Poly(p-phenylene sulfide)/liquid crystalline polymer blends. II. Crystallization kinetics

The crystallization kinetics of blends made of poly(p-phenylene sulfide) (PPS) with a liquid crystalline polymer (LCP) was studied. The blends were found to be immiscible by dynamic mechanical thermal analysis (DMTA). Results of non-isothermal and isothermal crystallization experiments made by differential scanning calorimetry (DSC) showed that both components had their crystallization temperatures increased; also the LCP melting temperature was found to increase in the blends. It was concluded that the addition of LCP to the PPS increased the PPS overall crystallization rate due to heterogeneous nucleation. The fold interfacial free energy, σ_e of the PPS in the blends was observed not to vary with composition. © 1996 John Wiley & Sons, Inc.     

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.     

Blends of polypropylene resins with a liquid crystalline polymer. I. Isothermal crystallization

The isothermal crystallization kinetics of blends of different polypropylene (PP) resins and a liquid crystalline polymer (LCP) after two different melting conditions (200 and 290°C) were studied by DSC and polarized light optical microscopy. The resins were a homopolymer (hPP), a random copolymer with ethylene (cPP), and a maleic anhydride grafted PP (gPP). The LCP was Vectra A950, a random copolymer made of 75 mol % of 4‐hydroxybenzoic acid and 25 mol % of 2‐hydroxy,6‐naphthoic acid. It was observed that the overall crystallization rates of all the blends after melting at 200°C were higher than those after melting at 290°C. The LCP acted as a nucleating agent for all the PP resins; however, its nucleating effect was stronger for the hPP than for the cPP and gPP resins. After both melting conditions, an increase was observed in the overall crystallization rate of the hPP and gPP resins with the increase in the amount of LCP, but not in the cPP crystallization rate. The fold surface free energy σ_e of hPP and cPP in the blends decreased, but increased in the gPP blends. Finally, all the PP resins formed transcrystallites on the LCP domain surfaces. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 916–930, 2003     

Effect of high-performance polymers on crystallization and multiple melting behavior of poly(phenylene sulfide)

The crystallization and multiple melting behavior of poly(phenylene sulfide) (PPS) and its blends with amorphous thermoplastic bisphenol A polysulfone (PSF) and phenolphthalein poly(ether ketone) (PEK-C), crystalline thermoplastic poly(ether ether ketone) (PEEK), and thermosetting bismaleimide (BMI) resin were investigated by a differential scanning calorimeter (DSC). The addition of PSF and PEK-C was found to have no influence on the crystallization temperature (T_c) and heat of crystallization (ΔH_c) of PPS. A significant increase in the value of T_c and the intensity of the T_c peak of PPS was observed and the crystallization of PPS can be accelerated in the presence of the PEEK component. An increase in the T_c of PPS can also be accelerated in the BMI/PPS blend, but was no more significant than that in the PEEK/PPS blend. The T_c of PPS in the PEEK/PPS blends is dependent on the maximum temperature of the heating scans and can be divided into three temperature regions. The addition of a second component has no influence on the formation of a multiple melting peak. The double melting peaks can also be observed when PPS and its blends are crystallized dynamically from the molten state. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 637–644, 1998     

Melting,crystallization behaviors,and nonisothermal crystallization kinetics of PET/PTT/PBT ternary blends

The melting, crystallization behaviors, and nonisothermal crystallization kinetics of the ternary blends composed of poly(ethylene terephthalate), poly(trimethylene terephthalate) (PTT) and poly(buthylene terephthalate) (PBT) were studied with differential scanning calorimeter (DSC). PBT content in all ternary blends was settled invariably to be one‐third, which improved the melt‐crystallization temperature of the ternary blends. All of the blend compositions in amorphous state were miscible as evidenced by a single, composition‐dependent glass transition temperature (T_g) observed in DSC curves. DSC melting thermograms of different blends showed different multiple melting and crystallization peaks because of their various polymer contents. During melt‐crystallization process, three components in blends crystallized simultaneously to form mixed crystals or separated crystals depending upon their content ratio. The Avrami equation modified by Jeziorny and the Ozawa theory were employed to describe the nonisothermal crystallization process of two selected ternary blends. The results spoke that the Avrami equation was successful in describing the nonisothermal crystallization process of the ternary blends. The values of the t_1/2 and the parameters Z_c showed that the crystallization rate of the ternary blends with more poly(ethylene terephthalate) content was faster than that with the lesser one at a given cooling rate. The crystal morphology of the five ternary blends investigated by polarized optical microscopy (POM) showed different size and distortional Maltese crosses or light spots when the PTT or poly(ethylene terephthalate) component varied, suggesting that the more the PTT content, the larger crystallites formed in ternary blends. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Rheology and thermal properties of liquid crystalline copolyester and poly(ethylene 2,6-naphthalate) blends

