Molding isotactic

Studies of the orientation phenomena in injection molding have shown that irrespective of the molding conditions and type of thermoplastic, molecular orientation is higher near the walls and decreases toward the interior. " " Low crystallinity and flow-induced structures have been observed near the walls for injection molded isotactic polypropylene parts. " High modulus materials have also been obtained with some injection molding techniques. " ... 

Varga, J., Mudra, I. and Ehrenstein, G.W. (1988) Morphology and properties of p-nucleated injection-molded isotactic polypropylene. Conference Proceedings, Antec 98 (SPE, Inc. Technical Pap>ers, XLIV. Vol HI pp. 3492-3496). 

Mendoza et al. (2003) studied experimentally the influence of processing conditions on the spatial distribution of the molecular orientation in injection molded isotactic polypropylene (iPP) plates. They found that the anisotropy of injection molded semi-crystalline polymers is governed by the orientation of the crystalline phase, and the distribution of the orientation strongly depends on the shear rate. Doufas et al. (2000), followed by Zheng and Kennedy (2001), have applied a rigid dumbbell model to simulate crystalline orientation in injection molded semicrystalline polymers. The model reads, in the form used by Zheng and Kennedy (2001, 2004) ... 

Most studies on crystallization have considered virgin polymers without additives. However, in many injection-molded products, various additives such as colorants are usually added and these are known to affect the crystallization behavior. The topic has been recently tackled by Hadinata et al. (2008), Zheng et al. (2008, 2010), Lee Wo and Tanner (2010), and Zhu et al. (2009). These authors investigated the FIC behavior of an injection-molded isotactic polypropylene (iPP) mixed... 

Kalay G and Bevis M J (1997) Processing and physical property relationships in injection-molded isotactic polypropylene. 1. Mechanical properties, J Polym Sci, Part B Polym P/tj/s 35 241-263. 

Yi X, Chen C, Zhong GJ, Xu L, Tang JH, Ji X, Li ZM (2011) Suppressing the skin-core structure of injection-molded isotactic polypropylene via combination of an in situ microfibrillar network and an interfacial compatibilizer. J Phys Chem B 115(23) 7497-7504... 

The crystallinity and crystallite size of injection molded isotactic polypropylene was measured by wide angle X-ray diffraction(WAXD) and the distinct skin-core morphology was visible under a polarizing optical microscope. The results show that the crystal structures are dependent on the injection molding processing conditions. The crystallinity and crystallite size decreases with the distance from the gate. The skin layer thickness is thinner with the higher injection temperature. 

The mass fraction crystallinity of molded PHB samples is typically around 60%. As shown in Table 3, PHB resembles isotactic polypropylene (iPP) with respect to melting temperature (175-180°C), Young s modulus (3.5-4 GPa) and the tensile strength (40 MPa). In addition, the crystallinity of iPP is approximately 65% [18]. Accordingly, the fracture behavior of PHB may be anticipated to be tough at room temperature. Molded PHB samples do indeed show ductile behavior, but over a period of several days at ambient conditions, they slowly become more brittle [82, 85, 86]. Consequently, the elongation to break of the ultimate PHB (3-8%) is markedly lower than that of iPP (400%). 

Isostatic molding, 18 300 Isostatic refractory pressing, 21 504 Isostearic acid, physical properties, 5 35t Isotachophoresis, 9 738, 742, 748 Isotacticity, of polypropylene, 20 529 Isotactic PB resins, thermal properties of, 20 417... 

Poly(4-Methylpentene-1). It was first discovered by Natta, later researched by many companies for synthetic fiber, and finally commercialized by ICI as a specialty molding resin. It is mainly isotactic, 40-65% microcrystalline, and has the lowest density of any plastic, 0.83, which may be approaching the theoretical minimum. 

Polypropylene owes its current market success to the development of coordination polymerization. Before 1957 it was not produced commercially because radical polymerization gives an atactic polymer that is amorphous and has poor mechanical properties. Using a coordination catalyst, however, enables the production of an isotactic polymer that is semicrystalline. This material is stiff and hard and has a high tensile strength. Among its many useful products are rope, molded objects, and furniture. 

Isotactic Polystyrene. The familiar steam molding of pre-expanded particles has so far not been applied successfully to isotactic polystyrene. However, the polymer has been foamed, according to three disclosed methods. For example, finely divided acetone-insoluble polymer, with a melting point in excess of 200°C., is blended with a liquid selected from methylene chloride, aromatic hydrocarbons, or halogenated aromatic hydrocarbons. This blend is then heated (84). A mixture of molten polymer and methyl chloride, propane, or butane is suddenly depressurized (8). Foam may also be generated in a continuous manner directly from a butyllithium-initiated polymerization conducted in the presence of a 4/1 blend of benzene and petroleum ether (15). 

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