Crystallization kinetics of poly(1,4‐butylene‐co‐ethylene terephthalate)

The crystallization kinetics of poly(butylene terephthalate) (PBT), poly(ethylene terephthalate) (PET), and their copolymers poly(1,4‐butylene‐co‐ethylene terephthalate) (PBET) containing 70/30, 65/35 and 60/40 molar ratios of 1,4‐butanediol/ethylene glycol were investigated using differential scanning calorimetry (DSC) at crystallization temperatures (T_c) which were 35–90 °C below equilibrium melting temperature . Although these copolymers contain both monomers in high proportion, DSC data revealed for copolymer crystallization behaviour. The reason for such copolymers being able to crystallize could be due to the similar chemical structures of 1,4‐butanediol and ethylene glycol. DSC results for isothermal crystallization revealed that random copolymers had a lower degree of crystallinity and lower crystallite growth rate than those of homopolymers. DSC heating scans, after completion of isothermal crystallization, showed triple melting endotherms for all these polyesters, similar to those of other polymers as reported in the literature. The crystallization isotherms followed the Avrami equation with an exponent n of 2–2.5 for PET and 2.5–3.0 for PBT and PBETs. Analyses of the Lauritzen–Hoffman equation for DSC isothermal crystallization data revealed that PBT and PET had higher growth rate constant G_o, and nucleation constant K_g than those of PBET copolymers. © 2001 Society of Chemical Industry     

Mechanical,thermal properties and isothermal crystallization kinetics of biodegradable poly(butylene succinate-<Emphasis Type="Italic">co</Emphasis>-terephthalate) (PBST) fibers

Biodegradable copolymer poly(butylene succinate-co-terephthalate) (PBST), with 70 mol% butylene terephthalate (BT), was melt-spun into fibers with take-up velocity of 2 km/min. The mechanical and thermal properties of the as-spun fibers were investigated through tensile test, DSC and TGA. Compared to poly(butylene terephthalate) (PBT) fibers, PBST fibers exhibited lower initial tensile modulus and higher tensile elongation at break which indicated their better flexibility. DSC results showed high melting temperature (ca.180.7 °C) of PBST fibers helpful to the textile processing compared to other biodegradable polyesters. Furthermore, isothermal crystallization behaviors of PBST fibers at low and high supercoolings were investigated by DSC and DLI, respectively. The measurement of crystallization kinetics at low supercoolings indicated that Avrami exponent n for PBST fibers was at a range of 2.9 to 3.3, corresponding to the heterogeneous nucleation and a 3-dimensional spherulitic growth. Similar results were given for isothermal crystallization behavior at high supercoolings investigated by DLI technique. Additionally, the equilibrium melting temperature of PBST fibers was obtained for 206.5 °C by Hoffman-Weeks method. Further investigation through DLI measurement provided the temperature at maximum crystallization rate for PBST fibers located at about 90 °C, which was very useful to polymer processing.     

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     

Synthesis and crystallization behavior of segmented copolyesters/silica composites

Silica were introduced to segmented copolyester system (poly(butylene terephthalate)‐poly(ethylene terephthalate‐co‐isophthalate‐co‐sebacate) (PBT‐PETIS)) by in situ polymerization. Investigations on melting behavior and crystalline structure were undertaken, and the dispersion situation of silica in segmented copolyester composites was detected. A diverse crystallization characteristic has been found when the modified Avrami analytical method was applied to investigate nonisothermal crystallization behavior of the composites. Crystallization rate was restricted rather than be promoted by increasing loading of silica. The values of Avrami exponent ranged from 2.25 to 2.45, presenting a mechanism of three‐dimensional spherulitic growth with heterogeneous nucleation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1052–1058, 2006     

Nonisothermal crystallization kinetics of poly(butylene terephthalate)/multiwalled carbon nanotubes nanocomposites prepared by in situ polymerization

Poly(butylene terephthalate)/multiwalled carbon nanotubes (PBT/MWNT) nanocomposites were prepared by in situ ring‐opening polymerization of cyclic butylene terephthalate oligomers (CBT). The nonisothermal crystallization behavior of the neat PBT and the PBT/MWNT nanocomposites was analyzed quantitatively. The results reveal that the combined Avrami/Ozawa equation exhibits great advantages in describing the nonisothermal crystallization of PBT and its nanocomposites. The presence of MWNTs has the nucleation effect promoting crystallization rate for the nanocomposites, and the maximum one is observed in the nanocomposite having 0.75 wt % MWNT content. On the other hand, the addition of MWNTs has the impeding effect reducing the chain mobility and retarding crystallization, which is confirmed by the crystallization activation energies. However, the nucleation effect of MWNTs plays the dominant role in the crystallization of PBT/MWNT nanocomposites, in other words, the incorporation of MWNTs is increasing the crystallization rate of the nanocomposites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40849.     

