Fractionated Crystallization Behavior Research Articles

A method for studying nucleating additives in high-density polyethylene via crystallization of micro-droplets in immiscible blends

Typically, the study of additives with nucleating ability towards high-density polyethylene (HDPE) is challenging, because of the exceedingly high intrinsic nucleation density of this polymer, which prevents the detection of mild nucleation effects with standard calorimetric methods. Here we propose a novel method to tackle this issue by making use of the fractionated crystallization, observed when blending HDPE with polystyrene (PS). In this system, a small amount of HDPE is dispersed into droplets of around 1 μm size in the amorphous matrix and, due to the presence of droplets ensembles free of nucleating heterogeneity, the achievable undercooling is greatly enlarged with respect to bulk HDPE. As such, it is found that various potentially nucleating additives affect the fractionated crystallization behavior of the blend, forming populations of droplets which crystallize at distinctly higher temperatures with respect to that of neat HDPE/PS. On the contrary, bulk additivated HDPEs do not show meaningful differences in their peak crystallization temperatures. The method was applied to the technological problem of shrinkage and warpage in injection moulded coloured HDPEs, revealing that the critical behavior of a particular coloured masterbatch could be clearly associated with its higher nucleating efficiency with respect to a “non-critical” masterbatch. Moreover, the calculation of the fraction of crystallization enthalpy in selected temperature ranges allowed to determine in a semi-quantitative way the nucleation efficiency of several additives. Thus, the proposed fractionated crystallization approach proved to be successful in the notoriously difficult task of assessing different HDPE nucleating additives.

Selective localization of nanohydroxyapatite in poly(3-hydroxybutyrate)/polycaprolactone blends composites and its effects on crystallization and molecular dynamics

This work deals with the thermodynamic selective localization of hydroxyapatite nanoparticles (Hap) and its effects on crystallization and molecular dynamics in immiscible polyester blend films based on poly(3-hydroxybutyrate) (PHB, 90 wt%) and polycaprolactone (PCL, 10 wt%). Polymer blend composite films were obtained through solution casting method and characterized by contact angle (surface energy measurements), ultraviolet–visible spectroscopy (UV–Vis), elemental mapping, X-ray diffraction (WAXD), differential scanning calorimetry (DSC), polarized optical microscopy (POM) and time domain nuclear magnetic resonance (TD-NMR) techniques. It was found that hydroxyapatite (Hap) is selectively localized in the PHB phase and consequently, nanoparticles strongly influenced the PHB crystallization behavior. DSC and POM results indicated that hydroxyapatite nanoparticles acted as a nucleating agent. However, no significant changes in crystallinity degree were observed by WAXD. Fractionated crystallization behavior was observed for PCL droplets and the increase in the Hap concentration promoted heterogeneous nucleation on the droplets surface due to the nanoparticles close to the interface. Molecular dynamics studies by TD-NMR suggested a disordered Hap nanoparticles distribution inside the polymer matrix, leading to slower dynamics in the semirigid fraction of the sample´s magnetization, typically attributed to restricted polymeric chains close to the particle’s surface.

Interrogation of fractional crystallization behavior of a newly exploited chiral resolution method for racemic 1-(pyridin-2-yl)ethylamine via DFT-D3 calculations of cohesive energy

A novel chiral separation method for 1-(pyridin-2-yl)ethylamine is developed and the underlying energetics is investigated by DFT-D3.

Novel Compatibilized Nylon-Based Ternary Blends with Polypropylene and Poly(lactic acid): Fractionated Crystallization Phenomena and Mechanical Performance.

