In-Line Chemical Composition Monitoring for the Injection Molding Process of Biodegradable Polymer Blends Using Simultaneous Measurement of Near-Infrared Diffuse Reflectance and Transmission Spectra.

In the processing of polymer blends and composites, in-line near-infrared (NIR) spectroscopy enables monitoring of the composition and its composite uniformity and contributes to rapid process development and quality control. However, in the injection molding process, the study of the composition of polymer materials has been delayed due to high-pressure conditions. Our research group developed NIR probes for transmission and diffuse reflectance measurements that can withstand high-pressure and temperature conditions up to 130 MPa and 200 °C. In this research, transmission and diffuse reflectance spectra were measured inline during the injection molding process of polymer blends of poly(lactic acid) and polybutylene succinate adipate. The intensity of each polymer band in the second-derivative spectra exhibited a monotonic increase or decrease in response to changes in the blend ratio. Using transmission and diffuse reflectance spectra as explanatory variables of the partial least squares regression model simultaneously, the model showed high estimation accuracy for the entire region of the blend ratio. Finally, this model was applied to monitor the polymer changeover operation, and the change in the blend ratio in the molded product was successfully estimated in line.

Cellulose nanofiber reinforced poly (lactic acid) with enhanced rheology, crystallization and foaming ability.

The incorporation of micro-/nano-particles is one of the most efficient approaches to reinforce poly (lactic acid) (PLA). However, introducing the inorganic particles which can compromise the green nature of PLA. Herein, we proposed a green strategy to add biodegradable cellulose nanofibers (CNFs) into the PLA matrix for eliminating its low melt strength and slow crystallization rate. Well-dispersed hydrophobic-modified CNFs in the PLA matrix were obtained through the combination of acetylation surface modification and the melt-compounding technology. The PLA/CNF composites notably improved crystallization properties and melt elasticity, compared with the neat PLA. Additionally, the foaming behavior of PLA was dramatically enhanced by introducing 2 wt% modified CNFs. At an ultralow pressure of 1.5 MPa, the prepared PLA/CNF nanocomposite foams exhibited the highest expansion ratio approximately 20.4. These results demonstrated that CNFs were extraordinarily helpful in enhancing the foamability of PLA, which are expected to be applied as a sustainable packaging material.

Novel Approaches to In-Situ ATR-FTIR Spectroscopy and Spectroscopic Imaging for Real-Time Simultaneous Monitoring Curing Reaction and Diffusion of the Curing Agent at Rubber Nanocomposite Surface.

Here, we propose a novel attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy method for simultaneously monitoring the curing reaction and the diffusion behavior of curing agents at the surface of rubber in real-time. The proposed scheme was demonstrated by fluorine rubber (FKM) and FKM/carbon nanotube (CNT) nanocomposites with a target curing agent of triallyl-isocyanurate (TAIC). The broadening and the evolution of the C=O stretching of TAIC were quantitatively analyzed to characterize the reaction and the diffusion. Changes in the width of the C=O stretching indicated the reaction rate at the surface was even faster than that of the bulk as measured by a curemeter. The diffusion coefficient of the curing agent in the course of heating was newly calculated by the initial increase in the absorbance and our model based on Fickian diffusion. The diffusion coefficients of TAIC during curing were evaluated, and its temperature and filler dependency were identified. Cross-sectional ATR-FTIR imaging and in situ ATR-FTIR imaging measurements supported the hypothesis of the unidirectional diffusion of the curing agent towards the heated surface. It was shown that our method of in situ ATR-FTIR can monitor the degrees of cure and the diffusion coefficients of curing agents simultaneously, which cannot be achieved by conventional methods, e.g., rheological measurements.

Highly Ordered Nanocellular Polymeric Foams Generated by UV-Induced Chemical Foaming.

Nanocellular polymer foams have shown significant potential for industrial applications because of their superior thermal, mechanical, and optical properties. Some of these properties may be further improved by enhancing the ordering of cell structures. However, it is challenging for conventional foaming methods to control both the cell size and ordering at the nanoscale. Here, we show an innovative method to produce highly ordered nanocellular polymer foams by incorporating the self-assembly of an asymmetric diblock copolymer with the UV-induced chemical foaming technique. The minor domains are designed to generate a gaseous compound from the partial cleavage of the functional group. It is demonstrated that the gas-producing reaction can be accelerated at a temperature low enough to prevent melting of the whole self-assembled template, by mixing a small amount of photoacid generator into the copolymer, followed by UV irradiation. The result is the production of polymer foams with the nanoscale cells highly aligned to the self-assembled domains.

Effect of Cellulose Nanofiber (CNF) Surface Treatment on Cellular Structures and Mechanical Properties of Polypropylene/CNF Nanocomposite Foams via Core-Back Foam Injection Molding.

