Crystallization Of PET Research Articles

Change in Concentration of Amorphous Region Due to Crystallization in PTT/PET Miscible Blends.

In a miscible crystalline/crystalline blend of poly(trimethylene terephthalate) (PTT) and poly(ethylene terephthalate) (PET), the PET spherulites grew at 240 °C when the PTT content was 30 wt% or less. The growth rate of PET spherulites decreased with time due to the exclusion of PTT from the growth front of PET spherulites into the amorphous region, resulting in a three-stage crystallization process. Due to the exclusion, the spherulite growth stopped before the volume filling of the PET spherulites, causing the formation of an excluded PTT amorphous region. When the temperature was lowered from 240 °C to 210 °C, the PTT spherulites grew in the excluded PTT amorphous region. The spherulite growth rate of PTT in the excluded PTT amorphous region was equivalent to that of a blend of 60-70 wt% PTT in 30/70 PTT/PET. These results suggest a significant change in the PTT concentration in the amorphous region, from the initial PTT content of 30 wt% to 60-70 wt%, due to the exclusion of PTT during the melt crystallization of PET at 240 °C.

Prediction of tensile modulus based on parameters of crystalline structure in polyethylene terephthalate with cold crystallization ability

This work aims to adopt a simple modulus prediction method for the crystalline poly(ethylene-terephthalate) (PET), which has strong cold-crystallization ability. Based on a single melting curve generated by calorimetry, crystallinity and average melting temperature can easily be evaluated and consequently, tensile modulus can be predicted. Nonetheless, in the case of polymers with cold crystallization behavior, such as PET, the melting process is affected by cold crystallization, impeding the simple calculation of the aforementioned important parameters. In this paper, the techniques to eradicate cold crystallization during calorimetry are presented. Accordingly, the results of a tensile modulus prediction model are presented and discussed. The crystallization and melting characteristics of PET were measured by differential scanning calorimetry (DSC). The mechanical properties of the specimens were estimated by standardized tensile tests. The specimens, which were used for mechanical tests were fabricated using conventional injection molding. The samples were annealed at different temperatures in order to obtain different crystalline structures. The results clearly indicate that the prediction technique is capable to describe the tensile modulus of PET accurately in the case of very diverse crystalline structures.

Rapid Crystallization and Fluorescence of Poly(ethylene terephthalate) Using Graphene Quantum Dots as Nucleating Agents.

In this study, graphene quantum dots (GQDs) with a diameter of ~3 nm were successfully synthesized and incorporated into a poly(ethylene terephthalate) (PET) matrix to fabricate PET/GQDs nanocomposites. The impact of GQDs on the crystallization and thermal stability of the PET/GQDs nanocomposites was investigated. It was observed that the addition of only 0.5 wt% GQDs into the nanocomposites resulted in a significant increase in the crystallization temperature (peak temperature) of PET, from 194.3 °C to 206.0 °C during the cooling scan process. This suggested that an optimal concentration of GQDs could function as a nucleating agent and effectively enhance the crystallization temperature of PET. The isothermal crystallization method was employed to analyze the crystallization kinetics of the PET/GQDs nanocomposites, and the data showed that 0.5 wt% GQDs significantly accelerated the crystallization rate. Furthermore, the incorporation of GQDs into the PET matrix imparted photoluminescent properties to the resulting PET/GQDs nanocomposites. The PET crystals with GQDs as crystal nuclei and the crazes caused by defects played a vital role in isolating and suppressing the concentration quenching of GQDs. This effect facilitated the detection of defects in PET.

Strain induced crystallization of PET under biaxial conditions. From laboratory tests to injection stretch-blow molding

Conventional biaxial testing and free stretch blow molding (ISBM) of preforms were conducted in parallel to analyze the biaxial behavior of PET and the resulting strain-induced crystallization (SIC) under bi-axial conditions. Stretch blowing has promoted complex loading paths combining most of the simple paths used at the laboratory scale, which are analyzed locally using marked preforms. The time-temperature superposition principle is shown to apply under biaxial conditions up to high strain, which has facilitated the definition of experimental sets and mechanical comparisons. X-ray diffraction was used to analyze the crystal microstructure and texture. In ISBM, the texture is not a simple image of the final deformation state in terms of orientation. The organized phase that is induced is probably an imperfect crystal capable of evolving in time and the strain hardening under biaxial conditions could be a gradual phenomenon as in uniaxial stress. A scenario is proposed.

