Effect of silica nanoparticles on solid state polymerization of poly(ethylene terephthalate)

In the present study, the effect of silica nanoparticles, on the solid state polycondensation (SSP) kinetics of poly(ethylene terephthalate) (PET) is thoroughly investigated. At silica concentrations less than 1 wt% and reaction temperatures between 200 and 230 °C higher intrinsic viscosity (IV) values were measured, compared to neat PET at all reaction times. However, with 1 wt% of nanosilica (n-SiO₂), the IV increase of the nanocomposites was similar to that of neat PET and a further increase to 5 wt% n-SiO₂ resulted in significantly lower IV values. A simple kinetic model was also employed to predict the time evolution of IV, as well as the carboxyl and hydroxyl content during SSP. The kinetic parameters of the transesterification and esterification reactions were estimated at different temperatures with or without the addition of n-SiO₂. The activation energies of both reactions were determined together with the concentration of inactive end-groups. From the experimental measurements and the theoretical simulation results it was proved that n-SiO₂ in small amounts (less than 1 wt%) enhances both the esterification and transesterification reactions at all studied temperatures acting as a co-catalyst. However, as the amount of nanosilica increases a number of inactive hydroxyl groups were estimated corresponding to participation of these groups in side reactions with the nanosilica particles. These side reactions lead initially to branched PET chains and eventually (5 wt% n-SiO₂ concentration) to crosslinked structures.     

Isothermal melt-crystallization and melting behavior for three linear aromatic polyesters

Isothermal crystallization and subsequent melting behavior for three different types of linear aromatic polyester, namely poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate) (PTT), and poly(butylene terephthalate) (PBT), were investigated (with an emphasis on PTT in comparison with PET and PBT). These polyesters were different in the number of methylene groups (i.e. 2, 3, and 4 for PET, PTT, and PBT, respectively). Isothermal crystallization studies were carried out in a differential scanning calorimeter (DSC) over the crystallization temperature range of 182-208 °C. The wide-angle X-ray diffraction (WAXD) technique was used to obtain information about crystal modification and apparent degree of crystallinity. The kinetics of the crystallization process was assessed by a direct fitting of the experimental data to the Avrami, Tobin, and Malkin macrokinetic models. It was found that the crystallization rates of these polyesters were in the following order: PBT>PTT>PET, and the melting of these polyesters exhibited multiple-melting phenomenon. Lastly, the equilibrium melting temperature for these polyesters was estimated based on the linear and non-linear Hoffman-Weeks (LHW and NLHW) extrapolative methods.     

Transesterification reaction of the BaSO4‐filled PBT/poly(ethylene terephthalate) blend

For the poly(butylene terephthalate) (PBT)/poly(ethylene terephthalate) blend system, the addition of a barium sulfate (BaSO₄) particle, the surface of which was modified with a titanate coupling agent, suppressed the transesterification reaction. The polyester chain ends, considered one of the main sites of transesterification reactions, were blocked through a chemical reaction with the surface hydroxyl groups of the BaSO₄ particle; a block copolymer‐like architecture was obtained with a BaSO₄ linkage. The formation of the block copolymer‐like structure for the polyesters stuck to the BaSO₄ particle facilitated crystallization by providing a crystallization nucleus without a significant transesterification reaction, resulting in higher mechanical properties. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2589–2597, 2001     

Chain extension of polyesters PET and PBT with N,N′-bis (glycidyl ester) pyromellitimides. I

Three N,N′-bis (glycidyl ester imide) of pyromellitic acid (diepoxides) were prepared and were used as chain extenders for poly (ethylene terephthalate) (PET) and poly (butylene terephthalate) (PBT). The typical reaction conditions for the coupling of the polyester macromolecules were heating with the chain extender under argon atmosphere above the melting temperature (280°C for PET and 250°C for PBT) for several minutes. The Characterization of the samples, obtained at variable residence times in the reactor, was based on solution viscosity measurements and carboxyl and hydroxyl end-group determinations. Two of the diepoxides used gave satisfactory results. Starting from a PET having intrinsic viscosity [η] = 0.60 dL/g, and carboxyl content CC = 42 eq/10⁶ g, one could obtain PET with [η] = 1.15 dL/g and CC = 16 eq/10⁶ g within 30 min at 280°C. Analogous results were observed for PBT. The hydroxyl content of polyester in all cases was increased. When the quantity of the chain extender used was higher than that theoretically required for its reaction with all carboxyl end groups of the polyester, this resulted in some gel formation indicative of crosslinking. © 1995 John Wiley & Sons, Inc.     

