Hydrolytic degradation behavior of poly(butylene succinate)s with different crystalline morphologies

The effect of crystalline morphology on the hydrolytic degradation behavior of poly(butylene succinate) (PBS) in an alkaline solution was investigated by using scanning electron microscopy, gel permeation chromatography, and weight loss measurement. Morphological changes were induced on PBS samples by different thermal treatments (i.e., melt quenching or isothermal crystallization) at a constant overall degree of crystallinity. It was found that even with a similar degree of crystallinity, the hydrolytic degradation rate of an isothermally crystallized sample at 60°C was higher than that of a melt‐quenched sample. This was due to the difference in the internal morphology of the spherulites: the internal structure of spherulite in an isothermally crystallized sample consists of coarse and loosely packed fibrils whereas a melt‐quenched sample contains finer and tightly packed fibrils. This result suggested that the internal structure of the spherulite of PBS samples plays an important role in the hydrolytic degradation for this experimental condition. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1025–1033, 2001     

Enzymatic degradation kinetics of poly(butylene succinate) nanocomposites

In this work, poly(butylene succinates) (PBS)/organically modified layered silicates (OMLS) composites were prepared by solution blending. The degradability of PBS, PBS/layered silicates and PBS/OMLS nanocomposites have been investigated using enzymatic degradation method. Effects of layered silicates and OMLS contents on the degradation behavior of PBS were explored. The results reveal that the degradability of the composites was both enhanced by the addition of layered silicates or OMLS as compared to the pristine PBS sample. The calculated data based on the autocatalytic model show that the degradation kinetics of PBS/layered silicates composites is the chain scission process with the following autocatalytic reactions, which is very similar to that of pure PBS matrix. On the other hand, the surface-catalyzed reaction model may be more suitable to describe the degradation behavior of the PBS/OMLS nanocomposite. Moreover, the results show that rate-controlling step of the degradation reaction for PBS/OMLS nanocomposite is more probable to be the desorption step.     

Melting behavior and crystallization kinetics of sulfonated poly(butylene isophthalate)

The melting behavior and the crystallization kinetics of sulfonated poly(butylene isophthalate) random copolymers were investigated by means of differential scanning calorimetry. The multiple endotherms, commonly observed in polyesters, were found to be influenced both by composition and crystallization temperature. By applying the Hoffman‐Weeks method, the equilibrium melting temperatures of the copolymers under investigation were obtained. The presence of a crystal‐amorphous interphase was evidenced and its amount was found to increase as the sulfonated unit content was increased. Isothermal melt crystallization kinetics of the sample containing the lowest amount of sulfonated units was analyzed according to the Avrami treatment. The introduction of such units was found to decrease the overall crystallization rate of poly(butylene isophthalate). Values of Avrami's exponent n close to 3 were obtained, independently of crystallization temperature, in agreement with a crystallization process originating from predetermined nuclei and characterized by three‐dimensional spherulitic growth.     

Nonisothermal crystallization kinetics of novel biodegradable poly(butylene succinate-co-2-methyl-1,3-propylene succinate)s

Two novel poly(butylene succinate-co-2-methyl-1,3-propylene succinate)s, PBMPSu 95/5 and PBMPSu 90/10, were characterized as having 6.5 and 10.8 mol% 2-methyl-1,3-propylene succinate (MS) units, respectively, by ¹H NMR. A differential scanning calorimeter (DSC) and a polarized light microscope (PLM) employed to investigate the nonisothermal crystallization of these copolyesters and poly(butylene succinate) (PBSu). Morphology and the isothermal growth rates of spherulites under PLM experiments at three cooling rates of 1, 2.5 and 5 °C/min were monitored and obtained by curve-fitting. These continuous rate data were analyzed with the Lauritzen-Hoffman equation. A transition of regime II→III was found at 96.2, 83.5, and 77.9 °C for PBSu, PBMPSu 95/05, and PBMPSu 90/10, respectively. DSC exothermic curves at five cooling rates of 1, 2.5, 5, 10 and 20 °C/min show that almost all of the nonisothermal crystallization occurred in regime III. DSC data were analyzed using modified Avrami, Ozawa, Mo, Friedman and Vyazovkin equations. All the results of PLM and DSC measurements reveal that incorporation of minor MS units into PBSu markedly inhibits the crystallization of the resulting polymer.     