Remarkably enhanced crystallization behavior and impact toughness of poly(ethylene terephthalate) via introducing phenyl–terminated hyperbranched polyester

Rigid benzene ring structure on the backbone of poly(ethylene terephthalate) (PET) results in its slow crystallization rate. In present work, we proposed to incorporate a versatile nucleating agent with the combination of efficient heterogeneous nucleation and promoting crystal growth. Herein, phenyl–terminated hyperbranched polyester (HBP-Bz) was introduced. Polarized optical microscopy and differential scanning calorimetry results showed that HBP-Bz demonstrates superior heterogeneous nucleation effect. The crystallization temperature of PET is increased by nearly 20 K with the addition of 1% HBP-Bz. The main reason for HBP-Bz to accelerate PET crystallization is to increase the nucleation rate and density, and further increase in HBP-Bz content is favorable for the elevation of crystal growth rate of PET. A possible crystallization promotion mechanism of HBP-Bz on PET was proposed on the basis of dynamic viscoelasticity analysis. Moreover, effectively improved crystallinity and refined spherulites lead to remarkable elevation in mechanical properties especially the toughness.

Influence of the Presence of Poly(butylene succinate) in the Poly(ethylene terephthalate) Recycling Process

Poly(butylene succinate) (PBS) is one of the contaminants in the Poly(ethylene terephthalate) (PET) recycling process. It is known that high contents of PBS in PET significantly reduce PET properties, but the effect of low contents on PET has yet to be studied. This work studied the influence of low contents of PBS on recycled PET. Five formulations of PBS in PET were prepared, and the properties of relative affinity, mechanical, thermal, and disintegration under composting conditions were assessed. The solubility parameter indicated that PET and PBS are miscible. However, FESEM images show slight marks of immiscibility, and the mechanical characterization results showed that PBS, even in low contents, reduced the mechanical properties of recycled PET, which proves that the materials are not miscible in the studied contents. The DSC results indicated that PBS could not be quickly detected in PET. However, its presence can be inferred by the reduction in PET crystallization degree. Finally, the presence of PBS up to 15 wt.% does neither affect the disintegration under composting conditions nor the thermal stability of recycled PET. The drop in mechanical properties shows that PBS must be removed from the PET waste stream to preserve the quality of the material.

Interfaces generation via severe plastic deformation – A new way to multiple shape memory polymer composites

Shape memory materials are classically described as a combination of switching and permanent domains for shape switching and shape recording, respectively. It is assumed that the interfaces between immiscible polymers could play a dual role - switching and permanent structural elements. In this work, we use severe plastic deformation as a method providing the formation of the interphases during the integration of thermodynamically immiscible polymers. By severe plastic deformation a composite gets much richer in interfaces than that obtained by melt blending. It can be used to produce effective multi-shape memory composites. A pair of immiscible polymers - acrylonitrile-butadiene-styrene copolymer (ABS) and poly(ethylene terephthalate) (PET) subjected to severe plastic deformation resulted in ABS/PET composite rich in interfaces with a broad glass transition. Strong plastic deformation by equal channel multi-angle extrusion resulted in the formation of large amount of intimate contact layers of ABS and PET and in strain-induced PET crystallization. Thermomechanical programming of such material rich in interfaces enabled a dual and triple shape memory with exceptional parameters.

Development of order during strain induced crystallization of polymers, case of PET

This study aims at enlightening the kinetics and the nature of the precursor for crystallization in strain induced crystallization (SIC) of PET, combining ex situ and in situ X-ray diffraction on well controlled tensile experiments. Attention is paid too to annealing to assess “stability” of the phases that are generated. It is concluded that SIC in PET consists in the appearance of ordered entities the periodicities of which are those of crystal. Strain hardening corresponds to perfectioning without leading to actual crystal under tension. The kinetics of formation can be directly related to the stress, whatever the set on tensile conditions (temperature, strain rate). However, microstructure of PET can evolve after loading in case of annealing.

