Crystallization and melting behavior of poly(ether ether ketone)/poly(aryl ether sulfone) blends

The crystallization and melting behavior of poly(ether ether ketone) (PEEK) in blends with poly(aryl ether sulfone) (PES) prepared by melt mixing are investigated by differential scanning calorimetry (DSC) and wide‐angle X‐ray scattering (WAXS). The presence of PES is found to have a notable influence on the crystallization behavior of PEEK, especially when present in low concentrations in the PEEK/PES blends. The PEEK crystallization kinetics is retarded in the presence of PES from the melt and in the rubbery state. An analysis of the melt crystallization exotherm shows a slower rate of nucleation and a wider crystallite size distribution of PEEK in the presence of PES, except at low concentrations of PES, where, because of higher miscibility and the tendency of PES to form ordered structures under suitable conditions, a significantly opposite result is observed. The cold crystallization temperature of the blends at low PES concentration is higher then that of pure PEEK, whereas at a higher PES concentration little change is observed. In addition, the decrease in heat of cold crystallization and melting, which is more prevalent in PEEK‐rich compositions than in pure PEEK, shows the reduction in the degree of crystallinity because of the dilution effect of PES. Isothermal cold crystallization studies show that the cold crystallization from the amorphous glass occurs in two stages, corresponding to the mobilization of the PEEK‐rich and PES‐rich phases. The slower rate of crystallization of the PEEK‐rich phase, even in compositions where a pure PEEK phase is observed, indicates that the presence of the immobile PES‐rich phase has a constraining influence on the crystallization of the PEEK‐rich phase, possibly because of the distribution of individual PEEK chains across the two phases. The various crystallization parameters obtained from WAXS analysis show that the basic crystal structure of PEEK remains unaffected in the blend. Further, the slight melting point depression of PEEK at low concentrations of PES, apart from several other morphological reasons, may be due to some specific interactions between the component homopolymers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2906–2918, 2003     

Isothermal crystallization and melting behavior of short carbon fiber reinforced poly(ether ether ketone) composites

Films of short carbon fiber reinforced poly(ether ether ketone) (PEEK) composite were formed by compression molding pellets for 10 min at 380 °C under air. A heating stage was used to prepare isothermally treated PEEK composites before DSC scan. The dependence of degree of crystallinity on the heating rate (10–80 °C/min) was investigated for specimens crystallized at different temperatures. The results indicated that 50 °C/min was an optimum heating rate to suppress the reorganization and to avoid the superheating of high crystallinity specimens with the sample weight of 10 mg. The upper peak temperature of double-melting peaks continued to increase with crystallization temperature. This peak temperature was related to the transition from regime II to III. The phenomenon of lower crystallinity and higher melting temperature supports the interpretation that the upper melting peak corresponded to crystals growing during the earlier stage of isothermal crystallization.     

Enhancing resistance of poly(ether ketone ketone) to high-temperature steam through crosslinking and crystallization control

Poly(aryl ether ketone)s (PAEKs) are promising materials for harsh environments, such as in high-temperature steam applications. Here, the effect of high-temperature steam on the crystallinity and mechanical properties of existing poly(ether ether ketone) (PEEK) and PEKK(T/I) polymers is investigated. Differential scanning calorimetry (DSC), wide-angle X-ray scattering or diffraction (WAXD), and dynamic mechanical analysis experiments show these materials undergo significant crystallization and reorganization after prolonged exposure to steam and suffer from embrittlement. In addition, we show that xanthydrol-based crosslinks can provide the dimensional stability and stabilize the PEKK crystal structure. Mechanical tests demonstrate that the ductility is preserved for longer exposures to steam compared to neat PEKK, whereas DSC and WAXD data indicate xanthydrol crosslinks effectively stabilize the crystal structure against steam-assisted crystallization. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47727.     

Nonisothermal crystallization behavior of poly(aryl ether ether ketone)

A study has been made of the crystallization behavior of poly(aryl ether ether ketone), PEEK, under nonisothermal conditions. A differential scanning calorimeter (DSC) was used to monitor the energetics of the crystallization process from the melt. For nonisothermal studies, the melt was crystallized by cooling at rates from 1°C/min to 10°C/min. A kinetic analysis based on the recently proposed model for nonisothermal crystallization kinetics to remedy the drawback of the Ozawa equation was applied. The Avrami exponent for the nonisothermal crystallization process was strikingly different from that of the isothermal process, which indicates different crystallization behaviors. The results agree with the morphological observation reported in the literature. This study shows that correct interpretation of the Avrami exponent provides valuable information about the crystal structure and its morphology.     

