The crystallization of tough thermoplastic resins in the presence of carbon fibers

The crystallization kinetics of the thermoplastic resins poly(phenylene sulfide) (PPS) and poly(aryl-ether-ether-ketone) (PEEK) in the presence and in the abscence of carbon fibers was studied. How carbon fiber surfaces in composites affect the crystallization of tough thermoplastic polymers that may serve as matrix resins were determined. The crystallization kinetics of such substances can provide useful information about the crystallization mechanisms and, thus, indicate if the presence of carbon fibers cause any changes in such mechanisms

Isothermal Crystallization Kinetics of In Situ Photo and Thermo Aged Poly(Ethylene Oxide) Using PhotoDSC

Isothermal crystallization of a high molecular weight PEO (Mw= 4.000.000) has been investigated using photoDSC. Combining light irradiation, heating and DSC analysis, photoDSC demonstrates a good capability to follow the in situ photo and thermo aging of semi crystalline polymers. Isothermal crystallization of PEO has been performed at 55°C. After aging at different temperatures ranging from 0 to 90°C and for various periods of time, the kinetics of this crystallization has been found fitting Avrami theory. Avrami exponent, n, was found between 0.9 and 1.4 revealing a one-dimensional growth process. It was also found that isothermal crystallization rate (i.e. reciprocal crystallization half-time) was time exposure, aging temperature and light intensity dependent which makes this kinetics parameter a good indicator to follow and to compare the degradation of the semi-crystalline polymers

A study of the applicability of nucleation theory to quasi-thermodynamic transformations of second and higher Ehrenfest-order

Transient and steady-state phenomena in temperature, stress, and electric, field intensity in ferroelectric polymers were investigated. The application and extension of the theory in the primary stage to the polarization domain nucleation and growth in ferroelectric polymers were developed. The kinetics of this growth were investigated. Expressions describing nucleation under the influence of an electric field were found through the expansion of the Gibbs' free energy in a Maclaurin series. The series was expanded in the electric field strength rather than the degree of undercooling. The resulting expressions were manipulated and applied to the case of nucleation of polarized domains in ferroelectric polymers. The kinetics of the nucleation and growth of polarized domains are also investigated. This was accomplished through the modification of the Johnson-Mehl-Avrami treatment of crystallization kinetics to be applicable to the growth of polarization domains in ferroelectric materials

LaRC TPI 1500 series polymers

The crystallization behavior and the melt flow properties of two batches of 1500 series LaRC-TPI polymers from Mitsui Toatsu Chemicals (MTC) were investigated. The characterization methods include Differential Scanning Calorimetry, the x ray diffractography and the melt rheology. The as-received materials possess initial crystalline melting peak temperatures of 295 and 305 C, respectively. These materials are less readily recrystallizable at elevated temperatures when compared to other semicrystalline thermoplastics. For the samples annealed at temperatures below 330 C, a semicrystalline polymer can be obtained. On the other hand, a purely amorphous structure is realized in the samples annealed at temperatures above 330 C. Isothermal crystallization kinetics were studied by means of the simple Avrami equation. The viscoelastic properties at elevated temperatures below and above glass transition temperature of the polymers were measured. Information with regard to the molecule sizes and distributions in these polymers were also extracted from melt rheology

Controlling the isothermal crystallization of isodimorphic PBS-ran-PCL random copolymers by varying composition and supercooling

In this work, we study for the first time, the isothermal crystallization behavior of isodimorphic random poly(butylene succinate)-ran-poly(e-caprolactone) copolyesters, PBS-ran-PCL, previously synthesized by us. We perform nucleation and spherulitic growth kinetics by polarized light optical microscopy (PLOM) and overall isothermal crystallization kinetics by differential scanning calorimetry (DSC). Selected samples were also studied by real-time wide angle X-ray diffraction (WAXS). Under isothermal conditions, only the PBS-rich phase or the PCL-rich phase could crystallize as long as the composition was away from the pseudo-eutectic point. In comparison with the parent homopolymers, as comonomer content increased, both PBS-rich and PCL-rich phases nucleated much faster, but their spherulitic growth rates were much slower. Therefore, the overall crystallization kinetics was a strong function of composition and supercooling. The only copolymer with the eutectic composition exhibited a remarkable behavior. By tuning the crystallization temperature, this copolyester could form either a single crystalline phase or both phases, with remarkably different thermal propertiesPeer ReviewedPostprint (published version

Influence of chain topology (cyclic versus linear) on the nucleation and isothermal crystallization of poly(L-lactide) and poly(D-lactide)

