Melt Mechanical Mixing

UHMWPE (before and after processing), and an enhancement of the overall mechanical properties. 

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There are several processing methods available to manufacture polymer/ CNTs nanocomposites. It may be considered essentially three methods to incorporate CNTs into polymeric matrices 1) solution mixing or film casting of suspensions of CNTs in soluble polymers 2) in situ polymerization of CNT-monomer polymer mixture and 3) melt mechanical mixing of CNTs with polymer. 

The main advantage of this method is that it enables grafting of the polymer macromolecules onto the sidewall of the CNTs. This technique is particularly important for the preparation of insoluble and thermally unstable polymers, which cannot be processed by solution casting or melt mechanical mixing. In situ polymerization can be applied for preparation of almost any CNT-polymer nanocomposite, which can be non-covalently or covalently bound to polymer matrix. Kaminsky et al. [53] prepared UHMWPE/ CNTs nanocomposites by in-situ polymerization using metallocene, and investigated the influence of the CNT concentration in the thermal... 

Figure 5 Dissolution rates of salicylic acid-benzoic acid mixtures. ( ) Benzoic acid from melt (O) salicylic acid from melt (A) salicylic acid from mechanical mix ( ) Benzoic acid from mechanical mix. (From Ref. 19.)... 

In practice, blends are often prepared by mechanical mixing in the melt. As a rule the products are demixed, but dispersed so finely that the phase structure can only be detected with a transmission electron microscope (TEM). 

Hill and Barham [133] showed by transmission electron microscopy that blends of high and low molar mass polyethylene melts were homogeneous with no detectable phase separation. The blends were prepared by solution mixing to obtain an initially homogeneous blend before the thermal treatment in the melt. It should be realised that the mechanical mixing of high and low molar mass linear polyethylenes to obtain a homogeneous melt may require considerable work and time. 

On the other hand, we discussed and presented in physical terms the very powerful melting mechanisms resulting from repeated, large deformations, forced on compacted particulate assemblies by twin co- or counterrotating devices. These mechanisms, which we refer to in Section 5.1, are frictional energy dissipation (FED), plastic energy dissipation (PED), and dissipative mix-melting (DMM). 

However, experimental studies (50), using either powder feed or pelletized feed with some recycled melt over the channel block into the feed port, have not exhibited drag removal melting but a dissipative mix-melting mechanism, discussed in Chapter 5. As... 

Fig. 10.12 Schematic representation of two melting mechanisms observed by Janssen (24) with PP processed in a double-flighted 47-mm counterrotating TSE operating at low rotational speeds, (a) Melting when the die pressure was set at the low value of 50 psi, where chamber-to-chamber leak pressure backflows are negligible, (b) Melting under the high die pressure of 2700 psi, which enables leak backflows, which result in chamber solid bed compaction and introduce the possibility of dissipative mix melting. [Reprinted by permission from L. P. B. M. Janssen, Twin Screw Extrusion, Elsevier Scientific, Amsterdam, 1978.]...

Fig. 10.34 Schematic representation of the two regions in the melting zone of CRNI TSEs with matched screw arrays. In the two regions (A), away from the tangent interscrew plane, the melting mechanism is that of SSEs. In the interscrew plane, a melt-particulates suspension undergoes dissipative mix-melting. [Reprinted by permission from R J. Nichols and F. Kher-adi, Melting in CRT Twin Screw Extruders, Mod. Plast., 61, 70 (1984).]...

The flow on the suspension visualized and simplified in the model just discussed generates VED and heats the pellets, but does not deform them. Thus, they do not include the dissipative mix-melting (DMM) melting mechanism, only VED. However, with the proper parameter adjustments, they are able to make fair predictions of the overall melting... 

Unmixed zones. All methods of welding stainless steel with a filler metal produce a weld fusion boundary consisting of base metal that has been melted, but not mechanically mixed with filler metal and a partially melted zone in the base metal. An unmixed zone has the composition of base metal, but the microstructure of an autogenous weld. The microsegregation and precipitation phenomena characteristic of autogenous weldments decrease the corrosion resistance of an unmixed zone relative to the parent metal. Unmixed zones bordering welds made from overalloyed filler metals can be preferentially attacked when exposed on the weldment surface.14,61... 

The earliest cast, composite binder was studied by Jet Propulsion Laboratories (JPL) and made use of molten asphalt (7). This material was heated until it formed a fluid melt, was mixed with oxidant, and the heated mixture cast into a motor cavity and allowed to cool. This system was poor because of the limited temperature range, the low solids content which could be formulated, and the poor mechanical properties of highly loaded asphalt. A chemically cured system was then introduced when acrylate monomers were mixed with oxidizer and curative (8). The mixture eould be cast, heated to cure temperature, and the acrylate polymerized to give a well consolidated grain. The basic deficiencies encountered... 

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