Viscosity, high solution, problems

Hexylene glycol was better than 2-butoxyethanol as a solvent for the trimellitic alkyd. It may also be of value with the acrylic resin, but high solution viscosity could be a problem. 

Wet spinning also overcomes the problems associated with the very high solution viscosities required for dry spinning. However, a suitable coagulant has yet to be found for the PHB systems. Spinning a PHB in chloroform solution into methanol, for example, results in too rapid precipitation of the polymer and the production of extremely brittle, voided fibres. 

The other important function of the binder is its effect upon the rheological properties of the coating mix. Starch, which is widely used, is unsuitable for use in its unmodified form because its solution viscosity is generally too high and also because of the problem of retrogradation. It is usually modified by reducing its molecular weight by either oxidative or hydrolytic (sometimes enzymatic) procedures. 

Sample introduction is a major hardware problem for SFC. The sample solvent composition and the injection pressure and temperature can all affect sample introduction. The high solute diffusion and lower viscosity which favor supercritical fluids over liquid mobile phases can cause problems in injection. Back-diffusion can occur, causing broad solvent peaks and poor solute peak shape. There can also be a complex phase behavior as well as a solubility phenomenon taking place due to the fact that one may have combinations of supercritical fluid (neat or mixed with sample solvent), a subcritical liquified gas, sample solvents, and solute present simultaneously in the injector and column head [2]. All of these can contribute individually to reproducibility problems in SFC. Both dynamic and timed split modes are used for sample introduction in capillary SFC. Dynamic split injectors have a microvalve and splitter assembly. The amount of injection is based on the size of a fused silica restrictor. In the timed split mode, the SFC column is directly connected to the injection valve. Highspeed pneumatics and electronics are used along with a standard injection valve and actuator. Rapid actuation of the valve from the load to the inject position and back occurs in milliseconds. In this mode, one can program the time of injection on a computer and thus control the amount of injection. In packed-column SFC, an injector similar to HPLC is used and whole loop is injected on the column. The valve is switched either manually or automatically through a remote injector port. The injection is done under pressure. 

This is a point to consider process improvements. One problem is that the biopolymers we can buy are not of constant quality. Would it be possible to get other materials that are more reliable (This would mean a major redo of the work in the lab.) At this point you should also obtain a good idea of the prices of the ingredients and the energy used in the process. These may force you to go back to the lab to change the process. A fairly obvious improvement is to reduce the amount of water. This will reduce the size of equipment, the energy requirement and the amount of waste. However, you may be limited by a low solubility of the polymers, or by too high a viscosity of the solutions produced. The stream of waste water is a nuisance, especially because it contains formaldehyde. Could we separate the formaldehyde and recycle it This might be possible with a membrane or with distillation. 

These mechanically based protein release methods have several undesirable properties. One problem is that extensive fragmentation of the cells makes the subsequent centrifugation difficult (2.3). Adding to the problem of cell fragment removal is the high viscosity imparted to the solution by the released nucleic acids (4). A nucleic acid removal step is necessary to decrease the solution viscosity and avoid potential interference with fractional precipitation and chromatography (5,). Another undesirable property is that the harsh action of mechanical disruption causes the release... 

Partly aromatic copoly(amide)s prepared by conventional processes have triamine contents greater than 0.5%. This effects a deterioration in the product quality and to problems in preparation by a continuous method. For example, dihexamethylenetriamine, formed from HMD is used in the preparation. Copoly(amide)s with a low trianune content have the same solution viscosity but lower melt viscosities compared with products of the same composition which have a higher triamine content. The processability and the product properties are significantly improved by a low triamine content. The dimerization of the diamine can be suppressed by using special methods of polymerization. Short residence times in the high-temperature stage of the polycondensation process suppress the formation of triamines. ... 

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