In this paper, ring closure click chemistry methods have been used to produce cyclic c-PLLA and c-PDLA of a number average molecular weight close to 10 kg/mol. The effects of stereochemistry of the polymer chains and their topology on their structure, nucleation and crystallization were studied in detail employing Wide Angle X-ray Scattering (WAXS), Small Angle X-ray Scattering (SAXS), Polarized Light Optical Microscopy (PLOM) and standard and advanced Differential Scanning Calorimetry (DSC). The crystal structures of linear and cyclic PLAs are identical to each other and no differences in superstructural morphology could be detected. Cyclic PLA chains are able to nucleate much faster and to produce a higher number of nuclei in comparison to linear analogues, either upon cooling from the melt or upon heating from the glassy state. In the samples prepared in this work, a small fraction of linear or higher molecular weight cycles was detected (according to SEC analyses). The presence of such “impurities” retards spherulitic growth rates of c-PLAs making them nearly the same as those of l-PLAs. On the other hand, the overall crystallization rate determined by DSC was much larger for c-PLAs, as a consequence of the enhanced nucleation that occurs in cyclic chains. The equilibrium melting temperatures of cyclic chains were determined and found to be 5 ºC higher in comparison with values for l-PLAs. This result is a consequence of the lower entropy of cyclic chains in the melt. Self-nucleation studies demonstrated that c-PLAs have a shorter crystalline memory than linear analogues, as a result of their lower entanglement density. Successive self-nucleation and annealing (SSA) experiments reveal the remarkable ability of cyclic molecules to thicken, even to the point of crystallization with extended collapsed ring conformations. In general terms, stereochemistry had less influence on the results obtained in comparison with the dominating effect of chain topology.“UPV/EHU Infrastructure: INF 14/38”; “Mineco/FEDER: SINF 130I001726XV1/Ref: UNPV13–4E–1726” and “Mineco MAT2014-53437-C2-P”, 'Ministerio de Economia y Competitividad (MINECO), code: MAT2015-63704-P (MINECO/FEDER, UE) and by the Eusko Jaurlaritza (Basque Government), code: IT-654-13. O.C acknowledges financial support from the European Commission and Région Wallonne FEDER program (Materia Nova) and OPTI²MAT program of excellence, by the Interuniversity Attraction Pole Program (P7/05) initiated by the Belgian Science Policy office and by the FNRS-FRFC. OC is Research Associate of the F.R.S.-FNRS. Organic Synthesis and Mass Spectrometry Laboratory thanks F.R.S.-FNRS for the financial support for the acquisition of the Waters QToF Premier and Synapt-G2Si mass spectrometers and for continuing support. Finally, all authors would like to acknowledge Research and Innovation Staff Exchange (RISE) H2020-MSCA-RISE-2017-778092, project BIODEST for promoting cooperation between the Mons team and the UPV/EHU team

The Crystallization Kinetics in Semicrystalline Nanocomposites

Růst krystalů zásadně ovlivňuje morfologii a tím také mechanické vlastnosti semikrystalických polymerů. Tato PhD práce přináší alternativní pohled na popis kinetiky krystalizace v polyolefinech plněných slabě interagujícími částicemi. V nanokompozitních materiálech vysoký specifický povrch plniva i při nízkých plněních zásadně ovlivňuje dynamiku řetězců. V blízkosti povrchu plniva začíná hrát významnou roli zpomalená reptace způsobená jak vzájemnými interakcemi plnivo-polymer tak prostorovým omezením mezi nanočásticemi. Růst krystalů byl zkoumán pomocí polarizovaného optického mikroskopu vybaveného horkým stolkem. Výsledky byly korelovány s teoretickými modely a rozsáhlými počítačovými simulacemi na molekulární úrovni. Pozorovaný pokles rychlosti růstu sférolitů v závislosti na obsahu plniva a molekulové hmotnosti matrice je interpretován na základě imobilizační teorie, tedy, zpomalení reptačního pohybu.The crystal growth greatly affects morphology and, thus, mechanical properties of semicrystalline polymers. In this PhD work, the effect of adding high specific surface area silica nano-filler on the crystallization kinetics of linear polyethylene was investigated. In nanocomposites, high specific surface area is able to alter the chain dynamics even at very low filler loadings. It is suggested that in the vicinity of the filler surface, polymer chains exhibit retarded reptation motion due to the chain immobilization caused by either the filler-polymer interaction or by chain confinement between closely packed nanoparticles. The polarized optical microscope equipped with a hot stage was employed to measure the spherulites growth rates in the medium crystallization regime II. It was shown that even weak interaction between PE chains and silica nano-filler above glass transition temperature leads to the substantial decrease of the spherulite growth rates. The measured data are correlated with predictions based on the theoretical models and computer simulations of molecular dynamics in the crystallizing nanocomposite. The observed decrease of spherulites growth rates, G, in dependence on both the silica nano-filler content and polyethylene molecular weight is interpreted utilizing the immobilization theory, thus, reduced reptation motion.

