Preventing failure in a plastic medical device requires a thorough understanding of the key fitne... more Preventing failure in a plastic medical device requires a thorough understanding of the key fitness for use criteria. This paper explores a case study of copolyester resin development for a device requiring clarity, toughness, chemical resistance, solvent bonding, printability, and ethylene oxide and gamma sterilization. Analyses included molecular weight, modulated DSC, fractography and functional testing.
La presente invention concerne des compositions aux polyesters donnant un rendement plus importan... more La presente invention concerne des compositions aux polyesters donnant un rendement plus important au calandrage. Elles s'obtiennent a partir d'un polyester dont le demi-cycle de cristallisation est d'au moins 5 minutes, dont la viscosite inherente est de 0,55 a 0,75 dl/g, et comportant un monomere ramifiant et comprenant un additif a liberation. Ces compositions aux polyesters associent une excellente resistance du fondu a une bonne reaction au cisaillement qui permet des vitesses plus elevees en ligne de calandrage avant la survenue de la fracture du fondu. L'invention concerne egalement, d'une part un procede de production de films ou de feuille par calandrage des compositions de l'invention, et d'autre part les films ou feuilles ainsi obtenues. Les compositions aux polyesters, films ou feuilles peuvent egalement comportant des plastifiants et/ou des ignifugeants permettant d'augmenter leur souplesse et d'autoriser leur utilisation dans des app...
Polyester resin calendered film or sheet of the composition has a haze value less than 5%. The po... more Polyester resin calendered film or sheet of the composition has a haze value less than 5%. The polyester resin composition is a crystallization half time from a molten state at least 5 minutes the polymer, and (i) salts of fatty acids or fatty acids containing a number of carbon atoms greater than 18, and (ii) a fatty acid containing more carbon atoms than 18 and 2 to 28 comprising a polyester comprising the alcohol containing carbon atoms, waxes, wherein the fatty acid salt or the ratio of the ester wax of fatty acid is 1: 1 or higher. In addition, the present invention is a manufacturing method of the haze value of the calendered film or sheet of less than 5%. Step of the method (1) step, and (3) 90 ° from the calendering roll for forming the step of calendering the polyester resin composition, (2) a film or sheet from the polyester resin composition to the calendering rolls recovering the film or sheet at an angle of less than by a step of forming a haze value of less than 5% of film or sheet.
Environmental stress cracking of amorphous poly(ethylene terephthalate) in aqueous sodium hydroxi... more Environmental stress cracking of amorphous poly(ethylene terephthalate) in aqueous sodium hydroxide was studied by using a fracture mechanics approach. Compact tension specimens were machined from injection-molded plaques and used to determine creep crack growth rate as a function of applied stress intensity factor. The effects of caustic concentration and polymer molecular weight on creep crack growth behaviour were determined. Fractographic analysis of the fracture surfaces showed that crack growth proceeded by the formation of novel discontinuous growth bands. The structure and mechanism of formation of these bands are discussed.
Gamma irradiation affects colour, most notably b, and total transmittance of all of the copolyest... more Gamma irradiation affects colour, most notably b, and total transmittance of all of the copolyesters used in this study. The changes in colour and total transmittance increase with increasing dose level and CHDM content of the copolyester. These changes are only temporary and decay with time after sterilisation. At the highest dose level, all of the resins showed a slight decrease in molecular weight. Small changes in mechanical properties can be attributed to physical ageing that occurs at the slightly elevated temperatures associated with gamma irradiation. The mechanical properties are, however, stable after irradiation indicating no continued effects of the sterilisation process.
Abstract The thermal degradation of poly(vinyl chloride) (PVC) blends with polyvinyl acetate (PVA... more Abstract The thermal degradation of poly(vinyl chloride) (PVC) blends with polyvinyl acetate (PVA) and ethylene-vinyl acetate copolymers containing 70% (EVA70) and 45% (EVA45) vinyl acetate by weight has been studied by thermogravimetry (TG) and direct pyrolysis-mass spectroscopy (DPMS). TG studies conducted at a heating rate of 10°C/min in a nitrogen atmosphere show that PVC blends with PVA, EVA70, and EVA45 are less thermally stable than would be predicted from the behavior of the pure polymers. DPMS shows that the dehydrochlorination of PVC and the deacetylation of PVA, EVA70, and EVA45 are accelerated in the blends relative to the pure polymers. The amount of destabilization appears to be related to the miscibility of the blend systems.
