PET Molecules Research Articles

Impact of dicarboxystilbene impurities on the properties of swift heavy ion latent tracks in PET films

We present a new hypothesis and supporting experimental evidence about the essential role played by small impurities of dicarboxystilbene in the process of UV treatment of PET films irradiated with swift heavy ions (SHI). This treatment both forms highly selective membranes with permeability values comparable to natural ones (the track-UV technique) and sharply accelerates the etching of latent tracks in membrane production (the track-etching technique). We hypothesize (1) that these high permeability value is due to the presence of a molecular motor of an Archimedes screw type in the central part of the latent track formed by photoinduced trans-cis isomerization of dicarboxystilbene molecules that are anchored in helical conformations in the latent track; and (2) that the acceleration of etching rates is due to the preferential accumulation of phenanthrene-type molecules in the central part of the latent track due to the existence of a cyclization channel for photoexcited molecules of cis-dicarboxystilbene. In the presence of alkali solution, phenanthrene molecules release electrons which behave as strong anions in aqueous solution, catalyzing alkaline hydrolysis of PET molecules in the central part of the track. We present experimental observations of photoinduced changes in transmission light intensity after track-UV light treatment of both pristine and SHI irradiated PET films that confirm the presence of trans-cis isomerization of dicarboxystilbene molecules and show their contribution to the formation of new helical conformations in SHI irradiated PET films during the light treatment.

Janus Structure Construction of Polyester-Cotton Fabrics for Achieving Excellent Moisture, Moisture-Permeability, and Antibacterial Capability.

Integration of hydrophobic and antibacterial functionalities into polyester-cotton blended (PTCO) textiles has attracted more attention but remains a challenge. Here, a Janus fabric with antibacterial effect, hydrophobicity, and enhanced moisture-permeability is fabricated using a "mist polymerization" approach. The PET fibers in the PTCO fabric are amino-functionalized through ammonolysis reactions of PET molecules with HDA, and mist treatments of poly lauryl methacrylate (PLMA) and poly(DMC-co-MA) (PDM) are applied on the two side surfaces of the PTCO-HDA fabric, respectively. The resulting Janus fabric exhibits an antibacterial rate of 99.9% against both E. coli and S. aureus, along with a hydrophobic property on its single side (PTCO-HDA@PLMA). Additionally, the establishment of a surface-free energy gradient across the fabric confers superior moisture-permeability to the Janus fabric, offering advantages in preserving textile comfort. Moreover, this approach does not significantly compromise the original fabric properties, such as mechanical strength, moisture permeability, and fabric softness. The proposed method offers a straightforward and scalable strategy for textile finishing, demonstrating great potential in expanding the application scope of PTCO fabrics, and it may hold a pivotal role in diverse applications, notably encompassing home textiles, wound dressings, and high-performance sportswear.

Progress in 3D printing of recycled PET

Filaments from blends of post-industrial, low-quality recycled poly(ethylene terephthalate) (RPET) and ethylene-butyl-acrylate-glycidyl-methacrylate (EBA-GMA) were extruded with different EBA-GMA contents, then specimens were 3D-printed by fused filament fabrication technology. It has been demonstrated that, when 0–90° layer order is applied, at 15 wt% EBA-GMA content the unnotched impact strength increases by two and a half times and the notched impact strength by nine times compared to samples printed from elastomer-free RPET. DSC and DMA measurements proved that EBA-GMA reactively bonds to PET molecules, which is indicated by the increment of rigid amorphous phase and glass transition temperature and the reduction of crystallinity. The co-polymer molecules formed in-situ during compounding create a Toughening Enhancer Interphase (TEI), which also remains after 3D printing and effectively enhances impact strength. The strain at break and tensile strength of the filaments are substantially higher than that of 3D-printed specimens due to the increasing shrinkage and the resulting increased porosity of the printed specimens with higher EBA-GMA content. However, the Young-modulus values are quite similar. The flexural strength of the 3D-printed specimens reaches 40–60% of the values of injection moulded samples. The proposed method enables the production of parts with arbitrary geometry and balanced mechanical properties from RPET, which may substitute acrylonitrile butadiene styrene.