Correlation between Grafting Density and Confined Crystallization Behavior of Poly(ethylene glycol) Grafted to Silica

The interfacial interactions of polymer-nanoparticles have dramatical effects on the crystallization behavior of grafted polymers. In this study, methoxy polyethylene glycol (MPEG) (molecular weights 750, 2000 and 4000 g mol−1) was grafted onto amino-modified nanosized silica (SiO2-NH2) by the “grafting to” method. The effects of the grafting density and molecular weight on the confined crystallization of grafted MPEG (MPEG-g-SiO2) were systematically investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and wide-angle X-ray scattering (WAXS). It was found that confinement effects are stronger when lower molecular weights of grafted MPEG are employed. These grafted MPEG chains are more difficult to stretch out on SiO2-NH2 surfaces than when they are free in the bulk polymer. Both crystallization temperature (Tc) and crystallinity of grafted MPEG chains decrease with reductions of grafting density. Additionally, covalent bonding effects and interfacial interaction confinement effects are strengthened by the decrease in grafting density, leading to an increase in decomposition temperature and to the disappearance of the self-nucleation Domain (i.e., Domain II), when self-nucleation experiments are performed by DSC. Overall isothermal crystallization kinetics was studied by DSC and the results were analyzed with the Avrami equation. An Avrami index of n≈3 was obtained for neat MPEG (indicating that instantaneous spherulites are formed). However, in the case of MPEG-g-SiO2 with the lowest grafting density, the Avrami index of (n) was less than 1 (first order kinetics or lower), indicating that nucleation is the determining factor of the overall crystallization kinetics, a signature for confined crystallization. At the same time, the crystallization from the melt for this MPEG-g-SiO2 with the lowest grafting density occurs at Tc ≈-30 ºC, a temperature close to the glass transition temperature (Tg) of MPEG, indicating that this confined MPEG crystallizes from homogeneous nuclei.This project was supported by the National Natural Science Foundation of China (21574141) and the Ministry of Science and Technology of China (2017YFE0117800). The authors gratefully acknowledge the funding of project BIODEST, Research and Innovation Staff Exchange (RISE) H2020-MSCA-RISE-2017-778092. The authors thank beamline BL16B1 (Shanghai Synchrotron Radiation Facility) for providing the beam time and helps during experiments

Polymer crystallinity and crystallization kinetics via benchtop 1 H NMR relaxometry: Revisited method, data analysis, and experiments on common polymers

Semi-crystalline polymers play an enormously important role in materials science, engineering, and nature. Two-thirds of all synthetic polymers have the ability to crystallize which allows for the extensive use of these materials in a variety of applications as molded parts, films, or fibers. Here, we present a study on the applicability of benchtop 1H NMR relaxometry to obtain information on the bulk crystallinity and crystallization kinetics of the most relevant synthetic semi-crystalline polymers. In the first part, we investigated the temperature-dependent relaxation behavior and identified T=Tg+100 K as the minimum relative temperature difference with respect to Tg for which the mobility contrast between crystalline and amorphous protons is sufficient for an unambiguous determination of polymer crystallinity. The obtained bulk crystallinities from 1 H NMR were compared to results from DSC and XRD, and all three methods showed relatively good agreement for all polymers. In the second part, we focused on the determination of the crystallization kinetics, i.e., monitoring of isothermal crystallization, which required a robust design of the pulse sequence, precise temperature calibration, and careful data analysis. We found the combination of a magic sandwich echo (MSE) with a short acquisition time followed by a CarrPurcell-Meiboom-Gill (CPMG) echo train with short pulse timings to be the most suitable for monitoring crystallization. This study demonstrates the application of benchtop 1H NMR relaxometry to investigate the bulk crystallinity and crystallization kinetics of polymers, which can lead to its optimal use as an in situ technique in research, quality control, and processing labs

Polymer crystallinity and crystallization kinetics via benchtop 1 H NMR relaxometry: Revisited method, data analysis, and experiments on common polymers

Semi-crystalline polymers play an enormously important role in materials science, engineering, and nature. Two-thirds of all synthetic polymers have the ability to crystallize which allows for the extensive use of these materials in a variety of applications as molded parts, films, or fibers. Here, we present a study on the applicability of benchtop 1H NMR relaxometry to obtain information on the bulk crystallinity and crystallization kinetics of the most relevant synthetic semi-crystalline polymers. In the first part, we investigated the temperature-dependent relaxation behavior and identified T=Tg+100 K as the minimum relative temperature difference with respect to Tg for which the mobility contrast between crystalline and amorphous protons is sufficient for an unambiguous determination of polymer crystallinity. The obtained bulk crystallinities from 1 H NMR were compared to results from DSC and XRD, and all three methods showed relatively good agreement for all polymers. In the second part, we focused on the determination of the crystallization kinetics, i.e., monitoring of isothermal crystallization, which required a robust design of the pulse sequence, precise temperature calibration, and careful data analysis. We found the combination of a magic sandwich echo (MSE) with a short acquisition time followed by a CarrPurcell-Meiboom-Gill (CPMG) echo train with short pulse timings to be the most suitable for monitoring crystallization. This study demonstrates the application of benchtop 1H NMR relaxometry to investigate the bulk crystallinity and crystallization kinetics of polymers, which can lead to its optimal use as an in situ technique in research, quality control, and processing labs