This paper presents an investigation into the behavior and performance of blends of Nylon 6 (PA6), polypropylene (PP), and poly(lactic acid) (PLA), compatibilized with maleic anhydride-grafted PP (PP-g-MA). The mechanical performance of ternary PA6/PP/PLA blends was superior to that of binary PA6/PP blends because of the addition of PLA. Through blending with PLA, the tensile and flexural strength and modulus were enhanced, maintaining performance similar to that of neat PA6. Tensile performance was further enhanced through reactive compatibilization of the blends with PP-g-MA due to the improved homogeneity of the materials. Impact behavior of the blends was found to be highly dependent on morphology, and the toughening behavior was observed at certain blending ratios. In PA6/PP blends, fractionated crystallization behavior was investigated through differential scanning calorimetry, in which both PA6 and PP droplets were crystallized at supercooled states. This effect was highly influenced by the presence of the compatibilizing agent and its effect on the morphology of the dispersed phase. As the droplet size of the dispersed phase was decreased to submicron levels, the efficiency of heterogeneous nucleation was limited. Crystallization of PLA in the blend was poor, but PP-g-MA was found to have an impact on its rate of crystallization.

Interfacial nucleation in iPP/PB-1 blends promotes the formation of polybutene-1 trigonal crystals

The formation of trigonal Form I′ crystals of polybutene-1 (PB-1) directly from melt has drawn much attention in past decades. In this study, we investigate the fractionated crystallization behavior of PB-1 within droplets formed by blending PB-1 with an excess of isotactic polypropylene (iPP) employing DSC, SEM, in situ synchrotron WAXD and FT-IR. When PB-1 is dispersed into a large number of small size droplets, the heterogeneous nucleation of Form II crystals can be inhibited because the number of droplets is larger than that of active nucleation sites for Form II (i.e., active heterogeneities originally present in bulk PB-1). The nucleation of the finely dispersed PB-1 droplets does not occur homogenously, but at the interface with the iPP matrix, which induces the crystallization of the droplets into Form I′. The crystallization rate of Form I′ at different temperatures was determined by Fourier transform infrared spectroscopy. It was found that trigonal Form I′ crystallizes faster when the content of PB-1 in the blend is lower, and the specific interfacial surface area is larger. The opposite effect has been observed for the kinetics of the metastable Form II formation. It is therefore suggested that Form I′ crystallization is driven by the nucleation of PB-1 at the crystalline iPP surface, which competes with the crystallization of Form II induced by nucleating heterogeneities present in PB-1 droplets.

Assessment of compatibilization efficiency of SEBS in the PP/PS blend

ABSTRACTThe compatibilization efficiency of styrene–ethylene/butylene–styrene (SEBS) triblock copolymer in immiscible polypropylene (PP)/polystyrene (PS) 20/80 blends was evaluated in terms of not only morphology, but also rheology and fractionated crystallization behavior. Besides varying SEBS loading, four different mixing protocols were used to vary SEBS dispersion state. PP2/PS/SEBS blend, prepared by two‐step method mixing PS and SEBS primarily, presents the largest droplet size (1.278 μm) at the critical compatibilizer concentration (CCC = 1 wt %). However, the CCC of blends prepared by the other protocols is 2 wt %. And at the CCC, PP/PS2/SEBS (two step method mixing PP and SEBS primarily) shows the smallest droplet size (0.908 μm), followed by PP/PS/SEBS (one step method). The rheology and crystallization behavior of PP/PS blends could also be utilized to assess the compatibilization efficiency of SEBS, but only in the case of mixing under the same protocol and the content of SEBS below a CCC. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46244.

Fractional crystallization behavior of PCL and PEG in blends

The crystallization behavior of poly(e-caprolactone)/poly(ethylene glycol) (PCL/PEG) blend was investigated by differential scanning calorimetry (DSC) and polarized microscopy (POM). Individual phase transition peaks in the DSC curves for both PEG and PCL in all the polymer blends with different PCL contents were observed. The crystallization and melting peak temperatures of PEG were at 41 and 65°C, respectively; while the crystallization and melting temperatures of PCL located at 28 and 56°C, respectively. In-situ POM results demonstrated that spherulites crystalline morphology was formed for both PCL and PEG homopolymers. In PEG/PCL blend, however, both the phase separation morphology and spherulitic morphology can be observed. In blends with 30 or 50 wt % PCL, the PCL component formed dispersed phase and crystallized at lower temperature. However, in blends with 70% PCL, the phase inversion behavior occurred. The continuous PCL phase crystallized at 35°C, while the PEG dispersed phase crystallized at a lower temperature. Fractional crystallization behavior of PEG and PCL was controlled by temperature. The spherulites growth rate of PEG was greatly influenced by temperature, instead of the content of PCL component in the PCL/PEG blends.

