VERIFICATION OF MEMBRANE STRUCTURAL INTEGRITY

FIELD OF THE INVENTION

[0001] The present invention generally relates to membranes, and more particularly to membranes comprising one or more layers having magnetic properties. These magnetic properties allow for the verification of the structural integrity of the membrane.

BACKGROUND OF THE INVENTION

[0002] Synthetic membranes, such as geomembranes and geosynthetics, are used around the globe in containment applications. They are commonly used to contain contaminants generated, for example, by the exploitation of mines, waste management, and petrochemistry. They may also be used to impound water, among many other applications.

[0003] Membrane integrity is key to environmental protection for multiple applications such as mining, waste management and aquaculture, to name a few, and during the installation of membranes over large areas, structural faults may occur due for a variety of reasons, including thermal constraints and the use of cutting tools. Validation of the membrane integrity is critical to conform to allowable leakage rates set by government agencies.

[0004] During the installation of these geomembranes over large areas, structural faults may occur due to thermal constraints and the use of cutting tools.

[0005] When first laid down with its surface easily accessible for integrity validation, such geomembrane faults can be revealed and patched efficiently. In those circumstances, a method which has been used to verify the integrity of the membrane is the spark test method, which involves the sweeping of a high voltage electric broom over the surface of the membrane, which can detect holes the size of a pinhole. [0006] Other methods which have been used to measure the damage to the exposed membranes include the Arc Test (ASTM D7953), the Spark Test (ASTM D7240) and the Water Puddle Test (ASTM D7002), which tend to be difficult to use, labour- intensive and expensive.

[0007] However, in many applications, such as when solid materials are contained by a membrane, a layer of protective soil (e.g., sand or rocks or clay) is added over the membrane which may cause movement and create weaknesses in a containment system (e.g., under environmental constraints). Moreover, the act of adding a layer of protective soil involves use of mechanical machinery on the membrane, which can cause wrinkles and other defects in the membrane prior to or during addition of the soil. Once buried, it is not possible to detect these faults visually or by use of a spark test inspection. The same is true of membranes which retain fluids.

[0008] A method that has been used to detect leaks and validate membrane integrity after it is covered is the dipole technique (as per ASTM D7007), which is based on the closing of an electrical loop between the covered membrane, the hole to the membrane backing and an electrode connected outside of the surveyed area.. This method can be used to detect leaks of at least one millimeter in diameter under approximately 1 meter of earthen material. However, the dipole technique requires on-site calibration of instruments and is dependent on environmental conditions, such as soil wetness or unfrozen soil. Also, the test site must be electrically isolated, and the earthen cover material must present the proper environment and composition to be conductive. Hence, the soil must be humid, which renders the technique sensitive to environmental changes. Further, the operator must be trained, the equipment re-calibrated periodically and the high voltage equipment moved on a meter-by-meter step fashion over thousands of square meters.

[0009] The dipole inspection technique described above works for fault detection but field application of the technique faces adoption barriers due to very slow manual displacement of the equipment, low convenience of use and to environmental factors, such as rain, snow, frozen soil and wet/dry soil. These elements are burdensome to the adoption and deployment of membranes that prevent contaminants from leaking into the environment, particularly in the midst of growing legislation and decreasing allowable leakage rates and precision.

SUMMARY OF THE INVENTION

[0010] As disclosed herein, a membrane is provided with magnetic particles having one or more magnetic properties which allows for the verification of the structural integrity of the membrane in a variety of environmental conditions, even when the membrane is covered, and independent of the composition of the membrane polymeric material.

[0011] The membrane disclosed herein includes, in at least one layer, magnetic particles and/or particles which are magnetized as part of the method of manufacturing the membrane, where the resulting membrane will exhibit substantially uniform magnetic properties but with anomalous magnetic properties at the location of faults in the membrane. The magnetic particles may advantageously be selected from particles of metallic oxides which have magnetic properties.

[0012] In one form, the membrane may comprise at least one layer or sheet of suitable material such as a polymer, with each layer being made from a given amount of a polyethylene (PE) masterbatch composition comprising a PE resin and additives, wherein the particles with magnetic properties are included as an additive to at least one of the membrane layers prior to extrusion. In another form, magnetic particles may be sprayed onto the surface of an extruded membrane. The magnetic particles may advantageously be substantially uniformly dispersed in or on the membrane. A dispersing agent may be used for this purpose when the particles are an additive with extrusion formation.

[0013] Another aspect of the disclosure herein is a method of making a PE membrane liner with at least one extruded layer having magnetic particles, including the following steps:

[0014] a. mixing a given amount of a PE master batch composition comprising a PE resin and additives; and [0015] b. extruding the PE formulation formed in step a) to form a single layer PE membrane liner,

[0016] wherein magnetic particles are added to or included on at least one polymeric layer to render the membrane magnetic.