Effect of dihydroxydiphenyl ether on poly(ether ether ketone)

A series of modified poly(ether ether ketone) (PEEK) polymers were synthesized by introduction of addition ether groups from dihydroxydiphenyl ether (DHDE) into the PEEK structure. The inherent viscosity of the DHDE-modified PEEK increased with reaction time at 320 °C. DSC thermograms showed the melting points of the obtained PEEK decreased with the increase of the DHDE content in the backbone. The degradation temperature (T_d) was slightly decreased by the introduction of DHDE. The crystallinity as measured via the X-ray diffraction (XRD) increases with the introduction of DHDE into the modified PEEK. The crystalline structure was identified as an orthorhombic structure with lattice constants a = 7.72 Å, b = 5.86 Å, and c = 10.24 Å. Due to the glass transition temperature (T_g) and the melting temperature (T_m) decreasing with the increase of the DHDE content in the reaction system. the processability of the resultant PEEK could be improved through this DHDE modification.     

Investigation on the crystallization behavior of poly(ether ether ketone)/poly(phenylene sulfide) blends

The morphology of nonisothermally crystallized poly(phenylene sulfide) (PPS) and its blend with poly (ether ether ketone) (PEEK) have been observed by polarized optical microscope (POM) equipped with a hot stage. The nonisothermal crystallization behavior of PPS and PEEK/PPS blend has also been investigated by differential scanning calorimetry (DSC). The maximum crystallization temperature for PEEK/PPS blend is about 15°C higher than that of neat PPS, and the crystallization rate, characterized by half crystallization time, of the PEEK/PPS blend is also higher than that of the neat PPS. These results indicate that the PEEK acts as an effective nucleation agent and greatly accelerates the crystallization rate of PPS. The Ozawa model was used to analyze the nonisothermal crystallization kinetics of PPS and its blends. The Avrami exponent values of neat PPS are higher than that of its blend, which shows that the presence of PEEK changed the nucleation type of PPS from homogeneous nucleation to heterogeneous nucleation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Crystallization behavior of poly(ether ether ketone ketone)

The melting behavior of semicrystalline poly(ether ether ketone ketone) (PEEKK) has been studied by differential scanning calorimetry (DSC). When PEEKK is annealed from the amorphous state, it usually shows two melting peaks. The upper melting peaks arise first, and the lower melting peaks are developed later. The upper melting peaks shown in the DSC thermogram are the combination (addition) of three parts: initial crystal formed before scanning; reorganization; and melting-recrystallization of lower melting peaks in the DSC scanning period. In the study of isothermal crystallization kinetics, the Avrami equation was used to analyze the primary process of the isothermal crystallization; the Avrami constant, n, is about 2 for PEEKK from the melt and 1.5 for PEEKK from the glass state. According to the Lauritzen-Hoffman equation, the kinetic parameter of PEEKK from the melt is 851.5 K; the crystallization kinetic parameter of PEEKK is higher than that of PEEK, and suggests the crystallizability of PEEKK is less than that of PEEK. The study of crystallization on PEEKK under nonisothermal conditions is also reported for cooling rates from 2.5°C/min to 40°C/min, and the nonisothermal condition was studied by Mandelkern analysis. The results show the nonisothermal crystallization is different from the isothermal crystallization. © 1996 John Wiley & Sons, Inc.     

聚苯酯对聚醚醚酮结晶行为的影响

用模压法制备了聚苯酯(Ekonol)／聚醚醚酮(PEEK)复合材料，通过X射线衍射(XRD)、差示扫描量热分析(DSC)考察了PEEK的结晶行为，并测定了复合材料的熔点、结晶温度和玻璃化转变温度。结果表明：Ekonol含量的大小对PEEK的结晶行为产生了直接影响，PEEK的相对结晶度随着Ekonol含量的增加而提高；Ekonol含量小于30％时，对复合材料的熔点、结晶温度和玻璃化转变温度影响不大，但含量大于30％时，材料的结晶温度、熔融温度下降，玻璃化转变温度提高。     

Crystallization behavior and mechanical properties of poly(aryl ether ether ketone)/poly(ether imide) blends

Crystallinity and mechanical properties of blends with different amounts of semicrystalline poly(aryl/ ether ether ketone) (PEEK) and amorphous poly(ether imide) (PEI) polymers have been studied. The blends, prepared by melt mixing, have been investigated by differential scanning calorimeter (DSC) to analyze the miscibility between the components and the final crystalline content. Moreover, for the 20/80 PEEK/PEI blend, crystallization in dynamic and isothermal conditions has been carefully investigated in order to find proper conditions for maximum development of crystallinity. Mechanical tests (static and dynamic) have been performed to evaluate the properties of the as-molded and crystallized blends and to compare them with those of crystalline PEEK and amorphous PEI neat resins. Finally, a few SEM observations have been performed to compare the fractured surface of the blend with those of the pure constituents.     

