Nonisothermal Cold Research Articles

An incremental isoconversional method for kinetic analysis based on the orthogonal distance regression.

The parameters obtained from a kinetic analysis of thermoanalytical data often exhibit a conversion-dependent behavior. A novel incremental isoconversional method able to deal with this phenomenon is proposed. The kinetic model is directly fitted to the experimental data using nonlinear orthogonal least squares procedure. The data are processed without transformations, so their error distribution is preserved. As the objective function is based on a maximum likelihood approach, reliable uncertainties of the parameters can be estimated. In contrast to other methods, the activation energy and the pre-exponential factor are treated as equally important kinetic parameters and are estimated simultaneously. Validity of the method is verified on simulated data, including a dataset with local nonlinearity in the temperature variation. A practical application on the nonisothermal cold crystallization of polyethylene terephthalate is presented.

Effect of biodegradable poly(ethylene adipate) with low molecular weight as an efficient plasticizer on the significantly enhanced crystallization rate and mechanical properties of poly(l-lactide)

The slow crystallization rate and low elongation at break are the main drawbacks of biodegradable poly(L-lactide) (PLLA) from a viewpoint of practical application. Such disadvantages of PLLA have been successfully resolved by blending with low molecular weight biodegradable poly(ethylene adipate) (PEA) in the present work. As a biodegradable plasticizer, PEA not only formed fully miscible and biodegradable polymer blends with PLLA but also apparently reduced the glass transition temperature of the blends. The increased chain mobility favored the nonisothermal cold and melt crystallization behaviors, increased the spherulitic growth rate, and accelerated the overall isothermal melt crystallization process of the blends; however, the blends had the same crystallization mechanism and crystal structures as neat PLLA. One of the exciting results was that the elongation at break value of an 80/20 PLLA/PEA blend was dramatically increased; therefore, for a wider practical application, the preparation of PLLA-based materials with fast crystallization rate, good mechanical properties, and complete biodegradability could be accomplished by the blending with a small amount of PEA with low molecular weight as an efficient plasticizer.

Non-isothermal cold crystallization kinetics of poly(lactic acid)/poly(butylene adipate-co-terephthalate)/treated calcium carbonate composites

The non-isothermal cold crystallization behaviors of poly(lactic acid) (PLA)/poly(butylene adipate-co-terephthalate)/titanate-treated calcium carbonate (T-CaCO3) composites were studied by means of differential scanning calorimetry. The activation energies (E a) of non-isothermal cold crystallization were calculated by Kissinger’s method. It is found that Jeziorny’s and Mo’s methods well describe the non-isothermal cold crystallization kinetics of neat PLA and PLA composites, while Ozawa’s model fails. The cold crystallization rate and E a of PLA composites are greater than those of neat PLA. It is attributed to the dual effect (heterogeneous nucleating agent and physical hindrance) of T-CaCO3 on the cold crystallization.

On the Kissinger equation and the estimate of activation energies for non-isothermal cold crystallization of PET

The activation energy for nonisothermal cold crystallization of polyethylene terephthalate (PET) and its blends with 1% polystyrene (PS) and 1% styrene-acrylonitrile copolymer (SAN) were measured based on differential scanning calorimetry (DSC). The Kissinger method was used to compute the activation energies in all cases, obtaining mean values of 120, 100, and 85 kJ/mole for neat PET, PET/1%PS and PET/1%SAN. A modified Kissinger procedure is proposed to estimate activation energies in polymer systems in which the relative crystallinity - measured at constant heating rates - can be correlated by the Ozawa model with a temperature-independent exponent. Values of the activation energy of 115 and 160 kJ/mole were obtained for cold crystallization of PET in the PET/1%PS and PET/1% SAN blends using the modified Kissinger procedure.

