Melting Behavior Of Poly Research Articles

Effect of epoxidized soybean oil on melting behavior of poly(l-lactic acid) and poly(d-lactic acid) blends after isothermal crystallization

Abstract The effect of epoxidized soybean oil (ESO) on homocrystallization (HC) and stereocomplex (SC) formation behavior of poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) bends was investigated utilizing differential scanning calorimetry (DSC). Isothermal crystallization was performed on ESO/PLLA/PDLA blends with varying ESO contents (0, 5, 8, and 10 wt%) and temperatures (90 °C, 120 °C, and 150 °C) for a different duration (12.5, 25, and 125 min). It was found that the ESO could effectively inhibit HC crystallization and promote SC crystallization. For the sample without ESO (ESO-0), the isothermal crystallization temperature and duration had little effect on the melting behavior, whereas sample with 5 wt% ESO (ESO-5), HC crystallization decreased while SC crystallization continued to increase with increasing duration. Additionally, at higher crystallization temperatures with constant ESO content, the melting temperature of SC crystals did not significantly change, suggesting that ESO did not degrade PLLA/PDLA blends. These findings imply that ESO modifies crystallization kinetics, suppressing HC formation and enhancing SC formation, which could benefit for specific material properties and applications.

Effect of post-polymerization on the crystallization and melting behavior of poly(butylene terephthalate)

In this paper, the chemical and physical structures of poly (butylene terephthalate) (PBT) after different thermal treatments, in the range of 180–260 °C and up to 10 h, were systematically investigated. Nuclear magnetic resonance and Fourier transform infrared spectroscopy results showed that the chemical structure of PBT did not change significantly after treatment. The thermal stability of the heat-treated samples, reflected by the decomposition temperature shown in thermogravimetric analysis, was the same as that of the untreated samples. During the treatment, the molecular weight increased, while the polydispersity remained essentially constant (∼2). The highest increase in molecular weight was observed when the samples were subjected to heat treatment near the melting point temperature (220 °C). Importantly, the crystallization temperature of the samples changed with heat treatment temperatures and times, while the melting point remained essentially constant.

Melt-induced transition in thickness and interfacial molecular orientation of poly(ethylene oxide) thin films

Melting behavior of poly(ethylene oxide) (PEO) in thin films was examined by observing the variations of thickness (Δd) and interfacial molecular orientation using ellipsometry and sum-frequency generation (SFG) spectroscopy, respectively. The thinner PEO films exhibited a smaller ratio of Δd to the film thickness on melting, indicating a lower degree of crystallinity (χ). For the as-cast films, this thinning effect was more evident on hydrophilic substrates than on hydrophobic substrates. For the annealed films, the thinning effect was less dependent on the substrates. These results imply that the decrease in the χ of PEO with decreasing thickness originates from two factors: reduced chain dynamics at the substrate interface and crystallization confined to a limited space, which are dominant for the as-cast and annealed films, respectively. The SFG measurements detected characteristic signals originating from crystallized PEO at the air/PEO and PEO/substrate interfaces.

Crystallization and melting behavior of poly(ether ketone ketone) (PEKK) copolymers synthesized by facile one-step method

Crystallization and melting behavior of poly(ether ketone ketone) (PEKK) copolymers synthesized by facile one-step method

Effects of end groups and entanglements on crystallization and melting behaviors of poly(ε-caprolactone).

