Novel copolyesters based on poly(alkylene dicarboxylate)s: 2. Thermal behavior and biodegradation of fully aliphatic random copolymers containing 1,4-cyclohexylene rings

Aliphatic poly(butylene 1,12-dodecanedioate) is an interesting biodegradable polyester characterized by high thermal stability and high crystallinity, but low melting temperature. In order to improve the performances of this polymer some novel fully aliphatic random copolyesters have been prepared starting from 1,4-butanediol and different molar ratio of 1,12-dodecanedioc acid and 1,4-cyclohexanedicarboxylic acid. The copolymers have a notable resistance to thermal degradation, thermal properties which vary as a function of the composition, and maintain the mechanical characteristics of the poly(alkylene dicarboxylate). In particular, the copolymer containing the 70 mol% of 1,4-cyclohexanedicarboxylate units improves the thermal properties of the poly(butylene 1,12-dodecanedioate) and presents a very high biodegradation rate, higher than those of the two parent homopolymers. This behavior has been correlated to the low level of crystallinity of the sample and to the composition of the amorphous phase. Therefore, these novel fully aliphatic copolymers represent an interesting new class of copolyesters which can balance good physical properties and high biodegradability.     

Incorporation of a flame retardancy enhancing phosphorus-containing diol into poly(butylene terephthalate) via solid state polycondensation: A comparative study

The phosphorus-containing aliphatic-aromatic diol 2-[4-(2-hydroxy-ethoxy)-3-(10-oxo-10-H9-oxa-10-λ5-phospha-phenanthrene-10-yl)-phenoxy]-ethanol, a potential flame retardant, was incorporated into poly(butylene terephthalate) (PBT) by solid state polycondensation. Thus, polymers with various ratios of PBT/DOPO-diol and number-average molar masses up to 57,000 g mol⁻¹ could be prepared. Their molar masses were higher than those of copolyesters with comparable composition obtained by direct melt polycondensation. Structures and properties of copolyesters produced by both methods were not significantly different after melt processing. Their thermal properties and combustion behaviour were investigated by means of DSC, TGA, and pyrolysis combustion flow calorimetry. Combustion studies revealed high char yields, very low heat release capacities and high limiting oxygen index (LOI) at rather low P-contents, indicative of better flame-retardancy properties.     

聚乙二醇共聚对苯二甲酸丁二醇酯的合成及在生物材料中的应用

综述了聚醚酯热塑性弹性体聚忆二醇／聚对苯二甲酸丁二醇酯（PEG／PBT）的合成、组成与性能关系及其在组织工程和药物缓释体系等方面的应用研究进展。PEG／PBT是一类力学性能优良、可降解和生物相容性良好、极具应用潜力的生物材料。     

Effect of a polyetheramine additive on the melt-flowability of poly(butylene terephthalate)

A polyetheramine (PEA) was added to poly(butylene terephthalate) (PBT) to improve its melt-flowability. Fourier transform infrared (FTIR) and solution proton nuclear magnetic resonance spectroscopy (¹H-NMR) were employed to check the change in chemical structure after compounding, while differential scanning calorimetry (DSC), wide angel X-ray diffraction (WAXD), capillary rheometer and a universal testing machine were used to investigate the thermal properties, crystal structure, rheological behavior and mechanical properties of PBT/PEA blends. The results revealed that a loading of 1.0wt% PEA in PBT drastically improved its melt-flowability without the loss of thermal properties and tensile strength. As comparisons, blends of PBT with polyols such as pentaerythritol and di(trimethylolpropane) were also prepared and the properties were evaluated. It was found that the melt-flowability improvement from these polyols was much lower than that from PEA.     

Synthesis of poly(butylene terephtahlate) nanocomposites using anionic clays

The synthesis of poly(butylene terephthalate) (PBT) nanocomposites by in situ polymerisation method using an organo-modified layered doubled hydroxide is described. 4-Sulfobenzoic acid potassium salt, sodium dodecyl sulfate and dimethyl 5-sulfo isophthalate sodium salt were used as intercalating compounds to improve clay exfoliation. The thermal and dynamic mechanical properties of the nanocomposites prepared were investigated and compared to those of montmorillonite-type nanocomposites prepared by similar synthetic route. The nanocomposites obtained, independent of the degree of exfoliation, showed better dynamic mechanical properties respect to PBT homopolymer while improvements in thermal stability were achieved when dimethyl 5-sulfo isophthalate was used as intercalating agent, highlighting the importance of the interactions of ionic groups covalently linked to the polymer with the charged clay platelets.     