Crystallization kinetics of chain extended poly(lactic acid)/clay nanocomposites

The poly(lactic acid)/clay nanocomposites (PLACNs) were prepared by melt mixing method, then multiepoxide chain extender (CE) was added into PLACNs to induce the branched structure of poly(lactic acid) (PLA) chains. The nonisothermal cold crystallization and isothermal melting crystallization of PLA, PLACNs, and chain extended PLACNs (CEPLACNs) were characterized by DSC and studied by Avrami analysis. The results showed that the inducing of clay and CE affected the crystallization behavior of PLA in different way. Adding CE increased the overall crystallinity of PLA at cooling process, but clay had an opposite effect. Besides that, the addition of CE and clay increased the crystal nuclei number due to the heterogeneous nucleation mechanism. According to the crystallization kinetics study, the inducing of clay almost no effect on the crystal growth rate of PLA, but the branched structure had a pronounced effect for improving crystal growth rate of PLA. POLYM. COMPOS., 36:2123–2134, 2015. © 2014 Society of Plastics Engineer

Enhancing cold crystallization of poly(l-lactide) by a montmorillonitic substrate favoring nucleation

Abstract A montmorillonite (MMT) with nucleating surface (NMMT) supported by chemically calcium phenylphosphonic acid (PPCa), an effective nucleant for poly( l -lactide) (PLLA), was prepared through the chemical reaction between phenylphosphonic acid (PPOA) and calcium ion on the surface of MMT. Then, NMMT was introduced into PLLA via simple melt blending. The overall isothermal cold crystallization rates of PLLA were faster in the blends than in neat PLLA, indicative of the nucleating effect of the NMMT in the blends. The crystal structure of PLLA and its blends remained unchanged despite the addition of NMMT in the blends. For the nonisothermal cold crystallization, the crystallization process of PLLA was accelerated by increasing both heating rate and the NMMT contents. The Avrami equation and the combined Ozawa–Avrami model could describe it successfully. Moreover, the activation energy for nonisothermal cold crystallization of neat PLLA and its blends based on Friedman equation was estimated.

In situ ring-opening polymerization of poly(l-lactide)-graft-graphene oxide and its effect on the crystallization kinetics and morphology of biodegradable poly(l-lactide) at low loadings

Biodegradable poly(L-lactide) (PLLA) and graphene oxide (GO) nanocomposites were prepared by blending commercial PLLA with PLLA-g-GO at low loadings, which was synthesized via ring-opening polymerization using GO as the initiator and characterized with various techniques. Both the nonisothermal cold and melt crystallization behaviors and overall isothermal melt crystallization rates of PLLA have been enhanced significantly by PLLA-g-GO in the nanocomposites, relative to neat PLLA. PLLA-g-GO is more efficient than GO as a nucleating agent for the crystallization of PLLA, because PLLA is covalently grafted onto the surface of GO in PLLA-g-GO, which may provide better compatibility with the PLLA matrix and improve the nucleation ability.

Crystallization behavior, morphology, and mechanical properties of poly(lactic acid)/tributyl citrate/treated calcium carbonate composites

In this article, poly(lactic acid) (PLA) composites containing titanate coupling agent treated calcium carbonate (T-CaCO3) and tributyl citrate (TBC) were prepared via melt blending. The crystallization, morphology, mechanical properties, and nonisothermal cold crystallization kinetics of PLA composites were studied by means of differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), polarized light microscopy (PLM), scanning electron microscopy (SEM), and mechanical tests, respectively. The results show that TBC promotes crystallization of PLA. Both T-CaCO3 and TBC significantly decrease the spherulitic size, but the crystal structure of PLA is not changed. A synergistic toughening effect is obtained by the combination of T-CaCO3 and TBC. The nonisothermal cold crystallization kinetics of PLA composites is well described by Mo's method. The activation energies (ΔE) of nonisothermal cold crystallization were calculated by Kissinger and Takhor methods, respectively. It is found that the addition of T-CaCO3 and TBC increases ΔE, but it also increases the cold crystallization rate. POLYM. COMPOS., 35:1570–1582, 2014. © 2013 Society of Plastics Engineers

