Co[poly(ethylene terephthalate-p-oxybenzoate)] and its blends with poly(ethylene terephthalate): Transesterification reaction and fractured surface morphology

A series of co[poly(ethylene terephthalate-p-oxybenzoate)] copolyesters, viz., P28, P46, P64, and P82, were synthesized. These copolyesters were blended with poly(ethylene terephthalate) (PET) at the level of 10 wt % at 293°C for different times. The results from proton NMR analysis reveal that a significant amount of the transesterification has been detected in the cases of PET/P28, PET/P46, and PET/P64 blends. The blending time necessary before any transesterification reaction could be detected depends on the composition of copolyester, e.g., a time less than 3 min is needed for both PET/P28 and PET/P46 blends, while a longer time of 8–20 min is needed for the PET/P64 blend. It is concluded that the higher the mol ratio of the POB moiety in the copolyester is the longer the blending time needed to initiate the transesterification. The degree of transesterification is also increased as the duration of melt blending is prolonged. Two-phase morphology was observed by scanning electron microscopy (SEM) micrographs in all the blends. It was observed that the more similar the composition between the copolyester and PET in the blends is the better the miscibility or interfacial adhesion between the two phases. Moreover, the miscibility can be markedly improved by the duration of melt blending. © 1996 John Wiley & Sons, Inc.     

A study on blends of liquid crystalline copolyesters with polycarbonate. II. Transesterification control

The inhibited and catalyzed ester exchange (transesterification) during melt blending of poly(bisphenol-A carbonate) (PC) and liquid crystalline poly(oxybenzoate-co-ethylene terephthalate) (POB–PET 40/60; P46) was investigated with differential scanning calorimetry. It was found that the ester exchange between P46 and PC was effectively inhibited for a 20% P46 blend at 240°C, as further confirmed by nuclear magnetic spectroscopy. When the blending temperature and P46 concentration increased, only the transesterification between the PET segment in P46 and PC took place under inhibition. The morphology of the blends was analyzed with scanning electron microscopy and displayed a disconnected interface between P46 and PC under inhibition. Conversely, the transesterification took place between the POB segment in P46 and PC when a catalyst was added. © 1996 John Wiley & Sons, Inc.     

Interchange reactions between poly(ethylene terephthalate) and its copolyesters

Poly(ethylene terephthalate) (PET) was blended with two kinds of co[poly-(ethylene terephthalate-p-oxybenzoate)] (POB-PET) copolyester, designated P46 and P64. The PET and POB-PET copolyester were combined in the ratios of 85/15, 70/30, and 50/50. The blends were melt-mixed in a Brabender Plasticorder at 275, 285, and 293°C for different times. The interchange reactions detected by proton nuclear magnetic resonance analysis occur during the processing at a greater level if the blending time increases. The interchange reactions are as a function of temperature, blending times, and composition of blends. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1591–1595, 1998     

Recycling poly(ethylene terephtalate) wastes: Properties of poly(ethylene terephtalate)/polycarbonate blends and the effect of a transesterification catalyst

The article addresses the issue of recycling of poly(ethylene terephtalate) (PET) by melt blending with polycarbonate (PC). PET/PC blends containing various amounts of the immiscible polymers were prepared in a twin‐screw extruder. Selected compositions were also prepared in the presence of an Sn‐based catalyst to assess the influence of transesterification during melt mixing. The degree of miscibility in the blends was studied using differential scanning calorimetry, scanning electron microscopy, and mechanical testing. PET/PC blends exhibit enhanced tensile properties in comparison to neat components for compositions of PET higher than 50% and these properties are improved by the addition of a transesterification catalyst. The PET/PC blend containing 20 wt% of PC, prepared with stannous octoate, shows the smallest size of the dispersed phase because of transesterification reactions that generate copolymer molecules at the interface between the immiscible polymers. The melting temperature of PET is decreased with the increase of the PC content in blends extruded in the presence of the catalyst. Also, the temperatures of the cold crystallization of PET are higher than those of similar blends without added catalyst. Both features give rise to better molding properties because of a shortening of the cooling time in the range of 50–90 wt% of PET. POLYM. ENG. SCI. 46:1378–1386, 2006. © 2006 Society of Plastics Engineers     

