Molecular Orientation of Poly(ethylene naphthalate)/Poly(ethylene terephthalate) Copolymers Utilizing Polarized Raman Spectra

Flame Retardant Nano-Structured Fillers from Huntite/Hydromagnesite Minerals

In the current study, we propose a simple hydrothermal pathway to synthesize nano-structured Mg(OH)₂ after application of thermal decomposition followed by hydration of commercial minerals based on hydromagnesite and huntite. The synthesis of nano-materials is performed without the use of any catalyst. The effect of decomposition temperature on the hydrothermal synthesis of Mg(OH)₂ is extensively studied. It is shown that the morphology of resulting structures consists typically of particles ~200 nm in diameter and ~10 nm in thickness. Study of the structure at the molecular level designates the composition and supports the nano-sized characteristics of the produced materials. The associated thermal properties combined with the corresponding optical properties suggest that the material may be used as a flame retardant filler with enhanced transparency. In this concept, the flame retardancy of composite coatings containing the produced nano-sized Mg(OH)₂ was examined in terms of limiting oxygen index (LOI), i.e., the minimum concentration of oxygen that just supports flaming combustion.

Peculiar behavior of the ester carbonyl vibrational modes in anisotropic aliphatic and semi-aromatic polyesters

The current work reports on a systematic study related to the vibrational modes of the ester carbonyl group in drawn polyesters. We have observed and try to explain how the presence of aromatic units in the molecular structure substantially affects the respective elements of the Raman tensor in contrast to the dipole moment derivative vector which is only marginally influenced. The work is based on the collection of polarized Raman spectra and FTIR dichroism measurements on the one hand and on DFT calculations on the other. The experimental data were obtained from uniaxially stretched aliphatic and semi-aromatic polyesters. The calculations were applied on relevant oriented oligomers and allowed the extraction: (i) of reliable Raman/FTIR vibrational spectra and (ii) the components of the dipole moment derivative and Raman tensor of the vibrational modes and in particular the ones involving the ester carbonyl group. Experimental data indicate that the intensity of the ester carbonyl band is considerably enhanced in the Raman spectra of semi-aromatic polyesters, which results from a considerable enhancement of the related coupling coefficient. Furthermore, the angles of the principle Raman tensor axis are rotated so that the element of the tensor with the greatest value is oriented towards the direction designated by the segment. The latter explains the peculiar experimentally indicated anisotropy, through the ester carbonyl stretching, for the case of semi-aromatic polyesters, which is totally different with that observed in the aliphatic ones.

Collagen orientation probed by polarized Raman spectra can serve as differential diagnosis indicator between different grades of meniscus degeneration

The purpose of the present study was to analyze normal and degenerated menisci with Raman methodology on thin sections of formalin fixed paraffin embedding tissues and to correlate the Raman findings with the grade of meniscus degeneration. Menisci (n = 27) were removed from human knee joints after total knee replacement or meniscectomy. Following routine histopathological analysis to determine the grade of meniscal lesions obtained from healthy and degenerated formaline fixed paraffin embedded (FFPE) meniscal sections, Raman polarization approach was applied to evaluate the orientation of collagen fibrils in different levels of the same 5 μm thick FFPE meniscal tissue sections, used for histopathological assessment. We collected Raman spectra in two different polarization geometries, v-HH and v-VV, and calculated the mean value of the v-HH/v-VV intensity ratio of two Raman bands, sensitive and non-sensitive to the molecular orientation. The collagen specific amide I band at 1665 cm^-1, has the higher sensitivity dependence on the Raman polarization. The mean values of ratio v-HH/v-VV of the 1665 cm^-1 peak intensity was significantly higher in healthy, mean ± SD: 2.56 ± 0.46, compared to degenerated menisci, mean ± SD: 1.85 ± 0.42 (p = 0.0014). The mean values of v-HH/v-VV intensity ratio were 2.18 and 1.50 for low and high degenerated menisci, respectively (p < 0.0001). The difference of peak intensities in the two laser polarizations is decreased in the degenerated meniscus; this difference is diminishing as the degeneration increases. The v-HH/v-VV ratio was also of significant difference in low as compared to control and high grade meniscus lesions (p = 0.036 and p < 0.0001, respectively) offering valuable information for the approach of its biology and function. In the present study we showed that the 5 μm thick sections can be used for Raman analysis of meniscal tissue with great reliability, in terms of sensitivity, specificity, false-negative and false-positive results. Our data introduce the interesting hypothesis that compact portable Raman microscopy on tissue sections can be used intra-operatively for fast diagnosis and hence, accurate procedure design in the operating room.