Controlling PA6/PET adhesion to facilitate interfacial fracture

Microfibers get often produced in the form of bicomponent polymer systems. The materials of choice are Nylon 6 (PA6) and poly(ethylene terephthalate) (PET). This combination of PA6 and PET is preferable because of its beneficial attributes (i.e., thermal stability, mechanical strength, etc.). PA6 and PET exhibit high adhesion when processed at elevated temperatures due to chemical bonds formation by aminolysis of the ester group in PET with a secondary amine in PA6. These fibers are split/fibrillated by mechanical energy (hydroentangling or needle punching). For energy input, it is desirable to have adhesion between the PA6 and PET materials that is not too strong to allow for easy polymer splitting. Therefore, we developed a method for tailoring the PA6/PET interface adhesion by adding modifiers that react preferentially with the PA6 component. The reactivity between PA6 and PET was investigated by spin coating thin films of PA6 and PET on silicon wafers and annealing them at high temperatures. The reaction between PET and small molecules containing secondary amines (i.e., caprolactam, diallyamine, diethylamine, and diisopropylamine) shows a chemical bond between the ester group in PET and the secondary amine group. The poly(styrene-alt-maleic anhydride) (PSMA) and poly(octadecene-alt-maleic anhydride) (POMA) were chosen as model polymer interfacial modifiers. The feasibility of modifying secondary amines is examined by reacting the two modifiers, PSMA and POMA, with small molecules containing secondary amine groups. PA6 and PET display high fracture toughness (i.e., adhesion strength) at elevated temperatures and longer annealing times because of strong interactions between the amine and ester groups in PA6 and PET, respectively. We then assess the adhesion strength between PA6 and PET modified with PSMA and POMA. Both modifiers reduce interfacial adhesion strength between PA6 and PET. Therefore, it is feasible to tailor adhesion at the PA6/PET interface, which could prove helpful in microfibers production.

Assembly of Biomolecular Gigastructures and Visualization with the Vulkan Graphics API.

Building and displaying all-atom models of biomolecular structures with millions or billions of atoms, like virus particles or cells, remain a challenge due to the sheer size of the data, the required levels of automated building, and the visualization limits of today’s graphics hardware. Based on concepts introduced with the CellPack program, we report new algorithms to create such large-scale models using an intermediate coarse-grained “pet representation” of biomolecules with 1/10th the normal size. Pet atoms are placed such that they optimally trace the surface of the original molecule with just ∼1/50th the original atom number and are joined with covalent bonds. Molecular dynamics simulations of pet molecules allow for efficient packing optimization, as well as the generation of realistic DNA/RNA conformations. This pet world can be expanded back to the all-atom representation to be explored and visualized with full details. Essential for the efficient interactive visualization of gigastructures is the use of multiple levels of detail (LODs), where distant molecules are drawn with a heavily reduced polygon count. We present a grid-based algorithm to create such LODs for all common molecular graphics styles (including ball-and-sticks, ribbons, and cartoons) that do not require monochrome molecules to hide LOD transitions. As a practical application, we built all-atom models of SARS-CoV-2, HIV, and an entire presynaptic bouton with 1 μm diameter and 3.6 billion atoms, using modular building blocks to significantly reduce GPU memory requirements through instancing. We employ the Vulkan graphics API to maximize performance on consumer grade hardware and describe how to use the mmCIF format to efficiently store such giant models. An implementation is available as part of the YASARA molecular modeling and simulation program from www.YASARA.org. The free YASARA View program can be used to explore the presented models, which can be downloaded from www.YASARA.org/petworld, a Creative Commons platform for sharing giant biomolecular structures.

The Effect of ZnO on the Failure of PET by Environmental Stress Cracking.

The aim of the present work is to evaluate the effect of NaOH solution as a stress cracking agent on the thermal and tensile properties of PET and PET/ZnO composites. The solutions were applied during tensile testing and the effects were monitored by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and testing the actual mechanical properties. The rate of crystallization was increased when the samples were exposed to NaOH, as observed by both cold and melt crystallization; this is possibly due to the reduction in molar mass of the PET molecules caused by NaOH. During melting, the DSC peaks became more complex, which is probably due to the distinct macromolecular mass, as well as crystallites with different sizes and levels of perfection. According to TGA analyses, no drastic changes were observed on the thermal stability of PET due to the action of NaOH. The tensile properties were shown to decrease drastically upon exposure to NaOH, which is the main symptom of stress cracking, leading to increased fragility, as also observed in the scanning electron microscopy (SEM) images. The presence of ZnO improved PET crystallization and provided some protection against the harmful effects of NaOH.