Herein, lightweight nanocomposite foams with expansion ratios ranging from 2⁻10-fold were fabricated using an isotactic polypropylene (iPP) matrix and cellulose nanofiber (CNF) as the reinforcing agent via core-back foam injection molding (FIM). Both the native and modified CNFs, including the different degrees of substitution (DS) of 0.2 and 0.4, were melt-prepared and used for producing the polypropylene (PP)/CNF composites. Foaming results revealed that the addition of CNF greatly improved the foamability of PP, reaching 2⁻3 orders of magnitude increases in cell density, in comparison to those of the neat iPP foams. Moreover, tensile test results showed that the incorporation of CNF increased the tensile modulus and yield stress of both solid and 2-fold foamed PP, and a greater reinforcing effect was achieved in composites containing modified CNF. In the compression test, PP/CNF composite foams prepared with a DS of 0.4 exhibited dramatic improvements in mechanical performance for 10-fold foams, in comparison to iPP, with increases in the elastic modulus and collapse stress of PP foams of 486% and 468%, respectively. These results demonstrate that CNF is extraordinarily helpful in enhancing the foamability of PP and reinforcing PP foams, which has importance for the development of lightweight polymer composite foams containing a natural nanofiber.

Analysis of molecular orientation in polymeric spherulite using polarized micro attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopic imaging.

Micro ATR-FTIR spectroscopic imaging enables the visualization of two-dimensional chemical distribution at a higher spatial resolution than macro-transmission FTIR imaging approach. In this study, micro ATR-FTIR imaging was applied for analysis of a specific morphology in a spherulite of poly(3-hydroxybutyrate) (PHB). The PHB spherulites crystallized at an isothermal condition, showed the fine band structure due to the twisting lamellar crystals during the spherulite growth under the polarized optical microscope (POM). In addition, the band structure observed in the PHB spherulite was the double band pattern in which the higher and lower birefringence banded areas alternatively appear due to the three-dimensional orientation of crystallographic axes and the biaxial refractive index ellipsoid of PHB crystalline structure. Micro ATR-FTIR spectroscopic imaging was employed for detecting the double band structure in the PHB spherulite. However, the obtained spectral images did not indicate any band structures. To detect the difference of molecular orientation among the double band structures, the micro ATR-FTIR imaging was performed with a linear polarizer at four different angles. The mean values of absorbance in each measured area changed depending on the polarizer angle. The in-plane molecular orientation to the tangential direction of spherulite, caused by the dependence of the average absorbance on the polarizer angles, was determined by the position of measured area in the spherulite and the linear dicroism of each of the spectral band used. To visualize the small difference of molecular orientation in the double band structure, micro ATR-FTIR images of the dichroic differences at three spectral bands were calculated from two different sets of polarizer angles. The micro ATR-FTIR images representing the dichroic differences displayed their corresponding distributions among three spectral bands. The complementary distributions of the dichroic difference were caused by the crystallographic orientation of b- and c-axes and were successfully visualized to reveal the pattern with the features less than 10 µm in size. The results achieved in this study were due to two advantages of the polarized micro ATR-FTIR imaging: the high spatial resolution of micro ATR-FTIR imaging technique, and the high sensitivity of polarization measurements. Thus, this work demonstrates the power of this spectroscopic approach for such analytical investigation.

Near-Infrared Hyperspectral Absorption/Scattering Imaging Method Using Multiple Ground Plates for Evaluating Polymer Composites.

This paper proposes a nondestructive method of evaluating polymer composites using near-infrared (NIR) diffuse reflection spectroscopy with multiple ground plates. Wavelength-dependent absorption and reduced scattering coefficients were acquired to evaluate the chemical structure and the concentration of the substances from absorption and to determine the size and the dispersity of filler in the polymer domain from scattering. NIR spectra of the sample were measured on multiple ground plates, namely, "ground-plate-dependent" diffuse reflection spectra. The effects of the external reflection on the ground-plate-dependent diffuse reflection spectra were subsequently removed. The internal reflection coefficient was calculated based on the difference between the diffuse reflectances of the neat resin and ground plates without prior information on the incident angle of light and the refractive index of sample. The external reflection coefficient was evaluated by the gap of diffuse reflectances between the sample and a white ground plate. After the corrections of reflections, the spectra were fitted by a physical model of light propagation based on the two-flux theory to acquire the absorption and the reduced scattering coefficients. The calculated absorption coefficients indicated a good linear relationship with particle concentration. The calculated reduced scattering coefficients agreed with the theoretical values by Mie scattering theory. It was demonstrated that the proposed method achieved the simultaneous evaluation of particulate-filler concentrations and sizes in polymer composites.

Author Correction: Orientational Mapping Augmented Sub-Wavelength Hyper-Spectral Imaging of Silk.

