Combining X-ray scattering with dielectric and calorimetric experiments for monitoring polymer crystallization (original) (raw)
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Review of Scientific Instruments, 2000
A novel experimental setup is described which allows one to obtain detailed information on structural and dynamical changes in polymers during crystallization. This technique includes simultaneous measurements of small angle-wide angle x-ray scattering and dielectric spectroscopy ͑SWD͒. The capabilities of the technique have been probed by following in real time the crystallization process of a model crystallizable polymer: poly͑ethylene terephthalate͒. By performing these experiments, simultaneous information from both, the amorphous and the crystalline phase is obtained providing a complete description of changes occurring during a crystallization process. The SWD technique opens up new promising perspectives for the experimental study of the relation between structure and dynamics in materials science.
Early stages of polymer crystallization—a dielectric study
Polymer, 2003
The existence and the formation of pre-ordered structures as the initial step during the complex process of polymer crystallization are discussed controversially. Most of the findings and interpretations are based on scattering experiments, which test small density differences between the assumed precursors of the crystals and the surrounding melt. Because of the low contrast the interpretation of experimental results become often speculative. In contrast relaxation experiments are probing motions in the sample and are therefore independent on density contrast. During crystallization, material is transformed from the liquid to the solid state. Consequently, motions typical for a liquid become impossible and do not longer contribute to the measured signal. For pre-ordered structures we expect some changes in mobility too because of the changes in conformation on pre-ordering.
The measurement of the crystallinity of polymers by DSC
Polymer, 2002
The procedures adopted and the inherent assumptions made in the measurement of crystallinity of polymers by differential scanning calorimetry (DSC) are reviewed. The inherent problem in all DSC measurements is concurrent recrystallisation and melting of the polymer sample on heating to the melting point and the variation of the enthalpies of crystallisation and melting, heat capacities and degree of crystallinity with temperature. A First Law procedure is suggested which involves heating the sample between two set temperatures, T 1 and T 2 . T 1 is selected by the requirement that the degree of crystallinity of the sample should not change either with temperature or time, and be representative of the sample during its use. T 1 is taken to be ambient or just above the glass transition temperature. T 2 is taken to be just above the observed last trace of crystallinity. Integrating the observed speci®c heat difference between the sample and the completely amorphous material during these two temperature ranges determined the residual enthalpy of fusion at T 1 . Problems are noted in the use of this procedure in that the speci®c heat of the liquid should not be arbitrarily chosen since this leads to systematic errors in the heat of crystallisation.
2012
The control and optimization of heat transfer during the forming of thermoplastic parts is of primary importance since they impact on the quality of final parts. The modelling of this transfer requires accurate knowledge of the polymer thermo-physical properties, and also of the parameters describing the crystallization, this latter data being very sensitive to the thermal history for semi-crystalline polymers. The experimental determination of these parameters requires the use of many instruments, which is time consuming. To address this issue, a home-built instrumented mould was designed to measure and identify several properties from a single experiment. Specific volume, transverse thermal conductivity in amorphous and solid states can be estimated as a function of the temperature. Parameters of a crystallization kinetics model are identified with a non invasive procedure. Our methodology is illustrated on a well-known semi-crystalline thermoplastic. Identified parameters are compared with literature results.
Polymer, 2003
The isothermal cold crystallization of poly(ethylene naphthalene-2,6-dicarboxylate) was investigated by simultaneous small and wide angle X-ray scattering and dielectric spectroscopy (DS). By this experimental approach, simultaneously collected information was obtained about the specific changes occurring in both crystalline and amorphous phases during crystallization, namely about the chain ordering through wide angle X-ray scattering, about the lamellar crystals arrangement by means of small angle X-ray scattering, and about the amorphous phase evolution by means of DS. The results indicate that average mobility of the amorphous phase suffers a discontinuous decrease upon passing from the primary to the secondary crystallization regime. We interpret these results assuming that the restriction to the mobility of the amorphous phase occurs mainly in the amorphous regions between the lamellar stacks and not in the amorphous regions within the lamellar stacks. q
Thermochimica Acta, 1978
We previously introduced a non-isoeern@ technique &ing _TGA to study fhe kinetics of so&b&I transforxnations TGA can only be applied 0systeznsundergoingweightchange.Forthisreason,,ate0 systezns undergoing weight change. _For this reason, ,a te0systeznsundergoingweightchange.Forthisreason,,atexni&e using Th&maI X-ray Analysis m) was deveioped. The technique i&ok% the dete@nation of the % &ystaUinity vs. temperature cur~$ &d its &t derivativF_ The folkking equation w& de&& an4 found to be applicable. The KIug and AIexander technique for-the qnantitkion of a crystalline corn-_ pound in a powder mixture using an internal &ndard~~_~ to determine the crystaUinity of each sampIe stu4ied_ The technique was. applied to the p&e transformation for. a semicrystalline, 1Ow density,' che&ca%y cro&nked pOlyettiylene polym& The enthalpy fat the crys~e-amorphous tran&ormatiOn was found to be 13-2 kca!@&i~_ For a high density, n~n-crossbked po&&~lek, the ent+aIp$ was 2Q.8 kca@quiv. A technique to caIcu@te the length $6 Crystalline segment fkom _ the kin&ic~dak was ako developed and showed that&e cry&l&e @g&s x&z& 65 and 30 & respectively_ ..-_
2011
The paper gives general information about the advantages of using synchrotron radiation in investigation of polymer liquid crystals. Examples are given with thermotropic polymer liquid crystal Poly(heptane-1,7-dyil-4,4’biphenyldicarboxylate). The melt formation of smectic liquid crystal phase and consequent crystallization at decreasing temperature is depicted. Detailed description of different structural parameters, derivable from appropriate analysis of the experimental results, is given. With the aim of all those parameters an overall hierarchical structuring during phase transitions could be revealed. Since some basic terms about liquid crystals and polymer liquid crystals are given, the paper would serve as an introductory reading in the field.
Macromolecular Symposia, 2006
The crystallization of the isotactic poly(propylene) (i-PP) has been studied carrying out measurements by means of a special calorimeter connected to a microscope and a digital acquisition system of images. The analysis of Polarized Optical Microscopy images has allowed the appraisal of nucleation density and growth rate in isothermal and non isothermal conditions. The results obtained in isothermal conditions have been analyzed through the Kolmogoroff model and the crystallinity calculated from the model has been compared with that obtained from the calorimetric measurements.