Orientation of Poly(ε-caprolactone) in Its Poly(vinyl chloride) Blends Crystallized under Strain: The Role of Strain Rate

The blends of high and low molecular weights poly(ε-caprolactone) (PCL) with poly(vinyl chloride (PVC) were prepared. The samples before and after the crystallization of PCL were uniaxially stretched to different draw ratios. The orientation features of PCL in a stretched crystalline PCL/PVC blend and crystallized from the amorphous PCL/PVC blends under varied strains were studied by wide-angle X-ray diffraction (WAXD) diffraction. It was found that a uniaxial stretching of crystalline PCL/PVC blend with high molecular weight PCL results in the c-axis orientation along the stretching direction, as is usually done for the PCL bulk sample. For the stretched amorphous PCL/PVC blend samples, the crystallization of high molecular weight PCL in the blends under a draw ratio of λ = 3 with a strain rate of 6 mm/min leads to a ring-fiber orientation. In the samples with draw ratios of λ = 4 and 5, the uniaxial orientation of a-, b-, and c-axes along the strain direction coexist after crystallization of high molecular weight PCL. With a draw ratio of λ = 6, mainly the b-axis orientation of high molecular weight PCL is identified. For the low molecular weight PCL, on the contrary, the ring-fiber and a-axis orientations coexist under a draw ratio of λ = 3. The a-axis orientation decreases with the increase of draw ratio. When the λ reaches 5, only a poorly oriented ring-fiber pattern has been recognized. These results are different from the similar samples stretched at a higher strain rate as reported in the literatures and demonstrate the important role of strain rate on the crystallization behavior of PCL in its blend with PVC under strain.

Poly(ethylene Terephthalate) Carbon-Based Nanocomposites: A Crystallization and Molecular Orientation Study

Hybrid polymeric materials incorporating carbon nanostructures or inorganic constituents stand as a promising class of materials exhibiting distinct but also complementary features. Carbon nanotubes have been proposed as unique candidates for polymer reinforcement; however, sustained efforts are further needed in order to make full use of their potential. The final properties of the reinforced polymer are controlled in part by the morphology and the eventual molecular orientation of the polymer matrix. In the present study, multiwall carbon nanotubes (MWCNTs) were utilized in order to reinforce polyethylene terephthalate (PET) composites. The effect of CNTs on the crystallization and the orientation of the structurally hybridized polymeric material has been investigated from the perspective of assessing their impact on the final properties of a relevant nanocomposite product. Functionalized MWCNTs were used to achieve their optimal dispersion in the polymer matrix. The physical properties of the composites (i.e., crystallinity and orientation) were characterized via differential scanning calorimetry, X-ray diffraction, and polarized Raman microscopy. The addition of well-dispersed CNTs acted as a nucleation agent, increasing the crystallization of the polyethylene terephthalate matrix and differentiating the orientation of both CNTs and macromolecular chains.