Effect of Molecular Orientation on the Cold Crystallization of Amorphous–Crystallizable Polymers: The Case of Poly(trimethylene terephthalate)

The effect of molecular orientation on cold crystallization of amorphous crystallizable polymers was examined using poly(trimethylene terephthalate) (PTT) films drawn to different draw ratios and strain rates. A combination of differential scanning calorimetry (DSC) and polarized Fourier transform infrared (FTIR) spectroscopy was employed to examine structural evolution and nonisothermal crystallization kinetics. The cold crystallization temperature (Tc), cold crystallization exotherm (ΔHc), and subsequent melting temperature (Tm) were carefully correlated to the overall molecular orientation. For the first time, the overall molecular orientation was shown to have an inverse relationship to the cold crystallization temperature, as well as the cold crystallization exotherm. Nonisothermal cold crystallization has not occurred when the overall orientation exceeded the critical value of 0.43. The kinetics of nonisothermal cold crystallization of PTT with a different overall molecular orientation has been investigated and the Avrami equation has been applied to evaluate the kinetic parameters. An increase in the rate constant and a decrease in the Avrami exponent suggested that cold crystallization is faster for a PTT film with a high overall molecular orientation and a change in growth geometry with orientation. This study demonstrates that overall molecular orientation affects the cold crystallization kinetics of amorphous–crystallizable polymers.

Non-isothermal cold crystallization behavior and kinetics of poly(l-lactide): effect of l-lactide dimer

The effects of l-lactide dimer as additives on the crystallization behavior of poly(l-lactide) (PLLA) films were studied. Hence, neat PLLA films and PLLA containing l-lactide (5 % w/w) (PLLA/La) were prepared in dichloromethane at room temperature via solution casting. The non-isothermal cold crystallization of PLLA films were studied using differential scanning calorimetry at various heating rates including 2.5, 5, 7.5, 10 and 15 °C/min. However, the X C% was increased for PLLA/La films in comparison with neat PLLA films. The crystallization kinetics was then analyzed by the Avrami, Jeziorny, Ozawa and Mo kinetic models. It is found that all the kinetic models were established to describe the experimental data fairly well except the Ozawa model. The values of t 1/2, Z C and F(T) indicated that the crystallization rate increased with increase in heating rates for PLLA and PLLA/La films. However, l-lactide dimer incorporated in PLLA films accelerates the crystallization process of PLLA at the high heating rate. The nucleation constant (K g) and the surface free energy (σ e) based on Lauritzen–Hoffman theory indicated that these parameters for PLLA/La films is lower than neat PLLA.

Crystallization behavior of poly(lactide)/poly(β‐hydroxybutyrate)/talc composites

AbstractThe morphology and miscibility of commercial poly(lactide) (PLA)/poly(β‐hydroxybutyrate) (PHB, from 5 to 20 wt %) blends prepared by melt extrusion method, were investigated using differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) observations. The results show that for all the studied blend contents, PLA/PHB blends are immiscible. The effects of PHB and talc on the nonisothermal cold crystallization kinetics of PLA were examined using a differential scanning calorimetry (DSC) at different heating rates. PHB acted as a nucleating agent on PLA and the addition of talc to the blend yielded further improvement, since significant increase in the enthalpy peak was observed for samples containing 10 wt % PHB and talc (from 0.5 to 5 phr). The crystallization kinetics were then examined using the Avrami–Jeziorny and Liu–Mo approach. The simultaneous presence of PHB and talc induced a decrease of the crystallization half time. The evolution of activation energies determined with Kissinger's equation suggests that blending with PHB and incorporating talc promote nonisothermal cold crystallization of PLA. The synergistic nucleating effect of PHB and talc was also observed on isothermal crystallization of PLA from the melt. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

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%.

