Search results for "Relative Humidity"
showing 10 items of 156 documents
Water barrier properties of treated-papers and application to sponge cake storage
2006
Abstract Water barrier properties of three treated papers and of one plastic film were compared and the potential of these packaging films to prevent moisture loss from a sponge cake during storage in standard conditions (25 °C and 50% relative humidity gradient) was evaluated. Sorption isotherms were established at 25 °C for both sponge cake and papers, from which diffusivity values in papers were determined for the whole range of A w . Permeability of packaging films was determined in standard conditions. Water sorption was close for all papers, regardless of their treatment, whereas water diffusivity was reduced by coating or calendering. Water vapor permeability in papers was controlled…
Hydration and water holding properties of cross-linked lignite humic acids
2014
Abstract Lignite and lignite humic acids, which are used as soil amendments sometimes, are supposed to improve soil properties such as water holding capacity. The structure of those materials is composed of various organic molecules stabilized mostly by weak interactions. Therefore, excess of water causes only partial swelling, but most of the physical structure is destabilized. This accelerates the desiccation and hampers their application as natural hydrogel-like substances. In order to stabilize the structure of lignite humic acids and improve the water holding capacity, we applied formaldehyde cross-linking procedure based on covalent coupling of aromatic humic acids moieties. By combin…
Physical modeling of heat and moisture transfer in wet bio-sourced insulating materials.
2018
Simultaneous heat and moisture transfers in bio-sourced insulating materials are significant phenomena in thermal metrology. The present study focuses on these phenomena by experimental and numerical approaches based on the asymmetric hot-plate method. In this paper, a bio-sourced insulating material based on flax fibers is developed. The thermal and hygric properties of the sample are then investigated in the humid atmosphere. The temperature is maintained at 30 °C, and the relative humidity varies between 30% and 90% RH. A physics-based model of simultaneous heat and moisture transfer is developed for thermal conductivity estimation. This model is discretized with finite difference method…
Water transport in epoxy/MWCNT composites
2013
Moisture and water uptake of epoxy/multi-wall carbon nanotube (MWCNT) composites was studied in a wide range of atmosphere relative humidity and temperatures. Addition of up to 1 wt.% of MWCNTs into the neat epoxy resulted to the twofold decrease of the diffusivity, while the levels of moisture/water uptake remained unchanged. The positive effect on the reduction of the diffusion coefficient diminishes with the increase of temperature. Differences in the water transport properties and plasticization ability of the neat polymer and its nanocomposites are explained by the free volume considerations and the polymer–water interactions, which are verified by the results of thermomechanical analy…
A new approach to studying sponge cake aroma after storage in treated paper and plastic packaging by direct gas chromatography–olfactometry (D-GC–O)
2007
The objective of this study was to use D-GC–O to compare the global odour of a sponge cake flavoured with either a ‘viennoiserie’ aromatic note or a simplified mixture of aroma compounds (used for physicochemical studies), then stored in a glass packaging (inert and impermeable) or in pouches made with treated papers or with plastic packaging, in accelerated ageing conditions (high temperature and relative humidity gradient). After 1 week of storage, the flavoured sponge cake headspace was SPME-extracted directly into the packaging and analysed by D-GC–O. The sponge cake global odour was better retained if plastic film rather than treated-papers was used, for both flavourings. Changes in th…
Three-Dimensional Microstructural Properties of Nanofibrillated Cellulose Films
2014
Abstract: Nanofibrillated cellulose (NFC) films have potential as oxygen barriers for, e.g., food packaging applications, but their use is limited by their hygroscopic characteristics. The three-dimensional microstructure of NFC films made of Pinus radiata (Radiata Pine) kraft pulp fibres has been assessed in this study, considering the structural development as a function of relative humidity (RH). The surface roughness, micro-porosity, thickness and their correlations were analyzed using X-ray microtomography (X–μCT) and computerized image analysis. The results are compared to those from scanning electron microscopy and laser profilometry. Based on a series of films having varying amounts…
Bactrocera oleae. Fattori naturali di controllo
2019
Bactrocera oleae. Natural control factors. Natural control factors (parasitoids and climatic factors) influencing the olive fruit fly, Bactrocera oleae, are analysed comparing two different areas of cultivated and wild olives, Sicily and the Western Cape of South Africa. Bactrocera oleae has a similar level of parasitization in both areas, much higher in wild olives than in cultivated ones. Climatic conditions are much more important than climatic factors, influencing the growth of olive fruit fly populations, producing a higher level of infestation in more humid and rainy productive seasons.
Humidity effect on ammonia sensing properties of substituted and unsubstituted cobalt phthalocyanines
2012
In this paper, we studied the effect of humidity on the response of cobalt phthalocyanine-containing resistors to ammonia, in the ppm range. We pointed out the fact that, when alternating exposure periods with recovery periods, the humidity effect had to be carefully studied, in correlation with the flow variation. Thus, for a sulfonated cobalt phthalocyanine, the effect of NH(3) was totally screened as soon as the relative humidity (RH) was above 10%. On the contrary, when using unsubstituted cobalt phthalocyanine (CoPc) as sensing material, the sensors' response to NH(3) appears to be quite stable in a wide RH range, allowing a discrimination between 12, 25 and 50 ppm of NH(3) over the 10…
Impact of relative air humidity fluctuations on the survival of Listeria monocytogenes : application to improve hygiene in food processing environment
2016
Environmental hydration fluctuations influence microorganism viability and activity. The air relative humidity (RH) is a potentially effective parameter to control the development and the persistence of pathogenic microorganisms. However, efficiency of this parameter remains not well characterized compared to others environmental factors such as pH or temperature. Drying is the final step of cleaning and disinfection processes used in the food industry. However, if this process is empirically used, it could also be used to improve the decontamination of surfaces in premises and reduce the persistence of microorganisms. Despite cleaning and disinfection, Listeria monocytogenes is commonly fo…
High-Resolution Fluorescence Spectra of Airborne Biogenic Secondary Organic Aerosols: Comparisons to Primary Biological Aerosol Particles and Implica…
2021
Aqueous extracts of biogenic secondary organic aerosols (BSOAs) have been found to exhibit fluorescence that may interfere with the laser/light-induced fluorescence (LIF) detection of primary biological aerosol particles (PBAPs). In this study, we quantified the interference of BSOAs to PBAPs by directly measuring airborne BSOA particles, rather than aqueous extracts. BSOAs were generated by the reaction of d-limonene (LIM) or α-pinene (PIN) and ozone (O3) with or without ammonia in a chamber under controlled conditions. With an excitation wavelength of 355 nm, BSOAs exhibited peak emissions at 464–475 nm, while fungal spores exhibited peak emissions at 460–483 nm; the fluorescence intensit…