Physical ageing studies in polyetherimide ULTEM 1000

American Journal of Engineering and Applied Sciences, 2009

Problem statement: Polyetherimide (PEI) has several uses such as electrical insulation. It can undergo different constraints like heat or high voltage which influence its performances as insulator. In this study, the effects of heating on structural and electrical properties of polyetherimide (Ultem 1000) are studied. Approach: PEI samples were heated at different temperatures below the glass transition temperature (175, 190 and 205°C). Different complementary techniques were used to investigate structural alterations and dielectric relaxations. These are infrared (IR) spectroscopy, Differential Scanning Calorimetry (DSC), Thermally Stimulated Depolarisation Current (TSDC) technique and Dielectric Spectroscopy (DS). Results: Physical ageing was revealed in heated samples by DSC analysis. DS and TSDC results have shown that dipolar relaxations are affected by heating. The amount of relaxing dipoles decreases when the material is heated at 190°C. Conclusion/Recommendations: The heatin...

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.

Journal of Applied Polymer Science, 1995

The developments of physical aging in phenolphthalein poly(ary1-ether-ketone) (PEK-C) and poly(ary1-ether-sulfone) (PES-C) with time at two aging temperatures up to 20 K below their respective glass transition temperatures (T, = 495 and 520 K) have been studied using differential scanning calorimetry (DSC). Substantial relaxation within the aging course of several hours were observed by detecting T, decreasing during physical aging process at the two aging temperatures. The relaxation processes of both polymers are extremely nonlinear and self-retarding. The time dependencies of their enthalpies during the initial stages of annealing were approximately modeled using the Narayanaswamy-Tool model. The structure relaxation parameters obtained from this fitting were used to predict the possibility of physical aging occurring at their respective using temperatures.

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.

Thermochimica Acta, 2017

Physical aging on wholly amorphous polylactide (PLA) has been performed by means of standard differential scanning calorimetry (DSC) and fast scanning calorimetry (FSC) just below its glass transition. Compared to the in-situ aging study through the standard DSC, an increase of 80 to 90 % has been observed in the enthalpy recovery by FSC investigations. Such increase has been related to the high cooling rates used by FSC. Besides, an influence of the sample geometry has been measured when glasses are vitrified by high cooling rates. This implies that the critical thickness involved in the physical aging acceleration is cooling rate dependent. High cooling rates allow to reach the thermodynamic equilibrium, as observed from physical aging investigations by FSC. In addition, few ng of material analyzed by FSC are representative of the bulk one analyzed by standard DSC, when the glass is formed in the same conditions.

Journal of Non-Crystalline Solids, 1998

Samples of amorphous poly (ethylene terephthalate) (PET) vitri®ed under dierent cooling rates and a series of samples of poly (methyl methacrylate) (PMMA) of various tacticities have been characterized by dierential scanning calorimetry (DSC), thermally stimulated current (TSC) and thermally stimulated creep (TSCr). The a relaxation and retardation modes, associated with the glass transition, have been analyzed. The dielectric relaxation mode observed in PET has relaxation times following a compensation law with compensation parameters independent of physical aging. Contrarily, the maximum value of the activation enthalpy increases upon aging. The anelastic retardation mode observed in PMMA is also constituted of retardation times following a compensation law. In that case, the T c A T g lag varies according to the chain conformation. It is also interesting to note that the maximum of the activation enthalpy increases with the level of local interactions. This evolution is due to the increasing of the domain sizes in which molecular mobility takes place. Ó

2008 Annual Report Conference on Electrical Insulation and Dielectric Phenomena, 2008

An atypical enhancement of both the dielectric properties and the static (dc) conductivity in polyimide (PI) films has been observed using isothermal dielectric relaxation spectroscopy at 300°C under air atmosphere during short-term thermal aging (up to 200h). Simultaneously, an increase of the dielectric strength of PI is observed. Despite a close similarity with the typical electrical signature of the crystallization phenomenon occurring in semi-crystalline polymers, DSC measurements have not revealed the presence of an exothermic crystallization peak in PI up to 500°C thus denying this assumption. In this paper, a cross-linking reaction under oxidant atmosphere is therefore proposed for explaining such electrical improvements. Indeed, oxygen diffusion in the polymers' bulk is generally followed by the formation of links between macromolecular chains leading the molecular and charge motions more difficult. This phenomenon, inducing usually an enhancement of the electrical and mechanical properties, is also supported by FTIR chemical changes of PI during aging and theoretical cross-linking mechanisms in presence of oxygen.

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.

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.

Thermochimica Acta, 2001

A standard power-compensation Perkin-Elmer DSC-2 was modi®ed for temperature modulation experiments. Samples of amorphous poly(ethylene terephthalate) were aged in the DSC at temperature, T a , for time, t a below the amorphous T g . The progress of enthalpic relaxation was measured using conventional and modulated temperature DSC (MTDSC). By conventional DSC the extent of enthalpic relaxation was found to increase with ageing time accompanied by an apparent shift in the glass transition to a higher temperature. Using MTDSC the non-reversing enthalpic transition could be separated from the reversing glass transition. By MTDSC the extent of enthalpic relaxation was also found to increase with ageing time. However, by studying the reversing component it was found that there is no increase in the glass transition temperature with increased ageing time. It was found that the kinetics of enthalpic relaxation were more accurately determined by conventional DSC than MTDSC. #