Physical ageing in glassy polymers. An i.r. spectroscopic investigation of poly(ethylene terephthalate) (original) (raw)
Related papers
Physical aging of semicrystalline polyethylene terephthalate was studied using differential scanning calorimetry (DSC). PET samples with crystallinity content of 0.28 were aged at two different temperatures, 25 and 45°C. The samples were stored for several days and periodically tested using DSC method. The glass transition temperature for the samples aged at 25°C was about 73-74°C, and the position and intensity of endothermic peaks were approximately constant. Higher glass transition of the samples aged at 45°C, 73-86°C, was attributed to the enthalpy relaxation process of amorphous regions of semicrystalline PET. For the samples aged at 45°C, the endothermic peaks shifted to higher temperatures with increasing aging time. The position of the endothermic peaks determined by the temperature of the maximum, Tmax, tended to increase with aging time for samples aged at 45°C, and the intensity of the peaks continuously increased with time; however, the results showed that the aging of PET samples at 45°C even after 120 days continued the enthalpic relaxation of semicrystalline PET and that the process could be studied by DSC method. The results also showed that the aging process could affect the final degree of crystallinity of c-PET samples and the samples stored at 45°C showed higher degree of crystallinity than the samples aged at 25°C.
The very long-term physical aging of glassy polymers
The thermodynamic behavior of glasses well below the glass transition temperature (T g) is scarcely explored due to the long time scales required for such investigation. Here, we characterize the thermodynamic state of several polymer glasses aged for about 30 years at room temperature, that is, at more than 100 K below their respective T g (s). To this aim we employ differential scanning calorimetry (DSC), which, via the specific heat, allows characterizing the enthlapy attained after a certain aging protocol and the way the glass with such enthalpy devitrifies when heated. We complement these results with extensive DSC studies on these polymers aged in the same conditions of temperature for time scales ranging from minutes to months. The main outcome of the present work is that these polymers aged in these conditions reach a plateau in the enthalpy with partial enthalpy recovery and devitrify well below T g. This result provides compelling evidence for the existence of a fast mechanism of equilibrium recovery, beyond the standard slow one in proximity of T g. The analogy with other kind of glasses is highlighted, stigmatizing the uni-versality of such behavior. Finally, the way the fast mechanism of equilibrium recovery could be exploited to obtain glasses with low energy state is discussed.
Physical Aging Behavior of a Glassy Polyether
2021
The present work aims to provide insights on recent findings indicating the presence of multiple equilibration mechanisms in physical aging of glasses. To this aim, we have investigated a glass forming polyether, poly(1-4 cyclohexane di-methanol) (PCDM), by following the evolution of the enthalpic state during physical aging by fast scanning calorimetry (FSC). The main results of our study indicate that physical aging persists at temperatures way below the glass transition temperature and, in a narrow temperature range, is characterized by a two steps evolution of the enthalpic state. Altogether, our results indicate that the simple old-standing view of physical aging as triggered by the α relaxation does not hold true when aging is carried out deep in the glassy state.
Physical ageing and glass transition in amorphous polymers as revealed by microhardness
Journal of Materials Science, 1989
Microhardness (MH) data as a function of temperature for two amorphous polymers [poly(methylmethacrylate) and poly(vinylacetate)] and two semicrystalline polymers [poly(ethyleneterephthalate) and poly(arylether ether ketone)] quenched into the amorphous state are presented. It is shown that MH can conveniently detect the glass transition temperature (T g) for the above mentioned polymers. Molecular rearrangements taking place above and belowT g, such as physical ageing leading to a more compact molecular packing, and thermal expansion can also be followed by means of MH measurements. Finally, the presence of a crystalline phase in these materials has been shown to shift theT g value towards higher temperatures.
Progress in Polymer Science, 1995
The general area of physical aging of polymers is reviewed. Various phenomenological aspects are introduced and discussed in terms of bulk structural changes evidenced by dilatometric and calorimetric studies, and are compared with the wide variety of information available from microstructural investigations involving spectroscopic and scattering techniques. Current models for describing the relaxation kinetics of the non-equilibrium glassy state are compared. Finally, the effects of physical aging on mechanical properties are reviewed, highlighting especially those areas which remain controversial.