碳纳米管对聚酯相容共混体系酯交换反应的影响

采用熔融共混制备了聚对苯二甲酸丙二酯(PTT)/聚对苯二甲酸丁二酯(PBT)共混体系以及碳纳米管(C NTs)填充改性的三元复合体系,通过核磁共振波谱仪(NMR)研究了CNTs对共混基体组分间酯交换反应的影响,并结合透射电子显微镜( TEM)、沉降实验等多种测试结果初步探讨了影响的机理.研究结果表明,PTT/PBT为典...     

Characterization of cross-linking structure in terephthalate polyesters formed through material recycling process by pyrolysis-gas chromatography in the presence of organic alkali

Typical terephthalate polyesters such as poly(butylene terephthalate) (PBT) and poly(ethylene terephthalate) (PET) were characterized by pyrolysis-gas chromatography (Py-GC) in the presence of tetramethylammonium hydroxide in terms of the cross-linking structure formed during their material recycling. In the pyrograms of PBT and PET thermally treated at 270 °C for 1 h, which were prepared as model polymers containing cross-linking structures, an additional peak was commonly observed as well as the main reactive pyrolysis products for the original polyesters such as dimethyl terephthalate. Based on the observed spectra obtained by Py-GC/mass spectrometry and Py-GC/Fourier transform infrared spectrometry measurements, this peak was assigned to the product reflecting a biphenyl-type cross-linking structure. Furthermore, in the pyrograms of kneaded PBT and PET samples also at 270 °C for a total of 1 h, which were prepared to simulate material recycling, the same peak for the cross-linking structure was also observed, although its intensity was slightly lower than that in the samples thermally treated in air. This fact verified that the biphenyl-type cross-linking structure would be considerably formed during the recycling of PBT and PET, which might in turn contribute to the deteriorated properties of the recycled materials from waste polyesters. Moreover, difference in the formation of the cross-linking between PBT and PET is discussed on the basis of the observed results.     

Chain structure and thermal behavior of reactive blends of PET/LCP with bis(2-oxazoline)

The sequence structure and thermal behavior of reactive blends of poly(ethylene terephthalate) (PET) with the liquid crystalline copolyester 60 PHB/PET containing 60 mol % of p-hydroxybenzoic acid (PHB) with addition of bis(2-oxazoline) (BOZ) were studied in detail. ¹H NMR results indicate that both the number average sequence length of PET and PHB segments (L _PET and L _PHB) decrease with increasing mixing time and temperature via transesterification between PET and LCP. The transesterification is promoted in the presence of BOZ. As a consequence, the sequence structure and in turn the crystallization both from the glassy and the melt state and the melting behavior are markedly affected.     

Halogen-free flame retarded poly(butylene terephthalate) (PBT) using metal oxides/PBT nanocomposites in combination with aluminium phosphinate

The flame retardancy of poly(butylene terephthalate) (PBT) containing aluminium diethlyphosphinate (AlPi) and/or nanometric metal oxides such as TiO₂ or Al₂O₃ was investigated. In particular the different active flame retardancy mechanisms were discovered. Thermal analysis, evolved gas analysis (TG-FTIR), flammability tests (LOI, UL 94), cone calorimeter measurements and chemical analyses of residues (ATR-FTIR) were used. AlPi acts mainly in the gas phase through the release of diethylphosphic acid, which provides flame inhibition. Part of AlPi remains in the solid phase reacting with the PBT to phosphinate-terephthalate salts that decompose to aluminium phosphate at higher temperatures. The metal oxides interact with the PBT decomposition and promote the formation of additional stable carbonaceous char in the condensed phase. A combination of metal oxides and AlPi gains the better classification in the UL 94 test thanks to the combination of the different mechanisms.     

