Isothermal Crystallization Behavior Research Articles

Crystallization of double crystalline block copolymer/crystalline homopolymer blends: 2. crystallization behavior

We examined the isothermal crystallization behavior of poly(ɛ-caprolactone) (PCL) chains (that is, PCL blocks and PCL homopolymers) in binary blends consisting of PCL-block-polyethylene (PCL-b-PE) copolymers and PCL homopolymers using simultaneous synchrotron small-angle X-ray scattering/wide-angle X-ray diffraction (SAXS/WAXD) and independently using Fourier transform infrared spectroscopy (FTIR). Because the crystallizable temperature of PE blocks was significantly higher than that of PCL chains, the PE block crystallized first upon quenching to form a crystalline lamellar morphology (PE lamellar morphology) and subsequently the PCL chain crystallized within this morphology. We prepared two blends by considering the miscibility of PCL homopolymers in microphase-separated melts; when the PCL homopolymer was localized between PCL blocks in the lamellar microdomain (dry brush), the crystallinity of PCL chains showed a composition-dependent asymptotic increase at the late stage of crystallization, suggesting the individual crystallization of PCL homopolymers and PCL blocks to yield separate PCL lamellar crystals in the PE lamellar morphology. When the PCL homopolymer was uniformly mixed with PCL blocks (wet brush), the time evolution of crystallinity was identical to that of PCL blocks irrespective of composition, indicating that the crystallization of PCL chains was virtually controlled by that of PCL blocks to form a mixed crystal of PCL blocks and PCL homopolymers. We examined the crystallization behavior of poly(ɛ-caprolactone) (PCL) chains in binary blends of PCL-block-polyethylene copolymers and PCL homopolymers using synchrotron SAXS/WAXD. When PCL homopolymers were localized between PCL blocks in lamellar microdomains (dry brush), the crystallinity of PCL chains showed a composition-dependent increase, suggesting the formation of separate PCL lamellar crystals. When PCL homopolymers were uniformly mixed with PCL blocks (wet brush), the time evolution of crystallinity was identical to that of PCL blocks, indicating the formation of a mixed crystal of PCL blocks and PCL homopolymers.

Poly(l‐lactic acid) with the organic nucleating agent N,N,N′‐tris(1H‐benzotriazole) trimesinic acid acethydrazide: Crystallization and melting behavior

ABSTRACTN,N,N′‐Tris(1H‐benzotriazole) trimesinic acid acethydrazide (BD) was synthesized from 1H‐benzotriazole acetohydrazide and trischloride to serve as an organic nucleating agent for the crystallization of poly(l‐lactic acid) (PLLA). First, the thermogravimetric analysis of BD exhibited a high thermal decomposition temperature; this indicated that BD maybe used as a heterogeneous nucleating agent of PLLA. Then, the effect of BD on the crystallization and melting behavior of PLLA was investigated through differential scanning calorimetry, depolarized light intensity measurements, and wide‐angle X‐ray diffraction. The appearance of a nonisothermal crystallization peak and increases in the glass‐transition temperature and the intensity of the diffraction peak suggested that the presence of BD accelerated the overall PLLA crystallization. Upon cooling at a rate of 1°C/min, the addition of just 0.5 wt % BD to PLLA increased the onset crystallization temperature from 101.4 to 111.3°C, and the nonisothermal crystallization enthalpy increased from 0.1 to 38.6 J/g. The isothermal crystallization behavior showed that the crystallization half‐time of PLLA with 0.5 wt % BD (PLLA/0.5% BD) decreased from 49.9 to 1.1 min at 105°C. However, the equilibrium melting point of PLLA/0.5% BD was lower than that of the pristine PLLA; this resulted from the increasing nucleating density of PLLA. The melting behavior of PLLA/0.5% BD further confirmed that BD improved the crystallization of PLLA, and the double‐melting peaks of PLLA/0.5% BD were assigned to melting–recrystallization. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42402.

