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Isothermal crystallization kinetics of poly(ethylene terephthalate)s of different molecular weights
Abstract
The isothermal crystallization kinetics and morphology of poly(ethylene terephthalate) (PET) polymers of different molecular weights have been studied by means of differential scanning calorimetry and transmission microscopy (TM). The kinetic parameters of Avrami exponent n, the rate constant k, half time t
1/2, rate at 50 % crystallinity, τ
1/2 for crystallization of different PETs were evaluated from double logarithmic plots of log {−ln[1 − X(t)]} versus log t, where X(t) is extent of crystallinity at a given crystallization temperature. The crystallization rate of polymers with high molecular weight found to be lower than that of polymers with low molecular weight, at the same crystallization temperature. It was found that the nucleation mechanism and growth dimension of polymers with low molecular weight are different from those of polymers with high molecular weight. The results of TM and isothermal crystallization kinetics showed a consistent trend for the crystallization of all PET polymers studied, comprising a primary stage and a secondary stage. The activation energy in the PET polymers of low molecular weight was found to be lower than that of polymers with high molecular weight.
... 15 We found that the conventional PET pretreatment method using the extruder reduced the molecular weight of PET, 43,44 and the low molecular weight PET tended to recrystallize. 45 To avoid this situation, oven melting was used to pretreat the PET substrate. GPC and DSC analysis showed that our pretreated PET powder had an average molecular weight of 22.2 kDa, which was similar to that of recycled PET (RPET, 24.5 kDa) and twice higher than that of extruded PET (11.5 kDa). ...
Poly(ethylene terephthalate) (PET) is the most abundant polyester plastic and is causing serious environmental pollution. Rapid biological depolymerization of PET waste at large scale requires powerful engineered enzymes with excellent performance. Here, we designed a computational strategy to analyze the ligand affinity energy of enzymes to PET chains by molecular docking with the dynamic protein conformations, named Affinity analysis based on Dynamic Docking (ADD). After three rounds of protein engineering assisted by ADD, we drastically enhanced the PET-depolymerizing activity of leaf-branch-compost cutinase (LCC). The best variant LCC-A2 depolymerized >90% of the pretreated, post-consumer PET waste into corresponding monomers within 3.3 h at 78 °C, and over 99% of the products were terminal depolymerization products (terephthalic acid and ethylene glycol), representing the fastest PET depolymerization rate reported to date in the bioreactor under optimal conditions. Structural analysis revealed interesting features that improved the ligand affinity and catalytic performance. In conclusion, the proposed strategy and engineered variants represent a substantial advancement of the biological circular economy for PET.
... These qualities make it to be one of the most demanded and broadly used semi-crystalline thermoplastic polyesters with applications in the fields of beverage bottles, packaging, textiles. There have been wide investigations on crystallization kinetics and the effect of crystallization on tensile properties of PET [30][31][32][33]]. Yet, not many studies have been reported that examine the kinetics and mechanisms of cold crystallization and scarcely any study has been seen by the present authors that investigates the effect of cold crystallization kinetics on the prediction of mechanical properties. ...
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.
... This indicates that the H-PET component of the bicomponent filaments contributes to the neck melting peak and the L-PET component to the main melting peak. This is because H-PET has a higher molecular weight, hence it is more difficult to crystallise than L-PET [21][22][23]. As a result, the L-PET component has a low-orientation, high crystallisation supramolecular structure, while the H-PET component has a high orientation and low crystallisation structure in the bicomponent filaments. ...
Self-crimp side-by-side bicomponent filaments (SBSBFs) were prepared via melt spinning using two kinds of polyethylene terephthalate (PET) with great disparity of intrinsic viscosity. The influence of the volume ratio on the surface morphology, crystallinity, crimping properties, mechanical properties and shrinkage properties of the bicomponent filaments was investigated using wide-angle X-ray diffraction, a differential scanning calorimetry (DSC), scanning electron microscope, etc. As the proportion of the low-viscosity component increases, the shrinkage in boiling water or hot air, as well as the shrinkage force and the sonic orientation factor of the bicomponent filaments decrease, and the DSC heating curves change from double peaks to a single peak. These phenomena should be ascribed to the high orientation and low crystallinity of the high-viscosity PET component and low orientation and high crystallinity of the low-viscosity PET component. Moreover, the crimp property of the bicomponent filament with a volume ratio of 50:50 is superior to those with other volume ratios.
... The kinetics of the isothermal crystallization process was studied by Zheng et al. [20] and by Zendehzaban and Shamsipur [21]. Research has shown that increasing the aging temperature significantly affects the quality of crystallites as well as the melting point. ...
The influence of the thermo-oxidative aging semi-crystalline polyethylene terephthalate process on the thermal and mechanical properties was analysed in the article. For this purpose, PET was aged at 140 °C for 21, 35 and 56 days. The research showed that as a result of aging, the amount of the crystalline phase increases by about 8%, which translates into the properties of the aged material. The glass transition and melt temperature of lamellar crystals formed during first and second crystallisation increase with aging. The mechanical properties of the material were analysed in the temperature range of 25 to 75 °C. The tests were showing an increase in Young's modulus and a decrease in elongation at the break as a result of aging. This phenomenon was particularly visible during tests at 75 °C and during the morphological observation of the fracture surface, where the fracture character of the material changes from ductile to brittle. In the case of the material aged for the longest time, the temperature has a negligible influence on the elongation at break.