Characterization of Using Infused PLA for 3D Printed Radiation Shielding

Abstract 3D printing has been integrated in various applications in biomedical and medical imaging. A prominent new field is that of radiation protection and shielding, where the introduction of infused filaments makes it possible to manufacture customized 3D printed shielding. In this study we examine the use of a Polylactic Acid (PLA) infused with tungsten to shield a Positron Emission Tomography / Computer Tomography (PET/CT) scanner. The goal is to reduce the effects of the radiation emitted from outside the field-of-view (FOV) on the PET image and to protect the PET electronics against the X-rays from the CT. The shielding properties were examined using the radioactive sources Ba-133, Na-22, and Cs-137, as well as two X-ray sources with energy ranging from 20 to 125 kV. For X-rays below 40 kV, less than 1 cm of the tungsten infused shielding was sufficient to block more than 95% of the X-ray beam intensity. However, only around 30% of the 511-keV rays from Na-22 was attenuated by 3.5 cm of the 3D printed material. Our results support the application of tungsten infused PLA materials to shield the PET electronics. However, further studies are required to determine if shielding the PET crystals with tungsten infused PLA can improve image quality by reducing the contribution of scattered rays from outside the FOV. Additionally, our results show new possibilities for the use of infused filament in the field of Xray imaging. For example, where lead coverings or skirts are excessively bulky or rigid, it could be employed to optimize shielding for radiation-sensitive organs.

Synergistic effect of organic-Zn(H2PO2)2 and lithium containing polyhedral oligomeric phenyl silse-squioxane on flame-retardant, thermal and mechanical properties of poly(ethylene terephthalate)

Abstract A novel synergy flame retardant system of poly(ethylene terephthalate) (PET)/organic-Zn(H2PO2)2/lithium containing polyhedral oligoheptyl silse-squioxane (Li-Ph-POSS) composites was prepared by the melt-blending method to improve the flame retardancy of PET. The synergistic effect of organic-Zn(H2PO2)2 and Li-Ph-POSS on the flame retardancy, thermal, and mechanical properties of the PET composites was investigated by the limiting oxygen index, vertical burning test, cone calorimeter, thermogravimetric analysis, differential scanning calorimeter, tensile tester, and dynamic mechanical analysis, respectively. The results show that the synergistic flame retardant effect between organic-Zn(H2PO2)2 and Li-Ph-POSS improves both the flame retardancy and the crystallization of PET. Moreover, the Li-Ph-POSS has a positive effect on the mechanical property of PET. This work provides a promising strategy for mitigating the fire hazard of PET using this synergy flame retardant system.

Enhanced crystallization and properties of poly(ethylene terephthalate) nanocomposites with zeolites from 3D to 2D topologies

To improve the low crystallization rate and long molding cycle of Poly(ethylene terephthalate) (PET), series of PET nanocomposites incorporated small quantities of zeolites with different topologies were blended by melt compounding. The nucleation influence of 3-dimensional zeolites Y, ZSM-5 and 2-dimensional zeolite MCM-22P on the crystallization manner of PET was analyzed by non-isothermal and isothermal crystallization, quantitative evaluation of nanoparticle dispersion and morphology of nanoparticles. The results show that all PET/zeolite nanocomposites exhibit higher crystallization temperature and faster crystallization rate than PET due to large specificsurfacearea of zeolites and their superior dispersion in the PET matrix. Among them, PET/MCM-22P nanocomposites remarkably improved the crystallization behavior, thermal stability and oxygen barrier properties, which is related to the layered morphology of MCM-22P and hydrogen bond interactions between MCM-22P and PET. It is revealed that MCM-22P can provide more heterogeneous nucleation sites for PET by exfoliation in melting compounding. Furthermore, the nucleation mechanism induced by MCM-22P was investigated by the means of Mozhishen method, Avrami equation and theory of Hoffman-Lauritzen. The results indicate that the incorporation of MCM-22P can decrease the free energy of nucleation and fold surface in PET crystallization process, thus improving the crystallinity.

Improve the compatibility and crystallization ability of polyhedral oligomeric silsesquioxanes and poly (ethylene terephthalate) by using transesterification method

AbstractIn the present study, an investigation was conducted on the effects of polyhedral oligomeric silsesquioxane (POSS) on the mechanical, morphological, and thermal properties of PET‐based nanocomposites. When the epoxy groups reacted with the PET end groups, the transesterification catalyst zinc acetylacetonate was introduced to facilitate the reaction between PET matrix and EPOSS. As clearly observed in the SEM image, 3 wt% POSS was added to PET matrix, the size of POSS particles was lower than 50 nm. As revealed from the EDX spectrum, the silicon signal was located in the EPOSS agglomerated particles and exhibited an even distribution in the entire PET matrix, which demonstrated a unique dispersion. Furthermore, it was reported that EPOSS exhibited nucleating agent performance, which suggested the higher temperature for melting crystallization (Up to 205.6°C while neat PET only reached 194.3°C). On the whole, EPOSS was revealed to act as a nucleating agent, whereas it could significantly facilitate the crystallization of PET by expediting the nucleation. Moreover, it could, to a certain extent, improve the mechanical properties of PET. These findings were attributable to the fact that PET and EPOSS exert a more comprehensive interface effect and a higher dispersion effect through the transesterification reaction.