Physical properties and crystallization behavior of poly(lactide)/poly(methyl methacrylate)/silica composites

ABSTRACTPoly(lactide)/poly(methyl methacrylate)/silica (PLA/PMMA/SiO2) composites were fabricated using a twin‐screw extruder. Nanosilica particles were incorporated to improve the toughness of the brittle PLA, and a chain extender reagent (Joncryl ADR 4368S) was used to reduce the hydrolysis of the PLA during fabrication. Highly transparent PLA and PMMA were designated to blend to obtain the miscible and transparent blends. To estimate the performance of the PLA/PMMA/SiO2 composites, a series of measurements was conducted, including tensile and Izod impact tests, light transmission and haze measurements, thermomechanical analysis, and isothermal crystallization behavior determination. A chain extender increases the ultimate tensile strength of the PLA/PMMA/SiO2 composites by ∼43%, and both a chain extender and nanosilica particles increase Young's modulus and Izod impact strength of the composites. Including 0.5 wt % nanosilica particles increase the elongation at break and Izod impact strength by ∼287 and 163%, respectively, compared with those of the neat PLA. On account of the mechanical performances, the optimal blending ratio may be between PLA/PMMA/SiO2 (90/10) and PLA/PMMA/SiO2 (80/20). The total light transmittance of the PLA/PMMA/SiO2 composites reaches as high as 91%, indicating a high miscible PLA/PMMA blend. The haze value of the PLA/PMMA/SiO2 composites is less than 35%. Incorporating nanosilica particles can increase the crystallization sites and crystallinities of the PLA/PMMA/SiO2 composites with a simultaneous decrease of the spherulite dimension. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42378.

Confinement crystallization of poly(l-lactide) induced by multiwalled carbon nanotubes and graphene nanosheets

Two sets of multiwalled carbon nanotubes (MWCNTs)/PLLA nanocomposites and graphene nanosheets (GNSs)/PLLA nanocomposites with various MWCNTs and GNSs loadings prepared by a melt blending approach were investigated in terms of both nonisothermal and isothermal crystallization behaviors. The results indicated that MWCNTs and GNSs not only acted as heterogeneous nucleating agents for PLLA crystallization but also restricted the mobility and diffusion of PLLA chains. At low MWCNTs and GNSs concentrations, the nucleation effect of MWCNTs and GNSs was dominant to achieve accelerated overall crystallization kinetics. As the MWCNTs and GNSs concentration rose up to 2.0 and 2.5 mass%, respectively, the MWCNTs and GNSs network structures were formed in the PLLA matrix, which were proved by solid-like rheological behavior at low frequencies in rheological measurement. With further increasing concentration of MWCNTs above the critical concentration, an enhanced nucleation density but an almost unchanged overall crystallization rate for the MWCNTs/PLLA nanocomposites indicated that the expected increase in the crystallization promoting effect from more MWCNTs was offset by some confining effect. However, for GNSs, the formed network structure provided a more severely confined space for PLLA crystal nucleation and growth in contrast to MWCNTs, resulting in the decreased nucleation density and retarded crystallization rate.

Synthesis, characterization and isothermal crystallization behavior of poly(butylene succinate)-b-poly(diethylene glycol succinate) multiblock copolymers

In order to modify the properties of poly(butylene succinate), poly(diethylene glycol succinate) (PDGS) segment was incorporated by chain-extension reaction of dihydroxyl-terminated PBS and PDGS precursors using hexamethylene diisocyanate as a chain extender to form PBS-b-PDGS multiblock copolymers. The chemical structure and basic physical properties of the multiblock copolyesters were characterized by nuclear magnetic resonance spectroscopy, differential scanning calorimeter (DSC), wide angle X-ray diffraction, and tensile testing. The results suggested that the incorporation of PDGS segments would increase the elongation at break of PBS significantly while decrease its melting temperature and crystallization temperature slightly. The isothermal crystallization kinetics studied by DSC and polarized optical microscopy indicated that the crystallization rate of the multiblock polymers decreased gradually with increasing PDGS segment content while the crystallization mechanism kept unchanged and the spherulitic growth rate of the multiblock copolymers decreased gradually with increase in PDGS content due to its diluent effect to the crystallization of PBS segments. Copyright © 2015 John Wiley & Sons, Ltd.

