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This study explores the impact of different levels of halloysite nanotubes (HNT) and d-isomer on the non-isothermal crystallization behavior of the polylactic acid (PLA). The processing conditions, thermal flow, molecular orientation and the presence of nanofillers can affect the crystallinity and properties of PLA. In this work, PLA-based nanocomposite filaments were produced and their crystallization kinetics was studied. The data obtained through experiments, using differential scanning calorimetry at various cooling rates, were analyzed employing the Jeziorny and Mo models. And the activation energy of crystallization was determined by the Friedman method. The results showed that the growth of PLA crystals is three-dimensional, the HNT can accelerate the crystallization process, and crystallization occurs at higher temperatures in the presence of flow. The activation energy increased with addiction of more HNT in the nanocomposite. The study also found that the d-isomer has a more significant influence on the crystallization of PLA than HNT, which can inhibit crystal formation in some cases. These findings provide insights into the factors that can influence the properties of PLA nanocomposites and how they can be optimized. [ABSTRACT FROM AUTHOR]

We have developed an analytical method to quantitatively analyze differential scanning calorimetry (DSC) experimental data. This method provides accurate determination of thermal properties such as equilibrium melting temperature, latent heat, change of heat capacity which can be performed automatically without intervention of a DSC operator. DSC is one of the best techniques to determine the thermal properties of materials. However, the accuracy of the transition temperature and enthalpy change can be affected by artifacts caused by the instrumentation, sampling, and the DSC analysis methods which are based on graphical constructions. In the present study, an analytical function (DSCN(T)) has been developed based on an assumed Arrhenius crystal size distribution together with instrumental and sample-related peak broadening. The DSCN(T) function was successfully applied to fit the experimental data of a substantial number of calibration and new unknown samples, including samples with an obvious asymmetry of the melting peak, yielding the thermal characteristics such as melting and glass transition temperature, and enthalpy and heat capacity change. It also allows very accurate analysis of binary systems with two distinct but severely overlapping peaks and samples that include a cold crystallization before melting. [ABSTRACT FROM AUTHOR]

In this work, the effect of uniaxial stretching on the crystallization and melting behaviors, miscibility, crystal structure, and mechanical properties of neat poly(L-lactide) (PLLA) and miscible PLLA/poly(vinyl acetate) (PVAc) blends was investigated. Stretching process could generate remarkable influence on thermal properties of neat PLLA and PLLA/PVAc blend. With stretching ratio increasing, macromolecular chains orientation and crystallization were promoted, resulting in a decrease in cold crystallization temperature and an increase in glass transition temperature, and a significant increase in crystallinity. In addition, after stretching process PVAc still inhibited the crystallization of PLLA. PLLA/PVAc blends were completely miscible blend system which had only one glass transition temperature before and after stretching process, and phase separation did not occur after stretching process. When stretch ratio increased, amorphous PVAc had greater influence on the tanδ transition peak and storage modulus increased markedly, which was benefit to the improvement of heat resistance. The α′ crystal form was produced in blends after stretching process. Stretching process with moderate stretch ratio can be utilized to improve the mechanical properties of PLLA with simultaneous enhancement of tensile strength, fracture strain and stiffness. The findings in this work provide an insightful understanding of the effect of stretching process on miscible PLLA blend and the improvement of toughness, which will facilitate the large-scale practical application of PLLA. [ABSTRACT FROM AUTHOR]

The structural and thermal properties of sodium niobium phosphate glass are studied to analyse its suitability for immobilizing long-lived radioactive waste from nuclear reprocessing plants. Two series of sodium niobium phosphate glasses such as (A) xNb2O5–(50−x)Na2O–50P2O5 and (B) xNb2O5–(50−x/2)Na2O–(50−x/2) P2O5 (x = 0, 10, 20, 30, 40 mol.%) are prepared by the conventional melt–quenching technique. The influence of the incremental addition of Nb2O5 on the structural and thermal properties of the above two series is investigated. The FTIR and Raman spectra of these glasses revealed that the number of [NbO6] octahedral chain increases with Nb content and dominates as the major structural unit over the number of PO4 tetrahedra unit. The glass transition temperature (Tg), crystallization temperature (Tc) and melting temperature (Tm) are measured by using a differential scanning calorimeter (DSC). Other thermal stability parameters such as Hruby (KH), Angell (KA), Saad–Poulain (KSP) and Weinberg (KW), the total relaxation time of transformation and fragility are evaluated and compared between different composition of glasses. For both series A and B, the glass transition temperature increases with Nb content, suggesting the formation of a larger number of P–O–Nb or Nb–O–Nb linkages compared to the PO4 tetrahedra, resulting in a more rigid network. This is confirmed by Raman spectra which show an increase in the number of Nb–O–Nb bonds with Nb content. The major crystalline phases formed by devitrifying these glasses are identified by XRD and are found to be mainly NaPO3, NbOPO4, Na2Nb6P4O26 and Na4Nb8P4O32. [ABSTRACT FROM AUTHOR]

In this work, poly(ethylene glycol) (PEG)/boron nitride nanosheets (BNNS) masterbatch was prepared by freeze-drying their ultrasonically homogenized aqueous suspension, followed by melt-mixing with poly(lactic acid) (PLA) to fabricate the nanocomposites. The effect of PEG and BNNS on the crystallization behavior of PLA was investigated. The dynamic mechanical properties, thermal conductivity and thermal stability of the nanocomposites were also evaluated. It was found that, under quiescent conditions, PEG and BNNS had a synergistic effect on accelerating the nonisothermal crystallization of PLA. Unexpectedly, under injection molding conditions, the combination of PEG and BNNS had a negative effect on PLA crystallization. This can be ascribed to the plasticizing effect of PEG, which relaxes the orientation of PLA chains and retards flow-induced crystallization. Dynamic mechanical analysis (DMA) showed that the presence of BNNS enhanced the heat resistance of PLA only when PLA was crystallized, while further incorporation of PEG had a negative effect. Nevertheless, simultaneous use of PEG and BNNS had a synergistic effect on enhancing the thermal conductivity of PLA. [ABSTRACT FROM AUTHOR]

Metal ions, as common impurities in the crystallization process of explosives, have a significant influence on the crystal quality and performance. The effects of Fe3+, Zn2+, Ca2+ and Na+ ions on the crystallization and thermal properties of octogen (HMX) were studied. And the defect distribution as well as formation process of the explosive crystals doped with the metal ions were analysed. ICP, XPS and an etching method were utilized to characterize the contents and distributions of residual metal ions in the HMX crystals. The effects of the metal ions on the thermal decomposition and phase transition of HMX were obtained based on DSC-TG and in situ XRD. The mechanism of the influence of the metal ions on the crystallization of HMX was also explored. The results showed that the metal ions would change the nucleation growth mode of HMX to form dispersed crystalline HMX. The residual metal ions were mainly adsorbed on the crystal surface and included in the crystal. The metal ions had a significant influence on the thermal properties of HMX, with Ca2+ and Fe3+ inhibiting the thermally induced phase transition of HMX, Na+ promoting the phase transition of HMX, and the effect of Zn2+ on the phase transition of HMX depending on its concentration. The growth mechanism of doped HMX was lamellar stacking, and the metal ions changed the quality of the crystal by hindering the growth step of the HMX crystal. Since the crystal quality is highly related to the thermal performance, the safety of the explosive is affected. [ABSTRACT FROM AUTHOR]