Isothermal Crystallization Behavior Research Articles

Isothermal Crystallization Behavior of PP and PP-g-GMA Copolymer at High Undercooling

Isothermal Crystallization Behavior of PP and PP-<i>g</i>-GMA Copolymer at High Undercooling

Compatibility and physical properties of poly(lactic acid)/poly(ethylene terephthalate glycol) blends

Blends of poly(lactic acid) (PLA) and poly(ethylene terephthalate glycol) (PETG) of various compositions were prepared by melt compounding and their compatibilities, physical properties, and isothermal crystallization behaviors were investigated. The calculated solubility parameters of PETG are similar to those of PLA. The interaction parameter between PLA and PETG was derived from the Flory-Huggins theory and predicted that PLA and PETG are miscible when PETG contents are below 22 wt%. In accordance with this result, the tan δ peak and glass transition temperatures of blends determined from dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) showed a single peak at PETG contents lower than 22 wt%. Tensile test results showed that the elongation at the break of blends increased with an increase in PETG content. DSC and isothermal crystallization results showed that PETG accelerates the crystallization rate of PLA at PETG contents lower than 22 wt%, indicating that PETG acts as a nucleation agent in the crystallization of PLA. Wide angle X-ray diffraction results (WAXD) showed that the crystalline structure of PLA is not affected by the incorporation of PETG. Open image in new window

Isothermal Crystallization Behavior of Poly (L-lactic Acid)/ Surface-Grafted Silica Nanocomposites

The Poly(L-lactic acid)(PLLA)/surface-grafting silica(g-SiO2) nanocomposites were prepared by melt blending. The isothermal crystallization behavior of PLLA/g-SiO2 nanocomposites with different content of g-SiO2 was investigated by optical depolarizer. In isothermal crystallization from melt, the induction periods and half times for overall PLLA crystallization (95°C Tc 120°C) were affected by the crystallization temperature and the content of g-SiO2 in nanocomposites. The results showed that g-SiO2 as a kind of heterogeneous nucleating agent can reduce induction periods and half times for overall PLLA crystallization. The thermal properties of PLLA/g-SiO2 samples were also investigated by differential scanning calorimetry (DSC), The results showed that the crystalline degree of PLLA was improved as the presence of g-SiO2.

Isothermal and Nonisothermal Cold Crystallization Behaviors of Asymmetric Poly(l-lactide)/Poly(d-lactide) Blends

Isothermal and nonisothermal cold crystallization behaviors of asymmetric poly(l-lactide) (PLLA)/poly(d-lactide) (PDLA) blends at PDLA loadings of 0–20 wt % were investigated in this work. Formation of the stereocomplex in the blends was confirmed by differential scanning calorimetry and wide-angle X-ray diffraction. For both neat PLLA and its blends, the overall isothermal cold crystallization rates increase with increasing crystallization temperature; moreover, the overall isothermal cold crystallization rates of PLLA are faster in the blends than in neat PLLA, indicative of the nucleating agent effect of the stereocomplex formed in the blends. Crystallization mechanism and crystal structure of PLLA remain unchanged despite the PDLA loading. For the nonisothermal cold crystallization, the crystallization process of PLLA is accelerated by increasing both heating rate and the PDLA loading up to 10 wt %. The Ozawa equation failed to fit the crystallization process, while the Tobin equation could describe it well in the relative degree of crystallization range of 0–75%.

Isothermal crystallization of poly(β-propiolactone) blocks starting from lamellar microdomain structures of double crystalline poly(β-propiolactone)-block-polyethylene copolymers

The isothermal crystallization behavior of poly(β-propiolactone) (PPL) blocks starting from lamellar microdomain structures (LMS) formed in molten PPL-block-polyethylene (PPL-b-PE) copolymers has been examined using time-resolved synchrotron small-angle X-ray scattering and Fourier transform infrared spectroscopy as a function of the crystallinity of PE blocks χPE. For getting PPL-b-PE copolymers with varying χPE, the amount of ethyl branches in PE blocks was controlled during polymerization. The crystallizable temperature of PE blocks was slightly higher than that of PPL blocks and the crystallization rate of PE blocks was extremely fast, so the crystallization of PE blocks occurred first on quenching to form the crystallized LMS, in which the PPL block crystallized. The time evolution for the crystallinity of PPL blocks χPPL showed an exponential-type increase with no induction time. In contrast, LMS was replaced with the crystallized lamellar morphology and χPPL showed a sigmoidal time evolution in PPL-b-PE with a higher amount of ethyl branches, where the PE block did not crystallize (i.e., χPE = 0) prior to the crystallization of PPL blocks. It was concluded that the prompt crystallization of PE blocks just after quenching reinforced the existing LMS to make it stable against subsequent crystallization, yielding the confined crystallization of PPL blocks.