Orientation and mechanical properties of PBT and its blends with a liquid-crystalline copolyester

Blends of poly (butylene terephthalate) (PBT) and a liquid-crystalline copolyester (60 mol % poly(p-hydroxy benzoic acid)/40 mol % polyethylene terephthalate) (LCP) were prepared in the melt state. The investigation of mechanical properties indicated that, for the processing conditions used, neither the addition of up to 30 wt % LCP to PBT nor the cooling history affected significantly the tensile modulus E. For oriented specimens, a marked improvement of E was obtained for all the blends, and increased with the LCP content. This improvement was more marked for slowly cooled samples. X-ray diffraction was used to quantify the orientation of the crystalline PBT and liquid-crystalline LCP phases. It was shown that neither the thermal history nor the presence of up to 30 wt % LCP affected the orientation behavior of the PBT crystalline phase. For the LCP phase, measurements were not possible for concentrations lower than 10 wt %, and were more difficult and less precise than for PBT. Nevertheless, it was possible to show that a better orientation was obtained for the slowly cooled samples and for higher concentrations of LCP in the blends. This correlated with the enhancement of mechanical properties observed for the oriented samples.     

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     

Effects of comonomer sequential structure on thermal and crystallization behaviors of biodegradable poly(butylene succinate‐co‐butylene terephthalate)s

In this work, new investigations on the effect of comonomer sequential structure on the thermal and crystallization behaviors and biodegradability have been implemented for the biodegradable poly(butylene succinate‐co‐butylene terephthalate) (PBST) as well as aliphatic poly(butylene succinate) (PBS). At first, these copolyesters were efficiently synthesized from dimethyl succinate and/or dimethyl terephthalate and 1,4‐butanediol via condensation polymerization in bulk. Subsequently, their molecular weights and macromolecular chain structures were analyzed by gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR) spectroscopy. By means of differential scanning calorimeter (DSC) and wide‐angle X‐ray diffractometer (WAXD), thermal and crystallization behaviors of these synthesized aromatic–aliphatic copolyesters were further explored. It was demonstrated that the synthesized copolyesters were revealed to have random comonomer sequential structures with thermal and crystallization properties strongly depending on their comonomer molar compositions, and that crystal lattice structures of the new crystallizable copolyesters shifted from the monoclinic crystal of semicrystalline PBS to triclinic lattice of the poly(butylene terephthalate) (PBT) with increasing the terephthalate comonomer composition, and the minor comonomer components were suggested to be trapped in the crystallizable component domains as defects. In addition, the enzymatic degradability was also characterized for the copolyesters film samples. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1635–1644, 2006     

Synthesis and Characterization of Block Copolymers of Poly(Butylenes Terephthalate-Co-Adipate)

The block copolyesters of poly(butylene terephthalate)(PBT) and poly(butylene adipate)(PBA) were prepared by a novel two-stage method. In the first stage, high molecular weight PBT and PBA were melt mixed in the presence of 1,4-butanediol at 275 °C. In the second stage, vacuum was applied to raise the molecular weight. The extent of transesterification was controlled by the proportion of 1,4-butanediol. The sequence distribution and the thermal properties of the block copolyesters were characterized by NMR and DSC respectively.     

Synthesis and structure of elastomeric poly[ester-block-ether]s

Different poly[ester-block-ether] (PEE) elastomers have been prepared in a two-stage process, namely transesterification followed by polycondensation in the melt. These terpolymers consisted of poly(butylene terephthalate) (PBT), poly(oxytetramethylene) (PTMO) and dimerized fatty acid (DFA). The content of PTMO and DFA blocks was changed at a constant PBT mass ratio of 50. Supermolecular structure of synthesized polymers was investigated using optical microscopy (OM) and transmission electron microscopy (TEM). Thermal and mechanical properties were examined by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMTA). An influence of dimerized fatty acid on the segment's comiscibility (phase separation) was estimated.     