Unusual Fractional Crystallization Behavior of Novel Crystalline/Crystalline Polymer Blends of Poly(ethylene suberate) and Poly(ethylene oxide) with Similar Melting Points

Novel crystalline/crystalline polymer blends of biodegradable poly(ethylene suberate) (PESub) and biocompatible poly(ethylene oxide) (PEO) were prepared through a solution and casting method. The basic thermal properties, including both glass transition temperature and melting point, of both of the components are very close to each other. The two components are miscible as no obvious phase separation can be detected, forming novel miscible polymer blends of two crystalline polymers. PESub/PEO blends show two or three crystallization exotherms at different supercoolings. The complex crystallization behaviors are attributed to the occurrence of the fractional crystallization of the minor component of the blends. Depending on the blend composition, the major component of the blend crystallizes first and the minor component crystallizes later. During the crystallization of the major component, the amorphous minor component is completely included the interlamellar region of the major component or most of the amorphous minor component is expelled out of the interlamellar region while only a few is incorporated between the lamellae of the major component. In both cases, the fractional crystallization of the minor component occurs at large supercooling because of the confinement effect of the lamellae of the major component. In the present work, the fractional crystallization of PESub or PEO may occur at large supercooling when its content is low. PESub/PEO blends may be the first model that the fractional crystallization of each component occurs at large supercooling when its content is low; thus, they provide a rare system to study the unique crystalline morphology and crystallization behavior of miscible crystalline/crystalline polymer blends. Such research is very interesting and challenging for a better understanding of the crystalline morphology and crystallization behavior of crystalline polymer blends from both academic and practical viewpoints.

Confined Nucleation and Growth of Poly(ethylene oxide) on the Different Crystalline Morphology of Poly(butylene succinate) From a Miscible Blend

The confined and fractional crystallization behavior of poly(ethylene oxide)(PEO) in miscible poly(butylene succinate)(PBS)/PEO blends has been investigated. Both nucleation and growth of PEO cryst...

Fractionated crystallization and morphology of PP/PS blends in the presence of silica nanoparticles with different surface chemistries

The fractionated crystallization behavior of polypropylene (PP) droplets in its 20/80 blends with polystyrene (PS) in the presence of hydrophilic or hydrophobic fumed silica nanoparticles was studied by using differential scanning calorimetry, scanning electron microscopy, and transmission electron microscopy. It was found that the fractionated crystallization of PP droplets in the PS matrix was promoted by adding a low content of hydrophobic or hydrophilic nanoparticles due to their morphological refinement effect. However, discrepancies in the fractionated crystallization behavior of PP droplets occurred as the nanoparticle content increased. The crystallization became dominated by the heterogeneous nucleation effect of high content of hydrophilic nanoparticles, which possibly migrated into PP droplets during mixing and significantly suppressed their fractionated crystallization. In contrast, the morphological refinement effect still played a dominated role in promoting the fractionated crystallization of PP droplets in PP/PS blends filled with higher content hydrophobic nanoparticles as a result of the efficiently morphological refinement effect.

