BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a composite membrane tubing system and their integration into pervaporation or heat/mass exchange systems such as drying or humidifying gases, purification, medical, analytical, HVAC and oil & gas applications. The process for manufacturing above-mentioned tubular systems is provided.

Background

Polyether block amides (PEBAs) are a family of high performance block copolymers consisting of soft polyether (PE) blocks and rigid polyamide (PA) blocks marketed under the PEBAX® and VESTAMID® brands by Arkema Inc and EVONIK Resource Efficiency Gmbh, respectively. Arkema first commercialized PEBAX® thermoplastic elastomers in 1981 as part of an initiative to develop “soft” nylon materials. PEBAX® has the general formula of: HO—(CO-PA-CO—O-PE-O)n—H.

PA block is in a rigid semi-crystalline phase, which contributes to high end mechanical properties and can be optionally bio-based from 28 to 97%, according to ASTM D6866. While PE block has very low glass transition temperature, about −60° C. which provides outstanding properties at low temperature. In addition, PE block can be tuned to hydrophobic or hydrophilic.

PEBA is a high-performance thermoplastic elastomer with these following characteristics: resistance against a wide range of chemicals, low density among thermoplastic elastomers, superior mechanical and dynamic properties including, flexibility, impact resistance, energy return, fatigue resistance, and these properties are maintained at low temperature, such as lower than −40° C.

PEBA is used in medical products such as catheters for its flexibility, its good mechanical properties at low and high temperatures, and its softness.

It is also widely used in the manufacture of electric and electronic goods such as cables and wire coatings, electronic device casings, components, etc. PEBA can be used to make textiles as well as breathable film, fresh feeling fibers or non-woven fabrics. These compounds will find various applications in sports, optical, and electronics, where toughness and lightness are crucial. Some hydrophilic grades of PEBA are also used for their anti-static and anti-dust properties. Since no chemical additives are required to achieve these properties, products can be recycled at end of life.

Because of its unique copolymer structure, hydrophilic PEBA films offer a combination of mechanical strength, and ease of processing. Unlike microporous products, the monolithic structure of these PEBA films are a barrier to liquid water and bacteria and exhibit a high moisture vapor transmission rate (MVTR). Each of these advantages make PEBA films breathable. This material is ideal for many applications such as construction house-wrap films, breathable textiles for sports, packaging, and selective membranes.

To achieve even higher MVTR, PEBA films need to be very thin. However, thinner films demonstrate poor mechanical strength and dimensional stability. Traditionally, to date, thicker membranes are produced. Thicker membranes have high transmission resistance, and lower pervaporation performance. In fact, breathable PEBA films are generally melt extruded into a thin monolithic film above 25 microns, which limits their application.

SUMMARY OF THE INVENTION

The invention is related to ultra-thin composite PEBA tubes made from elastomeric polyether block amide (PEBA), preferably ultra-thin composite PEBA membranes and modules comprising these composite tubes. In an exemplary embodiment, a porous scaffold support, such as a porous polymeric material or membrane, is combined with PEBA to enable the reinforced composite membrane to be ultra-thin, wherein the wall thickness of the composite PEBA tube is less than 50 μm, and preferably less than 25 μm and more preferably less than 10 μm and even more preferably less than 5 μm. An ultra-thin composite PEBA film may be made into a PEBA pervaporation tube by wrapping a composite PEBA film and bonding or attaching the overlap areas. A composite PEBA tube can be made by spirally wrapping or longitudinally wrapping a composite PEBA film or wrapping a porous scaffold support around an ultra-thin walled extruded PEBA tube. A mandrel may be used for wrapping the composite PEBA film thereon. These thin composite PEBA tubes, may be used as pervaporation tubes that can be incorporated into a pervaporation module. The wrapped composite PEBA pervaporation tube may have fused areas wherein at least a portion of the overlap area is fused together.

The porous scaffold support may include a porous material and the PEBA may be coated thereon and may fill, at least partially the pores of the porous material or membrane. An exemplary porous scaffold support material is a porous polymer material of polyethylene or polypropylene, and may be a porous fluoropolymer material or membrane, such as an expanded fluoropolymer. An exemplary expanded fluoropolymer is expanded polytetrafluoroethylene (PTFE). An exemplary porous scaffold support material has a thickness that is less than about 25 microns, less than about 20 microns, less than about 10 microns and more preferably less than about 5 microns. A thin porous material is preferred as it will allow for higher rates of moisture transfer through the composite PEBA tube. A porous scaffold support, such as an expanded fluoropolymer or porous polyethylene or polypropylene, may have very small pores, wherein the average pores size is no more than about 10 microns, no more than about 5 microns, no more than about 1 micron, no more than about 0.5 microns and any range between and including the values provided. The average pore size can be determined use a coulter porometer, wherein the Minimum Pore Size is defined at the point where the wet curve meets the dry curve. The Mean Pore Size is defined as the point at which the amount of flow through the sample on the wet curve is exactly 50 percent of the amount of flow at the same pressure when the sample is dry. A small average pore size may be desirable to enable PEBA to imbibe into the pores of the porous scaffold material. The smaller the pore size the greater the capillary forces to pull the solution or melted PEBA therein.