Emission Spectrum Analysis of Two Typical Partial Discharge Forms Under High Frequency Square Wave Voltages

Although the increase in frequency improves the transmission efficiency of high-frequency transformer, a higher probability of insulation failure is caused by high-frequency partial discharges. Through a high-frequency experimental platform, emission spectrum tests on two types of insulation faults were carried out under high-frequency square wave voltages. Subsequently, the influence of frequency and voltage amplitude on the light intensity and the number of photons of emission spectrum caused by air corona were studied. Finally, the variation of the spectrum of the partial discharge occurring at the interface of gas-solid insulation with frequency was analyzed. The results show that, the characteristic spectrum of air corona is composed of the near-ultraviolet spectrum, which is caused by the energy level transition of N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> molecules, and the number of photons of air corona is positively correlated with voltage amplitude and frequency. Partial discharges at the gas-solid insulation interface have band spectrums in the visible light region and the near-infrared light region except for the near-ultraviolet spectrum due to the energy level transitions of outer layer electronics and the vibrations of C-H chemical bonds of PET molecules. This paper preliminarily verified the feasibility of applying the emission spectrum diagnostic method to two typical partial faults under high-frequency square wave voltages.

Development of PBT/Recycled-PET Blends and the Influence of Using Chain Extender

In this study, PBT/recycled-PET blends were developed using a twin-screw extruder. A commercial chain extender (Joncryl ADR 4468) was also used to melt mix with PBT/recycled-PET blend systems. Firstly, Joncryl at different loadings was extruded with recycled-PET to explore the influence of branching on melt behavior and crystallization of PET. The effect of blending recycled-PET with PBT on the final properties was then explored at different blending ratios (25w/75w, 50w/50w and 75w/25w). Similar blends were subsequently prepared while incorporating chain extender. Melt behavior, phase miscibility, crystallization behavior, solid viscoelastic properties, tensile and impact properties of the blends were eventually analyzed using differential scanning calorimeter (DSC), melt flow indexer (MFI), dynamic mechanical analyzer (DMA), and tensile and Izod notched impact testing, respectively. The results showed that the addition of chain extender increased the melt viscosity of PET and at the low contents enhanced the PET’s crystallization rate. On the other hand, the blends of PBT/recycled-PET are fully miscible in the amorphous region whereas the crystalline phases are immiscible subsequent to a fast cooling. The PBT and PET molecules could also co-crystallize and be fully miscible in crystalline phases upon slow cooling of the melt. Blending recycled-PET with PBT didn’t suppress the tensile properties of PBT, however it could enhance the PBT’s ductility and reduce its impact strength. The chain extender didn’t influence the mechanical properties much.

Effects of Modified Graphene Oxide on Thermal and Crystallization Properties of PET.

In this article, graphene oxide nanosheets grafted with low molecular weight poly(ethylene terephthalate) were in situ synthesized via carboxylation, acyl chlorination and grafting modification in order to improve the compatibility between GO and PET phases and enhance the thermal stability and crystallization properties of PET. Fourier Transform Infrared (FTIR), X-ray Photoelectron Spectroscopy (XPS), and Atomic Force Microscopy (AFM) characterization results demonstrated that LMPET chains have been successfully grafted onto the surface of GO. To further investigate the influence of modified GO on properties of PET, modified PET was prepared by incorporating the GL-g-LMPET nanofillers into the PET matrix using the melt-blending method. Due to the similar polarity and strong interaction between LMPET and PET molecules, GL-g-LMPET nanofillers were homogeneously dispersed in PET matrix. Thermal properties and crystallization properties of obtained nanocomposites were systematically characterized using Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), and Thermo Gravimetric Analysis (TGA). Results show that GL-g-LMPET nanofillers could improve the thermal stability of PET, e.g., increase up to 16.6 °C in temperature at the maximum rate of weight loss. In addition, the GL-g-LMPET also acts as an efficient nucleating agent for PET, exhibiting (1) higher crystallization temperatures; (2) higher degrees of crystallinity; and (3) faster rates of crystallization.