Nonisothermal crystallization kinetics of biodegradable poly(butylene succinate)/poly(vinyl phenol) blend

Nonisothermal melt crystallization kinetics of biodegradable PBSU/PVPh blend was investigated with differential scanning calorimetry (DSC) from the viewpoint of practical application. PBSU/PVPh blends were cooled from the melt at various cooling rates ranging from 2.5 to 40°C/min. The crystallization peak temperature decreased with increasing the cooling rate for both neat and blended PBSU. Furthermore, the crystallization peak temperature of PBSU in the blend was lower than that of neat PBSU at a given cooling rate. Two methods, namely the Avrami equation and the Tobin method, were used to describe the nonisothermal crystallization of PBSU/PVPh blend. It was found that the Avrami equation was more suitable to predict the nonisothermal crystallization of PBSU/PVPh blend than the Tobin method. The effects of cooling rate and blend composition on the crystallization behavior of PBSU were studied in detail. It was found that the crystallization rate decreased with decreasing the cooling rate for both neat and blended PBSU. However, the crystallization of PBSU blended with PVPh was retarded compared with that of neat PBSU at the same cooling rate. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 972–978, 2007     

A morphological study of poly(butylene succinate)/poly(butylene adipate) blends with different blend ratios and crystallization processes

Morphologies of PBS/PBA blends varying in blend ratio at different crystallization temperatures of PBS component were studied using optical and atomic force microscopies. It was found that interspherulitic phase segregation of PBA takes place at high temperature, e.g. 100 °C, for all blend compositions due to the high diffusion length. On the contrary, no interspherulitic phase segregation of PBA at 75 °C occurs at all, consistent with a shorter diffusion length. It was further found that the PBA melt acted as a diluter, affecting the morphology of PBS, which in turn influenced the phase separation behavior of PBA remarkably. At 100 °C, with increasing PBA concentration, the resultant open structure of PBS caused by the diluting effect of the PBA melt makes it necessary to retain some portion of the PBA melt between the PBS lamellae. This leads to the concurrence of interlamellar and interspherulitic phase segregations. An even higher PBA content results in the occurrences of all three phase separation options, i.e. interlamellar, interfibrillar and interspherulitic phase segregations. At 75 °C, in blends with PBA as a minority phase, mainly interlamellar segregation of PBA occurs. For a 50/50 blend, interlamellar and interfibrillar phase segregations take place simultaneously. For a PBA in-rich blend, PBS forms only a spherulitic framework, filled in with the PBA lamellar crystals, indicating that interfibrillar mode is the main phase separation process.     

Nonisothermal crystallization kinetics of poly(butylene terephthalate)/montmorillonite nanocomposites

The melt intercalation method was employed to prepare poly(butylene terephthalate) (PBT)/montmorillonite (MMT) nanocomposites, and the microstructures were characterized with X‐ray diffraction and transmission electron microscopy. Then, the nonisothermal crystallization behavior of the nanocomposites was studied with differential scanning calorimetry (DSC). The DSC results showed that the exothermic peaks for the nanocomposites distinctly shifted to lower temperatures at various cooling rates in comparison with that for pure PBT, and with increasing MMT content, the peak crystallization temperature of the PBT/MMT hybrids declined gradually. The nonisothermal crystallization kinetics were analyzed by the Avrami, Jeziorny, Ozawa, and Mo methods on the basis of the DSC data. The results revealed that very small amounts of clay (1 wt %) could accelerate the crystallization process, whereas higher clay loadings reduced the rate of crystallization. In addition, the activation energy for the transport of the macromolecular segments to the growing surface was determined by the Kissinger method. The results clearly indicated that the hybrids with small amounts of clay presented lower activation energy than PBT, whereas those with higher clay loadings showed higher activation energy. The MMT content and the crystallization conditions as well as the nature of the matrix itself affected the crystallization behavior of the hybrids. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3257–3265, 2006     

Isothermal crystallization kinetics and melting behaviors of poly(butylene terephthalate) and poly(butylene terephthalate‐co‐fumarate) copolymer

The isothermal crystallization kinetics and melting behaviors after isothermal crystallization of poly(butylene terephthalate) (PBT) and poly(butylene terephthalate‐co‐fumarate) (PBTF) containing 95/5, 90/10, and 80/20 molar ratios of terephthalic acid/fumaric acid were investigated by differential scanning calorimetry. The equilibrium melting temperatures of these polymers were estimated by Hoffman–Weeks equation. So far as the crystallization kinetics was concerned, the Avrami equation was applied and the values of the exponent n for all these polymers are in the range of 2.50–2.96, indicating that the addition of fumarate does not affect the geometric dimension of PBT crystal growth. Crystallization activation energy (ΔE) and nucleation constant (K_g) of PBTF copolymers are higher than that of PBT homopolymer, suggesting that the introduction of fumarate hinders the crystallization of PBT in PBTF. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Radiopaque iodinated poly(ester-urethane)s based on poly(butylene succinate): Retarded crystallization and dual recrystallization behaviour

