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     

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     

Nonisothermal melt crystallization kinetics of poly(ethylene terephthalate)/Barite nanocomposites

Poly(ethylene terephthalate) (PET)/Barite nanocomposites were prepared by direct melt compounding. The nonisothermal melt crystallization kinetics of pure PET and PET/Barite nanocomposites, containing unmodified Barite and surface‐modified Barite (SABarite), was investigated by differential scanning calorimetry (DSC) under different cooling rates. With the addition of barite nanoparticles, the crystallization peak became wider and shifted to higher temperature and the crystallization rate increased. Several analysis methods were used to describe the nonisothermal crystallization behavior of pure PET and its nanocomposites. The Jeziorny modification of the Avrami analysis was only valid for describing the early stage of crystallization but was not able to describe the later stage of PET crystallization. Also, the Ozawa method failed to describe the nonisothermal crystallization behavior of PET. A combined Avrami and Ozawa equation, developed by Liu, was used to more accurately model the nonisothermal crystallization kinetics of PET. The crystallization activation energies calculated by Kissinger, Takhor, and Augis‐Bennett models were comparable. The results reveal that the different interfacial interactions between matrix and nanoparticles are responsible for the disparate effect on the crystallization ability of PET. POLYM. COMPOS., 31:1504–1514, 2010. © 2009 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     

Non-isothermal crystallization kinetics of poly(ethylene terephthalate)/mica composites

The non-isothermal crystallization kinetics of pure poly(ethylene terephthalate) (PET), PET/mica and PET/TiO₂-coated mica composites were investigated by differential scanning calorimetry with different theoretical models, including the modified Avrami method, Ozawa method and Mo method. The activation energies of non-isothermal crystallization were calculated by Kissinger method and Flynn–Wall–Ozawa method. The results show that the modified Avrami equation and Ozawa theory fail to describe the non-isothermal crystallization behavior of all composites, while the Mo model fits the experiment data fair well. It is also found that the mica and TiO₂-coated mica could act as heterogeneous nucleating agent and accelerate the crystallization rates of PET, and the effect of TiO₂-coated mica is stronger than that of mica. The result is further reinforced by calculating the effective activation energy of the non-isothermal crystallization process for all composites using the Kissinger method and the Flynn–Wall–Ozawa method.     

Nonisothermal crystallization kinetics of nucleated poly(ethylene terephthalate)

Studies of the nonisothermal crystallization kinetics of poly(ethylene terephthalate) nucleated with anhydrous sodium acetate were carried out. The chemical nucleating effect was investigated and confirmed with Fourier transform infrared and intrinsic viscosity measurements. The Avrami, Ozawa, and Liu models were used to describe the crystallization process. The rates of crystallization, which initially increased, decreased at higher loadings of the additive. The activation energy, calculated with Kissinger's method, was lower for nucleated samples. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Nonisothermal crystallization kinetics of poly(ethylene terephthalate)/clay nanocomposites prepared by melt processing

In this study, cold and melt crystallization behaviors of amorphous poly(ethylene terephthalate) (PET)/clay nanocomposites were investigated. Two nanocomposite samples with the same amount of inorganic content were prepared by melt processing using natural montmorillonite (Na‐MMT) and organo‐modified montmorillonite (org‐MMT). Depending on the clay structure, clay dispersion into PET and crystallization behavior of the samples were studied using X‐ray diffraction and differential scanning calorimetry methods, respectively. Effects of clay structure and organic groups between clay layers in org‐MMT on the melt crystallization kinetics of the samples were 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 and Augis–Bennett models. Exfoliated structures were obtained in the nanocomposite samples prepared with both the Na‐MMT and org‐MMT. From the kinetics study, it was found that the melt‐crystallization rate of the sample prepared with the Na‐MMT was higher than that prepared with the org‐MMT at a given cooling rate. It can be concluded that organic ammonium groups in the org‐MMT decelerate the crystallization rate of PET chains possibly by affecting the chain diffusion and folding. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

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.     

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     

Commingled poly(butylene terephthalate)/unidirectional glass fiber composites: Influence of the process conditions on the microstructure of poly(butylene terephthalate)

The microstrocture of poly(butylene terephthalate) (PBT) has been investigated at the different stages of the manufacture of a new generation of composite materials, i.e., commingled Twintex® PBT/glass fiber composites. From differential scanning calorimetry and wide angle X‐ray scattering analysis in addition to density measurements and optical microscopy observations, it was concluded that the different stages of the composite manufacture induce some changes in the crystalline forms of PBT. In particular, the drawing of PBT can promote the formation of the β phase. The analysis of the crystallization kinetics points out the nucleation role played by the fibers. It is concluded that the growth of a transcrystalline region in the vicinity of fibers is promoted by the elevated pressure and temperature used in the manufacturing process of the composites.     