A correlation between the yield behavior of copolymers based on poly(ethylene terephthalate) and ... more A correlation between the yield behavior of copolymers based on poly(ethylene terephthalate) and poly(1,4-cyclohexylenedimethylene terephthalate) (PCT) and their secondary relaxation motions is established. The yield stress decreases as the cyclohexylene content increases for different temperatures and strain rates. The activation volume based on Eyring's model of yielding increases as the copolymers become more PCT-like, while the activation energy does not exhibit any significant change. We speculate that the conformational changes of the cyclohexylene rings reduce the barriers between chain segments sufficiently to facilitate chain slippage. This is supported by the increased dynamic fluctuation found by positron annihilation lifetime spectroscopy. The crazing stress of the copolyesters increases with increasing cyclohexylene content. We propose that the formation of stable microvoids is impeded by local stress relaxation; hence craze formation is retarded. The ductile/brittle transition is viewed as a competition between yielding and crazing with changes in the transition temperature dependent on activation of molecular motions of the cyclohexylene groups.
The fracture toughness of a core-shell rubber modified polycarbonate-copolyester blend was determ... more The fracture toughness of a core-shell rubber modified polycarbonate-copolyester blend was determined by using the J-integral approach. Single-edge notch bend specimens were tested at room temperature using a crosshead speed of lmm mint. The resistance curve for the blend was not affected by specimen width, direction of crack growth with respect to mouldflow direction, and sidegrooving. Fractographic analysis suggested that the matrix debonded from the rubber particles thus relieving the triaxial stresses and enabling the matrix to yield more easily. The initiation of crack growth in the J-tests was observed to occur shortly after the onset of non-linearity in the load-deflection curve. Consequently, an attempt was made to describe fracture in this blend by using linear elastic fracture mechanics.
The effect of impact-modifier concentration and particle size on the fatigue resistance of an amo... more The effect of impact-modifier concentration and particle size on the fatigue resistance of an amorphous thermoplastic copolyester of dimethyl terephthalate with ethylene glycol and 1,4-cyclohexanedimethanol (KODAR®* PETG) was determined. Fatigue crack propagation (FCP) rate at a given value of stress intensity factor range, ΔK, decreased by a factor of four with the addition of an impact modifier, if the inherent viscosity of the PETG remained constant. The FCP rate did not vary with modifier concentration or particle size. However, the value of ΔK at instability did increase with increasing modifier content and particle size appeared to alter the FCP mechanism. in fatigue tests on unnotched specimens, neat PETG was more fatigue resistant than the impact-modified blends, suggesting that the modifier particles reduced the number of cycles required to initiate a crack.
The toughness of amorphous copolyester sheets was assessed by the essential work of fracture (EWF... more The toughness of amorphous copolyester sheets was assessed by the essential work of fracture (EWF) concept. While the yielding-related work of fracture terms did not change significantly, the necking-related parameters strongly decreased with decreasing entanglement density of the copolyesters having different amounts of cyclohexylenedimethylene (CHDM) units in their backbones. Furthermore, copolyesters with high CHDM content and thus less entanglement density showed full recovery of the necked region beyond the glass transition temperature, i.e. the ‘plastic’ zone in the related specimens formed by cold drawing and not by true plastic deformation. By contrast, the copolyester with negligible amount of CHDM did not show this shape recovery. Modulated differential scanning calorimetry (MDSC) revealed that the necking in the latter system was accompanied by strain-induced crystallization. The superior work hardening in the necking stage of the respective poly(ethylene terephthalate) (...
