The crystallization morphology evolution of polyoxymethylene/poly(ethylene oxide) blend micropart prepared under microinjection molding conditions

This article is the first study on the microinjection molding and the effects of the microprocessing parameters on the crystallization and orientation of polyoxymethylene/poly(ethylene oxide) (POM/PEO) blend, which has better toughness and self‐lubricity compared with the neat POM and therefore is a better candidate material for making microparts like microgears with higher performances. The crystalline and phase morphologies were investigated by polarized light microscope (PLM), differential scanning calorimeter (DSC) and scanning electron microscope (SEM). The crystalline orientation of the microparts was evaluated by two‐dimensional wide‐angle X‐ray diffraction (2D‐WAXD) and Herman's orientation function. The experimental results showed that both POM and POM/PEO microparts prepared by microinjection molding exhibited three distinct layers, i.e., skin layer, shear layer and core layer, while the latter had thicker shear layer but thinner skin layer and core layer. PEO was well dispersed in POM matrix. The spherulite size, the melting point as well as the crystallinity of POM in the POM/PEO blend decreased due to the interference of PEO in the crystallization of POM. A shish‐kebab structure was observed in the shear layers of the POM/PEO microparts. The effects of processing parameters on the thicknesses of different layers of the POM/PEO microparts were investigated. With increase of the injection speed or decrease of the mold temperature, the skin layer and the core layer became thicker, while the shear layer and the oriented region became thinner. However, the influence of the injection pressure was not obvious. Also, the processing parameters affected the crystalline orientation of the POM/PEO microparts. With increase of the injection speed or decrease of the mold temperature, the orientation function f decreased, indicating a lower degree of orientation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40538.     

Miscible crystalline/crystalline polymer blends of polyoxymethylene copolymer/poly(ethylene oxide) with interpenetrated spherulites and enhanced properties

Miscibility and crystallization behavior of a polymer blend consisting of two crystalline components, polyoxymethylene copolymer (Co‐POM) and poly(ethylene oxide) (PEO), have been investigated. Experimental results indicate that Co‐POM is thermodynamically miscible with PEO, as shown by the existence of single‐composition dependent glass transition temperature over the entire composition range. The crystal structures and spherulitic morphologies of (Co‐POM)/PEO blends were studied by X‐ray diffraction, differential scanning calorimetry, scanning electron microscopy, and polarizing light microscopy. It was found that the PEO spherulites crystallized within the matrix of the crystals of the pre‐existing Co‐POM phase and resulted in a high extent of interfibrillar segregation. The unique interpenetrated crystalline structure was beneficial for the sufficient contact between the two components and significantly improved both the toughing and the lubricating effect of PEO on the POM matrix. On incorporation of 30 wt% PEO, the notched impact strength of POM was enhanced from 6.7 to 10.3 MPa, by about 53.7%, while the elongation at break increased from 28.5% to 121.0%, by about 3.2 times. Furthermore, the friction coefficient drastically decreased from 0.35 to 0.17, demonstrating the enhanced tribological performance of the miscible blends. J. VINYL ADDIT. TECHNOL., 22:479–486, 2016. © 2015 Society of Plastics Engineers     

Influence of shearing on crystallization of polyoxymethylene/high density polyethylene blend

The influence of rotating shear on morphology, crystallization behavior, and crystalline structure of polyoxymethylene (POM) and high density polyethylene (HDPE) blend was investigated by polarized light microscopy (PLM) connected with a CSS450 shearing hot‐stage, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X‐ray diffraction. The experimental results showed that the crystalline and dispersion morphology of POM/HDPE (50/50) blend were strongly affected by shearing, while the crystallization temperature and rate of crystallization of POM in the sheared blend increased with no significant change in the crystalline structure of the blend. In the unsheared blend, phase separation appeared between POM and HDPE which crystallized separately and the bicontinuous phase morphology was formed. But for the sheared blend, a large number of compact and regular shish‐kebabs emerged in POM phase and the phase domains of HDPE oriented along the direction of shear flow separating from one another so that the shearing aggravated the phase separation. There is no special interaction between POM and HDPE and these two polymers crystallized individually, differing from that of POM/PEO blend. J. VINYL ADDIT. TECHNOL., 24:147–153, 2018. © 2016 Society of Plastics Engineers     

Effect of injection speed on phase morphology,crystallization behavior,and mechanical properties of polyoxymethylene/poly(ethylene oxide) crystalline/crystalline blend in injection processing