... In addition, there are a few related studies on the effect of the increased molecular weight with trifunctional chain extenders on the crystallization, flow, and mechanical property of PET. 34,35 Therefore, in this study, the chain-extending products of PET with different molecular weights were prepared by the chemical chain-extending method using isocyanate trimer as a chain extender. The effect of chainextending PET with different molecular weights on the crystallization and mechanical properties was studied by using a differential scanning calorimeter, X-ray diffractometer, polarizing microscope, and universal testing machine. ...
In this work, poly(ethylene terephthalate) (PET) chain-extending products with different molecular weights were prepared by reactive extrusion using isocyanate trimer (C-HK) as the trifunctional chain extender. The effect of the chain extender C-HK on the intrinsic viscosity, melt flow property, crystallization behavior, crystallization morphology, and mechanical property of PET was investigated. The results showed that when the content of the chain extender was increased from 0.6 to 1.4 wt%, the viscosity average molecular weight of PET was effectively increased from 2.36 × 10⁴ to 5.46 × 10⁴ g·mol–1. After the chain extending, the crystallinity and the time of semicrystallization of PET were significantly decreased. After the isothermal crystallization at 220 °C for 5 min, the spherulites formed by pure PET became larger. With the increase in molecular weight of PET after chain extension, its spherulite size was significantly decreased without changing the crystalline structure. The chain-extended PET also exhibited more excellent bending-resistant and impact-resistant properties. While the tensile strength of PET after chain extension was slightly decreased, the bending strength was increased by a maximum value of 56.8%, and the impact strength was increased by a maximum value of five times.
Structural and thermal studies of Polyethylene terephthalate (PET) and reorganized PET (RPET) are done using XRD and DSC. XRD results show that there is more crystallinity in RPET than PET suggesting overall more freedom to chain movement in RPET than in PET, which is due to less chain entanglement in RPET. Nonisothermal Crystallization kinetics of PET and RPET was studied using the Avrami model and Lauritzen Hoffman Theory. Avrami showed strong secondary crystallization for PET and RPET. The Lauritzen–Hoffman parameters (Kg & U*) were estimated using Vyazovkin-Sbirrazzuoli’s isoconversional approach and Lauritzen-Hoffman method using G = 1/t0.5. The isoconversional method regime transition (I-II) at 197℃ and 190 ℃ for PET and RPET, respectively. The U* values calculated for PET and RPET are 5151 J/mol and 1981 J/mol respectively in regime II. σe and q values are lower for RPET which confirms less entanglement in RPET. Overall, PET & RPET are structurally different & show different thermal behavior.
Waterborne polyurethane (WPU) dispersions with different molecular weights of soft segment and different contents of hard segment were synthesized by using polyethylene glycol adipate diol (PBA), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI) as the main raw materials. The crystallization behavior of WPU films under isothermal and non-isothermal conditions were characterized by DSC, and their crystallization kinetics were investigated by Avrami equation and Mo Zhishen equation, respectively. The non-isothermal crystallization kinetics results showed that the non-isothermal crystallization kinetics parameters F(T) increased with the increase of relative crystallinity, which suggested that enhancement of activation temperature could improve the crystallization rate and initial bonding strength of WPU adhesive. The isothermal crystallization kinetics results indicated that a correspondence could be found between isothermal crystallization kinetics parameters t1/2 of WPU films and the open time of WPU adhesive. The larger the t1/2 of WPU films was, the longer the open time of WPU adhesive would have.
The goals of the investigation were: to indicate the methods of characterization of recycled polymers, to show general tendencies in properties deterioration and characterize recyclates on Central Europe and European Community markets. The properties and composition of scrap poly(ethylene terephthalate) from several sources were characterized by: TGA, DSC, FTIR, tensile properties, dynamic viscosity, intrinsic viscosity and thermo-oxidative stability. We found that all PET regrinds contained admixture of other polymers (0.1–5 wt%). The presence of more than 50 ppm PVC makes PET worthless for advanced application as film forming, because it catalyzes the hydrolysis and reduces the strength of material. Although the individual flakes of recycled PET show almost unchanged molecular characteristics and properties, the processed regrinds always exhibit worse properties. Partial restoration of recycled PET properties can be achieved by careful working, removing the dust fraction and by proper drying. The difference between studied PET's results from different applied recycling procedure. Admixtures of polymers without compatibilizer always deteriorate tensile properties. Various levels of stability of polymer viscous flow during film and tape extrusion were observed, depending on composition of recycled PET from various sources. Microgels were observed in all samples during film extrusion.
Crystallization within the discrete spheres of a block copolymer mesophase was studied by time-resolved x-ray scattering. The cubic packing of microdomains, established by self-assembly in the melt, is preserved throughout crystallization by strong interblock segregation even though the amorphous matrix block is well above its glass transition temperature. Homogeneous nucleation within each sphere yields isothermal crystallizations which follow first-order kinetics, contrasting with the sigmoidal kinetics normally exhibited in the quiescent crystallization of bulk polymers.