Nonisothermal Crystallization Kinetics of Poly(lactic acid)/Nanosilica Composites

Poly(lactic acid) (PLA)/nanosilica composites were prepared by blending the PLA and nanosilica in chloroform and then evaporating the solvent to form the composite films in a dish. The Ozawa and Mo equations were used to characterize the nonisothermal cold crystallization kinetics of the PLA/nanosilica composites. The results indicated that the Ozawa equation was not successful while the Mo equation was successful to describe the nonisothermal crystallization kinetics of PLA/nanosilica composites. The values of crystallization activation energy (E c) of the samples were calculated by the Kissinger method. Although the sample crystallization rates were enhanced with the increase of nanosilica content, the samples exhibited increased E c in the presence of nanosilica. The results showed that nanosilica had an effect on both the nucleation and the crystal growth of PLA, promoting the nucleation but interfering with the molecular motion of PLA in the crystallization process.

Effect of copolymerization on crystallization kinetics of semicrystalline polyimides

AbstractIsothermal melt crystallization kinetics and nonisothermal cold crystallization kinetics of co‐PI based on 3, 3′, 4, 4′‐biphenyltetracarboxylic dianhydride (s‐BPDA)/1, 3‐bis‐(4‐aminophenoxy) benzene (TPER)/4, 4′‐oxydianiline(4, 4′‐ODA), and TPER PI (s‐BPDA/TPER) have been investigated. Avrami equation was used to analyze isothermal melt crystallization progress of TPER PI and co‐PI, primary crystallization processes was found to be changed as the introduction of 4, 4′‐ODA. Total activation energy ΔE for TPER PI and co‐PI were found to be −404 and −86 kJ mol−1 by Arrhenius equation. Jeziorny's analysis, Ozawa's analysis, and Mo's approach were used to investigate nonisothermal cold crystallization progress of TPER PI and co‐PI. Activation energy ΔEnon for TPER PI and co‐PI were found to be 247 and 193 kJ mol−1 by Kissinger equation. The result indicated that co‐PI exhibited lower crystallization rate than TPER PI when isothermally crystallized from melt, but higher crystallization rate under cold nonisothermal crystallization progress. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Microstructure and nonisothermal cold crystallization of PLA composites based on silver nanoparticles and nanocrystalline cellulose

Poly(lactic acid) (PLA) based high performance nanocomposites, were prepared using an innovative combination of nanocrystalline cellulose and silver nanoparticles. Binary and ternary systems were prepared by solvent casting process and their morphological, mechanical and thermal responses were investigated. Pristine (CNC) and surfactant modified cellulose nanocrystals (s-CNC) and silver (Ag) nanoparticles were used, and the effect of cellulose crystal nano-dimension, cellulose modification, and the combination of cellulose nanostructures with silver nanoparticles, was investigated. The important industrial problem of slow crystallization of PLA was addressed by the use of cellulose nanocrystals as biobased nucleating agents and the nonisothermal cold crystallization behaviour of reinforced binary and ternary systems was studied.The presence of surfactant on the nanocrystal surface favoured the dispersion of CNC in the PLA matrix while the thermal investigations and the nonisothermal crystallization studies underlined the ability of s-CNC to act as nucleation agent in both binary and ternary nanocomposites.

Effect of ZnO nanofillers treated with triethoxy caprylylsilane on the isothermal and non-isothermal crystallization of poly(lactic acid)

The crystallization of PLA-silane surface-treated ZnO nanocomposites was investigated by DSC and compared to that of neat PLA. Several modes of crystallization were considered: isothermal and non-isothermal cold crystallization and also isothermal and non-isothermal melt crystallization. The kinetics of cold crystallization were studied using different methods, namely the Avrami and Ozawa-Flynn-Wall models, to calculate activation energies and kinetic constants. In contrast to what is typically observed when the foreign particles are added in a polymer matrix, the silane surface-treated ZnO delayed the crystallization of PLA and made it more difficult to start. The nucleation activity of the ZnO nanoparticles, ϕ, was calculated and found to be greater than 1 (ϕ = 1.7). This indicated that ZnO played an anti-nucleating role in the crystallization of PLA nanocomposites. This effect has been linked mainly to the interactions between the silane groups onto the surface of nanoparticles and PLA macromolecules. These interactions which reduce the mobility of polymer chains have been evidenced by rheological experiments.

