Polyethylene, crystalline Lamellar

The morphologies of various copolymers composed of polyethylene oxide), PEO, and poly (1,2-butylene oxide), PBut, were recently reviewed by Ryan et al. [61]. The corresponding phase diagrams of PEO-fr-PBut, PBut-fo-PEO-fo-PBut and PEO-fo-PBut-fo-PEO melts are depicted in Fig. 11. In all phase diagrams the semi-crystalline lamellar phase was not attained because of the copolymers low melting points. 

Equation (2) suggests that the volume fraction of crystalline material controls the microhardness value of a pol5mier. However, it was soon recognized the large influence of the crystalline lamellar thickness U upon microhardness in case of chain-folded and chain-extended polyethylene (PE) (4). Based on a thermodynamic approach, the dependence of hardness on the average crystal thickness was derived (15) ... 

The technique was first applied to polyethylene and i-polypropylene revealing itself to be sensitive to crystallinity, lamellar orientation, crystal structure, and crystal defects (55). Thus it penetrates between lamellae attacks lamellar side surfaces more than their fold surfaces, a- more than /3-i-polypropylene and removes dislocation cores preferentially. As with chlorosulfonation, it allows systematic study of samples by cutting them open where desired. But it can also reveal the particular character of external or fracture surfaces, neither of which is usually random. 

Sakurai T, Nagakura H, Gondo S, Nojima S. Crystallization of poly(e-caprolactone) blocks confined in crystallized lamellar morphology of poly(c-caprolactone)-Wock-polyethylene copolymers effects of polyethylene crystallinity and confinement size. Polym J 2013 45 436-443. 

H. G. Kilian, M. Pietralla (Polymer 7P, 664-672, 1978) derive from the anisotropy A of the thermal diffusivity a = X/cpp of oriented polyethylenes that the intrinsic anisotropy Ai of the orienting, partly crystalline lamellar clusters increases with the degree of crystallinity (Aj = 7 to 26, linear extrapolation yields Aj = 2 for the fully amorphous and Aj = 50 for a completely crystalline cluster) the average degree of orientation of the lamellae, , as determined from thermal measurements agrees very well with X-ray data the observed increase of orientation with draw ratio is more rapid than it would be in affine deformation. 

Orientation affeets the permeability of polyethylene by changing its degree of crystallinity, lamellar organization, and molecular constraints. Strain-induced crystallization may increase the degree of crystallinity, while noncrystalline regions become better paeked as a function of orientation [47,48], both of which reduce the free volume of the system and hence reduce its permeability. Not withstanding, the effects of orientation are complex, and contradictory results have been reported [49]. 

A) is much smaller than the lamellar length of ordinary PE crystals ( 100A), thus the PE chains are prevented from folding. In this manner, extended-chain crystalline nanofibers of linear polyethylene with an ultrahigh molecular weight (6,200,000) and a diameter of 30 to 50 nm are formed. 

Fig. 10. Schematic structure models of the bulk-crystallized polyethylene samples. 1, II, and 111 indicate the crystalline, interfacial, and interzonal regions, respectively. Models A, B, C, D, and E express the molecular crystal, unpeeled crystal, disheveled unpeeled crystal, and lamellar crystals for medium and large molecular weight samples, respectively66), f and x designate the lamellar thickness and the extended molecular chain length, respectively...

The microhardness of LDPE fractions and of high-density polyethylene (HOPE) samples has been studied as a function of molecular weight in the range of about 2 X 10 up to 4 X 10 (Baltd Calleja et al, 1997). Details of the lamellar structure were determined by TEM. The observed decrease of microhardness with increasing molecular weight is mainly due to the increase in thickness of the interlamellar layers (i.e. a decrease of crystallinity). After chemical treatment with chlorosul-phonic acid and with OSO4, samples show a drastic increase in microhardness. 

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