Polymer melt surface

Cox and Macosko (19) have reported experimental results on measurements of the melt-surface temperature upon exit from the capillary using infrared pyrometry, which senses the radiation emitted by the hot polymer melt surface. Their work also included the numerical simulation of viscous heating in a capillary, a slit, and an annular die, using a method resembling that of Gerrard et al. (13). They used a boundary condition at the die wall in between the isothermal and adiabatic case, —k(dT/dr) = h T — To) at the wall, where 7o is the die temperature far from the melt-die interface as well as the inlet melt... 

Using the techniques outlined in section 2.2, values of the surface energies of a variety of polymer melts are now available. Values for some polymer melts of high relative molecular mass are tabulated in table 2.2, with values for some small-molecule liquids in table 2.3, for comparison. Qualitatively, we notice that the polymer melt surface tensions are quite comparable with those of analogous small molecules non-polar molecules have lower surface tensions than do polar molecules, irrespective of whether they are polymeric. 

Theodorou DN. Variable-density model of polymer melt surfaces, structure and surface tension. Macromolecules 1989 22 4578 589. 

Recently we proposed a weight and poljrmer liquids. Thig theory was developed by com-bininggt j lattice fluid (LF) model with the density gradient theory of inhomogeneous fluids. The main objective of this paper is to illustrate that this method of estimating polymer melt surface tensions is superior to existing empirical or semi-empirical methods. 

Three other methods have been widely used to estimate polymer melt surface tensions. The oldest of these methods is based on the parachor method first proposed for small molecules by Sugden. ... 

Physically or chemically modifying the surface of PET fiber is another route to diversified products. Hydrophilicity, moisture absorption, moisture transport, soil release, color depth, tactile aesthetics, and comfort all can be affected by surface modification. Examples iaclude coatiag the surface with multiple hydroxyl groups (40), creatiag surface pores and cavities by adding a gas or gas-forming additive to the polymer melt (41), roughening the surface... 

The interaction effect between a dispersion medium and a filler on the net-formation in a filled polymer melt is mostly visuallized in the fact that the finishing treatment of the surface of solid particles results in a significant change of the position of the flow curve of the filled polymer on the whole, and yield stress as well [5, 8-10]. 

This closeness of 0 to zero explains the existence of a gas-oversaturated solution area in the polymer melt, when P < Pg, but the entire volume of gas remains in the solution. The degree of oversaturation, particularly upon free foaming (not in flow) can be 2- to 3-fold. In real polymer compositions, there are always solid admixtures, which have poor wetting areas. This reduces the degree of oversaturation at the interface melt-molding tool. Moreover, bubble nuclei can result from fragmentation of gas bubbles in the polymer [16]. Another factor that promotes the formation of bubble nuclei is the presence of localized hot points in the polymer melt they act as nuc-leation centres. Hot points appear either after a chemical reaction in the melt polymer [17], or in overheated areas on the surface of metal equipment [18]. Density of nucleation can be improved via introduction of various agents that reduce tension of the polymer [19]. 

A polymer coil does not only possess a structure on the atomistic scale of a few A, corresponding to the length of covalent bonds and interatomic distances characteristic of macromolecules are coils that more or less, obey Gaussian statistics and have a diameter of the order of hundreds of A (Fig. 1.2) [17]. Structures of intermediate length scales also occur e. g., characterized by the persistence length. For a simulation of a polymer melt, one should consider a box that contains many such chains that interpenetrate each other, i. e., a box with a linear dimension of several hundred A or more, in order to ensure that no artefacts occur attributable to the finite size of the simulation box or the periodic boundary conditions at the surfaces of the box. This ne-... 

Function by coating the metal surface of a die, effectively changing the interfacial properties between metal and polymer melt. Counter processing problems by lowering the melt viscosity or improving mixing and... 

Another characteristic of this solution is its proneness to crystallization and polymerization. When parts of the exhaust system are constantly welted by Adblue on the same spot, undesired urea crystals or polymers may form if the exhaust line temperature is lower than 300°C. This phenomenon will result in uncontrolled ammonia production when the crystals or polymers melt or sublimate after being heated at significantly higher temperatures (T > 350°C). This may result in ammonia release. Furthermore, the crystals or polymers can also have an impact on the SCR catalyst cells by reducing the catalyst surface and thus reducing the catalyst performances. 

These additives reduce the friction between the polymer aggregates or crystallites and also lower the adhesion between the polymer melt and metal surfaces (which occurs in rollers, extruders). This results in ... 

The surface finish of injection-moulded foamed articles are not ideal because of external defects, burst bubbles, etc. This can be avoided by sandwich moulding. This is accomplished by initially injecting a slug of polymer melt into the mould followed immediately by a polymer containing a blowing agent, which chases the initial polymer into all the interstices. 

The structures of the solid-melt interface and the melt confined within a narrow gap are of great significance in diverse areas of research such as lubrication, adhesion, or in future nanometer science. It is well recognized that the melt of n-alkanes, and other simple molecules show anomalous oscillations in density, viscosity, etc. vs. depth from the surface showing the presence of marked layer structures in the melt [40]. Even in polymer melts similar layering phenomena were suggested near the solid surface [41], but no pronounced ordering or the onset of crystallization were reported. 

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