Orientation of films

The crystallization tendency of polycarbonates in the pure state is limited. Kampf (JO) found that the first spherulites appear only after heating at 180°C. for eight days more pronounced crystallization occurs only after heating at 190°C. for the same period of time. Orientation of films or fibers does not cause any crystallization, and relatively small improvement of elastic properties is noted. 

PLA is a polymer that may not be well suited to injection moulding. Its rate of crystallisation is too slow to allow cycle times typical of those for commodity thermoplastics such as polystyrene. Stress induced crystallisation that can enhance PLA crystallisation is better suited to processes such as fibre spinning or biaxial orientation of film. 

The high heat resistance and asymmetric structure of PNI hamper to the orientation of films made from these polymers. However, even a uniaxial orientation of PNI based on dodecamethylenediamine = 0.81 dl/g) at 260 °C leads to an increase in the tensile strength o from 60 to 160-200 N/m and in the elongation at break from 7 to 30% [40]. 

Reprinted by permission of Kluwer Academic Publishers from Schuur, G. and Van Der Vegt, A. K., Orientation of films and fibrillation in Structure and Properties of Oriented Polymers, Ed. I. M. Ward, Chap. 12, pp.413-453, Applied Science Publishers, London, 1975). 

Figure 11.10 Orientation of film made from counter-rotating die results in curl. 

Figure 11.12 Orientation of film made with the tri-rotating die.

Tentering v. Biaxial orientation of film or sheet by means of a tentering frame. 

Figure 16.16 (a) Schematic molecular growth orientations of films of 17-20 on Si/Si02 substrates, (b) Plots of the observed d spacing versus molecular core length (n) for DFH-nTs (solid line) and isoDFH-nTs (broken line) (top) and DH-nTs (solid line) and isoDH-nTs (broken line) (bottom). Adapted with permission from A. Facchetti, M.-H. Yoon, M. Mushrush, C. R. Hutchison, M. A. RatnerandT.J. Marks,). Am. Chem. Soc., 126, 13859(2004). Copyright 2004 American Chemical Society... 

We therefore have the possibility that the acoustic wavelength is of the same order as the dimensions of bubbles and therefore the lateral dimensions of foam films. This possibility is ignored in the theoretical treatment of acoustic defoaming by Nevolin [76]. That acoustic waves could cause symmetrical thickness oscillations in those films of a similar wavelength has in fact been suggested by Sandor and Stein [59]. This implies some kind of resonance where the lateral dimension of the film is some integer of the acoustic wavelength. It is perhaps easier to see how this could happen in the case of a film vertically oriented parallel to the sound pressure wave. Clearly, however, the actual orientations of films in a typical polydisperse foam are essentially mostly random, with, however, the exception of the dome-shaped films at the top of a foam column. 

Monoaxially and biaxially oriented films of fiuoropolymer are made by melt extrusion of the resin into flat webs or tubes. The main function of orientation is to enhance the mechanical properties of the film such as tensile break strength and tear resistance. The decision to orient is usually made according to the requirements of the end use for mechanical properties. See Sec. S.2.2.3 for a discussion of biaxial orientation of films. All process surfaces that contact molten fluoropolymers must be corrosion resistant because of the formation of corrosive compounds such as HF and HCl from the high temperature degradation of these plastics. Section 7.8 provides information about selection of construction materials for fiuoropolymer processing equipment. 

Also, besides qualitative identification of functionality, infrared can serve to analyze for cis, Irans structures, determination of crystallinity, orientation of films, as well as a quantitative analysis of components present. 

WAXS measurements were taken at the different orientation of film position relative to X-ray irradiation beam. For all samples, the dififracto-grams reveal the existence of axial cylindrical texture in PVA. The axis of texture coincides with extrusion direction, and hence the PVA molecules in quasi-crystalline fields oriented along extrusion direction. In samples with 10 and 20 wt.% of PHB a well-defined axial texture of PHB crystallites is evident, where the texture axis coincides with direction of extrusion as well. However, the PHB crystallites oriented relative to the texture axes so that the extrusion direction in line with the axis a of elementary crystalline cell. Hence, the axes of PHB molecules are normally oriented relative to extrusion direction. 

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