Secondary Nucleation Theory Research Articles

Isothermal Crystallization, Melting Behavior and Mechanical Properties of Polyethylene Terephthalate (PET) and Reorganized PET (RPET)

Analysis of the isothermal crystallization kinetics of polyethylene terephthalate (PET) and reorganized PET was carried out using differential scanning calorimetry (DSC). Reorganization of PET process results in material with widely different organizations, structures, and morphologies of their polymer chains and different material properties. In thermal study of PET and RPET, the Avrami equation explained the primary stage of the isothermal crystallization of both PET and RPET. In the crystallization process of PET and RPET, the secondary crystallization occurred simultaneously with the primary crystallization and the two processes obeyed different Avrami time dependences. Lauritzen–Hoffman’s (L-H) secondary nucleation theory and the Lauritzen Z-test explained the microscopic description of the crystallization kinetics. The L-H analysis revealed that both PET and RPET crystallization followed regime I to II transitions at temperatures between 194 and 240 The folding surface free energies of RPET, determined from the Lauritzen–Hoffman equation, were = 61.2 erg/cm2 and 64.9 erg/cm2; and the works of chain folding were q = 7.38 Kcal/mol and 7.83 Kcal/mol, for regime I and regime II, respectively, whereas for PET they were = 50.2 erg/cm2 and 70.4 erg/cm2; and the works of chain folding were q = 6.06 Kcal/mol and 8.49 Kcal/mol, for regime I and regime II, respectively. Polarized optical microscopy observations showed that different morphologies were developed in RPET than PET when crystallized from the melt. The mechanical properties and morphology of PET and RPET were studied using a universal tensile machine and atomic force microscopy, respectively. The morphological study, the mechanical properties and the thermal behavior of RPET confirmed that the RPET had an enhanced crystallization rate and mechanical parameters.

Biobased nucleation agents for poly-L-(lactic acid) — Effect on crystallization, rheological and mechanical properties

In the present work, the nucleating aptitude for poly-L-(lactic acid) (PLLA) of several biobased nanoparticles (NPs) with different morphologies and surface properties, including cellulose nanofibrils with and without lignin (LCNFs and CNFs) as well as cellulose, chitin and starch nanocrystals (CNCs, ChNCs and SNCs), was investigated. A single melt-processing step using a small amount of poly(ethylene glycol) (PEG) as carrier for the NPs was adopted to prepare films with the same nanofiller content of 1 wt%. The nucleation efficiency was investigated by differential scanning calorimetry using Avrami's and Lauritzen–Hoffman's secondary nucleation theory. The crystallization half-time was found to change considerably according to the morphology and surface properties of the NPs, with the lowest time observed for CNFs and CNCs, followed by ChNCs, SNCs and LCNFs. Comparing the surface energy components of the different nucleating agents, it was found that the nanofiller with the highest γp had the lowest t1/2 and demonstrated the most effective nucleating aptitude. The evolution of the melt rheological properties of the different compositions, and the mechanical and optical properties of the films with and without a short annealing treatment were also studied.

Effect of ionic interactions on crystallization of star telechelic poly(l-lactide) ionomers

Effect of ionic interactions on crystallization properties of star telechelic poly(l-lactide) ionomers was studied by performing isothermal crystallization experiments. We report a comparison between star PLLA and star telechelic PLLA ionomer. It was evident that the ionic interactions in the ionomer affected the crystallization rate as well as modified the spherulitic morphology. Employing Avrami analysis on the isothermal crystallization data we show that star PLLA shows faster crystallization at higher temperatures (closer to melting point) than the star PLLA ionomer. However, a reversal of this trend in crystallization is observed at lower temperatures (closer to glass transition temperature). The origin of high temperatures behaviour comparison is explained in terms of the higher secondary nucleation barrier for ionomers using the famous Lauritzen- Hoffman secondary nucleation theory. However, we point out that the assumption of equal diffusion barrier in this theory limits its range of applicability. In order to explain the low temperature behaviour, we invoke the activation energy comparison in PLLA and ionomer using rheological studies. We show that although the presence of ions in the polymer impede the secondary nucleation process, its effect is only observed at higher temperatures.

Tannic Acid-Induced Surface-Catalyzed Secondary Nucleation during the Amyloid Fibrillation of Hen Egg-White Lysozyme.

