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Spherulites homopolymers

Morphology. Observations with the light microscope, under polarized light, showed that the end blocks in the case of both types of polymers crystallized in the form of the usual spheru-lites, but not as well as the analogous homopolymer, H2-l,4-polybutadiene. The formation of the spherulites was improved with increasing end-block content and/or higher molecular weight of the end blocks. [Pg.105]

SEM micrographs of two members of these polymers (HB and HBIB-50) are shown in Figure 7 to provide further evidence for superstructure on the micron level within the solution cast films. One can directly observe the surface of the spherulitic structure of the HB homopolymer as well as in that of the copolymer HBIB-50. Clearly, the level of structure (-5 pm) is well above that of the individual domains of either HB or HI and reflects the possible primary nucleation and subsequent growth behavior common to spherulitic semicrystalline polymers. The Hv patterns shown in... [Pg.131]

This unfavorable aging process is a major drawback for the commercial use of the PHB homopolymer. Reducing the spherulite radius by means of a nucleating agent did result in a minor increase of the maximum elongation by only a few percent, which is still insufficient for tough applications [18]. [Pg.269]

The isothermal crystallization of PEO in a PEO-PMMA diblock was monitored by observation of the increase in radius of spherulites or the enthalpy of fusion as a function of time by Richardson etal. (1995). Comparative experiments were also made on blends of the two homopolymers. The block copolymer was observed to have a lower melting point and lower spherulitic growth rate compared to the blend with the same composition. The growth rates extracted from optical microscopy were interpreted in terms of the kinetic nucleation theory of Hoffman and co-workers (Hoffman and Miller 1989 Lauritzen and Hoffman 1960) (Section 5.3.3). The fold surface free energy obtained using this model (ere 2.5-3 kJ mol"1) was close to that obtained for PEO/PPO copolymers by Booth and co-workers (Ashman and Booth 1975 Ashman et al. 1975) using the Flory-Vrij theory. [Pg.310]

The morphology of a polyethylene blend (a homopolymer prepared from ethylene is a blend of species with different molar mass) after crystallisation is dependent on the blend morphology of the molten system before crystallisation and on the relative tendencies for the different molecular species to crystallise at different temperatures. The latter may lead to phase separation (segregation) of low molar mass species at a relatively fine scale within spherulites this is typical of linear polyethylene. Highly branched polyethylene may show segregation on a larger scale, so-called cellulation. Phase separation in the melt results in spherical domain structures on a large scale. [Pg.61]

Under defined conditions, the toughness is also driven by the content and spatial distribution of the -nucleating agent. The increase in fracture resistance is more pronounced in PP homopolymers than in random or rubber-modified copolymers. In the case of sequential copolymers, the molecular architecture inhibits a maximization of the amount of the /1-phase in heterophasic systems, the rubber phase mainly controls the fracture behavior. The performance of -nucleated grades has been explained in terms of smaller spherulitic size, lower packing density and favorable lamellar arrangement of the /3-modification (towards the cross-hatched structure of the non-nucleated resin) which induce a higher mobility of both crystalline and amorphous phases. [Pg.99]

For homopolymers, the temperature dependence of the isothermal spherulite growth rate, G, is described by Eq 3.1 [Turnbull and Fischer, 1949] ... [Pg.250]

Long et al. [1991] investigated the crystaUiza-tion behavior in blends of PP with LLDPE. They found the crystallization temperature of the PP matrix, T, to decrease slightly upon the addition of LLDPE. However, the degree of crystaUinity, X, and the spheruUte growth rate, G, were not affected. The authors concluded that the overall crystaUiza-tion rate of PP in the matrix decreased due to a decreasing primary nuclei density. The latter was confirmed in O. M. experiments by the increased size of the PP spherulites upon the addition of LLDPE. However, Zhou and Hay [1993] reported that with the addition of LLDPE to PP, the crystallization rate remained similar as for the PP homopolymer. [Pg.270]

For pure iPP and PB-1 homopolymers and their respective blends, the spherulite radius increases linearly with time t for all T, investigated. For all samples, the isothermal radial growth rate G was calculated at different as G = dR /dt. Generally, the G values decrease an increase in the values and with increase in the amount of noncrystallizable component in the blend. As shown in Fig. 6.1, where the relative G values of the iPP-based blends are reported for = 125°C, the depression of the G values was more pronounced for the blends prepared with HOCP as the second component. [Pg.125]

A quantitative measure of isothermal crystallization is the crystallization half-time, Crystallization times expressed as the reciprocal of (crystallization rate) are shown in Figure 9.4 as a function of crystallization temperature. These results indicate that the fastest crystallization for the PDS homopolymer can be obtained at approximately 47°C. For the sake of comparison, Figure 9.4 also includes spherulitic growth rates from HSOM. [Pg.120]

Overall crystallization rate (from DRS) and spherulitic growth rate (from HSOM) for PDS homopolymer as a function of temperature. [Pg.121]

Copolymers of isotactic propylene (iPP) with a-oleflns also exhibit diffraction peaks due to iPP crystallites. As one would predict, increasing the a-olefln content decreases the percent crystallinity. When the copolymer is blended with iPP homopolymer, the copolymer will cocrystallize with the homopolymer, a phenomenon that is rare in polymers. Cocrystallization is believed to substantially contribute to the improved mechanical properties found in the blend (Starkweather, 1980). Large spherulites are not generally found in these blends as opposed to the homopolymer, and the crystal form is monoclinic rather than smectic (Kresge, 1984). [Pg.614]


See other pages where Spherulites homopolymers is mentioned: [Pg.271]    [Pg.188]    [Pg.131]    [Pg.133]    [Pg.133]    [Pg.44]    [Pg.45]    [Pg.102]    [Pg.181]    [Pg.56]    [Pg.280]    [Pg.317]    [Pg.321]    [Pg.323]    [Pg.31]    [Pg.32]    [Pg.90]    [Pg.45]    [Pg.191]    [Pg.679]    [Pg.576]    [Pg.44]    [Pg.90]    [Pg.44]    [Pg.83]    [Pg.134]    [Pg.271]    [Pg.796]    [Pg.218]    [Pg.272]    [Pg.345]    [Pg.347]    [Pg.346]    [Pg.119]    [Pg.134]    [Pg.50]    [Pg.177]    [Pg.278]   
See also in sourсe #XX -- [ Pg.177 , Pg.179 ]




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