Based upon kinetic Monte Carlo simulations of crystallization in a simple polymer model we present a new picture of the mechanism by which the thickness of lamellar polymer crystals is constrained to a value close to the minimum thermodynamically stable thickness, l_{min}. The free energetic costs of the polymer extending beyond the edges of the previous crystalline layer and of a stem being shorter than l_{min} provide upper and lower constraints on the length of stems in a new layer. Their combined effect is to cause the crystal thickness to converge dynamically to a value close to l_{min} where growth with constant thickness then occurs. This description contrasts with those given by the two dominant theoretical approaches. However, at small supercoolings the rounding of the crystal profile does inhibit growth as suggested in Sadler and Gilmer's entropic barrier model.
The isothermal crystallization kinetics of poly(trimethylene terephthalate) (PTT) have been investigated using differential scanning calorimetry (DSC) and polarized light microscopy (PLM). Enthalpy data of exotherm from isothermal crystallization were analyzed using the Avrami theory. The average value of the Avrami exponent, n, is about 2.8. From the melt, PTT crystallizes according to a spherulite morphology. The spherulite growth rate and the overall crystallization rate depend on crystallization temperature. The increase in the spherulitic radius was examined by polarized light microscopy. Using values of transport parameters common to many polymers (U* = 1500 cal/mol, T-infinity = T-g - 30 degrees C) together with experimentally determined values of T-m(0) (248 degrees C) and T-g (44 degrees C), the nucleation parameter, k(g), for PTT was determined. On the basis of secondary nucleation analyses, a transition between regimes III and II was found in the vicinity of 194 degrees C (Delta T congruent to 54 K). The ratio of k(g) of these two regimes is 2.1, which is very close to 2.0 as predicted by the Lauritzen-Hoffman theory. The lateral surface-free energy, sigma = 10.89 erg/cm(2) and the fold surface-free energy, sigma(e) = 56.64 erg/cm(2) were determined. The latter leads to a work of chain-folding, q = 4.80 kcal/mol folds, which is comparable to PET and PET previously reported. (C) 2000 John Wiley & Sons, Inc.
Multiwalled carbon nanotubes (MWNTs) (diameter range, 10-20 nm) were functionalized with 4-methoxybenzoic acid and 4-ethoxybenzoic acid via a Friedel-Crafts reaction in polyphosphoric acid to afford methoxybenzoyl-and ethoxybenzoyl-functionalized MWNTs. As-received MWNT, methoxy-benzoyl-functionalized (MeO-MWNT), and ethoxybenzoyl-functionalized (EtO-MWNT) nanotubes were dispersed in ethylene glycol (EG). Because of the structural similarity, the mixture of EtO-MWNT (0.4 wt %) and EG was a homogeneous dispersion, whereas MeO-MWNT and pristine MWNT were dispersed in EG rather heterogeneously at the same loading. In situ polycondensation of EG and terephthalic acid in the presence of pristine MWNT, MeO-MWNT, or EtO-MWNT was carried out to generate the corresponding MWNT/PET, MeO-MWNT/PET, and EtO-MWNT/PET nanocomposites. High molecular weight poly(ethylene terephthalates) (PETs), with intrinsic viscosity range 0.6-0.7 dL/g (o-chlorophenol at 30 (0.1 °C), were obtained in all cases. In comparing the images from scanning electron microscopy (SEM) taken at the same magnification for these nanocomposites, it is clear that the MWNT/PET system has poor MWNT dispersion and the MeO-MWNT/PET system has a better dispersion. However, EtO-MWNT in PET matrix is most homogeneously dispersed, and the interfacial boundary between EtO-MWNT and PET matrix is practically nondiscernible.
A study has been made of the crystallization behaviour of poly(ether-ether-ketone), PEEK, under isothermal and non-isothermal conditions. A differential scanning calorimeter was used to monitor the energetics of the crystallization process from the melt and from the rubbery amorphous state. During isothermal crystallization, relative crystallinity develops with a time dependence described by the Avrami equation, with exponent n = 3. Greater absolute crystallinity develops during melt crystallization, nearly twice that which develops from the rubbery state, for comparable rates of crystallization. For non-isothermal studies, amorphous films were crystallized by heating or cooling at rates from 1°C/min to 50°C/min. A large fraction of crystallinity, from 0.45 to 0.70, develops by secondary processes. A kinetic treatment based on the Avrami equation is presented to describe the primary processes leading to non-isothermal crystallization. We have calculated activation energies of 68 kcal mol−1 for crystallization from the melt, and 52 kcal mol−1 for crystallization from the rubbery amorphous state. Results of isothermal and non-isothermal crystallization of PEEK are compared with those of poly(ethylene terephthalate).
Isothermal crystallization and subsequent melting behavior of mesoporous molecular sieve (MMS) filled poly(ethylene terephthalate) (PET) composites have been investigated at the designated temperature by using differential scanning calorimeter (DSC). The commonly used Avrami equation was used to fit the primary stage of the isothermal crystallization. The Avrami exponents n were evaluated to be 2 < n < 3 for the neat PET and composites. MMS particles acting as nucleating agent in composite accelerated the crystallization rate with decreasing the half-time of crystallization. The crystallization activation energy calculated from the Arrhenius' formula was reduced as MMS content increased. It is shown that the MMS particles made the molecular chains of PET easier to crystallize during the isothermal crystallization process. Subsequent differential scanning calorimeter scans of the isothermally crystallized samples exhibited different melting endotherms. It is found that much smaller or less perfect crystals formed in composites due to the interaction between molecular chains and the MMS particles. The crystallinity of composites was enhanced by increasing MMS content. (c) 2005 Elsevier Ltd. All rights reserved.