[0017] In another form, the manufacturing method includes co-extruding at least two polymeric layers (such as disclosed in U.S. Patent Application No. US 2017/0320303, which is hereby incorporated by reference in its entirety), where magnetic particles are included as an additive to at least one polymeric layer to render the membrane magnetic.

[0018] Membranes, including geomembranes, may be advantageously used in the following industries: mining, petrochemical, coal ash, coal seam gas, shale gas, biogas, aquaculture, agriculture, waste management, water, landscaping, floating cover applications and geomembrane panels for fabrication. The membranes may also be used as geomembrane liners in applications such as bioreactors landfills, hot liquid storage, coal seam gas brine ponds, geothermal waste water ponds, or the like.

[0019] The magnetic feature of the membrane may be used to detect the integrity of the membrane by using a method and/or apparatus capable of detecting magnetic properties in membranes, it being recognized that such membranes will exhibit substantially uniform magnetic properties but with anomalous magnetic properties at the location of faults in the membrane.

[0020] Other and further aspects and advantages of the present invention will be better understood upon reading of the illustrative embodiments about to be described and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a partial perspective view of a membrane as described herein with multiple layers; and

[0022] Figure 2 is an illustration of different membrane magnetization techniques. DETAILED DESCRIPTION

[0023] A novel membrane with magnetic properties allowing for the verification of the structural integrity of the membrane is described herein.

[0024] The terminology used herein is in accordance with definitions set out below.

[0025] As used herein % or wt.% means weight % unless otherwise indicated. When used herein % refers to weight % as compared to the total weight percent of the phase or composition that is being discussed.

[0026] As used herein,“magnetic particles” consist of particles which have magnetic properties sufficiently magnetically susceptible that their magnetic property may be detected through a layer of material such as would be encountered in an intended use, including particularly a geomembrane covered by material in a geotechnical site.

[0027] By "about", it is meant that the value of weight %, time, pH or temperature can vary within a certain range depending on the margin of error of the method or device used to evaluate such weight %, time, pH or temperature. A margin of error of 10% is generally accepted.

[0028] In one aspect of the disclosure herein, a membrane with magnetic properties includes at least one layer of a polymeric material having additives including magnetic particles (e.g., powder).

[0029] As illustrated in Fig. 1A, at geotechnical sites, a magnetically functionalized membrane 10 incorporating polarized (magnetized) magnetic particles 14 (see Fig. 1 B) may be advantageously laid over a containment area 16 and covered with material 18 as explained in further detail hereafter. The membrane 10 may have one or more layers, with Fig. 1 B showing by way of example a membrane 10 with three layers 10a, 10b, 10c, with the magnetic particles 14 included in one sheet (one of the layers: 10a). (Note that discrete visible particles 14 are shown in Fig. 1 B for illustration purposes, though in application such particles 14 only be powder particles having a diameter of 1-150 microns and may not be so discretely visible.) [0030] The particles 14 may be polarized solely by the Earth’s magnetic field, or may most advantageously be polarized during the membrane manufacturing process and before being installed in the area 16 by passing the membrane 10 with metallic magnetic particles 14 close to a magnetizer apparatus 20 which incorporates strong magnets. As illustrated in Figures 2A-2B, the membrane 10 can be magnetized in plane, out of plane or with arbitrary magnetization with an appropriate permanent magnet configuration (or by the Earth’s magnetic field as mentioned). Figure 2A, for example, shows that the membrane 10A is polarized with magnetic lines perpendicular to the membrane plane, and Fig. 2B shows a polarized membrane with magnetic lines being parallel to (i.e., aligned with the plane of) the membrane 10B.

[0031] More specifically, the magnetically functionalized membrane 10 may advantageously be one or more layers of a polymeric material, with the polymeric material selected from synthetic polymers including, without limitation, polypropylene (PP), polyethylene (PE), and polyvinyl chloride (PVC), as would be understood by one of skill in the art. Moreover, PE may be selected, without limitation, from the group consisting of Linear Low Density PE (LLDPE), Low Density PE (LDPE), Medium Density PE (MDPE) and High Density PE (HDPE).

[0032] Magnetic particles 14 are included with at least one layer of the membrane 10 by, for example, mixing with polyethylene or other resin in a masterbatch before extruding, and/or spraying on the membrane 10, with the magnetic particles 14 being disbursed and generally uniform throughout the membrane layer in which included (e.g., sheet 10a in Fig. 1 B). The particles 14 may be any compound or material (e.g., some ceramics and metals) exhibiting suitable magnetic properties, as well as mixtures thereof including, advantageously, Permalloy, AINiCo, SmCo, Co (Cobalt), CoO, FeCoO, Nd (Neodymium), Fe ³ 0 ⁴ (Magnetite), Ni (nickel) and/or Gd (Gadolinium), with the particles 14 comprising about 1% to 30% by weight of the membrane layer in which the particles are incorporated, and preferably about 1% to 10% by weight.

