Thermodynamic properties in the liquid state of high melting polymers containing phenylene and naphthylene groups

A modified mathematical model based on the melting and recrystallization of an initial distribution of melting temperatures satisfactorily predicts the melting behavior of PET in differential scanning calorimetry. The simulated DSC curves produced in this work agreed fairly well not only with experimental DSC curves performed by Holdsworth et al., but also with the DSC traces provided by SSP PET pellets. The model, taking into account the initial distribution of melting points and the distribution of melting points for the recrystallized material, succeeded in analyzing the origin of dual endotherms of PET with various thermal histories, thereby elucidating the effect of changing crystallization temperature and time, the heating rate in the DSC heating scan, as well as the SSP process on the melting behavior of PET completely. Furthermore, it has been analytically proven that the crystallinity measured on a DSC diagram could not be equal to the weight percentage of crystalline state in the initial specimen. The deviation of the measured crystallinity, as observed relevant to the melting and recrystallization processes, is caused by the changes of the heat of fusion with the melting temperature as well as the difference of heat capacities of liquid and solidstate polymer.

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“…same temperature dependence but shifted down by 0.406 J g 01 k 01 , which is the DC* p at the glass transition temperature for PET. 25,27 …”

Section: M[t(t)]g[t(t)]dtmentioning

confidence: 98%

“…Seeing the linear relationships of C pl and C ps vs. temperature T, 27 the last term of eq. (20), dQ 2 / dT, is responsible for the baseline.…”

Section: M[t(t)]g[t(t)]dtmentioning

confidence: 99%

Dual melting endotherms in the thermal analysis of poly(ethylene terephthalate)

Qiu

Tang

Huang

et al. 1998

J. Appl. Polym. Sci.

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“…For several of the well known semicrystalline polyesters, a rigid amorphous phase was hypothesized [14,36,37]. The interphase is defined as that portion of noncrystalline material, which does not mobilize at the glass transition temperature and therefore does not contribute to the observed specific heat increment.…”

Section: Thermodynamic Parametersmentioning

confidence: 99%

Memory effect in melting behaviour, crystallization kinetics and morphology of poly(propylene terephthalate)

et al. 2003

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Crystallization kinetics and melting behaviour of poly(propylene terephthalate) (PPT) were investigated by means of differential scanning calorimetry and hot-stage optical microscopy. Isothermal crystallization kinetics was analysed according to the Avrami treatment. The effects of temperature and duration of melting on the overall rate of isothermal crystallization were studied: the rate was found to decrease with increasing melting temperature and melting time. This result was discussed on the basis of the gradual destruction of predetermined athermal nuclei. Values of the Avrami exponent close to 3 were obtained, regardless of the adopted thermal treatment and the crystallization temperature, T c , in agreement with a crystallization process originating from predetermined nuclei and characterized by three-dimensional spherulitic growth. As a matter of fact, spacefilling spherulites were observed by optical microscopy at all T c 's, independent of the applied thermal treatments. For each of them, the rate of crystallization became lower as T c increased, as usual at low undercooling where the crystallization process is controlled by nucleation. The observed multiple endotherms, which are commonly displayed by polyesters, were influenced by T c and ascribed to melting and recrystallization processes. Linear and non-linear treatments were applied in order to estimate the equilibrium melting temperature for PPT, by using the corrected melting temperatures. The non-linear estimation yielded an about 33°C higher value with respect to the one obtained by means of the linear approach. Through the analysis of secondary nucleation theory, the classical II→III transition was found to occur at a temperature of 194°C. The average work of chain folding for nucleation was determined to be c. 5.2 kcal/mol. The heat of fusion was correlated to the specific heat increment for samples with different degree of crystallinity and the results were interpreted on the basis of the existence of an interphase, whose amount was found to depend on the thermal treatment the polymer was subjected to.

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“…C p (liquid) of PBT (J K −1 mol −1 ) is fully based on experimental data. It is a linear function of temperature, as seen for many polymers, and has been taken from the ATHAS Data Bank2, 38 as follows: The total C p value of liquid PBT can also be approximated from an addition scheme from contributions of the various structural groups to other polymers: where N

_{CH_{2}}

, N COO , and N

_{C_{6} H_{4}}

are the numbers of the respective groups in the repeating unit of PBT. With eq 10 ( N

_{CH_{2}}

= 4, N COO = 2, and N

_{C_{6}}

H 4 = 1), the calculated C p (liquid) value for PBT is The C p (liquid) values calculated from eq 11 are about 4% lower than those from eq 9 at 510 and 520 K. More details about the experimental and calculated C p (liquid) values of PBT can be found in ref.…”

Section: Cp Values Of the Solid And Liquid Statesmentioning

confidence: 99%

Heat capacity of poly(butylene terephthalate)

Pyda

Nowak-Pyda

Mays

et al. 2004

J Polym Sci B Polym Phys

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The low‐temperature heat capacity of poly(butylene terephthalate) (PBT) was measured from 5 to 330 K. The experimental heat capacity of solid PBT, below the glass transition, was linked to its approximate group and skeletal vibrational spectrum. The 21 skeletal vibrations were estimated with a general Tarasov equation with the parameters Θ1 = 530 K and Θ2 = Θ3 = 55 K. The calculated and experimental heat capacities of solid PBT agreed within better than ±3% between 5 and 200 K. The newly calculated vibrational heat capacity of the solid from this study and the liquid heat capacity from the ATHAS Data Bank were applied as reference values for a quantitative thermal analysis of the apparent heat capacity of semicrystalline PBT between the glass and melting transitions as obtained by differential scanning calorimetry. From these results, the integral thermodynamic functions (enthalpy, entropy, and Gibbs function) of crystalline and amorphous PBT were calculated. Finally, the changes in the crystallinity with the temperature were analyzed. With the crystallinity, a baseline was constructed that separated the thermodynamic heat capacity from cold crystallization, reorganization, annealing, and melting effects contained in the apparent heat capacity. For semicrystalline PBT samples, the mobile‐amorphous and rigid‐amorphous fractions were estimated to complete the thermal analysis. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4401–4411, 2004

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Thermodynamic properties in the liquid state of high melting polymers containing phenylene and naphthylene groups

Cited by 29 publications

References 27 publications

Dual melting endotherms in the thermal analysis of poly(ethylene terephthalate)

Dual melting endotherms in the thermal analysis of poly(ethylene terephthalate)

Memory effect in melting behaviour, crystallization kinetics and morphology of poly(propylene terephthalate)

Heat capacity of poly(butylene terephthalate)

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