Incompletely melted polymer

Knob mixers work well to eliminate fine striations in color uniformity and thermal gradients. Since knob mixers are primarily distributive mixers, they are not suited for mitigating solid polymer fragments from an incomplete melting process. 

Figure 9 shows the effect of polymer composition on the physical properties of a series of PET copolymers containing p-hydroxybenzoic acid and hydroquinone. The tensile strength, flexural modulus, and Izod impact strength all have maximum values for polymers containing about 50 mol % PET and 50 mol % PHB/THQ combined. The increase in physical properties is believed to reflect the increase in liquid crystallinity of the polymer melts as the combined PHB/THQ components approach 50 mol %. The lower physical properties values obtained at the 70 to 80 mol % PHB/THQ levels may result from incomplete melting of the polymers at the 280°C melt temperature. 

Carefully conducted experiments have shown that it is possible for spherulites to develop sporadically in both time and space in thin polymer films.(22,23,101,102) Repetitive experiments have indicated that spheruhtes do not necessarily form in identical positions if complete melting of the sample is ensured. However, a study of poly(decamethylene terephthalate) has shown that although spherulites are formed sporadically in time, they appear in identical positions within the sample.(103) Experimental evidence showed that for this sample the spheruUtic centers are initiated from a fixed number of heterogeneities. There is a strong tendency for spherulites to appear in the same position in the field of view after successive crystallizations.(73,74,104-106) In some cases this observation is solely a result of incomplete melting.(33,36,102) In others, it can also be due to the presence of a finite number of nucleation catalysts in the polymer melt. 

Apparently, the formation of the microporous structure within the PVdF—HFP copolymer was of critical importance to the success of Bellcore technology, and the ion conductivity was proportional to the uptake of the liquid electrolyte. To achieve the desired porosity of PVdF film, Bellcore researchers prepared the initial polymer blend of PVdF with a plasticizer dibutylphthalate (DBP), which was then extracted by low boiling solvents after film formation. Thus, a pore-memory would be left by the voids that were previously occupied by DBP. However, due to the incomplete dissolution of such high-melting DBP during the extraction process, the pore-memory could never be restored at 100% efficiency. Beside the total volume of pores thus created by the plasticizer. 

A too high temperature may lead to degradation of the polymer. g. A too low T involves the risk of incomplete or non-homogeneous melting of the material. 

This is another ramification of incomplete response of polymers, because the experimental time is smaller than the relaxation time of the system of macromolecules. As expected, weld lines are mechanically weak and have optical properties that differ from those of the bulk, making them visible. Furthermore, they result in film or tube gauge nonuniformities, probably because of the different degree of swelling of the melt in the neighborhood of the weld line. They also induce cross-machine pressure nonuniformities. To overcome these problems, basic cross-head die designs (Fig. 12.42) have been devised in which the mandrel is mechanically attached to the die body in such a way that obstacles are not presented to the flow in the annular region. 

The detected current is influenced considerably by any incomplete contact between sample and electrode, bubbles, grain boundary, and so on. So it is necessary to be careful in preparing the contact conditions for the sample and electrode interface in polymer systems. When the polymers are flexible films or soft paste, good contact is obtained by simply pressing. For hard or brittle polymer systems, it is difficult to get good contact by the pressing pressure. To improve the contact, it is necessary to melt the polymer material or to sputter electrode material on the... 

In the story of numerical flow simulation, the ability to predict observed and significant viscoelastic flow phenomena of polymer melts and solutions in an abrupt contraction has been unsuccessful for many years, in relation to the incomplete rheological characterization of materials, especially in elongation. The numerical treatments have often been confined to flow of elastic fluids with constant viscosity, described by differential constitutive equations as the Upper Convected Maxwell and Oldroyd-B models. Fortunately, the recent possibility to use real elastic fluids with constant viscosity, the so-called Boger fluids [10], has narrowed the gap between experimental observation and numerical prediction [11]. 

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