The non-isothermal equation was extended to describe non-isothermal cold crystallization kinetics of oriented polymers. The validity of the equation was examined by using a DSC crystallization curve of oriented poly(ethylene terephthalate) (PET) fibers with a constant heating rate. The double cold crystallization peaks appeared in the DSC curve. The relative degrees of crystallinity at different temperatures were analyzed by using the equation. The results show that the value of the Avrami exponent near to 1 at lower temperatures implies the bundle-like crystal growth geometry and the value of the Avrami exponent near to, 2, at higher temperatures implies the higher dimension crystal growth geometry. The first crystallization process crystallizes at faster rate than that of the isotropic sample, while the second process crystallizes at slower rate than that of isotropic sample. If a simple single process model was used, the value of the Avrami exponent, 0.77, was obtained. The result shows the simple single process model cannot describe the processes of crystallization of oriented PET fibers satisfactorily.
A Tektronix-31 programmable calculator interfaced to a Perkin Elmer differential scanning calorimeter, model 2, substantially improves the accuracy of measuring the time-dependent development of the degree of crystallinity (× 10) and hence improves the quality of the rate data. Storing energy flow data at preset time intervals directly into the memory of the calculator improves the accuracy of the measurement of time, and enables the evaluation of the onset of crystallization and the baseline of the calorimeter initially. This substantially improves the measurement of the degree of crystallinity developing with time by integrating the energy flow data over the time interval from the onset of crystallization. Polyethylene samples are studied since their rate constants have a marked temperature dependence which enables the accuracy of the analytical procedure to be assessed. Primary and secondary crystallization processes are separated.
Summary
Allylester resin tethered to layered silicate was synthesized by in-situ polymerization method and was cured by tert-butylperbenzoate (TBPB) directly. We ascertained the existing of carbonyl and benzyl groups which come from diallyl terephtalate
in the gallery of layered silicates using the thermogravimetric analysis (TGA) and FT-IR. The residual weight and new IR peaks
of the clay, which is treated by in-situ polymerization, imply that the hydroxy group of intercalant takes part in the polymerization of allylester resin. Also, its
nanocomposite was characterized by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD patterns
and TEM photographs indicate that the basal spacing (d
001
) of the nanocomposite made by in-situ polymerization is larger than those of the nanocomposite made by a simple mixing.
Differential scanning calorimetry (DSC) and temperature modulated DSC (MTDSC) have been used to investigate the melting behaviour of poly(ethylene terephthalate) (PET). Multiple melting endotherms were observed even at high heating rates, e.g. 160Kmin−1 and these have been attributed to the presence of two different distributions of lamella thickness and re-crystallisation (reorganisation) on heating. This has been confirmed by MTDSC—the presence of endotherms and an exotherm in the reversing component of the heat flow during heating. Examination of the endotherms of samples heating stepwise indicated that further crystallisation took place above the isothermal crystallisation temperature (Tc). Some part of this was associated with lamella thickening and crystal perfecting. The multiple melting endotherms observed are a consequence of the balance between the melting and re-crystallisation and the lamella thickness distribution existing within the sample, prior to heating. The triple melting endotherms observed are attributed to the melting of secondary and primary lamellae produced on crystallisation and to thickened lamellae produced during heating to the melting point.
Following upon the general theory in Part I, a considerable simplification is here introduced in the treatment of the case where the grain centers of the new phase are randomly distributed. Also, the kinetics of the main types of crystalline growth, such as result in polyhedral, plate‐like and lineal grains, are studied. A relation between the actual transformed volume V and a related extended volume V1 ex is derived upon statistical considerations. A rough approximation to this relation is shown to lead, under the proper conditions, to the empirical formula of Austin and Rickett. The exact relation is used to reduce the entire problem to the determination of V1 ex, in terms of which all other quantities are expressed. The approximate treatment of the beginning of transformation in the isokinetic range is shown to lead to the empirical formula of Krainer and to account quantitatively for certain relations observed in recrystallization phenomena. It is shown that the predicted shapes for isothermal transformation‐time curves correspond well with the experimental data.
Spherulitic morphologies and overall crystallization kinetics of miscible poly(vinylidene fluoride) (PVDF)/poly(butylene succinate-co-butylene adipate) (PBSA) blends were studied by polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and wide-angle X-ray diffraction (WAXD). PVDF and PBSA crystallize separately in the blends. For the high-Tm component PVDF, the crystallization mechanism does not change, while both the spherulitic growth rate and the overall crystallization rate of PVDF decrease with increasing crystallization temperature and the PBSA content in the blends. Much more attention has been directed to the spherulitic morphologies and overall crystallization kinetics of the low-Tm component PBSA, which are affected not only by blend composition and crystallization temperature but also strongly by the preexisting crystals of the high-Tm component PVDF in the blends. PBSA spherulites nucleate in the matrix of the PVDF spherulites and continue to grow until impinging on other PBSA spherulites. The overall crystallization rate of PBSA is accelerated in the blends compared with that of neat PBSA, which reduces with increasing crystallization temperature despite blend composition for the PBSA-rich blends. The presence of the preexisting PVDF crystals shows two opposite effects on the overall crystallization of PBSA, i.e., enhanced nucleation ability and slower crystal growth rates.