Crystallinity of isothermally and nonisothermally crystallized poly(ether ether ketone) composites

PEEK/carbon fiber composites were prepared by a modified diaphragm forming machine under vacuum. The study of the degree of crystallinity versus the differential scanning calorimetry (DSC) heating rate indicated that 50°C/min was an optimal heating rate to suppress the reorganization of the specimens crystallized between 315°C and 255°C and to avoid superheating the specimens. A high volume of fibers constrained the spherulitic growth by an impingement mechanism, which depressed the crystallization rate and reduced the crystallinity. Thus the crystallization was still in process even after 240 min annealing at 300°C. The effect of the cooling rate on the degree of crystallinity was simulated and investigated in DSC at a heating rate of 50°C/min. The results indicated that the cooling rates ranging from 1°C/min to 100°C/min could be divided into five regions that were associated with a high volume of fiber and the crystallization regime. A Time-Temperature-Transformation diagram superposed on the Continuous-Cooling-Transformation curves allows us to predict the amount of crystallization in different regimes. The data points for the DSC method deviated from the prediction at the cooling rates above 60°C/min because of the recrystallization during DSC heating scans.     

Pore structure and properties of poly(ether ether ketone) hollow fiber membranes: influence of solvent‐induced crystallization during extraction

Poly(ether ether ketone) (PEEK) hollow fiber membranes were prepared by a thermally induced phase separation method with polyetherimide as diluent, and N‐methyl pyrrolidone (NMP), dichloromethane and a composite extractant composed of NMP, ethanolamine and water as extractant. The effects of the different solvents induced crystallization on the pore structure during extraction and the properties of the PEEK hollow fiber membranes were investigated in detail. The crystallization behaviors of the membranes were characterized by DSC and XRD. The effect of the extractants on the microscopic morphologies, pore structures, water fluxes and mechanical properties of the membranes were investigated. The results showed that the extraction ability of the composite extractant was the most significant, followed by NMP and dichloromethane. The crystallinity of the hollow fiber was 39.0% before extraction and was elevated to 39.2% after the extraction with NMP, 46.6% with dichloromethane and 46.7% with the composite extractant, which shows that dichloromethane and the composite extractant have strong ability to induce the crystallization of PEEK. The inner and outer surfaces of the membranes obtained after extraction by the composite extractant had the largest pore size and the highest surface porosity. The most probable pore diameter of the membranes obtained after extraction by NMP, dichloromethane and the composite extractant was 23.26 nm, 24.43 nm and 24.43 nm, respectively, which indicated that solvent‐induced crystallization was beneficial for the formation of larger pores. The pure water flux of the PEEK membrane prepared by the composite extractant was the largest, but the tensile strength was the lowest. © 2019 Society of Chemical Industry     

碳纤维增强聚醚醚酮的非等温结晶行为与力学性能

利用聚酰亚胺(PI)作为碳纤维(CF)界面改性剂,制备了界面改性碳纤维增强聚醚醚酮(MCF/PEEK)复合材料。采用差示扫描量热仪(DSC)讨论了CF及其界面改性对PEEK非等温结晶行为的影响机制与作用规律,并基于莫志深法研究了MCF/PEEK的非等温结晶动力学;借助DSC和小角X射线散射仪(SAXS)表征不同降温速率下PEEK基体的结晶结构,采用万能试验机评价了MCF/PEEK的力学性能。结果发现:CF对PEEK的结晶有较为明显的异相成核促进作用,经过PI界面改性之后成核作用有所下降,但结晶行为仍较纯PEEK更容易发生,整体结晶速率更快;随冷却速率的增大,基体结晶度、片晶厚度与长周期均减小,MCF/PEEK的拉伸强度与模量也显著减小,层间断裂韧性提高。     

