Polyethylene relative crystallinity

Careful work is necessary to remove all preferred orientation from powder samples. Figure 1 shows results obtained with polyethylene terephthalate (PET) fibers. Curve is a typical azimuthal scan of the 010 peak (20 = 17,5°) for a bundle of parallel fibers placed perpendicularly to the x-ray beam. Curve b is the same scan carried out on a "powder" sample, showing that all preferred orientation is removed in our conditions of moulding (350 kg/ m2). For each kind of fiber, it is necessary to do preliminary trials to find the best experimental conditions. For PET fibers, we show on Figure 2 the relative crystallinity index and the residual orientation plotted against the cut-lengh. (5). 

Figure 32 Crystallization kinetics for the poly(ethylene oxide) block in triblock terpolymers with a rubbery end biock (poiybutadiene-Wocfr-polystyrene-b/oc/f-poly(ethylene oxide)) or a crystalline end block (polyethylene-b/oc/f-polystyrene-Wock -poiy(ethylene oxide)) (a) deveiopment of the relative crystallinity with crystallization time during isothermal crystallization at 49.5 °C, and (b) inverse of experimentai crystaiiization haif-time as a function of crystallization temperature. Reprinted with permission from Boschetti-de-Fierro, A. etal. Macromol. Chem. Phys. 2008,209,476- 87. ...

Fig. 9.14 Plot of log crystallinity, or relative crystallinity, against log time for representative polymers, (a) Linear polyethylene, M = 122000 (34) (b) linear polyethylene A/ = 8 x 10 (34) (c) poly(l,3-dioxolane) (38) (d) poly(phenylene sulfide) (37).

Fig. 11.25 Plot of relative crystallinity against log time for superposed linear polyethylene blends of M = 9000 and 370000. Compositions indicated IV, M = 370000 II, M = 9000. Crystallization temperature 130 °C. (Data from Ohno (37))...

Figure 11.13 isothermal crystallization data for high-density polyethylene, (a) Crystallinity-time curves in isothermal crystallization at various temperatures, b) Plots of crystallinity versus relative time t/t, where t is time when the crystallization proceeds to 50%. (From Ref 22.) From J. Appl. Polym. Sci., vol. 17, Nakamura, K., K. Katayama, and T. Amano Some aspects of nonisothermal crystallization of polymers II. Consideration of the isokinetic condition, Copyright 1973 by John Wiley Sons, Inc. Reprinted by permission of John Wiley Sons, Inc. 

Fig. 22. Nomialized pull-off energy measured for polyethylene-polyethylene contact measured using the SFA. (a) P versus rate of crack propagation for PE-PE contact. Change in the rate of separation does not seem to affect the measured pull-off force, (b) Normalized pull-off energy, Pn as a function of contact time for PE-PE contact. At shorter contact times, P does not significantly depend on contact time. However, as the surfaces remain in contact for long times, the pull-off energy increases with time. In seinicrystalline PE, the crystalline domains act as physical crosslinks for the relatively mobile amorphous domains. These amorphous domains can interdiffuse across the interface and thereby increase the adhesion of the interface. This time dependence of the adhesion strength is different from viscoelastic behavior in the sense that it is independent of rate of crack propagation.

E-plastomers, particularly the high- and medium-density materials, have found extensive use in films [17]. They are valued for their excellent seal character which allows the formation of mechanically strong seals at relatively low temperatures compared to traditional low-density polyethylene (LDPE). In addition, these E-plastomers can be obtained in a range of crystallinities and softness. These higher-density materials are typically made in the blown-film process and are used for protective film covers and disposable bags. 

Free radical vinyl polymerization, the oldest process, leads to branched low density polyethylene (LDPE). Macromolecules have numerous short branches, which reduce the melting point, tensile strength and crystallinity. Polymers are relatively flexible because of the high volume of the branched molecule and the low crystallinity. 

Based on the results obtained to date, which have been summarized above for several different semicrystalline polymers— linear and low density (branched) polyethylene, polytrimethylene oxide, polyethylene oxide and cis polyisoprene—it is concluded that the relatively fast segmental motions, as manifested in Tq, are independent of all aspects of the crystallinity and are the same as the completely amorphous polymer at the same temperature. Furthermore, it has previously been shown that for polyethylene, the motions in the non-crystalline regions are essentially the same as those in the melts of low molecular weight ii-alkanes. (17)... 

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