Copolyester Research Articles

Structure and plastic deformation of aromatic main-chain mesomorphic copolyesters

Thermodynamic characteristics of inelastic deformation (work W def, heat Q def, and stored energy ΔU def) are studied for aromatic main-chain copolyesters (CPEs) based on p-hydroxybenzoic acid and poly(ethylene terephthalate) (Rodrun and SKB-1), p-hydroxybenzoic acid, naphthalene carboxylic acid, and terephthalic acid with hydroquinone and dioxyphenyl (HX-6000 and HX-7000). The samples are deformed under an active uniaxial compression by ɛdef ≈ 50% at room temperature. All CPEs are semicrystalline polymers; their degree of crystallinity is (depending on their prehistory) 5–30%, and the melting temperature of crystallites is 275–350°C. Seemingly, the glassy component of CPEs includes two interpenetrating glassy structures, S-1 and S-2, with different glass-transition temperatures Tg: 90–120 and 250–270°C, respectively. During loading, all coexisting crystalline and glassy structures of CPEs store residual strain ɛres. The kinetics of the temperature-stimulated strain recovery of ɛres is measured. In component S-1, strain recovery occurs in the temperature interval ranging from T room to 120°C. In the crystalline phase, this process occurs in the melting-temperature interval. In component S-2, strain recovery ɛres commences at T > 120°C. In CPEs, all structural components are involved in deformation at different ɛdef. At small strains only component S-1 is deformed; then, at ɛdef ≈ 10–15%, component S-2 is involved in the deformation. Crystallites join this process at ɛdef > 20–25% (ɛ y = 8–10%). In CPE, two modes of deformation arise: reversible elastic (retarded elastic) and true plastic irreversible deformation. True plastic permanent strain always exists in the deformed CPEs. Deformation of all CPEs proceeds easier than that of all “common” glassy polymers (polystyrene, poly(methyl methacrylate), etc.). In CPEs, the yield stress and compressive modulus appear to be ≈40–50% lower than in “common” glassy polymers. It seems that the mesomorphic structure of LC CPEs enhances the elementary plastic processes in them. Thermodynamic characteristics of the S-1 phase plasticity are compared with the behavior of “common” glassy polymers. At the early stages of loading, nearly all mechanical work of deformation W def spent is stored in phase S-1 in the form of δU def, as in all “common” glassy polymers. This fact implies that the inelastic deformation of LC glasses commences with the nucleation of small-scale and localized intermolecular transformations of the nonconformational type. In both mesomorphic and “common” glassy polymers, the stage of nucleation of such transformations controls the overall kinetics of the inelastic and plastic deformation. Nucleation does not depend on chain rigidity, a circumstance that conflicts with the model of forced elasticity. It seems that crystallites in CPE are deformed according to crystallographic mechanisms. Currently, neither the structure nor the deformation mechanism of component S-2 is known.

Studies on aliphatic -aromatic random copolyester- based nano-biocomposite materials

Aliphatic-aromatic biodegradable random copolyester, poly (butylene succinate-co-butylene isophthalate) PBSI was synthesised by a two step direct melt polycondensation method. This copolyester was characterised by solubility, viscosity measurements, IR, 1 H NMR, 13 C NMR and thermal studies. But, to be a real alternative to classical synthetic polymers and find applications, biodegradable polymer properties have to be enhanced. Synthesis of nano-biocomposites, which are obtained by incorporation of nanofillers into a biomatrix, is an interesting way to achieve the polymers with characteristic property. In present study, the nano- biocomposites were synthesised by dispersing different weight percentage (1, 3 and 5 %) of organo modified montmorillonite clay (OMMT) into the biodegradable polyester matrix by solvent intercalation method. The structural characterisation and thermal analysis have been carried out to understand better the relationship between the nanofillers structuring and the properties of nano-biocomposites. The X-ray diffraction patterns obtained for the systems confirmed the nanodispersion of OMMT-clay in the polyester networks. The results show that the clay incorporation and the obtained structures enhanced the thermal properties of PBSI, and thus may increase the applicability of this biodegradable polymer in different fields.

In vitro degradation of a biodegradable polyurethane foam, based on 1,4‐butanediisocyanate: A three‐year study at physiological and elevated temperature

Biodegradable polyesterurethanes (PUs) may be used as scaffold materials for tissue regeneration applications, because of their excellent mechanical properties. In this study, the degradation of highly porous PU foams was evaluated in vitro. The PU had amorphous soft segments of DL-lactide/epsilon-caprolactone and uniform hard segments, synthesized from 1,4-butanediisocyanate and butanediol. The foams were degraded for 3 years in a Sörensen buffer solution (pH 7.4) at 37 and 60 degrees C. Dimensions of the foams, intrinsic viscosity, mass loss, thermal properties, and composition of the remaining material were evaluated. Copolyester (CP) foams of DL-lactide/epsilon-caprolactone served as controls. The PU foams kept their dimensions for 20 weeks at 37 degrees C, whereas CP foams collapsed after 3 weeks. PU mass loss reached a maximum of 80% at both 37 and 60 degrees C. CP mass loss reached 99.9% at 60 degrees , and 92% at 37 degrees C after 3 years. The degradation processes at 37 and 60 degrees C are initially the same, but eventually degradation products with different thermal properties are being formed. (1)H NMR studies showed that the hard urethane segments of the PU do not degrade in vitro at pH 7.4. It was concluded that the PU material has favorable characteristics for a scaffold material. Compared to long-term in vivo results of the same PU these in vitro results are not representative for the in vivo situation and therefore total resorption has to be investigated in long-term in vivo studies.