Blends of a poly(ethylene 2,6-naphthalate) (PEN) and a liquid crystalline copolyester (LCP), poly(benzoate-naphthoate) were prepared in a twin-screw extruder. Specimens for thermal properties were investigated by means of an instron capillary rheometer (ICR) and scanning electron microscopy (SEM). The blend viscosity showed a minimum at 10 wt% of LCP and increased with increasing LCP content above 10 wt% of LCP. Above 50% of LCP and at higher shear rate, phase inversion occured and the blend morphology was fibrous and similar to pure LCP. The ultimate fibrillar structure of LCP phase appeared to be closely related to the extrusion temperature. By employing a suitable deformation history, the LCP phase may be elongated and oriented such that a microfibrillar morphology can be retained in the solid state. Thermal properties of the LCP/PEN blends were studied using DSC and a Rheovibron viscoelastomer. These blends were shown to be incompatible in the entire range of the LCP content. For the blends, the T_g and Tm were unchanged. The half time of crystallization for the LCP/PEN blends decreased with increasing LCP content. Therefore, the LCP acted as a nucleating agent for the crystallization of PEN. The dimensional and thermal stability of the blends were increased with increasing LCP content. In studies of dynamic mechanical properties, the storage modulus (E′) was improved with increasing LCP content and synergistic effects were observed at 70 wt% of LCP content. The storage modulus for the LCP/PEN 70/30 blend is twice that of PEN matrix and exceeded pure LCP.     

Application of the parallel Avrami model to crystallization of poly(etheretherketone)

We have reexamined the parallel Avrami model recently proposed by Velisaris and Seferis (1) to describe the non-Isothermal crystallization of poly(etheretherketone), PEEK. We show that, based on considerations of morphology development, the crystallization process with the larger Avrami exponent has the higher melting point, whereas the process with the smaller Avrami exponent has the lower melting point. This assignment differs from that of Velisaris and Seferis. In addition, we have used the infinite crystal melting point, as required by crystallization theory, to determine the Avrami rate parameters for the two processes. With this revision of the parallel Avrami model, we have applied the model to non-isothermal crystallization of APC-2 PEEK composite. Under the assumption that the linear growth rate determines the Avrami rate parameter, both the transport activation energy, U, and the kinetic parameter, K_g, are found to compare favorably with the values previously determined from isothermal crystallization of neat resin PEEK.     

Isothermal crystallization kinetics and melting behavior of in situ compatibilized polyamide 6/Polyethylene-octene blends

We developed in situ compatibilization technology to improve the compatibility between polyamide 6 (PA 6) and polyethylene-octene (POE). In the present work, we investigated the isothermal crystallization and melting behavior of PA 6/POE blends using differential scanning calorimetry (DSC). All specimens exhibited double melting peaks at lower temperature and single melting peaks at higher temperature. The Avrami exponent and equilibrium melting temperature were obtained by analysis of DSC experimental data using the Avrami equation and Hoffman-Weeks theory, respectively. It has demonstrated that the crystallization model of PA 6 for all specimens might be a mixture with two-dimensional, circular, three-dimensional growth with thermal nucleation. We further calculated the nucleation parameter (K _g ) from the obtained crystallization kinetics data using Lauritzen-Hoffmann equation. It was found that the K _g values of the compatibilized PA 6 were lower than that of pure PA 6 whereas increased with the increase of POE content, which was related to the better dispersion of POE and the interaction between PA 6 and the in situ formed POE-g-MAH. Additionally, the spherulite morphology was observed by polarized optical microscopy (POM).     

Thermal studies of blends of poly(phenylene sulfide) (PPS) with poly(phenylene sulfide sulfone) (PPSS) and with poly(phenylene sulfide ether) (PPSE)

The miscibilities of poly(phenylene) sulfide/poly(phenylene sulfide sulfone) (PPS/PPSS) and poly(phenylene) sulfide/poly(phenylene sulfide ether) (PPS/PPSE) blends were invesigated in terms of shifts of glass transition temperatures T_g of pure PPS, PPSS, a dn PPSE. The crystallization kinetics of PPS/PPSS blends was also studied as a function of molar composition. The PPS/PPSS and PPS/PPSE blends are respectively partially and fully miscible. PPSE shows a plasticizing effect on PPS as does PPS on PPSS, which necessarily improves te processibility in the respective systems. We can control T_g and melting temperature T_m of PPS by varying amounts of PPSE in blends. The melt crystallization temperature T_mc of PPS/PPSE blends was higher than that of the PPSE homopolymer. Therefore, these blends require shorter cycle times in processing than pure PPSE. The overall rate of crystallization for PPS/PPSS blends follows the Avrami equation with an exponent ?2. The maximal rate of crystallization for PPS/PPSS blends occurs at a temperatre higher by 10°C than that for PPS, while the crystallization half time t_1/2 is 4 times shorter. In the cold crystallization range, crystal growth rates increase and Avrami exponents decrease significantly as the temperature increases.     

