Crystallinity effects polypropylene

The crystallization peak temperature increased when epoxy resin was added to polypropylene, that is, the uncured and cured epoxy particles acted as effective nucleating agents and accelerated the crystallization of PP in the blends. When cured dynamically, the smaller epoxy particles in the blends resulted in the increase in the number of nucleating agents and hence accelerated the crystallization of polypropylene. Blending polypropylene with epoxy resin resulted in the decrease of crystallinity of polypropylene and increased the melting temperature T of polypropylene than those of pure polypropylene. 

S. Bualek-Limcharoen, 1. Samran, T. Amomsakchai, and W. Meesiri. Effect of compatibUizers on mechanical properties and morphology of in-situ composite film of thermotropic liquid crystalline polymer/polypropylene. Polym. Eng. ScL, 39 312-320, 1999. 

Studies on Ugnocellulosic material modification were also cmiducted by Nekkaa et al. [18]. The cellulose fibers obtained from Spanish broom (Spartium junceum) were subjected to silane s action to improve adhesion between composite components. Thermal analysis confirmed the nucleating effect uprm the addition of unmodified fibers, while the addition of modified fibers did not significantly influence the crystallinity of polypropylene matrix. 

Hobbs has shown (12) that the abilities of two morphologically different, but chemically identical, graphite fibres to nucleate isotactic polypropylene differed considerably. The same author also showed (13) that a carbon r lica of a crystalline isotactic polypropylene surface could increase the nucleation of the polymer during recrystallisation. Thus, the physical, not chemical, nature of the nucleating agent has determined its effectiveness. In the present work we have changed the surface chemistry of a particulate filler, without... 

Crystalline polymers show the greatest interaction with minerals. In amorphous polymers, minerals merely increase stiffness, with little or no reinforcing effect. Polypropylene, high density polyethylene, thermoplastic polyester and polyamides are crystalline polymers. Low density polyethylene, polystyrene and polycarbonate are amorphous. 

P.Y.62 is thermally stable up to 250°C. It has a considerable effect on the shrinkage of HDPE and other partially crystalline polymers. The pigment is an equally suitable colorant for polystyrene and polyurethane and lends color to polypropylene spin dyeing products with minimal application requirements. 

Polypropylene (PP) is a semicrystalline commodity thermoplastic produced by coordination addition polymerization of propylene monomer [197]. Most frequently, stereospecific Ziegler-Natta catalysts are used in industrial processes to produce highly stereospecific crystalline isotactic (iPP) and syndiotactic (sPP) polymer with a small portion of amorphous atactic PP as a side product. Polymerization of non-symmetrical propylene monomer yields three possible sequences however, the steric effect related to the methyl side group highly favors the head-to-tail sequence. The occurence of head-to-head and tail-to-tail sequences produces defects along the PP chain [198]. Presence of such defects affects the overall degree of crystallinity of PP. 

The structure of crystalline polymers may be significantly modified by the introduction of fillers. All aspects of the structure change on filling, crystallite and spherulite size, as well as crystallinity, are altered as an effect of nucleation [9]. A typical example is the extremely strong nucleation effect of talc in polypropylene [10,11], which is demonstrated also in Fig. 2. Nucleating effect is characterized by the peak temperature of crystallization, which increases significantly on the addition of the filler. Elastomer modified PP blends are shown as a comparison crystallization temperature decreases in this case. Talc also nucleates polyamides. Increasing crystallization temperature leads to an increase in lamella thickness and crystallinity, while the size of the spherulites decreases on... 

TABLE 1. Effect of Selected Additives on Crystallinity and Haze of Extruded Polypropylene... 

We will first quote the case of mixed crystal formation among polymers containing different isotopic species, such as isotactic polypropylene and polydeuteropropylene (52). In such a case, not only the resulting crystallinity is of the same order of magnitude as that of the separate pure polymers, but the X-ray diffraction effects are virtually identical, due to the same van der Waals radii of hydrogen and deuterium. 

Substitute for Conventional Vulcanized Rubbers, For this application, the products are processed by techniques and equipment developed for conventional thermoplastics, ie, injection molding, extrusion, etc. The S—B—S and S—EB—S polymers are preferred (small amounts of S—EP—S are also used). To obtain a satisfactory balance of properties, they must be compounded with oils, fillers, or other polymers compounding reduces costs. Compounding ingredients and their effects on properties are given in Table 8. Oils with high aromatic content should be avoided because they plasticize the polystyrene domains. Polystyrene is often used as an ingredient in S—B—S-based compounds it makes the products harder and improves their processibility. In S—EB—S-based compounds, crystalline polyolefins such as polypropylene and polyethylene are preferred. Some work has been reported on blends of liquid polysiloxanes with S—EB—S block copolymers. The products are primarily intended for medical and pharmaceutical-type applications and hardnesses as low as 5 on the Shore A scale have been reported (53). 

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