A new criterion for evaluating different plasticizers the ability of suppression of the transition in plasticized PVC blends. Accordingly, the suppression ability is proportional to the PVC-plasticizer compatibility, expressed either by the critical solution temperature, CST, or by the interaction parameter related to the difference between the solubility parameters of the blend components. The criterion is, however, valid for low plasticizer contents (<5%w/w) only, as long as the transitions are not overlapped by the transitions, shifted towards lower temperatures due to the effect of the plasticizer. For higher plasticizer contents the transition starts to overlap the transition and the suppression ability of the plasticizer depends increasingly on the efficiency of the plasticizer i.e. on the depression of the glass transition temperature of PVC (related to theTg of the plasticizer). Accordingly, plasticizers with both good efficiency (lowTg) and compatibility are more effective in the suppression than plasticizers which have only a higher compatibility but also a highTg (i.e. reduced efficiency).One of the authors, Tiberiu Vilics, thanks the Konferenz der Deutschen Akademien der Wissenschaften; and Volkswagen Stiftung; for financial support for a research fellowship at the Institut für Makromolekulare Chemie, Freiburg. The financial support of the Deutsche Forschungsgemeinschaft (SFB 60) is greatfully acknowledged. 相似文献
Thermal behavior of mixtures composed of cellulose acetate butyrate (CAB), carboxymethylcellulose acetate butyrate (CMCAB),
or cellulose acetate phthalate (CAPh), and sorbitan-based surfactants was investigated as a function of mixture composition
by means of differential scanning calorimetry (DSC). Surfactants with three different alkyl chain lengths, namely, polyoxyethylenesorbitan
monolaurate (Tween 20), polyoxyethylenesorbitan monopalmitate (Tween 40), and polyoxyethylene sorbitan monostearate (Tween
60) were chosen. DSC measurements revealed that Tween 20, 40, and 60 act as plasticizers for CAB, CMCAB, and CAPh (except
for Tween 60), leading to a dramatic reduction of glass transition temperature (Tg). The dependence of experimental Tg values on the mixture composition was compared with theoretical predictions using the Fox equation. Plasticization was strongly
dependent on mixture composition, surfactant hydrophobic chain length, and type of cellulose ester functional group. 相似文献
Based on free volume, an equation has been derived enabling calculation of glass transition temperature (Tg) of plasticized polymers, knowing the plasticizer content, the thermal expansion coefficients and values of Tg of the polymer and plasticizer. Determined and calculated Tg are in satisfactory agreement up to the plasticizer concentration which dissolves the polymer. 相似文献
Nowadays, the microscopic mechanism controlling the distribution of local glass transition temperatures (Tgs) across thin polymer films is still unclear and thus large‐scale applications of polymer films are restricted. Dynamic Monte Carlo simulations are performed to investigate the key factors dominating the distribution of layer Tgs in two kinds of capped ultrathin films with and without attractive polymer–substrate interactions, respectively. For the film without polymer–substrate interaction, the interfacial layer Tg is lower than the middle layer Tg. Additionally, the layer Tgs and the layer segment densities below Tg are linearly correlated, indicating that polymer density determines the distribution of layer Tgs. However, for the films with polymer–substrate interactions, the interfacial layer Tg increases dramatically with the raise of interfacial interactions, while the middle layer Tg decreases slightly. The interfacial layer Tg is proportional to the strength of interfacial interaction, while the middle layer Tg is linearly correlated with the segment density of the middle layer below Tg. Namely, interfacial interaction is the main factor dominating the interfacial layer Tg, while segment density controls the middle layer Tg.