Influence of nanofiller dimensionality on the crystallization behavior of HDPE/carbon nanocomposites

AbstractThe isothermal and nonisothermal crystallization behavior of high density polyethylene (HDPE) containing various zero, one, and two dimensional (0‐D, 1‐D, and 2‐D) carbon nanofillers were investigated by means of differential scanning calorimetry. For a given temperature, the isothermal crystallization incubation time of HDPE became longer with the addition of lower dimensional carbon nanofillers, and the isothermal crystallization rate got slower. The values of Avrami and Tobin exponents indicated that the isothermal crystallization of HDPE followed two‐dimensional crystal growth in the presence of 2‐D and 1‐D carbon nanofillers, while exhibited three‐dimensional heterogeneous crystal growth in the presence of 0‐D carbon nanofillers. Contrary to the isothermal study, the nonisothermal crystallization of HDPE was accelerated in the presence of lower dimensional nanofillers. The nonisothermal crystallization data were finally analyzed using Ozawa and Mo methods. It was observed that only Mo approach could successfully describe the nonisothermal crystallization process of HDPE and HDPE/carbon nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Effect of the mesoporous structure of titanium silicate (TS-1) zeolite on the melting behavior and isothermal crystallization behavior of poly(butylene succinate)/TS-1 zeolite hybrid composites

In this study, we investigated the effects of mesoporous titanium silicate (TS-1) zeolite on the melting behavior and isothermal crystallization in poly(butylene succinate) (PBS)/TS-1 zeolite hybrid composites (PTHC). Isothermal crystallization results revealed that TS-1 zeolite acted as a nucleation agent in PTHC, thus the t 1/2 of PTHC was faster than that of homo-PBS. However, the nucleation effect of TS-1zeolite did not depend on the TS-1 zeolite content. The large surface area of the mesoporous structure readily formed molecular chains inside and outside of the pore mouths of TS-1 zeolite, covering the nucleation site, as a result of the byproduct deposition during polymerization. At isothermal crystallization, temperatures ranging from 88 to 92 °C, nucleation of TS-1 zeolite occurred because of the presence of free byproducts and the formation of a molecular chain in the pore mouths. In contrast, isothermal temperatures ranging from 80 to 84 °C resulted in ineffective nucleus activation because of the steric hindrance in the porous structure. Synchrotron small-angle X-ray scattering (SAXS) analysis revealed that TS-1 zeolite can accelerate lamellar recrystallization during heating.

Isothermal crystallization and mechanical properties of poly(butylene succinate)/layered double hydroxide nanocomposites

Biodegradable poly(butylene succinate) (PBS) and layered double hydroxide (LDH) nanocomposites were prepared via melt blending in a twin-screw extruder. Isothermal crystallization and subsequent melting behavior, thermal stability, crystal structure, spherulitic morphology and mechanical properties of PBS and its nanocomposites were studied by DSC, TGA, WAXD, POM and DMA in detail. The crystallization rate of PBS in its nanocomposites was accelerated by the addition of LDH, due to its heterogeneous nucleation effect. The Avrami equation successfully described the isothermal crystallization kinetics of the nanocomposites. The melting profile of PBS/LDH composites and pure PBS showed the very similar Tc-dependent DSC traces. The TGA analysis revealed that the catalyst effect of Mg and/or Al metals reduced the thermal decomposition temperature of PBS. The spherulite size of PBS/LDH nanocomposites decreased and the spherulite density increased remarkably with an increase of LDH, however, the crystalline structure was not influenced by the presence of LDH, as evidenced by the same diffraction peaks from WAXD patterns. The DMA results indicated that a significant enhancement of the modulus of the nanocomposites was achieved.