Microphase separation induced by competitive hydrogen bonding interactions in semicrystalline triblock copolymer/homopolymer complexes

Microphase separation through competitive hydrogen bonding interactions in ABC/D triblock copolymer/homopolymer complexes is studied for the first time. This study investigated self-assembled nanostructures that are obtained in the bulk, by the complexation of a semicrystalline polystyrene-block-poly(4-vinylpyridine)-block-poly(ethylene oxide) (SVPEO) triblock copolymer with a poly(4-vinyl phenol) (PVPh) homopolymer in tetrahydrofuran (THF). In these complexes, microphase separation takes place due to the disparity in intermolecular interactions among PVPh/P4VP and PVPh/PEO pairs. At low PVPh concentrations, PEO interacts relatively weakly with PVPh, whereas in the complexes containing more than 30 wt% PVPh, the PEO block interacts considerably with PVPh, leading to the formation of composition-dependent nanostructures. SAXS and TEM results indicate that the cylindrical morphology of a neat SVPEO triblock copolymer changes into lamellae structures at 20 wt% of PVPh then to disordered lamellae with 40 wt% PVPh. Wormlike structures are obtained in the complex with 50 wt% PVPh, followed by disordered spherical microdomains with size in the order of 40–50 nm in the complexes with 60–80 wt% PVPh. Moreover, when the content of PVPh increases to 80 wt%, the complexes show a completely homogenous phase of PVPh/P4VP and PVPh/PEO with phase separated spherical PS domains. The fractional crystallization behavior in SVPEO and complexes at lower PVPh content was also examined. A structural model was proposed to explain the microphase separation and self-assembled morphologies of these complexes based on the experimental results obtained. The formation of nanostructures and changes in morphologies depend on the relative strength of hydrogen bonding interactions between each component block of the copolymer and the homopolymer.

Effects of crystallization condition of poly(ethylene succinate) on the crystallization of poly(ethylene oxide) in their blends

The effects of the crystallization temperatures of poly(ethylene succinate) (PES) on the crystallization behavior of poly(ethylene oxide) (PEO) in their blends were investigated by means of differential scanning calorimetry, atomic force microscopy, and laser confocal fluorescent microscopy. It was found that confined and fractional crystallization of PEO takes place in the PES/PEO blends at all blend ratios if PES is crystallized at higher crystallization temperatures. And morphological observation gives a direct evidence of the different location distribution of PEO, resulting in the confined and fractional crystallization behavior.

Effect of Moringa Oleifera Oil Blending on Fractional Crystallization Behavior of Palm Oil

The objective of this study was to see the effect of Moringa oleifera oil blending on the fractional crystallization behavior of palm oil. Palm oil blended with Moringa oleifera oil at 20% (w/w) was subjected to crystallization using a dry process at 21 and 18°C and a solvent process at 15 and 10°C. After recording the quantitative recoveries of the liquid and solid fractions, their fatty acid and triacylglycerol compositions, and the thermal profiles were determined by using gas liquid chromatography, high performance liquid chromatography, and differential scanning calorimetry, respectively. Results showed that the yield recoveries of liquid fractions under solvent-assisted crystallization were higher than those obtained by dry-crystallization conditions. Almost all of the liquid fractions isolated had experienced a significant (p < 0.05) increase in oleic acid as well as triolein contents. Among the solid fractions, those isolated by dry-crystallization were found to be higher (p < 0.05) in oleic acid and triolein contents than the reference stearin sample. Although the thermal profiles of the solid and liquid fractions derived by different methods looked similar to those of the two reference samples, remarkable differences were noticed with regard to the onset of crystallization and the position of the thermal transitions.

Mechanisms of nucleation and crystal growth in a nascent isotactic polypropylene/poly (ethylene-co-octene) in-reactor alloy investigated by temperature-resolved synchrotron SAXS and DSC methods

