The effect of annealing on the crystallization of poly(ethylene terephthalate)/polycarbonate blends

The effect of annealing on the morphology and subsequent crystallization kinetics of poly (ethylene terephthalate)/polycarbonate blends have been investigated using differential scanning calorimetry (DSC), polarized light microscopy, and scanning electron microscopy (SEM). During annealing transesterification and phase coarsening occurred, and the final properties were compromizes between these two competing effects. Initially, the effect of phase separation dominated and the rate of cold crystallization of PET increased. Transesterification, however, became increasingly important and the rate of crystallization decreased progressively until finally the blend completely lost the ability to crystallize. At this stage in the reaction a single glass transition was observed and uniform glassy material observed in the SEM. The maximum crystallinity of the blend achieved on heating showed the same trend in first increasing and then decreasing with annealing time. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2129–2136, 2004     

State of order in blends of poly(butylene terephthalate) with poly(ethylene terephthalate) or polycarbonate

Blends of PBT with PET or PC were studied by X-ray diffraction and DSC for different conditions of crystallization. PBT and PET crystallize very similarly, though they are recognized as partially compatible in the melt. In the PBT/PC blends X-ray diffraction examinations show crystallization of PC after 4 h of annealing. In the melt, both components are compatible. T_g-calculations indicate a plasticizing effect. In both kinds of blends, PBT crystallizes faster than PC or PET. Fast crystallization processes were examined by X-ray diffraction measurements with synchrotron radiation.     

Effect of transesterification products on the miscibility and phase behavior of poly(trimethylene terephthalate)/bisphenol A polycarbonate blends

Blends of poly(trimethylene terephthalate)/bisphenol A polycarbonate (PTT/PC) with different compositions were prepared by melt blending. The effect of transesterification on the miscibility and phase behavior of the blends was studied using DSC, DMA, and ¹H NMR. The DMA results revealed a two-phase system with partial miscibility. DSC thermograms of the first heating scan showed a crystallizable system in which addition of PC-phase reduces the degree of crystallinity. However, the cooling and also the second heating scans revealed the complete miscibility of all the blends. It was concluded that annealing at 300 °C (to remove thermal history of the blends) caused the constituents to undergo the transesterification reaction, which changes the blend to a miscible system. The miscibility is due to formation of block copolymers with different block lengths which also suppress the crystallization of the system. The degree of randomness and sequence lengths of the copolymers were determined to analyze the extent of transesterification reaction and structure of the system. It was observed that as the reaction progresses, the degree of randomness increases and the sequence length of the copolymers decreases. Moreover, both increase of reaction time and temperature increased the extent of reaction. The results of DSC and ¹H NMR showed that a small amount of reaction is needed to change this system to a miscible blend.     

Influence of copolymer composition of polyestercarbonate on miscibility with poly(butylene terephthalate)

Blends of poly(butylene terephthalate) (PBT) and polyestercarbonate (PEC), copolyesters consisting of polycarbonate (PC) and polyarylate (PAr), have been studied by thermal analysis to determine miscibility. The PBT blends with PAr and PEC containing 30 wt % of carbonate unit or less appeared to be miscible, and the tendency for stable single‐phase was observed to decrease as the content of carbonate unit in PEC copolymer increased. As determined with the crystalline phase behavior, the miscibility of PEC with PBT appeared to have a maximum around 10 ∼ 30 wt % of carbonate content in PEC copolymer, and this result was attributed to the internal repulsion effect between ester and carbonate repeating units in PEC copolymer. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 803–811, 2000     

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.     

Electrical conductivities of carbon nanotube-filled polycarbonate/polyester blends

Carbon nanotube (CNT)-filled polycarbonate (PC)/poly(butylene terephthalate) (PBT) and polycarbonate (PC)/poly(ethylene terephthalate) (PET) blends containing 1 wt% CNTs over a wide range of blend compositions were prepared by melt mixing in a torque rheometer to investigate the structure-electrical conductivity relationship. Field emission scanning electron microscopy was used to observe the blend morphology and the distribution of CNTs. The latter was compared with the thermodynamic predictions through the calculation of wetting coefficients. It was found that CNTs are selectively localized in the polyester phase and conductive blends can be obtained over the whole composition range (20 wt%, 50 wt% and 80 wt% PBT) for CNT-filled PC/PBT blends, while conductive CNT-filled PC/PET blends can only be obtained when PET is the continuous phase (50 wt%, 80 wt% PET). The dramatic difference in the electrical conductivity between the two types of CNT-filled PC/polyester blends at a low polyester content (20 wt%) was explained by the size difference of the dispersed phases on the basis of the transmission electron microscope micrographs.     