The topology including end groups, entanglement loops, and tie molecules has a significant impact on the rheological and crystallization behavior and consequently on the functionality of a polymer. Unentangled, weakly entangled, and strongly entangled poly(ε-caprolactone)s (PCLs) with end groups and various molecular weights were synthesized. POM and DSC were used to observe spherulite growth and characterize thermal properties during crystallization and melting. The viscosity and structure of the samples were probed by rheology and X-ray analysis, respectively. The crossover of the scaling relationship of viscosity vs molecular weight demonstrates that the samples cover a wide range of entanglement density, and the bulky end groups cause deviations from the classical scaling laws. In situ simultaneous SAXS/WAXS investigations showed that the crystal structure of PCLs did not change with end groups and heating. The results of POM and DSC imply that the end groups and entanglements affect the crystallization rate and the spherulite morphology. The melting of PCLs containing end groups was found to be a multi-step process involving various nanoscale crystalline structures. The evolution of nanoscale crystalline structures of isothermally crystallized PCLs during heating was analyzed by fitting 1D SAXS profiles, and the continuous structural evolution was found to be a process influenced by end groups and entanglements. The results show that end groups and entanglements affect the chain dynamics and lead to constrained crystallization behavior and the formation of metastable structures, ultimately affecting the structure evolution during melting.

PLLA crystallization kinetics in dependence of molecular weight

Abstract The effect of molecular weight Mwon the polymorphous crystallization and melting behavior of poly(Llactide) PLLA (L206, L210 and L214) were systemically studied by differential scanning calorimetry (DSC). Melting and reorganization of conformationally disordered crystals (α′-phase) of PLLA are analyzed with respect to the cooling rate qcin a range between about 4 and 50 K/min and the heating rate qhin a range between about 5 and 200 K/min. It was shown that the α′- to α-crystalline phase transition prior to the dominant melting depends on cooling rate qcand Mw. Unlike very high-MwPLLA L214, for low-MwPLLA L206 crystallized at high qc, the α′-form crystals only partially transformed into the α-modification, and certain amounts of α′-form crystals melted directly without α′- to α-transition during the heating process. With increasing qc, the melting of PLLA L210 changed from phase-transition- and -melting mechanism to the common melt-recrystallization mechanism. It was also found that the polymorphism of PLLA significantly affected the crystallization kinetics. Consequently, the reorganization of α′-crystals into stable α- crystals could be inhibited by fast heating (qh> 150 K/min).

Confined crystallization and melting behaviors of poly(ethylene glycol) end‐functionalized by hydrogen bonding groups: Effect of contents for functional units

Confined crystallization and melting behaviors of poly(ethylene glycol) end‐functionalized by hydrogen bonding groups: Effect of contents for functional units

Melting behavior of PET with sulfonated polypropylene wax

The effects of sulfonate group and composition of sulfonateionomer (SPSN) with low molecular mass on the morphologies, non-isothermal crystallization and melting behaviors of poly(ethylene terephthalate) (PET) in PET/SPSN blends are investigated by thermogravimetric analysis (TG). Sulfonateionomer (SPSN) is synthesized from polypropylene wax by two steps, and at 300°C the mass loss of SPSN is only 1wt % with a good thermal stability. The result shows that sulfonateionomer could is an effective nucleating agent.

Crystallization and melting of poly(butylene terephthalate) and poly(ethylene terephthalate) investigated by fast-scan chip calorimetry and small angle X-ray scattering

The crystallization and melting behaviors of poly(butylene terephthalate) (PBT) and poly(ethylene terephthalate) (PET) were examined by Hoffman-Weeks (H–W), Gibbs-Thomson (G-T), and thermal Gibbs-Thomson (t-G-T) plots constructed by using fast-scan calorimetry and small-angle X-ray scattering. With PBT and PET, neither an H–W nor a G-T plot could be utilized for the determination of the equilibrium melting point (TM0) of chain-extended infinite-size crystals. The thermal Gibbs-Thomson plot utilizes the change in the melting point and the heat of fusion of chain-folded crystals during the secondary stage of isothermal crystallization. TM0 was determined from a t-G-T plot, and the results were in good agreement with the literature values for PBT and PET. G-T and t-G-T plots suggested a temperature-dependent folding surface free energy (σe), as has been proposed by Hoffman et al. The σe values obtained with G-T and t-G-T plots support the consistency of the analysis.