LLDPE/SEBS-g-MAH体系的等温结晶动力学

采用差示扫描量热法(DSC)研究了SEBS-g-MAH对LLDPE等温结晶行为的影响,并通过偏光显微镜(POM)观察了LLDPE及LLDPE/SEBS-g-MAH共混体系的结晶形态。结果表明,SEBS-g-MAH的加入阻碍了LLDPE分子链的规则排列,影响了链段在结晶扩散迁移规整排列的速度,使得结晶速率变慢,结晶活化能升高,对LLDPE晶体生长起了抑制作用,晶粒尺寸减小。用Avrami方程进行等温结晶动力学研究表明,LLDPE/SEBS-g-MAH共混体系的半结晶时间t1/2明显增大,Avrami指数n对结晶温度有依赖性,kn值随温度的升高而减小。利用Hoffman理论计算了球晶生长过程中晶核的折叠表面自由能σe为0.136 J.m-2,SEBS-g-MAH的加入使得σe增大了9.6%。     

Blends of a bottle grade polyethylene terephthalate copolymer and a liquid crystalline polymer. Part I: Injection molding morphology and rheological properties

Blends of a bottle grade polyethylene terephthalate copolymer (PET) with a liquid crystalline polymer (LCP) were prepared by injection molding. The thermal transitions, the morphology and the rheological properties of the pure components and of the blends were measured by dynamic mechanical analysis (DMTA), scanning electron microscopy (SEM) and capillary and parallel plates rheometry, respectively. The blends displayed only one T_g; the B60 and B80 compositions showed the highest LCP β‐transition, which has been correlated to good barrier properties. In all the blends a “skin‐core” type morphology was observed; the core region had two phases while the skin region showed only one fibrillar phase. The viscosity measurements gave an indication that the interface was strong, probably due to transterifications reactions that occurred during the tests. On creep recovery, the increasing addition of the LCP to the PET increased the blends elastic recovery. On stress growth, the highest stress overshoot was displayed by the pure LCP; this polymer actually presented two overshoots that were also observed in some of the blends at high shear rates.     

Crystallization behaviour of cellulose acetate butylate/poly(butylene succinate)‐co‐(butylene carbonate) blends

The kinetics of the isothermal crystallization process from the melt of pure poly(butylene succinate)‐co‐(butylene carbonate) (PBS‐co‐BC) and its blends with cellulose acetate butylate (CAB) (10–30 wt%) was studied by differential scanning calorimetry (DSC) and the well‐known Avrami equation. In the blends, the overall crystallization rate of PBS‐co‐BC became slower with increasing CAB content. The equilibrium melting temperature ( ) of PBS‐co‐BC decreased with increasing CAB content, which was similar to that with other miscible crystalline/amorphous polymer blends. The slower crystallization kinetics of PBS‐co‐BC in the blends was explicable in terms of a diluent effect of the CAB component. By application of Turnbull–Fisher kinetic theory for polymer–diluent blend systems, the surface free energy (σ_e) of pure PBS‐co‐BC and of the blends was obtained, indicating that the blend with CAB resulted in a decrease in the surface free energy of folding of PBS‐co‐BC lamellar crystals. Copyright © 2006 Society of Chemical Industry     

Crystallization kinetics of compatibilized blends of liquid crystalline polymer with PEEK

A fully aromatic thermotropic liquid crystalline polyester (TLCP) has been blended with poly(ether ether ketone) (PEEK). Multiblock copolymer (BCP) was used as the compatibilizer in the concentration at 2 phr. The isothermal crystallization kinetics and morphology of compatibilized blends were studied using differential scanning calorimetry (DSC) and polar light micrograph (PLM). TLCP acted as a heterogenous nucleation sites to accelerate the crystallization for PEEK. However, PEEK crystallization rates decreased with increasing TLCP fraction. Isothermal crystallization exotherms showed that the addition of BCP retarded crystallization of PEEK in PEEK/TLCP blend, which was probably resulted from the constraint effect of BCP as well as the size reduction of PEEK spherulite domain. The equilibrium melting temperature of PEEK for blends was below that of pure PEEK. After adding BCP, it decreased further. Morphological analysis showed that it was difficult to discern the single PEEK spherulites when BCP was added. POLYM. COMPOS., 27:642–650, 2006. © 2006 Society of Plastics Engineers     

