Oriented polystyrene

Hadziioannou G, Wang LH, Stein RS, Porter RS. Small-angle neutron scattering studies on amorphous polystyrene oriented by solid-state coextrusion. Macromolecules 1982 15 880. 

Analysis of Experimental Data for Polystyrene Orientation during Stress Relaxation Using Semigrand Canonical Monte Carlo Simulation. 

Fig. 4 X-ray refraction topography of a polystyrene sample with highly oriented micro cracks induced by strain in vertical direction.

The refractograp of figure 4 shows highly oriented micro cracks of a polystyrene sample. The orientation of the cracks is perpendicular to the mechanical strain direction. The X-ray refracted intensitiy can be interpreted as crack density, i.e. the inner surfaces within a unit volume. Changing the tilt angle (of polystyrene and polystyrene blend samples) with respect to the primary beam leads to significantly different distributions of crack orientation (Fig. 5). 

BiaxiaHy oriented films have excellent tensile strength properties and good tear and impact properties. They are especially well regarded for their brilliance and clarity. Essentially all poly(ethylene terephthalate) film is biaxiaHy oriented, and more than 80% of polypropylene film is biaxiaHy oriented. Polystyrene film is oriented, and a lesser amount of polyethylene, polyamide, poly(vinyl chloride), and other polymers are so processed. Some of the specialty films, like polyimides (qv), are also oriented. 

Hard baked goods such as cookies and crackers have a relatively low water and high fat content. Water can be absorbed, and the product loses its desirable texture and becomes subject to Hpid rancidity. Packagiag for cookies and crackers includes polyolefin-coextmsion film pouches within paperboard carton sheUs, and polystyrene trays overwrapped with polyethylene or oriented polypropylene film. Soft cookies are packaged in high water-vapor-barrier laminations containing aluminum foil. 

Poly(phenylene ether). The only commercially available thermoplastic poly(phenylene oxide) PPO is the polyether poly(2,6-dimethylphenol-l,4-phenylene ether) [24938-67-8]. PPO is prepared by the oxidative coupling of 2,6-dimethylphenol with a copper amine catalyst (25). Usually PPO is blended with other polymers such as polystyrene (see PoLYETPiERS, Aromatic). However, thermoplastic composites containing randomly oriented glass fibers are available. 

Whether or not a polymer is rubbery or glass-like depends on the relative values of t and v. If t is much less than v, the orientation time, then in the time available little deformation occurs and the rubber behaves like a solid. This is the case in tests normally carried out with a material such as polystyrene at room temperature where the orientation time has a large value, much greater than the usual time scale of an experiment. On the other hand if t is much greater than there will be time for deformation and the material will be rubbery, as is normally the case with tests carried out on natural rubber at room temperature. It is, however, vital to note the dependence on the time scale of the experiment. Thus a material which shows rubbery behaviour in normal tensile tests could appear to be quite stiff if it were subjected to very high frequency vibrational stresses. 

Deliberately oriented polystyrene is available in two forms filament (mono-axially oriented) and film (biaxially oriented). In both cases the increase in tensile strength in the direction of stretching is offset by a reduction in softening point because of the inherent instability of oriented molecules. 

The largest outlet for polystyrene is in packaging applications. Specific uses include bottle caps, small jars and other injection moulded containers, blown containers (a somewhat recent development but which has found rapid acceptance for talcum powder), vacuum formed toughened polystyrene as liners for boxed goods and oriented polystyrene film for foodstuffs such as creamed... 

It may be prepared in two stereo-regular forms, cis- and trans-. The cii-polymer, which crystallises in zig-zag form, has a of 235°C, whilst the fran -polymer, which crystallises in helical form, melts at the much lower temperature of 145°C. Tensile strengths of both forms are reportedly similar to that of Penton whilst the tensile modulus of 2300 MPa is about twice as high. Unfortunately the material is rather brittle with an impact strength only about half that of polystyrene although this may be improved by orientation. 

Luy, B Kobzar, K Knor, S Furrer, Heckmann, D., Kessler, H. Orientational properties of sUetched polystyrene gels in organic solvents and the suppression of their residual H NMR signals./. Am. Chem. Soc. 2005, 327, 6459-6465. 

---