Textured semi-crystalline polymers

Fig. 9.5 A sketch of a channel-die compression device used in producing highly textured semi-crystalline polymers in plane-strain compression.

Lee, B. J., Parks, D. M., and Ahzi, S. (1993b) Micromechanical modeling of large plastic deformation and texture evolution in semi-crystalline polymers, J. Mech. Phys. Solids, 42, 1651-1687. 

However, obtaining useful structural information concerning the lamellar texture of semi-crystalline polymers or the phase distribution in polymer blends or block copolymers is often complicated by the fact that the variation in electron density between the stmctural components of interest is insufficient to provide meaningful image contrast. In such circumstances, additional sample preparation procedures, beyond ensuring that the sample is sufficiently thin, are required. 

Polyolefin foams are easier to model than polyurethane (PU) foams, since the polymer mechanical properties does not change with foam density. An increase in water content decreases the density of PU foams, but increases the hard block content of the PU, hence increasing its Young s modulus. However, the microstructure of semi-crystalline PE and PP in foams is not spherulitic, as in bulk mouldings. Rodriguez-Perez and co-workers (20) showed that the cell faces in PE foams contain oriented crystals. Consequently, their properties are anisotropic. Mechanical data for PE or PP injection mouldings should not be used for modelling foam properties. Ideally the mechanical properties of the PE/PP in the cell faces should be measured. However, as such data is not available, it is possible to use data for blown PE film, since this is also biaxially stretched, and the texture of the crystalline orientation is known to be similar to that in foam faces. 

XRD diffraction studies was also carried out to analyze the crystallinity of the polymers 3(a-d) and was performed at room temperature. To avoid the trace of the solvents, powder samples were placed on a zero-background quartz plate, placed for 20 s. in an oven preheated to 110 °C, quenched to room temperature using a N2 purge, and then analyzed in the diffractometer. The XRD patterns are shown in Fig. 12.6. All the polymers show similar multiple sharp diffraction peaks in the range of 20 = 11.0°-30.0° which indicates the crystalline to semi-crystalline nature of the polymers. This may be due to the slight difference in the chemical structures of these polymers. Furthermore, the results of the x-ray diffraction were in agreement with the POM textures, and this confirmed that the synthesized polymers 3(b-d) were in liquid crystal phases (nematic mesophase). 

The current paper emphasizes the relationship between drawing temperature, mechanical behavior, and crystal texture. Specifically, it describes crystallization of this polymer after deformation in the semi-solid state, and role of the molten and oriented portions of the crystalline phase. 

---