Polymer, 2002
The aim of this work is to determine the relaxation times of the cooperative conformational rearrangements of the amorphous phase in semi-crystalline poly(ethylene terephthalate) (PET) and compare them with those calculated in amorphous PET. Samples of nearly amorphous polymer were prepared by quenching and samples with different crystallinity fractions were prepared from the amorphous one using cold crystallisation to different temperatures. The differential scanning calorimetry (DSC) thermograms measured on samples rapidly cooled from temperatures immediately above the glass transition show a single glass transition which is much broader in the case of high-crystallinity samples than in the amorphous or low-crystallinity PET. To clarify this behaviour, the samples were subjected to annealing at different temperatures and for different periods prior to the DSC measuring heating scan. The thermograms measured in samples with low crystallinity clearly show the existence of two amorphous phases with different conformational mobility, these are called Phases I and II. Phase I contains polymer chains with a mobility similar to that in the purely amorphous polymer, while Phase II shows a much more restricted mobility, probably corresponding to conformational changes within the intraspherulitic regions. The model simulation allows to determine the temperature dependence of Phase II relaxation times, which are independent from the crystallinity fraction in the sample and around two decades longer than those of the amorphous polymer at the same temperature. q
Glass Transition and Physical Aging of Confined Polymers Investigated by Calorimetric Techniques
This chapter reviews the recent activity on the study of glass dynamics in polymers subjected to geometrical confinement. Special attention is dedicated to glassy dynamics in thin polymer films. Nonetheless, other kind of confinement, such as polymer nanocomposites and nanospheres, are dealt with. In this context, it is shown how calorimetric techniques contributed to significant advancement in the topic. After introducing the established phenomenology and the recent findings on the glass transition, the factors that affect the nonequilibrium glass dynamics in confinement, that is, the glass transition temperature (Tg) and the physical aging, are discussed. In light of numerous experimental evidences, it is remarked how arguments exclusively based on the alteration of the rate of spontaneous fluctuations are insufficient to catch the behavior of nonequilibrium dynamics. The role of free interfaces, not enslaved by underlying adsorbed layers, is emphasized for the comprehension of the ability of confined polymer glasses to maintain equilibrium when cooled—testified by a reduction Tg—and accelerated equilibrium recovery in the glassy state. Given the fact that these results imply that confined systems with large free interface are able to access low energy states in short-time scales, the final part of the chapter is dedicated to recent advancements toward the clarification of questions of paramount importance in glass science. In particular, the experimental evidence for the existence of the ideal glass transition is discussed.
Effect of physical aging on nano- and macroscopic properties of poly(methyl methacrylate) glass
Polymer, 2005
Physical aging of amorphous poly(methyl methacrylate) has been studied by low frequency Raman scattering, broad-band dielectric spectroscopy, low frequency high resolution mechanical spectroscopy and differential scanning calorimetry. The material was subjected to different thermal histories by isothermal aging. A consistent relationship between the changes caused by the physical aging in nanostructure and molecular dynamics has been found. The aging makes the structure more homogeneous at a scale of few nanometers, bringing it to a structural state of lower energy. These structural changes affect mainly the a-relaxation, however, some increase in the relaxation strength as well as an increase in the activation energy of the b-relaxation is also observed. q
Physical ageing studies of poly(ethylene terephthalate) using SANS and DSC
Physica B-condensed Matter, 2006
The process of physical ageing in a blend of deuterated and hydrogenated poly(ethylene terephalate) has been investigated using a combination of differential scanning calorimetry (DSC) and small-angle neutron scattering (SANS). The development of an endothermic peak on the glass transition has been shown using DSC. Furthermore, the radius of gyration was found to decrease during physical ageing. r
Long time response of aging glassy polymers
Rheologica Acta, 2014
Aging amorphous polymeric materials undergo free volume relaxation, which causes slowing down of the relaxation dynamics as a function of time. The resulting time dependency poses difficulties in predicting their long time physical behavior. In this work, we apply effective time domain approach to the experimental data on aging amorphous polymers and demonstrate that it enables prediction of long time behavior over the extraordinary time scales. We demonstrate that, unlike the conventional methods, the proposed effective time domain approach can account for physical aging that occurs over the duration of the experiments. Furthermore, this procedure successfully describes timetemperature superposition and time -stress superposition. It can also allow incorporation of varying dependences of relaxation time on aging time as well as complicated but known deformation history in the same experiments. This work strongly suggests that the effective time domain approach can act as an important tool to analyze the long time physical behavior of aging amorphous polymeric materials. J J t t