PBT-b-PEO-b-PBT triblock copolymers: Synthesis,characterization and double-crystalline properties

We demonstrated here a facile method to synthesize novel double crystalline poly(butylene terephthalate)-block-poly(ethylene oxide)-block-poly(butylene terephthalate) (PBT-b-PEO-b-PBT) triblock copolymers by solution ring-opening polymerization (ROP) of cyclic oligo(butylene terephthalate)s (COBTs) using poly(ethylene glycol) (PEG) as macroinitiator and titanium isopropyloxide as catalyst. The structure of copolymers was well characterized by ¹H NMR and GPC. TGA results revealed that the decomposition temperature of PEO in triblock copolymers increased about 30 °C to the same as PBT copolymers, after being end-capped with PBT polymers. These triblock copolymers showed double crystalline properties from PBT and PEO blocks, observed from DSC and WAXD measurements. The melting and crystallization peak temperatures corresponding to PBT blocks increased with PBT content. The crystallization of PBT blocks showed the strong confinement effects on PEO blocks due to covalent linking of PBT blocks with PEO blocks, where the melting and crystallization temperatures and crystallinity corresponding to PEO blocks decreased significantly with increment of PBT content. The confinement effect was also observed by SAXS experiments, where the long distance order between lamella crystals decreases with increasing PBT length. For the triblock copolymer with highest PBT content (PBT₅₄-b-PEO₂₂₇-b-PBT₅₄), this effect shows a 30 °C depression on PEO crystals' melting temperature and 77% on enthalpy, respectively, compared to corresponding PEO homopolymer. The crystal morphology was observed by POM, and amorphous-like spherulites were observed during PBT crystallization.     

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     

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     

Ternary blends of acrylic rubber,poly(butylene terephthalate), and liquid crystalline polymer: Influence of interactions on thermal and dynamic mechanical properties

The ternary blends of acrylate rubber (ACM), poly(butylene terephthalate) (PBT), and liquid crystalline polymer (LCP) were prepared by varying the amount of LCP but fixing the ratio of ACM and PBT, using melt mixing procedure. The influence of interactions on thermal and dynamic mechanical properties of the blends was investigated over the complete composition range. The techniques applied were Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetry (TG), and dynamic mechanical analysis (DMA). The FTIR spectroscopy analysis showed reduction in the intensity of the peak corresponding to epoxy groups of ACM with increasing heating time at 290°C. This implies that there is a chemical reaction between the epoxy and end groups of PBT and LCP. Glass transition temperature (T_g) and melting temperature (T_m) of the blends were affected depending on the LCP weight percent in the ACM/PBT blend, respectively. This further suggests the strong interfacial interactions between the blend components. In presence of ACM, the nucleating effect of LCP was more pronounced for the PBT phase. The thermogravimetric study showed improved thermal stability for the blends with the increasing LCP content. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3904–3912, 2006     

Study of poly(trimethylene terephthalate) as an engineering thermoplastics material

Poly(trimethylene terephthalate) (PTT) was systematically studied as an engineering thermoplastics material. Crystallization rates, crystalline degrees, and mechanical properties of two commercial PTT polymers and one glass fiber–reinforced PTT compound were investigated and compared with those of poly(butylene terephthalate) (PBT). PTT raw polymers have crystallization temperature (T_c) values around 152°C, and their kneaded polymers show T_c values of about 177°C, about 15°C lower than the values of PBT polymers used in this study. From the exothermic heat values of DSC measurements, both PTT and PBT show the crystalline degree order greater than 30%. Injection‐molded PTT specimens and PBT specimens exhibit crystalline degrees from 18 to 32% and 23.8 to 30%, respectively. PTT polymers show higher tensile and flexural strengths, but lower impact strengths and elongations than those of PBT polymers. The low elongation behavior of PTT does not change with the intrinsic viscosity and the molder temperature. PTT‐GF30 promotes better mechanical properties than those of PBT‐GF30, close to those of PET‐GF30. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1657–1666, 2004     

