Dielectric spectroscopy measurements of the sub-Tg relaxations in amorphous ethyl cellulose: A relaxation magnitude study

Amorphous ethyl cellulose exhibits three secondary relaxations at temperatures below its glass transition. The fitted parameters that describe these processes and the comparison with other polysaccharides allow to ascribe the relaxations to lateral groups on one hand and to local main chain motion on the other hand. Their contributions to the dielectric constant overlap and induce a broad dielectric losses peak. The amplitude of one of these relaxations is found to decrease regularly with time. It is believed it comes from a gradual change of the polar groups chemical environment that constrains their motion

Dielectric spectroscopy measurements of the sub-Tg relaxations in amorphous ethyl cellulose: A relaxation magnitude study

Amorphous ethyl cellulose exhibits three secondary relaxations at temperatures below its glass transition. The fitted parameters that describe these processes and the comparison with other polysaccharides allow to ascribe the relaxations to lateral groups on one hand and to local main chain motion on the other hand. Their contributions to the dielectric constant overlap and induce a broad dielectric losses peak. The amplitude of one of these relaxations is found to decrease regularly with time. It is believed it comes from a gradual change of the polar groups chemical environment that constrains their motion

Study of release kinetics of small and high molecular weight substances dispersed into spray-dried ethylcellulose microspheres.

Spray-dried ethylcellulose microspheres were used as matrices for the encapsulation of a fungal lactase and/or small paramagnetic probes (Tempol or Tempo). Their dissolution in water was studied. Kinetics fitted with the model Q = kt(n) of Korsemeyer et al. [Int. J. Pharm. 15 (1983) 25] exhibited a non-Fickian diffusion. The calculated diffusional exponent (n) values were near 0.26 whatever the encapsulated probes. The release rates (k) were only slightly different for paramagnetic probes and lactase. This result indicated that the probes' release mechanisms are not diffusion controlled. Other factors such as matrix porosity and probe solubility in the matrix and in water could influence the probes' release rate

Chapter 10 : Water Activity in Foods

International audienceThis chapter focuses on the role of water in the physical stability of foods with an emphasis on texture stability of foods with an emphasis on texture (i.e. crispness, softness, stickiness) and structure characteristics (i.e. crystallization, caking, collapse, etc.) of the products. The efficiency of water as a plasticizer is based on water's affinity for other molecules and its ability to form a homogeneous mix without phase separation. The consequence of water plasticization on the material's mechanical properties has often been compared with the plasticization resulting from a temperature increase. Because the physical stability may affect several time‐scales, an optimal control of the humidity will be required during processing, handling, transportation, storage, and consumption. When the effects of water cannot be overcome by the product's composition, technological solutions may lay in the design of moisture barriers or by a strict control of the temperature