The impact of nanoclay on the crystal growth kinetics and morphology of biodegradable poly(ethylene succinate) composite

The impact of nanoclay on the isothermal crystal growth kinetics and morphology of biodegradable poly(ethylene succinate) (PES) is reported. A PES composite (PESNC) containing 5 wt% organically modified montmorillonite, was prepared via solvent casting method. The structural study of PESNC, using X-ray diffraction and optical microscope, showed the formation of micro-intercalated composite. The isothermal crystallization behavior of neat PES and PESNC was studied by differential scanning calorimetry, polarized optical and atomic force microscopes. Results show that the supercooling effect of neat PES reduces after composite formation. The Lauritzen–Hoffman secondary nucleation theory (the LH-model) was employed to understand the crystal growth mechanism of these systems. According to the LH-model, only one transition between regime II and regime III was found, but no transition from regime I to II was detected.

Isothermal Crystallization Kinetics of Poly(phenylene Sulfide)/ZnO Composites

Poly (phenylene sulfide) (PPS)/nano-ZnO composites were prepared by DAKA miniature blending instrument. Isothermal crystallization behavior of PPS composites at 245°C, 250°C, 255°C and 260°C were investigated by means of DSC. The crystallization time of PPS composites is shorter than which of neat PPS at the same crystallization temperature. The Avrami equation was used to analyze DSC data. Results showed that neat PPS is homogeneous nucleation at lower crystallization temperature, which is heterogeneous nucleation at higher crystallization temperature contrarily. PPS/nano-ZnO composites are heterogeneous nucleation at various crystallization temperature, nano-ZnO particles play a role of nucleating agent.

Isothermal crystallization and melting behaviors of nano TiO2 -modified polypropylene/polyamide 6 blends

Titanium dioxide (TiO2) nanoparticles were functionalized with toluene-2,4-diisocyanate and then polypropylene/polyamide 6/(PP/PA6) blends containing functionalized-TiO2 were prepared using a twin screw extruder. Isothermal crystallization and melting behavior of the as-prepared composites were investigated using differential scanning calorimetry and wide-angle X-ray diffraction. Isothermal crystallization analysis shows that the TiO2 nanoparticles have two effects on PP/PA6 blends, i.e., it can favor the improvement of crystallization ability and decrease the crystallization rate of PP/PA6 blends. The improvement of crystallization ability is superior over decreasement of crystallization rate of PA6 chains caused by TiO2, therefore PA6 in PP/PA6/TiO2 nanocomposites have higher crystallization rate than that of PA6 in pure PP/PA6 blends, which indicated TiO2 nanoparticles favored the crystallization of PA6. The TiO2 nanoparticles show no effects on the equilibrium melting temperature (T) values of PP phase but decreases the T values of PA6 phase. In addition, the TiO2 nanoparticles did not change the crystalline polymorph of PP/PA6 blends basically; however, favored the formation of β-PP. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Highly improved crystallization behavior of poly(L‐lactide) induced by a novel nucleating agent: substituted‐aryl phosphate salts

In this work, a novel nucleating agent (NA) based on substituted‐aryl phosphate salts was introduced into poly(L‐Lactide) (PLLA). The nonisothermal and isothermal crystallization behaviors of nucleated PLLA samples were investigated through differential scanning calorimetry (DSC), wide angle X‐ray diffraction, and polarized optical microscope (POM). Furthermore, the effect of annealing treatment on the cold crystallization behaviors of nucleated samples was also investigated. The results show that the crystallization of PLLA, whether for the melt crystallization (including nonisothermal and isothermal crystallization process) or for the cold crystallization (including the cold crystallization occurring during the DSC heating process and during the annealing process), is greatly dependent upon the content of NA. At relatively lower NA content (≤0.1 wt%), the nucleation effect of NA is inconspicuous, however, at higher NA content (≥0.2 wt%), it exhibits great nucleation effect for the crystallization of PLLA. Further results show that the double endothermic peak of PLLA depends on the temperature applied for the crystallization. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Suppressing of γ-Crystal Formation in Metallocene-Based Isotactic Polypropylene during Isothermal Crystallization under Shear Flow