Crystallization kinetics for simulation of processing of various polyesters

The approach to determine crystallization kinetic parameters based on the DSC nonisothermal crystallization experiments is applied to poly(butylene terephthalate) (PBT) and poly(ethylene‐2,6‐naphthalate) (PEN). The differential form of the Nakamura equation and master curve approach are used. The isothermal induction times are obtained from nonisothermal induction times according to the concept of induction time index. The correction of temperature lag between the DSC furnace and the sample is incorporated. The corrected nonisothermal crystallization kinetic data is shifted with respect to an arbitrarily chosen reference temperature to obtain the master curve. By fitting the obtained master curve with the Hoffman‐Lauritzen equation, the model parameters for the crystallization rate constant are obtained. The relative crystallinity measured at different cooling and heating rates is described by these model parameters. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 102: 2847–2855, 2006     

Study on co[poly(butylene terephthalate‐p‐oxybenzoate)] thermotropic copolyester. II. Thermal behavior and crystalline morphology

The POB/PBT copolyesters, designated B28, B46, B64, and B82, were prepared from p‐acetoxybenzoic acid (PAB) and poly(butylene terephthalate) (PBT). The polymeric products obtained were then ground and subjected to solid‐state polymerization under vaccum for 4 h. The melting and crystallization behaviors of these copolyesters haven been studied by differential scanning calorimetry (DSC). In the DSC scan of the POB‐rich composition, the endothermic peak shows obscurely, and enthalpy of fussion becomes small due to the change in the crystalline morphology from isotropic to anisotropic. In general, the melting point of the copolyester is increased by the solid‐state polymerization reaction. Also, thermogravimetric analysis (TGA) were performed with these samples obtained. It was found that the decomposition temperature (T_d ) is increased as the POB content is increased. Effects of composition and solid‐state polymerization on the decomposition temperature of copolyesters are also discussed. The crystalline morphology of copolyester was investigated with a Zeiss polarized optical microscope. It was found that the POB/PBT copolyesters with 60 mol % POB was shown to be highly anisotropic. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2363–2368, 2000     

Entropically‐driven ring‐opening polymerization of cyclic butylene terephthalate: Rheology and kinetics

Cyclic butylene terephthalate oligomers (CBT) with ultra‐low melt viscosity can be polymerized into poly (butylene terephthalate) (pCBT) via entropically‐driven ring‐opening polymerization (ED‐ROP) in a short time (ranging from several seconds to 10 min) with no chemical emission and no heat generation during the polymerization process. Due to no heat generation, dynamic rheological measurements were used to monitor the polymerization of CBT from 220 to 250°C. The polymerization was accompanied by a steep increase of the melt viscosity and modulus in isothermal rheological tests, and much faster at higher temperature. With rheological results, reptation theory and Double reptation model were adopted to determine the variation of the molecular weight and concentration with time for pCBT. According to the ED‐ROP mechanism of CBT, kinetics equations were also established to simulate the polymerization process. Furthermore, using the results of variation of molecular weight with time for pCBT and kinetics equations, the polymerization rate constants for initiation and propagation steps were evaluated, and the activation energy was also obtained. It was proved that rheological method is a convenient and reliable way to investigate the kinetics of ED‐ROP of CBT. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Melting behavior and crystallization kinetics of poly(butylene terephthalate‐co‐diethylene terephthalate) and poly(butylene terephthalate‐co‐triethylene terephthalate) copolyesters

The melting behavior of poly(butylene terephthalate‐co‐diethylene terephthalate) and poly(butylene terephthalate‐co‐triethylene terephthalate) copolymers was investigated by differential scanning calorimetry after isothermal crystallization from the melt. Multiple endotherms were found for all the samples, and attributed to the melting and recrystallization processes. By applying the Hoffman‐Weeks' method, the equilibrium melting temperatures of the copolymers under investigation were obtained. Two distinct peaks in the crystallization exothermic curve were observed for all the samples. Both of them appeared at higher times than that of PBT, indicating that the introduction of a comonomer decreased the crystallization rate. The observed dependence of this latter on composition was explained on the basis of the content of ether–oxygen atoms in diethylene and triethylene terephthalate units, and of the different sizes of these units. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3545–3551, 2001     

Kinetics of isothermal and non‐isothermal crystallization of poly(butylene terephthalate)/ liquid crystalline polymer blends