Though stress oscillation phenomena can be triggered by static and dynamic tensile loading in amo... more Though stress oscillation phenomena can be triggered by static and dynamic tensile loading in amorphous (co)polyesters, they have nothing in common. Static loading-caused stress oscillation appears to be controlled by strain-induced crystallization and related heat release and thus can be observed only in crystallizable polymers. On the other hand, dynamic loading-induced stress oscillation is a more universal phenomenon as related to the natural frequency of the test set-up. The latter was established by determining the natural frequency of the instrumented anvil via fast Fourier transformation using a crystallized poly(ethylene terephthalate) (cPET) specimen failing brittlely. When the instrumented tensile impact response of amorphous PET (aPET) and commercial copolyesters (Eastar® PCTG and A150, respectively) has been filtered by considering the natural frequency of the test configuration, the related fractograms no longer showed stress oscillation. It was concluded that samples ...
Abstract The fatigue crack propagation ( FCP ) behaviour of a plasticized cellulose acetate-propi... more Abstract The fatigue crack propagation ( FCP ) behaviour of a plasticized cellulose acetate-propionate (CAP) was determined as a function of temperature. Changes in FCP behaviour with temperature were analogous to changes produced by varying plasticizer concentration. A temperature-plasticizer concentration equivalence based on their effect on yield strength was proposed to predict the FCP behaviour of CAP over limited plasticizer concentration and temperature ranges.
The fracture toughness of an amorphous copolyester (COP) of different sheet thickness (0.5, 3 and... more 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 weis 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 w. 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. G 1997 Elsevier Science Ltd.
Specimens from amorphous copolyester (aCOP) sheets of merent composition and molecular mass chara... more Specimens from amorphous copolyester (aCOP) sheets of merent composition and molecular mass characteristics were subjected to instrumented tensile impact loading in the speed range of 2-3.7 m/s at ambient temperature. Stress oscillation was observed in the necking phase, especially for the aCOP with smaller entanglement density. It was found that the appearance of stress oscillation is limited to a given frequency or strain rate range (estimated by the ratio of the incident speed and clamped specimen length). Necking occurred by cold drawing which was evidenced by the shape recovery of the broken specimens when heated above the glass transition temperature (Tg-90°C). According to polarized light microscopy and differential scanning calorimetry (DSC), the stress oscillation was generated by diffuse shear banding without crystallization. This is the first report according to the authors' knowledge on the stress oscillation phenomenon in amorphous polymers in which crystallization was not involved.
Preventing failure in a plastic medical device requires a thorough understanding of the key fitne... more Preventing failure in a plastic medical device requires a thorough understanding of the key fitness for use criteria. This paper explores a case study of copolyester resin development for a device requiring clarity, toughness, chemical resistance, solvent bonding, printability, and ethylene oxide and gamma sterilization. Analyses included molecular weight, modulated DSC, fractography and functional testing.
La presente invention concerne des compositions aux polyesters donnant un rendement plus importan... more La presente invention concerne des compositions aux polyesters donnant un rendement plus important au calandrage. Elles s'obtiennent a partir d'un polyester dont le demi-cycle de cristallisation est d'au moins 5 minutes, dont la viscosite inherente est de 0,55 a 0,75 dl/g, et comportant un monomere ramifiant et comprenant un additif a liberation. Ces compositions aux polyesters associent une excellente resistance du fondu a une bonne reaction au cisaillement qui permet des vitesses plus elevees en ligne de calandrage avant la survenue de la fracture du fondu. L'invention concerne egalement, d'une part un procede de production de films ou de feuille par calandrage des compositions de l'invention, et d'autre part les films ou feuilles ainsi obtenues. Les compositions aux polyesters, films ou feuilles peuvent egalement comportant des plastifiants et/ou des ignifugeants permettant d'augmenter leur souplesse et d'autoriser leur utilisation dans des app...
Polyester resin calendered film or sheet of the composition has a haze value less than 5%. The po... more Polyester resin calendered film or sheet of the composition has a haze value less than 5%. The polyester resin composition is a crystallization half time from a molten state at least 5 minutes the polymer, and (i) salts of fatty acids or fatty acids containing a number of carbon atoms greater than 18, and (ii) a fatty acid containing more carbon atoms than 18 and 2 to 28 comprising a polyester comprising the alcohol containing carbon atoms, waxes, wherein the fatty acid salt or the ratio of the ester wax of fatty acid is 1: 1 or higher. In addition, the present invention is a manufacturing method of the haze value of the calendered film or sheet of less than 5%. Step of the method (1) step, and (3) 90 ° from the calendering roll for forming the step of calendering the polyester resin composition, (2) a film or sheet from the polyester resin composition to the calendering rolls recovering the film or sheet at an angle of less than by a step of forming a haze value of less than 5% of film or sheet.