Transesterification reaction of polyarylate and copolyester (PETG) blends

Transesterification reactions between polyarylate (PAr) and a copolyester (PETG) have been investigated by proton nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FTIR), and differential scanning calorimetry. Blends of PAr and PETG were prepared by melt mixing and solution-casting with weight fractions of PAr in the blends varying from 0.90 to 0.10. The PETG is a copolyester containing ethylene-1,4-cyclohexylene dimethylene terephthalate. From the thermal analysis of the PAr/PETG melt blends, a single glass transition temperature is observed, which indicates a miscibility between the PAr and PETG. The benzene insoluble fraction of the PAr/PETG (50/50) melt blends and solution-cast blends were characterized using NMR and FTIR. The results of NMR and FTIR support the conclusion that transesterification reactions between the PAr and PETG occurred under the melt blending conditions applied.     

Blends of poly(ethylene terephthalate) with co[poly(ethylene terephthalate-p-oxybenzoate)]. II. Composition effect on the rate of crystallization

Poly(ethylene terephthalate) (PET) was blended with four different kinds of co[poly(ethylene terephthalate-p-oxybenzoate)] copolyesters, designated P28, P46, P64, and P82, with the level of copolyester varing from 1 to 15 wt %. All samples were prepared by melt-mixing in a Brabender Plasticorder for 8 min. The crystallization behavior of samples were then studied via DSC. The results indicate that these four copolyesters accelerate the crystallization rate of PET in a manner similar to that of a nucleating agent. The acceleration of the PET crystallization rate was most pronounced in the PET/P28 blends with a maximum level at 10 wt % of P28, and in the PET/P28 blends, at 5 wt % of P82. The melting endotherm onset temperatures and the melting peak widths for the blends are comparable with those of neat PET. These results imply that the stability of PET crystalline phase in the blends does not change by blending. The observed changes in crystallization behavior, however, are explained by the effect of the physical state of the copolyester during PET crystallization as well as the content of the p-oxybenzoate (POB) moiety in corporated into the blends. © 1995 John Wiley & Sons, Inc.     

Co[poly(ethylene terephthalate-p-oxybenzoate)] thermotropic copolyester. II. X-ray diffraction analysis

A series of co[poly(ethylene terephthalate-p-oxybenzoate)] thermotropic copolyester with different compositions were prepared by the copolymerization of either poly(ethylene terephthalate) (PET) polymer or its oligomer with p-acetoxy-benzoic acid. The polymeric products were subjected to solid-state polymerization for various time intervals. Effects of composition ratio and solid-state polymerization time on X-ray diffraction behavior were investigated. It is found that the effect of transesterification induced by solid-state polymerization causes an increase in crystallinity with the copolyesters having high mol % of p-oxybenzoic acid (POB) moiety and causes a decrease in crystallinity with the copolyesters having high mol % of PET moiety. In general, the crystallinity of copolyesters is first increased and then decreased as solid-state polymerization time proceeds. However, the crystallinity of copolyester having POB/PET = 80/20 composition is increased generally at 4-h solid-state polymerization. It is also found that the crystallinity of copolyesters is decreased by quenching. The copolyester based upon either PET oligomer with 4-h solid-state polymerization or PET polymer with 8-h solid-state polymerization shows the most similar X-ray diffraction pattern with that of Eastman 10109. © 1993 John Wiley & Sons, Inc.     

Reactive compatibilization of the poly(ethylene terephthalate)/liquid crystalline polymer blends by solid epoxy resin as a coupling agent

A selected reactive coupling agent can be served as an effective compatibilizer for certain immiscible and incompatible blends should both blend constituents possess the necessary functional groups that can react with the coupling agent at comparable rates. Solid epoxy resin with two epoxide endgroups per molecule was demonstrated to be an efficient reactive compatibilizer for the incompatible blends of poly(ethylene terephthalate) (PET) and copolyester liquid crystalline polymer (LCP) by functioning as a coupling agent. The main chain structure of the epoxy resin is neither identical not miscible with PET and LCP and tends to reside at interface during melt mixing. This preferential residence gives the epoxy compatibilizer greater opportunity to react with both PET and LCP simultaneously to produce the in situ–formed epoxy-b-LCP mixed copolymer. This in situ–formed mixed copolymer is highly effective in compatibilizing the PET/LCP blends. This reactive epoxy compatibilizer enhances the LCP fibril formation and results in substantial improvements on stiffness and toughness of the PET/LCP blends. © 1996 John Wiley & Sons, Inc.     

