Calendering, thermoplastics

It is possible to calender thermoplastics onto fabrics to obtain a reinforcing effect. 

Separating Force between Rolls in an Experimental Calender A cellulose acetate-based polymeric compound is calendered on a laboratory inverted, L-shaped calender with 16-in-wide rolls of 8 in diameter. The minimum gap between the rolls is 15 mil. The sheet width is 15 in. Calculate the separation force and the maximum pressure between a pair of rolls as a function of exiting film thickness, assuming that film thickness equals the gap separation at the point of detachment. Both rolls turn at 10 rpm. The polymer at the calendered temperature of 90°C follows a Power Law model with m = 3 x 106 dyne.s"/cm2 and n = 0.5. [Data based partly on J. S. Chong, Calendering Thermoplastic Materials, J. Appl. Polym. Sci., 12, 191-212 (1968).]... 

Calendering. Thermoplastic materials can be formed into thin sheets by calendering, a process by... 

The formaldehyde approach is stiU used by Futamura Chemical (Japan). They make spun-laid viscose nonwovens where the hydroxymethylceUulose xanthate derivative formed from formaldehyde ia the spia bath allows the fibers to bond after layiag. This process was originally developed by Mitsubishi Rayon (30), who later found that the derivative was thermoplastic, and the web could be calender-bonded (120°C) prior to regeneration (31). 

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... 

Deformation of a polymer melt—either thermoplastic or thermosetting. Processes operating in this way include extrusion, injection moulding and calendering, and form, in tonnage terms, the most important processing class. 

The principles of thermoplastic melt processing can perhaps best be illustrated by reference to Figure 8.1 illustrating extrusion, injection moulding, bottle blowing and calendering operations. In order to realise the full potential of the process it is necessary to consider the following factors ... 

It is possible to calender two different thermoplastics to fabricate a two-layer article. 

An important step in the manufacture of any plastic product is the fabrication or the shaping of the article. Most polymers used as plastics when manufactured are prepared in pellet form as they are expelled from the reactor. These are small pieces of material a couple of millimeters in size. This resin can then be heated and shaped by one of several methods. Thermoset materials are usually compression molded, cast, or laminated. Thermoplastic resins can be injection molded, extruded, or blow molded most commonly, with vacuum forming and calendering also used but to a lesser extent. 

The major bulk processed thermoplastic using calendering is PVC sheets and films including blends and copolymers. A sample recipe to produce PVC sheet might include a plasticizer such as a dialkyl phthalate, pigment, filler, lubricant, and stabilizer. 

Fig. 6.27 Comparison between experimental pressure profile for plasticized thermoplastic resin (34) and theoretical pressure profiles for n — 1 and n — 0.25 calculated by Kiparissides and Vlachopoulos (35). The theoretical curves were calculated both by finite element method and analytically by way of Gaskell type models, as discussed in this section, giving virtually identical results. [Reprinted by permission from C. Kiparissides and J. Vlachopoulos, Finite Element Analysis of Calendering, Polym. Eng. Set, 16, 712-719 (1976).]...

The calendering process is commonly used for shaping high melt viscosity thermoplastic sheets and is particularly suitable for polymers susceptible to thermal degradation or containing substantial amounts of solid additives. This is because the calender can convey large rates of melt with a small mechanical energy input (compared to an extruder). 

J. Vlachopoulos and C. Kiparissides, An Analysis of Thermoplastics in Calendering, paper presented at the 26th Canadian Chemical Engineering Conf., Toronto, Canada, 1976. 

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