Polyethylene monoclinic phase

The monoclinic phase is formed at high crystallization pressure in addition to commonly observed orthorhombic phase in polyethylene. The nucleation of monoclinic phase is encotrraged by nanoclay even at low crystallization pressmes. ... 

Concerning the mechanical destruction of polymers, an interesting fact was reported. This is a phase transformation in the crystal structure from the normal orthorhombic to a monoclinic phase due to mechanical degradation. Kurokawa et al. studied the increase of the monoclinic phase after ball-milling of polyethylene. Yemni and McCullough concluded that the monoclinic phase is more stable energetically... 

Tr ws-poly(l,4-butadiene) has two crystal forms, a monoclinic phase which is stable at low temperatures and a hexagonal phase which is stable at high temperatures. The hexagonal phase of this polymer is similar to the hexagonal phase of polyethylene it... 

Crystals of polyethylene, PE, exist in three different modifications. The well known orthorhombic modification, a metastable monoclinic phase, and a hexagonal phase that appears at high pressure. 

The monoclinic crystal form of polyethylene (also referred to as the triclinic form) is a metastable phase formed under conditions of elongation [18,19]. It may be present to a small extent in commercial samples that have undergone cold working after initial molding. Temperatures in excess of 60-70°C cause it to revert to the orthorhombic form [20]. The monoclinic phase is sometimes present in nascent granules of ultrahigh molecular weight polyethylene due to... 

In a similar manner, the ethylene-octene copolymer crystallized directly via the orthorhombic phase without the intervention of the anticipated hexagonal phase as would be anticipated in linear polyethylenes at these high pressures and temperatures (at approximately 3.8 kbar and around 200 °C). At 100 °C, see Fig. 15, the d values for (110) and (200) orthorhombic reflections are 4.08 A and 3.71 A. When the sample is cooled below 100 °C, a new reflection adjacent to the (110) orthorhombic peak appears at 80 °C. The position of the new reflection is found to be 4.19 A and so corresponds to a new phase. No change in the intensity of the existing (110) and (200) reflections is observed, however the intensity of the amorphous halo decreases, which suggests that the appearance of the new reflection (d = 4.19 A) is solely due to the crystallization of a noncrystalline component. On cooling further as the new reflection intensifies, the (110) and (200) orthorhombic reflections shift gradually. However, at 50 °C, the (100) monoclinic reflection appears with a concomitant decrease in the intensity of the (110) orthorhombic reflec-... 

Wittmann JC, Lotz B. Epitaxial crystaUization of monoclinic and orthorhombic polyethylene phases. Polymer 1989 30 27-34. 

Figure 8.2 The various contact planes obtained so far for the epitaxial crystallization of the orthorhombic and monoclmic phases of polyethylene on substrates with matching periodicities. The corresponding interchain spacings correspond to the first and the second nearest neighbor chains with periodicities of 0.446,0.494, and 0.744 nm for the orthorhombic (110), (100), and (010) planes and 0.404 nm, 0.523 nm and 0.918 nm for the monoclinic (010), ([210]), and ([410]) planes, respectively. Reproduced from Reference [11] with permission of Per-gamon Press.

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