ROOFING MEMBRANE WITH DETECTABLE WEAR INDICATOR

Description

RELATED APPLICATION

The present application claims priority to U.S. Provisional Patent Application Ser. No. 63/726,047, entitled Roofing Membrane with Colored Wear Indicator, filed Nov. 27, 2024, the entire disclosure of which is incorporated herein by reference in its entirety for all purposes.

TECHNICAL FIELD

The present invention relates to roofing membranes.

BACKGROUND OF THE INVENTION

Roofing products such as membranes and walkways are installed and in service for upwards of 20-30 years. Once installed, many roofing membranes will degrade due to exposure to sunlight and other environmental factors. This degradation is evident by a reduction in overall product thickness. At some critical thickness, the watertightness of the roofing membrane is compromised. For fabric reinforced roofing membranes, this is typically when the layers encapsulating the fabric are worn away. Roof failures then occur due to the reduced physical performance in these worn away areas.

Without early detection, roof failures can occur, leading to costly repairs and potential damage to the underlying structures. Unfortunately, due to the nature of installation, the ability to monitor this thickness wear is difficult and often requires destructive test cuts to be done. These destructive tests require cuts to be made in the roofing membrane to view the cross section product thickness. Afterwards, the cut must be patched with new membrane or accessories to prevent water ingress. In other situations, the detection of these worn areas is challenging due to most fabric reinforcement being undyed polyester, which is a transparent polymer. As a result, it is hard for an inspector to easily see the wear and damage to the roofing membrane until the water-tightness is compromised.

What is instead desired is a simple and effective system for a roofing inspector to view or otherwise detect the wear of the membrane over time so that corrective repair action can be taken in a timely manner.

SUMMARY OF THE INVENTION

The present invention provides a variety of non-destructive tests (including visual inspection and various spectroscopic analyses) for quickly identifying wear and tear of roofing membranes. In preferred aspects, the present system provides a roofing membrane, comprising: (a) a bottom ply layer; (b) a scrim layer on top of the bottom ply layer; and (c) a top ply layer on top of the scrim layer. In accordance with the present system, at least one of the bottom ply layer, scrim layer or top ply layer comprises a wear indicator that is progressively more or less detectable by non-destructive testing as the top ply layer is worn away over time.

In various aspects, the wear indicator is a colored region in one of the layers that becomes progressively more visible to an observer as the top ply layer is worn away over time. For example, the colored region may be a portion of the bottom of the top ply layer, a portion of the scrim layer, or even a portion of the bottom ply layer, wherein the colored region has a different color than a top portion of the top ply layer. The differently colored layer may also be one of a plurality of layers in the top ply layer underneath the very top portion of the top ply layer.

In alternate preferred aspects, the wear indicator comprises at least one tracer compound that is disposed in one of the layers of the roofing membrane. In one example, the tracer compound is disposed in the top ply layer and it becomes progressively less detectable as the tracer compound is remove as the top ply layer is worn away over time. In another example, the tracer compound is disposed below the upper regions of the top ply layer (i.e.: deeper in the membrane) and it becomes progressively more detectable as the top ply layer is worn away over time.

In preferred aspects, this tracer compound is detectable by spectroscopic analysis. For example, it may optional be detected by x-ray fluorescence (XRF), x-ray photoelectron spectroscopy (XPS), energy dispersive spectrometry (EDS), NIR or Fourier transfer infrared measurement (FTIR) including attenuated total reflectance Fourier transfer infrared measurement (ATR-FTIR). The tracer compound(s) may also be detected by detecting its fluorescence, phosphorescence or photoluminescence.

In some embodiments, the top ply layer preferably has an upper portion having a first color and a lower portion having a second color. As a result, as the upper portion of the top ply layer becomes worn away over time an observer will see the color of the lower portion of the top ply layer (which is just above the central scrim layer). The advantage of this approach is that an inspector on the roof will quickly and easily see the color change in the worn through areas of the roofing membrane. This makes visual inspection quick, easy and simple.