In this work, poly(ethylene oxide) (PEO) was added into polyoxymethylene (POM) as a new modifier, and the effects of the injection speed on the phase morphology, crystallization behavior, and the mechanical properties of the POM/PEO crystalline/crystalline blend were investigated. The results showed that with the increase in the injection speed, the size of PEO phase decreased, and the location of PEO changed from the amorphous region between POM spherulites to that between crystal lamella fibers or between crystal lamellas in POM, which was favorable to prevent the craze growing to the crack and effectively absorb the impact energy. As a result, the notched impact strength of the blend increased from 7.8 to 11.3 kJ/m². POLYM. ENG. SCI., 52:1938–1944, 2012. © 2012 Society of Plastics Engineers     

Casting solvent effect on crystallization behavior and morphology of poly(ethylene oxide)/poly(methyl methacrylate)

Poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) blends were prepared by casting from either chloroform or benzene solvents. After casting from solvents, all samples used in this study were preheated to 100°C and held for 10 min. Then, the solvent effect on the crystallization behavior and thermodynamic properties were studied by differential scanning calorimeter (DSC). Also, the morphology of spherulite of casting film was studied by polarized optical microscope. From the DSC and polarizing optical microscopy (POM) results, it was found that PEO/PMMA was miscible in the molten state no matter which casting solvent was used. However, the crystallization of PEO in the chloroform‐cast blend was more easily suppressed than it was in the benzene‐cast blend. Relatively, the chloroform‐cast blend showed the greater melting‐point depressing of PEO crystals. Also, the spherulite of chloroform‐cast film showed a coarser birefringence. It was supposed that the chloroform‐cast blend had more homogeneous morphology. It is fair to say that polymer blends, cast from solvent, are not necessarily in equilibrium. However, the benzene‐cast blends still were not in equilibrium even after preheating at 100°C for 10 min. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1627–1636, 2000     

Isothermal crystallization and melting behaviors of nylon 11/nylon 66 alloys by in situ polymerization

Nylon 11/nylon 66 alloys were prepared by in situ polymerization. Analysis of the isothermal crystallization behaviors of nylon 11/nylon 66 alloys was carried out using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The crystallization kinetics of the primary stage under isothermal conditions could be described by the Avrami equation. The crystal morphology observed by means of polarized optical microscope (POM). In the DSC scan after isothermal crystallization process, the multiple melting behaviors were found and each melting endotherm has a different origin. The real-time XRD measurements confirmed that no crystalline transition existed during the isothermal crystallization process. The multiple endotherms were experimentally evidenced due to melting of the recrystallizated materials or the lamellae produced under different crystallization processes. The equilibrium melting point of samples for isothermal crystallization was also evaluated.     

β成核剂含量对等规聚丙烯性能的影响

研究了一种β成核剂(CHB-5)的含量对等规聚丙烯(iPP)结晶性能和力学性能的影响。用广角X射线衍射(WAXD)研究CHB-5诱导iPP晶型的变化,用差示扫描量热法(DSC)分析CHB-5对iPP熔融行为和结晶行为的影响,用偏光显微镜(POM)观察CHB-5诱导iPP结晶形态的变化。结果表明,CHB-5的加入使iPP的成核能力增强;CHB-5可降低iPP的熔融温度,提高其结晶温度和结晶起始温度,加快结晶速率;CHB-5能降低球晶尺寸;CHB-5的加入可使iPP缺口冲击强度提高。     

Melting behaviour of poly(butylene succinate) in miscible blends with poly(ethylene oxide)

The melting behavior of poly(butylene succinate) (PBSU) in miscible blends with poly(ethylene oxide) (PEO), which is a newly found polymer blends of two crystalline polymers by our group, has been investigated by conventional differential scanning calorimetry (DSC). It was found that PBSU showed double melting behavior after isothermal crystallization from the melt under certain crystallization conditions, which was explained by the model of melting, recrystallization and remelting. The influence of the blend composition, crystallization temperature and scanning rate on the melting behavior of PBSU has been studied extensively. With increasing any of the PEO composition, crystallization temperature and scanning rate, the recrystallization of PBSU was inhibited. Furthermore, temperature modulated differential scanning calorimetry (TMDSC) was also employed in this work to investigate the melting behavior of PBSU in PBSU/PEO blends due to its advantage in the separation of exotherms (including crystallization and recrystallization) from reversible meltings (including the melting of the crystals originally existed prior to the DSC scan and the melting of the crystals formed through the recrystallization during the DSC scan). The TMDSC experiments gave a direct evidence of this melting, recrystallization and remelting model to explain the multiple melting behavior of PBSU in PBSU/PEO blends.     

