Capillary penetration in cellulose and polyethylene porous media: effect of contact with vapours and partial saturation with a non-miscible liquid

Capillary penetration for the development of a method for the assessment of shelf-life of foods

Temperature sensitive foods require monitoring of their time–temperature history in order to assure their safety and high quality. The same holds for other perishable products such as medical and pharmaceutical. The best means to have information on the time–temperature history of a product is by having measurement of these variables along the whole product shelf-life. As an answer to this need several time–temperature indicators have been developed and commercialized for monitoring the quality of food products. In this work a full history time–temperature indicator (TTI) has been designed and developed based on capillary penetration of safe and low surface tension liquids in micro porous polyethylene porous media. For the development of the indicator the appropriate porous media and penetration liquids were selected and capillary penetration of the selected liquids took place at two different temperatures. Based on the results of the capillary penetration experiments the TTI was developed and a prototype was evaluated in a food product in order to assess its capability to be used in food packaging. The results showed that the TTI is simple in use and could provide a quantitative and easy-to-read response. Moreover, the response of the TTI could be calibrated by changing several design parameters, in order to match the quality deterioration kinetics of the specific food product to be monitored.

Plant Nanomaterials and Inspiration from Nature: Water Interactions and Hierarchically Structured Hydrogels

Recent developments in the area of plant-based hydrogels are introduced, especially those derived from wood as a widely available, multiscale, and hierarchical source of nanomaterials, as well as other cell wall elements. With water being fundamental in a hydrogel, water interactions, hydration, and swelling, all critically important in designing, processing, and achieving the desired properties of sustainable and functional hydrogels, are highlighted. A plant, by itself, is a form of a hydrogel, at least at given states of development, and for this reason phenomena such as fluid transport, diffusion, capillarity, and ionic effects are examined. These aspects are highly relevant not only to plants, especially lignified tissues, but also to the porous structures produced after removal of water (foams, sponges, cryogels, xerogels, and aerogels). Thus, a useful source of critical and comprehensive information is provided regarding the synthesis of hydrogels from plant materials (and especially wood nanostructures), and about the role of water, not only for processing but for developing hydrogel properties and uses.

Height-time and weight-time approach in capillary penetration: Investigation of similarities and differences

Capillary penetration is commonly used in a wide range of applications such as oil recovery, textile engineering and food technology. Furthermore, it is a useful tool for surface characterization of powders and porous media. Two are the commonest experimental methods to study capillary penetration: the height-time and the weight-time technique. However, it is not clear whether the two approaches provide the same results. This work aims to investigate similarities and differences between the two approaches and assess whether it is possible to replace one with another. To this end, capillary penetration experiments were performed in different porous media where the pore size distribution and shape varied. Height and weight data were recorded simultaneously. It was found that results of the two experimental approaches are not always equivalent and that this depends on the porous medium properties. In some cases results depended on the degree of saturation of the porous medium with the penetrating liquid. An analysis of weight-time data to provide pore size distribution as a function of pore volume is proposed. Furthermore, two different approaches of the fractal theory were applied and the time exponent, the material fractal dimension and the tortuosity fractal dimension were determined.