The effect of shear flow on isothermal crystallization behavior of γ-crystals in metallocene-based isotactic polypropylene melt was investigated by in situ synchrotron wide-angle X-ray diffraction (WAXD). In the sample under weak shear (at strain of 300% for 30 s duration), simultaneous evolution of α- and γ-crystals occurred, and the final fraction of γ-crystals (fγ) was 0.66, which was identical to the undeformed sample (PP-Static). In this scenario, α-crystals probably served as effective seeds for nucleation of γ-crystals. In the samples under strong shear (at strain of 500% for 30 s duration or long-time continuous shear at strains of 100% and 500%), the sequential emergence of α- and γ-crystals was observed. In this case, molten polymer chains were probably constrained by the surrounding crystals after intense short-time shear and/or maintained their extended chain conformation after long-time shear. These oriented chains had little chance to form the γ-crystals directly, behaving very differently from the relaxed chains. Under strong shear fields, the emergence of γ-crystals was delayed or inhibited, whereas the fγ value was also decreased rapidly. A simple model for the possible pathway of γ-crystal formation in the strong shear environment was proposed.

Study on crystallization behaviour of co-polyamide 66 containing triaryl phosphine oxide

In this paper, the isothermal crystallization and non-isothermal crystallization behaviour of flame retardant co-polyamide 66 (FR-PA66) containing triaryl phosphine oxide (TPO) were researched by employing differential scanning calorimetry (DSC), polarized optical microscopy (POM), respectively. The effects of TPO groups on nucleation mechanism, nucleation pattern and crystallization rate of FR-PA66 were discussed in detail. Experimental results show that TPO unit does not nucleate first during crystallization process of FR-PA66. The nucleation mechanism and nucleation pattern of FR-PA66 do not virtually change with incorporation of TPO groups when compared with polyamide 66 (PA66). The mainly crystallization process of FR-PA66 is still free nucleation and growing during the prime crystallization stage, and is unimensional nucleation and growing during the second crystallization stage. But at the second crystallization stage, we think there is a para-crystal forming with the main-crystal unimensional nucleation and growing. In addition, incorporation of TPO groups result in the decrement of both nucleation rate and crystallization rate of FR-PA66, and the increment of crystallization activation energy. Hence the TPO groups were unfavourable for FR-PA66 crystallization. In addition, incorporation of TPO groups also result in the decrement of crystallization region of FR-PA66, and increment of spherulite defect.

Isothermal Crystallization Kinetics of Fiber/Polylactic Acid Composites and Morphology

The isothermal crystallization behavior of fiber including glass fiber, carbon fiber and basalt fiber reinforced PLA composites was investigated by differential scanning calorimetry (DSC).The morphology of isothermally crystallized fiber/PLA composites was observed by polarized optical microscope (POM) equipped with a hot stage. The results showed that the presence of fiber greatly accelerated the bulk crystallization rate of PLA and changed the crystalline morphology of PLA from the spherulites to transcrystallization. And the reason for the development of transcrystallization was considered to be relevant to the compatibility of the interface between fibers and PLA.

Effect of Organoclay Platelets on Crystallization of Polytrimethylene Terephthalate/Polyethylene-octene-g-maleic Anhydride Blends: Isothermal Crystallization

The blends of poly(trimethylene terephthalate) (PTT) with maleic anhydride-grafted poly(ethylene-octene) (POE-g-MA) and organoclay (OMMT) were prepared by melt-blending. The effects of organoclay platelets on the isothermal crystallization behaviors of PTT/POE-g-MA blend were examined using differential scanning calorimetry. The crystallization kinetics of the primary stage under isothermal conditions could be described by the Avrami equation, with values of the Avrami exponent between 2.01 and 2.81 for all samples. The crystallization rate parameter, K, decreased with increase of melt-crystallization temperature for all samples. The activation energies for isothermal crystallization were determined by the Arrhenius equation.