Effect of composition and molecular structure on the LC phase of PHB-PEN-PET ternary blend

Poly(p-hydroxybenzoic acid) (PHB)–poly(ethylene terephthalate) (PET) 8/2 thermotropic liquid crystalline copolyester, poly(ethylene 2,6-naphthalate) (PEN), and PET were mechanically blended to pursue the liquid crystalline (LC) phase of ternary blends. The torque values of blends with increasing PHB content abruptly decreased above 40 wt % of PHB content because the melt viscosity of ternary blends dropped. Glass transition temperature and melting temperature of blends increased with increasing PHB content. The tensile strength and initial modulus of blends were low at 10 and 20 wt % PHB. However, the blends containing above 30 wt % PHB were improved with increasing PHB content due to the formation of fibrous structure. The blend of 20 wt % PHB formed irregularly dispersed spherical domains, and the blends of 30–40 wt % PHB showed LCP ellipsoidal domains and fibrils. In the polarized optical photographs, the blends of 40 wt % PHB showed pseudo LC phases. The degree of transesterification and randomness of blends were increased with blending time. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1065–1073, 1998     

Role of 2‐hydroxyethyl end group on the thermal degradation of poly(ethylene terephthalate) and reactive melt mixing of poly(ethylene terephthalate)/poly(ethylene naphthalate) blends

In an attempt to minimize the acetaldehyde formation at the processing temperatures (280–300°C) and the outer–inner transesterification reactions in the poly (ethylene terephthalate) (PET)–poly(ethylene naphthalate) (PEN) melt‐mixed blends, the hydroxyl chain ends of PET were capped using benzoyl chloride. The thermal characterization of the melt‐mixed PET–PEN blends at 300°C, as well as that of the corresponding homopolymers, was performed. Degradations were carried out under dynamic heating and isothermal conditions in both flowing nitrogen and static air atmosphere. The initial decomposition temperatures (T_i) were determined to draw useful information about the overall thermal stability of the studied compounds. Also, the glass transition temperature (T_g) was determined by finding data, indicating that the end‐capped copolymers showed a higher degradation stability compared to the unmodified PET and, when blended with PEN, seemed to be efficient in slowing the kinetic of transesterification leading to, for a finite time, the formation of block copolymers, as determined by ¹H‐NMR analysis. This is strong and direct evidence that the end‐capping of the ? OH chain ends influences the mechanism and the kinetic of transesterification. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

The crystallization rate of poly(ethylene terephthalate) accelerated by co[poly(butylene terephthalate‐p‐oxybenzoate)] copolyesters

Poly(ethylene terephthalate) (PET) was blended with three different kinds of co[poly(butylene terephthalate‐p‐oxybenzoate)] copolyesters, designated B28, B46, and B64, with the level of copolyester varying from 1 to 15 wt %. All samples were prepared by solution blending in a 60/40 by weight phenol/tetrachloroethane solvent at 50°C. The crystallization behavior of samples was then studied via differential scanning calorimetry. The results indicate that these three copolyesters accelerate the crystallization rate of PET in a manner similar to that of a nucleating agent. The acceleration of PET crystallization rate was most pronounced in the PET/B28 blends with a maximum level at 10 wt % of B28. The melting temperatures for the blends are comparable with that of pure PET. The observed changes in crystallization behavior are explained by the effect of the physical state of the copolyester during PET crystallization as well as the amount of copolyester in the blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 587–593, 2000     

Morphology and enzymatic degradation of thermoplastic starch–polycaprolactone blends

This study's aim was to evaluate the effect of processing conditions on the morphology and enzymatic degradation of 50/50 (w/w) thermoplastic starch–polycaprolactone blends. The blends, produced from native potato starch, glycerol, and polycaprolactone in a melt mixer using different mixing speeds and temperatures, were cocontinuous, and the blends were very homogeneous. Enzymatic hydrolysis was performed using Bacillus licheniformis alpha‐amylase and Aspergillus niger glucoamylase on both milled and intact samples. The thin layer of polycaprolactone (≈ 5 μm) formed on the surface of the thermoplastic starch–polycaprolactone blends during compression molding strongly reduced the rate of enzymatic hydrolysis. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2594–2604, 1999     