Nonisothermal crystallization of reprocessed poly(ethylene terephthalate)

Poly(ethylene terephthalate) was submitted to five reprocessing cycles by extrusion. The materials were analyzed with oligomer and after oligomer extraction. The nonisothermal crystallization of the five samples was investigated by differential scanning calorimetry. Samples with oligomer content and carboxylic end group concentrations between 44 and 98 eqw × 10⁶ g presented a nonlinear correlation with the crystallization temperature. After the oligomer extraction of the polymer, this correlation is linear. The nonisothermal crystallization results were analyzed using the Ozawa model. The polymers containing oligomers obey the Ozawa model for the first reprocessing cycle. After oligomer extraction, the polymers obey the Ozawa model from the first to the third reprocessing cycle. In both cases, the exponential n values are close to 2.0. For the other cycles, deviations from this model occur. The activation energy was calculated using the Kissinger and Varma models. The values obtained for the five reprocessed samples were inversely proportional to the molar mass when analyzed by both models. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 525–531, 2004     

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     

Nonisothermal crystallization kinetics of poly(ethylene terephthalate) and poly(methyl methacrylate) blends

The nonisothermal crystallization kinetics of poly(ethylene terephthalate) (PET) and poly(methyl methacrylate) (PMMA) blends were studied. Four compositions of the blends [PET 25/PMMA 75, PET 50/PMMA 50, PET 75/PMMA 25, and PET 90/PMMA 10 (w/w)] were melt‐blended for 1 h in a batch reactor at 275°C. Crystallization peaks of virgin PET and the four blends were obtained at cooling rates of 1°C, 2.5°C, 5°C, 10°C, 20°C, and 30°C/min, using a differential scanning calorimeter (DSC). A modified Avrami equation was used to analyze the nonisothermal data obtained. The Avrami parameters n, which denotes the nature of the crystal growth, and Z_t, which represents the rate of crystallization, were evaluated for the four blends. The crystallization half‐life (t_½) and maximum crystallization (t_max) times also were evaluated. The four blends and virgin polymers were characterized using a thermogravimetric analyzer (TGA), a wide‐angle X‐ray diffraction unit (WAXD), and a scanning electron microscope (SEM). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3565–3571, 2006     

Miscibility and crystallization kinetics of poly(trimethylene terephthalate)/amorphous poly(ethylene terephthalate) blends

The miscibility and crystallization kinetics of the blends of poly(trimethylene terephthalate) (PTT) and amorphous poly(ethylene terephthalate) (aPET) have been investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). It was found that PTT/aPET blends were miscible in the melt. Thus, the single glass transition temperature (T_g) of the blends within the whole composition range and the retardation of crystallization kinetics of PTT in blends suggested that PTT and aPET were totally miscible. The nucleation density of PTT spherulites, the spherulitic growth, and overall crystallization rates were depressed upon blending with aPET. The depression in nucleation density of PTT spherulites could be attributed to the equilibrium melting point depression, while the depression in the spherulitic growth and overall crystallization rates could be mainly attributed to the reduction of PTT chain mobility and dilution of PTT upon mixing with aPET. The underlying nucleation mechanism and growth geometry of PTT crystals were not affected by blending, from the results of Avrami analysis. POLYM. ENG. SCI., 47:2005–2011, 2007. © 2007 Society of Plastics Engineers     

The hydrolytic stability of glass fiber reinforced poly(butylene terephthalate), poly(ethylene terephthalate) and polycarbonate

The hydrolytic stability of glass fiber reinforced poly(butylene terephthalate) (PBT), poly(ethylene terephthalate) (PET) and polycarbonate (PC) was studied. The activation energies in kcal/mole for hydrolysis are 26 for PBT and 23 for PET. Both PBT and PET contain 30 percent glass fiber reinforcement. The hydrolysis rates for a series of experimental PC's containing 10, 30 and 40 percent glass were obtained from GPC data. These increase with glass concentration but are lower than that of the unreinforced PC. Melt flow rate changes are a good measure of the hydrolytic degradation of PET. However, in the time scale of these experiments, the tensile properties of glass reinforced PBT and PC do not correlate well with M?_w changes, unlike unreinforced PBT and PC polymers. Consequently, to compare these three glass fiber reinforced polymers, estimates of failure time must be based on changes in tensile strength rather than melt flow rate.     