Miscibility and transesterification in ternary blends of poly(ethylene naphthalate)/poly(trimethylene terephthalate)/poly(ether imide)

Miscibility and morphology of poly(ethylene 2,6-naphthalate)/poly(trimethylene terephthalate)/poly(ether imide) (PEN/PTT/PEI) blends were investigated by using a differential scanning calorimeter (DSC), optical microscopy (OM), wide-angle X-ray diffraction (WAXD), and proton nuclear magnetic resonance (¹H-NMR). In the ternary blends, OM and DSC results indicated immiscible properties for polyester-rich compositions of PEN/PTT/PEI blends, but all compositions of the ternary blends were phase homogeneous after heat treatment at 300 °C for more than 30 min. An amorphous blend with a single T _g was obtained in the final state, when samples were annealed at 300 °C. Experimental results from ¹H-NMR identified the production of PEN/PTT copolymers by so-called “transesterification”. The influence of transesterification on the behaviors of glass transition and crystallization was discussed in detail. Study results identified that a random copolymer promoted the miscibility of the ternary blends. The critical block lengths for both PEN and PTT hindered the formation of crystals in the ternary blends. Finally, the transesterification product of PEN/PTT blends, ENTT, was blended with PEI. The results for DSC and OM demonstrated the miscibility of the ENTT/PEI blends.     

Melt-crystallization behavior and isothermal crystallization kinetics of crystalline/crystalline blends of poly(ethylene terephthalate)/poly(trimethylene terephthalate)

The melt-crystallization and isothermal melt-crystallization kinetics of poly(ethylene terephthalate)/poly(trimethylene terephthalate) blends (PET/PTT) were investigated by differential scanning calorimetry (DSC) and polarized optical microscopy. Although PET and PTT in the binary blends are miscible at amorphous state, they will crystallize individually when cooled from the melt. In the DSC measurements, PET component with higher supercooling degree will crystallize first, and then the crystallite of PET will be the nucleating agent for PTT, which induce the crystallization of PTT at higher temperature. On the other hand, in both blends of PET80/PTT20 and PET60/PTT40, the PET component will crystallize at higher temperature with faster crystallization rate due to the dilute effect of PTT. So the commingled minor addition of one component to another helps to improve the crystallization of the blends. For blends of PET20/PTT80 and PET40/PTT60, isothermal crystallization kinetics evaluated in terms of the Avrami equation suggest different crystallization mechanisms occurred. The more PET content in blends, the fast crystallization rate is. The Avrami exponent, n = 3, suggests a three-dimensional growth of the crystals in both blends, which is further demonstrated by the spherulites formed in all blends. The crystalline blends show multiple-melting peaks during heating process.     

Compatibility studies of blends of polycarbonate and poly(ethylene terephthalate)

Blends of bisphenol-A polyarbonate (PC) and poly(ethylene terephthalate) (PET) has been investigated by differential scanning calorimetry and scanning electron microscopy. Blends were prepared by screw extrusion and solution casting with weight fractions of PC in the blends varying from 0.90 to 0.10. From the measured glass transition temperature (T_g) and apparent weight fractions of PC and PET dissolved in each phase, it appears that PET dissolves more in the PC-rich phase than does the PC in the PET-rich phase. The composition-dependent values of the Flory–Huggins polymer–polymer–interaction parameter were determined and found to be from 0.054 to 0.037 for extruded blends at 275°C and from 0.058 to 0.040 for solution casting at 25°C. The interaction parameter decreases with increasing PET concentration. This result is consistent with the values of the T_gs, the microscopy study, and the measured extrudate swell ratios which show that compatibility increases more in the PET-rich compositions than in the PC-rich compositions. The PC–PET blends are not microscopically miscible for all the blend compositions.     

Rheological and thermal study of delayed crystallization in poly(butylene terephthalate)/ethylene‐co‐ethyl acrylate blends

The effects of the composition and resulting morphology on the crystallization and rheology of blends containing poly(butylene terephthalate) (PBT) and an ethylene‐co‐ethyl acrylate (EEA) copolymer, two immiscible polymers, were studied over the entire range of volume fractions. Differential scanning calorimetry (DSC) thermograms recorded during cooling showed important differences, mainly in terms of the PBT crystallization temperatures, depending on the blend composition. In addition to the classical crystallization peaks of PBT and EEA, a third crystallization peak appeared for blends containing less than 60% PBT. This peak was attributed to a delayed crystallization of PBT. This phenomenon was examined in terms of homogeneous crystallization. Linear viscoelastic measurements allowed the delayed crystallization behavior in these polymer blends to be displayed. Indeed, the variation of the storage modulus with the temperature showed increasing steps during cooling. These sudden increases appeared at temperatures very close to those at which the crystallization peaks were observed in the DSC experiments. This behavior was verified for different blend compositions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 714–721, 2004     

Reaction to fire of recycled poly(ethylene terephthalate)/polycarbonate blends

In the present paper, we study the effect of both morphology and compatibilization on the reaction to fire of blends of recycled poly(ethylene terephthalate) (PETr) with recycled polycarbonate (PCr). It is shown that while the flame retardancy of blends containing less than 50% w/w of PCr increases almost linearly with PCr content, blends containing more than 50% w/w of PCr react to fire like pure PCr. This change of reaction to fire correlates with the formation of a continuous PCr phase in the blend.The compatibilization of the blend by a trans-esterification reaction leading to the formation of copolymers at the interface decreases the overall fire performances due to PETr chain breaking as a side effect which results in a strong decrease of blend viscosity and of the temperature at which mass loss begins.     