Polylactide (PLA)/poly(butylene succinate) (PBS) blend films modified with a compatibilizer and a plasticizer were hot‐melted through a twin screw extruder and prepared by hydraulic press. Toluene diisocyanate (TDI) and polylactide‐grafted‐maleic anhydride (PLA‐g‐MA) were used as compatibilizers, while triethyl citrate and tricresyl phosphate acted as plasticizers. The effects of the type and content of compatibilizer and plasticizer on the mechanical characteristics, thermal properties, crystallization behavior, and phase morphology of the PLA/PBS blend films were investigated. Reactive compatibilization at increasing levels of TDI improved the compatibility of the PLA and PBS, affecting the toughness of the films. As evidenced by scanning electron microscope, the addition of TDI enhanced the interfacial adhesion of the blends, leading to the appearance of many elongated fibrils at the fracture surface. Furthermore, PLA/PBS blending with both TDI and PLA‐g‐MA led to an acceleration of the cold crystallization rate and an increment of the degree of crystallinity ( ). Toluene diisocyanate could be a more effective compatibilizer than PLA‐g‐MA for PLA/PBS blend films. The synergistic combination of compatibilizer and plasticizer brought a significant improvement in elongation at break and tensile‐impact toughness of the PLA/PBS blends, compared with neat PLA. Their failure mode changed from brittle to ductile due to the improved compatibility and molecular segment mobility of the PLA and PBS phases. Differential scanning calorimeter results revealed that the plasticizers triethyl citrate and tricresyl phosphate changed the thermal behavior of Tcc and Tm, affecting α′ and α crystal formations. However, these plasticizers only slightly improved the thermal stability of the films. 相似文献
The glass transition temperature of thermosets is determined by alternating differential scanning calorimetry (ADSC), which is a temperature modulated DSC technique. The different values of the glass transition obtained from heat flow measurements (total and reversible) and heat capacity (modulus of the complex heat capacity) are analysed and compared with the values obtained by conventional DSC. The effect of the sample mass on the values of Tg, heat capacity and phase angle has been analysed. The effect of the thermal contact between sample and pan has been studied using samples cured directly inside the pan and disc-shaped samples of different thickness. The results obtained for the thermal properties and the phase angle are compared and analysed. The modulus of the complex heat capacity enables the determination of the dynamic glass transition, Tg, which is frequency dependent. The apparent activation energy ofthe relaxation process associated with the glass transition has been evaluated from the dependence of Tg on the period of the modulation.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
We report the results of an investigation by differential scanning calorimetry (DSC) of two mobility controlled processes in the amorphous phas e of semicrystalline PEEK — enthalpy relaxation below the glass transition (Tg) and secondary crystallization aboveTg. Both result in the observation of an endothermic peak just above the annealing temperature in the DSC scan of the polymer — the enthalpy recovery peak and the low temperature melting peak, respectively. There is a striking similarity in the time and temperature dependence of the endothermic peak for these two processes. These results are reminiscent of those obtained from small strain creep studies of physical aging of semicrystalline PEEK below and aboveTg.We gratefully acknowledge support of this work by the National Science Foundation, Science and Technology Center for High Performance Polymeric Adhesives and Composites under DMR grant 91-2004 and by an NSF Young Investigator Award (DMR 93-57512). 相似文献
The glass transition temperature Tg of partially sulfonated polystyrene has been measured dilatometrically as a function of degree of sulfonation. A semitheoretical relationship between Tg and degree of sulfonation has been derived by treating the strong-acid polymer as a highly polar copolymer of styrene and styrenesulfonic acid. The Tg of copolymer has been found to increase linearly up to 0.15 weight fraction of styrene-sulfonic acid wA as given by: where TgB is the glass transition temperature of loosely crosslined (1%) polystyrene matrix. Our experimental results agree well with theoretical relations developed on the basis of the iso-free-volume state of glass transition applied to sulfonated polystyrene. The marked linear increase in copolymer Tg with the styrenesulfonic acid is accounted for by the effect of progressively higher intermolecular forces due to the highly polar sulfonic acid substituents. 相似文献
Thermal properties of new ionic liquids (ILs) were investigated by thermogravimetry (TG/DTG) and differential scanning calorimetry
(DSC). Chlorides, tetrafluoroborates and hexafluorophosphates of (−)mentholpyrrolidinium and (−)-mentholimidazolium cations
revealed good thermal stability at air atmosphere. Morphological characteristics of poly(methyl methacrylate) (PMMA) matrices
doped with 10% of these ILs were also investigated by DRX and water absorption test. Into the matrix, they exhibited a very
satisfactory pattern concerning the polymer thermal stabilization. DSC results show that some of these ILs also present plasticizer
features since they can lower the polymer glass transition temperature (Tg) up to 317.15 K. 相似文献
The physical ageing characteristics of glucose, fructose, and their mixtures were studied using standard differential scanning calorimetry (DSC). The inflection, onset, midpoint,half-height, and endpoint glass transition temperature (Tg), fictive temperature (Tf), and relaxation enthalpy (H) were measured as a function of ageing time. The relationship between H and Tf was evaluated. The time dependence of H was fit using the Cowie and Ferguson model. The ageing rate was expressed in terms of the average relaxation time (<>) and the entropy production (P). It was found that the fructose component decreased the rate of ageing of the mixtures.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献