reflectance prism, the silica gel starts to absorb the OA molecules due to the molecular-level interaction based on hydrogen bonding between the COOH of OA and the OH of silica gel. The substantial level of variation of spectral feature is readily observed during the absorption of OA onto silica gel. 2D correlation analysis of the time-dependent IR spectra reveals fine details of absorption dynamics of OA molecules depending on the molecular structure. The predominant absorption of the monomers occurs at the onset of the absorption, and it is then quickly followed by the decrease in the dimers. In other words, the dissociation of the liquid crystals occurs via the disuniting of the tightly packed OA dimers.

A series of data analysis techniques, including multiple-perturbation two-dimensional (2D) correlation spectroscopy and kernel analysis, were used to demonstrate how these techniques can sort out convoluted information content underlying spectroscopic imaging data. A set of Raman spectra of polymer blends consisting of poly(methyl methacrylate) (PMMA) and polyethylene glycol (PEG) were collected under varying spatial coordinates and subjected to multiple-perturbation 2D correlation analysis and kernel analysis by using the coordinates as perturbation variables. Cross-peaks appearing in asynchronous correlation spectra indicated that the change in the spectral intensity of the free C O band of the PMMA band occurs before that of the C O⋯H O band arising from the molecular interaction between PMMA and PEG. Kernel matrices, generated by carrying out 2D correlation analysis on principal component analysis (PCA) score images, revealed subtle but important discrepancy between the patterns of the images, providing additional interpretation to the PCA in an intuitively understandable manner. Consequently, the results provided apparent spectroscopic evidence that PMMA and PEG in the blends are partially miscible at the molecular level, allowing the PMMAs to respond to the perturbations in different manner.

The purpose of this review article is to outline the recent progress in near-infrared (NIR) imaging technology with particular emphasis on new instrumentation. Superior features of NIR imaging such as suitability for nondestructive and in-situ analysis, transmission ability, availability of optical fibers, high-speed monitoring and stability are very attractive not only for laboratory-based studies but also for diverse practical applications. In this review, introduction to chemical imaging is described, and then, a comparison among NIR, infrared (IR) and Raman imaging are made. Furthermore, the features of new NIR imaging instruments developed by our research group in collaboration with Yokogawa Electric Corporation and Sumitomo Electric Industries, Ltd. are discussed. Finally, some examples of applications of NIR imaging are introduced. Particularly, the performance and usefulness of the newly-developed imaging devices are demonstrated through their applications to pharmaceutical tablets and polymers.

Changes in the crystallinity of microcrystalline cellulose (MCC) inside pharmaceutical tablets during storage were monitored by near infrared (NIR) diffuse reflectance spectroscopy to investigate transient variation at the molecular level. The MCC used in the tablets was ground before tablet formulation to intentionally cause a decrease in crystallinity. The variation in crystalline structure of MCC was evaluated from the intensity of NIR spectra peaks ascribed to OH groups in the crystalline region. The MCC exhibited clear signs of recrystallisation during 63 days of storage. In addition, the recrystallisation became even more pronounced when the MCC was stored under high-humidity conditions. Results also showed that the inclusion of anhydrous silicic acid induces a clear delay in recrystallisation by restricting the penetration of water molecules into the tablets. The findings derived from NIR spectra were substantiated by differential thermal analysis. The results from this study suggest that crystallinity of MCC inside tablets can be controlled by other excipients during storage, which has useful applications for controlling pharmaceutical product performance during storage.

A rheo-optical characterization technique based on near-infrared (NIR) spectroscopy is developed specifically to probe the submolecular-level deformation caused during a mechanical test. An illustrative example of the mechanical deformation of low-density polyethylene (LDPE) is provided to show how it can be utilized. A set of NIR spectra of the polymer sample were collected by using an acousto-optic tunable filter (AOTF) NIR spectrometer coupled with a tensile testing machine as an excitation device. While the substantial level of variation of spectral intensity was readily captured during the mechanical deformation of the LDPE, main feature of the NIR spectra was overwhelmed by the contribution from the baseline change. Projection 2D correlation analysis was then applied to selectively extract the signal contribution from the baseline fluctuation. The 2D correlation spectra revealed the predominant extension of amorphous tie chains followed by the rotation of crystalline lamellae, which induce elastic and plastic deformation of the LDPE, respectively.

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.