Continuous pyrolysis of poly-(ethylene terephthalate) (PET) was performed in a conical spouted-bed reactor. This reactor is especially suitable for this process, because of its excellent hydrodynamic behavior and its versatility. An optimization of the operating conditions has been performed to avoid particle agglomeration and defluidization, given that these are serious problems that hinder plastic waste pyrolysis. Moreover, the influence of temperature in the pyrolysis product distribution was studied in the range of 500−600 °C. PET pyrolysis led to a high yield of gas fraction, a low amount of liquids, a significant yield of solid fraction, and a solid residue that remained in the reactor coating sand particles. The main products obtained are carbon monoxide, carbon dioxide, benzoic acid, and acetaldehyde.
The efficiency of poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl C61 butyric acid methyl ester (PCBM) bulk heterojunction solar cells dramatically depends on the molecular weight of the donor polymer P3HT. Only for P3HTs with a number-average molecular weight (Mn) of >10 000 have high power conversion efficiencies of >2.5% been reached. This behavior is caused by distinctly reduced charge carrier (hole) mobility in the donor phase of the devices built from lower Mn P3HT samples. The reduced performance of such devices is related to a reduced intermolecular ordering (π-stacking) of the P3HT phase. These findings highlight the important role of the molecular weight in semicrystalline semiconducting polymers for the device performance and may help in the further development of novel, efficient, lower band gap donor polymers for photovoltaic applications.
Polymer−clay nanocomposites of styrene and methyl methacrylate have been prepared by bulk, solution, suspension, and emulsion polymerization as well as by melt blending. Two different organic modifications of montmorillonite have been used: one contains a styryl monomer on the ammonium ion while the other has no double bond. The organic modification as well as the mode of preparation determines if the material will be exfoliated or intercalated. Exfoliation is more likely to occur if the ammonium ion contains a double bond which can participate in the polymerization reaction, but the mere presence of this double bond is not sufficient to always produce an exfoliated system. Solution polymerization always produced intercalated systems. Neither thermogravimetric analysis nor the tensile modulus can be used to evaluate the type of nanocomposite that has been formed.
Poly(ethylene terephthalate) (PET) taken from post-consumer soft-drink bottles was subjected to alkaline hydrolysis with aqueous sodium hydroxide after cutting it into small pieces (flakes). A phase transfer catalyst (trioctylmethylammonium bromide) was used in order the reaction to take place in atmospheric pressure and mild experimental conditions. Several different reaction kinetics parameters were studied, including temperature (70–95°C), NaOH concentration (5–15 wt.-%), PET average particle size, catalyst to PET ratio and PET concentration. The disodium terephthalate received was treated with sulfuric acid and terephthalic acid (TPA) of high purity was separated. The 1H NMR spectrum of the TPA revealed an about 2% admixture of isophthalic acid together with the pure 98% terephthalic acid. The purity of the TPA obtained was tested by determining its acidity and by polymerizing it with ethylene glycol using tetrabutyl titanate as catalyst. A simple theoretical model was developed to describe the hydrolysis rate. The apparent rate constant was inversely proportional to particle size and proportional to NaOH concentration and to the square root of the catalyst amount. The activation energy calculated was 83 kJ/mol. The method is very useful in recycling of PET bottles and other containers because nowadays, terephthalic acid is replacing dimethyl terephthalate (the traditional monomer) as the main monomer in the industrial production of PET.
This paper covers the recent research carried out by the authors on the chemical recycling of poly(ethylene terephthalate) (PET) taken from post‐consumer soft‐drink bottles. The chemical recycling techniques used are critically reviewed and the authors' contribution is highlighted. Hydrolysis in either an alkaline or acid environment was employed in order to recover pure terephthalic acid monomer that could be repolymerized to form the polymer again. Alkaline hydrolysis was carried out in either an aqueous NaOH solution or in a non‐aqueous solution of KOH in methyl cellosolve. A phase‐transfer catalyst was introduced in alkaline hydrolysis, in order that the reaction takes place at atmospheric pressure and in mild experimental conditions. The reaction kinetics were thoroughly investigated, both experimentally and theoretically, using a simple, yet precise, kinetic model. Moreover, glycolysis was examined as an effective way for the production of secondary value‐added materials. The glycolysated PET products (oligomers) can be used as raw materials for the production of either unsaturated polyester resins (UPR) or methacrylated oligoesters (MO). UPR can subsequently be cured with styrene in ambient temperature to produce alkyd resins used as enamel paints or coatings. MO are potential monomers that can be cured either by UV irradiation or temperature to produce formulations used as coatings for wood surfaces, paints, or other applications. Thus, recycling of PET does not only serve as a partial solution to the solid‐waste problem, but also contributes to the conservation of raw petrochemical products and energy.