Copolyesterification between poly(butylene terephthalate), terephthalic acid and hydroquinone diacetate: a kinetic analysis

The kinetics of liquid crystalline copolyester synthesis via melt transesterification between poly(butylene terephthalate) (PBT), terephthalic acid (TA) and hydroquinone diacetate (HQDA) is examined. Two different copolyester compositions PBT30/(HQDA+TA) 70 and PBT 50/(HQDA+TA) 50 mol% ratio were synthesized. The ratio of HQDA to TA was kept constant for all the reactions.The copolyesters were synthesized via melt polycondensation route at 265°C, 275°C and 285°C using two different transesterification catalysts, zinc acetate and dibutyl tin oxide. A key postulation assumed in this work is that the reaction originates between TA and HQDA to form a dimer which slices PBT chain. The copolyesterification rate constant for a system containing butylene glycol a more nonpolar moiety compared to ethylene glycol in poly(ethylene terephthalate) has been determined. The activation energy values for the different copolymer systems has also been determined. The rate constants for the uncatalyzed and catalyzed copolyesterification reaction and the activation energy values for the reaction have been determined.     

Nanocomposite of montmorillonite with telechelic sulfonated poly(butylene terephthalate): Effect of ionic groups on clay dispersion, mechanical and thermal properties

Telechelic ionomeric poly(butylene terephthalate) nanocomposites with organically modified clays have been prepared by the melt intercalation technique both in Brabender mixer and in twin screw-extruder. The presence of ionic groups tethered at the end of the polymer chains permits electrostatic interaction between the polymer and the surface of an organically modified clays providing a thermodynamic driving force for the dispersion of the clay platelets in the polymer matrix. The improved dispersion has been verified by TEM and XRD analyses. Nanocomposites with telechelic polymers present therefore consistently higher thermo-mechanical properties and improved thermal and hydrolytic stability respect to nanocomposites with standard PBT. Nanocomposite obtained using PBT with 3% telechelic ionic groups and with 5% of clay present a heat deflection temperature that is 48 °C higher compared to that of the commercial material. The presence of the clay also slightly increases the thermal and hydrolytic stability respect to standard PBT.     

Glycolysis of poly(ethylene terephthalate) (PET) using basic ionic liquids as catalysts

The glycolysis of poly(ethylene terephthalate) (PET) was studied using several ionic liquids and basic ionic liquids as catalysts. The basic ionic liquid, 1-butyl-3-methylimidazolium hydroxyl ([Bmim]OH), exhibits higher catalytic activity for the glycolysis of PET, compared with 1-butyl-3-methylimidazolium bicarbonate ([Bmim]HCO₃), 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) and 1-butyl-3-methylimidazolium bromide ([Bmim]Br). FT-IR, ¹H NMR and DSC were used to confirm the main product of glycolysis was bis(2-hydroxyethyl) terephthalate (BHET) monomer. The influences of experimental parameters, such as the amount of catalyst, glycolysis time, reaction temperature, and dosages of ethylene glycol on the conversion of PET, yield of BHET were investigated. The results showed a strong influence of the mixture evolution of temperature and reaction time on depolymerization of PET. Under the optimum conditions of m(PET):m(EG): 1:10, dosage of [Bmim]OH at 0.1 g (5 wt%), reaction temperature 190 °C and time 2 h, the conversion of PET and the yield of BHET were 100% and 71.2% respectively. Balance between the polymerization of BHET and depolymerization of PET could be changed when the reaction time was more than 2 h and contents of catalyst and EG were changed.     

Morphology of poly(butylene terephthalate)–poly(ethylene terephthalate‐co‐isophthalate‐co‐sebacate) segmented copolyesters

Segmented copolyesters, namely, poly(butylene terephthalate)–poly(ethylene terephthalate‐co‐isophthalate‐co‐sebacate) (PBT‐PETIS), were synthesized with the melting transesterification processing in vacuo condition involving bulk polyester produced on a large scale (PBT) and ternary amorphous random copolyester (PETIS). Investigations on the morphology of segmented copolyesters were undertaken. The two‐phase morphology model was confirmed by transmission electron microscopy and dynamic mechanical thermal analysis. One of the phases was composed of crystallizable PBT, and the other was a homogeneous mixture of PETIS and noncrystallizable PBT. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2257–2263, 2003     