The melting behavior and isothermal and non‐isothermal crystallization kinetics of poly(butylene terephthalate) (PBT)/thermotropic liquid crystalline polymer (LCP), Vectra A950 (VA) blends were studied by using differential scanning calorimetry. Isothermal crystallization experiments were performed at crystallization temperatures (T_c), of 190, 195, 200 and 205°C from the melt (300°C) and analyzed based on the Avrami equation. The values of the Avrami exponent indicate that the PBT crystallization process in PBT/VA blends is governed by three‐dimensional morphology growth preceded by heterogeneous nucleation. The overall crystallization rate of PBT in the melt blends is enhanced by the presence of VA. However, the degree of PBT crystallinily remains almost the same. The analysis of the melting behavior of these blends indicates that the stability and the reorganization process of PBT crystals in blends are dependent on the blend compositions and the thermal history. The fold surface interfacial energy of PBT in blends is more modified than in pure PBT. Analysis of the crystallization data shows that crystallization occurs in Regime II across the temperature range 190°C‐205°C. A kinetic treatment based on the combination of Avrami and Ozawa equations, known as Liu's approach, describes the non‐isothermal crystallization. It is observed that at a given cooling rate the VA blending increases the overall crystallization rate of PBT.     

IPA改性PBT共聚酯结晶性能研究

聚对苯二甲酸丁二醇酯（PBT）是重要的半结晶性热塑性聚酯,差别化的聚酯产品需要差别化的结晶性能。文章合成得到间苯二甲酸（IPA）含量0～20%改性PBT共聚酯样品,DSC分析表明改性共聚酯的结晶熔点及结晶熔融焓下降,且随IPA含量的增加近似呈线性减小。     

Effects of size and shape of dispersed poly(butylene terephthalate) on isothermal crystallization kinetics and morphology of poly(lactic acid) blends

The isothermal crystallization kinetics and morphology of the poly(lactic acid) (PLA) blends containing three different sizes of both spherical and fibrous poly(butylene terephthalate) (PBT) domains have been comparatively investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The dynamic DSC measurement reveals that PBT domains significantly increase the degree of crystallinity of the PLA. Furthermore, the Avrami model is employed to evaluate the crystallization kinetics under isothermal conditions and it is found that PBT acts as nucleating agent, leading to a high overall crystallization rate constant k and shortened crystallization half time t_1/2. Furthermore, the crystallization rate of PLA is promoted with the incorporation of PBT with a large specific surface area. The average Avrami index n of all samples lies within the range of 3.3 ? 4.0, suggesting that morphologies of PBT do not affect the nucleation mechanism; however, the depression of equilibrium melting temperature in the blends ascribes the reductions of perfectness and size of the PLA crystallites. Besides, the nucleation of PLA crystallites around PBT fibers is probably faster than those around PBT spheres because the PBT chains oriented at the fiber surface as a result of flow‐induced crystallization during melt stretching may serve as the primary nuclei for PLA chains to drastically crystallize at the fiber surface. POLYM. ENG. SCI., 56:258–268, 2016. © 2015 Society of Plastics Engineers     

Nonisothermal crystallization kinetics of poly(butylene terephthalate)/epoxidized ethylene propylene diene rubber/glass fiber composites

Nonisothermal crystallization kinetics of poly(butylene terephthalate) (PBT)/glass fiber (GF) and PBT/epoxidized ethylene propylene diene rubber (eEPDM)/GF composites were investigated by differential scanning calorimetry (DSC) at a cooling rates of 2.5, 5, 10, and 20 °C/min, respectively. Morphologies of samples were observed with scanning electron microscopy and polarized optical microscopy. The specimens were prepared by melt blending. Analyses of the melt crystallization data by various macrokinetic models such as Jeziorny‐modified Avrami, Liu–Mo models, and Lauritzen–Hoffman equation revealed that GF accelerated the crystallization rate of PBT; furthermore, the eEPDM had two functions: on the one hand, eEPDM promoted PBT to form nuclei; on the other hand, eEPDM hindered the diffusion of polymer chains, but the nucleation effect exceeded the diffusion effect, thus, the eEPDM could increase the crystallization rate of PBT in PBT/eEPDM/GF. These results were further supported by the effective activation energy calculated by isoconversional method of Friedman. POLYM. ENG. SCI., 59:330–343, 2019. © 2018 Society of Plastics Engineers     

Diffusion of butanediol in poly(butylene terephthalate) (PBT) melt and analysis of pbt polymerization reactor with surface renewal

A reactor with surface renewal, originally designed for poly(ethylene terephthalate) (PET) polymerization, was applied for poly(butylene terephthalate) (PBT) polymerization. A comprehensive model including side reactions was developed and compared with the experimental results. The diffusivity of butanediol (BD) in PBT melt was measured separately by desorption experiments (D_b ? 1.08 × 10⁶ exp(?32600 / RT) (m²/min)). Optimum operating temperature for PBT polymerization was found to be around 250°C in order to avoid degradation.