Crystallization Kinetics of Linear and Long-Chain-Branched Polylactide

In this study, the non-isothermal cold crystallization and isothermal melt crystallization of both linear and long-chain-branched (LCB) polylactide (PLA) were investigated using a differential scanning calorimeter (DSC). Talc was used as a nucleating agent to promote crystallization. The effects of chain branching on PLA’s cold crystallization kinetics at different heating rates and on PLA’s melt crystallization kinetics under different temperatures were studied by using Avrami analysis. The results showed that LCB-PLAs have faster cold and melt crystallization rates than those of linear PLA, since branched chains can play a role of nucleating site. Talc is a powerful nucleating agent, especially for linear PLA, either in cold crystallization or melt crystallization process. It was seen that addition of talc to PLA improves the crystallinity of PLA samples with more linear structure, more effectively because of its role of crystal nucleation. In PLA samples with more branched structure, talc has the least effect on crystallinity suggesting that the branched structure dominated crystallization already regardless of the presence of talc. Isothermal melt crystallization experimental results also showed that branched PLAs crystallized much faster than linear PLA and talc could increase the melt crystallization rate of linear PLA, but not that of PLA with a more branched structure.

Isothermal and Nonisothermal Cold Crystallization Behaviors of Biodegradable Poly(l-lactide)/Octavinyl-Polyhedral Oligomeric Silsesquioxanes Nanocomposites

Isothermal and nonisothermal cold crystallization behaviors of biodegradable poly(l-lactide) (PLLA)/octavinyl-polyhedral oligomeric silsesquioxanes (ovi-POSS) nanocomposites at low ovi-POSS loadings were investigated in this work. For both neat PLLA and its nanocomposites, the overall isothermal cold crystallization rates increase with increasing crystallization temperature; moreover, the overall isothermal cold crystallization rates of PLLA increase with increasing the ovi-POSS loading in the nanocomposites relative to neat PLLA, indicative of the nucleating agent effect of ovi-POSS. Crystallization mechanism and crystal structure of PLLA remain unchanged despite the ovi-POSS loading. For the nonisothermal cold crystallization, the crystallization process of PLLA is accelerated by increasing both heating rate and the ovi-POSS loading. The Ozawa equation failed to fit the crystallization process, while the Tobin equation could describe it well. The activation energies of nonisothermal cold crystallization were calculated by the Kissinger method, which increase with increasing the ovi-POSS loading in the nanocomposites relative to neat PLLA.

Crystallization behaviors of biodegradable poly( l-lactic acid)/graphene oxide nanocomposites from the amorphous state

Crystallization behaviors of biodegradable poly( l-lactic acid) (PLLA)/graphene oxide (GO) nanocomposites at different GO loadings from the amorphous state were investigated in detail in this work. During the nonisothermal cold crystallization, the crystallization peak temperature of PLLA shifts to low temperature range in the nanocomposites with increasing the GO loading relative to neat PLLA despite heating rate; moreover, the overall nonisothermal cold crystallization has been accelerated with increasing heating rate for both neat PLLA and its nanocomposites. In addition, the variations of crystallization enthalpy of PLLA during isothermal and nonisothermal cold crystallization processes were also discussed. Relative to neat PLLA, the overall isothermal cold crystallization rate of PLLA is increased with increasing the GO loading in the nanocomposites despite crystallization temperature. The crystallization rate becomes faster with increasing crystallization temperature, while the crystallization mechanism and crystal structure remain unchanged for both neat PLLA and its nanocomposites.

Nonisothermal cold crystallization of poly(ethylene terephthalate)

Abstract