Accelerated weathering-induced degradation of poly(lactic acid) fiber studied by near-infrared (NIR) hyperspectral imaging

Nucleating and Plasticization Effects in Drawn Poly(Lactic Acid) Fiber during Accelerated Weathering Degradation

Changes in the polymer properties of poly(lactic acid) (PLA) fibers during drawing and degradation processes were analyzed using solid-state NMR, with the goal of elucidating morphological changes that influence fiber tensile properties. Combination of X-ray diffraction (XRD) and differential scanning calorimeter (DSC) indicated that the drawn PLA fibers consisted of different proportions of α crystalline and amorphous forms. ¹³C CP-MAS NMR spectra showed amorphous-like broad singlet signals, of which the full width at half maximum (FWHM) decreased with increasing crystallinity and crystal orientation. The T₁H value decreased by interaction with additives and increased with increasing crystal orientation. The interaction with additives also reduced T₁C values, which increased with increasing crystallinity. Use of organic clay enhanced the crystallization of high draw-ratio PLA fibers due to nucleation, which increased tensile strength; this effect gradually decreased with time during accelerated weathering. In contrast, the plasticization due to the addition of flexible polymers increased fiber elongation, which rapidly dropped during the degradation. Changes of FWHM, T₁H, and T₁C values indicated that the degradation occurred at sites within the amorphous portions of the PLA fibers containing organic clay, while the flexible polymers were preferentially degraded if they were present in the PLA fibers.

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.

High-Speed Scanning for the Quantitative Evaluation of Glycogen Concentration in Bioethanol Feedstock Synechocystis sp. PCC6803 Using a Near-Infrared Hyperspectral Imaging System with a New Near-Infrared Spectral Camera

In the present study, the high-speed quantitative evaluation of glycogen concentration accumulated in bioethanol feedstock Synechocystis sp. PCC6803 was performed using a near-infrared (NIR) imaging system with a hyperspectral NIR spectral camera named Compovision. The NIR imaging system has a feature for high-speed and wide area monitoring and the two-dimensional scanning speed is almost 100 times faster than the general NIR imaging systems for the same pixel size. For the quantitative analysis of glycogen concentration, partial least squares regression (PLSR) and moving window PLSR (MWPLSR) were performed with the information of glycogen concentration measured by high performance liquid chromatography (HPLC) and the calibration curves for the concentration within the Synechocystis sp. PCC6803 cell were constructed. The results had high accuracy for the quantitative estimation of glycogen concentration as the best squared correlation coefficient R² was bigger than 0.99 and a root mean square error (RMSE) was less than 2.9%. The present results proved not only the potential for the applicability of NIR spectroscopy to the high-speed quantitative evaluation of glycogen concentration in the bioethanol feedstock but also the expansivity of the NIR imaging instrument to in-line or on-line product evaluation on a factory production line of bioethanol in the future.

Effects of Accelerated Weathering in Polylactide Biocomposites Reinforced with Microcrystalline Cellulose

The aim of this study was to reveal effects of accelerated weathering in neat polylactide (PLA) and its biocomposite reinforced with microcrystalline cellulose (MCC); compounded by twin-screw extrusion melt mixing and specimen shaping by injection molding. Weathering conditions were applied via consecutive steps of UV irradiation and humidity in accordance with ISO 4892–3 standards for 200 h. Various characterization techniques and mechanical tests indicated that photolysis, photo-oxidation and hydrolysis were the main degradation mechanisms leading to significant decrease in the molecular weight of PLA via main chain scission. Consequently, except elastic modulus other mechanical properties; strength, ductility and fracture toughness of PLA and PLA/MCC decreased substantially. However, after comparing the mechanical properties of the neat PLA and PLA/MCC biocomposite specimens having 200 h of accelerated weathering, it was concluded that; for the outdoor applications use of PLA/MCC biocomposite (with only 3 wt% MCC) was extremely beneficial compared to using neat PLA. For example, tensile strength is more than 91 % beneficial while strain at break ductility is more than 2.7 times beneficial.