High throughput software-based gradient tree boosting positioning for PET systems

The supervised machine learning technique Gradient Tree Boosting (GTB) has shown good accuracy for position estimation of gamma interaction in PET crystals for bench-top experiments while its computational requirements can easily be adjusted. Transitioning to preclinical and clinical applications requires near real-time processing in the scale of full PET systems. In this work, a high throughput GTB-based singles positioning C++ implementation is proposed and a series of optimizations are evaluated regarding their effect on the achievable processing throughput. Moreover, the crucial feature and parameter selection for GTB is investigated for the segmented detectors of the Hyperion IID PET insert with two main models and a range of GTB hyperparameters. The proposed framework achieves singles positioning throughputs of more than 9.5 GB/s for smaller models and of 240 MB/s for more complex models on a recent Intel Skylake server. Detailed throughput analysis reveals the key performance limiting factors, and an empirical throughput model is derived to guide the GTB model selection process and scanner design decisions. The throughput model allows for throughput estimations with a mean absolute error (MAE) of 175.78 MB/s.

2D X-ray diffraction and molecular modelling of the crystalline structure of polyesters under uniaxial stress

Studying the crystalline structure of uniaxially and biaxially drawn polyesters is of great importance due to their wide range of applications. In this study, we shed some light on the behaviour of PET and PEN under uniaxial stress using experimental and molecular modelling techniques. Comparing experiment with modelling provides insights into polymer crystallisation with extended chains. Experimental x-ray diffraction patterns are reproduced by means of models of chains sliding along the c-axis leading to some loss of three-dimensional order, i.e. moving away from the condition of perfect register of the fully extended chains in triclinic crystals of both PET and PEN. This will help us understand the mechanism of polymer crystallisation under uniaxial stress and the appearance of mesophases in some cases as discussed herein.

Inducing nano-confined crystallization in PLLA and PET by elastic melt stretching.

Based on the widely studied poly(l-lactic acid) (PLLA) and polyethylene terephthalate (PET) that are brittle in their fully crystalline form, this Letter shows that they can be made to be super ductile, heat resistant and optically clear by creating nano-sized crystals while preserving the entanglement network. Atomic force microscopic images confirm the perceived nano-confined crystallization. Time-resolved X-ray scattering/diffraction measurements reveal the emergence of cold crystallization during either stress relaxation from large stepwise melt-stretching or annealing of pre-melt-stretched PLLA and PET above Tg. Mechanical tests show that these polymers in such a new state are rigid even well above Tg, e.g., at 100 °C.

Effect of nucleating agents on the non‐isothermal crystallization and degradation kinetics of poly(ethylene terephthalate)

Poly(ethylene terephthalate) (PET) was synthesized by two steps, namely (a) transesterification and (b) polycondensation. Various analytical instruments were used for the characterization of neat PET. The sodium salt of nucleating agents added with PET was synthesized by the in‐situ method under the same experimental conditions. The influence of CO2Na, ONa, SO3Na, PO3Na on the crystallization properties of PET was tested. The aromatic SO3Na nucleated PET exhibited the highest crystallization temperature (Tc) value of 211.4°C with the degradation temperature (Td) value of 446.9°C. The energy of activation (Ea) for the degradation and crystallization of PET was determined using various kinetic models. The modified Avrami equation showed the 3D crystal growth of PET, which was further evidenced by polarized optical microscopy (POM). The second stage of degradation consumed a higher amount of thermal energy. The experimental results were compared with the literature values.

A new analytical protocol for high precision U–Th–Pb chemical dating of xenotime from the TTG gneisses of the Bundelkhand Craton, central India, using CAMECA SXFive Electron Probe Micro Analyzer

Xenotime is a significant accessory mineral which is being extensively used for precise U–Th–Pb geochronology by Electron Microprobe Analysis (EPMA). This paper presents a protocol for high analytical precision (<3% uncertainties on the measured ages) developed for the accurate estimation of U–Th and Pb content in xenotime using SXFive EPMA at the Department of Geology, Banaras Hindu University, by deploying five spectrometers attached with TAP, LIF, LPET, LTAP and PET crystals. The protocol is applied to the xenotime grains of tonalite-trondhjemite-granodiorite-gneiss (TTG) rocks from the geochronologically well-constrained terrain of the Bundelkhand Craton, central India. The obtained xenotime age 2929±23 Ma of TTGs is in agreement with the earlier published Neoarchaen 2697±3 Ma Pb–Pb zircon ages from the same area which validates the authenticity of the analytical method developed at the BHU-EPMA facility.

