Orientation cold-stretching

Fibers oriented by stretching to 4 x original length by cold drawing (two pulleys at different speeds) or by spin drawing as it is being cooled... 

Cold stretched films were difficult to produce and upon stretching exhibited little. If any, orientation. From Table III It Is obvious that of the ten samples stretched only specimens U2 and U8 did not fall upon being loaded. These samples were stretched at 90, and 110 c. SALS was performed on all the samples, but only samples U2 and U8 were used In the SAXS, UAXD, and SEM experiments. Figure 9 shows the resulting Hv SALS patterns for some of the cold stretched films. The patterns are circular Indicating no orientation. Confirming this lack of orientation are SAXS patterns that showed cylindrical symmetry and UAXD patterns of the films that yielded circular diffraction rings. 

The prefemps mdided in a standard injection molding m hine. The cold preforms am then shipped randomly to a special sttetch blow machine, wto% they are oriented, reheated, stretch and blown. 

Fig. 10. Sketch of the transformations of the oriented chains during deformation, in-between are additional amorphous chains a) lamellae with some tie-molecules, b) elastic shear-deformation of lamellae imder small load and reorientation with respect to the load, c) fracture of lamellae into smaller blocks due to local stress concentration caused by tie molecules, d) stretched aligned, but not re-crystallised chains between the blocks during stretching at higher temperatures, e) some of the fibrillar arranged molecules crystallise, final stage in the case of hot stretched iPP, f) further dissolution of the blocks creating more extended chains at room temperature, g) finally, there are several strands of extended chains, not crystallised, with some amorphous regions in between, final stage in the case of cold stretched rPP.

The collection of diffraction data of polymers in a solid mesophase for the structural analysis is generally performed on imiaxially oriented samples (fibers) [152-154]. Oriented fibers of high polymers in a mesomorphic form may be easily obtained by extrusion procedures from solution or melt and/or by cold stretching procedures. 

Cold drawing (cold stretching) n. A stretching process performed at a temperature below a thermoplastic s melting range to orient the material and improve the tensile modulus and strength. 

The formation of the hollow fiber membrane via TIPS process has not been studied very much. Kim et al. [13] prepared poypropylene hollow fiber membrane from polypropylene/soybean oil mixture. The membrane was formed by the TIPS process and subsequent cold-stretching. The hollow fiber became more oriented by increasing the melt-draw ratio defined as the ratio of take-up speed to the extrusion of the polymer solution. The cold-stretching of the hollow fiber membranes remarkably increased the membrane porosity. 

Compression molded (150°C for 3 minutes press chilled with cold water immediately thereafter) samples of poly(trans-l,4-hexadiene) (14) and poly(5-methyl-l,4-hexadiene) were examined with a General Electric (XRD-3) X-ray unit. Transmission Laue X-ray photographs were taken using nickel filtered copper X-radiation. Samples were stretched to four times of their original lengths to obtain oriented fibers. The fiber patterns were obtained in a flat plate film holder with the specimen to film distance standardized at 5 centimeters. X-ray diffraction patterns were similarly obtained for the hydrogenated sample of poly(5-methyl-l,4-hexadiene). 

Crystallizable polymers tend to form randomly oriented crystallites which are oriented when the polymer is stretched or cold drawn at temperatures below the Tm. Crystallization under pressure may result in a fibrillar structure or extended chain structure. 

Polymer sheets are cooled without stretching by convected cold air (or an inert gas), by immersion into a fluid bath, or by passage over chilled rolls. Flat films are usually stretched and oriented uniaxially and cooled by either of the methods previously mentioned. Films are also cast and cooled on rolls for optimal clarity purposes. 

Fig. 13.16 Schematic representation of the flow pattern in the advancing front between two parallel cold walls. Black rectangles denote the stretching and orientation of a fluid particle approaching the central region of the front. The curved shape of the front causes fluid particles initially oriented in the y direction to end up on the wall, oriented in the x direction. The velocity profile upstream from the front is in the x direction and is viewed from a coordinate system located on the front. [Reprinted by permission from Z. Tadmor Molecular Orientation in Injection Molding, J. Appl. Polym. Sci., 18, 1753 (1974).]...

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