The effect of temperature and pressure on polycaprolactone morphology

The morphology and melting behavior of poly(ε-caprolactone) (PCL) processed at varying pressure-temperature-time conditions (2000–20,000 lbf, 22–70 °C, and 5–15 min) were studied using polarized light microscopy (PLM), differential scanning calorimetry (DSC), and X-Ray diffraction (XRD). Samples processed well below the melting region at 22 °C displayed minimal to no birefringent properties, with broadened crystalline XRD scattering patterns, indicative of plastic crystal mesophase morphology. Plastic crystal quantity was shown to gradually increase from 16% to 30% with processing pressure increasing from 2000 lbf to 20,000 lbf. The mechanism of this formation is thought to be the result of crystal disorganization upon plastic deformation, related to the low-energy barrier slip-planes in the crystalline structure. With sufficient chain mobility achieved at higher processing temperatures (50 °C and 60 °C), samples displayed broad birefringent strokes under PLM and were characterized by XRD scattering patterns of broad anisotropic arcs around the equator of the 2D azimuthal pattern, which are indicative of condis crystal mesophase orientation. As opposed to plastic crystal, the condis crystal quantities showed no correlation with increased pressure, ranging between 28% and 40% as processing pressure increased. The additional chain mobility at these temperatures is thought to enable the mesophase to orient radially (normal to the direction of the external load), allowing the transition from plastic crystal to condis crystal. Thus, this paper reports the formation of four distinct morphologies upon processing PCL namely; crystalline, condis crystal mesophase, plastic crystal mesophase, and amorphous.

Phase Transition and Melt-Recrystallization Behavior of Poly(Butylene Adipate) Investigated by Simultaneous Measurements of Wide-Angle X-Ray Diffraction (WAXD) and Differential Scanning Calorimetry (DSC).

Simultaneous measurements of wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) were carried out to investigate the phase transition and melting behaviors of poly(butylene adipate) (PBA). Thermal expansion changes along the a and b axes of the β form unit cell are different from each other during the heating process. At the beginning of the β to αH (high-temperature α phase) phase transition, the β phase melts very fast, while the recrystallization of the αH phase is delayed and slowed. With the further increment of the temperature, the melting rate of the β phase slows down, while the recrystallization of the αH phase accelerates. The diffraction peak intensity ratios of the β(020):β(110) and αH(020):αH(110) diffraction peaks during the first heating process have similar value. However, the above value is different from the value of α(020):α(110) during the following melt-crystallization process. This difference comes from the different orientations of the crystal lattices of the α and αH(β) crystals to the substrate plane, which indicates that the αH phase inherits the orientation of the β phase during phase transition and the orientation of αH form crystals is different from the α form crystals that crystallized from the melt.

Crystallization and melting behaviors of poly(vinylidene fluoride) examined by fast-scan calorimetry: Hoffman-Weeks, Gibbs-Thomson and thermal Gibbs-Thomson plots

Crystallization and melting behaviors of chain-folded polymer crystals have been examined by fast-scan calorimetry (FSC) combined with small angle X-ray scattering (SAXS) and wide angle X-ray diffraction (WAXD) for poly(vinylidene fluoride). The melting point of lamellar crystals formed isothermally at Tc was measured by FSC in terms of the heating rate dependence and calibrated on the basis of the modeling of melting kinetics for the determination of the melting point at zero heating rate TM. The Hoffman-Weeks (H-W) plot of TM against Tc was on a linear straight line over Tc range broader than 30 K, and suggested the equilibrium melting point TM0 ≅ 200 °C of chain-extended infinite-size crystals of the α form. On the other hand, utilizing crystalline lamellar thickness dc determined by SAXS, both of the Melting and Crystallization lines in the Gibbs-Thomson (G-T) plots of TM and Tc against (dc)−1, respectively, were found to seriously deviate from linear straight lines. By examining the secondary stage of crystallization on long time isothermal annealing at Tc in terms of the changes in TM and the specific heat of fusion Δhfs by FSC, a newly proposed thermal G-T plot of TM against (Δhfs)−1 has confirmed the reliability of TM0 of the α form determined by the H-Wplot and the Tc dependent folding surface free energy σe, which brings the curved Melting and Crystallization lines in the G-T plots. In addition, on long time isothermal annealing, the changes in dc by SAXS and in crystallite size by WAXD have confirmed the molecular origin of the increase in TM and Δhfs in the secondary stage with thickening and perfecting of metastable chain-folded polymer crystals.