The lower portion of the top ply layer may optionally have a darker or different color than the upper portion. Since the upper portion of the membrane's top ply layer is typically white, clear, grey or lightly colored, it will be easy for an inspector to visually spot the worn down areas of the roofing membrane (where the bottom color becomes visible as the upper portions of the white, clear, grey or lightly colored roofing membrane are slowly removed over time). Importantly, however, any other colors or color combinations may be used as well, all keeping within the scope of the present invention.

In other preferred approaches, the lower portion of the top ply layer comprises two layers and the bottom layer is a different color than the upper layer. For example, the upper layer may be yellow and the bottom layer may be red. As a result, after some wear and tear occurs, the inspector will start to see the yellow layer. The yellow color would caution the inspector to the wear and tear. As the top ply layer is further degraded and more material is removed, the color would change to red. The red color would be a warning of the possibility of imminent failure of the roof (due to the fact that the top ply layer has now been almost completely worn away down to the scrim layer). These various colors and patterns can be incorporated into the roofing membrane by adding various colored dyes and pigments.

In some preferred embodiments, the colored lower portion of the top ply layer may be thinner than the upper uncolored portion of the top ply layer. The advantage of this design approach is that the membrane will maintain its normal color right up to the point of near imminent failure.

In other preferred aspects, different fluorescent or phosphorescent properties of different tracer compounds in the various layers of the roofing membrane are used as an indication of the amount of wear and tear of the roofing membrane. Specifically, the present invention also provides a roofing membrane, wherein the top ply layer has an upper portion having a first fluorescent or phosphorescent property, and a lower portion (or portion at a lower depth) has a second fluorescent or phosphorescent property. As the upper portion of the top ply layer is worn away over time an inspector or observer can then detect the second fluorescent or phosphorescent property of the lower portion of the top ply layer. For example, the inspector can apply special lighting to the roof such that the worn down areas of the roofing membrane will glow or fluoresce.

Preferably, the choice of pigment color used may favor those pigments that are opaque or white under normal illuminations. The benefit of this is that the membrane appearance will not be too affected until the proper lighting conditions are used at inspection.

In yet other preferred embodiments, the scrim layer is colored. As the top ply layer is worn away over time, the roofing inspector will start to see the color of the scrim layer below. Once the colored scrim layer starts to become visible through the thinning top ply layer, the inspector will immediately realize that the roofing membrane has worn away to a degree that it needs to be repaired or replaced. In short, the present invention optionally provides a roofing membrane, comprising: a bottom ply layer; a scrim layer on top of the bottom ply layer; and a top ply layer on top of the scrim layer, wherein the scrim layer is colored.

In preferred embodiments, the colored scrim layer has visual indicia printed thereon such as a corporate logo. As a result, an inspector seeing the visual indicia start to appear through the worn down top ply layer will immediately realize that the roofing membrane has worn away. Having a corporate logo printed on the scrim will result in the inspector seeing this corporate logo. This has the advantage of both promoting the company who supplied the initial roofing membrane as the most likely source of the replacement roofing membrane. In addition, the presence of the corporate logo will confirm that the existing roofing membrane was made by the advertised company.

In optional preferred aspects, the scrim layer may instead contain a tracer compound having fluorescent or phosphorescent material. As such, when an inspector shines a (black) light onto the roof, the scrim will fluoresce, alerting the inspector to the severity of the wear damage to the roof. Combinations of colored and fluorescing materials are also contemplated within the scope of the present invention.

In short, the present invention optionally provides a roofing membrane, comprising: a bottom ply layer; a scrim layer on top of the bottom ply layer; and a top ply layer on top of the scrim layer where, in various embodiments, an upper surface of the top ply layer is a different color or has a tracer compound with different fluorescent or phosphorescent property than one of the layers or portions of the layers positioned below. As such, when the upper portion(s) of the top ply layer is worn away over time, an observer will either see or spectroscopically detect a different color or detect a different physical property from the color or physical property of the upper portion of the top ply layer. As described above, in one approach the top ply layer and the scrim layer may have different colors, or upper and lower portions of the top ply layer may be different colors or have different fluorescent or phosphorescent properties. An advantage of the present system is that pigments or coloring additives do not appreciably affect the membrane performance. In addition, they can be used to make it invisible to the end user until inspection.

