Process for increasing the permeability of plastic membrane

• US 4,430,278 A
• Filed: 02/01/1982
• Issued: 02/07/1984
• Est. Priority Date: 02/01/1982
• Status: Expired due to Fees

• Current Assignee: Newhart-Jones Limited
• Original Assignee: Newhart-Jones Limited
• Inventors: Jones, John L. Sr.
• Primary Examiner(s): Czaja, Donald E.
• Assistant Examiner(s): Becker, Mary A.
• Application Number:
  US06/344,293
• Time in Patent Office: 736 Days
• Field of Search: 264/22, 264/25, 264/26, 264/558, 264/564, 264/41, 264/DIG. 43, 264/DIG. 17, 264/DIG. 47, 264/45.6, 201/2.5, 210/640, 210/642, 210/645, 210/650, 210/651, 210/652, 210/653, 210/654, 210/655, 219/10.41, 219/10.55 R, 219/10.69
• US Class Current: 264/474
• CPC Class Codes: B01D 61/246 Membrane extraction
• CPC Class Codes: B01D 67/0083 Thermal after-treatment
• CPC Class Codes: B01D 67/009 with wave-energy, particle-radiation or plasma
• CPC Class Codes: B26F 1/26 Perforating by non-mechanical means, e.g. by fluid jet

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 (MgCl₂), 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.

Claims

1. A process useful in increasing the permeability of a thermoplastic composition membrane to waste excreta molecules of human urine, comprising:

forming a thick wall, small diameter tube by extruding a thermoplastic composition, free of plasticizer, through a tubing die, disposing said tube in a water solution bath having a controlled temperature above room temperature, said water solution bath containing waste excreta crystalline molecules found in human urine,

continuously injecting said controlled temperature water solution from said water bath into said tubing die and then into the plastic tubing interior at a water solution volume flow rate cooperating with the plastic tubing formation rate, causing tubing expansion into a thin wall membrane having a wall thickness not more than 0.005 cm, as the membrane tubing remains immersed in said water solution bath, said membrane tubing expansion being controlled to provide a selected outside stretched tubing membrane diameter,

maintaining the stretched membrane in said controlled temperature water solution bath for a controlled time period, providing saturation of the membrane,

removing said stretched membrane from said water bath and removing excess surface water from said stretched membrane, and,

irradiating said stretched membrane with microwave energy of the frequencies absorbed by water molecules in said stretched membrane, providing a more microporous membrane with increased permeability to waste excreta human urine chemical molecules found in human urine.

2. A process useful in increasing the permeability of a thermoplastic composition membrane to selected chemical molecules, comprising:

forming a thick wall, small diameter tube by extruding a thermoplastic composition, free of plasticizer, through a tubing die, disposing said tube in a aqueous solution bath having a specific concentration of solvents selected from methanol, ethanol, propanol, isopropanol, and acetone disposed in said water bath, said aqueous solution having controlled aqueous solution temperature, said aqueous solution having a temperature not less than the equivalent to the glass transition temperature (Tg) of the thermoplastic composition,

continuously injecting aforesaid controlled temperature aqueous solution from said solution bath into said tubing die and then into the plastic tubing interior at a solution volume flow rate cooperating with the plastic tubing formation rate, causing tubing expansion into a thin wall tubing having a wall thickness not more than 0.005 cm, as the tubing remains immersed in said solution bath, said tubing expansion controlled to provide a selected stretched outside tubing membrane diameter,

maintaining the stretched membrane in said controlled temperature aqueous solution bath for a controlled time period, at a temperature providing saturation of the membrane with said aqueous solution,

removing said stretched membrane from said aqueous solution bath and removing excess surface solution from said stretched membrane, and,

irradiating said stretched membrane with microwave energy of the frequencies absorbed by the absorbed solution molecules disposed in said stretched membrane, vaporizing said aqueous solution out of said stretched membrane, providing a more microporous membrane with increased permeability to small molecular weight chemical molecules.