Ultrasound-Assisted Alkaline Hydrolysis of Waste Poly(Ethylene Terephthalate) in Aqueous and Non-aqueous Media at Low Temperature

This work demonstrates an attempt to depolymerize the waste poly(ethylene terephthalate) (PET) at low temperature using 20 kHz frequency ultrasound. Alkaline hydrolysis of PET was carried out in an aqueous as well as in methanolic medium. Ultrasound has shown a significant enhancement in the rate of alkaline hydrolysis of PET in methanol compared to an aqueous medium. The rate of alkaline hydrolysis of PET increases with an increase in the temperature and alkali concentration. PET conversion of 69% and 46% was observed with and without ultrasound, respectively, using 10% (w/w) sodium hydroxide (NaOH)-methanol solution at 50°C temperature in 60 min. Pure terephthalic acid was recovered from the PET and characterized using Fourier-transform infrared spectroscopy and acid number. The shrinking core model was proposed for the reaction mechanism with surface reaction as the rate of the controlling step. Kinetic analysis indicates almost equal activation energy and yet shows a significant difference in the frequency factor with and without ultrasound-assisted alkaline hydrolysis. Thus, ultrasound does not alter the intrinsic mechanism of PET hydrolysis. The reason for enhancement in the rate of reaction may be the ultrasound-induced micro-mixing and thereby the frequency of interaction between PET and NaOH molecules.

Looking for the key to secrets of RNA under the lamp-post.

Looking for the key to secrets of RNA under the lamp-post.

Effect of annealing and biaxial deformation on the dielectric properties of composites of multiwall carbon nanotubes and poly(ethylene terephthalate)

The dielectric properties of composites of poly(ethylene terephthalate) (PET) with MWCNTs were investigated over a wide frequency and temperature range below and close to the electrical percolation threshold. In composites with 1 wt.% multiwall carbon nanotubes (MWCNT) inclusions, the dielectric properties below room temperature are mostly determined by β relaxation, as a consequence of the rotation of PET molecules. In stretched samples, the CNTs are oriented at about 45 deg to the stretch direction. Such deformation increased the potential for molecular rotation. However, annealing after stretching increased homogeneity of the composite and decreased the potential barrier for polymer chain rotation. Electrical conductivity effects and Maxwell-Wagner polarization mostly cause the dielectric properties of the samples with 2% MWCNT inclusions. The potential barrier for carrier tunneling is lowest in the annealed sample.

Effects of carbon nanotube functionalization and annealing on crystallization and mechanical properties of melt-spun carbon nanotubes/poly(ethylene terephthalate) fibers

Abstract To generate poly(ethylene terephthalate) (PET) fibers with enhanced mechanical properties, we prepared melt-spun PET fibers that incorporated pristine, acid-treated, and functionalized multi-walled carbon nanotubes (MWNTs) with 2-phenylethyl alcohol and 4-phenyl-1-butanol. The incorporation of MWNTs into the melt-spun fibers resulted in increased crystallization of PET but lower breaking stress than that of pure PET fibers, even in those containing well-dispersed functionalized MWNTs. The breaking stress of drawn composite fibers was also lower than that of pure PET fibers prepared at the same draw ratio. However, the annealing of melt-spun fibers enhanced the mechanical properties and crystallization, and the annealing effect was more dominant for composite fibers with functionalized MWNTs. These findings indicate that the presence of well-dispersed MWNTs disturbs the crystallization and orientation of PET molecules in highly stressed fibers, which differs from MWNT-induced crystallization of PET molecules in relaxed fibers.