Carbon particulate and controlled-hydrolysis assisted extrusion foaming of semi-crystalline polyethylene terephthalate for the enhanced thermal insulation property

This work presents a facile method to produce low-density PET foams using pristine semi-crystalline resin by moisture-induced controlled-hydrolysis in a tight processing window (moisture content ∼ 0.12 wt.%). We investigated the effect of moisture and moisture containing activated carbon (AC) on the foam expansion ratio, cell morphology, and PET resin degradation and crystallization properties. Controlled-hydrolysis increased the melt-flow rate of PET resin (intrinsic viscosity: 0.52 to 0.54 dL/g) without losing crystallinity, and thus the PET foams possess better tensile properties (∼2 MPa stress and ∼100% strain) and higher thermal stability (&gt;200°C) than chemically modified PET foams. The foam density could be made as low as ∼ 0.15 g/cm3 using a lab scale twin-screw extruder. A strand array die was also designed to produce plate-shaped foam samples. AC allowed easier control of the moisture content and delayed resin degradation in extrusion. Both AC and micrographite (mGr) could stabilize the PET foam morphology in extrusion and serve as good infrared attenuation agents (IAAs) in a simulated housing thermal insulation experiment.

Phosphonated Poly(ethylene terephthalate) ionomers as compatibilizers in extruded Poly(ethylene terephthalate)/Poly(m-xylylene adipamide) blends and oriented films

Blends of poly(ethylene terephthalate) (PET) and poly(m-xylylene adipamide) (MXD6) were successfully compatibilized by using a phosphonated PET ionomer in the Na+ form (Na+-PPET) as a compatibilizer. The compatibilized 90:10 (by weight) polyester/polyamide blends containing various amounts of the phosphonated polyester were prepared by melt mixing in a twin-screw extruder. Scanning electron microscopy (SEM) revealed that the extruded blends contained spherical MXD6 domains dispersed in the PET matrix. The phase-separated MXD6 domain size decreased with increasing ionic monomer concentration, and the efficient compatibilization was attributed to specific interactions between the ionic phosphonate groups on the Na+-PPET ionomer and the amide linkages of MXD6. Thermal analysis suggested that the small MXD6 domains nucleated the crystallization of PET upon cooling as indicated by a shift of crystallization temperature of PET to higher temperatures. Furthermore, the specific interactions appeared to inhibit crystallization of MXD6. Biaxial orientation of melt processed films of the blends with a draw ratio of 3 × 3 transformed the spherical MXD6 domains into high aspect ratio platelets that were oriented in the plane of the film. Compared to the uncompatibilized base blends, optical property characterization on the oriented films revealed a decreased haziness by 56% and an improved transparency by 35% with 0.22 mol% of phosphonated ionic monomers incorporated in the polyester component. Moreover, a 33% decrease in oxygen permeability was found for the oriented Na+-PPET/PET/MXD6 blend composition containing 0.11 mol% of phosphonated monomers.

Crystallization behaviors of poly(ethylene terephthalate) (PET) with monosilane isobutyl-polyhedral oligomeric silsesquioxanes (POSS)

The crystallization behaviors of poly(ethylene terephthalate) (PET) with monosilane isobutyl-polyhedral oligomeric silsesquioxanes (POSS) were investigated in detail. It is observed that POSS acts as an effective nucleating agent under appropriate concentration in the PET system. Polarized optical microscopy (POM) results showed that POSS improved the nucleation density of PET. Besides, the transmission electron microscopy (TEM) observation demonstrated POSS dispersed mostly at the nanometer scale throughout the PET matrix. The crystal structures of POSS and PET/POSS were analyzed using wide-angle X-ray diffraction (WAXD). Moreover, non-isothermal crystallization kinetics of PET and PET/POSS were studied using Mo’s method. The PET/POSS system demonstrated the lower value of F(T) than pure PET, indicating that the lower cooling rate was required to attain a specified relative crystallinity for the system. The comparison of the crystallization activation energy (ΔE) showed that the POSS nanoparticles improved the crystallization of PET through an acceleration of the nucleation process. Furthermore, the isothermal crystallization behaviors were also investigated using classic Avrami method. Overall, POSS can act as a nucleating agent and greatly improve the crystallization of PET through accelerating the nucleation process.