Isothermal Crystallization Behavior of PLA/PIL Composites<sup></sup>

The effect of Poly (ionic liquid) (PIL) on the crystallization of polylactide (PLA) has been investigated by means of differential scanning calorimetry. The nonisothermal crystallization result showed that PIL enhanced the crystallization of PLA. The Avrami method was used to describe the isothermal crystallization behavior of PLA/PIL composites. The Avrami exponent (n) revealed that the PIL accelerated PLA crystallization through heterogeneous nucleation.

Isothermal Crystallization Study of (2CaO · SiO2-3CaO · P2O5) Solid Solution in the 45 mass% CaO-30 mass% SiO2-20 mass% FeOt-5 mass% P2O5System at 1623 K

The isothermal crystallization behavior of (2CaO · SiO2–3CaO · P2O5) solid solution in the CaO–SiO2–FeOt–P2O5 slag system with 1.5 basicity, 20 mass% FeOt and 5 mass% P2O5 at 1623 K (1350 °C) was conducted by using Single Hot Thermocouple Technique (SHTT), and the results suggested that the precipitated (2CaO · SiO2–3CaO · P2O5) solid solution mainly showed dendritic structure and the second arm would grow with the development of holding time during the isothermal crystallization process. The crystallization of (2CaO · SiO2–3CaO · P2O5) solid solution was almost accomplished around 1800 s, and the crystallization rate decreased with the extension of holding time. Besides, it was found that the phosphorus distribution ratio between the (2CaO · SiO2–3CaO · P2O5) solid solution and the liquid increased rapidly during the initial stage from 10 to 60 s, then it reduced gradually. Finally, it reached to a steady value around 1800 s. Those results could provide a fundamental guidance for the design of multiphase slag for the deep dephosphorization process during hot metal treatment.

Isothermal Crystallization Behavior of Cu<sub>42</sub>Zr<sub>42</sub>Al<sub>8</sub>Ag<sub>8</sub> BMG Investigated with Electrical Resistance Measurement

The isothermal crystallization behavior of the Cu42Zr42Al8Ag8 bulk metallic glasse (BMG) was studied by the electrical resistance method. The increasing local activation energy means that the crystallization of the Cu42Zr42Al8Ag8 BMG becomes more and more difficult during the isothermal process. In the stage that the crystallized volume fraction falls into the range of 25–85%, the crystallization of the Cu42Zr42Al8Ag8 BMG is diffusion-controlled growth with a decreasing nucleation rate.

Influence of Thermal Cross‐Linking Temperature on the Crystallization Behavior of Poly(phenylene sulfide)

ABSTRACTThe isothermal and nonisothermal crystallization behaviors of poly(phenylene sulfide) (PPS) are systematically investigated by differential scanning calorimetry. The results indicate that the thermal cross‐linking temperature have an important impact on crystallization behaviors of PPS apparently. With the increase in the thermal cross‐linking temperature, the crystallization properties are promoted. It is attributed to the chemically cross‐linking points and formation of network structures during the high thermal cross‐linking temperature, which lead to increment of the effective nucleating sites. Meanwhile, kinetic analysis of crystal growth demonstrates that the regime transitions of PPS crystal growth, from regime III to regime II and from regime II to regime I, can be really observed at different thermal cross‐linking temperatures, respectively. The temperature of regime III/II and II/I transitions decreases with the increase in cross‐linking temperature.

Crystallization behavior of functional polypropylene grafted graphene oxide nanocomposite

With an aim to understand a role of grafted graphene oxide (GO) in crystallization process of polymer, isothermal and non-isothermal crystallization behaviors of a functional polypropylene grafted GO nanocomposite were investigated systematically.