Amyloid fibrillation by hen egg white lysozyme under the influence of tannic acid was investigated by atomic force microscopy and fluorescence spectroscopy. Tannic acid was found to be able to induce the formation of amyloid fibrils with an interesting mixed morphology. Such morphology features with the existence of areas of thickening alternating with areas of normal height. This novel modulation effect of tannic acid on amyloid fibrillation was interpreted by the established surface-catalyzed secondary nucleation theory. We further performed a fluorescence quenching study to investigate the intermolecular interaction between tannic acid and lysozyme. The results support that lysozyme and tannic acid interact with each other mainly through hydrophobic interactions. We also discussed why hydrogen-bonding interaction is not a dominant factor in the interaction between tannic acid and lysozyme though tannic acid contains a significant amount of hydroxyl groups. Our work provides new insight into the effect of tannic acid, a well-known amyloid inhibitor, on amyloid fibrillation.

Non-isothermal crystallization behavior, rheological properties and morphology of poly(ε-caprolactone)/graphene oxide nanosheets composite films

In the present study, the non-isothermal crystallization behavior of solution cast poly(ε-caprolactone) (PCL)/graphene oxide (GO) nanocomposite (PCL/GO) films was investigated at a different cooling rate. The loading concentration of GO (0.25–1% w/w) increased the crystallization temperature (Tc) of PCL matrix at a constant cooling rate. Various model equations were tested to describe the non-isothermal crystallization kinetics of the PCL/GO blend films. The results indicated that the Avrami analysis modified by Jeziorny equation described well the non-isothermal crystallization kinetics of tested samples. The crystallization activation energy was calculated applying the differential isoconversional method of Friedman, and the values ranged between −250 and −100kJ/mol with an expected decrease of the energy in depending on the quantity of% GO content. Hoffman-Lauritzen secondary nucleation theory parameters, Kg and U* were evaluated using the isoconversional approach of Vyazonvkin and Sbirazuoli, highlighting a shift for the change of regime I/regime II from 305 to 313K in dependence of GO content. Oscillatory rheology of PCL/GO blends on melt exhibited a transition of liquid-like to solid-like property. The mechanical strength of the blend improved significantly when the GO concentration was maintained at 0.75wt% or more. The peak height of the AFM confirmed the doping of GO into the PCL matrix.

Influence of graphene nanosheets on stereocomplex crystallization behaviors of star‐shaped poly (D(L)‐lactide) stereoblock copolymer

The nanocompsites of star‐shaped poly(D‐lactide)‐co‐poly(L‐lactide) stereoblock copolymers (s‐PDLA‐PLLA) with two‐dimensional graphene nanosheets (GNSs) were prepared by solution mixing method. Crystallization behaviors were investigated using differential scanning calorimetry, polarized optical microscopy, and wide angle X‐ray diffraction. The results of isothermal crystallization behaviors of the nanocompsites clearly indicated that the GNS could remarkably accelerate the overall crystallization rate of s‐PDLA‐PLLA copolymer. Unique stereocomplex crystallites with melting temperature about 207.0°C formed in isothermal crystallization for all samples. The crystallization temperatures of s‐PDLA‐PLLAs shifted to higher temperatures, and the crystallization peak shapes became sharper with increasing GNS contents. The maximum crystallization temperature of the sample with 3 wt% GNS was about 128.2°C, ie, 15°C higher than pure s‐PDLA‐PLLA. At isothermal crystallization processes, the halftime of crystallization (t0.5) of the sample with 3 wt% GNS decreased to 6.4 minutes from 12.9 minutes of pure s‐PDLA‐PLLA at 160°C.The Avrami exponent n values for the nanocomposites samples were 2.6 to 3.0 indicating the crystallization mechanism with three‐dimensional heterogeneous nucleation and spherulites growth. The morphology and average diameter of spherulites of s‐PDLA‐PLLA with various GNS contents were observed in isothermal crystallization processes by polarized optical microscopy. Spherulite growth rates of samples were evaluated by using combined isothermal and nonisothermal procedures and analyzed by the secondary nucleation theory. The results evidenced that the GNS has acceleration effects on the crystallization of s‐PDLA‐PLLA with good nucleation ability in the s‐PDLA‐PLLA material.

Transcrystallization of polypropylene in the presence of polyester/cellulose nanocrystal composite fibers

Pristine cellulose nanocrystal (CNC) and acetylated one (aCNC) were used as the modifier to change the surface properties of poly(trimethylene terephthalate) (PTT) fibers for the transcrystallization study of polypropylene (PP). The results reveal that all three kinds of fibers, including the neat PTT, PTT/CNC and PTT/aCNC ones can induce PP transcrystallization. But the PTT/aCNC fiber-filled PP system shows the most remarkable transcrystallization behavior because of the highest nucleation density of PTT/aCNC fiber. The long period and lamellar thickness of two composite fiber-filled PP systems increase as compared with the neat PTT fiber-filled one, which is caused by the reduced system undercooling and higher surface energy level of composite fibers. Accordingly, the former two systems show the lower transcrystal growth rates than the latter, which is further analyzed by the secondary nucleation theory. This work can provide useful information on the control of PP transcrystallization using the CNC-filled polyester composite fibers.