The nucleation and lamellar growth mechanisms of nascent isotactic polypropylene/poly(ethylene-co-octene) (N-iPP/PEOc) in-reactor alloy were investigated with temperature-resolved synchrotron small angle X-ray scattering (SAXS), differential scanning calorimeter (DSC) and polarized optical microscopy (POM) methods. We have observed two crystallization peaks (fractionated crystallization behavior) during cooling process in N-iPP/PEOc in-reactor alloy. We also determined that the crystallinities from that two crystallization peaks were dependent on liquid–liquid phase separation (LLPS) time with t0.10 and t−0.28, respectively. It was explained that the fractionated crystallization behavior in the N-iPP/PEOc in-reactor alloy system was caused by crystal nucleation occurring in the iPP rich domain by heterogeneous nucleation and at interface of iPP and PEOc rich domains by the fluctuation assisted nucleation. The fluctuation assisted nucleation only occurred at interface of iPP and PEOc domains by concentration fluctuation through the coupling of liquid–liquid spinodal decomposition and the cross-over to crystal nucleation process. Both lamellar crystals formations from heterogeneous and fluctuation assisted nucleation in N-iPP/PEOc were probed by temperature-resolved SAXS during cooling process. Our results provide the physical model for the multiple nucleation and crystal growth mechanisms in the multi-component, multi-phase polymer systems such as in-reactor alloy or blend.

Fractionated crystallization and self‐nucleation behavior of poly(ethylene oxide) in its miscible blends with poly(3‐hydroxybutyrate)

AbstractThe fractionated crystallization and self‐nucleation behavior of poly(ethylene oxide) (PEO) component in the miscible PEO/poly(3‐hydroxybutyrate) (PHB) binary blends were investigated using differential scanning calorimetry (DSC) and small‐angle X‐ray diffraction (SAXS) under different crystallization conditions. The distribution of PEO component in the PEO/PHB blend greatly influences its fractionated crystallization behavior. The active heterogeneities, on which the semicrystalline components in the molten state can nucleate at a small supercooling, are favored to locate out of the interlamellar regions of PHB crystals during the crystallization of PHB component. The PEO component confined in the interlamellar regions of PHB crystals crystallizes at an extremely large supercooling, which is induced by the homogeneous nucleation or less active heterogeneities, while the PEO component expelled out of the interlamellar regions of PHB crystals can crystallize at a small supercooling due to the nucleation induced by active heterogeneities. In addition, the self‐nucleation behavior of PEO component in the PEO/PHB blend is also affected by the active heterogeneities and the distribution of PEO phase in the blend. Different from the block copolymer systems, the PEO component confined into the interlamellar regions of PHB crystals can not be self‐nucleated in the PEO/PHB blend without a nucleating agent (NA). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

FRACTIONATED CRYSTALLIZATION OF HDPE IN PS/POE/HDPE/SBS BLENDS

The fractionated crystallization behavior of the minor dispersed HDPE phase in PS/POE/HDPE/SBS quaternary blends was investigated by differential scanning calorimetry (DSC). Interestingly, we found that the fractionated crystallization behavior of HDPE was molecular weight dependent. At a fixed composition, HDPE with lower molecular weight showed more obvious fractionated crystallization behavior than HDPE with higher molecular weight. This was ascribed to a finer dispersion of HDPE with lower molecular weight, as evidenced by SEM observations. The fractionated crystallization behavior of HDPE in the blends became less obvious with increasing of its content, due to a change of phase morphology from droplet to co-continuous structure. Correspondingly, a change of tensile toughness of the blends from brittle to ductile mode was observed.

Crystallization and melting behaviors of polystyrene- b-poly(ethylene- co-butene) block copolymers

Non-isothermal and isothermal crystallization behaviors of polystyrene- b-poly(ethylene- co-butene) (PSt- b-PEB) block copolymers with different compositions and chain lengths were investigated by differential scanning calorimetry (DSC). The results show that crystallization of PEB block is strongly dependent on the composition. Crystallization temperature ( T c), melting temperature ( T m) and fusion enthalpy (Δ H f) increase rapidly with PEB volume fraction ( V E) for block copolymers with V E below 50%, but there is little change when PEB block becomes the major component. Glass transition temperature ( T g) of the PSt block and order–disorder transition temperature ( T ODT) of block copolymers also have a weak effect. The isothermal crystallization kinetics results show that Avrami exponent ( n) was strongly dependent on the composition and crystallization temperature. For the block copolymers with V E below 38.7 vol%, the values of n vary between 0.9 and 1.3, indicating that crystallization is confined. For the PSt- b-PEB block copolymers with V E higher than 50%, fractionated crystallization behavior is usually observed. A two-step isothermal crystallization procedure is applied to these block copolymers. It is found that breakout crystallization occurs at higher T c, but confined at lower T c. Two overlapped melting peaks are observed for the block copolymers with fractionated crystallization behavior after two-step crystallization, and only the higher melting peak corresponding to breakout crystallization can be used to derive equilibrium melting temperature.