When tracer compounds are used, the tracer compound may be white or opaque such that it does not perceptively change the color of the roofing membrane. The tracer compound may optionally be a pigment or a Group Il metal compound or a transition metal, including but not limited to strontium or zirconium. The tracer compound may also be an organic dye (which may be encapsulated as needed).

Optionally, the tracer compound may be disposed in a gradient at different depths or in different concentrations in different layers or at different depths in the roofing membrane. Optionally as well, a plurality of different tracer compounds can be used at different depths in the roofing membrane, all keeping within the scope of the present invention.

As can be seen, the present system thereby provides a clear and easy non-destructive method for inspectors to assess the health of the roof. As such, unexpected roof failures can be prevented by allowing for timely maintenance and repair.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a sectional elevation view of a newly installed roofing membrane.

FIG. 1B corresponds to FIG. 1A after some of the top ply has worn off.

FIG. 1C corresponds to FIG. 1B after all of the top ply has worn off and the scrim layer has been exposed.

FIG. 2 is a sectional elevation view of a roofing membrane having a top ply layer with a lower color pigmented portion.

FIG. 3A is a sectional elevation view of a newly installed roofing membrane having a top ply layer with a lower portion having two layers of two different colors.

FIG. 3B corresponds to FIG. 3A after the top ply has been worn part-way down to the upper color layer.

FIG. 3C corresponds to FIG. 3B after the top ply has been fully worn down to the upper color layer.

FIG. 3D corresponds to FIG. 3C after the top ply has been worn away down to the lower color layer.

FIG. 4A is a sectional elevation view of a newly installed roofing membrane having a top ply layer comprising two separate layers with a tracer compound in the lower of the two top ply layers.

FIG. 4B is a sectional elevation view of a newly installed roofing membrane having a bottom ply layer with a tracer compound therein.

FIG. 4C is a sectional elevation view of a newly installed roofing membrane having a top ply layer with a higher concentration of tracer compound at greater depths of the top ply layer.

FIG. 4D is a sectional elevation view of a newly installed roofing membrane having a top ply layer with a lower concentration of tracer compound at greater depths of the top ply layer.

FIG. 4E is a sectional elevation view of a newly installed roofing membrane having a top ply layer comprising two separate layers with a different tracer compound in each of the two separate layers.

FIG. 4F is a sectional elevation view of a newly installed roofing membrane having a different tracer compound in each of the top ply and bottom ply layers.

DETAILED DESCRIPTION OF THE DRAWINGS

In preferred embodiments as seen in FIGS. 1A to 4F, the present system comprises a newly installed roofing membrane 5 is placed on top of a roofing structure (not shown). Roofing membrane 5 includes a top ply layer 10, a middle reinforcing scrim layer 20 and a bottom ply layer 30. The top and bottom ply layers 10 and 30 of the roofing membrane may be made of TPO as is common in the industry and the reinforcing scrim 20 may be made of PET as is also common in the industry. Roofing membrane 5 may also be made of EPDM, PVC or other suitable material.

FIGS. 1A to 3D present embodiments of the present invention with differently colored layers in the roofing membrane. FIGS. 4A to 4F present embodiments of the present invention with various tracer compounds in the various layers of the roofing membrane. In accordance with the present invention, all embodiments of the present invention illustrated herein involve non-destructive testing (which may include visual detection of color change or spectroscopic detection of tracer compounds in the roofing membrane).

Referring first to FIGS. 1A to 1C, a colored scrim layer 20 is provided. In accordance with the present invention, scrim layer 20 is colored in some manner. For example, it may be dyed a red color. Typically, top ply layer 10 is made of a material that is white, clear, grey or lightly colored. Accordingly, at the start of the membrane 5's life as seen in FIG. 1A, the red scrim layer 20 will not be visible through the top layer 10. Over time, however, as the roof degrades and the top ply layer is worn away, the upper layer 10 will become thinner and thinner as seen in FIG. 1B. Eventually, the upper layer 10 will completely wear away as seen in FIG. 1C. At some period of time between FIGS. 1B and 1C, the colored scrim layer 20 will start to become visible to an inspector on the roof looking down at the top of the roofing membrane. As such, the inspector will immediately see those areas of the roofing membrane that are worn down where the colored scrim 20 will start to show through the remaining portions of upper layer 10.