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The isothermal crystallization kinetics and morphology of poly(ethylene terephthalate)–poly(ethylene oxide) (PET30–PEO6) segmented copolymer, and poly(ethylene terephthalate) (PET) and poly(ethylene oxide) (PEO) homopolymers have been studied by means of differential scanning calorimetry (DSC) and a transmission electron microscope (TEM). It is found that the nucleation mechanism and growth dimension of PEO in the copolymer are different from that in the homopolymer, which is attributed to the effect of the crystallizability of PET-blocks. Furthermore, the crystallization rate of PEO-blocks in the copolymer is slower than that in the homopolymer because the PET-blocks phase is always partially solidified at the temperatures when PEO-blocks begin to crystallize. In contrast, the isothermal crystallization rate of PET-blocks in the copolymer is faster than that in the homopolymer because the lower glass transition temperature of the PEO-blocks (soft blocks) increases the mobility of the PET-blocks in the copolymer.
A lamellae-forming poly(ethylene oxide)-b-polystyrene (EOS) has been blended with a polystyrene homopolymer (PS) and a PS oligomer (PSO), respectively, to obtain miscible polymer blends (denoted as EOS/PS-32 and EOS/PSO-32, respectively). Both blends exhibit cylindrical microphase morphologies, with the PEO volume fractions being 0.32. The order–disorder transition temperatures (TODT) of both blends are 175 and 84°C, respectively, as determined by temperature-dependent small angle X-ray scattering experiments. The glass transition temperature of the PS matrix (TgPS) for the EOS/PS-32 blend is 64°C as determined by differential scanning calorimetry (DSC), while that for the EOS/PSO-32 blend is only 16°C. Thus, by controlling the crystallization temperatures (TcPEO), two kinds of nano-confined PEO crystallizations have been achieved in these blends: when TODT≫TgPS>TcPEO in the EOS/PS-32 blend, the PEO-block crystallization is confined under a hard PS confinement, while for TODT>TcPEO≳TgPS in the EOS/PSO-32 blend, the PEO-block crystallization is confined under a soft PS confinement. DSC and wide-angle X-ray experiments show that the crystallizations of the PEO blocks in these two confinement environments behave differently. The PEO-block crystallization kinetics in the hard confinement is much slower than that in the soft confinement. The DSC kinetics studies show that for Tc<30°C, the ln K values in the Avrami equation for both blends appear similar, while the n parameter for the EOS/PSO-32 is higher than that for the EOS/PS-32 blend. The melting temperature and weight percent crystallinity of the PEO crystals in the soft confinement environment are higher than those in the hard confinement environment, indicating that the PEO crystals developed in the soft confinement environment possess higher thermodynamic stability than in the hard confinement environment. Furthermore, heating the PEO crystals in the soft confinement environment can continuously increase their thermodynamic stability through a crystal thickening process, by which the soft confinement environment is partially destroyed.
Ultradrawing of films of high-molecular-weight polyethylene (M̄w = 1.5 × 106) produced by gelation crystallization from solution is discussed. The influence of the initial polymer volume fraction (ϕ) on the maximum draw ratio (λmax) of the dried films is examined in the temperature region from 90–130°C. The results can be described very well by the relation λmax = λ ϕ−1/2 where λ is the (temperature-dependent) maximum draw ratio of the melt-crystallized film. An attempt is made to discuss the marked influence of the initial polymer volume fraction on λmax in terms of the deformation of a network with entanglements acting as semipermanent crosslinks.
The isothermal crystallization kinetics of poly(trimethylene terephthalate) (PTT) have been investigated using differential scanning calorimetry (DSC) and polarized light microscopy (PLM). Enthalpy data of exotherm from isothermal crystallization were analyzed using the Avrami theory. The average value of the Avrami exponent, n, is about 2.8. From the melt, PTT crystallizes according to a spherulite morphology. The spherulite growth rate and the overall crystallization rate depend on crystallization temperature. The increase in the spherulitic radius was examined by polarized light microscopy. Using values of transport parameters common to many polymers (U* = 1500 cal/mol, T∞= Tg − 30 °C) together with experimentally determined values of T (248 °C) and Tg (44 °C), the nucleation parameter, kg, for PTT was determined. On the basis of secondary nucleation analyses, a transition between regimes III and II was found in the vicinity of 194 °C (ΔT ≅ 54 K). The ratio of kg of these two regimes is 2.1, which is very close to 2.0 as predicted by the Lauritzen–Hoffman theory. The lateral surface-free energy, σ = 10.89 erg/cm2 and the fold surface-free energy, σe = 56.64 erg/cm2 were determined. The latter leads to a work of chain-folding, q = 4.80 kcal/mol folds, which is comparable to PET and PBT previously reported. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 934–941, 2000
The melt intercalation method was employed to prepare poly(butylene terephthalate) (PBT)/montmorillonite (MMT) nanocomposites, and the microstructures were characterized with X-ray diffraction and transmission electron microscopy. Then, the nonisothermal crystallization behavior of the nanocomposites was studied with differential scanning calorimetry (DSC). The DSC results showed that the exothermic peaks for the nanocomposites distinctly shifted to lower temperatures at various cooling rates in comparison with that for pure PBT, and with increasing MMT content, the peak crystallization temperature of the PBT/MMT hybrids declined gradually. The nonisothermal crystallization kinetics were analyzed by the Avrami, Jeziorny, Ozawa, and Mo methods on the basis of the DSC data. The results revealed that very small amounts of clay (1 wt %) could accelerate the crystallization process, whereas higher clay loadings reduced the rate of crystallization. In addition, the activation energy for the transport of the macromolecular segments to the growing surface was determined by the Kissinger method. The results clearly indicated that the hybrids with small amounts of clay presented lower activation energy than PBT, whereas those with higher clay loadings showed higher activation energy. The MMT content and the crystallization conditions as well as the nature of the matrix itself affected the crystallization behavior of the hybrids. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3257–3265, 2006
Synthesis of poly(ethylene 2,5-furandicarboxylate) (PEF) and the characterization of the ensuring material in comparison with poly(ethylene terepthalate) (PET) was reported. Monomer was prepared in 98% yield by reacting 2,5-furandicarboxylic acid (FCA) with a hundred fold excess of ethylene glycol (EG) for 6 hours at 75°C in the presence of small amounts of aqueous HCl and vacuum removing the excess diol after neutralization. The ensuing white PEFs were found to dissolve only in trifluoroacetic acid (TFA) and in hot tetrachloroethane (TCE), among the numerous potential solvents tested. The h NMR spectra in CF3COOD bore a striking resemblance to that of PET in the same solvent with the resonance of the H3 and H4 furan protons at 7.43 ppm, and that of the ester CH2 at 4.78 with the expected 1:2 integration ratio. Thermogravimetric analysis of PEFs showed that they were thermally stable up to δ300°C and degraded thereafter.