In Vivo Monitoring of the Growth of Fertilized Eggs of Medaka Fish (Oryzias latipes) by Near-Infrared Spectroscopy and Near-Infrared Imaging-A Marked Change in the Relative Content of Weakly Hydrogen-Bonded Water in Egg Yolk Just before Hatching

The present study develops further our previous study of in vivo monitoring at the molecular level of the embryonic development in Japanese medaka fish (Oryzias latipes) using near-infrared (NIR) spectroscopy and NIR imaging. NIR spectra were measured nondestructively for three major parts of fertilized medaka eggs (the embryonic body, oil droplets, and egg yolk) from the first day after fertilization to the day just before hatching (JBH). Changes in the contents of chemical components such as proteins, water, and lipids were monitored in situ during embryonic development. A marked change in the relative content of weakly hydrogen-bonded water was observed in the egg yolk JBH. Principal component analysis (PCA) was carried out using the NIR spectra data of the egg yolk and embryo on the fifth day after fertilization. The PCA clearly separates the egg yolk data from the embryo body parts. Principal component PC1 and PC2 loading plots suggest that the hydrogen bonding structure of water in the egg yolk is considerably different to those of the other parts and the fraction of weakly hydrogen-bonded water in the egg yolk is smaller than that in the embryonic body. NIR images developed from the intensities of peaks of second derivative spectra owing to water and proteins show their different distribution patterns. Images of the ratio of strongly and weakly hydrogen-bonded water confirmed that oil droplets and embryonic body parts have higher and lower ratios, respectively, of strongly hydrogen-bonded water than do the other parts. The images developed from the intensity of the peaks at 4864 and 4616 cm⁻¹ related to the proteins indicated that the egg yolk contains a higher concentration of protein than do the other parts. The peaks at 5756 and 4530 cm⁻¹ caused by the protein secondary structures of α-helix and β-sheet showed the configuration of the egg cell membrane. The present study might lead to new understanding at the molecular level regarding the growth of fertilized eggs and provides a new tool to visualize egg development in a nondestructive manner.

Near-Infrared Spectroscopy and Imaging Studies of Fertilized Fish Eggs: In Vivo Monitoring of Egg Growth at the Molecular Level

In this work, the growth of fertilized Japanese medaka (Oryzias latipes) eggs was monitored in vivo at the molecular level using near-infrared (NIR) spectroscopy and NIR imaging. NIR spectra were recorded noninvasively for three major parts of a fertilized medaka egg, the embryonic body, the oil droplets, and the yolk, from the first day after fertilization to the day before hatching. Principal component analysis (PCA) revealed that water, protein, and lipid contents in the egg yolk and oil droplets changed significantly just before hatching. The ratio of the characteristic peaks due to proteins and lipids in the second derivative spectra suggested that the relative concentration of proteins to lipids was constant in the egg yolk, while it dramatically increased just before hatching in the oil droplets. Furthermore, linear discriminant analysis (LDA) predicted the hatching possibility on the next day with 100% and 99.3% accuracy for yolk and oil droplets data, respectively. Two types of NIR images were developed in situ using the band intensities of the lipids and proteins in the second derivative spectra. The egg’s protein and lipid content was successfully visualized noninvasively. This technique should enable noninvasive quality testing of fertilized eggs in the future.

A review of recent trends in polymer characterization using non-destructive vibrational spectroscopic modalities and chemical imaging

This review focuses on the recent developments in vibrational spectroscopy and chemical imaging (i.e. Raman, Near Infrared, Mid Infrared) to characterize polymers in diverse forms, their behaviour and transient phenomenon. First, important polymeric properties and traditional methods of their characterization are outlined. Then relative advantages & disadvantages have been presented of different characterization methods are presented. This is followed by a detailed review of applications of chemical imaging and spectroscopic techniques in polymer characterization, including the limitations encountered. The article ends with a discussion on the future of chemical imaging with regards to polymer characterization.