Environmental stress cracking of amorphous poly(ethylene terephthalate) in aqueous sodium hydroxi... more Environmental stress cracking of amorphous poly(ethylene terephthalate) in aqueous sodium hydroxide was studied by using a fracture mechanics approach. Compact tension specimens were machined from injection-molded plaques and used to determine creep crack growth rate as a function of applied stress intensity factor. The effects of caustic concentration and polymer molecular weight on creep crack growth behaviour were determined. Fractographic analysis of the fracture surfaces showed that crack growth proceeded by the formation of novel discontinuous growth bands. The structure and mechanism of formation of these bands are discussed.
Gamma irradiation affects colour, most notably b, and total transmittance of all of the copolyest... more Gamma irradiation affects colour, most notably b, and total transmittance of all of the copolyesters used in this study. The changes in colour and total transmittance increase with increasing dose level and CHDM content of the copolyester. These changes are only temporary and decay with time after sterilisation. At the highest dose level, all of the resins showed a slight decrease in molecular weight. Small changes in mechanical properties can be attributed to physical ageing that occurs at the slightly elevated temperatures associated with gamma irradiation. The mechanical properties are, however, stable after irradiation indicating no continued effects of the sterilisation process.
Abstract The thermal degradation of poly(vinyl chloride) (PVC) blends with polyvinyl acetate (PVA... more Abstract The thermal degradation of poly(vinyl chloride) (PVC) blends with polyvinyl acetate (PVA) and ethylene-vinyl acetate copolymers containing 70% (EVA70) and 45% (EVA45) vinyl acetate by weight has been studied by thermogravimetry (TG) and direct pyrolysis-mass spectroscopy (DPMS). TG studies conducted at a heating rate of 10°C/min in a nitrogen atmosphere show that PVC blends with PVA, EVA70, and EVA45 are less thermally stable than would be predicted from the behavior of the pure polymers. DPMS shows that the dehydrochlorination of PVC and the deacetylation of PVA, EVA70, and EVA45 are accelerated in the blends relative to the pure polymers. The amount of destabilization appears to be related to the miscibility of the blend systems.
A correlation between the yield behavior of copolymers based on poly(ethylene terephthalate) and ... more A correlation between the yield behavior of copolymers based on poly(ethylene terephthalate) and poly(1,4-cyclohexylenedimethylene terephthalate) (PCT) and their secondary relaxation motions is established. The yield stress decreases as the cyclohexylene content increases for different temperatures and strain rates. The activation volume based on Eyring's model of yielding increases as the copolymers become more PCT-like, while the activation energy does not exhibit any significant change. We speculate that the conformational changes of the cyclohexylene rings reduce the barriers between chain segments sufficiently to facilitate chain slippage. This is supported by the increased dynamic fluctuation found by positron annihilation lifetime spectroscopy. The crazing stress of the copolyesters increases with increasing cyclohexylene content. We propose that the formation of stable microvoids is impeded by local stress relaxation; hence craze formation is retarded. The ductile/brittle transition is viewed as a competition between yielding and crazing with changes in the transition temperature dependent on activation of molecular motions of the cyclohexylene groups.
The fracture toughness of a core-shell rubber modified polycarbonate-copolyester blend was determ... more The fracture toughness of a core-shell rubber modified polycarbonate-copolyester blend was determined by using the J-integral approach. Single-edge notch bend specimens were tested at room temperature using a crosshead speed of lmm mint. The resistance curve for the blend was not affected by specimen width, direction of crack growth with respect to mouldflow direction, and sidegrooving. Fractographic analysis suggested that the matrix debonded from the rubber particles thus relieving the triaxial stresses and enabling the matrix to yield more easily. The initiation of crack growth in the J-tests was observed to occur shortly after the onset of non-linearity in the load-deflection curve. Consequently, an attempt was made to describe fracture in this blend by using linear elastic fracture mechanics.