In this work, the isothermal crystallization kinetics of polytrimethylene terephthalate (PTT) was first investigated from two temperature limits of melt and glass states. For the isothermal melt crystallization, the values of Avrami exponent varied between 2 and 3 with changing crystallization temperature, indicating the mixed growth and nucleation mechanisms. Meanwhile, the cold crystallization with an Avrami exponent of 5 indicated a character of three-dimensional solid sheaf growth with athermal nucleation. Through the analysis of secondary nucleation theory, the classical regime I→II and regime II→III transitions occurred at the temperatures of 488 and 468 K, respectively. The average work of chain folding for nucleation was ca. 6.5 kcal mol−1, and the maximum crystallization rate was found to be located at ca. 415 K. The crystallite morphologies of PTT from melt and cold crystallization exhibited typical negative spherulite and sheaf-like crystallite, respectively. Moreover, the regime I→II→III transition was accompanied by a morphological transition from axialite-like or elliptical-shaped structure to banded spherulite and then non-banded spherulite, indicating that the formation of banded spherulite is very sensitive to regime behavior of nucleation.
PET nanocomposites were prepared using montmorillonite with different organic modifiers (Cloisite® 15A, 30B and 10A). TEM, WAXD and DSC were used for the characterization. Nanocomposites of intercalated and exfoliated morphologies were obtained, and an average maximum distance between the platelets was observed in the intercalated morphology. The clay nucleated the PET crystallization process, and the nucleating effect was higher when Cloisite 10A was used. This study allowed the evaluation of the characteristics of the organic modifiers' influence on the intercalation and exfoliation processes in PET. Tactoids were obtained when only apolar modifiers were present. It was observed that PET nanocomposites were intercalated and exfoliated when polar modifiers were present.
Asymmetric diblock copolymers of polystyrene (PS) and poly(methylmethacrylate) (PMMA), PS(S-b-MMA), having cylindrical microdomains of PMMA, are model systems to generate nanoporous thin films. With controlled interfacial interactions or applied external electric fields, the cylindrical microdomains can be oriented normal to the surface. Exposure to deep UV radiation degrades the PMMA and crosslinks the PS matrix. After rinsing with a selective solvent, a nanoporous film is obtained. By changing the molecular weight, smooth porous films with hexagonal arrays of pores having diameters ranging from 14 to 50 nm were obtained. The results show that molecular weight is a convenient, simple means of controlling pore diameter.
The isothermal cold crystallization of poly(ethylene terephthalate) was investigated by simultaneous small and wide angle X-ray scattering (SAXS and WAXS) and dielectric spectroscopy (DS). By this experimental approach (SWD), simultaneously collected information was obtained about the specific changes occurring in both crystalline and amorphous phases during crystallization. The main features which are directly derived from our experiments can be explained assuming the formation of a heterogeneous multiple lamellar population arrangement. The rigid amorphous phase can be associated with the intra-lamellar stack amorphous phase. The restriction of the amorphous phase mobility mainly occurs in the inter-lamellar stacks regions probably due to the formation of secondary lamellae.
To overcome certain demerits of recycling and incineration, researchers across the world have focused on development of value added products from waste plastics such as liquid and gaseous fuel, activated carbon and monomer recovery. Thermogravimetic analysis (TGA) is one of the widely used techniques to study the pyrolysis reaction kinetics. A kinetic model is necessary to predict the reactor behaviour as well as product range distribution. This paper investigates the thermal pyrolysis kinetics of poly(ethylene terephthalate) (PET) from different sources of soft drink bottles such as M/s Coca Cola and M/s Pepsi. Thermal degradation is carried out in dynamic condition at three different heating rates of 10, 15 and 25 K min−1 under nitrogen atmosphere. A simple nth order kinetic model is proposed to study the thermal degradation of waste plastics. Kinetic parameters are obtained from three dynamic TGA curves at three different heating rates using ASTM E698 and from one TGA curve at the heating rate of 10 K min−1 using nth order model techniques. PET pyrolysis exhibits 70–80% weight loss in the temperature range of 653–788 K. The nth order model technique better predicts the experimental data than ASTM E698 technique. Values of activation energy obtained by nth order model technique are 322.3 and 338.98 kJ/mole for Coca Cola and Pepsi samples, respectively.