A correction to this article has been published and is linked from the HTML version of this paper. The error has been fixed in the paper.

Evolution of cellular morphologies and crystalline structures in high-expansion isotactic polypropylene/cellulose nanofiber nanocomposite foams.

Herein, the development of cell morphology and crystalline microstructure of injection-molded isotactic polypropylene/cellulose nanofiber (PP/CNF) composite foams with 2-10-fold expansion ratios was investigated through scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), and small-angle X-ray scattering (SAXS). Compared with isotactic polypropylene (iPP) foams, the added CNF improved the cell morphology and resulted in a great reduction in cell size. Additionally, the PP lamella orientation and crystal type were notably altered during the core-back FIM process. As the expansion ratio increased, the original isotropic lamellae in the iPP foams were transformed into an oriented lamellar structure and then further transformed into a typical shish-kebab structure, while hybrid shish-kebab structures were simultaneously generated in the high-expansion PP/CNF nanocomposite foams. Accordingly, the highest content of ß-crystals was observed in the low-expansion iPP foams. In contrast, the ß-crystal content in PP/CNF composites decreased monotonously as the expansion ratio increased, which resulted from the combined effects of CNF's nucleating ability for α-crystals and the more dominant extensional flow effect assisted by the added CNF.

Orientational Mapping Augmented Sub-Wavelength Hyper-Spectral Imaging of Silk.

Molecular alignment underpins optical, mechanical, and thermal properties of materials, however, its direct measurement from volumes with micrometer dimensions is not accessible, especially, for structurally complex bio-materials. How the molecular alignment is linked to extraordinary properties of silk and its amorphous-crystalline composition has to be accessed by a direct measurement from a single silk fiber. Here, we show orientation mapping of the internal silk fiber structure via polarisation-dependent IR absorbance at high spatial resolution of 4.2 µm and 1.9 µm in a hyper-spectral IR imaging by attenuated total reflection using synchrotron radiation in the spectral fingerprint region around 6 µm wavelength. Free-standing longitudinal micro-slices of silk fibers, thinner than the fiber cross section, were prepared by microtome for the four polarization method to directly measure the orientational sensitivity of absorbance in the molecular fingerprint spectral window of the amide bands of ß-sheet polypeptides of silk. Microtomed lateral slices of silk fibers, which may avoid possible artefacts that affect spectroscopic measurements with fibers of an elliptical cross sections were used in the study. Amorphisation of silk by ultra-short laser single-pulse exposure is demonstrated.

Unprecedented Development of Ultrahigh Expansion Injection-Molded Polypropylene Foams by Introducing Hydrophobic-Modified Cellulose Nanofibers.

Herein, an ultrahigh 18-fold expansion of isotactic polypropylene (iPP)/cellulose nanofiber (CNF) nanocomposite foams was achieved for the first time using a core-back foam injection molding technique. It was found that CNFs were well dispersed and aligned along the cell wall in the core-back direction. Interestingly, the formations of a hybrid shish-kebab of CNFs and classic shish-kebab of PP were simultaneously achieved in the PP/CNF composites. Finally, we proposed that the combination of local strong melt strength, probably resulting from the strong alignment of CNFs and subsequent formation of hybrid shish-kebab structures, and weak melt strength in the unreinforced PP melt might be the driving force for remarkably enhancing the PP foamability.

Near-Infrared Spectroscopic Evaluation of the Water Content of Molded Polylactide under the Effect of Crystallization.

During melt processing, the moisture inside polylactide (PLA) easily induces hydrolysis, which deteriorates the mechanical and thermal properties of the product. The state of dryness of resin pellets must be monitored to prevent PLA hydrolysis. In this study, near-infrared (NIR) spectroscopy was applied to measure water content in PLA. In addition, the shape of the NIR spectrum is also affected by crystallization, which could lead to a reduction in the accuracy of evaluating the water content. The objective of this research is to construct a robust model for estimating the water content with varying dispersive extents of crystallization. Two methods for estimating water content measured during a drying process were conducted: the integration of absorbance and partial least squares (PLS) regression were conducted to estimate the water contents in PLA considering the effect of crystallization. The slope of the calibration line of the water content obtained from integrating absorbance varied between PLA with different crystallinities. This is due to the overlap between the NIR band of water and that of PLA crystal in the range of 5100-5400 cm-1. We found that the shape of the NIR spectrum was changed by crystallization, and the crystallinity, compared to the thickness of lamellae, was the dominant factor determining such a change of NIR spectra. The PLS model of water content constructed from only amorphous PLA showed large error of estimation in crystallized PLA. In contrast, the PLS model constructed from both amorphous and crystallized PLA estimated the water contents with lower errors. This was because latent variables obtained from both amorphous and crystallized PLA cancelled the effect of crystallization on NIR spectra.