Effects of preform deformation behavior on the properties of the poly(ethylene terephthalate) bottles

AbstractPlastics bottles made out of poly(ethylene terephthalate) (PET) are usually produced by injection stretch blow molding. Optimization of the process parameters is necessary to achieve bottles with adequate top load and burst strength. However, doing so experimentally is time‐consuming and costly. To overcome this difficulty, simulation packages based on finite element analysis methods have been developed. In this study, process optimization of a 350‐mL PET fruit juice bottle was carried out by means of BlowView and ANSYS simulation packages. BlowView was used for the ISBM process simulation and ANSYS for structural analysis of the bottles. The bottles were produced under different process conditions where the timing of the stretch rod movement was varied in relation to the activation of the blow pressure. The simulation results obtained through the both simulation packages were compared with experimental results. It was found that bottles of highest quality were produced if the sequencing of axial stretching and radial inflation results in simultaneous biaxial deformation of the preform. Truly biaxial orientation of PET molecules improved both top‐load and burst resistances of the bottles. The structural simulation studies performed by the ANYSYS simulation package validated most of our experimental findings. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Stress cracking and chemical degradation of poly(ethylene terephthalate) in NaOH aqueous solutions

AbstractStress cracking is one of the most frequent causes of premature failure of polymers, affecting also engineering polymers like PET. In this work, the stress cracking behavior of injection moulded PET was investigated using sodium hydroxide (NaOH) aqueous solutions in various concentrations as active fluids. The application of mechanical load to the sample bars was done in a tensile testing machine, using the ordinary tensile test and also a relaxation procedure. The results showed that all NaOH solutions were aggressive stress cracking agents for PET, reducing mechanical properties and causing catastrophic failure with a significant surface damage. The occurrence of hydrolysis reactions was also observed when NaOH solutions were applied in combination with tensile loads, causing a reduction in molar mass of PET molecules. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Changes in HER2 expression in breast cancer xenografts after therapy can be quantified using PET and (18)F-labeled affibody molecules.

In vivo imaging of human epidermal growth factor receptor type 2 (HER2) expression may allow direct assessment of HER2 status in tumor tissue and provide a means to quantify changes in receptor expression after HER2-targeted therapies. This work describes the in vivo characterization of the HER2-specific N-2-(4-(18)F-fluorobenzamido)ethyl]maleimide ((18)F-FBEM)-Z(HER2:342) Affibody molecule and its application to study the effect of 17 (dimethylaminoethylamino)-17-demethoxygeldanamycin (17-DMAG) on HER2 expression by PET. To assess the correlation of signal observed by PET with receptor expression, we administered the tracer to athymic nude mice bearing subcutaneous human breast cancer xenografts with different levels of HER2 expression. To study the downregulation of HER2, we treated the mice with 4 doses (40 mg/kg) of 17-DMAG, an inhibitor of heat-shock protein 90, known to decrease HER2 expression. The animals were scanned before and after treatment. After the last scan, the mice were euthanized and tumors were frozen for receptor analysis. The tracer was eliminated quickly from the blood and normal tissues, providing high tumor-to-blood and tumor-to-muscle ratios as early as 20 min after injection. The high-contrast images between normal and tumor tissue were recorded for BT474 and MCF7/clone18 tumors. Low but still detectable uptake was observed for MCF7 tumors, and none for MDA-MB-468. The signal correlated with the receptor expression as assessed by immunohistochemistry, Western blot, and enzyme-linked immunosorbent assay. The levels of HER2 expression estimated by post-treatment PET decreased 71% (P < 4 x 10(-6)) and 33% (P < 0.002), respectively, for mice bearing BT474 and MCF7/clone18 tumors. These changes were confirmed by the biodistribution studies, enzyme-linked immunosorbent assay, and Western blot. Our results suggest that the described (18)F-FBEM-Z(HER2:342) Affibody molecule can be used to assess HER2 expression in vivo by PET and monitor possible changes of receptor expression in response to therapeutic interventions.

Stress cracking e ataque químico do PET em diferentes agentes químicos

A análise de resistência ao stress cracking (ESCR) do PET foi feita em corpos de prova de tração moldados por injeção, utilizando vários agentes químicos (metanol, etanol, propanol, butanol e soluções de hidróxido de sódio em diferentes concentrações). Foram realizados ensaios dinâmicos e estáticos de tração. Durante os testes os corpos de prova foram mantidos em contato com os agentes e as propriedades mecânicas monitoradas. Os resultados evidenciam que todas as soluções de hidróxidos de sódio testadas são agentes agressivos de ESC por diminuírem as propriedades mecânicas do polímero, ocasionando falha catastrófica. Já os demais fluidos, apesar de não terem efeito significativo nas propriedades do PET, afetam drasticamente sua aparência superficial. Observou-se também a ocorrência de ataque químico nos ensaios com NaOH, resultando em redução nas massas molares.