The effect of poly(ethylene glycol) mixed with poly(l‐lactic acid) on the crystallization characteristics and properties of their blends

The non‐isothermal and isothermal crystallizations of extruded poly(l ‐lactic acid) (PLLA) blends with 10, 20 and 30 wt% poly(ethylene glycol) (PEG) were investigated with differential scanning calorimetry. The formation of α‐form crystals in the blend films was verified using X‐ray diffraction and an increase in crystallinity indexes using Fourier transformation infrared spectroscopy. Crystallization and melting temperatures and crystallinity of PLLA increased with decreasing cooling rate (CR) and showed higher values for the blends. Although PLLA crystallized during both cooling and heating, after incorporation of PEG and with CR = 2 °C min^?1 its crystallization was completed during cooling. Increasingly distinct with CR, a small peak appeared on the lower temperature flank of the PLLA melting curve in the blends. A three‐dimensional nucleation process with increasing contribution from nuclei growth at higher CR was verified from Avrami analysis, whereas Kissinger's method showed that the diluent effect of 10 and 20 wt% PEG in PLLA decreased the effective energy barrier. During isothermal crystallization, crystallization half‐time increased with temperature (T_ic) for the blends, decreased with PEG content and was lower than that of pure PLLA. In addition, the Avrami rate constants were significantly higher than those of pure PLLA, at the lower T_ic. Different crystal morphologies in the PLLA phase were formed, melting in a broader and slightly higher T_m range than pure PLLA. The crystallization activation energy of PLLA decreased by 56% after the addition of 10 wt% PEG, increasing though with PEG content. Finally, PEG/PLLA blends presented improved flexibility and hydrophilicity. © 2019 Society of Chemical Industry     

Crystallization and melting behavior of partially miscible six‐armed poly(l‐lactic acid)/poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) blends

The crystallization kinetics and spherulitic morphology of six‐armed poly(L‐lactic acid) (6a‐PLLA)/poly(3‐hydroxybutyrate‐co?3‐hydroxyvalerate) (PHBV) crystalline/crystalline partially miscible blends were investigated with differential scanning calorimetry and polarized optical microscopy in this study. Avrami analysis was used to describe the isothermal crystallization process of the neat polymers and their blends. The results suggest that blending had a complex influence on the crystallization rate of the two components during the isothermal crystallization process. Also, the crystallization mechanism of these blends was different from that of the neat polymers. The melting behavior of these blends was also studied after crystallization at various crystallization temperatures. The crystallization of PHBV at 125°C was difficult, so no melting peaks were found. However, it was interesting to find a weak melting peak, which arose from the PHBV component for the 20/80 6a‐PLLA/PHBV blend after crystallization at 125°C, and it is discussed in detail. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42548.     

Melting behavior,isothermal and nonisothermal crystallization kinetics of EPPE/mLLDPE blends

Melting behavior and crystallization kinetics of easy processing polyethylene (EPPE) and the blends of EPPE/mLLDPE were studied using differential scanning calorimetry at various crystallization temperature and cooling rates. The Avrami analysis was employed to describe the isothermal and nonisothermal crystallization process of pure polymers and their blends, and a method developed by Mo was applied for comparison. Kinetic parameters such as the Avrami exponent (n), the kinetic crystallization rate constant (k and k_c), the peak temperatures (T_p), and the half-time of crystallization (t_1/2), etc. were determined. The appearance of double melting peaks and the double crystallization peaks of the polymers showed that the main chain and the branches crystallize seperately, but the main chains of two polymers can crystallize together and mLLDPE act as nuclei while EPPE crystallizes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Miscibility, thermal properties and polymorphism of syndiotactic polystyrene/poly(styrene-co-α-methyl styrene) blends