Biodegradable poly(L‐lactic acid)/poly(butylene succinate‐co‐adipate) blends: Miscibility, morphology, and thermal behavior

AbstractBlends of two biodegradable and semicrystalline polymers, poly(L‐lactic acid) (PLLA) and poly(butylene succinate‐co‐adipate) (PBSA), were prepared by solvent casting in different compositions. The miscibility, morphology, and thermal behavior of the blends were investigated using differential scanning calorimetry and optical microscopy. PLLA was found to be immiscible with PBSA as evidenced by two independent glass transitions and biphasic melt. Nonisothermal crystallization measurements showed that fractionated crystallization behavior occurred when PBSA was dispersed as droplets, evidenced by multiple crystallization peaks at different supercooling levels. Crystallization and morphology of the blends were also investigated through two‐step isothermal crystallization. For blends where PLLA was the major component, different content of PBSA did not make a significant difference in the crystallization mechanism and rate of PLLA. For blends where PBSA was the major component, the crystallization rate of PBSA decreased with increasing PLLA content, while the crystallization mechanism did not change. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Phase behavior and crystallization in blends of a low molecular weight polyethylene- block-poly(ethylene oxide) diblock copolymer and poly(hydroxyether of bisphenol A)

The phase behavior, morphology and crystallization in blends of a low-molecular-weight ( M n = 1400) double-crystalline polyethylene- block-poly(ethylene oxide) (PE-PEO) diblock copolymer with poly(hydroxyether of bisphenol A) (PH) were investigated by differential scanning calorimetry, transmission electron microscopy and small-angle X-ray scattering. The symmetric PE-PEO diblock copolymer consists of a PH-miscible PEO block and a PH-immiscible PE block. However, PH only exhibits partial miscibility with the PEO block of the copolymer in the PH/PE-PEO blends; both macrophase and microphase separations took place. There existed two macrophases in the PH/PE-PEO blends, i.e., a PH-rich phase and a PE-PEO copolymer-rich phase. The PE block of the copolymer in the blends exhibited fractionated crystallization behavior by homogeneous nucleation. There appeared three crystallization exotherms related to the crystallization of the PE block within three different microenvironments in the PH/PE-PEO blends.

Self‐Nucleation Behavior of the Polyethylene Block as Function of the Confinement Degree in Polyethylene‐Block‐Polystyrene Diblock Copolymers

AbstractA series of well defined polyethylene‐b‐polystyrene diblock copolymers (ExSyz, where x and y represent the composition in weight % and z the molecular weight in Kg/mol) has been synthesized in a wide composition range by sequential anionic polymerization. The molecular weight of the PE block was kept constant. A fractionated crystallization behavior was observed for the PE block within E26S74105 (PE cylinders) and E11S89244 (PE spheres). When the PE blocks form a continuous or percolated phase (PE, E79S2141 and E53S4751), a “classic” self‐nucleation behavior (where the usual three self‐nucleation domains are obtained) was observed. When the PE block is located within isolated microphases (having dimensions on the nanometer scale) and a fractionated crystallization was detected (E26S74105 and E11S89244), the fraction of crystals formed at higher temperatures exhibits a “classic” self‐nucleation behavior, while those crystals that crystallized at the largest supercooling (lower exotherms) can only be self‐nucleated at lower temperatures where annealing of unmolten material has already started. An unusual fractionated crystallization behavior for isolated, spherical PE microphases (E11S89244) is reported.