In preferred examples, the scrim layer 20 may be colored a dark color to be readily visible. In other preferred embodiments, scrim layer 20 may have visual indicia such as a company or corporate logo printed thereon. The advantage of having a company logo (i.e.: the logo of the company that manufactured roofing membrane 5) printed on scrim 20 is that when an inspector begins to see this logo, the inspector will know the identity of the membrane's manufacturer. This form of “advertising” would be helpful in generating return business for the supplier of the original roofing membrane (i.e.: when the inspector orders a new replacement roofing membrane).

Traditionally, white membranes utilize titanium dioxide and black membranes utilize carbon black to give the appropriate color and other UV benefits. Additionally, some membranes incorporate other additives to give a range of colors. These additives include organic dyes, inorganic oxide pigments, and special effect pigments and dyes. For example, chromium oxides can impart green colors, iron oxides can impart red colors, and cobalt oxide can impart blue colors. These additives may be used in accordance with the present coloring system approach if desired.

In optional embodiments, the scrim layer 20 need not be colored to be optically detected by an inspector. Instead, the scrim may contain a fluorescent or phosphorescent tracer compound material. As such, the inspector can shine a (black) light onto the top of the roofing membrane to cause scrim layer 20 to fluoresce. The present system also contemplates the use of both colored and fluorescent materials in the scrim layer.

FIG. 2 shows an alternate embodiment of the present system in which top ply layer 10 includes both an upper portion 12 and a lower portion 14 above the central scrim layer 20. As understood herein, portions 12 and 14 can be separate layers that are bonded together or separate regions of the same layer. In this example, lower portion 14 is colored while upper portion 12 may be white, clear, grey or light-colored. Lower portion 14 may be colored with various dyes or pigments, as appropriate. Lower portion 14 may also be colored to be darker than upper portion 12. Over time, as upper portion 12 is worn away, an inspector looking at the roof will start to see the colored lower portion 14. The advantage of this embodiment as compared to the embodiment of FIGS. 1A to 1C is that in FIG. 2, less of the top layer 10 would be removed before it is visually apparent to the inspector that the roofing membrane needs to be replaced.

Preferably, the lower portion 14 of the top ply layer 10 is a darker color than the upper portion 12 of the top ply layer 10. In addition, the lower portion 14 of top ply layer 10 may be thinner than the upper portion 12 of top ply layer 10. Having lower portion 14 be thinner than upper portion 12 would allow the roofing membrane to retain its normal color right up to the point in time that it would need to be replaced.

Next, as seen in FIGS. 3A to 3D, the lower portion 14 of the top ply layer 10 may itself comprise two layers 16 and 18 which are made of different colors. For example, the upper layer 16 may be yellow and the bottom layer 18 may be red. (It is to be understood that any other colors or color combinations may be used as well, all keeping within the scope of the present invention). Over time as the top upper portion of roofing membrane 5 is worn down, layer 12 will be removed, revealing yellow layer 16 below. The appearance of layer 16 can then act as a caution to the inspector that the roofing membrane 5 is wearing thin. Finally, if no repairs or replacement are performed, layer 16 will be worn away such that red bottom layer 18 will start to appear. The appearance of red layer 18 will be a stronger indication to an inspector that the roofing membrane is becoming critically thin.

In various embodiments, the different visual colors of layers 16 and 18 can be replaced or enhanced with tracer compound materials having different fluorescent or phosphorescent properties. As the upper portion 12 of the top ply layer 10 is worn away over time an observer can detect a second fluorescent or phosphorescent property in layer 14 or even a third fluorescent or phosphorescent property if such properties are different in layers 16 and 18.

As can be appreciated, the present system provides a roofing membrane, comprising: a bottom ply layer; a scrim layer on top of the bottom ply layer; and a top ply layer on top of the scrim layer, wherein an upper portion of the top ply layer 10 may have a different color or has a different fluorescent or phosphorescent property than one of the layers (14, 16, 18) or portions of the layers below such that when the upper portion of the top ply layer 10 is worn away over time, an observer will see a different color or spectroscopically detect a different fluorescent or phosphorescent property from the color or fluorescent or phosphorescent property of the upper portion of the top ply layer.

