Polymer stretching methods

Preparation of highly oriented thin films of polymers film stretching method [2, 3,16,17]... 

Fig. 10.3 Scheme of the preparation of nanopmous polymer template by stretch method and LCP composite film with mesogens highly aligning along with the stretch direetion (a). SEM images of the initial porous polymer film (b) and the polymer eomposite film after filling with LC mixture and polymerization (C). Reproduced with permission from [38]. Copyright 2013... 

Nevertheless, hydrophobically associating water-soluble polymers present challenges to both the synthetic and characterization chemists. Hydrophobically associating water soluble polymers are often difficult to synthesize because of problems associated with mixing oil-soluble and water-soluble reagents/ monomers. Similarly, since only small levels of hydrophobe are needed for rheology control, characterization of hydrophobe contents often stretch the detection limits of conventional polymer characterization methods. 

HoUow-fiber fabrication methods can be divided into two classes (61). The most common is solution spinning, in which a 20—30% polymer solution is extmded and precipitated into a bath of a nonsolvent, generally water. Solution spinning allows fibers with the asymmetric Loeb-Soufirajan stmcture to be made. An alternative technique is melt spinning, in which a hot polymer melt is extmded from an appropriate die and is then cooled and sohdified in air or a quench tank. Melt-spun fibers are usually relatively dense and have lower fluxes than solution-spun fibers, but because the fiber can be stretched after it leaves the die, very fine fibers can be made. Melt spinning can also be used with polymers such as poly(trimethylpentene), which are not soluble in convenient solvents and are difficult to form by wet spinning. 

The modulus of the polymer is an average of the stiffnesses of its bonds. But it obviously is not an arithmetic mean even if the stiff bonds were completely rigid, the polymer would deform because the weak bonds would stretch. Instead, we calculate the modulus by summing the deformation in each type of bond using the methods of composite theory (Chapter 25). A stress d produces a strain which is the weighted sum of the strains in each sort of bond... 

Lower-density E-plastomers have found alternate use in cast film processes to make elastic film laminates with good breathability which contain laminates of liquid impermeable extensible polymeric films with extensible-thermoplastic-polymer-fiber nonwovens and nonwoven webs of polyethylene-elastomer fibers as the intermediate layers. The development relates to a breathable film including an E-plastomer and filler that contributes to pore formation after fabrication and distension of the film. The method and extent of distension is designed to produce a breathable film by stretching the film to form micropores by separation of the film of the E-plastomer from the particulate solids. This film is useful for manufacture of absorbent personal-care articles, such as disposable diapers and sanitary napkins and medical garments. In detail, these constructions comprise a liquid impermeable extensible film comprising polyolefins. The outer layer contains extensible-thermoplastic-polymer-fiber nonwovens, and an elastic intermediate layer contains nonwoven webs of fiber E-plastomers. The intermediate layer is bonded to the film layer and the outer... 

Sometimes the hazy optical properties of polypropylene are a detriment to its use in thin films. To address this problem, as well as to improve physical properties and reduce material costs, we can orient the molecular chains by stretching the polymer film after it has left the extrusion die. There are two methods of orienting films, film blowing, shown in Fig. 11.6, and tentering, shown in Fig, 19.6. 

Stretching a polymer in two perpendicular directions, either successively or by blowing a bubble of molten material, leads to its biaxial orientation, which strongly improves mechanical properties in the stretching directions and/or gas permeability (e.g., biaxial orientation of polypropylene leads to BOPP (for biaxially oriented polypropylene) or biaxial orientation of poly(ethylene terephthalate) gives CC>2-impermeable bottles for carbonated beverages.) (Characterisation methods for determining molecular orientation are considered in Chapter 8.)... 

Finally, as in macro-Raman experiments, orientation-insensitive spectra can also be calculated for spectromicroscopy. A method has been developed recently for uniaxially oriented systems and successfully tested on high-density PE rods stretched to a draw ratio of 13 and on Bombyx mori cocoon silk fibers [65]. This method has been theoretically expanded to biaxial samples using the K2 Raman invariant and has proved to be useful to determine the molecular conformation in various polymer thin films [58]. 

---