Recent progress of near-infrared (NIR) imaging--development of novel instruments and their applicability for practical situations--

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.

Thermal behavior of poly(lactic acid)-nanocomposite studied by near-infrared imaging based on roundtrip temperature scan

The thermal behavior of poly(lactic acid) (PLA) was studied by near-infrared imaging to provide a molecular-level understanding of the physical improvement caused by nanoclay dispersion. A set of PLA samples, each having different nanoclay dispersion, was prepared under varying sonication time. Crystallinity variation of the polymer interacting with the nanoclay particles was analyzed by a roundtrip temperature scan below the melting temperature. Namely, the samples underwent heating and then cooling in the opposite way during the spectral measurement. The discrepancy of the spectral feature between the heating and the cooling indicated the development of the hysteresis associated with the cold crystallization of the PLA lamellae. The generation of the spectral residuals revealed the inner working mechanism of how the polymer structure undergoes variation depending on the presence of the clay particles and their dispersions. The sonication brings substantial dispersion of the nanoclay over the polymer matrix. The nanoclay particles then induce the additional development of the crystalline structure due to the molecular interaction between the PLA and nanoclay arising from the presence of enormous surface area, which in turn induces variation of mechanical strength to the polymer.

Potential of a newly developed high-speed near-infrared (NIR) camera (Compovision) in polymer industrial analyses: monitoring crystallinity and crystal evolution of polylactic acid (PLA) and concentration of PLA in PLA/Poly-(R)-3-hydroxybutyrate (PHB) blends

This study was carried out to evaluate a new high-speed hyperspectral near-infrared (NIR) camera named Compovision. Quantitative analyses of the crystallinity and crystal evolution of biodegradable polymer, polylactic acid (PLA), and its concentration in PLA/poly-(R)-3-hydroxybutyrate (PHB) blends were investigated using near-infrared (NIR) imaging. This NIR camera can measure two-dimensional NIR spectral data in the 1000-2350 nm region obtaining images with wide field of view of 150 × 250 mm(2) (approximately 100  000 pixels) at high speeds (in less than 5 s). PLA with differing crystallinities between 0 and 50% blended samples with PHB in ratios of 80/20, 60/40, 40/60, 20/80, and pure films of 100% PLA and PHB were prepared. Compovision was used to collect respective NIR spectra in the 1000-2350 nm region and investigate the crystallinity of PLA and its concentration in the blends. The partial least squares (PLS) regression models for the crystallinity of PLA were developed using absorbance, second derivative, and standard normal variate (SNV) spectra from the most informative region of the spectra, between 1600 and 2000 nm. The predicted results of PLS models achieved using the absorbance and second derivative spectra were fairly good with a root mean square error (RMSE) of less than 6.1% and a determination of coefficient (R(2)) of more than 0.88 for PLS factor 1. The results obtained using the SNV spectra yielded the best prediction with the smallest RMSE of 2.93% and the highest R(2) of 0.976. Moreover, PLS models developed for estimating the concentration of PLA in the blend polymers using SNV spectra gave good predicted results where the RMSE was 4.94% and R(2) was 0.98. The SNV-based models provided the best-predicted results, since it can reduce the effects of the spectral changes induced by the inhomogeneity and the thickness of the samples. Wide area crystal evolution of PLA on a plate where a temperature slope of 70-105 °C had occurred was also monitored using NIR imaging. An SNV-based image gave an obvious contrast of the crystallinity around the crystal growth area according to slight temperature change. Moreover, it clarified the inhomogeneity of crystal evolution over the significant wide area. These results have proved that the newly developed hyperspectral NIR camera, Compovision, can be successfully used to study polymers for industrial processes, such as monitoring the crystallinity of PLA and the different composition of PLA/PHB blends.