Crystallization and melting behavior of poly(L-lactic acid) modified with salicyloyl hydrazide derivative

This work evaluated the influence of a novel organic nucleating agent, salicyloyl hydrazide derivative (BS), on the crystallization and melting behavior of poly(L-lactic acid) (PLLA). Differential scanning calorimetry revealed that the incorporation of BS (0.2 to 3 wt %) significantly promoted the crystallization of PLLA on cooling at 1 °C/min. At BS content of 1.5 wt % in PLLA matrix, the highest effectiveness of crystallization process was observed, this result was further demonstrated by X-ray diffraction analysis of non-isothermal crystallization behavior at different cooling rate and measurements after isothermal crystallization. X-ray diffraction studies showed also that the addition of BS did not change the crystalline structure of PLLA. Based on the effect of the predetermined melting temperature on the crystallization behavior of PLLA/BS, the optimum process temperature of 190 °C was found. The comparative study on the melting behavior of PLLA/BS composite under different conditions (cooling rate, melting temperature) also confirmed the ability of BS to promote the nucleation of PLLA crystallization. The crystallization of PLLA/BS composite depends on the concentration of BS additive, crystallization temperature and time as well as heating rate.

Studies on the effects of 4,4′-dihydroxyphenyl on crystallization and melting behavior of poly (butylene terephthalate)

Abstract The blends of poly (butylene terephthalate) (PBT) and 4,4′-dihydroxyphenyl (DHP) were prepared by melt blending, and the effects of DHP on the crystallization and melting behaviors of PBT were investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and polarized optical microscopy (POM). The results showed that crystallization temperature and crystallinity of PBT apparently decreased with the addition of DHP. A remarkably decline in crystallization rate of PBT was achieved, and the blends had higher σ e and q values than that of pure PBT as analyzed based on the Avrami equation and Lauritzen-Hoffman equation. The crystal structure of PBT did not change by the addition of DHP, while the spherulite size of PBT decreased.

Morphology, crystallization and melting behaviour of poly(trimethylene terephthalate)/thermotropic liquid crystalline polymer blends

The miscibility, crystallization and melting behaviour of poly(trimethylene terephthalate)/thermotropic liquid crystalline polymer (LCP) blends were studied using differential scanning calorimetry. The blends were found to form primarily an immiscible system. The addition of LCP accelerated the overall rate of crystallization and caused a depression in equilibrium melting temperature, especially at low LCP content. Lauritzen–Hoffman analysis showed that the addition of LCP caused a reduction in the fold surface energy and increased the regime II to III transition temperature.

Effect of Optical Purities on the Crystallization and Melting Behaviors of Poly( L -lactic acid)

Effect of Optical Purities on the Crystallization and Melting Behaviors of Poly( L -lactic acid)

Role of N,N'-bis(1H-benzotriazole) adipic acid acethydrazide in crystallization nucleating effect and melting behavior of poly(L-lactic acid)

The enhancement of crystallization performance is very important in semicrystalline polymers for broadening their practical application. In this study, N,N'-bis(1H-benzotriazole) adipic acid acethydrazide (BA) was synthesized from 1H-benzotriazole and adipic acid in order to evaluate the heterogeneous nucleating performance of poly(L-lactic acid) (PLLA). Through the investigation of non-isothermal crystallization behavior of PLLA containing different BA content using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD), it was clear that BA was able to significantly promote the crystallization of PLLA compared to pristine PLLA, and the addition of BA resulted in an increase in the onset and peak crystallization temperatures and in the non-isothermal crystallization enthalpy. Furthermore, 1 wt% BA was found to be the optimal concentration, achieving the best nucleating effect for PLLA. The cooling rate was a key factor affecting the non-isothermal crystallization peak. The set final melting temperature also affected crystallization, as a result of the solubility of BA in the PLLA matrix and the thermal decomposition of PLLA at the set temperature. Comparative study of the melting behavior of PLLA and PLLA/BA further confirmed the nucleating interaction of BA with PLLA. Differences in melting behavior were largely dependent on the competition between the crystallization rate and the relevant heating or cooling rate.

