New trends in polylactide (PLA)-based materials: “Green” PLA-Calcium sulfate (nano)composites tailored with flame retardant properties

Starting from gypsum, a by-product of lactic acid fabrication process, novel “green” composites have been produced by melt-blending polylactide (PLA) and this filler after a previous specific dehydration to obtain anhydrite II (AII). Such a material is potentially interesting in biodegradable/rigid packaging and in technical applications requiring rigidity, heat resistance and dimensional stability. In order to obtain PLA-AII composites characterized by specific end-use flame retardant properties, the addition of selected organo-modified layered silicates (OMLS) was considered. Co-addition of AII and OMLS leads to PLA (nano)composites characterized by good (nano)filler dispersion, thermal stability and adequate mechanical resistance. The flame retardant properties as shown by cone calorimetry showed significant increase in the ignition time compared to neat PLA and a substantial decrease, i.e., ca. 40%, of the maximum rate of heat release, whereas the UL94 HB test was successfully passed revealing non-dripping effect and extensive char formation. The study represents a new approach in formulating novel PLA grades with improved characteristic features.     

Sol–gel synthesis and crystallisation of 3CaO·2SiO2 glassy powders

A gel of composition 3CaO·2SiO₂ was synthesised by means of sol–gel route involving hydrolysis of tetramethyl orthosilicate (TMOS) with calcium nitrate in alcoholic medium, and polycondensation reaction. The gel was submitted to DTA and TGA analysis and the resulted material was examined by FTIR spectroscopy and X-ray powder diffractometry. The thermal treatments required for the gel into glass conversion led to a partially devitrified product. The XRD analysis showed that the structure obtained is highly depolymerised.     

Long range correlation of hydrophilicity and flexibility along the calcium binding protein chains

Long range correlation concerning hydrophilicity and flexibility along a number of 80 calcium binding protein sequences is confirmed by using spectral analysis and detrended fluctuations analysis methods, as well as by Hurst exponent calculations. There are no significant differences between the correlation properties concerning these properties for the two structural subfamilies, extended and compact, of the calcium binding proteins and they are also similar with the correlation properties revealed by other investigated proteins. This result sustains the hypothesis that the long range correlation of hydrophilicity and flexibility along the chain is a common feature of proteins.     

Observation of single Ca ions for trace isotope analysis

We developed an ion trap — laser cooling system for observing the laser induced fluorescence (LIF) of a single ion, in the view of utilizing it for the trace isotope analysis of Ca. We observed stepwise LIF signals, which correspond to the numbers of trapped ⁴⁰Ca⁺ ions (⁴⁰Ca/Ca = 96.9%). The detection efficiency was evaluated and the observation of single ions demonstrated the experimental feasibility of trace isotope analysis. Furthermore, as the next step towards trace isotope analysis, we report observation of the even calcium isotopes, ⁴⁴Ca (⁴⁴Ca/Ca = 2.09%) and ⁴⁸Ca (⁴⁸Ca/Ca = 0.187%), without the use of a selective loading method.     

Conductometric and microcalorimetric analysis of the alkaline-earth/alkali-metal ion exchange onto polyacrylic acid

The specificity of the exchange between divalent (Di²⁺ = Ca²⁺ or Ba²⁺) and monovalent (M⁺ = Li⁺, Na⁺ or K⁺) ions onto a polyacrylic chain is examined using conductometric and microcalorimetric techniques. Assuming the formation of a bidentate complex between the Di²⁺ and the carboxylate groups, the conductometric data give the exchange ratio (Di²⁺/M⁺) and the speciation of the acrylic groups. No significant difference is observed between the three alkali-metal ions for a given Di²⁺ ion. Comparisons between Ca²⁺ and Ba²⁺ show a stronger hydrophobicity of the former as it precipitates at a complexation ratio r = 0.33 versus r = 0.45 for the Ba²⁺ salt. Microcalorimetric data show that all Di²⁺/M⁺ exchange energies are positive and depend significantly on the type of cations. The largest displacement energy (the more positive) is found for the binding of Ca²⁺ with sodium polyacrylate (8.13 kJ · mol⁻¹) and the smallest for Ba²⁺ with lithium polyacrylate (1.88 kJ · mol⁻¹). The interpretation of the data leads to the conclusion that specificity of the Di²⁺ binding originates in the dehydration phenomenon and specificity between the three alkali-metal ions is due to the decrease in the electrostatic bond strength with an increase in the ionic radii. The Di²⁺/M⁺ exchange is entropically driven. Received: 28 January 1999 Accepted in revised form: 7 April 1999     

Influence of processing variables on the formation of La2Zr2O7 in transferred arc plasma torch processing