Lignin-coated cellulose nanocrystals as promising nucleating agent for poly(lactic acid)

We report the effect of lignin-coated cellulose nanocrystals (L-CNCs) on the crystallization behavior of poly(lactic acid) (PLA). PLA/L-CNC nanocomposites were prepared by melt mixing, and the crystallization behavior of PLA was investigated using differential scanning calorimetry. Isothermal crystallization data were analyzed using Avrami and Lauritzen–Hoffman secondary nucleation theory, while the equilibrium melting temperature was determined using the nonlinear Hoffman–Weeks method. The lignin-coated cellulose nanocrystals acted as a nucleating agent and significantly increased the rate of crystallization and degree of crystallinity of PLA in PLA/L-CNC nanocomposites. The Avrami exponent, n, increased in the presence of L-CNCs, displaying a conversion from lamellar morphology to two-dimensional crystal growth. PLA/L-CNC nanocomposites also gave lower values of the nucleation parameters, $$K_{\text{g}}$$ and σ e, due to a reduction in the activation energy for nucleation.

Thermal properties and crystallization kinetics of poly(butylene suberate)

In this work, we synthesized poly(butylene suberate) (PBSub) with a weight average molecular weight of 3.64 × 104 g/mol from the monomers of butanediol and suberic acid via a two-step melt polycondensation method. The basic thermal behaviors, overall isothermal melt crystallization kinetics, crystal structure, spherulitic morphology and growth, thermal stability, and hydrolytic degradation of PBSub were systematically investigated for the first time. PBSub has a low glass transition temperature of about −61 °C, a melting point of 55.2 °C, and an equilibrium melting point of 61.4 °C. The overall isothermal melt crystallization kinetics of PBSub was investigated at different crystallization temperature values and analyzed by the Avrami equation. PBSub has an average Avrami exponent value of about 3, suggesting that the crystallization mechanism of PBSub may correspond to three-dimensional truncated sphere growth with athermal nucleation. An obvious spherulitic morphology was observed for PBSub, and the spherulitic growth rates decrease with increasing crystallization temperature. PBSub exhibits a crystallization regime II to regime III transition on the basis of the secondary nucleation theory. The crystal structure study reveals that PBSub is highly crystalline, presenting strong diffraction peaks and a great crystallinity of about 55%. The thermogravimetric analysis study demonstrates that PBSub has both a high decomposition temperature at 5 wt% weight loss of about 377 °C and a high temperature at the maximum degradation rate of about 421 °C, suggesting its good thermal stability. PBSub may undergo a hydrolytic degradation, which may be of interest for its end use as a degradable material in some special application fields.

Isoconversional kinetic analysis of DSC data on nonisothermal crystallization: Estimation of Hoffman-Lauritzen parameters and thermal transitions in PET/MMT nanocomposites

The differential isoconversional method of Friedman is applied to non-isothermal melt crystallization DSC data to obtain effective activation energy ΔE. In comparison to neat PET, ΔE of intercalated 93A MMT clay nanocomposites (PCNs) decreased and highly dependent on the clay content. Hoffman-Lauritzen (H–L) secondary nucleation theory parameters, Kg and U* were evaluated using isoconversional approach of Vyazovkin and Sbirrazzuoli. Crystallization regime transition from regime III is observed at 190°C for neat PET, which shifted to higher temperature range 200°C–208 °C for PCNs. The Kg parameters for both regimes for PET are consistent with our isothermal experiments and reported in literature. However, the Kg values of nanocomposites are highly sensitive to the temperature dependent nucleation activity and ΔE of PET chain motion in melt and are not very much comparable with our isothermal results. Nevertheless, the observed results clearly indicate that the 93AMMT clay layers predominantly act as heterogeneous nucleating sites.

