Crystalline phase, polypropylene

Deformation Behavior of P-Crystalline Phase Polypropylene and Its Rnhber-Modified Blends... 

Tjong, S.C., Shen, J.S. and Li R.K.Y. (1996) Morphological behavior and instrumented dart impact properties of P-crystalline phase polypropylene. Polymer, 37, 2309-2316. 

It is known the case of i-PP, for which the copolymerization with small amounts of ethylene tends to stabilize the y form [84] for instance, by melt crystallization of a copolymer with 6% by mol of ethylene more than 80% of the crystalline phase is in the y form [85], It is also known that the obtainment of the y form by melt crystallization, is also favored for samples of low molecular mass [86, 87] and for stereoblock fractions [88]. This seems to suggest that, whenever the preferential crystallization of the y-form is observed, there is the concomitant occurrence of a reduction in the polymer of the length of the chain stretches with polypropylene head to tail constitution and isotactic configuration. 

Small-angle X-ray scattering (SAXS) data have made it possible to deduce the localisation of organic additives (pigments) in the bulk of isotactic polypropylene (iPP) [344]. This work has confirmed that the additives are located in the amorphous phase, in spite of their crucial influence on the formation of the crystalline phase of iPP. SAXS has also been used to study the 3D structure of different carbon-black aggregates, and silica-filled SBR rubber compounds [345]. 

Figure 1.3 Chain conformation of isotactic polypropylene in its crystalline phases.

The data from this table illustrate the semicompatibility of the phase between isotactic polypropylene and the high density polyethylene with block copolymer without gross interference in the domain structure or the crystalline phases that exist in these TPR s. 

Since pneumatic conveying is largely applied to transport granular polymers and on the other hand even smallest amounts of attrition of these solids cannot be tolerated the results presented are focused on these materials. Polymers of four chemically different polymer classes were examined. Polypropylene (PP) and polyethylene (PE) belong to the semicrystalline polymers, which possess both, an amorphous phase and a crystalline phase. The polymethylmethacrylates (PMMA) and polystyrenes (PS) are fully amorphous. Some material properties of the polymers are summarized in Table 1. 

Utilization of the single hydrogen bond between pyridine and benzoic acids in SLCP s has been a source of inspiration for other groups in the development of main-chain supramolecular polymers based on diacids and dipyridines.53-56 Supramolecular rod-coil polymers have been developed by assembly of 4,4 -bipyridines and telechelic polypropylene oxide with benzoic acid end-groups, which show highly ordered liquid crystalline phases.57 The use of tartaric acid derivatives in combination with bipyridine units resulted in the formation of hydrogen-bonded, chiral main-chain LCP s, as has been shown by circular dichroism measurements, optical microscopy, and X-ray data.58,59... 

Using this developed methodology, the structural behaviors of polyethylene and paraffins, vinyl polymers such as poly (vinyl alcohol) and polypropylene, etc., in the solution have been successfully elucidated on the basis of their observed spectra [2, 24-28]. Also, this can be applied to noncrystalline and crystalline phases in polymers. 

Vieth and Wuerth (2Ji) found negative deviations from the simple two phase model for semicrystalline polypropylene suggesting that the presence of crystallites in some way reduces the sorptive capacity of the amorphous phase. However, analysis of samples using x-ray diffraction revealed the presence of a less stable crystalline phase having a lower density. Since the crystalline volume fraction is commonly determined from density measurements, the presence of a second, less dense (however, still impermeable) crystalline phase would seem... 

The Tc- and Tm2-values of these poly(1-olefin)s are plotted in Figure 1.15 as a function of the number of C-atoms in the side-chain. Besides, Tm- and Tc-values of the main-chain crystalline phases as present in polypropylene (PP), poly 1-butene (P1B) and poly 1-pentene (PIP) ... 

The heating and cooling data for (PP/PE)-g-IA systems show the phase transitions typical of the homopolymers, which indicates a lack of compatibility between the crystalline phases of the polymers. However, the temperature-dependent location of the peaks that describe the phase transitions in (PPZPE)-g-l A systems changes with the blend composition and does not usually coincide with respective values for the homopolymers. It should be underlined that the crystallization temperature of the polypropylene component in the blends is 5-11°C higher than that of the PP homopolymer, whereas the typical variations in the melting point of PP are less significant. The (PPZPE)-g-IA systems of 99 1 ratio show a maximum Ter for the... 

Figure 13.9 Evolution of long spacing of the crystalline phase of the polypropylene all along the PP/ PA 6 binary system with modified interfaces.

The crystalline phase birefringence can be divided by the refractive index difference n — n for the crystal, to give 2. However, there is also a contribution to the birefringence from the molecular orientation of the amorphous phase. Figure 3.32 shows the contributions to the overall birefringence of polypropylene films, hot stretched at 110°C by different amounts. The increase in the orientation with strain is non-linear and it differs between the phases. 

Menyhard et al. [9] reported the generation of polymer blends based on the P-modification of polypropylene. The authors studied the melting and crystallization characteristics as well as the structure and polymorphic composition of the blends by polarized light microscopy (PLM) and differential scaiming calorimetry (DSC). It was observed that the most important factor of the formation of the blend with P-crystalline phase when semicrystalline polymers were added to isotactic polypropylene (iPP) was the a-nucleation... 

The dielectric loss factors d of the pure polypropylene and the composites containing the lignocellulosic materials derived from hemp and flax are presented in Figs. 14 and 15 as a function of the temperature for the frequency of 1000 Hz. Pure polypropylene is known to exhibit two characteristic features (Kotek et al., 2005) a glass relaxation p>eak around 263 K and a high - temperature ( 323 K) shoulder associated with chain relaxation in the crystalline phase. These features cannot be detected by the Dielectric Relaxation... 

Mixtures of clay platelets and polymer chains compose a colloidal system. Thus in the melt state, the propensity for the clay to be stably dispersed at the level of individual disks (an exfoliated clay dispersion) is dictated by clay, polymer, stabilizer, and compatibilizer potential interactions and the entropic effects of orientational disorder and confinement. An isometric dimension of clay platelets also has implications for stability because liquid crystalline phases may form. In addition, the very high melt viscosity of polypropylene and the colloidal size of clay imply slow particulate dynamics, thus equilibrium structures may be attained only very gradually. Agglomerated and networked clay structures may also lead to nonequilibrium behavior such as trapped states, aging, and glassy dynamics. 

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