The transferred arc plasma (TAP) torch process has various noteworthy features such as extremely high temperatures, low environmental impact and short processing time which makes it the most suitable technique for synthesizing ceramic composite materials. Furthermore, it is a direct two-step technique which by its virtue of high temperature and power density paves way for high production rate. Hence in this study, an effort has been made to utilize the TAP torch processing technique for the bulk production of La₂Zr₂O₇ with time effectiveness from the mixture of La₂O₃ and ZrO₂ powders (1:2 mol ratios) which were ball milled for 4 h. For this purpose, transferred arc plasma torch was specially designed in laboratory scale level and the operating parameters were optimized in order to achieve maximum La₂Zr₂O₇ formation efficiency. In this study, the phase and microstructure formation of the processed samples was analyzed via X-ray diffraction (XRD) and scanning electron microscope (SEM) images respectively. Moreover, EDX analysis was incorporated to highlight the superior influence of the longer processing time on the stoichiometric ratio of ZrO₂/La₂O₃ in the processed sample as against input power and the gas flow rate.     

Surface structures and osteoblast response of hydrothermally produced CaTiO3 thin film on Ti-13Nb-13Zr alloy

This study investigated the surface characteristics and in vitro biocompatibility of a titanium (Ti) oxide layer incorporating calcium ions (Ca) obtained by hydrothermal treatment with or without post heat-treatment in the Ti-13Nb-13Zr alloy. The surface characteristics were evaluated by scanning electron microscopy, thin-film X-ray diffractometry, X-ray photoelectron spectroscopy, atomic force microscopy and contact angle measurements. In vitro biocompatibility of the Ca-containing surfaces was assessed in comparison with untreated surfaces using a pre-osteoblast cell line. Hydrothermal treatment produced a crystalline CaTiO₃ layer. Post heat-treatment at 400 °C for 2 h in air significantly decreased water contact angles in the CaTiO₃ layer (p < 0.001). The Ca-incorporated alloy surfaces displayed markedly increased cell viability and ALP activity compared with untreated surfaces (p < 0.001), and also an upregulated expression of various integrin genes (α1, α2, α5, αv, β1 and β3) at an early incubation time-point. Post heat-treatment further increased attachment and ALP activity in cells grown on Ca-incorporated Ti-13Nb-13Zr alloy surfaces. The results indicate that the Ca-incorporated oxide layer produced by hydrothermal treatment and a simple post heat-treatment may be effective in improving bone healing in Ti-13Nb-13Zr alloy implants by enhancing the viability and differentiation of osteoblastic cells.     

Continuous Preparation of Calcite,Aragonite and Vaterite,and of Magnesium‐Substituted Amorphous Calcium Carbonate (Mg‐ACC)

The three water‐free calcium carbonate polymorphs calcite, aragonite and vaterite were prepared from aqueous solutions without additives using standard laboratory equipment in a continuous process. Variation parameters were the way of mixing, the solution concentrations, and the reactor residence time. The samples were crystallographically and chemically pure, but a thorough elemental analysis revealed the presence of small amounts of sodium carbonate which was not detectable by X‐ray powder diffraction. The continuous process avoids the inherent variability of batch syntheses. By adapting the crystallization parameters, magnesium‐substituted amorphous calcium carbonate (molar ratio of Mg:Ca of 1:2.68) was prepared in this continuous process.     

Mineralization of biomimetically carboxymethylated collagen fibrils in a model dual membrane diffusion system

In the present work, we show for the first time, that N^?-carboxymethyllysine is the major product of the in vitro non-enzymatic glycation reaction between fibrillar collagen and glucuronic acid. Dual diffusion membrane system was effectively used for oriented crystal growth of octacalcium phosphate/hydroxyapatite on the biomimetically carboxymethylated collagen fibrils. We hypothesize that the function of biomimetically carboxymethylated collagen is to increase the local concentration of corresponding ions in such a way that a critical nucleus of ions can be formed, leading to the formation of the mineral under specific micro-environment conditions achieved by using diffusion membrane system.     

海螺状碳酸钙的可控合成与荧光性能

采用液相沉淀法,以硝酸铋[Bi(NO_3)_3]为添加剂来调控碳酸钙晶体的形状与大小,制备了海螺状碳酸钙粒子.通过扫描电子显微镜(SEM)、X射线衍射仪(XRD)、热重分析仪(TGA)、原子荧光光谱仪(AFS)等对产物的结构和性能进行了表征.结果表明,在60℃条件下,添加20 mL浓度为2 g/L的Bi(NO_3)_3溶液可得到海螺状球霰石型碳酸钙粒子,且其荧光性明显增强.在碳酸钙的成核过程中,Bi~(3+)的加入起到了显著的调控作用.