Nonisothermal crystallization kinetics and morphology of poly(ethylene terephthalate) modified with poly(lactic acid)

The nonisothermal crystallization kinetics of poly(ethylene terephthalate) (PET) copolymers modified with poly(lactic acid) (PLA) were investigated with differential scanning calorimetry, and a crystal morphology of the samples was observed with scanning electron microscopy. Waste PET (P100) obtained from postconsumer water bottles was modified with a low‐molecular‐weight PLA. The PET/PLA weight ratio was 90/10 (P90) or 50/50 (P50) in the modified samples. The nonisothermal melt‐crystallization kinetics of the modified samples were compared with those of P100. The segmented block copolymer structure (PET‐b‐PLA‐b‐PET) of the modified samples formed by a transesterification reaction between the PLA and PET units in solution and the length of the aliphatic and aromatic blocks were found to have a great effect on the nucleation mechanism and overall crystallization rate. On the basis of the results of the crystallization kinetics determined by several models (Ozawa, Avrami, Jeziorny, and Liu–Mo) and morphological observations, the crystallization rate of the samples decreased in the order of P50 > P90 > P100, depending on the amount of PLA in the copolymer structure. However, the apparent crystallization activation energies of the samples decreased in the order of P90 > P100 > P50. It was concluded that the nucleation rate and mechanism were affected significantly by the incorporation of PLA into the copolymer structure and that these also had an effect on the overall crystallization energy barrier. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Effect of functionalized elastomer addition on mechanical and interfacial properties of poly (butylene terephthalate)/glass fiber composites

In this study the effect of incorporation of ethylene‐co‐glycidylmethacrylate (GMA)‐co‐n‐butyl acrylate (nBA) terpolymer with an epoxy functional group, on the mechanical performance of short glass fiber (SGF)/Poly (butylene terephthalate) (PBT) composites has been investigated. Tensile test showed that incorporation of rubber phase in PBT/SGF composites results in loss of strength. However impact measurement exhibited an increase in impact strength with an increase in rubber content. Tensile and impact properties are discussed in terms of interfacial shear strength and morphology of composites. Morphological observation by SEM revealed a thin layer of polymer adhering to the surface of glass fibers indicating that epoxy functional group in the modifier reacts with fiber surface and PBT matrix. This reactivity of epoxy functional group is also supported by FTIR observations. The composites are also analyzed for % crystallinity using DSC and a strong correlation is found to exist between interfacial shear strength and % crystallinity. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Crystalline morphology and isothermal crystallization kinetics of poly(ethylene terephthalate)/clay nanocomposites

A poly(ethylene terephthalate) (PET)/montmorillonite clay nanocomposite was synthesized via in situ polymerization. Microscopic studies revealed that in an isothermal crystallization process, some crystallites in the nanocomposite initially were rod‐shaped and later exhibited three‐dimensional growth. The crystallites in the nanocomposite were irregularly shaped, rather than spherulitic, being interlocked together without clear boundaries, and they were much smaller than those of neat PET. With Avrami analysis, the isothermal crystallization kinetic parameters (the Avrami exponent and constant) were obtained. The rate constants for the nanocomposite demonstrated that clay could greatly increase the crystallization rate of PET. The results for the Avrami exponent were consistent with the observation of the rodlike crystallites in the PET/clay nanocomposite during the initial stage. Wide‐angle X‐ray scattering and Fourier transform infrared studies showed that, in comparison with neat PET, the crystal lattice parameters and crystallinity of the nanocomposite did not change significantly, whereas more defects may have been present in the crystalline regions of the nanocomposite because of the presence of the clay. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1381–1388, 2004     

Nonisothermal crystallization behavior and UV screening ability of poly(ethylene terephthalate)/carbon black transparent films

A UV absorbent was blended with virgin carbon black to prepare modified carbon black (m-CB) using a solid phase modification. The mixed solutions of poly(ethylene terephthalate) (PET)/CB and PET/m-CB were coated on glass substrates to fabricate light screening films. Scanning electron microscopy (SEM) showed that m-CB had better dispersibility than CB in PET matrix. Nonisothermal crystallization kinetics of virgin PET, PET/CB, and PET/m-CB films were investigated by differential scanning calorimetry (DSC). The data were described by a modified Avrami model. The results showed CB and m-CB acted as nucleating agents and increased the crystallization rate of PET. But due to the low crystallization capacity of copolymerized PET (co-PET) matrix, the nucleating effects were not as obvious as expected. The addition of 4 wt% m-CB improved the UV screening ability of the composite film significantly and just slightly increased their haze.