Processing, thermoplastics melting model

Figure 5 shows the structural model for elastomers. Table 3 presents the classification and applications of elastomers. TPE are two-phase or multiphase plastics (block copolymers) with elastic properties similar to those of elastomers, but with a melting temperature that allows for processing as with thermoplastics. Figure 6 illustrates the classification of TPE. 

SINCE the discovery of liquid crystalline phenomenon for low molecular weight liquid crystals (LMWLCs) more than 100 years ago, anisotropic ordering behaviors of liquid crystals (LCs) have been of considerable interest to academe [1-8], In the 1950s, Hory postulated the lattice model for various problems in LC systems and theoretically predicted the liquid crystallinity for certain polymers [1-3], As predicted by the Hory theory, DuPont scientists synthesized lyotropic LCPs made of rigid wholly aromatic polyamide. Later, Amoco, Eastman-Kodak, and Celanese commercialized a series of thermotropic main-chain LCPs [2]. Thermotropic LCPs have a unique combination of properties from both liquid crystalline and conventional thermoplastic states, such as melt processibility, high mechanical properties, low moisture take-up, and excellent thermal and chemical resistance. Aromatic main-chain LCPs are the most important class of thermotropic LCPs developed for structural applications [2,4-7]. Because they have wide applications in high value-added electronics and composites, both academia and industry have carried out comprehensive research and development. 

The entanglement of the polymer chains at the weld line is related to their diffusion rate, which is a function of temperature and melt viscosity of the polymer [95]. The holding pressure in the cavity and the injection speed can also affect the weld line strength [96]. Many predictive models for the weld line strength of thermoplastic amorphous polymers in relation to the viscoelastic properties and processing conditions such as the melt temperature, the mold temperature, and the holding time, have been proposed [97-99]. 

A mathematical model was presented for studying the melt flow behaviour of thermoplastic natural rabber (TPNR) in a double feed extrusion system. The model predicted the processing parameters in the feed and main extruders, from which the optimum processing conditions for TPNR were obtained. The double feed system enabled better mixing to occur in the main extruder. 20 refs MALAYSIA... 

Fused deposition modeling (FDM) is an additive solid-based process as shown in Figure 15.6. A solid thermoplastic polymer is heated to the melting temperature and deposited through a nozzle in narrow strips in the y-direction. The nozzle is moved in the x-direction as subsequent strips are laid down (or the platform can be moved in the -X direction). The thickness t of each layer can be as small as 0.(X)4 in. (0.10 mm) and the width as small as O.Olin. (0.25 mm). The jc, y motion of the process for each layer is similar to that of an inkjet printer and thus the extension of this to RP is also known as 3D printing. 

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