Miscibility and properties of poly(l-lactic acid)/poly(butylene terephthalate) blends

Binary blends of poly(l-lactide) (PLLA) and poly(butylene terephthalate) (PBT) containing PLLA as major component were prepared by melt mixing. The two polymers are immiscible, but display compatibility, probably due to the establishment of interactions between the functional groups of the two polyesters upon melt mixing. Electron microscopy analysis revealed that in the blends containing up to 20% of poly(butylene terephthalate), PBT particles are finely dispersed within the PLLA matrix, with a good adhesion between the phases. The PLLA/PBT 60/40 blend presents a co-continuous multi-level morphology, where PLLA domains, containing dispersed PBT units, are embedded in a PBT matrix. The varied morphology affects the mechanical properties of the material, as the 60/40 blend displays a largely enhanced resistance to elongation, compared to the blends with lower PBT content.     

Selective production of benzene and naphthalene from poly(butylene terephthalate) and poly(ethylene naphthalene-2,6-dicarboxylate) by pyrolysis in the presence of calcium hydroxide

Poly(butylene terephthalate) (PBT) and poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) were pyrolysed in a fixed bed reactor in the presence of calcium hydroxide (Ca(OH)₂) in order to obtain benzene and naphthalene, respectively. In these experiments different ratios of polymer and Ca(OH)₂ were used. Also the temperature was varied in a range between 600 °C and 800 °C. It was found that the highest yield of benzene (67%) was obtained at a temperature of 700 °C and a molar Ca(OH)₂/PBT ratio of 10. The amount of carbon, fixed in the reactor residue after the experiment, was reduced from 56% for pure PBT to 38% under these conditions. Aromatic byproducts were reduced, as well, while the amount of 1,3-butadiene increased. Tetrahydrofuran was just formed under the influence of Ca(OH)₂.For PEN, the optimal conditions were found at a temperature of 600 °C and a molar Ca(OH)₂/PEN ratio of 5. A naphthalene yield of 80% from PEN was obtained. The rise of the naphthalene yield was caused by a more effective decomposition of the polyester by Ca(OH)₂, which led to the reduction of carbon in the reactor residue after the experiment from 59% for pure PEN to 10% under optimised conditions. The part of aromatic byproducts changed just slightly.     

Synthesis of patterned polymer brushes from flexible polymeric films

Surface-initiated polymerizations were carried out from polymeric surfaces of commercially important polyester films, poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN). These plastic films were modified prior to polymerization by plasma oxidation, exposing surface hydroxyl groups, in order to immobilise patterned self assembled monolayers (SAMs) of trichlorosilane initiator, through the soft lithographic method of microcontact printing (μCP). Subsequently, polymerizations were initiated from the surface via controlled atom transfer radical polymerization (ATRP), under aqueous conditions, to create patterned brushes of the thermo-responsive polymer poly(N-isopropyl acrylamide) (PNIPAM). By creating patterned, rather than homogeneous brushes characterization was made possible by atomic force microscopy (AFM).     

Colour formation in poly(ethylene terephthalate) during melt processing

The discolouration, that occurs in virgin poly(ethylene terephthalate) - PET during melt processing, was studied using various bulk and surface analytical techniques. Proton nuclear magnetic resonance (¹H NMR) was used to study the bulk chemical changes occurring in the polymer during thermo-oxidative degradation. Chemical derivatisation with trifluoroacetic anhydride (TFAA) was used to label the hydroxyl groups introduced on the polymer surface by thermal oxidation.From the surface analysis studies using photoacoustic Fourier transform infrared spectroscopy (PA/FT-IR), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) and X-ray photoelectron spectroscopy (XPS) it was evident that colour formation starts initially with the hydroxylation of the terephthalic ring. Further, the formation of additional carbonyl functionalities and conjugated chromophoric systems complete the colour formation process.     