Surface modification of multiwall carbon nanotubes and its effect on mechanical and through‐plane electrical resistivity of PEMFC bipolar plate nanocomposites

In this work, we showed how the functionalization of multiwall carbon nanotubes (MWCNT) by nitric acid (HNO₃) and their predispersion into poly (butylene terephthalate) (PBT) improved the through‐plane electrical conductivity and mechanical properties of co‐continuous morphology polyvinylidene fluoride (PVDF)/poly (ethylene terephthalate) (PET)/carbon black (CB)/graphite (GR)/MWCNT nanocomposites. First, when MWCNT were functionalized with HNO₃ then premixed with PBT, they showed no aggregations inside the PBT matrix due to their improved interfacial interactions and chemical compatibility with the PBT matrix. Then, when PBT/(HNO₃‐functionalized MWCNT) mixture was added in small quantities to (PET/PVDF)/(CB/GR) composites, it decreased significantly their through‐plane resistivity and enhanced their impact and flexural properties. Its synergistic effect also led to the best proton exchange membrane fuel cell bipolar plate prototypes (smoother surface, without any cracks).     

An efficient halogen-free flame retardant for glass-fibre-reinforced poly(butylene terephthalate)

Compared with poly(butylene terephthalate) (PBT), glass-fibre-reinforced poly(butylene terephthalate) (GF-PBT) is difficult to flame retard with halogen-free flame retardants. In the present study, the aluminium salt of hypophosphorous acid (AP) was used as a flame retardant for GF-PBT. A series of flame-retardant GF-PBT composites was prepared via melt compounding. The flame retardance and combustion behaviour of the composites were studied by limiting oxygen index (LOI), vertical burning test (UL-94) and cone calorimetric test. Thermal behaviours and thermal decomposition kinetics were investigated by thermogravimetric analysis (TGA) under N₂ atmosphere. The addition of AP to the composites could result in an increased LOI value, a UL-94 V-0 (1.6 mm) classification and a better fire performance in cone calorimetric tests. The char morphology observation after flame-retardant tests, calculation of decomposition kinetics, X-ray photoelectron spectroscopy (XPS) and infra-red spectral analysis of the char residue confirmed the condensed-phase flame-retardant mechanism. Furthermore, the mechanical properties of the flame-retardant composites were not deteriorated, retaining an acceptable level.     

Recycled carbon fiber reinforced poly(butylene terephthalate) thermoplastic composites: fabrication,crystallization behaviors and performance evaluation

The thermoplastic composites based on poly(butylene terephthalate) (PBT) and recycled carbon fiber (RCF) were prepared through simple melt compounding by a twin‐screw extruder. An effective approach was utilized to clean and treat the RCF surface with a concentrated solution of nitric acid and then a solution of diglycidyl ether of bisphenol A as macromolecular coupling agent so as to improve the interfacial adhesion between the RCF and PBT matrix. As a result, the reinforcing potential of the RCF was enhanced substantially, and the mechanical properties, heat distortion temperature, and thermal stability of PBT could be significantly improved by incorporating this surface‐treated RCF. The morphologies of fracture surfaces indicated that the RCF achieved a homogeneous dispersion in the PBT matrix due to a good interfacial interaction between fiber and PBT. The investigations on the crystallization behaviors and kinetics demonstrated that the RCF acted as a nucleation agent for the crystallization of PBT, and the crystallization rate and nucleation density of PBT were increased remarkably due to the heterogeneous nucleating effect of RCF in the matrix. These features may be advantageous for the enhancement of mechanical properties, heat resistance, and processability of PBT‐based composites. This study may provide a design guide for carbon fiber‐reinforced PBT composites with a great potential as well as a low cost for industrial and civil applications. Copyright © 2012 John Wiley & Sons, Ltd.     

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.     

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     

Preparation of Long Glass Fiber Reinforced Poly(butylene terephthalate) Composites with Chemical Bonding Interphase

Long glass fiber reinforced poly(butylene terephthalate) composites (LGF/PBT) were prepared by a new process. PBT oligomers with low melt viscosity were impregnated into the reinforcing glass fiber and then grafted to the reinforcing glass fiber surface treated with a silane coupling agent during solid‐state polymerization. The reinforcing glass fiber, after removing ungrafted PBT from LGF/PBT, was investigated with the result showing the presence of a grafted PBT layer on the surface of treated glass fiber. The mechanical properties of the composites were significantly improved owing to the grafting of the PBT macromolecules. The fiber length distribution and fiber arrangement in the injection molded composites were also studied and the results showed that a small amount long glass fiber could be connected at junction points in the composites, which were of benefit to the mechanical properties of the composites.     