Transreactions in poly trimethylene terephthalate/bisphenol-A polycarbonate (PC) blends analysed by pressure-volume-temperature measurements

The effect of annealing on the miscibility and thermal properties of poly trimethylene terephthalate (PTT)/bisphenol-A polycarbonate (PC) blends was examined using pressure-volume-temperature (PVT) measurements. The PTT/PC blends were thermally annealed at 260 °C for different times to induce various extents of transesterification reactions between the two polymers. The non-annealed blends are immiscible and exhibit the thermal properties of the blend components. Upon annealing, the original semi-crystalline morphology transforms to an increasingly amorphous nature. PVT and WAXS analysis confirmed that the PTT/PC blends completely lost their crystallinity when annealed at 260 °C for a period of 120 min or longer, indicating the formation of random co-polyesters due to chemical transreactions between the PTT and PC. The further increase in the specific volume with annealing time also indicates that after reaching a completely amorphous co-polymer the transesterification continuous until a fully random copolymer is formed.     

Relaxation behavior of poly(ethylene terephthalate)/poly(ethylene naphthalene 2,6‐dicarboxylate) blends prepared by cryogenic blending

A method including cryogenic grinding, melt pressing from the molten state, and quenching was used to prepare blends of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalene 2,6‐dicarboxylate) (PEN) in which the two phases were highly dispersed. The effect of melt‐pressing times on the thermal properties and relaxation behavior of PET/PEN films were characterized with differential scanning calorimetry and dielectric spectroscopy. For short melt‐pressing times, two glass‐transition, two crystallization, and two melting peaks were observed, indicating the presence of PET‐rich and PEN‐rich phases in these blends. Longer melt‐pressing times revealed a single glass transition and a single α‐relaxation process, showing that PET–PEN block copolymers were likely to be formed during the melt pressing. The experimental findings were examined in terms of the transesterification reactions between the blend components, as revealed by ¹H NMR measurements. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2570–2578, 2002     

Effect of reactive compatibilization on the properties of poly(butylene terephthalate)/acrylonitrile–ethylene–propylene–diene–styrene blends

Blends of poly(butylene terephthalate) (PBT) with 30 wt % acrylonitrile–ethylene–propylene–diene–styrene (AES) were prepared with methyl methacrylate (MMA)/glycidyl methacrylate (GMA)/ethyl acrylate (EA) terpolymers (MGEs) as compatibilizing agents. These acrylic terpolymers were miscible with the styrene–acrylonitrile (SAN) phase of AES, whereas the epoxide groups of GMA could react with the PBT end groups; this could lead to the formation of grafted copolymers (PBT‐g‐MGE) at the PBT/AES interface during the melt processing of the blends if at least a fraction of this interface was formed between the PBT and SAN phases. This study found evidence of the aforementioned interfacial structure through the effectiveness of the MGE terpolymers in promoting the compatibilization, as evaluated by dynamical mechanical analysis, through the increase in the viscosity of the blends, and through the reduction of the AES particle size dispersed in the PBT matrix. These effects became more intense with an increase in the overall concentration of GMA in the blends and with a reduction of the molecular weight of MGE. Another effect promoted by the compatibilization was a remarkable reduction of the brittle–ductile transition temperatures of the blends, which was correlated with the reduction of the AES particle size. However, this correlation between the brittle–ductile transition temperatures and particle size did not hold for the blend with the lowest AES particle size, which showed a high ductile–brittle transition temperature. These mechanical behaviors were examined on the basis of the current theory of the toughening of thermoplastics, which takes into account the importance of the rubber interparticle distance and the cavitation process of these particles. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1244–1259, 2005     

Block copolymers of poly(ethylene terephthalate–polybutylene terephthalate). I. Preparation and crystallization behavior

Block copolymers of two crystallizable compounds, poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT), were developed with PET as the major component and the amount of PBT varying from 1.0 to 20.0 wt %. These block copolymers were prepared by end-group coupling of preformed oligomers. All polymers prepared were of equivalent molecular weight as determined by the intrinsic viscosity method. Thermal properties were determined by differential thermal analysis (DTA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). With increasing PBT content, the block copolymers showed a general decrease in the values of glass transition temperature, melting temperature, initial decomposition temperature, and maximum decomposition temperature. The heat of fusion and heat of crystallization first increased and then decreased slightly. Rates of crystallization were determined by measuring density as a function of time of isothermal crystallization carried out at 95°C. It was found that small amounts of PBT increased the crystallization rate considerably over that of PET. Random copolymers did not show this phenomenon and behaved more like pure PET. The crystallization behavior of block copolymers was analyzed by the Avrami equation and Avrami exponents were determined. Results were explained on the basis that the faster-crystallizing PBT blocks crystallized first and provided built-in nucleation sites for the subsequent crystallization of PET, thus resulting in a relatively fast-crystallizing copolyester.     

