Preliminary permeation experiments

Two different types of preliminary permeation experiments were performed on MFC films manufactured from blends of LLDPE (matrix) and PET (reinforcing) to ascertain if there was any enhancement of barrier properties occurring in comparison to neat LLDPE films. 

Oxygen was used as the penetrant gas because of the negative effect it has on the quality of milk. The first experiment investigated the effect of a film s PET content on its oxygen permeability, and the second studied the influence of the draw ratio applied during manufacturing of the MFC. For more information on the process used to produce MFCs, refer to Chapter 11, S. Fakirov. 

Films with PET content between 0 to 60 wt% were produced and tested. Blends with greater than 30 wt% microfibrils were unable to consolidate into films suitable for permeability testing, with voids occurring at the pellet boundaries. 

A variety of extrusion, drawing and pressing parameters were used to create blends containing one of four different dispersion shapes for the reinforcing polymer (PET). The intended dispersion shapes were spheres, cigars/platelets, microfibrils and nanofibrils. It was expect- 

Sample Extrusion diameter (mm) Drawing ratio conditions Orientation 

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Following the ALD process, the Vycor tubes were surface modified using APTS. Preliminary permeation experiments were then done for pure and mixed gas (CO2 and N2) at 373 K and 303 kPa to calculate the ALD-APTS-modified membrane separation properties. The mixed gas experiments were performed under the following three conditions to check for any hysteresis due to the chemical nature of CO2 adsorption on amine ... 

Particular attention is addressed to the permeate flux and to this purpose some preliminary experiments were realized on a different configuration of membrane photoreactor with a submerged membrane module located separately from the photoreactor. Bubbled oxygen on the membrane surface has the roles to reduce the catalyst deposition, to increase the flux through the membrane and to facilitate the photocatalytic reaction. 

An increase in the retention and the capacity of the FFF channel, and an increase in the selectivity, can be obtained by modifying the surface of the channel wall on which the solute is accumulated with the aid of transversal barriers as shown by Giddings et al. [68]. These barriers form spaces in which the solvent does not move, and where the solute can permeate both in and out by diffusion only. Consequently, the fractionation characteristics mentioned above are improved. The channels established transversally could be used to trap even the second phase, and to combine thus the action of field strength and the partition between the phases. Preliminary results were obtained in experiments with the fractionation of PS standards by the TFFF method using the channel with transversal slits [68]. The results proved, in principle, the applicability of this system. 

Conditions for selective hydrolysis do not apply uniformly to all polyols because of variations in stability among their acetal structures. This has frequently meant that the acid strength chosen was based on preliminary experiments. GLC methods and gel permeation chromatography have been proposed as means of selecting optimum conditions for the release of glycosyl alditols and residual oligosaccharide or polysaccharide, and the rate at which formaldehyde is produced by periodate oxidation of the hydrolysis mixture offers another diagnostic method. Methanolysis, rather than hydrolysis, has been advanced as an experimental variation that can reduce the amount of artifact formation associated with the use of aqueous acid. 

Laboratory experiments may also be necessary to aid in the selection and preliminary design of separation operations. The separation of gas mixtures requires consideration of absorption, adsorption, and gas permeation, all of which may require the search for an adequate absorbent, adsorbent, and membrane material, respectively. When nonideal liquid mixtures are to be separated, laboratory distillation experiments should be conducted early because the possibility of azeotrope formation can greatly complicate the selection of adequate separation equipment, which may involve the testing of one or more solvents or entrainers. When solids are involved, early laboratory tests of such operations as crystallization, filtration, and drying are essential. 

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