Miscible blends of polylactide and poly(methyl methacrylate): Morphology, structure, and thermal behavior

ABSTRACTThe miscibility of polylactic acid (PLA) and atactic poly(methyl methacrylate) (PMMA) blends is investigated as a function of composition. The blends quenched from the melt show the presence of a single glass transition temperature dependent on the composition. The equilibrium melting temperature is determined using the Hoffman‐Weeks method and a depression is observed with increasing content of the PMMA component. The PLA spherulite growth rate and the overall isothermal crystallization rates decrease with increasing the amount of the amorphous component. The increase of the long period value as a function of the PMMA content in the blend is due to the segregation of PMMA component in the amorphous PLA interlamellar regions. The Lauritzen‐Hoffman secondary nucleation theory analysis shows that the segregation of the PMMA in the interlamellar region induces an increase in the surface entropy of folding. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 1168–1177

Evaluation of polyesters from renewable resources as alternatives to the current fossil-based polymers. Phase transitions of poly(butylene 2,5-furan-dicarboxylate)

Poly(butylene 2,5-furan dicarboxylate) (PBF) is an alipharomatic polyester that can be prepared using monomers derived from renewable resources such as 2,5-furan dicarboxylic acid and 1,4-butanediol. In the present work the thermal behavior of PBF was studied. Multiple melting was observed during heating traces of samples isothermally crystallized from the melt using differential scanning calorimetry (DSC). The wide angle X-ray diffraction (WAXD) patterns did not reveal the presence of a second crystal population, or a crystal transition upon heating. DSC study showed that the phenomena are closely related to recrystallization. Temperature modulated DSC (TMDSC) tests indeed evidenced enhanced recrystallization. The equilibrium melting point was estimated to be 184.5 °C using the linear Hoffman–Weeks extrapolation. The heat of fusion of the pure crystalline polymer was found equal to 129 J/g or (27.35 kJ/mol), a little lower than that of PBT. The Lauritzen–Hoffman secondary nucleation theory was used and the surface energy values and the work of chain folding were found to be comparable to those of PBT, but quite lower than those of poly(ethylene terephthalate) (PET). The non-isothermal crystallization on cooling and the cold-crystallization of quenched samples were also studied. Condensed spherulites were observed on isothermal crystallization under large supercoolings by using polarized optical microscopy (POM), while the spherulites turned to ring-banded morphology at higher temperatures. In every case the nucleation density was high.

Crystallization Regimes and Spherulitic Morphology of Poly(trimethylene terephthalate/isophthalate) Random Copolyesters

The crystallization regimes and spherulitic morphology of poly (trimethylene terephthalate/isophthalate) (TI) random copolyesters were studied in this work. A hot stage polarizing microscope was used to observe morphology and measure growth rate of the spherulite of TI copolyesters. Lauritzen-Hoffman secondary nucleation theory was applied to investigate crystallization kinetics and regimes of TI copolyesters. Results show that the spherulitic growth rate decreased with an increase in isophthalic acid content of the copolyesters. The analysis of Lauritzen-Hoffman secondary nucleation theory shows that regime I, II, and III were observed in TI11 and TI21. Regime III was observed in TI29. The spherulitic morphology of TI11, TI21, and TI29 changed from elliptical-shaped spherulite to irregular spherulite and then to normal spherulite at the regime transitions.

Isothermal crystallization kinetics of poly(trimethylene terephthalate)/multiwall carbon nanotubes composites

The isothermal crystallization kinetics of poly(trimethylene terephthalate) (PTT) in the presence of varying amounts of multiwall carbon nanotubes (MWCNT) have been investigated using differential scanning calorimetry (DSC) and analyzed using Avrami and secondary nucleation theory. Polarized light microscopy (PLM) was used to study the crystal morphology of PTT/MWCNT composites. The results showed that the presence of MWCNTs in PTT acted as an effective nucleating agents and lead to the spherulitic morphology. The decrease in the spherulites size on MWCNT addition was observed by polarized light microscopy. Using values of transport parameters ( $$ U* = 1500{\text{ cal mol}}^{ - 1} , \, \Updelta T =T_{\text{g}} - 30\, $$ °C) together with experimentally determined values of equilibrium melting temperature [ $$ T^{\text{o}}_{\text{m}} $$ (245.2 °C)] and glass transition temperature [ $$ T_{\text{g}} $$ (45 °C)], the nucleation parameter, $$ K_{\text{g}} $$ and $$ \sigma_{\text{e}} $$ were determined for PTT and PTT/MWCNT composites according to Lauritzen–Hoffman theory. The decrease in the values of these parameters on MWCNT addition is in agreement with the fact that the rate of crystallization of PTT increased in the presence of MWCNTs.