Thermal ageing of polycarbonate/poly(butylene terephthalate) blends

Thermal ageing of PC/PBT blends and alloys has been studied with dynamic mechanical, calorimetric, and tensile dilatometry tests during creep. The substantial embrittlement occuring in PC/PBT during ageing is tentatively explained in terms of an unusually high densification of the amorphous phase. The phase boundaries have been found to increase in strength during ageing, improving the load bearing properties of the material.     

Fire retardant poly(ethylene terephthalate)/polycarbonate/triphenyl phosphite blends

Flame retardant recycled PET blends containing PC and triphenyl phosphite (TPP) have been designed using the following sequential processing strategy: PET and PC are first melt blended with a transesterification catalyst, allowing the compatibilisation of the blend, before adding TPP. The presence of this last component was shown to stop the transesterification reaction between PET and PC, avoiding chain breaking. In addition, TPP acts as a chain extender of PET, allowing the average chain length to be increased. The optimized blends obtained present “V-0” UL94 rating due to a better thermal stability leading to low flammability and to the development of an important, stable and covering char layer, resulting in self-extinguishability and very low Heat Release Rates during combustion.     

Compatibilizing effect of transesterification product between components in bisphenol-A polycarbonate/poly(ethylene terephthalate) blend

The compatibilizing effect of a random copolymer, which is the transesterification product, on its corresponding blend system of bisphenol-A polycarbonate/poly(ethylene terephthalate) (PC/PET) has been studied using a Differential Scanning Calorimeter and a Phase Contrast Microscope. It was found that after a long time of transesterification between PET and PC (50/50, wt %), the obtained product, that is, TCET random copolymer, is miscible with individual homopolymers of PC and PET. The addition of the TCET copolymer into the immiscible PC/PET blend can make the glass transitions of the PC-rich phase and PET-rich phase approach each other, and eventually merge into a single glass transition when the content of TCET in the ternary mixture reaches 60 wt %. Meanwhile, the phase structure images showed that with the increasing content of the TCET copolymer in the ternary blends, the size of the phase domains decreases and the phase domains further diminish at 60 wt % TCET. All these results proved the compatibilizing effect of TCET copolymer on the PC/PET blends in their ternary mixture. The mechanism of the compatibilizing effect is directly related to the reduction of the interfacial tension between PC-rich and PET-rich phase domains in the presence of increasing amounts of TCET copolymer in the ternary blends. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2960–2972, 1999     

Transesterification and crystallization behavior of poly(butylene succinate)/poly(butylene terephthalate) block copolymers

The block copolymers of poly(butylene succinate) (PBS) and poly(butylene terephthalate) (PBT) were synthesized by melt processing for different times. The sequence distribution, thermal properties, and crystallization behavior were investigated over a wide range of compositions. For PBS/PBT block copolymers it was confirmed by statistical analysis from ¹H-NMR data that the degree of randomness (B) was below 1. The melting peak (T_m) gradually moved to lower temperature with increasing melt processing time. It can be seen that the transesterification between PBS and PBT leads to a random copolymer. From the X-ray diffraction diagrams, only the crystal structure of PBS appeared in the M1 copolymer (PBS 80 wt %) and that of PBT appeared in the M3 (PBS 50 wt %) to M5 (PBS 20 wt %) copolymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 147–156, 1998     

Influence of compatibilization on the mechanical behavior of poly(trimethylene terephthalate)/poly(ethylene-octene) blends

Poly(trimethylene terephthalate) (PTT) based blends toughened with up to 30 wt.% of a partially maleinized poly(ethylene-octene) copolymer (mPEO) were obtained by melt mixing. The blends were composed of two pure amorphous phases and a partially crystalline PEO phase. The rubber modification clearly compatibilized the blends leading to a decrease in the dispersed phase size. The decrease was not enough to attain the brittle-tough transition, but an increase in the shear rate gave rise to an additional decrease in the dispersed phase size and in the interparticle distance (IDc) that led to very high toughness values (15-fold the notched impact strength of the matrix) at rubber contents above 25 wt.%. The critical interparticle distance of the blends was 0.17 μm. A comparison between this IDc and those of PBT/mPEO and PET/mPEO blends was explained in terms of their interfacial tensions.