Polystyrenes coextrusion

The production of foamed films and sheets from polypropylene and polystyrene is discussed, with particular reference to packaging applications. Advantages of foamed materials for this application are examined, and the chemical and physical foaming processes are described. Extrusion technology for film and sheet by chemical and physical foaming processes is discussed, and recent developments in the coextrusion of multilayer packaging trays for the food industry are considered. 

In general only the simpler materials can be thermoformed on cylinders using vacuum (e.g. PVC, polystyrene, PVdC coated PVC). Platens using pressure forming, particularly with plug assistance, not only offer more uniform blisters but can utilise the more complex materials, e.g. Aclar/PVC, polypropylene, coextrusions (Figure 13.4). 

Fina . [FinaChem.] Polystyrene resins for inj. molding, coextrusion, blow molding, extruded foam, thermoforming, lamination, film, consumer prods., me al and laboratory parts, tumblers. 

Polystyrene. [Novacor Ltd.] Crystal or inqract polystyrene for medical nxdd-ii housewares, sheet glazing, coextrusion, oriented sheet, inj. blow molding, inj. foam, thermoformed drink-ware, rigid pkg., audio cassettes, cosmetic molding, electronic pkg., lab-ware, toys, closures blending resin. 

Trimmed and faced blocks are stained by immersion in a 10% solution of HgO in trifluor-oacetic acid for 10-60 min. Samples are washed in a dilute solution of trifluoroacetic acid followed by distilled water. Poly(phenylene oxide) (PPO) appears to have a higher mercury uptake than polystyrene in a bonded laminate of the two films [6]. Blends made by coextrusion of Kraton G and PPO show dispersed particles in a matrix. Kraton G is the lighter contrast polymer as it seems to take up less of the stain than the PPO. In summary, mercuric trifluoroacetate staining has been shown for several polymers where the dispersed phase particles are differentiated by this stain. The method has limited application. 

Recently Hadziioannou et al. (106) prepared amorphous polystyrene with extrusion ratios up to 10, using a solid-state coextrusion technique. Their poly-... 

Figure 10.15. Flow of a high-impact polystyrene resin (Dow Styron 484) through a 61-cm channel with a square cross section that is 0.9525 cm on a side. A special feedblock brings in concentric layers, which are colored for contrast, (a) At the channel entrance, (b) At the channel exit, (c) Computed secondary flow. Reprinted with permission from J. Dooley, Viscoelastic Flow Effects in Multilayer Polymer Coextrusion, Ph.D. dissertation. Technical University of Eindhoven, the Netherlands, 2002.

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. 

Recently, a novel method to prepare multilayers and nanolayers from a sequential coextrusion process has been introduced. In this method, the number of layers can be largely increased at the expense of reducing the thickness of the coextruded layers. It is also possible to obtain nanodroplet dispersions by annealing such multilayer coextruded ensemble. The following systems have been studied employing this method polyethylene/ polystyrene (PE/PS), polypropylene/polystyrene (PP/ PS), polycarbonate/poly(ethylene terephtalate) (PC/ PET), and poly(ethylene oxide)/ethylene acrilic acid copolymer (PEO/EAA). The crystallization behavior within the nanolayers and within the spheres that are obtained after heating and coalescence of the nanolayers has also been studied [18,33,66,94,104, 111, 140-143]. 

Coextrusion is an important process for manufacturing layered plastic composites, such as film, sheet, and tubing (Middleman, 1977 Schrenk and Alfrey, 1983 Schrenketal., 1963). A costly alternative would be the fabrication of individual layers of plastics followed by conventional lamination and coating. An additional advantage of the coextrusion technique is its ability to handle extremely thin films on the order of 10 xm. One of the most colorful applications of this technique is the iridescent film, which consists of hundreds of very thin layers of alternating low and high refractive indices. A typical example of this type of film consists of 116 layers of poly(methyl methacrylate) (PMMA) with refractive index 1.49 and 115 layers of polystyrene (PS) with refractive index 1.59 and total film thickness of about 20 o.m (Radford et al., 1973). 

---