Synthesis and properties of thio‐containing poly(ether ether ketone)s

A series of thio‐containing poly(ether ether ketone) (PEESK) polymers was synthesized by the introduction of thio groups from 4,4′ thiodiphenol (TDP) into the poly(ether ether ketone) (PEEK) structure via reaction between the phenol and aromatic fluoride groups. The effect of the thio groups on the properties of the PEESK materials was investigated. Differential scanning calorimetry (DSC) analysis and X‐ray diffraction (XRD) patterns show a depression in the crystallinity of the PEESKs with incorporation of the content of thio groups in the backbones. The crystalline structure was identified as an orthorhombic structure with lattice constants of a = 7.52 Å, b = 5.86 Å and c = 10.24 Å for all crystallizable PEESKs. The crystalline structures of the thio‐containing PEEK polymers were the same as that of the neat PEEK, which means the thio‐containing block in the whole thio‐containing PEEK molecule is almost excluded from the crystalline structure and the crystals are completely formed by ‘non‐thio’ blocks only. Due to the glass transition temperature (T_g) and melting temperature (T_m) depression with increase in the TDP content in the reaction system, the processability of the resultant thio‐containing PEEKs could be effectively improved. Copyright © 2004 Society of Chemical Industry     

Isothermal crystallization behavior of nano-alumina particles-filled poly(ether ether ketone) composites

The isothermal crystallization behavior of nano-alumina particle-filled poly(ether ether ketone) (PEEK) composites has been investigated using differential scanning calorimeter. The results show that all the neat PEEK and nano-alumina-filled PEEK composites exhibit the double-melting behavior under isothermal crystallization. The peak crystallization times (τ_p) for all the neat PEEK and PEEK/aluminum oxide (Al₂O₃) composites increase with increasing crystallization temperature. Moreover, the crystallinity of the PEEK/Al₂O₃ composite with 7.5 wt % nano-filler content reached the maximum value of 44.8% at 290°C, higher than that of the neat PEEK polymer. From the lower value in τ_p and higher value in X_c for the PEEK/Al₂O₃ composites, the inclusion of the nano-alumina into the PEEK matrix favored the occurrence of heterogeneous nucleation. The Avrami exponents n of all the neat PEEK and PEEK/Al₂O₃ composites ranged from 2 to 3, and the n values for PEEK/Al₂O₃ composites were slightly higher than that of the neat PEEK polymer, indicating that the inclusion of the nano-filler made the crystallization mechanism more complex. However, the growth rate of crystallization was lowered as the nano- filler was introduced, and the decrease in growth rate reduced the grain size of the PEEK spherulites because of the lowering of molecule mobility during isothermal crystallization. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Functionalized poly(ether ether ketone): Improved mechanical property and acellular bioactivity

Poly(ether ether ketone), PEEK, was functionalized by addition of pendant functional groups, that is, acetyl, carboxylic, acyl chloride, amide, and amine groups in the benzene ring of polymer backbone without substituting the parent (ether or ketonic) functional groups of polymer to improve the mechanical and surface adhesivity with acellular inorganic biomaterials. The functional groups of virgin PEEK and functionalized PEEK were identified by Fourier transform infrared spectroscopy and ¹³C nuclear magnetic resonance. The crystallinity was studied by X‐ray diffraction and further supported by differential scanning calorimetry (DSC) analysis. Similarly, the change in glass transition temperature was confirmed by the DSC and dynamic mechanical analysis (DMA). The improved mechanical property was also evaluated by DMA. The excellent surface adhesivity and bioactivity were revealed by acellular in vitro test using simulated body fluid. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Structure,crystallization, and properties of poly(aryl ether ether ketone ketone)s containing meta-phenyl links and their copolymers

Poly(aryl ether ether ketone ketone)s (PEEKK) containing meta-phenyl links and their series of copolymers were synthesized and investigated by both X-ray and differential scanning calorimetry (DSC) methods. Results showed that the heat properties of this kind of copolymer depended greatly on the content of meta-phenyl links in the copolymer system, in which occurred the lowest melting point. Results from X-rays showed that PEEKK containing meta-phenyl links had no (111) crystal face diffraction. These proved that meta-phenyl links had introduced asymmetrical factors, which had produced poor crystal structure and difficulty in crystallization. Even so, the modification of PEEKK by introducing the meta-phenyl links improved the polymer composite performances, e.g., the copolymer M₂, which kept performances close to PEEKK but better than PEEK. DSC results of M₂ showed that its Avrami number (n) was 1.5 and its crystal grew fibrously from isothermal crystallization of the melting state, while for the nonisothermal crystallization from the melting state, n was 4.4 to the spherical crystal growth, and the activation energy (ΔE) of crystallization was 184 kJ/mol, which was less than the ΔE of 296 kJ/mol for PEEKK crystallized from the nonisothermal melting state. When M₂ was isothermally crystallized from the rubber state, its n was 2 to the disklike crystal growth, while its n was 4.6 to the spherulitic crystal growth for the nonisothermal crystallization state of melting. The isothermal crystallization process was different from the nonisothermal process in the crystal nucleation and growth for M₂. © 1996 John Wiley & Sons, Inc.     