Reactive blending of poly(ethylene terephthalate) with a liquid crystalline copolyester and polyhydroxyether

Poly(ethylene terephthalate) modified with a dianhydride (PET–anhydride) was melt‐blended with a liquid crystalline copolyester (Vectra A) in the presence of a small amount of a liquid crystalline polyhydroxyether. The mechanical properties of a blend consisting of PET–anhydride/Vectra A/polyhydroxyether were drastically improved compared to blends without polyhydroxyether or without anhydride. Melt‐spun fibers of PET–anhydride/Vectra A/polyhydroxyether in a 80/20/0.75 weight ratio displayed a much higher tensile modulus (17 GPa) and tensile strength (214 MPa) than did a 80/20 PET–anhydride/Vectra A blend (4 GPa and 60 MPa, respectively). A similar increase in modulus and strength was found for a 90/10/0.75 relative to a 90/10 blend. The tensile moduli of the blends can well be described by the Tsai–Halpin equation. A better fibril formation was observed, which was attributed to an improved viscosity ratio. Reactions between the various functional groups during melt processing were indicated by viscosity measurements. The polyhydroxyether may act as a reactive compatibilizer which improves the interfacial adhesion, chemically and/or physically. WAXD recordings of both blends showed a crystalline and highly oriented Vectra phase. The PET phase was unoriented and amorphous in a PET/Vectra blend and semicrystalline and weakly oriented in a PET/Vectra/polyhydroxyether blend. Postdrawing of the various blend fibers to λ = 4 increased the modulus by about 40% and the tensile strength by more than 100%, mainly through orientation of the PET phase. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1107–1123, 1999     

Rheology and transesterification between polycarbonate and polyesters

Rheological behavior of polycarbonate (PC)–polyester blends is studied. The miscibility and rheological behavior are discussed. Effect of catalyst, tetra‐n‐butyl orthotitanate on the transesterification reactions for a [60 (PC):40 (PET or PBT)] blend is studied rheologically. The blends were mixed for different spans of time for rheological study. The blends are analyzed on the basis of the mechanism suggested by other researchers. As the mixing time is increased, the blends show decrease in viscosity. Random copolymers also are amorphous in nature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2039–2047, 2007     

Miscibility study on blend of thermotropic liquid crystalline polymers and polyester

The miscibility of thermotropic liquid crystalline polymers (TLCPs) and polyester blends was investigated with thermal and morphological analyses, as well as transesterification. TLCPs composed of 80 mol % para‐hydroxybenzoate (PHB) and 20 mol % poly(ethylene terephthalate) (PET) or 60 mol % PHB and 40 mol % PET, and polyesters such as PET and poly(ethylene 2,6‐naphthalate) (PEN) were melt blended in an internal mixer. DSC analyses were performed to investigate the thermal transition behavior and to obtain thermodynamic parameters. All the blends showed only a single glass‐transition temperature, which means they are partially miscible in the molten state. The Flory–Huggins interaction parameter was calculated employing the Nishi–Wang approach, and negative values were obtained except for the P(HB8‐ET2)/PEN blends. Transesterification was investigated using ¹H‐NMR, and the change of chemical shift compared to pure PET or P(HB‐ET)s was observed in the P(HB‐ET)/PET blends. An intermediate chemical shift value (4.83 ppm) was observed in the P(HB6‐ET4)/PEN blends, which indicates transesterification occurred. The fractured surface morphology of scanning electron micrographs showed that the interfaces between the LC droplets and matrix were not distinct. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1842–1851, 2003     

Catalytic transesterification in polycarbonate–polycaprolactone systems

Bisphenol A polycarbonate (PC)–poly-ε-caprolactone (PCL) blends have been prepared by melt mixing in the presence of different catalysts using a Brabender plastograph and single-screw extruder at 240–260°C. Increased crystallizability [detected by differential scanning calorimetry (DSC)] of the PC component was observed in the blends obtained in the presence of p-toluenesulfonic acid. Acceleration of carbonate-carbonate exchange reactions is suggested as the main reason for the crystallizability enhancement. Results of solubility tests, DSC, and infrared (IR) spectroscopy evidence ester-carbonate transesterification taking place during PC–PCL blending in the presence of tetrabutoxy titanium and dibutyltin dilaurate. © 1994 John Wiley & Sons, Inc.     