Isothermal crystallization, subsequent melting behavior and non-isothermal crystallization of nylon 1212 samples have been investigated in the temperature range of 160–171 °C using a differential scanning calorimeter (DSC). Subsequent DSC scans of isothermally crystallized samples exhibited three melting endotherms. The commonly used Avrami equation and that modified by Jeziorny were used, respectively, to fit the primary stage of isothermal and non-isothermal crystallizations of nylon 1212. The Avrami exponent n was evaluated, and was found to be in the range of 1.56–2.03 for isothermal crystallization, and of 2.38–3.05 for non-isothermal crystallization. The activation energies (ΔE) were determined to be 284.5 KJ/mol and 102.63 KJ/mol, respectively, for the isothermal and non-isothermal crystallization processes by the Arrhenius' and the Kissinger's methods.
Coagulation method was first used to prepare nanocomposites of multi-wall carbon nanotubes (MWNT) and poly(ethylene terephthalate) (PET). The morphology of nanocomposites is characterized using transmission electronic microscopy and scanning electronic microscopy. A coating on MWNT by PET chains is observed by comparison of micrographs of purified MWNT and MWNT encapsulated by PET chains in the nanocomposites, and this coating is considered as evidence of interfacial interaction between MWNT and PET chains. Both electrical conductivity and rheological properties have been well characterized. With increasing MWNT loading, the nanocomposites undergo transition from electrically insulative to conductive at room temperature, while the melts show transition from liquid-like to solid-like viscoelasticity. The percolation threshold of 0.6 wt% (based on viscosity) for rheological property and 0.9 wt% for electrical conductivity has been found. The low percolation threshold results from homogeneous dispersion of MWNT in PET matrix and high aspect ratio of MWNT. The less rheological percolation threshold than electrical percolation threshold is mainly attributed to the fact that a denser MWNT network is required for electrical conductivity, while a less dense MWNT network sufficiently impedes PET chain mobility related to the rheological percolation threshold.
The cluster distribution approach is extended to investigate the crystallization kinetics of miscible polymer blends. Mixture effects of polymer-polymer interactions are incorporated into the diffusion coefficient. The melting temperature, activation energy of diffusion, and phase transition enthalpy also depend on the blending fraction and lead to characteristic kinetic behavior of crystallization. The influence of different blending fractions is presented through the time dependence of polymer concentration, number and size of crystals, and crystallinity (in Avrami plots). Computational results indicate how overall crystallization kinetics can be expressed approximately by the Avrami equation. The nucleation rate decreases as the blending fraction of the second polymer component increases. The investigation suggests that blending influences crystal growth rate mainly through the deposition-rate driving force and growth-rate coefficient. The model is further validated by simulating the experimental data for the crystallization of a blend of poly(vinylidenefluoride)[PVDF] and poly(vinyl acetate)[PVAc] at various blending fractions.
Poly(ethylene terephthalate) (PET) track-etched membranes with average pore diameters of 692 and 1629 nm were functionalized using the monomer N-isopropylacrylamide (NIPAAm) and a photoinitiated "grafting-from" approach in which a surface-selective reaction has been most efficiently achieved by combinations of the unmodified PET surface with benzophenone and, alternatively, of an aminated PET surface with benzophenone carboxylic acid. Consistent estimations of the pore diameters of the base PET membranes and of the effective grafted polyNIPAAm layer thicknesses on the PET pore walls were possible only on the basis of the permeabilities measured with aqueous solutions of higher ionic strength (e.g., 0.1 M NaCl). However, the permeabilities measured with ultrapure water indicated that the "electroviscous effect" was significant for both base membranes. The influences of membrane pore diameter, surface charge, and solution ionic strength could be interpreted in the framework of the space-charge model. Functionalized membranes with collapsed grafted polymer hydrogel layer thicknesses of a few nanometers exhibited almost zero values of the zeta potential estimated from the trans-membrane streaming potential measurements. This was caused by a "hydrodynamic screening" of surface charge by the neutral hydrogel. Very pronounced changes in permeability as a function of temperature were measured for PET membranes with grafted polyNIPAAm layers, and the effective layer thickness in the swollen state--here up to approximately 300 nm--correlated well with the degree of functionalization. The subtle additional effects of solution ionic strength on the hydrodynamic layer thickness at 25 degrees C were different from the effects for the base PET membranes and could be explained by a variation in the degree of swelling, resembling a "salting-out" effect. Overall, it had been demonstrated that the functionalized capillary pore membranes are well suited for a detailed and quantitative evaluation of the relationships between the synthesis, the structure, and the function of grafted stimuli-responsive polymer layers.
Macromolecular Physics (Academic
- B Wunderich