Elaboration et caractérisation mécanique de composites à matrice céramique unidirectionnels

International audienceDes composites à matrice céramique unidirectionnels (minicomposites) ont été élaborés par procédé CVI (Chemical Vapor Infiltration), pour des fractions volumiques de matrice variant entre 12 et 35%. La porosité a été évaluée par une méthode d'analyse d'images à partir de plusieurs sections d'un même minicomposite. Afin d'augmenter le taux de fibres (>50%) au sein d'un minicomposite, une méthode de guipage a été développée. L'objectif est de caractériser le comportement mécanique de ces minicomposites, par des essais de traction. Les mécanismes de fissuration matricielle et interfaciale sont modélisés par une approche énergétique, qui permet d'évaluer les énergies de rupture de la matrice et de l'interface fibre/matrice. Les essais expérimentaux et les réponses en traction simulées montrent que l'augmentation de la fraction volumique de matrice favorise l'amorçage de fissures matricielles et permet d'augmenter la déformation à rupture. A l'inverse, l'amorçage de fissures est retardé avec l'augmentation du taux de fibres

Monitoring carbon dioxide concentration for early detection of spoilage in stored grain

Field experiments were conducted in storage silos to evaluate carbon dioxide sensors to monitor spoilage in grain prior to spoilage detection by traditional methods such as visual inspections and temperature cables. Carbon dioxide concentrations in the storage silo were monitored up to eight months and correlated to the presence of stored-product insects, molds and mycotoxin levels in the stored grain. The data showed that safe grain storage was observed at CO2 concentrations of 400 to 500 ppm. Higher concentrations of CO2 clearly showed mold spoilage or insect activity inside the grain storage silo. Carbon dioxide concentrations of 500 to 1200 ppm indicated onset of mold infection where as CO2 concentrations of 1500 to 4000 ppm and beyond clearly indicated severe mold infection or stored-product insects infestation. The percent kernel infection was in the range of 30% for CO2 concentrations of 500 to 1000 ppm to 90% for CO2 concentrations of 9000 ppm. Fungal concentrations were in the range of 2.0 ×102 colony forming units per gram (cfu/g) at 500 ppm CO2 concentration to 6.5 ×107 cfu/g at 9000 ppm CO2 concentration. Fungi of genera Aspergillus spp., Penicillium spp., and Fusarium spp. were isolated from spoiled grain. High concentration of fungi and presence of mycotoxins (aflatoxin: 2 ppb and Deoxynivalenol (DON): 1 ppm) were correlated with high CO2 concentration in the silos. The findings from this research will be helpful in providing more timely information regarding safe storage limits, aeration requirements and costs of spoilage mitigation measures such as turning, aerating and fumigating grain. Additionally, it will provide information on preventive stored grain quality management practices that should reduce residue levels of mycotoxins, pesticides and other foreign material in our food supply. The CO2 monitoring technology will increase the quality and quantity of stored grain, while saving the U.S. and global grain production, handling and processing industry millions of dollars annually. Keywords: Carbon dioxide, Grain storage, Stored-product insects, Mold and mycotoxi

Nitrogen sources on TPOMW valorization through solid state fermentation performed by Yarrowia lipolytica

This manuscript reports the valorization of two-phase olive mill waste (TPOMW) as raw material and carbon source for solid state fermentation using Yarrowia lipolytica as biocatalyst. Due to its chemical characteristics, a combination of different raw materials (TPOMW and wheat bran, WB) was evaluated and two distinct nitrogen sources were applied as supplementation for lipase production. A TPOMW/WB ratio of 1:1 and supplementation with ammonium sulfate was chosen as the best condition. The productivity in 24 h reached 7.8 U/gh and, after four days of process, only decreased about 35%. Process pH ranged from 5.5-5.9, remaining in an acid range. Thus, the successful use of TPOMW, a watery solid by-product with high content of lipids, as raw material for Yarrowia lipolytica growth and lipase production provided an environmental friendly alternative to valorize such waste.The authors kindly acknowledge the financial aid and research scholarships given by CAPES. Maria Alice Zarur Coelho thanks CNPq (Proc. 308890/ 2013-2)