PPS／PEEK熔融共混物DSC多次扫描研究

借助ＤＳＣ研究ＰＰＳ／ＰＥＥＫ共混物熔融时间，ＰＥＥＫ粒径及ＰＰＳ组分对共混物中ＰＥＥＫ结晶熔融行为的影响，结果表明，ＰＥＥＫ粒径由５００～１０００μｍ减小至２００～５００μｍ时，ＰＥＥＫ与ＰＰＳ相互作用增大，ＰＥＥＫ的结晶峰由单峰分裂为双峰，其高温结晶峰向高温移动，峰强随熔融时间延长而减弱，低温结晶峰向低温移动，峰强随熔融时间延长而增大，熔融时间延长时，退火后ＰＥＥＫ的低温熔融峰强增大，而高温熔     

Isothermal crystallization kinetics of PEEK/Vectra® blends by DSC and time‐resolved synchrotron X‐ray diffraction

Thermal properties of blends of poly(aryl ether ether ketone), PEEK, with a thermotropic liquid crystalline polymer, Vectra®, were investigated by differential scanning calorimetry and X‐ray diffraction techniques. Isothermal crystallization experiments were performed over a wide range of crystallization temperatures and compositions to follow the effect of Vectra® content on the crystallization kinetics of PEEK. A reduction in the crystallization rate of PEEK was related to a change in the mechanism of crystallization of PEEK, controlled in turn by the concentration of Vectra® in the blend. The addition of Vectra® resulted in a significant enhancement in the crystallization rate of PEEK. In addition, a reduction in this parameter is shown at a blend of 30% of Vectra®. Differences in the crystallization behavior of PEEK are related to structural properties of these systems measured by simultaneous real time WAXS and SAXS experiments using synchrotron radiation. Results of melting behavior of PEEK, subsequent to isothermal crystallization, were interpreted based on the effects of Vectra® on the formation of two crystal families of PEEK. Melting temperatures of PEEK and crystallinity calculated from double endotherm are influenced by blending. POLYM. ENG. SCI., 46:1411–1418, 2006. © 2006 Society of Plastics Engineers     

Strain-induced crystallization behavior of poly(ether ether ketone) (PEEK)

Strain-induced crystallization of poly(ether ether ketone) (PEEK) was studied by the use of a parallel plate rheometer. The experimental variables included preheating time, crystallization temperature, and shear rate. The crystallization kinetics were characterized by means of an induction time defined as the time elapsed from the start of shearing to the onset of crystallization. The experimental results showed that the induction time for strain-induced crystallization of PEEK was significantly shorter than that for crystallization under quiescent condition, and that strain-induced crystallization was much less temperature dependent than quiescent crystallization. The activation energy for strain-induced crystallization was found to be 0.035kcal/mole, which was considerably smaller than the reported activation energy for quiescent crystallization. Photomicrographs of the sheared specimens indicated that PEEK crystallites orient along the flow direction.     

Phase behavior,crystallization, and morphology of poly(ether ether ketone)/polyarylate blends

The phase behavior, crystallization, and morphology of blends based on poly (ether ether ketone) [PEEK] and bisphenol-A polyarylate [PAr] are described. This system is partially miscible in the melt. Upon quenching to an amorphous glass the system displays two glass transitions corresponding to a nearly pure PEEK phase (T_g1) and a PAr-rich mixed phase (T_g2). The presence of the PAr has a strong retarding influence on the rate of crystallization of PEEK in the blends. Cold crystallization from the amorphous glass occurs in two stages with increasing temperature, corresponding to the mobilization of the PEEK-rich and PAr-rich phases, respectively. At lower cold-crystallization temperatures (below T_g2), the immobile PAr-rich phase constrains crystallization of the PEEK-rich phase, as manifested in both a decreased rate of crystallization and decreased bulk crystallinity. Dynamic relaxation studies of the crystallized blends reveal two glass-rubber relaxations originating from interlamellar amorphous populations in the PEEK-rich and PAr-rich phases. In the PAr-rich phase, there is no evidence of large-scale PAr exclusion to interfibrillar or interspherulitic regions.