3. A process useful in increasing the permeability of a thermoplastic composition membrane to selected chemical molecules, comprising:

forming a thick wall, small diameter tube by extruding a thermoplastic composition, free of plasticizer, through a tubing die, disposing said tube in a water solution bath having said solution disposed at a controlled temperature above room temperature, said solution containing non-volatile and volatile solute molecules selected from the class consisting of methanol, ethanol, propanol, isopropanol, acetone, sodium chloride, lithium chloride, potassium chloride, sodium carbonate, potassium carbonate, calcium chloride, magnesium sulfate, said water solution bath adaptively adjusted in composition to provide an aqueous soluble solution bath,

continuously injecting said controlled temperature water solution from said water bath into said tubing die and then into the plastic tubing interior at a water volume flow rate cooperating with the plastic tubing formation rate, causing tubing expansion into a thin wall membrane having a wall thickness not more than 0.005 cm, as the membrane tubing remains immersed in said water solution bath, said membrane tubing expansion being controlled to provide a selected outside tubing diameter,

maintaining the stretched membrane in said controlled temperature water solution bath for a controlled time period, at a temperature providing saturation of the membrane with said water solution,

removing said stretched membrane from said water solution bath, and removing excess surface water solution from said stretched membrane,

then immediately irradiating said stretched membrane with microwave energy of the frequencies absorbed by the absorbed water molecules disposed in said stretched membrane, vaporizing said water and any volatile solutes out of said stretched membrane, providing a more microporous membrane with increased permeability to selected small chemical molecules.

4. A process useful in increasing the permeability of a thermoplastic composition membrane to selected chemical molecules, comprising:

forming a thick wall, small diameter tube by extruding a thermoplastic composition, free of plasticizer, through a tubing die, disposing said tube in a water bath having water disposed at a controlled temperature above room temperature,

continuously injecting said controlled temperature water from said water bath into said tubing die and then into the plastic tubing interior at a water volume flow rate cooperating with the plastic tubing formation rate, causing tubing expansion into a thin wall tubing membrane having a wall thickness less than 0.005 cm, as the membrane tubing remains immersed in said water bath, said membrane tubing expansion being controlled to provide a selected outside tubing diameter and membrane thickness,

maintaining the stretched membrane in said controlled temperature water bath for a controlled time period, providing saturation of the membrane with said hot water in a controlled time period,

removing said stretched membrane from said water bath and removing excess surface water from said stretched membrane, and,

irradiating said stretched membrane with microwave energy of the frequencies absorbed by the water molecules disposed in said stretched membrane, vaporizing said water out of said stretched membrane, providing a more microporous membrane with increased permeability to small molecular weight molecules.

5. A process useful in increasing the permeability of a thermoplastic composition membrane to selected chemical molecules, comprising:

stretching a membrane of a thermoplastic composition, free of plasticizer, along one to two axes of orientation of said membrane, said membrane being immersed in a water bath at a controlled water temperature above room temperature during the stretching step, said stretching reducing the thickness of said membrane from at least a prior 0.015 cm to less than 0.005 cm thickness, said stretched membrane having absorbed water,

maintaining the stretched membrane in said controlled temperature water bath for a controlled time period providing saturation of the membrane with said hot water,

removing said stretched membrane from said water bath, and removing excess surface water from said stretched membrane, and,

then immediately irradiating said stretched membrane with microwave energy of the frequencies absorbed by the water molecules disposed in said stretched membrane, vaporizing said water out of said stretched membrane, providing a more microporous membrane with increased permeability to small molecular weight molecules.

6. In the process of claim 5, after removing said excess surface water from said stretched membrane, the further improvement comprising:

the step of immediately subjecting the absorbed water disposed in the stretched membrane to a temperature at least as low as 0°

C., thereby freezing the absorbed water in said stretched membrane, and,

irradiating aforesaid frozen water in said stretched membrane with microwave energy of the frequencies absorbed by water molecules disposed in said stretched membrane, subliming said water out of said stretched membrane.

7. The process of claim 6 wherein the further improvement comprises irradiating said frozen water with microwave frequency energy of 2450 MHz frequency and the like frequency absorbed by water molecules, subliming said disposed water out of said stretched membrane.

