Process for increasing the permeability of plastic membrane

Details Process for increasing the permeability of plastic membrane Process for increasing the permeability of plastic membrane

1982-02-01

1984-02-07

Czaja, Donald E.

Plastic and nonmetallic article shaping or treating: processes

Carbonizing to form article

Agglomeration or accretion

264 41, 264558, 264564, B29D 2700

Patent

active

044302789

ABSTRACT:
The regulated permeability of a thermoplastic membrane is modified by subjecting the thin membrane sheeting to warm to hot water, increasing the absorption of water in the membrane. The membrane is then rapidly heated with microwave radiation energy, typically at the 2450 MHz frequency absorbed by water, or heated in hot air. The water molecules absorbed in the membrane are explosively boiled out of the membrane, increasing the porosity of the membrane to water and also to other small molecules dissolved in water. The permeability of the plastic membrane is controlled by varying the concentration of water molecules initially absorbed in the hot membrane. Several types of plastic membrane having a relatively higher water absorption can be treated. The thin plastic membrane can be manufactured by extruding a small diameter, thick wall plastic tubing into hot water, and expanding the tubing with a hot water stream pumped into the inside of the tubing. The thin plastic sheet membrane can also be prepared by stretching a thicker plastic membrane in hot water. The hot water in which the plastic membrane is immersed can also contain small volatile, water-soluble molecules, such as methanol, ethanol, propropanol, and acetone, which can increase the permeability to selected small molecules of the plastic membrane on boiling out the solvents. Salt molecules of sodium chloride (NaCl), magnesium chloride (MgCl.sub.2), and the like in a hot water solution can form micro crystals in the thin-wall plastic membrane, which can be dissolved out at room temperature, further increasing the controlled permeability of the plastic membrane.

REFERENCES:
patent: 2979777 (1961-04-01), Goldman
patent: 3121760 (1964-02-01), Kline
patent: 3812224 (1974-05-01), Smith et al.
patent: 4076656 (1978-02-01), White et al.
Rubber and Plastics Age, vol. 44, No. 5, May 1963, p. 525 "Microwave Power for Fast Curing".
SPE Journal, vol. 24, Nov. 1968, pp. 29-32, "Plastics-Microwaves Pros and Cons".

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