Search Results
Abstract
Polyvinyl chloride (PVC)/organic-montmorillonite composites were prepared by melt intercalation. Their structures and properties were investigated with X-ray diffraction (XRD), differential scanning calorimetry (DSC) and mechanical testing. The results showed that PVC chains could be intercalated into the gallery of organically modified montmorillonite to form exfoliated PVC/organic-montmorillonite nanocomposites, and the glass transition temperatures of PVC/organic-montmorillonite composites were lower than that of neat PVC. However, the tensile strength, and both the Izod type and Charpy notched impact strengths of PVC/organic-montmorillonite nanocomposites were fitted with the linear expressions: t=535.07-6.39T g, s I=378.76-4.59T g and sC=276.29-3.59T g, respectively.
Abstract
The thermally induced phase separation behavior of hydrogen bonded polymer blends, poly(n-hexyl methacrylate) (PHMA) blended with poly(styrene-co-vinyl phenol) (STVPh) random copolymers having various vinyl phenol contents, was studied by temperature modulated differential scanning calorimetry (TMDSC).The enthalpy of phase separation was determined to be about 0.5 cal g–1 for one of the blends. A phase diagram was constructed from the TMDSC data for one of the blends. The kinetics of phase separation was studied by determining the phase compositions from the glass transition temperatures of quenched samples after phase separation. Subsequently, the phase separated samples were annealed at temperatures below the phase boundary to observe the return to the homogeneous state.
coordination number of the system increases resulting in cross-linking of chains of atoms. This results in increase in glass transition temperature ( T g ) with Sn content [ 13 ]. The present work reports the effect of Sn incorporation on thermal and physical
oxide reported to sulfonation degree. High glass transition temperatures of sulfonated polyphenylene oxide and high value obtained for ion exchange capacity (IEC) are the reasons to proceed the improving this materials. Experimental
were all of analytically pure grade and supplied by Guangzhou Chemical Reagent Co. butadiene–styrene (SB) latex was supplied by Shandong Zibo Qilong Chemical Co. Ltd. and the glass transition temperature ( T g ) which was measured as −46 °C
(DGEBA/DDS). In particular, in composites with 0.25 wt% CNT, E G ′ increases 27% with DDS and 16% with DDM [ 9 , 10 ]. With respect to the glass transition temperature ( T g ), the effect of CNT changes completely from one epoxy resin to other. When
Abstract
The paper presents the thermal properties of fibres made of a modified polyimideamide. The effects of as-spun draw ratio and deformation during the fibre drawing stage on the structure, thermal properties, moisture absorption and tenacity of the obtained fibres have been determined. Based on the findings obtained by the DTA and DSC methods, it has been found that the modification of the polymer under investigation causes its glass transition temperature to decrease through the increase of molecular mobility. At the same time, the heat-resistant fibres with the amorphous oriented structure are characterized by a tenacity of 16 cN/tex, good absorption properties and increased porosity. The thermal stability indices of the examined fibres have been determined on the basis of thermogravimetric curves obtained both under air and inert gas.
(viscosity-average molar mass, M v = 300,000 g mol −1 ) and poly( d , l -lactide) (number-average molar mass M n = 43,000 g mol −1 ) show on DSC traces two separate glass transition temperatures ( T g ) independently of the composition, indicating thus
the fact that crosslinking reduces flexibility and inhibits pyrolysis. Differential scanning calorimetry (DSC) has been used to identify the glass transition temperature in organically modified siloxanes. The glass transition is generally
Abstract
The heat capacity or the specific heat is for any crystalline, partially amorphous or completely amorphous substance or material a significant thermodynamic property. The glass transition may be regarded as the melting point of amorphous substances and materials, a transition property of an outstanding technical importance. A crucial point is the fact that the presence of a glass transition is an unequivocal proof of an amorphous content of a material. Furthermore, the change of the specific heat at the glass transition temperature enables the quantitative determination of the amorphicity on a relative or absolute level of any substance or material. The absolute determination of the amorphicity affords a calibration with a reference corresponding to the material under investigation. The crystallinity for this reference substance must be known from the preparation and or by any independent analytical method. The literature data for the specific heat and the glass transition of polystyrene were collected and evaluated. Data were found for the specific heat in literature from 10 to 470 K. The data were unified for each of the reported temperature in a mean value and the corresponding standard deviation was determined. An excellent conformity was found in the glassy state of polystyrene with standard deviations lower than 0.7%. The standard deviations above the glass transition were considerably higher. All these literature data were transferred for each of the literature sets separately into linear specific heat functions in the vicinity of the glass transition. One set of our measurements performed with the DSC 204 and with polystyrene SRM 705a as sample material was additionally integrated in the mean of these functions for the glassy state and the liquid amorphous state respectively. The addition of our results gave practically no change of the mean coefficients and only a decrease of the standard deviations. In such a way, the data with the best statistical base for the specific heat of polystyrene are listed in this paper ( ‘Conclusions’). The glass transition as a transition in and out of a non-equilibrium state, the glassy state, is sensitive to all kind of influences such as thermal and mechanical treatments as well as to the selected experimental conditions. Therefore, certain standardized conditions procedures must be fulfilled to get reproducible data. The literature data for the glass transition temperature were also used to get a mean value. However, two values were omitted for the formation of the mean, because the authors reported values, which were too low on the base of impurities present. The mean value of the glass transition for polystyrene is according to the literature 3692 K. A mean value of 3702 K was extrapolated for an infinite molecular mass. The DSC and TMDSC measurements for the three thermodynamic properties reported in this paper, namely the specific heat, the glass transition temperature and the corresponding change of the specific heat gave results without significant differences compared with the literature values. Atactic polystyrene is a rather ideal polymer together with sapphire as calibration substance to elucidate and validate the DSC and TMDSC procedures for the determination of the specific heat and the glass transition.