FIGS. 4A to 4F represent various embodiments of the present invention in which specific tracer compounds are added to one or more of the various layers of the roofing membrane 5.

In FIG. 4A, top layer 10 comprises two separate layers 12 and 14 with a tracer compound T disposed in the lower layer 14 of the two top ply layers. As more and more of top layer 12 is removed through normal wear and tear over time, top layer 12 becomes thinner. Accordingly, spectroscopic detection (for example with a hand-held device 15 show in FIG. 4A but relevant to FIG. 4A to 4F) will tend to detect more and more of the tracer compound T as top layer 12 becomes thinner.

In FIG. 4B, bottom layer 30 has tracer compound T disposed therein. Accordingly, spectroscopic detection will tend to detect more and more of the tracer compound T as top layer 12 becomes thinner.

In FIG. 4C, the tracer compound T is again placed in top layer 10. In this example however, a higher concentration of tracer compound T occurs at deeper depths in the layer. Specifically, near the top of top layer 10, the concentration of tracer compound T is low whereas as the bottom of top layer 10, the concentration of tracer compound T is higher. As such, spectroscopic detection will tend to detect more and more of the tracer compound T as top layer 12 becomes thinner.

FIG. 4D is basically the inverse of FIG. 4C. Specifically, the tracer compound T is again placed in top layer 10. In this example however, a lower concentration of tracer compound T occurs at deeper depths in the layer. As such, spectroscopic detection will tend to detect less and less of the tracer compound T as top layer 12 becomes thinner.

FIGS. 4C and 4D illustrate that the present invention can be used to detect the thinning of top layer 10 whether the concentration of tracer compound T increases or decreases, all keeping within the scope of the present invention.

FIG. 4E illustrates the situation of using two different tracer compounds T1 and T2. Tracer compound T1 is placed in top layer 12 and tracer T2 is placed in layer 14. As more and more of top layer 12 wears away over time, the operator will detect less and less of tracer compound T1 and more and more of tracer compound T2.

Lastly, FIG. 4F illustrates the situation where tracer compound T1 is placed in top layer 10 and tracer compound T2 is placed in bottom layer 30. Similar to FIG. 4E, as more and more of top layer 12 wears away over time, the operator will detect less and less of tracer compound T1 and more and more of tracer compound T2.

As described more fully below, the present invention may use a wide variety of tracer compounds T, T1 and T2.

As also described in more detail below, a variety of different non-destructive spectroscopic tests may be used to detect the presence (or absence) of the tracer compound T as the top of the roofing membrane degrades over time. In preferred aspects, an inorganic tracer compound is detected by spectroscopic analytical methods such as XRF, XPS, NIR, FTIR. Preferred characteristics of the inorganic tracer compound being added include low color contribution, being practically insoluble in water, not acting as prodegradants for UV or oxidation, and not typically being formulated in roofing compounds.

Many roofing membranes are white or pigmented in a specific color. Therefore, it is desired that the tracer compound T does not appreciably change the color of the roofing membrane. White or opaque compounds are therefore uniquely identified to fit this requirement as their tint strength may be overcome by other pigments such as titanium dioxide or mixed metal oxides.

Water solubility is undesired in the present tracer component T due to the roofing membranes being exposed to outdoor environmental conditions including rain and acid rain that could etch certain compounds. In addition, the present tracer compounds must also not accelerate UV or thermooxidation of the roofing compound to ensure longevity for the product lifespan. Incorporation of prooxidant additives would degrade the roofing membrane rapidly.

Preferably as well, the specific tracer compound that is selected should not be normally by found in roofing compounds in significant quantities. Or, if it is normally found in roofing, its baseline concentration should be established beforehand such that any detection of the tracer compound in the roofing membrane can be compared to this baseline.

In general, Group II metal compounds meet many of these criteria. Strontium and barium are preferred as beryllium is reactive and difficult to detect by XRF, radon is radioactive isotopes and not safe for this application, and calcium and magnesium are commonly found in fillers and fire retardants used in membranes.