Chain extension of polyesters PET and PBT with two new diimidodiepoxides. II

Two new diglycidyl ester compounds containing preformed imide rings for better thermal stability were prepared to be used as chain extenders for PET and PBT. The preparation of these compounds was carried out in two steps. In the first step, diimidodiacids were prepared from pyromellitic anhydride and 3-aminopropanoic acid or 4-(aminomethyl)benzoic acid. From these diimidoacids, in a second step, diimidodiepoxides were obtained by reaction with epichlorohydrin. The aforementioned diimidodiepoxides were used as chain extenders for poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) with satisfactory results. The polyester samples obtained from various residence times in the reactor, were characterized by solution viscosity measurements, carboxyl, and hydroxyl end-group determination. Starting from a PET having intrinsic viscosity ([η]) of 0.60 dL/g and carboxyl content (CC) of 42 equiv/10⁶ g, one could obtain PET with [η] of 1.16 and CC below 5 equiv/10⁶ g. The typical reaction condition for the coupling of PET was its heating with the chain extender under argon atmosphere above its melting temperature (280°C) for several minutes. Analogous results were obtained for PBT. The hydroxyl content in all cases was increased. © 1996 John Wiley & Sons, Inc.     

Thermal properties of multiblock thermoplastic elastomerswith oligoamide soft blocks derived from dimerized fatty acid

Two series of multiblock copolymers, poly(ester-block-amide)s (PEA) and poly(amide-block-amide)s (PAA), with the same type of oligoamide soft block were obtained. Oligoamide soft block was prepared from dimerized fatty acid and 1,6-hexamethylenediamine. Oligo(butylene terephthalate) (PBT) was used as oligoester hard block in the first series and oligolaurolactam (PA12) was oligoamide hard block in the second one. The thermal and mechanical properties of these copolymers have been investigated as functions of temperature and the hard/soft block ratio. DSC and DMTA revealed that the copolymers behaved as thermoplastic elastomers.     

Thermal degradation of polyesters by simultaneous TG-DTA/FT-IR analysis

A combination system of thermogravimetric/differential thermal analysis (TG-DTA) and Fourier-transform infrared absorption spectroscopy (FT-IR) was described. This simultaneous TG-DTA/FT-IR technique gave spectroscopic and weight loss information about the thermal degradation process of engineering polyesters; poly(ethylene terephthalate)(PET) and poly(butylene terephthalate)(PBT). The evolved gases from PET were benzoic acid, carbon dioxide and carbon monoxide, while those from PBT were terephthalic acid esters and benzoic acid esters.

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Zusammenfassung Es wird ein kombiniertes System aus TG-DTA und FT-IR beschrieben. Mit dieser simultanen TG-DTA/FT-IR-Technik wurden spektroskopische und Massenverlustangaben über die thermische Zersetzung technisch wichtiger Polyester, namentlich von Poly(ethylenterephthalat) (PET) und Poly(Butylenterephthalat) (PBT) ermittelt. Die aus PET freigesetzten Gase waren Benzoesäure, Kohlendioxid und Kohlenmonoxid, die aus PBT freigesetzten Gase hingegen Terephthalsäureester und Benzoesäureester.

     

The influence of different fillers on mechanical and physical properties of high-molecular-weight biodegradable aliphatic polyesters

Poly(ethylene succinate) and poly(butylene succinate) are synthetic biodegradable polymers, and much attention is paid to study the properties of pure polymers and the polymers modified by different comonomers and filling materials. The literature data on the physical properties of these polymers vary widely depending on their method of preparation and subsequent modifications. Most of the studies deal with low- and moderate-molecular-weight polymers or commercial grade polymers, modified by different comonomers and chain-extension agents. The data on pure high-molecular-weight polymers are scarce. In this work, we have prepared high-molecular-weight (MW range of (1.4–1.8) × 10⁵) poly(ethylene succinate) and poly(butylene succinate) by direct polycondensation at 200°C in a nitrogen flow without chain-extension agents. We have further studied the properties of pure polymers and examined the effect of different fillers (carbon nanotubes, SiO₂, Aerosil®) on the mechanical and physical properties of these polymers. Because of high-molecular-weight, the polymers possess increased tensile and storage moduli and thermostability. Even very low filler contents (up to 1 wt %) have a pronounced influence on the polymer properties: the polymer tensile and the storage modulus increases, the elongation at break decreases, and the thermal stability of the polymers decreases slightly. The effects of fillers are less pronounced compared with those for low- and moderate-molecular-weight polymers. When mixed together, poly(ethylene succinate) and poly(butylene succinate) crystallize independently from each other as evident from the mechanical and thermal analysis data.