Structural studies of poly(butyl acrylate) - poly(ethylene oxide) miktoarm star polymers

Structural behavior of miktoarm star polymers comprising poly(butyl acrylate) (PBA) and poly(ethylene oxide) (PEO) arms was studied by means of Differential Scanning Calorimetry (DSC), Wide Angle X-Ray Scattering (WAXS), Polarized Optical Microscopy (POM) and Fourier Transform Infrared Spectroscopy (FTIR) methods. The aim of this study was to correlate changes in the composition of the arms of the PBA/PEO miktoarm star polymers with their structures. As a consequence of increasing PBA content, the decrease in crystallinity of the studied PBA/PEO heteroarm star copolymers was observed. Regardless of the copolymer composition, fraction of oxyethylene units in the crystalline PEO phase was similar in all investigated systems. The POM images showed spherulitic morphology of the materials having low PBA content, while an increase in PBA arms fraction leads to the formation of less ordered structures. The analysis of FTIR vibrational spectrum indicates helical conformation of PEO chains in the crystalline phase. Isothermal crystallization studies carried out using the FTIR technique suggest the existence of isolated domains in the nanoscopic scale of investigated materials.     

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.     

聚丙烯/聚苯乙烯/膨润土共混体系的结晶性能和热性能研究

通过偏光显微镜(PLM)和光学解偏振仪对聚丙烯/聚苯乙烯/膨润土三元共混体系的结晶形态和等温结晶速率进行了研究。结果表明:共混体系所形成的球晶比纯聚丙烯(PP)所形成的球晶尺寸小,聚苯乙烯(PS)/膨润土(Garamite)复合粒子的加入导致PP的结晶成核和生长发生了改变,加快了PP的结晶速率。同时采用差示扫描量热仪(DSC)对该三元共混体系的热性能进行了研究,结果表明,随着膨润土含量的增加,共混体系熔融温度变高,结晶温度变高,结晶度下降。     

The effect of end groups of PEG on the crystallization behaviors of binary crystalline polymer blends PEG/PLLA

The effect of end groups (2OH, 1OH, 1CH₃ and 2CH₃) of poly(ethylene glycol) (PEG) on the miscibility and crystallization behaviors of binary crystalline blends of PEG/poly(l-lactic acid) (PLLA) were investigated by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). A single glass-transition temperature was observed in the DSC scanning trace of the blend with a weight ratio of 10/90. Besides, the equilibrium melting point of PLLA decreased with the increasing PEG. A negative Flory interaction parameter, χ₁₂, indicated that the PEG/PLLA blends were thermodynamically miscible. The spherulitic growth rate and isothermal crystallization rate of PEG or PLLA were influenced when the other component was added. This could cause by the change of glass transition temperature, T_g and equilibrium melting point, T⁰_m. The end groups of PEG influenced the miscibility and crystallization behaviors of PEG/PLLA blends. PLLA blended with PEG whose two end groups were CH₃ exhibited the greatest melting point depression, the most negative Flory interaction parameter, the least fold surface free energy, the lowest isothermal crystallization rate and spherulitic growth rate, which meant better miscibility. On the other hand, PLLA blended with PEG whose two end groups were OH exhibited the least melting point depression, the least negative Flory interaction parameter, the greatest fold surface free energy, the greatest isothermal crystallization rate and spherulitic growth rate.     

Study of the miscibility and crystallization behavior of poly(ethylene oxide)/poly(vinyl alcohol) blends

The miscibility and crystallization behavior of poly(ethylene oxide)/poly(vinyl alcohol) (PEO/PVA) blends were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and polarizing optical microscopy. Because the glass‐transition temperature of PVA was near the melting point of PEO crystalline, an uncommon DSC procedure was used to determine the glass‐transition temperature of the PVA‐rich phase. From the DSC and DMA results, two glass‐transition temperatures, which corresponded to the PEO‐rich phase and the PVA‐rich phase, were observed. It was an important criterion to indicate that a blend was immiscible. It was also found that the preparation method of samples influenced the morphology and crystallization behaviors of PEO/PVA blends. The domain size of the disperse phase (PVA‐rich) for the solution‐cast blends was much larger than that for the coprecipitated blends. The crystallinity, spherulitic morphology, and isothermal crystallization behavior of PEO in the solution‐cast blends were similar to those of the neat PEO. On the contrary, these properties in the coprecipitated blends were different from those of the neat PEO. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1562–1568, 2004     

热处理对PB-1/PP共混体系性能的影响

将等规聚丁烯-1(PB-1)与聚丙烯(PP)按80/20的配比在挤出机中熔融共混,制备PB-1/PP共混体系。用偏光显微镜、差示量热扫描仪、动态黏弹谱仪、电子拉力机等分别研究了热处理对共混体系的结晶形态、结晶性能、动态力学性能及力学性能的影响。结果表明:经过热处理后,PB-1组分晶型I的熔融温度和熔融焓略有提高,晶型II的熔融峰逐渐消失,而分散相PP的熔融温度和熔融焓基本保持不变,两相的球晶形态在宏观上没有发生明显的变化;共混合金的储能模量有较明显提高,损耗角正切值有所下降;热处理可以明显改善共混体系的力学性能。     