[0033] The amount of magnetic particles 14 may be varied according to the thickness of the membrane layer 10a, as well as the susceptibility of the particles 14 to magnetization, where the amount should not degrade membrane integrity and should provide a sufficiently strong magnetic signal or remanent magnetization capable of being detected by a membrane integrity testing device positioned above fill material 18 on top of the membrane 10. For example, if the remanent magnetization of AINiCo is two times as strong as FeCoO, a layer with A% by weight of AINiCo would provide essentially the same remanent magnetization as a layer having B% by weight of FeCoO, where B = 2A.

[0034] Further, while 1-30, or advantageously 2.5-15, percent by weight of magnetic particles 14 would generally be a suitable amount, it should also be understood that the total amount of such particles 14 per membrane area is particularly important regardless of the weight and thickness of the magnetized membrane layer. Thus, by way of example, if a membrane layer 10a is X mils thick and provides a suitable magnetic property with Y kg/m ² of particular magnetic particles, then a different thickness membrane layer should also provide a suitable magnetic property with the same amount ( i.e ., Y kg/m ² ) of the magnetic particles. Stated another way, where the suitable percentage by weight R of the magnetic particles 14 in a membrane layer (10a) X mils thick, then the suitable percent by weight of those magnetic particles for a layer which is Z mils thick would substantially be [R x (Z/X)] (i.e., the percentage by weight of the magnetic particles in the master batch is inversely proportionate to the thickness of the polymeric sheet).

[0035] Still further, it should be understood that suitable membranes 10 may be formed of multiple layers 10a, 10b, 10c, with the percent by weight of magnetic particles based on the layer into which the magnetic particles are added. Thus, for example, in a membrane 10 having three (3) layers as in Fig. 1 B, with one layer forming 90% of the membrane and the other two (2) layers forming 5% each of the membrane, if the magnetic particles are added to one of the layers forming only 5% of the membrane, the percent by weight of the magnetic particles would be high (e.g., near 30%) relative to the percent by weight of the magnetic particles (e.g., near 1 %) if added to the layer forming 90% of the membrane.

[0036] Sufficient particles 14 such as described above should be incorporated to ensure that the liner magnetic properties will be detectable (e.g., by a suitable magnetometer), without incorporating so many magnetic particles 14 as to hurt the integrity of the membrane 10 and/or making the membrane 10 prohibitively expensive. Thus it should be appreciated that particularly advantageous would be particles with remanent magnetization ( i.e ., magnetization left behind after an external magnetic field is removed, such as when a magnetizer apparatus 20 is used in the manufacture of the liner 10 as illustrated in Figs. 2A-2B). However, magnetic particles with high magnetic susceptibility and a low remanent magnetic field could also be used.

[0037] The magnetic particles 14 may advantageously be spherical and uniformly distributed throughout the layer 10a in which it is included, with the particle sizes varying from 1 to 75 microns for a layer thickness of 1 to 7 mils, or 1 to 150 microns for a layer thickness of 10 mils.

[0038] Carbon black may also be advantageously included as an additive to the membrane in concentrations, for example, of between about 2-3 percent by weight.

[0039] It should be appreciated that suitable magnetic membranes 10 as disclosed herein may be readily formed by incorporating magnetic particles as described into existing membrane formulations, including membranes available from many sources. Such membranes include numerous membranes available from Solmax International (see, e.g., https//www.solmax.com) of Varennes (Quebec), Canada, including, but not limited to, the following polyethylene (PE) geomembranes liners:

[0040] HDPE (High Density Polyethylene) Liner Series,

[0041] LLDPE (linear Low Density Polyethylene) Liner Series,

[0042] Premium HD Liner Series,

[0043] Premium LL Liner Series,

[0044] Sekoia HD Liner Series,

[0045] LiteEarth™ Synthetic T urf Earth Capping System,

[0046] HLR (Hot Liquid Rated) Liner Series,

[0047] BioCoverPro Liner Series, [0048] EZ-Fix Liner Series,

[0049] F3 Liner Series, or

[0050] R3 Liner Series,

[0051] and including, but not limited to, the following polyvinyl chloride (PVC) geomembrane liners:

[0052] PVC Fish Grade Series,

[0053] FGI 1115 Series,

[0054] PVC Potable Grade Series, or

[0055] XR5 Liner Series 8130 & 8138,

[0056] the membrane densities of which are typically approximately 1.20 g/cm ³ , and wherein the membrane thicknesses of which may typically vary between 0.75 and 1 mm.

[0057] While illustrative and presently preferred embodiments of the invention have been described in detail hereinabove, it is to be understood that the inventive concepts may be otherwise variously embodied and employed and that the appended claims are intended to be construed to include such variations except insofar as limited by the prior art.