Toughening of a copolyester with a maleated core‐shell toughener

Toughening of a copolyester with a maleated core‐shell toughener

Thickness dependence of work of fracture parameters of an amorphous copolyester

The fracture toughness of an amorphous copolyester (COP) of different sheet thickness (0.5, 3 and 6 mm) was determined by the essential work of fracture (EWF) concept using tensile-loaded deeply double-edge notched (DDEN-T) specimens. It was shown that this COP meets the basic requirement of the EWF concept, viz. full ligament yielding (marked by a load drop in the load-displacement curve) prior to the crack growth, in the thickness range studied. Based on the well-resolved yielding both the specific essential (we) and non-essential work of fracture (wp) were split in the contributing terms related to yielding (wI), and necking and fracture (wII). It was found that we is likely to be independent on the thickness range when plane stress conditions prevail, and thus represents a material parameter. This finding is at odds with previous results suggesting that we is thickness dependent. The development and size of the plastic zone were studied by light microscopy and infra-red thermography. The latter technique overestimated the plastic zone in thicker sheets by not differentiating between pure and diffuse yielding. © 1997 Elsevier Science Ltd.

Blue emission from polymer light-emitting diodes using non-conjugated polymer blends with air-stable electrodes

By dispersing a non-conjugated luminescent polymer and an electron-transporting material, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), into a hole-transporting polymer, poly(9-vinylcarbazole) (PVK), we have achieved improved efficiencies for blue light-emitting diodes (LEDs) fabricated with a copolyester (CPE) containing isolated 1,2-dinaphthylethene units. Quantum efficiencies of the LEDs with the solid dispersion of CPE and PBD in PVK as electroluminescent layer and indium as the electron injection electrodes are about 0.1% photons per electron, better by factor of 10 2 than similar devices made with only the CPE. The LEDs turn on at about 30 V and have a peak emission wavelength in the blue at 485 nm.

Dynamic Vulcanization of Thermoplastic Copolyester Elastomer/Nitrile Rubber Alloys

New thermoplastic elastomers, copolyester (CPET)/nitrile rubber (NBR) alloys, were developed by using various dynamic vulcanization tech niques, such as internal mixing, open mill mixing, and twin screw extrusion, or their combinations. The effects of the various manufacturing techniques on rheological and mechanical properties were compared. The study showed that the dynamic vulcanization method by a twin screw extruder is most suitable for the manufacture of CPET/NBR elastomeric alloys.

Melt flow and fiber properties of copolyesters

AbstractThe effect of modifying monomer [sodium 3,5‐di(carbonethoxy)benzene sulfonate] contents range from 1.5 to 4.5 mol % on the melt flow and fiber properties of copolyesters (COPET) dyeable with basic dyes was investigated. An Instron capillary rheometer was used to obtain data over shear rates ranging from 10 to 104 s−1 at 265, 275, and 285°C. The COPET's flow properties as a function of temperature, inherent viscosity, melting point, and modifying monomer content were determined. The drawn fibers annealed in oil and air at 80, 110, 130, 150, 175, and 200°C were studied by means of measurements of shrinkage ratio, crystallinity, birefringence, long period, sonic rate, and static state flexibility of molecular chain. All these showed that the large side group, SO3Na in COPET molecular chains causes an increase in chain rigidity and melt viscosity, and a decrease in crystallinity and orientation.

Hydrolysis of copolyesters containing aromatic and aliphatic ester blocks by lipase

Copolyesters (CPEs) prepared by the transesterification reaction between aromatic and aliphatic polyesters were hydrolyzed by Rhizopus delemar lipase. The susceptibility of CPEs to hydrolysis by this lipase dropped off rapidly during the initial stage of the transesterification reaction and increased gradually as the reaction proceeded. The susceptibility to hydrolysis decreased with increase in aromatic polyester content. It was concluded that the rigidity of the aromatic ring in the CPE chains strongly influenced their susceptibility to hydrolysis by this lipase.

Structure-Property Relationships in Polytetramethylene Terephthalate/Polytetramethylene Isophthalate Copolyesters Part I : Glass-Transition Temperatures

The glass-transition temperatures (Tg) of a series of polytetramethylene terephthalate/polytetramethylene isophthalate, copolyesters have been measured by a variety of methods including differential thermal analysis, dilatometry, and broad- line nuclear magnetic resonance. The values measured for Tg are discussed in relation to differences in copolymer com position, sample crystallinity and the method used in the measurement of Tg. An increase in the isophthalate content of the copolyester has been found to decrease T g, whereas annealing and increasing the test frequency have both been shown to raise Tg. Values calculated for the apparent activation energy of the glass-transition (Δ ETg) for the series of copoly esters are also reported. In addition, the influence of water on the Tg of polyesters has been investigated.

New Developments in Copolyester Ether Elastomers

New Developments in Copolyester Ether Elastomers