8. A process useful in increasing the permeability of a thermoplastic composition membrane to waste excreta molecules of human urine, comprising:

stretching a thin membrane of a thermoplastic composition, free of plasticizer, along one to two axes of orientation of said membrane, said membrane being immersed in a water solution bath at a water temperature above room temperature during the stretching step, said water solution bath containing waste excreta crystalline molecules found in human urine, said stretching step reducing the thickness of said thin sheeting from at least a prior 0.015 cm to less than 0.005 cm thickness, said stretched membrane having disposed therein absorbed water and said waste excreta molecules of human urine,

maintaining the stretched membrane in said controlled temperature water solution bath for a controlled time period at a temperature providing saturation of the membrane with the water and waste excreta urine solute molecules,

removing said stretched membrane from said water bath, and removing excess surface water solution from said stretched membrane,

then immediately irradiating said stretched membrane with microwave energy of the frequencies absorbed by the absorbed water molecules in said stretched membrane, providing a more microporous membrane with increased permeability to waste excreta human urine solute molecules found in human urine.

9. A process useful in increasing the permeability of a thermoplastic composition membrane to selected chemical molecules, comprising:

forming a thick wall, small diameter tube by extruding a thermoplastic composition, free of plasticizer, through a tubing die, disposing said tube in a water solution bath having a specific concentration of solvents selected from methanol, ethanol, isopropanol, and acetone, said aqueous solution having a controlled aqueous solution temperature above room temperature,

continuously injecting said controlled temperature aqueous solution from said solution bath into the tubing die and then into the plastic tubing interior at a solution volume flow rate cooperating with the plastic tubing formation rate, causing tubing expansion into a thin wall tubing having a wall thickness less than 0.005 cm, as the tubing remains immersed in said solution bath, said tubing expansion controlled to provide a selected outside tubing diameter and thickness,

maintaining the stretched membrane in said controlled temperature aqueous solution bath for a controlled time period, at a temperature providing saturation of the membrane with said aqueous solution,

removing said stretched membrane from said aqueous solution bath and removing excess surface solution from said stretched membrane, and,

irradiating said stretched membrane with microwave energy of the frequencies absorbed by the absorbed solution molecules disposed in said stretched membrane, vaporizing said aqueous solution out of said stretched membrane, providing a more microporous membrane with increased permeability to small molecular weight molecules.

10. The process for increasing the permeability of a thermoplastic composition membrane to the waste excreta molecules in the blood of a uremic patient requiring hemodialysis, the process comprising:

stretching a membrane of thermoplastic composition in an axis, said membrane being immersed in a water bath at a bath temperature not less than equivalent to the glass transition temperature (Tg) of the thermoplastic composition during the stretching step, said stretching step reducing the thickness of said membrane to less than 0.002 cm, aforesaid membrane having absorbed water therein;

immediately after the aforesaid stretching step, subjecting the absorbed water disposed in said stretched membrane to a temperature not more than the freezing point of said absorbed water, freezing the absorbed water disposed in said stretched membrane; and

,

irradiating aforesaid frozen water in said stretched membrane with microwave energy of frequencies absorbed by the water molecules disposed in said stretched membrane, vaporizing said water molecules out of said stretched membrane, providing a microporous membrane with increased permeability to said waste excreta molecules in the blood of a uremic patient.

11. The process of claim 10 wherein the further improvement comprises irradiating said frozen water with microwave frequency energy of 2450 MHz.

12. A process useful in increasing the permeability of a thermoplastic composition membrane to selected chemical molecules, comprising:

stretching a thin membrane of a thermoplastic composition, free of plasticizer, along one to two axes of orientation of said membrane, said membrane being immersed in a water solution bath containing non-volatile and volatile solute molecules selected from the class consisting of methanol, ethanol, propanol, isopropanol, acetone, sodium chloride, lithium chloride, potassium chloride, sodium carbonate, potassium carbonate, calcium chloride, magnesium sulfate, said water solution bath adaptively adjusted in composition to provide an aqueous soluble solution bath, at a controlled water temperature above room temperature during the stretching step, aforesaid stretching step reducing the thickness of said membrane from at least a prior 0.015 cm to less than 0.005 cm thickness, said stretched membrane having absorbed aforesaid water solution,

maintaining the stretched membrane in said controlled temperature water solution bath for a controlled time period, providing saturation of the membrane with said water solution,

removing said stretched membrane from said water solution bath, and removing excess surface water solution from said stretched membrane,

then immediately irradiating said stretched membrane with microwave energy of the frequencies absorbed by the absorbed water molecules disposed in said stretched membrane, vaporizing said water and any volatile solutes out of said stretched membrane, providing a more microporous membrane with increased permeability to selected chemical molecules.