Some transition metal compounds can also meet these criteria. Tin and zirconium are preferred. Specifically, strontium carbonate, zirconium oxide, barium sulfate, and tin oxide are contemplated as tracer compounds in accordance with the present invention.

In order to appropriately detect these elements, they must be present in amounts greater than the lower detection limit. For many of these contemplated non-destructive analysis methods, lower detection limits are typically in the range of 0.01% to 1% by weight. To result in the target weight percent of the element, loading of the target compound additive will be in the range of 0.01%-2%. Specific ranges will depend on the compound used and the analytical method used.

Preferred non-destructive analytical methods that could be used to detect tracer compounds would include x-ray fluorescence (XRF), x-ray photoelectron spectroscopy (XPS), energy dispersive spectrometry (EDS), attenuated total reflectance Fourier transform infrared (ATR-FTIR). Methods such as XRF and FTIR are preferred due to having portable instrumentation to allow for infield measurements. Most preferred is XRF due to ability to detect the elemental tracers at low quantities than other methods.

The present inventors have experimentally tested and verified various tracer compounds, as set forth below. As seen in Table 1 below, samples were produced using a UV stabilizer masterbatch for the White Reference, with TP Tracer 7 and 8 containing titanium dioxide as a white reflective pigment. The UV stabilizer masterbatch for the Black Reference and BP Tracer 6 did not contain titanium dioxide.

TABLE 1
Composition of Samples Produced and Tested

	White	TP	TP	Black	BP
	Reference	Tracer 7	Tracer 8	Reference	Tracer 6
Component	wt %	wt %	wt %	wt %	wt %

TPO Polymer	53.2	51.2	51.2	57.8	57.8
Inorganic Masterbatch	32	32	32	32	30
UV Stabilizer Masterbatch	14.8	14.8	14.8	7.2	7.2
Strontium Carbonate		2
Zirconium Dioxide			2
Black Masterbatch				3	3
Barium Sulfate					2

Color measurements were performed on the samples to measure difference from standard in the CIELAB color system. In this test, two colors can be compared in a term called delta E (dE) which is the distance between two points in CIELAB coordinates. It is generally recognized that >2 dE produces an observable color difference. In these samples, all dE were less than 2 indicating that impact to membrane color was negligible and these additives can be included without visual detection. Tables 2 and 3 below have color measurements of white and black compounds, respectively.

TABLE 2
Color measurements of white compounds

	Color	L*	a*	b*	dE

	White Reference	94.93	−0.23	2.89	0
	TP Tracer 7	93.45	−0.7	1.92	1.83
	TP Tracer 8	93.14	−0.73	2.2	1.98

TABLE 3
Color measurements of black compounds

	Color	L*	a*	b*	dE

	Black Reference	12.45	−0.15	−1.89	0
	BP Tracer 6	12.96	0.02	−0.67	1.33

In preferred tests, strontium carbonate was incorporated into a TPO roofing compound at 2% weight loading. In other preferred tests, zirconium dioxide was incorporated into a TPO roofing compound at 2% weight loading.

Testing was performed to measure elemental response of these compounds to prove their detection by non-destructive means. EDX is shown in Table 4 below and XRF is shown in Table 5 and indicates that tracer elements strontium (“Tracer 7”), zirconium (“Tracer 8”), and barium (“Tracer 6”) were detected in the specific samples. The table is shortened to only highlight elements that are intentionally added. It is evident that intentionally added elements may be detected at significant concentrations by non-destructive analytical methods.