Preparation and characterization of poly(butylene terephthalate)/poly(ethylene terephthalate) copolymers via solid‐state and melt polymerization

To increase the T_g in combination with a retained crystallization rate, bis(2‐hydroxyethyl)terephthalate (BHET) was incorporated into poly(butylene terephthalate) (PBT) via solid‐state copolymerization (SSP). The incorporated BHET fraction depends on the miscibility of BHET in the amorphous phase of PBT prior to SSP. DSC measurements showed that BHET is only partially miscible. During SSP, the miscible BHET fraction reacts via transesterification reactions with the mobile amorphous PBT segments. The immiscible BHET fraction reacts by self‐condensation, resulting in the formation of poly(ethylene terephthalate) (PET) homopolymer. ¹H‐NMR sequence distribution analysis showed that self‐condensation of BHET proceeded faster than the transesterification with PBT. SAXS measurements showed an increase in the long period with increasing fraction BHET present in the mixtures used for SSP followed by a decrease due to the formation of small PET crystals. DSC confirmed the presence of separate PET crystals. Furthermore, the incorporation of BHET via SSP resulted in PBT‐PET copolymers with an increased T_g compared to PBT. However, these copolymers showed a poorer crystallization behavior. The modified copolymer chain segments are apparently fully miscible with the unmodified PBT chains in the molten state. Consequently, the crystal growth process is retarded resulting in a decreased crystallization rate and crystallinity. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 882–899, 2007.     

Transesterification kinetics in the reactive blends of liquid crystalline copolyesters and poly(ethylene terephthalate)

The transesterification kinetics of poly(ethylene terephthalate) (PET)/copoly(oxybenzoate-p-terephthalate) (liquid crystalline polymer, LCP) (70/30 by weight) in the presence of small amount of bis(2-oxazoline) (BOZ) as chain extender was studied by using 1H nuclear magnetic resonance. The kinetic data was treated as a second-order reversible reaction, and it was found that the rate constants of transesterification at 270, 280 and 290 °C were 1.55×10⁻², 2.20×10⁻² and 3.01×10⁻² min⁻¹, respectively, the value of which was higher than the blend without addition of BOZ, 1.26×10⁻² min⁻¹, and the activation energy of PET/LCP transesterification was 84.4 kJ mol⁻¹.     

Surface modification of HDPE, PP, and PET films with KMnO4/HCl solutions

Surface modification of high-density-polyethylene (HDPE), polypropylene (PP), and poly(ethylene terephthalate) (PET) films was promoted by potassium permanganate solutions in HCl acidic medium using eight conditions by varying time, temperature, and oxidative solution concentration. This oxidation system introduced different amounts of carbonyl-carboxyl and hydroxyl groups onto the polymer surfaces. Drop water contact angle, FTIR, TGA, and SEM were used to assess oxidation efficiency and the surface changes suffered by the polymer film. The hydrophilicity of films obtained by contact angle was analyzed using a 2³ factorial design in Design-Expert^® program to obtain the main effects, the variance, and the interaction between the effects in action in the oxidation process.     

A New Approach to Prepare Poly(ethylene terephthalate)/Silica Nanocomposites with Increased Molecular Weight and Fully Adjustable Branching or Crosslinking by SSP

Summary: In the present study, it has been unexpectedly found that solid‐state polycondensation (SSP) can act as a facile method to prepare poly(ethylene terephthalate)/silica (PET/SiO₂) nanocomposites with high molecular weight and an adjustable degree of branching or crosslinking. Fumed silica, with its surface silanol groups, seems to participate in some kind of reaction, probably esterification with the hydroxy end‐groups of PET, during SSP, to act as a multifunctional chain extender. Differential scanning calorimetry and FT‐IR spectroscopy reveal this ability of the silanol groups. The molecular weight increase depends on the used temperatures of SSP as well as on the amount of SiO₂ added. As the amount of silica increases the rate of increase of the intrinsic viscosity slows because of the higher extent of branching. At 5 wt.‐% SiO₂ the extensive branching produces a crosslinked polymeric material. Such polyesters with increased molecular weight and low silica content could be suitable for blown bottle production, while the high SiO₂ content and adjustable branching or crosslinking could make them ideal high‐melt‐strength resins suitable for the preparation of low‐density closed‐shell foams.

Schematic representation of PET/SiO₂ crosslinked macromolecules.