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Summary A mathematical description of the dependence of softening temperature of poly(vinyl chloride) blends with solid-state chlorinated polyethylene on the degree of chlorination of polyethylene and the amount of chlorinated polyethylene were studied. A method for calculation the coefficients in the corresponding empiric equation was suggested. The latter can successfully be used for practical purposes in preparation of various composition with selected softening temperature.
Abstract
Thermomechanical analysis (TMA) in a tube-compressive mode can be used to characterize pitch in a reproducible and sensitive way. In a single experiment, this technique enables simultaneous determination of the glass transition temperature, the softening temperature and the rheological behaviour of a pitch sample. Results on a typical Australian coal-tar pitch are consistent with Bingham fluid behaviour above its softening temperature with a yield stress of the order of 100 Pa. In a similar test a petroleum pitch sample exhibited no yield stress.
Artificial ageing of double base rocket propellant
Effect on dynamic mechanical properties
Abstract
The ageing of double base rocket propellants (DB rocket propellants), which is a consequence of chemical reactions and physical processes that take place over time, has significant effect on their relevant properties (e.g. chemical composition, mechanical properties, ballistic properties, etc.). The changes of relevant properties limit the safe and reliable service life of DB rocket propellants. This is the reason why numerous research efforts are devoted to finding out reliable methods to measure the changes caused by ageing, to assess the quality at a given moment of time, and to predict remaining life-time of DB rocket propellants. In this work we studied dynamic mechanical properties of DB rocket propellant artificially aged at elevated temperatures, in order to detect and quantify changes in dynamic mechanical properties caused by the ageing. Dynamic mechanical properties were studied using dynamic mechanical analyser (DMA). The results obtained have shown that the ageing causes significant changes of DMA curve’s shape and positions. These changes are quantified by following some characteristic points on DMA curves (e.g. glass transition temperatures; storage modulus, loss modulus and tanδ at characteristic temperatures, etc.). It has been found out that the most sensitive parameters to the ageing process are: storage modulus at viscoelastic and softening region, peak width and height on loss modulus curve, glass transition and softening temperature, and tanδ at viscoelastic region.
softening temperature, while the linear coefficient of thermal expansion decreases with increasing B 2 O 3 content [ 15 ]. The analysis of the crystallization peak showed that for the borophosphate glasses with high P 2 O 5 content surface crystallization
Abstract
First casein was processed by pyrolysis and investigated under optimal thermal treatment condition to obtain a good quality adsorbent with high developed porosity structure and liquid product as a complex raw material for different kind of organic compounds with interesting properties and structures. The yields of hard residue, pitch, pyrolysis water and gases were determined and compared with the yields of pyrolysis products of other investigated different kind of organic materials. The chemical composition of pitch was determined as following: free carbons - 4.52%, organic acids - 0.64%, organic bases -38.00%, phenols - 7.75%, asphaltenes - 0.97%, paraffin's - 1.30%, neutral oils - 16.20% and preasphaltanes - 30.10%. The pitch was fractionated by air distillation into 3 liquid fractions with different boiling range and a bitumen like residue with a lower softening temperature.
Abstract
Attempts are made to use kinetics parameters from thermal decomposition experiments at high temperatures to predict service lifetimes of polymeric materials at lower temperatures. However, besides the obvious measurement and extrapolation errors (which can be considerable), there are two fundamental reasons why quantitative long range extrapolations can not be made for complex condensed phase systems. They are: 1) Arrhenius kinetics parameters can not be extrapolated through phase transitions or softening temperatures; 2) Arrhenius kinetics parameters can not be extrapolated through the ceiling temperature region. Satisfactory lifetime prediction methods can be developed only after a thorough analysis of the causes of service failure. A real method has been taken from literature to illustrate the correct procedures.
Abstract
The thermal expansion, density and molar volume of some binary borate glasses were measured before and after exposure to a gamma-ray dose of 103 kGy. The expansion curves for all glasses, which were measured from room temperature to above the softening temperature, displayed similar characteristics. Increase of the lead oxide content decreased the thermal coefficient of expansion, but the effects of different alkali metal cations were shown to depend on their ionic radii. The various proposed mechanisms of thermal expansion are dealt with. The experimental results could be explained by considering the bond strengths, the polarizing powers of the different cations and the damage produced by radiation. The possible compaction of the structure due to irradiation is also discussed.
Abstract
Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) were used to study the thermal behaviour of (50-x)Na2O-xTiO2-50P2O5 and 45Na2O-yTiO2-(55-y)P2O5 glasses. The addition of TiO2 to the starting glasses (x=0 and y=5 mol% TiO2) resulted in a nonlinear increase of glass transition temperature and dilatation softening temperature, whereas the thermal expansion coefficient decreased. All prepared glasses crystallize under heating within the temperature range of 300–610°C. The contribution of the surface crystallization mechanism over the internal one increases with increasing TiO2 content. With increasing TiO2 content the temperature of maximum nucleation rate is also gradually shifted from a value close to the glass transition temperature towards the crystallization temperature. X-ray diffraction measurements showed that the major compounds formed by glass crystallization were NaPO3, TiP2O7 and NaTi2(PO4)3. The chemical durability of the glasses without titanium oxide is very poor, but with the replacement of Na2O or P2O5 by TiO2, it increases sharply.
Abstract
To satisfy the needs for industrial standards for thermal analysis in the Japanese polymer industry, round-robin tests of differential scanning calorimetry (DSC), thermogravimetry (TG), thermomechanical analysis (TMA) and thermodilatometry (TD) have been carried out recently. The results are discussed in this short review. The DSC applications tested were not only for determination of transition temperature but also for measurements of the transition heat and heat capacity. The TG task group did not aim at longterm thermal endurance studies, but relative thermal stability in molding and estimation of filler content, residual solvent content, etc. TMA was found to be a useful tool for measuring softening temperature and heat distortion temperature, especially for high-temperature engineering plastics, instead of the Vicat test which has temperature limitations. For temperature calibration of DSC and TG, ICTA-NIST certified reference materials were used together with other potential temperature standards; some inorganic substances and alloys were not found to be preferable to pure metals. For TMA and TD metal plates were found to be very useful for temperature calibration. Analysis of the round-robin test results also clarified present status of practical applications of thermal analysis, such as reproducibility and causes of errors.