This work examined the miscibility, crystallization kinetics, melting behavior and crystal structure of syndiotactic polystyrene (sPS)/poly(styrene-co-α-methyl styrene) blends. Differential scanning calorimetry, polarized light microscopy and wide angle X-ray diffraction technique were used to approach the goals. The single composition-dependent T_gs of the blends and the melting temperature (T_m) depression of sPS in the blends indicated the miscible characteristic of the blend system at all compositions. Furthermore, the T_gs of the blends could be predicted by either of the Gordon–Taylor equation (with K=0.99) or the Fox equation with a slightly higher deviation. The dynamic and isothermal crystallization abilities of sPS were hindered with the incorporation of the miscible copolymer. Complex melting behavior was observed for melt-crystallized pure sPS and its blends as well. Nevertheless, the blends showed relatively simpler melting curves. Comparing with melt-crystallized samples, the cold-crystallized samples exhibited simpler melting behavior. The equilibrium melting temperature (T_m⁰) of β form sPS crystal determined from the conventional extrapolative method is 295.2 °C. The Flory–Huggins interaction parameter, χ, of the blends was estimated to be −0.27. The crystal morphology of sPS was disturbed in the blends. Only underdeveloped granular-like crystalline superstructure of sPS exhibited in cold-crystallized blends. Moreover, the existence of the copolymer in the blends apparently reduced the possibility of forming the less stable α form sPS crystals.     

Effect of the ionic liquid [bmim]PF6 on the nonisothermal crystallization kinetics behavior of poly(ether‐b‐amide)

Blending ionic liquid with crystalline polymer permits the design of new high‐performance composite materials. The final properties of these materials are critically depended on the degree of crystallinity and the nature of crystalline morphology. In this work, nonisothermal crystallization behavior of poly(ether‐b‐amide) (Pebax®1657)/room temperature ionic liquid (1‐butyl‐3‐methylimidazolium hexafluorophosphate, [bmim]PF₆) was investigated by differential scanning calorimetry. The presence of [bmim]PF₆ can retard the nucleation of Pebax®1657 and lead to the crystallization depression of the PA block and the crystalline disappearance of the PEO block. However, the dilution effect of the IL results in a higher growth rate of crystallization of PA block. The influence of [bmim]PF₆ content and cooling rate on crystallization mechanism and spherulitc structures was determined by the Avrami equation modified by Jeziorny and Mo's methods, whereas the Ozawa's approach fails to describe the nonisothermal crystallization behavior of Pebax®1657/[bmim]PF₆ blends. In the modified Avrami analysis, the Avrami exponent of PA blocks, n > 3, for pure Pebax®1657, while 3 > n > 2 for Pebax®1657/[bmim]PF₆ blends testifies the transformation of crystallization growth pattern induced by [bmim]PF₆ from three‐dimensional growth of spherulites to a combination of two‐ and three‐dimensional spherulitic growth. Further, lower activation energy for the nonisothermal crystallization of PA blocks of Pebax®1657 can be observed with the increase of [bmim]PF₆ content. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42137.     

Rheology and physical properties of ternary blends containing a thermotropic liquid crystalline copolyester

Ternary blends of polyarylate (PAR) U-Polymer 100, thermotropic liquid crystalline copolyester (LCP) Vectra A950, and a block copolyesterether Hytrel 7246 were investigated in terms of rheological properties, morphology, and mechanical properties. The PAR/Hytrel blend exhibited melting point depression and gave a unique single T_g over the entire range of blend compositions. Addition of Hytrel to the PAR/LCP blend decreased both dynamic viscosity and storage modulus over the normal processing temperature range. Further, it notably reduced the voids between the LCP domains and the matrix, and improved the mechanical properties. The optimum usage level of Hytrel proved to be 2 phr.     

Miscibility and melting behavior of poly(ethylene terephthalate)/poly(trimethylene terephthalate) blends

The miscibility and melting behavior of binary crystalline blends of poly(ethylene terephthalate) (PET)/poly(trimethylene terephthalate) (PTT) have been investigated with differential scanning calorimetry and scanning electron microscope. The blends exhibit a single composition‐dependent glass transition temperature (T_g) and the measured T_g fit well with the predicted T_g value by the Fox equation and Gordon‐Taylor equation. In addition to that, a single composition‐dependent cold crystallization temperature (T_cc) value can be observed and it decreases nearly linearly with the low T_g component, PTT, which can also be taken as a valid supportive evidence for miscibility. The SEM graphs showed complete homogeneity in the fractured surfaces of the quenched PET/PTT blends, which provided morphology evidence of a total miscibility of PET/PTT blend in amorphous state at all compositions. The polymer–polymer interaction parameter, χ₁₂, calculated from equilibrium melting temperature depression of the PET component was ?0.1634, revealing miscibility of PET/PTT blends in the melting state. The melting crystallization temperature (T_mc) of the blends decreased with an increase of the minor component and the 50/50 sample showed the lowest T_mc value, which is also related to its miscible nature in the melting state. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008