Molecular orientation of poly(ethylene terephthalate) and poly(butylene terephthalate) probed by polarized Raman spectra: a parallel study

Poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) samples uniaxially drawn above Tg and beyond the yield point exhibit significant differences in their molecular orientation behavior as probed by polarized Raman spectra. The quasi-amorphous PET samples, drawn close to the Tg, manifest considerable molecular orientation development; however, when drawn above Tg + 30 degrees C, they exhibit significant molecular orientation relaxation. The semi-crystalline PBT samples maintain prominent molecular orientation even when drawn 110 degrees C above Tg. The drawing process, in PET samples, when resulting in molecular orientation, is accompanied by a gauche-trans transformation of the glycol linkage and a concurrent initiation of crystallinity development. In PBT specimens, it gives rise to a coexistence of alpha- and beta-type crystalline phases. Phase alpha is predominant at high draw temperatures, i.e., Tg + 110 degrees C, while phase beta dominates at low draw temperatures, i.e., Tg + 10 degrees C. PBT samples, with beta-phase predominance, left at relevant draw temperatures without stress, exhibit a beta-alpha phase change though no molecular orientation relaxation occurs. A note is made of the fact that complete molecular orientation analysis of PBT segments utilizing the depol method gives more reliable results than the simplified analysis assuming a cylindrical tensor for the 1614 cm(-1) symmetric stretch of the para-disubstituted benzene ring of PBT. In this context, segments of PBT specimens rich in alpha-phase exhibit higher molecular orientation than those with beta-phase predominance.

The effect of the molecular orientation on the release of antimicrobial substances from uniaxially drawn polymer matrixes

A new method of controlled release of low molecular weight biocides incorporated in polymer matrixes is described. The molecular orientation of uniaxially drawn biocide doped polymer films is suggested as a significant parameter for controlled release monitoring. Triclosan, a well-established widespread antibacterial agent, has been incorporated into high density polyethylene (HDPE) films that have been subsequently uniaxially drawn at different draw ratios. The molecular orientation developed was estimated utilizing polarized mu-Raman spectra. Biocide incorporated polymer films, drawn at different draw ratios, have been immersed in ethanol-water solutions (EtOH) and in physiological saline. The release of Triclosan out of the polymer matrix was probed with UV-Vis absorption spectroscopy for a period of time up to 15 months. In all cases, although the film surface of the drawn samples exposed to the liquid solution was higher than the undrawn one, the relevant release rate from the drawn specimens was lower than the non-stretched samples depending on the molecular orientation developed during the drawing process. A note is made of the fact that no significant molecular orientation relaxation of the polyethylene films has been observed even after such a long time of immersion of the drawn films in the liquid solutions.

Vibrational spectroscopic study on the origin of stress oscillation during step-wise stretching in poly(ethylene terephthalate)

The origin of the phenomenon of stress oscillation during step-wise stretching at room temperature for amorphous poly(ethylene terephthalate) (PET) was investigated using vibrational spectroscopy. For the first time, transmission Fourier transform infrared (FT-IR), attenuated total reflection (ATR) FT-IR, and micro-Raman spectroscopies were used in order to investigate the correlation of the orientation of the molecular chains, their conformational transformations, and the appearance of stress-induced crystallization to the phenomenon of stress oscillation during the step-wise stretching procedure. The phenomenon of stress oscillation occurs when amorphous PET is exposed to mechanical stress during which the extension rate is increased in a step-wise manner. This phenomenon leads to the formation of a pattern of opaque and transparent stripes (''striated'' or oscillating region), clearly distinguished from the unstretched (''bulk'') and the ''necking'' regions. Both infrared and Raman spectroscopic investigations revealed that the main conformational transformations and a significant increase of the crystallinity occur simultaneously in the ''striated'' region. Polarized infrared experiments showed the presence of increased molecular orientation, which is more profound for the ''intense striated'' region. Finally, micro-Raman spectroscopy allowed the study of opaque and transparent stripes individually and showed that the opaque stripes are more crystalline. Thus, our findings provide conclusive experimental support for the theory, which directly correlates the appearance of the stress-oscillation phenomenon with the induction of crystallinity and heat release and is based on Barenblatt's model. Our study also provides new conformational assignments for the infrared bands in PET for the high-frequency region from 3200 to 3800 cm(-1). Specifically, the bands at 3336 cm(-1) and at 3298 cm(-1) have been attributed to the trans and gauche conformations, respectively.