Melt processing problems with

As an example of using a salt of a weak acid to overcome a processing problem, Hirsch et al. (1978) used the calcium salt of fenoprofen to overcome the low melting point of the free acid (40°C). By increasing the melting point, problems with frictional heat due to mechanical handling were overcome. 

Solution Casting. The production of unsupported film and sheet by solution casting has generally passed from favor and is used only for special polymers not amenable to melt processes. The use of solvents was generally very hazardous because of their flammabiUty or toxic nature. The cost of recovery and disposal of solvents became prohibitive for many lower price film appHcations. The nature of the drying operations leads to problems with solvent migration and retention that are not problems with melt-processed polymers. 

The ingenious process of melting suhlerranean sulfur with superheated water and forcing it to the surface with compressed air was devised and perfected by Herman Frasch in the period 1891-4. Oiiginally designed to overcome the problems of recovering sulfur from the caprock of salt domes far below the swamps and quicksands of Louisiana, the method is now also extensively used elsewhere To extract native sulfiu. ... 

When water (a Newtonian liquid) is in an open-ended pipe, pressure can be applied to move it. Doubling the water pressure doubles the flow rate of the water. Water does not have a shear-thinning action. However, in a similar situation but using a plastic melt (a non-Newtonian liquid), if the pressure is doubled the melt flow may increase from 2 to 15 times, depending on the plastic used. As an example, linear low-density polyethylene (LLDPE), with a low shear-thinning action, experiences a low rate increase, which explains why it can cause more processing problems than other PEs. The higher-flow melts include polyvinyl chloride (PVC) and polystyrene (PS). 

Solution condensations are also equilibrium processes, with the reaction often driven by removal of the by-product through distillation, salt formation, or precipitation. Many solution condensations are carried out near room temperature. Solvent entrapment is a problem, but since a reaction may occur under considerably reduced temperatures, compared to the melt process, thermally induced side reactions are minimized. Side reactions with the... 

We now turn to the melting of the Si (100) surface. This is a classic problem, whose microscopic details are not well understood. This is particularly true of covalent materials like Si, whose surfaces are characterized by reconstructions, steps, islands, and other surface defects - all of which are expected to play a role in the microscopic aspects of the melting process. As a first step towards this goal, we have carried out simulations of the melting process of the Si (100) surface with finite-temperature ab initio methods. 

A large fraction of the iron and steel produced today is recycled scrap. Since scrap does not require reduction, it can be melted down directly in an electric arc furnace, in which the charge is heated through its own electrical resistance to arcs struck from graphite electrodes above it. The main problem with this process is the presence of tramps (i.e., copper from electrical wiring, chromium, nickel, and various other metals) that accompany scrap steel such as crushed automobile bodies and that lead to brittleness in the product. Tin in combination with sulfur is the most troublesome tramp. Only the highest quality recycled steel—specifically, steel with no more than 0.13% tramps—can be used for new automobile bodies, and usually reprocessed scrap has to be mixed with new steel to meet these requirements. 

In this section, the mechanical properties resulting from melt processing of LCPs are not covered since they have been discussed in detail in earlier publications. Rather, an effoh is made to focus on the problems associated with melt processing and to explore possible solutions. As noted earlier, one of the... 

---