Effect of interaction between poly(ethylene terephthalate) and carbon nanotubes on the morphology and properties of their nanocomposites

AbstractPoly(ethylene terephthalate) (PET) nanocomposites were prepared by melt‐extruding mixtures of PET and functionalized multiwalled carbon nanotubes (MWNTs) with some interaction with PET molecules. For the functionalization of MWNTs, benzyl isocyanate and phenyl isocyanate with different molecular flexibility were employed on the surface of the MWNTs via chemical modification, respectively. The reaction for functionalization of MWNTs was confirmed by FTIR and transmission electron microscopy (TEM) measurements. TEM observations indicated that both benzyl and phenyl isocyanate groups covered the surface of the MWNTs after functionalization. The PET nanocomposites containing isocyanate groups showed improved mechanical properties, including the tensile strength and tensile modulus, compared with those with pristine and acid‐treated nanotubes. These improvements were ascribed to π–π interactions between the aromatic rings of PET molecules and the isocyanate group in MWNTs. The functionalized MWNTs showed a better dispersion of carbon nanotubes in the matrix polymer and a different fractured cross‐section morphology in scanning electron microscope measurements relative to the pristine MWNTs. The crystallinity of the functionalized MWNT‐PET nanocomposites was significantly higher than that of the pristine and acid‐treated MWNTs. FTIR results indicated that the presence of carbon nanotubes induced trans‐conformation of PET chains, and trans conformation was particularly dominant in PET composites incorporating MWNT‐phenyl. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 900–910, 2008

Effect of A-zeolite on the crystallization behavior ofIn-situ polymerized poly(ethylene terephthalate) (PET) nanocomposites

The crystallization behavior and fine structure of poly(ethylene terephthalate) (PET)/A-zeolite nanocomposites were assessed via differential scanning calorimetry (DSC) and time-resolved small-angle X-ray scattering (TR-SAXS). The Avrami exponent increased from 3.5 to approximately 4.5 with increasing A-zeolite contents, thereby indicating a change in crystal growth formation. The rate constant,k, evidenced an increasing trend with increases in A-zeolite contents. The SAXS data revealed morphological changes occurring during isothermal crystallization. As the zeolite content increased, the long period and amorphous region size also increased. It has been suggested that, since PET molecules passed through the zeolite pores, some of them are rejected into the amorphous region, thereby resulting in increased amorphous region size and increased long period, respectively. In addition, as PET chains piercing into A-zeolite pores cannot precipitate perfect crystal folding, imperfect crystals begin to melt at an earlier temperature, as was revealed by the SAXS profiles obtained during heating. However, the spherulite size was reduced with increasing nanofiller content, because impingement between adjacent spherulites in the nanocomposite occurs earlier than that of homo PET, due to the increase in nucleating sites.

Formation of micro-crystals in poly(ethylene terephthalate) fiber by a short heat treatment and their influence on the mechanical properties

The morphological change of poly(ethylene terephthalate) (PET) fibers by a short heat treatment under free-to-relax condition (i.e., without mechanical constraints imposed on the fibers during the treatment) was investigated. Heat treatment on polymeric fibers, in particular free-to-relax condition, has been known to lower the initial elastic modulus due to the relaxation of the amorphous molecules; however a short heat treatment at 190 °C for 1.2 s in the present study increased the initial modulus, whereas the yield strength was decreased significantly. During the short heat treatment, the PET molecules in the PET fibers were relaxed and became crystallized to some extent. The PET chains in the amorphous regions were also relaxed, promoting the formation of micro-crystals. These micro-crystals in the amorphous region can explain the increase in the initial modulus. The mechanism for such unusual behavior was investigated using mechanical tests, thermal stress analysis, wide and small angle X-ray diffraction, and FTIR spectrum analysis. Furthermore, a morphological model for the molecular arrangements in the PET fibers due to the short heat treatment is proposed, offering the possibility of developing PET fibers with shape retention function that can behave similarly to metal fibers.