Effects of molecular weight on the crystallization and melting behaviors of poly(L-lactide)

In this study, a series of monodispersed poly(L-lactide) (PLLA) were synthesized by the ring-opening polymerization with Schiff base aluminum catalyst, and the effects of the number-average molecular weight (M n) on the crystallization and melting behaviors of PLLA were investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). The total crystallization rate of PLLA was M n-dependent, which reached the maximum value for PLLA with M n of 18.6 kg/mol. In addition, when Mn of PLLA was 18.6 kg/mol, the melting enthalpy (ΔH m) showed a maximum value (87.1 J/g), which was the highest reported value till now. The critical temperature for change of crystal formation from δ- to α-form crystals increased in the isothermal crystallization process with M n increasing. In the reheating procedure, high-M n PLLA demonstrated a small exothermal peak prior to the dominant melting peak, corresponding to crystal transition from δ- to α-form, but low-M n PLLA didn’t show the peak of crystal transition. These different crystallization and melting behaviors were attributed to the different chain mobility of PLLA with different M n.

Crystallization and melting behavior of poly(ε‐caprolactone‐co‐δ‐valerolactone) and poly(ε‐caprolactone‐co‐L‐lactide) copolymers with novel chain microstructures

ABSTRACTNuclear magnetic resonance spectroscopy (NMR) characterization of the statistical copolymers of this study showed that the poly(ε‐caprolactone‐co‐L‐lactide)s, with ε‐caprolactone (ε‐CL) molar contents ranging from 70 to 94% and ε‐CL average sequence length (lCL) between 2.20–9.52, and the poly(ε‐caprolactone‐co‐δ‐valerolactone)s, with 60 to 85% of ε‐CL and lCL between 2.65–6.08, present semi‐alternating (R→2) and random (R∼1) distribution of sequences, respectively. These syntheses were carried out with the aim of reducing the crystallinity of poly(ε‐caprolactone) (PCL), needed to provide mechanical strength to the material but also responsible for its slow degradation rate. However, this was not achieved in the case of the ε‐caprolactone‐co‐δ‐valerolactone (ε‐CL‐co‐δ‐VAL). Non‐isothermal cooling treatments at different rates and isothermal crystallizations (at 5, 10, 21 and 37°C) were conducted by differential scanning calorimetry (DSC), and demonstrated that ε‐CL copolymers containing δ‐valerolactone (δ‐VAL) exhibited a larger crystallization capability than those of L‐lactide (L‐LA) and also arranged into crystalline structures over shorter times. The crystallization enthalpies of the ε‐CL‐co‐δ‐VAL copolymers during the cooling treatments and their heat of fusion (ΔHm) at the different isothermal temperatures were very large (i.e. ΔHc > 53 Jg−1) and in some cases, unrelated to the copolymer composition. In some compositions, such as the 60 : 40, Wide Angle X‐ray Scattering (WAXS) proved that that these two lactones undergo isomorphism and co‐crystallize in a single cell. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42534.

Unique Homo-Crystallization and Melting Behavior of Poly(L-lactic acid): Influence of Stereocomplex with Varied Structure

Homo-crystallization and melting behavior of poly(L-lactic acid) (PLLA) with poly(D-lactic acid) (PDLA) (≤10 wt.%) was studied. The different thermal history had been applied to exert structural variation on stereocomplex (SC). The PLLA/PDLA blend showed different crystallization and melting behavior when cooled from 250°C or 200°C. Double melting peaks were observed after the blend was cooled from 250°C. SC annealing at different temperatures exhibited significant effect for melt-crystallization of PLLA. Influence of initial melting condition before cooling was also investigated. The cold crystallization of amorphous blend initially was studied and some novel results had been observed.