Poly calendering

Poly(vinyl chloride). To be converted into film, poly(viayl chloride) [9002-86-22] (PVC) must be modified with heat stabilizers and plasticizers, which increase costs. Plasticized PVC film is highly transparent and soft, with a very high gas-permeation rate. Water-vapor transmission rate is relatively low. At present, PVC film is produced by blown-film extmsion, although casting and calendering are employed for heavier gauges (see Vinyl POLYAffiRS). 

Thermoplasticity. High molecular weight poly(ethylene oxide) can be molded, extmded, or calendered by means of conventional thermoplastic processing equipment (13). Films of poly(ethylene oxide) can be produced by the blown-film extmsion process and, in addition to complete water solubiUty, have the typical physical properties shown in Table 3. Films of poly(ethylene oxide) tend to orient under stress, resulting in high strength in the draw direction. The physical properties, melting behavior, and crystallinity of drawn films have been studied by several researchers (14—17). 

Thermoplastic Processing. Poly(ethylene oxide) resins can be thermoplasticaHy formed into soHd products, eg, films, tapes, plugs, retainers, and fillers (qv). Through the use of plasticizers (qv), poly(ethylene oxide) can be extmded, molded, and calendered on conventional thermoplastic... 

Unlike other water-soluble resins the poly(ethylene oxide)s may be injection moulded, extruded and calendered without difficulty. The viscosity is highly dependent on shear rate and to a lesser extent on temperature. Processing temperatures in the range 90-130°C may be used for polymers with an intrinsic viscosity of about 2.5. (The intrinsic viscosity is used as a measure of molecular weight.)... 

A mixture of powdered poly(vinyl chloride), cyclohexanone as solvent, silica, and water is extruded and rolled in a calender into a profiled separator material. The solvent is extracted by hot water, which is evaporated in an oven, and a semiflexible, microporous sheet of very high porosity ( 70 percent) is formed [19]. Further developments up to the 75 percent porosity have been reported [85,86], but these materials suffer increasingly from brittleness. The high porosity results in excellent values for acid displacement and electrical resistance. For profiles, the usual vertical or diagonal ribs on the positive side, and as an option low ribs on the negative side, are available [86],... 

Alkanesulfonates are widely used as an internal antistatic agent for poly(vinyl chloride) (PVC). Since alkanesulfonates cause hazing of unplasticized PVC in the normally used quantities of 1.0 to 1.5 parts per hundred parts resin (phr), its main use is in the manufacture of opaque PVC-calendered film. To produce transparent unplasticized articles, the addition of alkanesulfonates should not exceed 0.3 phr. Figure 40 shows the antistatic effect of alkanesulfonates in PVC. 

Figure 20 indicates the pyroelectric current in calender-rolled rigid poly (vinyl chloride) (PVQ (Furukawa and others, 1968). In Fig. 20, results are shown for fifteen specimens cut from a sheet of PVC film, with the polarity map as Fig. 21. The map shows a heterogeneity of polarity.

Fig. 20. Pyroelectric current of 15 specimens of poly(vinyl chloride) film cut out from a calender-rolled sheet as indicated in Fig. 21. Electrode area = 1 x 1 cm2 film thickness = 0.2 mm heating rate=6 K/min. Reproduced from Furukawa and others [J. Appl. Polymer Sci. 12,2675 (1968)] by permission of John Wiley Sons,...

Poly(vinyl chloride) films are produced in two main forms—unplasticized and plasticized—and over the years different machines have been manufactured to handle the two types. When calendering unplasticized PVC there is a tendency for small particles, usually referred to as crumbs , to fall away from the edges of the film and from the feed nip. Such crumbs then could fall on to the finished film, where they would stick and form defects. To avoid this, producers of unplasticized film usually prefer an L configuration in which the product travels up the stack and surface contamination of this kind is prevented. With plasticized PVC the problem of crumbs does not occur to any great extent and, as it is an advantage to have good access to the part of the calender where the finished film is made, an inverted L configuration is the most popular. 

Poly(vinyl chloride) may be calendered in plasticized or unplasticized form and thin film can be produced by calendering followed by stretching (with stretch ratios of up to 8 1). Such products have a very wide range of uses. 

Poly([ethyl acrylate]-g-plvalolactone) was found to be easily processable on conventional rubber working equipment. It was easily processable on a two-roll mill, had excellent calendering properties, could be compression molded at 225-230°C, and could be Injection molded at 225°C. Extrusion was more difficult requiring high temperatures (250°C) and slow extrusion rates. Physical properties of the graft copolymers were similar to those of the parent elastomeric polyacrylates that had been compounded with carbon block and chemically crossllnked. 

Since fully cured thermoset sheets cannot be resoftened, forming is not appKcable to them. Common materials subjected to thermoforming are thermoplastics such as polystyrene, cellulose acetate, cellulose acetate butyrate, PVC, ABS, poly(methyl methacrylate), low- and high-density polyethylene, and polypropylene. The bulk of the forming is done with extruded sheets, although cast, calendered, or laminated sheets can also be formed. 

Multilayer co-extrusion is another technique used in the preparation of starch/ synthetic sheets or films [164, 263-266], in which TPS is laminated with appropriate biodegradable polymers to improve the mechanical, water-resistance and gas-barrier properties of final products. These products have shown potential for applications such as food packaging and disposable product manufacture. Three-layer co-extrusion is most often practiced, in which a co-extrusion line consists of two single-screw extruders (one for the inner starch layer and the other for the outer polymer layers) a feedblock a coat-hanger-type sheet die and a three-roll calendering system [164]. Biodegradable polyesters such as PCL [164, 264], PLA [164, 263], and polyesteramide, PBSA and poly(hydroxybutyrate-co-valerate) [164] are often used for the outer layers. These new blends and composites are extending the utilization of starch-based materials into new value-added products. 

Tinolex Poly(vinyl chloride) rigid, calendered, PVC Tins Ind. Co. Ltd. 

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