A series of biodegradable radiopaque iodinated poly(ester-urethane)s (IPEUs) were synthesized by chain-extension of dihydroxylated poly(butylene succinate) (PBS–OH) and isophorone diisocyanate (IPDI) with iodinated bisphenol-A (IBPA). The effects of IBPA on the crystallization and melting behaviour of IPEUs were investigated by wide-angle X-ray diffraction (WAXD), polarized optical microscope (POM), differential scanning calorimetry (DSC), and temperature-modulated differential scanning calorimetry (TMDSC). WAXD results suggest that the PBS soft segments form only one crystal modification, and that the crystallinity of the samples decreases with increasing the amorphous hard segments. POM observation indicates that the ring-bands of spherulites disappear and then the spherulitic texture is disturbed with increasing the IBPA content. The analysis of isothermal crystallization kinetics shows that the crystallization of IPEUs is retarded by the introduction of IBPA chain extender with bulky pendent groups. In the DSC heating curves, at most four endothermic peaks were observed and their origins were examined. Two recrystallization exothermic peaks were observed for IPEUs in the nonreversible signals of TMDSC. The twice sequential melting–recrystallization–remelting model could be used to explain the multiple melting behaviour of IPEUs.     

Thermal degradation of poly(butylene terephthalate)

The thermal degradation of poly(butylene terephthalate) between 240° and 280°C has been studied by measurements of intrinsic viscosity, carboxyl end groups and weight loss. A first-order mechanism of fission, followed by elimination of butadiene, is proposed. The values of the kinetic constant and activation energy are in good agreement with those obtained for simple esters and poly(ethylene terephthalate).     

Mechanisms and kinetics of thermal degradation of poly(butylene succinate‐co‐propylene succinate)s

Poly(butylene succinate) (PBSu) and two PBSu‐rich poly(butylene succinate‐co‐propylene succinate)s were studied. Copolyesters were characterized as random copolymers, based on ¹³C‐NMR spectra. TGA‐FTIR was used to monitor the degradation products at a heating rate of 5°C/min under N₂. FTIR spectra revealed that the major products were anhydrides, which were formed following two cyclic intramolecular degradation mechanisms by the breaking of the weak O‐CH₂ bonds around succinate groups. Thermal stability at heating rates of 1, 3, 5, and 10°C/min under N₂ was investigated using TGA. The model‐free methods of the Friedman and Ozawa equations are useful for studying the activation energy of degradation in each period of mass loss. The results reveal that the random incorporation of minor propylene succinate units into PBSu did not markedly affect their thermal resistance. Two model‐fitting mechanisms were used to determine the mass loss function f(α), the activation energy and the associated mechanism. The mechanism of autocatalysis nth‐order, with f(α) = α^m(1 ? α)ⁿ, fitted the experimental data much more closely than did the nth‐order mechanism given by f(α) = (1 ? α)ⁿ. The obtained activation energy was used to estimate the failure temperature (T_f). The values of T_f for a mass loss of 5% and an endurance time of 60,000 h are 160.7, 155.5, and 159.3°C for PBSu and two the copolyesters, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and thermal behavior of random poly(butylene terephthalate/azelate) copolyesters

Poly(butylene terephthalate), poly(butylene azelate), and poly(butylene terephthalate/butylene azelate) random copolymers of various compositions were synthesized in bulk using the well‐known two‐stage polycondensation procedure, and characterized in terms of chemical structure and molecular weight. The thermal behavior was examined by thermogravimetric analysis and differential scanning calorimetry. As far as the thermal stability is concerned, it was found to be rather similar for all copolymers and homopolymers investigated. All the copolymers were found to be partially crystalline, and the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of melting temperature with respect to pure homopolymers. Flory's equation was found to describe the T_m–composition data and permitted to calculate the melting temperatures (T^°_m ) and the heats of fusion (ΔH_u) of both the completely crystalline homopolymers. Owing to the high crystallization rate, the glass transition was observable only for the copolymers containing from 30 to 70 mol % of the terephthalate units; even though the samples cannot be frozen in a completely amorphous state, the data obtained confirmed that the introduction of the aromatic units gave rise to an increase of T_g, due to a chain stiffening. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2694–2702, 1999     