Effects of mixing strategy on catalyst‐assisted reactive blending of polycarbonate and polyethylene terephthalate

Reactive melt mixing of polycarbonate (PC) and polyethylene terephthalate (PET) blends with constant composition of 80:20 in the presence of a freshly added catalyst was conducted through a two‐step method. At first, PC and PET underwent premixing and melt mixed in the absence of a fresh catalyst. Then, mixing continued with catalyst addition under the same previous condition. The effects of varied premixing times from 1 to 5 min and mixing intensity at rotor speeds of 30 and 50 rev/min (rpm) were separately evaluated in transesterification reaction. The results of solubility analysis showed that the longer premixing time and the higher mixing rate enhanced the rate and extension of reaction. Fourier transform infrared (FTIR) spectroscopy and thermal analysis by differential scanning calorimetry were conducted on specimens on the basis of solubility separations. The height ratio of carbonyl group peaks of PC and PET phases were calculated for their corresponding FTIR spectra. The height ratio for PET showed a good correlation with solubility data. Moreover, crystallinity of PET phase was influenced by the reaction which was analyzed by solubility parameters. J. VINYL ADDIT. TECHNOL., 25:127–133, 2019. © 2018 Society of Plastics Engineers     

Microstructure and crystallization of melt‐mixed poly(ethylene terephthalate)/poly(ethylene isophthalate) blends

Physical blends of poly(ethylene terephthalate) (PET) and poly(ethylene isophthalate) (PEI), abbreviated PET/PEI (80/20) blends, and of PET and a random poly(ethylene terephthalate‐co‐isophthalate) copolymer containing 40% ethylene isophthalate (PET₆₀I₄₀), abbreviated PET/PET₆₀I₄₀ (50/50) blends, were melt‐mixed at 270°C for different reactive blending times to give a series of copolymers containing 20 mol % of ethylene isophthalic units with different degrees of randomness. ¹³C‐NMR spectroscopy precisely determined the microstructure of the blends. The thermal and mechanical properties of the blends were evaluated by DSC and tensile assays, and the obtained results were compared with those obtained for PET and a statistically random PETI copolymer with the same composition. The microstructure of the blends gradually changed from a physical blend into a block copolymer, and finally into a random copolymer with the advance of transreaction time. The melting temperature and enthalpy of the blends decreased with the progress of melt‐mixing. Isothermal crystallization studies carried out on molten samples revealed the same trend for the crystallization rate. The effect of reaction time on crystallizability was more pronounced in the case of the PET/PET₆₀I₄₀ (50/50) blends. The Young's modulus of the melt‐mixed blends was comparable to that of PET, whereas the maximum tensile stress decreased with respect to that of PET. All blend samples showed a noticeable brittleness. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3076–3086, 2003     

Syntheses and characterization of poly(ethylene terephthalate) modified with p-acetoxybenzoic acid

Though the structure and properties of a copolyester of 40 mole % of polyethylene terephthalate (PET) and 60 mole % p-hydroxybenzoic acid (PHB) (PET/60PHB) and their blends have been well documented, no work has been reported in an open literature on the systematic investigation of the PET copolymers modified with broad range of p-acetoxybenzoic acid (PABA) composition as yet. In this study, several PETA-x copolyesters having various PABA compositions from 10 to 70 mole % were prepared by the melt reaction of PABA and PET without a catalyst, where x denotes the mole % of PABA. And the modified polyesters obtained were characterized by ¹H-NMR spectrophotometry, X-ray diffraction pattern, polarizing microscopy, thermal analysis, and rheometry. The anisotropic phase appeared when x is above 50 mole % of PABA, and especially for the x's of 60 and 70 mole %, the nematic liquid crystalline texture appeared clearly on the whole matrix. As the mole % of PABA increased, melting temperature, heat of fusion, crystalline temperature, degree of crystallinity, and the glass transition temperature of the modified PET were decreased, but the thermal stabilities of those copolyesters were increased. The dependence of melt viscosity on the shear rate for PETA-50 ∼ 70 followed the typical rheological behavior of liquid crystalline polymers. Finally, it was concluded that the PETA-x copolyesters having compositions of higher than 50 mole % of PABA exhibit the behavior of thermotropic liquid crystalline polymers. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1707–1719, 1999