The PEBA may be attached to the porous scaffold support by melt casting, wherein the PEBA is melted onto the porous scaffold support. The two layers may then be compresses to force the melted PEBA into the pores of the porous scaffold support. PEBA may also be solution cast onto or into the pores of a porous scaffold support. The PEBA may be dissolved in a solvent and the cast onto the porous scaffold support, wherein it may wick into the pores and substantially fill the pores to make a non-permeable composite film. In flat sheet assemblies, such as a vent or plate and frame pervaporation modules, it may be desirable to have minimal PEBA integration into the pores of the porous scaffold support and therefore melt casting may be preferred with little interpenetration of the PEBA into the pores. It is also possible to achieve a composite structure with minimal penetration by solution casting and tuning the solvent system to evaporate before the PEBA is able to penetrate the pore structure fully.

A composite PEBA film comprising the PEBA polymer and the porous scaffold support may be substantially non-porous, wherein the pores of the porous scaffold support are filled or blocked by the PEBA polymer such that the composite PEBA film has a Gurley densometer reading of about 100 seconds or more, and preferably 200 second or more; using a Gurley Densometer 4340 automatic densometer, from Gurley Precision Instruments, Troy N.Y.

The composite PEBA film may be wrapped to form a tube and may include overlap areas that are fused together. These overlap areas will be at least twice as thick as the composite PEBA film and therefore it may be desirable to keep the overlap area to a minimum percentage of the outer surface area of the composite PEBA tube, such as no more than about 30%, no more than about 25%, no more than about 20%, no more than about 10%, or even no more than about 5% outside surface area of the tube.

According to one embodiment of the present invention, there is provided a tubular structure made from a composite film of a porous scaffold support and PEBA copolymer. The tubular structures have overlapping fused areas.

According to one embodiment of the present invention, there is provided a process for the preparation of the composite membrane tubing by tape-wrapping a porous scaffold support around a mandrel. The mandrel is then passed through a heating chamber or an infrared chamber to fuse the wrapped tape into a continuous tubular structure. The tubular structure is then passed through a coating process wherein the membrane tube is coated with the PEBA copolymer. The assembly is then passed through heating chamber to dry the PEBA pervaporation tube. Then the tube is dipped in a swelling agent, such as water or a solvent, and removed from the mandrel. It may be necessary to provide internal pressure to the tube assembly to remove the PEBA tube from the mandrel.

According to one embodiment of the present invention, there is provided a process for the preparation of tubular structure adapted to pervaporate the fluid by spirally or longitudinally, also referred to as cigarette, wrapping one or more membranes around mandrel and using heat or infrared radiation on the assembly to fuse the wrapped membrane tapes into a continuous cylindrical tube. Then the tube is dipped in a swelling agent, such as water or a solvent, and removed from the mandrel. It may be necessary to provide internal pressure to the tube assembly to remove the PEBA tube from the mandrel. Note that an ultrasonic instrument, such as an ultrasonic welder, having an ultrasonic horn and anvil, such as a those available from Branson Ultrasonics Corp, Rochester N.Y., may be used to create very localized heat between the overlapped layers of the wrapped tube to fuse the layers together.

An alternative embodiment of the present invention involves extruding tubes to a very thin cross-sectional thickness and optionally reinforcing with a reinforcement after extrusion, such as by tape wrapping.

An exemplary PEBA composite film may include a biocide to prevent the formation of mold in a pervaporation module, as this is an ideal environment for mold to form. A biocide may be configured in the PEBA polymer, as a coating on the porous scaffold support, as a coating on the final PEBA layer, or a combination thereof. Any suitable biocide may be used and the concentration may be adjusted according to the use conditions.

According to one embodiment of the present invention, a tube reinforcement may be configured around the outside and/or inside of a composite PEBA tube to provide additional structural support and may comprise a structural mesh. A structural mesh may be configured around the PEBA tube(s) to provide additional structural rigidity. The structural mesh may comprise a plastic or metal material depending on the degree of reinforcement required. The metal may also be used to enhance heat transfer to the tubular structure to enhance pervaporation. The structural mesh may be secured on the ends of the tubular structure using an adhesive or a heat shrinking material, or a combination of the two.

