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The heat of fusion of nascent poly(4-methyl pentene-1)(P4MP) has been measured with a slow temperature-ramp. Two melting ranges have been observed. A broad endotherm is found mostly below the equilibrium melting temperature,T m,o. The total heat of fusion ΔH total is the sum of ΔH dsc, the melting enthalpy found by rapid heating and a second endotherm, ΔH network, a contribution associated with the heat of disordering of a physical network. Similar reported analysis have been presented before on polyethylene and isotactic polypropylene. The ΔH total for P4MP is found to be 100±10 J g−1, in the upper range of the expected values of ΔH o, the heat of fusion of perfect crystals. The value of ΔH total constitutes a lower limit of ΔH o in cases like that of P4MP where other methods lead to ambiguous results. The comparison ofT m andT d, the melting and dissolution temperatures, and other results support the hypothesis that the equilibrium phase at the melting of P4MP is partially rigid while it is a liquid (or a mixture of a glass and a liquid) at the dissolution.
Abstract
A novel gelling method was studied to stabilize phase change material Na2HPO4 · 12H2O with amylose grafted sodium acrylate. Gelled Na2HPO4 · 12H2O shows stable heat storage performance prepared at optimized conditions: 2.7mass/mass% sodium acrylate, 0.4 mass/mass% amylose, 0.05–0.09 mass/mass% N, N′-methylenebisacrylamide, 0.05–0.09 mass/mass% K2S2O8 and Na2SO3 (mass ratio 1:1), at 50 °C. Na2HPO4 · 12H2O was dispersed in gel network as tiny crystals less than 0.1 mm. Melting points were in the range 35.4 ± 2 °C. Short-term thermal cycling proves the effectiveness of the novel method for eliminating phase separation in the gelled salt. Adiabatic calorimetric measurement of heat capacities shows two phase transitions, which correspond to melting of Na2HPO4 · 12H2O and freezable bond water in gel, respectively. Heat of fusion of pure Na2HPO4 · 12H2O was determined as 260.9 J g−1. Distribution of extra water is: free water:freezable water:nonfreezing water = 0:0.85:0.15.
Thermoplastic polymers quality control
DSC baseline optimisation for heat of fusion measurements
A technique is proposed for improving the accuracy of the heat of fusion of semicrystalline polymers by DSC. The results of three commercially available instruments are compared.
Abstract
Differential scanning calorimetry (DSC) is a thermal analytical tool for preformulation studies. Extrapolated melting temperature (T P) and heat of fusion (ΔH f) can be used as parameters for optimizing the DSC performance. Two model pharmaceuticals acetaminophen and nicotinamide are used in this study. Using a factorial design for the experimental model and matrix analysis the results, the effect of sample mass, heating rate and the nitrogen flow rate were evaluated on the ΔH f values and T P values. Two levels for each of the procedural variables were used as a balanced experimental design with two sample sizes, two heating rates and two nitrogen flow rates. It was found that the change in the heating rate caused significant changes in the ΔH f values but not the T p values for acetaminophen. However, no significant effect was found for the T p value but ΔH f value was affected to a certain extent for nicotinamide.
samples KP-2a and KP-API2a stored at 25 °C show the single endotherm coming from the substance melting. Thermal parameters such as heat of fusion and melting point (onset) are similar for the initial and stored samples (Δ H ≈ 80 J/g and onset ≈ 120 °C
liquidus ( T L ) temperatures. Latent heat of fusion is defined in a body flux [ 23 ] 6 where ρ S is solidus density, H L is a latent heat of fusion and is a function determining the fraction of solid phase in the mushy zone. After
crystallinity calculated from the heat of fusion. In the present work, the effect of the rigid amorphous fraction (RAF) on the traditional amorphous fraction (TAF) will be discussed: the hysteresis peak at the glass transition of the TAF disappears under
thermal conductivity similar to metal, it has low latent heat of fusion. Eutectics are an additional option for PCMs. Eutectics are mixtures of two or more substances, including organic and organic, inorganic and inorganic, or organic and inorganic. The
Abstract
The thermal analytical study of most hydrophobic and hydrophilic D/L amino acids reveals significant hydropathy index correlation between the presence of water and crystalline amino acids. The TG derivative mass profiles for arginine and lysine (hydrophilic acids) at various time intervals of atmospheric exposure, show two distinct peaks, one between 50 and 60°C (unbound water), and one close to 100°C (bound-like water). The DSC heat-cool profiles for lysine and arginine confirmed the presence of these multiple waters with two heats of vaporization. The absence of these patterns from the TG and DSC for cysteine and phenylalanine (hydrophobic acids) further supports the conclusions.
the standard temperature and pressure. Heat of vaporization for water is 2,257 J g −1 . The heat of fusion (Δ H f ) is the result of the change in the phase of water from solid to liquid, which occurs at the melting temperature ( T m ). Heat of fusion