Two-stage crystallization kinetics modeling of a miscible blend system containing crystallizable poly(butylene terephthalate)

A modified two-stage kinetic model is proposed to describe the crystallization/solidification from the melt state of a miscible binary blend system comprising amorphous poly(ether imide) (PEI) and crystallizable poly(butylene terephthalate) (PBT). Differential scanning calorimetry (DSC) was employed to monitor the isothermal melt-crystallization of the PBT/PEI blends. A nonlinear regression method was adopted for estimating the kinetic parameters in accordance with the modified two-stage series-parallel model in comparison with the Avrami model. The results suggested that the crystallization of the PEI/PBT blends could be more precisely described by using the modified model, which properly takes into account the changing mechanisms from early to later stage of crystallization. For practical applications, an optimal temperature window for solidifying PEI/PBT miscible blends may be determined by utilizing this model.     

Nonisothermal crystallization kinetics of poly(butylene terephthalate)/poly(ethylene terephthalate)/glass fiber composites

The influences of the glass fiber (GF) content and the cooling rate for nonisothermal crystallization process of poly(butylene terephthalate)/poly(ethylene terephthalate) (PBT/PET) blends were investigated. The nonisothermal crystallization kinetics of samples were detected by differential scanning calorimetry (DSC) at cooling rates of 5°C/min, 10°C/min, 15°C/min, 20°C/min, 25°C/min, respectively. The Jeziony and Mozhishen methods were used to analyze the DSC data. The crystalline morphology of samples was observed with polarized light microscope. Results showed that the Jeziony and Mozhishen methods were available for the analysis of the nonisothermal crystallization process. The peaks of crystallization temperature (T_p) move to low temperature with the cooling rate increasing, crystallization half‐time (t_1/2) decrease accordingly. The crystallization rate of PBT/PET blends increase with the lower GF contents while it is baffled by higher GF contents. POLYM. COMPOS. 36:510–516, 2015. © 2014 Society of Plastics Engineers     

Lipase‐catalyzed synthesis of aliphatic poly(β‐thioether ester) with various methylene group contents: thermal properties,crystallization and degradation

A series of novel aliphatic poly(β‐thioether ester)s with various methylene group contents were prepared by direct lipase‐catalyzed polycondensation of the monomer with an acid‐labile β‐thiopropionate group. The polycondensation reaction using immobilized lipase B from Candida antarctica was carried out in diphenyl ether at 90 °C. Poly(β‐thioether ester)s with high molecular weights of 20 500–57 000 Da and narrow polydispersities in the range 1.40–1.48 were obtained. Thermogravimetric analysis, differential scanning calorimetry and wide‐angle X‐ray diffraction were used to investigate the thermal properties and crystal structures of these polyesters. All the poly(β‐thioether ester)s were semicrystalline polymers and thermally stable up to at least 200 °C. In vitro degradation studies showed that they can rapidly degrade under acidic conditions by the hydrolysis of the β‐thiopropionate groups, suggesting their potential as acid‐degradable polymeric materials. © 2019 Society of Chemical Industry     

Effects of filler type on the nonisothermal crystallization kinetics of poly(butylene terephthalate) (PBT) composites

In this study, melt‐crystallization behaviors of poly(butylene terephthalate) (PBT) composites including different types of inorganic fillers were investigated. Composite samples having 5 wt % of fillers were prepared by melt processing in a twin screw extruder using commercial grades of calcite (CA), halloysite (HL), and organo‐montmorillonite (OM) as filler. Depending on the filler type and geometry, crystallization kinetics of the samples was studied by differential scanning calorimetry (DSC) methods. Effect of filler type on the nonisothermal melt‐crystallization kinetics of the PBT was analyzed with various kinetic models, namely, the Ozawa, Avrami modified by Jeziorny and Liu‐Mo. Crystallization activation energies of the samples were also determined by the Kissinger, Takhor, and Augis–Bennett models. From the kinetics study, it was found that the melt‐crystallization rates of the samples including CA and HL‐nanotube were higher than PBT at a given cooling rate. On the other hand, it was also found that organo‐montmorillonite reduced the melt‐crystallization rate of PBT. It can be concluded that organic ammonium groups in the OM decelerate the crystallization rate of PBT chains possibly due to affecting the chain diffusion through growing crystal face and folding. This study shows that introducing organically modified alumina‐silicate layers into the PBT‐based composites could significantly reduce the production rate of the injection molded parts during the processing operations. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Fluorinated poly(butylene terephthalate): Preparation and properties