Isothermal melt crystallization behavior of neat poly(l-lactide) (PLLA) and PLLA/organically modified layered silicate (OMLS) nanocomposite studied by two-dimensional (2D) correlation spectroscopy

Isothermal melt crystallization behavior of neat poly(l-lactide) (PLLA) and PLLA/organically modified layered silicate (OMLS) nanocomposite was studied by using time-dependent infrared (IR) spectroscopy and transmission electron microscopy (TEM). Sets of time-dependent IR spectra reflecting the crystallization from the melt of the neat PLLA and PLLA/OMLS nanocomposite were collected at 105°C. Fine details of the crystallization behaviors were analyzed by two-dimensional (2D) correlation spectroscopy, and significant differences in the crystallization behaviors depending on the presence of OMLS were revealed. Namely, it was found that the crystalline lamellae of the PLLA nanocomposite grow along the layered silicate, while the orientation of the neat PLLA resulted in more disordered orientation because of the absence of the OMLS. The result derived from the 2D correlation analysis of the time-dependent IR spectra of PLLA samples showed good agreement with corresponding TEM images.

Novel Polypropylene/Inorganic Fullerene-like WS2 Nanocomposites Containing a β-Nucleating Agent: Isothermal Crystallization and Melting Behavior

The isothermal crystallization and subsequent melting behavior of isotactic polypropylene (iPP) nucleated with different nucleating agents (NAs) are investigated. Tungsten disulfide (IF-WS(2)) and N,N'-dicyclohexyl-2,6-naphthalene (NJ) and dual-additive mixtures are introduced into an iPP matrix to generate new materials that exhibit variable α- and β-polymorphism. As shown in previous work, small amounts of IF-WS(2) or NJ have a nucleating effect during the crystallization of iPP. However, the isothermal crystallization and melting behavior of iPP nucleated by dual α(IF-WS(2))/β(NJ) additive systems are dependent on both the NA composition balance and the crystallization temperature. In particular, our results demonstrate that it is possible to obtain any α-phase to β-phase content ratio by controlling the composition of NAs under appropriate isothermal crystallization conditions. The nucleating behavior of the additives can be illustrated by competitive nucleation, and the correlation between crystallization and melting temperatures and relative α- and β-crystals content in iPP in the nanocomposites is discussed.

Correlation between Crystallization Kinetics and Electroactive Polymer Phase Nucleation in Ferrite/Poly(vinylidene fluoride) Magnetoelectric Nanocomposites

Poly(vinylidene fluoride) (PVDF) nanocomposites with different ferrite nanoparticle loadings are interesting as, depending on ferrite type and content, the electroactive β-phase of the polymer is nucleated and the magnetoelectric coupling is induced. The isothermal crystallization behavior of ferrite/PVDF nanocomposites is studied using polarized optical microscopy, and the crystallization kinetic is analyzed by the Avrami theory in order to understand the crystallization conditions leading to the nucleation of the electroactive polymer phase. It is found that the nucleation kinetics is enhanced by the presence of ferrite nanoparticles, as evidenced by the increasing number of spherulites with increasing nanoparticle content and by the variations of the Avrami exponent. The crystallization velocity is intimately related to the polymer α- or β-phase formation in the nanocomposites and follows the order NiFe(2)O(4)/PVDF > CoFe(2)O(4)/PVDF > Ni(0.5)Zn(0.5)Fe(2)O(4)/PVDF for a given temperature and nanoparticle loading, which results in larger amounts of β-phase for CoFe(2)O(4)/PVDF and Ni(0.5)Zn(0.5)Fe(2)O(4)/PVDF nanocomposites.

Isothermal Crystallization Kinetics and Melting Behavior of a Luminescent Conjugated Polymer, Poly(9,9-Dihexylfluorene-Alt-2,5-Didodecyloxybenzene)

A study of the isothermal crystallization behaviors of poly(9,9-dihexylfluorene-alt-2,5-didodecyloxybenzene) (PF6OC12) was carried out using differential scanning calorimetry (DSC). The crystallization kinetics under isothermal conditions could be described by the Avrami equation. The Avrami exponent n ranges from 3.43 to 3.71 for PF6OC12 at crystallization temperatures between 100.0°C and 90.0°C, indicating a three-dimensional spherical crystal growth with homogeneous nucleation in the primary crystallization stage for the isothermal melt crystallization process. In the DSC scan, after the isothermal crystallization, multiple melting behavior was found. The multiple endotherms could be attributed to melting of recrystallized materials produced originally during different crystallization processes. According to the Arrhenius equation, the activation energy was determined to be 211.29 kJmol−1 for the isothermal melt crystallization of PF6OC12.