The effect of impact-modifier concentration and particle size on the fatigue resistance of an amo... more The effect of impact-modifier concentration and particle size on the fatigue resistance of an amorphous thermoplastic copolyester of dimethyl terephthalate with ethylene glycol and 1,4-cyclohexanedimethanol (KODAR®* PETG) was determined. Fatigue crack propagation (FCP) rate at a given value of stress intensity factor range, ΔK, decreased by a factor of four with the addition of an impact modifier, if the inherent viscosity of the PETG remained constant. The FCP rate did not vary with modifier concentration or particle size. However, the value of ΔK at instability did increase with increasing modifier content and particle size appeared to alter the FCP mechanism. in fatigue tests on unnotched specimens, neat PETG was more fatigue resistant than the impact-modified blends, suggesting that the modifier particles reduced the number of cycles required to initiate a crack.
The toughness of amorphous copolyester sheets was assessed by the essential work of fracture (EWF... more The toughness of amorphous copolyester sheets was assessed by the essential work of fracture (EWF) concept. While the yielding-related work of fracture terms did not change significantly, the necking-related parameters strongly decreased with decreasing entanglement density of the copolyesters having different amounts of cyclohexylenedimethylene (CHDM) units in their backbones. Furthermore, copolyesters with high CHDM content and thus less entanglement density showed full recovery of the necked region beyond the glass transition temperature, i.e. the ‘plastic’ zone in the related specimens formed by cold drawing and not by true plastic deformation. By contrast, the copolyester with negligible amount of CHDM did not show this shape recovery. Modulated differential scanning calorimetry (MDSC) revealed that the necking in the latter system was accompanied by strain-induced crystallization. The superior work hardening in the necking stage of the respective poly(ethylene terephthalate) (...
Though stress oscillation phenomena can be triggered by static and dynamic tensile loading in amo... more Though stress oscillation phenomena can be triggered by static and dynamic tensile loading in amorphous (co)polyesters, they have nothing in common. Static loading-caused stress oscillation appears to be controlled by strain-induced crystallization and related heat release and thus can be observed only in crystallizable polymers. On the other hand, dynamic loading-induced stress oscillation is a more universal phenomenon as related to the natural frequency of the test set-up. The latter was established by determining the natural frequency of the instrumented anvil via fast Fourier transformation using a crystallized poly(ethylene terephthalate) (cPET) specimen failing brittlely. When the instrumented tensile impact response of amorphous PET (aPET) and commercial copolyesters (Eastar® PCTG and A150, respectively) has been filtered by considering the natural frequency of the test configuration, the related fractograms no longer showed stress oscillation. It was concluded that samples ...
Abstract The fatigue crack propagation ( FCP ) behaviour of a plasticized cellulose acetate-propi... more Abstract The fatigue crack propagation ( FCP ) behaviour of a plasticized cellulose acetate-propionate (CAP) was determined as a function of temperature. Changes in FCP behaviour with temperature were analogous to changes produced by varying plasticizer concentration. A temperature-plasticizer concentration equivalence based on their effect on yield strength was proposed to predict the FCP behaviour of CAP over limited plasticizer concentration and temperature ranges.
The fracture toughness of an amorphous copolyester (COP) of different sheet thickness (0.5, 3 and... more 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 weis 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 w. 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. G 1997 Elsevier Science Ltd.
Specimens from amorphous copolyester (aCOP) sheets of merent composition and molecular mass chara... more Specimens from amorphous copolyester (aCOP) sheets of merent composition and molecular mass characteristics were subjected to instrumented tensile impact loading in the speed range of 2-3.7 m/s at ambient temperature. Stress oscillation was observed in the necking phase, especially for the aCOP with smaller entanglement density. It was found that the appearance of stress oscillation is limited to a given frequency or strain rate range (estimated by the ratio of the incident speed and clamped specimen length). Necking occurred by cold drawing which was evidenced by the shape recovery of the broken specimens when heated above the glass transition temperature (Tg-90°C). According to polarized light microscopy and differential scanning calorimetry (DSC), the stress oscillation was generated by diffuse shear banding without crystallization. This is the first report according to the authors' knowledge on the stress oscillation phenomenon in amorphous polymers in which crystallization was not involved.
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Papers by Eric Moskala