Polyethylene absorption isotherms, vinyl

Vinyl Chloride/Polyethylene Absorption Isotherms. The absorption isotherms have been determined by adding increasing quantities of vinyl chloride to an aqueous suspension of polyethylene. After saturation of the polyethylene, there is no further increase in the pressure with increasing quantities of vinyl chloride. The principal characteristics of the various polyethylenes examined are shown in Table I. 

Figure 2. Vinyl chloride/polyethylene absorption isotherms at different...

Figure 1 shows that two polyethylenes of nearly identical chemical nature (Alkathene WRM 19 and Microthene N 710) have nearly the same absorption isotherms in spite of their very different particle sizes. This proves that the vinyl chloride is homogeneously absorbed in the mass, not only adsorbed on the surface. Figure 1 also shows that, at 68°C, low-density polyethylenes (Alkathene WRM 19 and Microthene N 710) absorb much more vinyl chloride than does high-density poly-theylene (Eltex 6037). 

Into a 5-liter autoclave, continuously stirred at a speed of 450 rpm, water, a dispersing agent, and polyethylene (powder or pellets) are introduced in the proportions set forth in Table II. After introduction of the initiator, the vinyl chloride is injected in such a quantity that, at the polymerization temperature, the vinyl chlorides partial pressure is lower than the vapor pressure of pure vinyl chloride at the same temperature. The vinyl chloride quantities compatible with this condition are easily determined by the absorption isotherms. When the pressure has dropped to at least half of its maximum value, the nontransformed vinyl chloride is removed. After filtering, washing, and drying, the product is collected. 

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