An Investigation of the Effect of Chitosan on Isothermal Crystallization, Thermal Decomposition, and Melt Index of Biodegradable Poly(L-lactic acid)

Biodegradable chitosan (CS) was introduced into another biodegradable poly(L-lactic acid) (PLLA) to prepare the PLLA/CS composites, and the effect of CS on thermal behavior and melt index of PLLA was investigated using modern testing technologies including optical depolarizer, thermogravimetric analysis instrument, and melt index instrument. The relevant testing results showed that both crystallization temperature and CS concentration affected the isothermal crystallization behavior of PLLA. Compared to neat PLLA, thet1/2of PLLA/5% CS decreased from 2991.54 s to the minimum value 208.76 s at 105°C. However, thet1/2of PLLA/CS composites in high crystallization temperature zone was different from that in low crystallization temperature zone. The increase of CS concentration and heating rate made the thermal decomposition temperature of PLLA/CS composites shift to higher temperature. The melt index results indicated that 3% CS made the fluidity of PLLA become better.

Isothermal crystallization behavior of lard at different temperatures studied by DSC and real-time XRD

Differential scanning calorimetry and real-time X-ray diffraction using synchrotron radiation were used to study the isothermal crystallization formation mechanism of lard at 18, 20, 22 and 24°C. At 18°C, lard crystallized in three steps. A potential mechanism for these three steps was proposed. In the first step, part of the melt (the trisaturated triacylglycerols (TAGs)) crystallized in α crystals adopting a double length structure (2L), while the second step consisted of a polymorphic transition of these 2Lα crystals to β′ crystals with a triple length structure (3L). Extra 3Lβ′ crystals consisting of monounsaturated TAGs were also formed directly from the melt. In the third and last step, β crystals were formed due to a second polymorphic transition of trisaturated 3Lβ′ crystals to β crystals adopting a 2L structure. Above a cut-off temperature of 20°C lard crystallized in two steps: no formation of α crystals could be observed and 3Lβ′ crystals (trisaturated and monounsaturated TAGs) were formed directly from the melt. This proposed mechanism implies that lard crystallization is characterized by an overlap of fractionated crystallization and polymorphic transitions.

Crystallization behaviors of poly[(R)-3-hydroxybutyrate-co-4-hydroxybutyrate]/poly(ethylene glycol) graft TEMPO-oxidized cellulose nanofiber blends

To accelerate the crystallization rate of poly[(R)-3-hydroxybutyrate-co-4-hydroxybutyrate] [P(3HB-co-4HB)] that is a microbial and biodegradable polyester, poly(ethylene glycol) graft TEMPO-oxidized cellulose nanofiber (PEG-TOCN) was blended as a nucleating agent. The PEG was only blended and confirmed the effect on the difference between PEG-TOCN and PEG in all samples. The non-isothermal crystallization and isothermal crystallization behaviors of P(3HB-co-4HB) with three kinds of different 4HB contents blended with PEG-TOCN or PEG were investigated by differential scanning calorimeter, wide-angle X-ray diffraction, polarizing microscope and tensile test. The crystallization half time (t1/2) was drastically decreased by blended with PEG-TOCN, indicating that the crystallization rate was accelerated in all cases. The POM images showed that the PEG-TOCN worked effectively to increase both the growth rate and amounts of spherulites of P(3HB-co-4HB). In addition, the crystallinity of PEG-TOCN blending samples was higher than that of non-blended samples in all cases.

Effect of Graphene Nanoplatelets on Crystallization Kinetics of Poly (lactic acid)

Crystallization behavior of nanocomposite based on graphene nanoplatelets have been considered due to its critical effect on performance of the final product. In this study, nanocomposite based on Poly(lactic acid)/graphene nanoplatelets was prepared via solution method. To improve the dispersion of graphene nanoplatelets in the matrix, functionalization using acid treatment and acylation reaction were accomplished. Characterization of functionalization reaction and grafting reaction between Poly(lactic acid) (PLA) and functionalized graphene nanoplatelets was tracked by Fourier Transform Infrared Spectroscopy, Raman, elemental analysis, Fourier transform infrared attenuated total reflection, and thermogravimetry analysis. The results showed that the reaction was successfully performed. Transmission electron microscopy results demonstrated that a relatively fine dispersion of FGNp was achieved in the PLA matrix. Non-isothermal and isothermal crystallization behavior were studied using differential scanning calorimetry. Isothermal kinetic of crystallization was studied by combination of the DSC data and theory of Avrami.