TABLE 4
EDX of experimental compounds

		TP	TP	BP
	EDX	Tracer 7	Tracer 8	Tracer 6

	C	86.1%	86.6%	87.8%
	Ca	10.4%	9.9%	10.0%
	Ti	1.7%	1.6%	0.0%
	Sr	1.1%	0.0%	0.0%
	Zr	0.0%	1.2%	0.1%
	Ba	0.1%	0.1%	1.1%

TABLE 5
XRF of experimental white compounds

		TP	TP
	XRF	Tracer 7	Tracer 8

	Sr (wt %)	0.55%	ND
	Zr (wt %)	ND	0.39%

Lastly, to evaluate the use of multiple tracer components in a layered membrane structure, the compounds were layered on top of one another and measured by XRF. FIG. 4A represents both compounds present in “Membrane 23” and FIG. 4B represents only the strontium compound in “Membrane 25.” Significant measurement of both strontium and zirconium were detected in membrane 23 (FIG. 4A). Only significant amounts of strontium were detected in membrane 25 (FIG. 4B). The advantage of this approach is that, in the case of Membrane 25, the reduction in zirconium indicates that the top layer 12 is worn away and only the below layer 14 is present, meaning that significant thickness over scrim reduction occurred.

It is to be understood that in accordance with the present system, various tracer compounds T may be developed and incorporated into roofing membrane 5 in which either the presence or absence of specific tracer elements can indicate residual remaining life of the roofing membrane. Shown in Table 6 below is an example where the absence of zirconium indicated significant erosion.

TABLE 6
XRF of layered membrane

		Membrane	Membrane
	XRF	23	25

	Sr (wt %)	0.15%	0.20%
	Zr (wt %)	0.30%	0.00%

In accordance with one aspect of the present system, the tracer compound T was incorporated into the bottom layer 30 of roofing membrane 5 as shown in FIG. 4B. Tracer compound Tracer 6 (barium) was used. As the top layer 10 of roofing membrane 5 erodes, detection of the barium tracer compound T became stronger as the erosion continues.

In preferred aspects, non-destructive spectroscopic testing can comprise detecting fluorescence, phosphorescence or photoluminescence of the tracer compound. Both fluorescence and phosphorescence are photoluminescence properties of materials. Both methods emit light after some absorption of photons. Key differences in reference to the present invention are that fluorescence is characterized by a rapid emission of light that stops almost immediately when the excitation source is removed. Fluorescence involves a direct transition from an excited singlet state to the ground state. Phosphorescence has a delayed emission due to the electrons being trapped in a metastable state before returning to the ground state, causing a prolonged glow even after the excitation source is removed.

In preferred embodiments, the present tracer compounds can also include both organic dyes and inorganic compounds. Organic dyes, such as rhodamines and coumarins, give bright fluorescence under UV light, emitting vivid colors like pink, red, or green. They are often used in security applications and biological markers due to their high sensitivity. In optional aspects, they may be encapsulated to ensure stability during the high-temperature conditions of plastic extrusion and to protect them from UV degradation over time.

In other preferred aspects, inorganic photoluminescent materials are used, particularly those composed of inorganic compounds doped with rare earth metals, as they offer enhanced stability, making them preferable for use in high-temperature processing and outdoor applications. These target compounds can include both up-converting and down-converting phosphors. Up-converting materials, often based on compounds such as yttrium oxysulphide doped with rare earth elements like erbium (Er), thulium (Tm), or ytterbium (Yb), convert near-infrared light to visible light, providing unique luminescent properties. Down-converting phosphorescent materials include zinc sulfide doped with copper (ZnS:Cu), which emits a bright green glow in the dark after exposure to UV light, or strontium aluminate doped with europium and dysprosium (SrAl₂O₄:Eu,Dy), which has ability to emit green or blue light. These materials are advantageous due to their near colorless nature under ambient conditions, high thermal and UV stability, and ease of incorporation into TPO during extrusion processes.

When the target compound T is a pigment, the detection of the pigment requires that light of the appropriate excitation wavelength contact the pigment. Different pigments will have different excitation wavelength ranges. Exposure to light within this range will create the photoluminescent property needed; exposure to the excitation maximum will produce the most intense visual change. Preferably, inspection is done in low lighting conditions to better distinguish the photoluminescent effect. Concentration of the pigment in a roofing membrane must also be high enough to produce a visual change that is easily noticed upon excitation by the incoming light. As most membrane compounds contain TiO2 or other pigments, loading of the fluorescent pigment may preferably be carried out in the range of 5-10% by weight to achieve good visibility in most lighting conditions. The present inventors have experimentally viewed the fluorescence using a SrAl₂O₄:Eu, Dy compound placed in a thin layer over the scrim.