Phase inversion is the main technique used to produce hollow fibres. When the tertiary system hits the surface of the coagulation vessel it condenses and the fibres are formed. A number of parameters (design, spinnerets etc.. determine the morphology of the fibres and their performance.
Polymer solutions have prepared under strict conditions and injected into the spinnerets (P, T & η) insuring constant flow.
The ratios of the solvents used in the bore liquid are critical, and hence have to be controlled at all times.
The polymer solution is filtered down to 5 µ just before injecting it into the spinpacks. The polymer solution is fed at constant temperature, pressure and flow. The polymer solution flow distribution is critical in insuring well formed fibres. Fibre morphology is determined by the air gap and the ratio of the solvents used.
The consolidation of the fibres continue Excess Solvent is removed from the fibres through thorough in the Phase inversion vessel that gives washing at elevated temperatures the fibre its final characteristics and removes excess of unreacted polymers.
Washed out fibres are then dried to required level after insuring that pores will not close due to heating. Dried fibres are wound on a wheel and cut to the desired length after adding a protection film to be removed when making up the filter.
Molecular weight cut-off (MWCO)
MWCO has emerged as one of the most useful tools for characterising UF membranes. The early UF membranes were used for purification of biological solutions for retaining macromolecules such as proteins. Since macromolecules are characterised by their molecular weights, the ability of UF membranes to retain these macromolecules is based on their molecular weight. Thus, the term MWCO came into being for characterising UF membranes. It is arbitrarily defined as the molecular weight at which 90% of the macromolecular solute is rejected by the membrane.
Minimum permeability values that we have are like below and we can provide fibers that are above these values as well.
Pore Size Distribution
Separation of a feed stream into retentate and permeate happens by means of pores present in the membrane. The relation between the size of these pores and the size of a certain component of the feed stream will define if this component will pass through the membrane or will be retained. Species larger than the pore size will end up in the retentate stream, while the smaller species will pass through the membrane to form a permeate stream. Therefore, the pore size of the membrane is a critical parameter that defines its separation performance. Except for some specific cases, the pore size of a membrane is not uniform, but rather has a certain distribution which gives a rise to a more real-life parameter as pore size distribution. Pore size distribution is conventionally depicted in the shape of a graph with a curve that relates pores of different sizes with their abundance in the membrane. Depending on the range of pore sizes present in the membrane, pore size distribution can be either broad or narrow (or sharp).