Mechanical enhancement, morphology, and crystallization kinetics of polyoxymethylene-based composites with recycled carbon fiber

Recycled carbon fiber (RCF) was employed as a reinforcing material to prepare polyoxymethylene (POM)-based composites through a simple melting extrusion. An effective approach was developed to clean and modify the surface of the as-received RCF with nitric acid and then with a silane coupling agent. The mechanical evaluation demonstrated that a significant reinforcement was achieved for POM/RCF composites due to the improved interfacial adhesion between the fibers and the matrix. The thermal stabilities of the composites were also improved in the presence of RCF. The morphological observation of impact fracture surfaces indicated that the RCF gained a homogeneous dispersion in POM matrix due to good interfacial boding between fibers and matrix. The studies on nonisothermal and isothermal crystallization behaviors showed that RCF acted as a nucleation agent for the crystallization of POM domain in composites; therefore, the crystallization rate and nucleation density increased remarkably due to the heterogeneous nucleating effect of RCF. These crystallization features may be advantageous for the enhancement of mechanical performance and processability of POM-based composites.

Amino acids and poly(amino acids) as nucleating agents for poly(lactic acid)

Abstract In industry, rapid crystallization is often required. At present, the crystallization rate of poly(lactic acid) (PLA) is too low compared to industrial needs. In this paper, amino acids such as glycine and L-alanine and poly(amino acids) like polyglycine and poly-DL-alanine are considered as heterogeneous crystallization nucleating agents. The impact of adding these bio-based additives on the isothermal crystallization behavior of PLA was quantified and compared at different concentrations by using the so-called Lotz efficiency scale, which here is based on isothermal DSC measurements. In addition, rheological and rheo-optical techniques were used to monitor the isothermal crystallization. Our results indicate that polyglycine possesses a significant nucleating ability (60.5%) which is comparable to the industrially used talc (81.1%).

Crystallization kinetics of polyethylene/paraffin oil blend sheets formed by thermally induced phase separation with different molecular weights of polyethylene

Polyethylene/paraffin oil blend sheets with different molecular weights of polyethylene were prepared by thermally induced phase separation. Isothermal and non-isothermal crystallization behaviors of blend sheets were investigated by differential scanning calorimetry (DSC). Isothermal DSC curves were analyzed by Avrami equation, whereas non-isothermal DSC curves were analyzed by Jeziorny method and Mo method. Effective activation energy (ΔE) of isothermal and non-isothermal crystallization was calculated by Friedman method. Under isothermal condition, value of n in Avrami equation hovered at 2.1, and lgZ increased with the decrease of crystallization temperature. lgZ and ΔE of blend sheets with a larger molecular weight of polyethylene was smaller than that of blend sheets with smaller molecular weight. Under non-isothermal condition, value of n obtained by Jeziorny method hovered at 2.4, close to n of isothermal condition. lgZ c increased with the increase of cooling rate and decrease of molecular weight of polyethylene. ΔE of different blend sheets were close to each other. Crystal structures of blend sheets formed under non-isothermal condition were analyzed by X-ray diffraction (XRD) analysis. XRD analysis showed that molecular weight of polyethylene and cooling rate had slight influence on crystal structure and crystallinity of polyethylene/paraffin oil blend sheet.

