Stretch films

In oriented systems (fibres or stretched films), the scattered image often appears as a two-bar or a four-point pattern with the scattering maximum at or near the meridian (fibre axis). The one-dimensional scattered intensity along the meridian must be calculated by the projection method using the following fonnalism... 

Fig. 15. Production lines for stretched film tape (29) (a) continuous production line for film tape (b) discontinuous production lines for film and film tape.

Tables 4—6 Ust ASTM methods used for the characterization of PB and PMP. A number of specialized methods were developed for testing particular articles manufactured from polyolefins several of these determine the performance of PB and PMP film, including the measurement of the film s dart impact strength and tear strength. Dart impact strength is measured by dropping a heavy dart with a round tip on a stretched film. Tear resistance, which reflects the film s resistance to tear propagation, is measured with the Ehnendorf tear tester. Two values for the tear strength are usually reported, one in the machine dkection of the film and the other in the transverse dkection. Pipes manufactured from PB are tested by pressurizing them internally with water the time-to-burst failure is determined at various temperatures (46). The standard test method for haze and luminous transmittance (ASTM D1003) is used for the measurement of PMP optical characteristics.

It is generally claimed that metallocene polyethylenes (often abbreviated to m-PE) exhibit superior mechanical and optical properties as well as better organoleptic properties (resulting from the lower residue levels). As an example m-LLDPE is particularly favoured as a stretch film for wrapping because of the good prestretchability, high puncture resistance and tear strength, all of which are claimed to be better than with conventional LLDPE. 

Of greater interest in recent years have been the peculiar piezolectric properties"" of polyfvinylidene fluoride). In 1969 it was observed" that stretched film of the polymer heated to 90°C and subsequently cooled to room temperature in a direct current electric field was 3-5 times more piezoelectric than crystalline quartz. It was observed that the piezolectric strain coefficients were higher in the drawn film and in the normal directions than in the direction transverse to the film drawing. 

Biaxially stretched film has proved of value as a packaging material. Specific uses include blister packaging, snap-on lids, overwrapping, envelope windows and de luxe paekaging. 

Films stretch film, laminated film, shrinkable film... 

We now report that in the region of the absorption band the flow linear dichroism of a solution of 1 is positive (Fig. 3). Assuming that the nature of the flow orientation is of the usual kind, i.e., that the polymer chains in a random coil conformation which dominates in solution (34) tend to align with the flow direction, this observation provides additional support for the absolute assignment of the transition moment direction along the chain direction, even in solution. Similar conclusions based on polarization studies on a stretched film of poly(di-n-hexyl silane) have recently been reported (36). 

Bundle and coworkers196 first investigated the diffraction patterns obtained from stretched films of amylose obtained from maize starch ( B -modification). The dimensions of the orthorhombic unit cell were as follows. 

Lopez-Cervantes, J. and Paseiro-Losada, P. (2003). Determination of bisphenol A in, and its migration from, PVC stretch film used for food packaging. Food Addit. Contam., 20, 6, 596-606. 

The DNA-lipid cast film was stretched ca. three times in length (ca. 20 p.m thick) in the wet state, and X-ray diffraction patterns are shown in Fig. 7b. When the incident beam was irradiated parallel to the top edge of the stretched film, the circular reflection of 41 A was observed. When the beam was exposed parallel to the side edge and perpendicular to the film plane, the diffraction on the equator appeared as two spots of 41 A indicating a distance between the DNA-lipid strands and the diffraction on the meridian of 3.4 A. The distance between parallel stacked base-pairs was clearly observed [2-4]. These findings clearly show that DNA strands are ahgned... 

Fig. 7 X-ray diffraction patterns of a the as-cast film, b the stretched film of the DNA-lipid complex in water moisture, and c the stretched DNA-lipid film in the dry state. Open, two-headed arrows show the stretching direction of the film. Closed arrows show the incident beam of the X-rays. X-ray photographs of a and c were enlarged to show diffraction more clearly...

When the stretched film was dried in air (simply applying a hair-dryer for 2 min), only diffraction on the equator as two spots of 41 A was observed but not diffraction on the meridian for base-pairs (Fig. 7c). This suggests that the orientation of the base pairs is not perpendicular to the stretched direction, although the DNA strands are aligned parallel to the stretched direction. Figure 8 shows CD spectra of the cast film of the DNA-lipid complex in wet (a) and dry states (b). The CD spectrum of the wet film was consistent with a B-form structure of native DNA in fibers obtained from aqueous solution [1-3]. On the contrary, the CD spectrum in the dry state resembles the A-form of DNA in which the base pairs slant to the axis of the strands [2,3]. These results are consistent with CD spectra of the DNA-lipid complex in an organic solution DNA exists in the B-form in the presence of water and the C-form in the ab-... 

X-ray diffraction techniques can be used to establish the structure of crystalline polymers. Measurements are typically made on crystalline lamellar platelets grown from dilute solution, fibres or stretched films. Such methods have been applied to several different inorganic polymers. For example, based on measurements on stretched samples of silicone rubber, poly(dimethylsiloxane) (Me2SiO) has been shown to possess a helical conformation (Figure 8.4). ... 

Further, they can be used for medical purposes, such as press-through packages, disposable syringes, liquid medicine vials, and infusion bags. They are suitable for electric or electronic materials, such as wire coating. In addition, packaging films, such as wrapping films, stretch films, shrink films, and blister packs can be produced. 

Relative directions of the transition moment determined from polarized fluorescence (pol. fl.) or stretched film spectra (st.f.sp.) ... 

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