Temperature Dependence Of Shift Factor Research Articles

Definition of the rheological glass transition temperature in association with the concept of iso-free-volume

Small deformation dynamic oscillation was used to develop an index of physical significance for the rationalisation of the mechanical properties of high co-solute/biopolymer systems during vitrification. The index is based on the combined framework of Williams–Landel–Ferry equation with the free volume theory and is called the ‘rheological glass transition temperature, T g’ thus differentiating it from the empirical calorimetric T g used in thermal analysis. The rheological T g is located at the conjunction of two distinct molecular processes, namely: free-volume effects in the glass transition region and the predictions of the reaction-rate theory in the glassy state. The method of reduced variables was used to shift the mechanical spectra of shear moduli to composite curves. The temperature dependence of shift factors for all materials was identical provided that they were normalised at suitably different reference temperatures, which reflect iso-free-volume states. The treatment makes free volume the overriding parameter governing the mechanical relaxation times during vitrification of high co-solute/biopolymer systems regardless of physicochemical characteristics. We believe that potential applications resulting from this fundamental work are numerous for the food and pharmaceutical industries.

Effect of water on viscoelastic properties of oriental lacquer film

We noticed the Urushi film, by which oriental lacquer wares are prepared. The effect of water on mechanical properties of oriental lacquer film was investigated in a tensile test and a stress relaxation test. These tests were conducted under the various degrees of humidity. Oriental lacquer film had a tendency to became brittle under dry condition and to toughen under wet conditions. On the other hand, the film becomes sticky and soft under high humidity or in water. The relaxation modulus for this film was determined under the various degrees of humidity. This behavior changed largely depending upon humidity. Master curves on the result of stress relaxation test were prepared by applying the rule of time–temperature superposition. The temperature dependence of shift factor on the various degrees of humidity could be represented by the Williams–Landel–Ferry equation by changing two parameters, C1 and C2. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 315–321, 1998

Determination of shift factors from dynamic mechanical measurements at a constant frequency

The theoretical interrelation between linear viscoelastic responses and shift factors has been established for thermorheologically simple materials. The analysis of this interrelation shows that the temperature dependence of shift factors is determined by the temperature dependence of dynamic mechanical responses at a single frequency, and as a consequence the isochronal mechanical relaxation scans at one frequency actually carry a much information as isothermal scans at numerous temperatures. Bred on this theory a method has been proposed for obtaining shift factors end other useful information from isochronal dynamic data

THE EFFECT OF HEAT-TREATMENT ON THE STRESS RELAXATION AND RECOVERY OF THE DRAWN AND HEAT-TREATED POLYPROPYLENE FILAMENTS

The authors reported in the previous paper that the drawn (draw ratio=4) and heat-treated polypropylene (P. P) filaments show a reversible change of the stress on heating and cooling. In this investigation, stress relaxation and stress recovery of drawn and heat-treated samples, which were kept to the treated length after the treatment and subjected to deformation, were measured at various temperatures and analysed from the viewpoint of the time-temperature and stress-temperature superposision principles. The following results are obtained.1. Master curves of stress relaxation and recovery, subjected to the deformation from the treated length, can be constructed by shifting curves along the log (time) axis, respectively.2. Temperature dependence of shift factor (log aT) can be explained well by the Arrhenius' equation, and when the samples are heat-treated up to 100°C, the activation energy ΔH is 52.5kcal/mol for stress recovery and 39.2kcal/mol for stress relaxation, respectively, but when the samples are heat-treated up to different temperatures, ΔH varies.3. From the temperature and strain dependences of the shift factor (log aT•r), the following experimental equation is obtained. where r: strain (%), α: constant, R: gas constant.4. The constants ΔH and α are obtained for the samples heat-treated up to 100°C, 128°C and 140°C (Table 2).

Effect of flaws on the time-temperature superposition in the ultimate behavior of elastomers

Abstract The effect of flaws on the ultimate behavior of poly (β-hydroxyethyl methacrylate) swollen with water to equilibrium has been examined experimentally, by using test pieces containing model defects. For both the defect-free samples and samples with macrodefects the experimental dependences of the time to break on stress have been obtained at various temperatures. The curves corresponding to different temperatures are approximately parallel to each other, the temperature dependence of shift factors obeys the Williams-Landel-Ferry equation. The presence of macrodefects in the test pieces accounts for the change in shape of the time-to-break curves and influences distinctly the value of the characteristic temperature Ts determined from the temperature dependence of the shift factors. This effect has been ascribed to the high orientation in the roots of the macroscopic defects.