According to one embodiment of the present invention, a method for putting fittings at the ends of the tubes is provided. The fittings may be coupled to the composite PEBA tube by inserting a rigid plastic tubing at the ends of the PEBA tubing, and inserting into the plastic tubing different kinds of fittings such as compression, barbed, push-to-connect, etc. The assembly may be secured on the ends of the tubular structure using an adhesive or a heat shrinking material, or a combination of the two. Alternatively, tubes, with or without fittings, are inserted into a setting compound, or potted, into a tube sheet or header.

The manufacturing processes described above ensure that the tubes are much thinner than those described in the prior art. The thinness of the tubes along with the inherent nature of the material ensures tubes which permeate water, water vapor or a polar species to transmit across the tube wall at higher rates and lower cost.

According to one embodiments of the present invention, there are provided devices such as modules that employ pervaporative tubing to dry incoming air streams for medical, analytical, electrochemical and oil & gas purposes. Several pervaporative tubes are forced into a cylindrical structure which constitutes the “shell”. The pervaporative tubes are capped off and then dipped into potting resin. Once, the potting resin and seals all tubes in place, the process is repeated on the other end of the tubes. Finally, the ends are capped off with front and rear headers.

Ultra-thin PEBA composite membranes can be used to make tubes. These tubes are very strong, and therefore can take high pressure feed.

Because of the strength and thinness, there is less resistance to permeation and therefore higher performance systems.

Because of the ultra-thin structure, less material, both PEBA and porous scaffold support, are used to produce these tubes, therefore the units have inherently lower cost, and therefore the technology can be applied to wider range of applications beyond the current thick walled extruded tubes that are state-of-art in the market.

The pervaporation modules and pervaporation tubes comprising a PEBA copolymer and preferably an ultra-thin composite PEBA film are ideally suited for desalination, ionic liquid desiccation, waste processing, heat exchange, mass exchange and numerous other applications.

The desired ultra-thin composite PEBA tubing will also have the following merits: high dimensional stability; high moisture vapor transmission rate; lightweight; excellent toughness and tear resistance; easy for processing in a roll to roll scale up; low cost; anti-dust; recyclable; excellent virus and bacteria barrier; excellent liquid & odor barrier and hygienic.

The desired ultra-thin reinforced composite PEBA film should have the following features: no curl, easy to handle; good dimensional stability; high MVTR; lightweight; excellent toughness and tear resistance; easy to process in high volume, such as a roll to roll system; low cost; recyclable; flexible; act as an excellent virus and bacteria barrier; and be an excellent liquid & odor barrier and be hygienic.

Example 1

In one embodiment, an ultra-thin reinforced composite PEBA film is prepared by dissolving the PEBA, MV1074 from Arkema Inc., in ethanol/toluene (50 wt %: 50 wt % mix) at a 15% weight ratio. The mixture was stirred at 60° C. until homogenous and translucent. The PEBA polymer solution was then applied to a microporous polytetrafluoroethylene material which is tensioned around a chemically-resistant plastic frame. The polymer solution was then poured on to the microporous scaffold. The membrane was dried at room temperature. The final thickness of the membrane was 5 microns.

Example 2

In another embodiment, an ultra-thin reinforced composite PEBA film is prepared by dissolving the PEBA MH1657 polymer from Arkema Inc., in ethanol and water at a 20% weight ratio. The mixture was stirred until homogenous and translucent. The PEBAX® MH1657 polymer was then applied to a microporous polyethylene material using a doctor blade. The membrane was dried at room temperature for 8 hours. The membrane was then annealed in the oven for 5 minutes at 80° C. The final thickness of the membrane was 5 microns.

Example 3

In another embodiment, an ultra-thin reinforced composite PEBA/PFSA film is prepared by dissolving the 1.6 g PEBA polymer from Arkema Inc. and 0.4 g PerfluoroSulfonicAcid, (PFSA) in ethanol and water at a 20% weight ratio i.e. 2 grams of total polymer to 8 grams of solvent. The mixture was stirred until homogenous and translucent. The PEBA/PFSA blend polymer was then applied to a microporous polyethylene material with a doctor blade. The film was dried at room temperature for 24 hours. The final thickness of the film was 15 microns.

It will be apparent to those embodiments mentioned above can be scaled up to a roll-to-roll, continuous process.

Example 4

In another embodiment, an ultra-thin reinforced composite PEBA film is prepared by melt lamination of PEBA, MH1657 at about 20 micron onto expanded polytetrafluoroethylene (ePTFE) support scaffold materials. MH1657 was hot pressed with ePTFE at 200° C. for 90 seconds. The film was 7 micron and transparent.

The summary of the invention is provided as a general introduction to some of the embodiments of the invention and is not intended to be limiting. Additional example embodiments including variations and alternative configurations of the invention are provided herein.