Isothermal crystallization in Ce70Ga6Cu24 bulk metallic glass

The isothermal crystallization behaviors in a newly developed CeGaCu bulk metallic glass have been investigated through the classic differential scanning calorimeter (DSC) method. It is found that the apparent activation energy (Ea) strongly depends on the fraction (x) of isothermal crystallization. Johnson-Mehl-Avrami (JMA) formula was used to analyze the mechanism of crystallization and the obtained Avrami exponent (n) was discovered to show an obvious correlation with the crystallization fraction x. With the help of the relation between Ea and n, the nucleation and growth activation energies, En and Eg, were estimated to be 214–304 kJ/mol and 91 kJ/mol, respectively. This result suggests that the main energy barrier against crystallization in the present glass should be the nucleation of nucleates, rather than the growth of crystals. Such a large En is also believed to be responsible for the good glass forming ability of the CeGaCu alloy.

Long terminal linear alkyl group as internal crystallization accelerating moiety of poly(l-lactide)

Poly(l-lactide) (PLLA) polymers having terminal n-alkyl groups with a wide variety of lengths (C0–C22) were synthesized by ring-opening polymerization of l-lactide in the presence of coinitiators of l-lactic acid (C0), 1-hexanol (C6), 1-dodecanol (C12), and 1-docosanol (C22) and their segmental mobility and non-isothermal and isothermal crystallization behavior were investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffractometry (WAXD). Glass transition and cold crystallization temperatures of melt-quenched samples during heating decreased with an increase in the length of terminal n-alkyl groups. The enhanced PLLA segmental mobility and hydrophobic interaction-based accelerated PLLA nucleation by the presence of terminal long n-alkyl groups should have caused the accelerated non-isothermal and isothermal crystallization of PLLA segments traced by cold crystallization temperature during heating and by radial growth rate of spherulites, respectively. The crystallization accelerating effect became higher with the length of terminal n-alkyl groups. The effects of the length of terminal n-alkyl group on the crystalline growth mechanism of PLLA at the lowest crystallizable temperature was insignificant, whereas the effects of the length of terminal n-alkyl group on the nucleation mechanism of PLLA chains were significant and insignificant for PLLA having Mn of 6–7 × 103 of 2 × 104 g mol−1, respectively. WAXD measurements revealed that the transition crystallization temperature at which crystalline modification changes from δ-form to α-form was affected by the length of terminal n-alkyl group for PLLA having Mn of 6–7 × 103 g mol−1, but was not altered by the length of terminal n-alkyl group for PLLA having Mn of 2 × 104 g mol−1.

Studies on synergistic effect of CNT and CB nanoparticles on PVDF

Poly(vinylidene fluoride) (PVDF) nanocomposites with different loading of carbon nanotubes (CNT) and carbon black (CB) were prepared by melt blending method. The conductivity and mechanical properties of the nanocomposites were investigated. The results showed that percolation threshold of CNT/CB/PVDF nanocomposites appeared at a lower concentration (1.25 vol% CNT) than that of CNT/PVDF (>2.08 vol% CNT). The tensile strength of CNT/CB/PVDF nanocomposites was also improved, with 32.1% increase compared to PVDF and 18.0% increase compared to CNT/PVDF at loading of 1.25 vol% CNT/0.96 vol% CB. To explore the synergistic effect of CNT and CB, nonisothermal crystallization and isothermal crystallization behaviors of PVDF and its nanocomposites were studied by differential scanning calorimetry, and the crystallization morphology of them was observed under the three dimensional digital microscope with the polarized model. The crystallization rate of PVDF was speeded up markedly because of heterogeneous nucleation effect of nanoparticles, and CNT and CB nanoparticles had a synergistic effect on nucleation. Polarized microscope observation confirmed that spherulite size of PVDF became smaller owing to the accelerating of crystallization, which influenced the distribution of nanoparticles. The dispersion of nanofillers in matrix was observed by scanning electron microscope. It was revealed that CB could make CNT disperse more evenly in the PVDF matrix. The synergies network of CNT and CB is suggested to build in matrix, which improved conductivity and mechanical properties of PVDF nanocomposites. POLYM. COMPOS., 36:2248–2254, 2015. © 2014 Society of Plastics Engineers