Search results for "calcium carbonate"

Rheological and mechanical properties of biodegradable nanocomposites

2018

Polymer nanocomposites have gained huge interest over the last decade. However, traditional thermoplastic nanocomposites do not match the rising concern about environmental issues. Therefore, during the last years, the search for biodegradable polymer nanocomposites is gaining importance. Most of biobased (i.e. based on biodegradable/bioderived polymer matrices) nanocomposites have poly(lactic acid), PLA, as matrix. However, it is of clear interest to take into account also different biobased polymer matrices, such as MaterBi. In this work, we prepared bionanocomposites containing MaterBi or a PLA-based polymer matrix, with two different kinds of nanofillers (organomodified clay and nanosiz…

Well-defined carbohydrate-based polymers in calcium carbonate crystallization: Influence of stereochemistry in the polymer side chain on polymorphism…

2015

Abstract In this work we demonstrate the remarkable phase control on the crystallization of calcium carbonate by the stereochemistry of carbohydrate-based polymers. The polymers (poly(2-(2,3,4,6-tetra-O-acetyl-β- d -glucosyloxy)ethyl methacrylate) and poly(2-(2,3,4,6-tetra-O-acetyl-β- d -galactosyloxy)ethyl methacrylate)) have been synthesized from the respective glucose or galactose containing monomers (3 step synthesis) by RAFT polymerization leading to well-defined carbohydrate-based polymers with number averages of the molecular weights (Mw) of 10,000–18,000 g/mol and a dispersities (Đ) from 1.1 to 1.2. For the deprotected polymers we found differences in the phase selection of calcium …

Cementing agents involved in the macro- and microaggregation of a Mediterranean shrubland soil under laboratory heating

2014

The heating effect on aggregation and cementing agents of a Mediterranean soil was studied in two fractions (macro- and microaggregates) in different environments: under Quercus coccifera soil (UQ), under Rosmarinus officinalis soil (UR) and between plants or bare soil (BS). Samples were heated under laboratory conditions at different temperatures (220, 380, 500, 750 and 1000. °C) to establish their effects on the studied soil properties by comparison with unheated control samples (25. °C). Increasing temperature treatments caused significant changes in most soil variables. In both soil fractions, the presence of vegetation contributed to increase of the soil organic matter (SOM) content, w…

Nano‐Powdered Calcium Carbonate Reference Materials: Significant Progress for Microanalysis?

2019

Fast Solution Precursor Synthesis of the 2223 Phase: the Role of Lead in the Reaction Pathway

1994

ABSTRACTValuable mechanistic information, about the reaction pathway in the formation of the 2223 phase, has been obtained by the use of a solution synthesis route. The presence of lead in the starting mixture has remarkable effects on the nature and stability of the different intermediates: i) the grain size and morphology of Bi2CuO4 is severely changed, ii) calcium carbonate is partially decomposed to yield the calcium plumbate, iii) the 2201 phase results stabilized against the formation of the collapsed phase Bi17Sr16Cu7O49-δ, iv) the melting point of the intermediate 2212 is lowered by about 10 °C. All these effects, due to lead substitution, contribute to promote the formation of the …

Orchestin, a calcium-binding phosphoprotein, is a matrix component of two successive transitory calcified biomineralizations cyclically elaborated by…

2003

Orchestia cavimana is a crustacean that cyclically replaces its calcified cuticle during molting cycles in order to grow. Its terrestrial way of life requires storage of calcium during each premolt period, as calcareous concretions, in tubular diverticula of the midgut. During the postmolt period the stored calcium is reabsorbed and is translocated through the storage organ epithelium as calcified small spherules. In a previous study, we sequenced and characterized a remarkable component of the organic matrix of the premolt storage structures, Orchestin, which is a calcium-binding phosphoprotein. In this paper, we analyzed the spatiotemporal expression of the orchestin gene by Northern blot…

Spine and test skeletal matrices of the Mediterranean sea urchinArbacia lixula- a comparative characterization of their sugar signature

2015

15 pages; International audience; Calcified structures of sea urchins are biocomposite materials that comprise a minor fraction of organic macromolecules, such as proteins, glycoproteins and polysaccharides. These macromolecules are thought to collectively regulate mineral deposition during the process of calcification. When occluded, they modify the properties of the mineral. In the present study, the organic matrices (both soluble and insoluble in acetic acid) of spines and tests from the Mediterranean black sea urchin Arbacia lixula were extracted and characterized, in order to determine whether they exhibit similar biochemical signatures. Bulk characterizations were performed by mono-di…

Comparative ultrastructure and carbohydrate composition of gastroliths from Astacidae, Cambaridae and Parastacidae freshwater crayfish (Crustacea, De…

2012

21 pages; International audience; Crustaceans have to cyclically replace their rigid exoskeleton in order to grow. Most of them harden this skeleton by a calcification process. Some decapods (land crabs, lobsters and crayfish) elaborate calcium storage structures as a reservoir of calcium ions in their stomach wall, as so-called gastroliths. For a better understanding of the cyclic elaboration of these calcium deposits, we studied the ultrastructure of gastroliths from freshwater crayfish by using a combination of microscopic and physical techniques. Because sugars are also molecules putatively involved in the elaboration process of these biomineralizations, we also determined their carbohy…

The influence of ossein-hydroxyapatite compound ('Ossopan') on the healing of a bone defect.

1986

A study was undertaken in 60 adult rabbits in order to determine the effects of ossein-hydroxyapatite compound on bone healing. Standardized bony defects were produced in the distal femoral epiphyses, after which animals were randomized into four equal groups. An untreated group served as a control. One group received ossein-hydroxyapatite compound, 830 mg per day, a second group received bone mineral (ossein-hydroxyapatite compound reduced to ash, to remove organic constituents), 510 mg per day, and a third group received calcium carbonate, 650 mg per day. A series of fluorescent vital markers was administered to the animals from the 7th to the 32nd day after production of the defect. A th…

Analysis of radiolucent gallstones by computed tomography for in vivo estimation of stone components.

1990

. Successful oral litholytic and other non-operative therapies of gallstones require exact determination of the stone components. Since computed tomography (CT) provides highly sensitive measurement of density, we performed a study to evaluate whether CT measurement of stone density allows a prediction of the composition of radiolucent gallstones. Twenty-eight patients presenting with 29 radiolucent gallbladder (n= 17) or common bile duct stones (n=12) were included. Prior to operative or endo-scopic therapy the attenuation values (Hounsfield Units, HU) were assessed in vivo by CT under standardized conditions (Somatom II, 125 KV, 130 mAs). After surgical or endoscopic stone removal the con…