Fluorinated poly(butylene terephthalate) (PBT) can be easily prepared using a telechelic perfluoropolyether (PFPE) as a comonomer. The functional groups of the PFPE react completely with other monomers, but the distribution of the PFPE blocks is not homogeneous and in the final polymeric material there is a significant fraction of PFPE bonded to very short segments of polyester. Due to the very poor miscibility of PFPE and PBT, the PFPE is present as a separate phase dispersed in an almost pure PBT matrix. Accordingly, both thermal and mechanical properties of PBT are little affected by the PFPE. The presence of PFPE induces a slight improvement on the fracture resistance and on surface properties such as wear resistance and coefficient of friction. © 1994 John Wiley & Sons, Inc.     

Physical properties, crystallization kinetics, and spherulitic growth of well-defined poly(ε-caprolactone)s with different arms

Both well defined star-shaped poly(ε-caprolactone) having four arms (4sPCL) and six arms (6sPCL) and linear PCL having one arm (LPCL) and two arms (2LPCL) were synthesized and then used for the investigation of physical properties, isothermal and nonisothermal crystallization kinetics, and spherulitic growth. The maximal melting point, the cold crystallization temperature, and the degree of crystallinity of these PCL polymers decrease with the increasing number of polymer arms, and they have similar crystalline structure. The isothermal crystallization rate constant (K) of these PCL polymers is in the order of K_2LPCL>K_LPCL>K_4sPCL>K_6sPCL. Notably, the K of linear PCL decreases with the increasing molecular weight of polymer while that of star-shaped PCL inversely increases. The variation trend of K over the number of polymer arms or the molecular weight of polymer is consistent with the analyses of both nonisothermal crystallization kinetics and the spherulitic growth rate. These results indicate that both the number of polymer arms and the molecular weight of polymer mainly controlled the isothermal and nonisothermal crystallization rate constants, the spherulitic growth rate, and the spherulitic morphology of these PCL polymers.     

Crystallization of poly(butylene terephthalate)/poly(ethylene octene) blends: Isothermal crystallization

Poly(ethylene‐octene) (POE), maleic anhydride grafted poly(ethylene‐octene) (mPOE), and a mixture of POE and mPOE were added to poly(butylene terephthalate) (PBT) to prepare PBT/POE, PBT/mPOE, and PBT/mPOE/POE blends by a twin‐screw extruder. Observation by scanning electron microscopy revealed improved compatibility between PBT and POE in the presence of maleic anhydride groups. The melting behavior and isothermal crystallization kinetics of the blends were studied by wide‐angle X‐ray diffraction and differential scanning calorimeter; the kinetics data was delineated by kinetic models. The addition of POE or mPOE did not affect the melting behavior of PBT in samples quenched in water after blending in an extrude. Subsequent DSC scans of isothermally crystallized PBT and PBT blends exhibited two melting endotherms (T_mI and T_mII). T_mI was the fusion of the crystals grown by normal primary crystallization and T_mII was the melting peak of the most perfect crystals after reorganization. The dispersed second phase hindered the crystallization; on the other hand, the well dispersed phases with smaller size enhanced crystallization because of higher nucleation density. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Crystallization of poly(butylene terephthalate)/poly(ethylene octene) blends: Nonisothermal crystallization

Poly(ethylene octene) (POE), maleic anhydride grafted poly(ethylene octene) (mPOE), and a mixture of POE and mPOE were added to poly(butylene terephthalate) (PBT) to prepare PBT/POE (20 wt % POE), PBT/mPOE (20 wt % mPOE), and PBT/mPOE/POE (10 wt % mPOE and 10 wt % POE) blends with an extruder. The melting behavior of neat PBT and its blends nonisothermally crystallized from the melt was investigated with differential scanning calorimetry (DSC). Subsequent DSC scans exhibited two melting endotherms (T_mI and T_mII). T_mI was attributed to the melting of the crystals grown by normal primary crystallization, and T_mII was due to the melting of the more perfect crystals after reorganization during the DSC heating scan. The better dispersed second phases and higher cooling rate made the crystals that grew in normal primary crystallization less perfect and relatively prone to be organized during the DSC scan. The effects of POE and mPOE on the nonisothermal crystallization process were delineated by kinetic models. The dispersed phase hindered the crystallization; however, the well‐ dispersed phases of an even smaller size enhanced crystallization because of the higher nucleation density. The nucleation parameter, estimated from the modified Lauritzen–Hoffman equation, showed the same results. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008