Thermal Properties and Crystallite Morphology of Nylon 66 Modified with a Novel Biphenyl Aromatic Liquid Crystalline Epoxy Resin

In order to improve the thermal properties of important engineering plastics, a novel kind of liquid crystalline epoxy resin (LCER), 3,3′,5,5′-Tetramethylbiphenyl-4,4′-diyl bis(4-(oxiran-2-ylmethoxy)benzoate) (M1) was introduced to blend with nylon 66 (M2) at high temperature. The effects of M1 on chemical modification and crystallite morphology of M2 were investigated by rheometry, thermo gravimetric analysis (TGA), dynamic differential scanning calorimetry (DSC) and polarized optical microscopy (POM). TGA results showed that the initial decomposition temperature of M2 increased by about 8 °C by adding 7% wt M1, indicating the improvement of thermal stability. DSC results illustrated that the melting point of composites decreased by 12 °C compared to M2 as the content of M1 increased, showing the improvement of processing property. POM measurements confirmed that dimension of nylon-66 spherulites and crystallization region decreased because of the addition of liquid crystalline epoxy M1.     

Isothermal crystallization, melting behavior and crystalline morphology of syndiotactic polystyrene blends with highly-impact polystyrene

Syndiotactic polystyrene (sPS) blends with highly-impact polystyrene (HIPS) were prepared with a twin-screw extruder. Isothermal crystallization, melting behavior and crystalline morphology of sPS in sPS/HIPS blends were investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and polarized optical microscopy (POM). Experimental results indicated that the isothermal crystallization behavior of sPS in its blends not only depended on the melting temperature and crystallization temperature, but also on the HIPS content. Addition of HIPS restricted the crystallization of sPS melted at 320 °C. For sPS melted at 280 °C, addition of low HIPS content (10 wt% and 30 wt%) facilitated the crystallization of sPS and the formation of more content of α-crystal. However, addition of high HIPS content (50 wt% and 70 wt%) restricted the crystallization of sPS and facilitated the formation of β-crystal. More content of β-crystal was formed with increase of the melting and crystallization temperature. However, α-crystal could be obtained at low crystallization temperature for the specimens melted at high temperature. Addition of high HIPS content resulted in the formation of sPS spherulites with less perfection.     

Strengthening of poly(butylene adipate-co-terephthalate) by melt blending with a liquid crystalline polymer

Poly(butylene adipate-co-terephthalate) (PBAT) is a soft biodegradable polymer with a low melting temperature. PBAT has been melt-blended with a liquid crystalline polymer (LCP) aiming at preparing a new biodegradable polymer blend with improved mechanical properties. The phase structure and crystalline morphologies of the PBAT/LCP blends were investigated using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). It was found that the LCP domains are precisely dispersed in the PBAT matrix and that these domains act as the nuclei for PBAT crystallization. The nonisothermal crystallization temperature from the melt was dramatically shifted from 50°C to about 95°C by the addition of 20% LCP. In addition, the tensile modulus of the prepared blends increases gradually with increasing LCP content, indicating the excellent strengthening effects of LCP on the PBAT matrix. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Solvent effects on phase transition behavior of canola oil sediment

Differential scanning calorimetry (DSC) was used to study the melting and crystallization behavior of waxy sediment in canola oil and in mixtures (1:1, w/w) of oil and acetone or hexane under dynamic heating/cooling regimes. In the presence of a solvent, the DSC melting peak of sediment shifted to lower temperatures, suggesting that sediment was more soluble in the solvent/oil systems than in oil alone. This effect was greater with hexane than with acetone. The influence of a solvent on crystallization was more complex. With inclusion of hexane, the crystallization temperature of sediment was always lower than that in oil. With acetone, however, the crystallization temperature of sediment was slightly lower at high sediment content, but higher at low sediment content than in oil alone. The differences in melting and crystallization behavior of sediment in canola oil and the solvent/oil systems were attributed to solubility and viscosity effects. Variation in the crystalline solid structures of sediment was not evident from the melting enthalpies associated with the phase transformation.     

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     

Crystallization behavior of PHA/PEDEA oligoester blends

The crystallization behavior of oligoester blends prepared from crystalline poly(hexanediol adipate) (PHA) and amorphous poly(ethylene diethylene glycol adipate) (PEDEA) was studied using POM, WAXD, and DSC. The crystal form of both PHA and the blends are spherulites. The crystallinity, melting enthalpies, and crystallization rate increased with increased PHA content in the blends. Two sharp diffraction peaks of each blend were detected at the same position, where, respectively, 2θ = 21.3° and 24.1°. The research on the crystallization kinetics showed that the Avrami exponent of all the oligoester blends is approximately 4. It was demonstrated that the crystallization mechanism of PHA is not disturbed by amorphous PEDEA. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1363–1368, 2002; DOI 10.1002/app.10268