Melt molding

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]. 

The basics observed in molded products are always the same only the extent of the features varies depending on the process variables, material properties, and cavity contour. That is the inherent hydrodynamic skin-core structure characteristic of all IM products. However, the ratio of skin thickness to core thickness will vary basically with process conditions and material characteristics, flow rate, and melt-mold temperature difference. These inherent features have given rise to an increase in novel commercial products and applications via coinjection, gas-assisted, low pressure, fusible-core, in-mold decorating, etc. 

Melt molding is an alternative method of constructing three-dimensional scaffolds which has many advantages over membrane lamination. PLGA scaffolds... 

Fig. 6. Scanning electron photomicrograph of a PLGA 50 50 scaffold in the shape of a half-cylinder prepared by a melt molding method [35] using 35 wt% gelatin microspheres with diameters in the size range 300-500 pm. (Reproduced with permission from [35])...

Molded products can be obtained without employing melt molding methods, such as injection molding, extrusion molding, and... 

Regarding the spatial aspects of the enzymatic degradation of CA-g-PLLA, a surface characterization [30] was carried out for melt-molded films by atomic force microscopy (AFM) and attenuated total-reflection Fourier-transform infrared spectroscopy (ATR-FTIR) before and after the hydrolysis test with proteinase K. As exemplified in Fig. 3 for a copolymer of MS = 22, the AFM study showed that hydrolysis for a few weeks caused a transformation of the original smooth surface of the test specimen (Fig. 3a) into a more undulated surface with a number of protuberances of 50-300 nm in height and less than a few micrometers in width (Fig. 3b). The ATR-FTIR measurements proved a selective release of lactyl units in the surface region of the hydrolyzed films, and the absorption intensity data monitored as a function of time was explicable in accordance with the AFM result. 

Hot-Melt Molding. Hot molten plastisol is injected into a cooled mold to make products like fishing baits and novelties. 

Perfluoro alkoxy oxane PFA 260°C Similar to PTFE, but can be melted, molded and welded... 

Traditionally, solid polymers have required exposure to gaseous dopants over several days to achieve considerable conductivities. Table I compares these conductivity values for four polymers. With PPS as an example, a melt-molded film (0.25 itm thick) of the resin exposed to A5F5 (400 Tbrr) over four days at room temperature displays a final conductivity of ca. 10" 2 S/cm ... 

Figure 5 - Optical absorption of AsFs-doped PPS solid line, melt-molded film (ca.5 x 10 5an thick) doped with ASF5 dotted line, AsFg-doped PPS in ASF3 solution.

In most cases, PPS exhibits a pale yellow color. Even when PPS of high whiteness is obtained, it is easily colored during melt molding. Accordingly, in order to obtain PPS articles of high whiteness, special means are needed. Various means for decreasing discoloration have been used. ... 

Molded articles, in particular containers, such as bottles and jars, made from the polyester resin copolymers can be manufactured by using melt molding methods. Containers and bottles can be manufactured without the necessity of adding crystallization accelerators or crystallization retardants. The materials have low levels of acetaldehyde. ... 

Productivity is directly related to cycle time. There usually is considerable common knowledge about part geometry and process conditions that will provide a minimum cycle time (1-7, 32-52). Practices such as using thinner wall sections, cold vs. hot runners for TPs or hot vs. cold for TSs (Fig. 2-7), narrow sprues and runners, optimal size and location of coolant (or heat) channels, and lower melt/mold heat, when possible, will decrease the solidification time. 

Pipes, film, profiles, cable insulation, and knot-free nets are produced by extrusion. Extrusion with broad slits, for example to produce 20-100-/Ltni-thick film, is a special case. The film is then chilled by cold rolling or by water baths (melt-molding or chill rolling process). Broad slits are also used in what is called the extrusion coating of paper or cardboard with, for example, poly(ethylene). Papers thus treated can then be heat sealed. 

Poly(ethylene terephthalate) (PET) is cited as an example. The DSC curve for melt-molded PET (Figure 4.25, curve I) exhibits a deviation from... 

Figure 4.25 DSC curves for PET samples having various thermal histories. 1, Melt-molded PET sample II, doublestretcher formed PET sample 111, stretcher formed PET quenched from the molten state. Sample mass, 16mg 1 leating rate, 10 C min ...

Thermally induced phase separation Melt molding... 

Melt molding shares many similarities with TIPS and SC/PL. The starting materials include polymeric compounds with porogens, particles used to make pores, which are then placed inside a mold, hi contrast with TIPS, the polymer used is solid, granulated. 

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