Temperature dependences of solid structure and properties of biodegradable poly(butylene succinate-co-terephthalate) (PBST) copolyester

In this paper, studies of the temperature dependence for spherulitic growth of PBST copolyester bearing 70 mol% butylene terephthalate units (named as PBST-70) ranged from 70 to 170 °C were first reported based on the Lauritzen–Hoffman secondary nucleation theory. The results showed that maximum spherulitic growth rate of PBST-70 was obtained under crystallization temperature of 90 °C, and more perfect spherulites were formed via increasing isothermal crystallization temperature by POM measurement. The classical regime I → II and regime II → III transitions occurred at the temperatures of 150 and 110 °C, respectively, using the empirical universal values of U* = 6300 J mol−1 and T∞ = Tg − 30 K. Moreover, the effects of isothermal crystallization temperature on crystal lamellar thickness, thermal and tensile properties of PBST-70 were systematically investigated by small angle X-ray scattering, differential scanning calorimeter, and strength tester. The results indicated that the crystal lamellar thickness increased by increasing isothermal crystallization temperature. The endothermic peak shifted to higher temperature and the tensile properties of PBST-70 were enhanced under higher isothermal crystallization temperature.

Crystallization Behavior of Long-Chain Branching Polylactide

The crystallization behavior of long-chain branched (LCB) poly(l-lactide) (PLLA), which were successfully prepared by successive functional group reactions, was studied by nonisothermal and isothermal methods in a wide temperature range. The density of the nuclei for LCB samples during crystallization was much higher than that for linear PLLA. According to qualitative information about the chain topologies of the branched PLLAs, obtained by a combination of linear viscoelasticity and branch-on-branch (BOB) dynamic modeling, it should be the backbones of LCB that are able to act as nuclei and thus markedly enhance the crystallization rate of PLLA. Moreover, a kinetic analysis of crystallization was performed using secondary nucleation theory.

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.

Crystallization of novel poly(ε-caprolactone)-block-poly(propylene adipate) copolymers

Poly(e-caprolactone)-block-poly(propylene adipate) (PCL-block-PPAd) copolymers were prepared using a combination of polycondensation and ring opening polymerization of e-CL. 1H-NMR and 13C-NMR spectroscopy showed that the prepared copolymers were block. Also, the copolymer composition was calculated from NMR spectra and was found similar to the feeding ratio. The copolymers formed PCL crystals as was proved by WAXD. The crystallization rates and degree of crystallinity, measured from DSC crystallization experiments, decreased with PPAd content. The equilibrium melting points of PCL were estimated applying the Hoffmann–Weeks method and the observed melting point depression was analyzed using the Nishi–Wang equation which showed that there is some miscibility of the copolymer segments. Isothermal crystallization experiments after self-nucleation were performed to distinguish the nucleation and crystal growth stages during isothermal crystallization. The secondary nucleation theory was then used and the obtained data for crystallization rates, estimated from the inverse of the crystallization half-times, were analyzed. The resulting values for nucleation constant K g, and also for the surface free energies and work of chain folding, increased with PPAd content due to topological restrictions.

Impact of the nature and shape of cellulosic nanoparticles on the isothermal crystallization kinetics of poly(ε-caprolactone)

Polycaprolactone (PCL)/cellulose nanocomposites were prepared by mixing PCL with surface modified sisal nanowhiskers (CNW) and microfibrillated cellulose (MFC) extracted from sisal fibers. The influence of cellulosic nanoparticles on the crystallization behavior of PCL was investigated by differential scanning calorimetry. Isothermal crystallization data were modeled with Avrami’s kinetics, Lauritzen–Hoffman secondary nucleation theory and equilibrium melting points were determined with the Hoffman–Weeks method. The cellulose nanoparticles, acting as nucleating agents, drastically accelerate the crystallization of PCL while depressing its equilibrium melting by 9–10 °C. The crystallization of MFC-nanocomposites is slightly faster than that of CNW-nanocomposites, in agreement with the slightly lower bulk activation energy for crystallization and nucleation parameter in the former. The results are discussed based on the differences of specific surface area and surface chemistry of nanoparticles, as well as the confinement phenomenon.

An overview on the processing of polymers growth rate data and on the methods to verify the accuracy of the input parameters in crystallization regime analysis

This work reviews criteria for the successful application of regime analysis to polymers and also discusses the influence of accuracy of input variables on the results. Despite that it has often been stated that the uncertainty in the input parameters remarkably affects the trustworthiness of the outcomes of the regime analysis, the literature offers on the subject only a fragmentary information and there is no paper looking over all the effects of accuracy of the input parameters. Here the influence of errors in input parameters has been investigated and methods to test the reliability of thermodynamic outcomes have been discussed. Mathematical ways to ascertain the accuracy of the input parameters consist in comparisons between the growth rates expressed by the Hoffman–Lauritzen equation and their derivatives generated by means of the output of the regime analysis. These comparisons, under the hypothesis of validity of the secondary nucleation theory, allow excluding the presence of remarkable errors in input values and variables.