REINFORCING FIBER BLEND

BACKGROUND OF THE INVENTION

[001] The present invention relates generally to the field of pipe rehabilitation, commonly referred to as cured in place pipe (CIPP).

[002] A conventional pipe repair utilizes a pipe liner comprising a carrier web, which may be formed as a nonwoven felt and impregnated with resin. The carrier fiber holds the resin until the resin can be fully applied to the interior of a pipe, pressurized, and cured in place. In these applications, the carrier material, commonly polyester, is used to hold the resin, and contributes little, if any, strength and stiffness to the resin. In fact, the fiber is an inclusion in the resin and weakens the resin layer. Accordingly, the practice in the art is to target carrier fiber content in the composite as low as possible to maximize resin content, because the resin provides the reinforcement in this instance.

[003] U.S. Pat. No. 5,868,169, which is incorporated by reference, teaches the addition of a mesh or mat of fiberglass as a reinforcing layer in a lining for use in softlining pipe rehabilitation. In this method, the fiberglass mesh is incorporated between two layers of resin absorbing material such as nonwoven polyester felt. The reinforcing material is lightly bonded to the resin absorbing material layer and the layers are soaked with a volume of resin and pulled through a length of pipe. The lining hose is expanded to conform to the inner diameter of the pipe so that a resin layer with a discrete strengthening layer of fiberglass is formed on the inside of the pipe, and the fiberglass layer is not exposed on the inside of the pipe. In all instances according to this method, fiberglass fibers are not inserted or combined with low modulus fibers in a single layer, as the low modulus fibers would tend to lower the strength of the layer. [004] It is an object of the invention to provide improved resin-fiber composites for use in pipe linings and methods of use thereof.

SUMMARY OF THE INVENTION

[005] Thus, in one aspect, the invention is embodied as a pipe rehabilitation system comprising a tubular nonwoven felt liner comprising a blend of 5-95% by weight low modulus polymeric carrier fibers and 5-95% by weight high modulus reinforcing fibers, and a curable resin system infused in said nonwoven felt, said tubular nonwoven felt liner infused with resin adapted to be inverted through a pipe, expanded in the pipe, and cured in place.

[006] In embodiments, the pipe rehabilitation system may further comprise a nonwoven layer consisting of reinforcement fibers adjacent said layer having said blend of low modulus carrier fibers and high modulus reinforcing fibers, and said curable resin is infused in both the layer comprising a blend of carrier fibers and reinforcement fibers and the layer consisting of reinforcement fibers.

[007] In embodiments, the pipe rehabilitation system described comprises 50 to 90% by weight reinforcement fibers consisting of inorganic fibers selected from glass, basalt, carbon, silica, and alumina fibers or a combination thereof, or high strength polymer fibers selected from p-aramid and PBO, or a combination thereof; and 10 to 50% by weight carrier fibers selected from polyester and low modulus polymer fibers.

[008] In embodiments, the hybrid nonwoven felt consists essentially of a blend of ECR glass reinforcement fiber and polyester carrier fiber

[009] The pipe rehabilitation system according to embodiments of the invention utilizes a UV-curable resin or a heat curable resin. [0010] In embodiments, the hybrid liner is able to meet ASTM D 790 mean flexural strength requirement of at least 4500 psi and mean flexural modulus requirement of at least 250,000 psi, and at less thickness and overall weight than was conventionally practiced in CIPP.

[0011] In embodiments, the reinforcing fibers are ECR fibers having a length greater than 1 inch.

[0012] The invention is also embodied as a method for making and/or using a pipe rehabilitation liner, comprising: blending polyester carrier fibers and glass reinforcing fibers at a ratio in a range of 50:50 to 10:90 and carding to form a web; stabilizing the web by needlepunching, hydroentangling or thermal or ultrasonic bonding; forming the stabilized web into a tube; infusing the stabilized web with a resin, before or after forming the tube; inverting the tube in a pipe in need of rehabilitation; expanding the tube infused with resin in the pipe; and curing the resin in the web in place to effectuate rehabilitation.

[0013] In embodiments, the resin is UV-curable resin, and curing in place comprises irradiating the resin-inlused tube with UV light which is transmitted through the glass fibers into the nonwoven hybrid web. In such embodiments, the UV-transmissible fiber content may be maximized to facilitate the curing process.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which: [0015] Fig. 1A schematically describes a conventional multi-layer pipe liner 10, including cured-in-place installation around a pipe 12, according to the related art;

[0016] Fig. IB schematically describes a reduced thickness pipe liner 14, including cured-in-place installation around a pipe 16 according to embodiments of the invention comprising a homogeneous hybrid felt; and

[0017] Fig. 2 depicts a substantially linear variation of tensile strength and tensile modulus with increasing content of glass in a homogeneous blend of glass and polyester in a felt, according to embodiments of the invention.

[0018] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

DETAILED DESCRIPTION

[0019] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention.

[0020] In contrast to a typical fiber-resin composite system, in which the fiber component provides strength and/or stiffness to the end product, the composite used in a conventional liner for pipe lining exhibits, at best, similar properties to the resin. And most likely, the fibers of the carrier web act as inclusions in the resin due to incomplete bonding to the resin and detract from the resin performance. [0021] Accordingly, in embodiments of the present invention, high modulus reinforcing fibers are blended with low modulus carrier fibers to form a homogeneous fabric component configured for resin infusion having sufficient content of high modulus fiber (such as fiberglass) to increase the modulus of the composite liner, and sufficient loft in the carrier fiber web to ensure thickness retention and provide the necessary mechanical properties. The blended hybrid material is then inlused with resin.

[0022] In selecting relative amounts of reinforcing fiber and carrier fiber, increased stiffness imparted by the reinforcing fiber component is not the only consideration. A 10- fold increase in stiffness does not translate to a 10-fold reduction in material requirement. Beam stiffness is dependent on thickness and shape of the beam, and thickness is weighted to the 3rd power, so thickness holds significant weight in determining beam stiffness. In order to reduce thickness at the same level of effectiveness there needs to be a significant increase in material modulus, and thickness retention is an important consideration when adding reinforcing fibers.

[0023] Carrier fibers used in embodiments of the invention include fibers that do not contribute significantly to the strength or stiffness of the resin matrix. Most polymer-based fibers fall into this category, including polyolefins, polypropylene, polyesters, nylons, PPS, and epoxy. Some natural fibers may be used as carrier fibers in the hybrid liner according to the invention.

[0024] Resins that can be used in the invention generally fall into three categories: polyester, epoxy, and phenolics. These have modulus values of approximately 1-4 GPa, 2- 5 GPa, and 8-10 GPa, respectively. Polyester fiber has a modulus around 2 GPa. The lowest glass fiber is around 50 GPa. In this light, while the designation is somewhat arbitrary, fibers having 20 GPa modulus or less are carrier fibers (this is around the point that composite modulus would be doubled if used in the 50/50% felt blend). Fibers having modulus in a range of 20-50 GPa could be either reinforcing or carrier (most natural fibers fall into this range), and fibers having modulus higher than 20 GPa, and preferably greater than 50 GPa would be reinforcing fibers.

[0025] Reinforcing fibers used in embodiments of the invention are fibers that contribute significantly to the strength and/or stiffness of the resin matrix. Such fibers include at least inorganic fibers, such as various grades of glass, basalt, carbon, silica, and alumina, and may include high strength polymer fibers, such as p-aramid or PBO. Natural fibers may be reinforcing or carrier fibers, depending on the properties of the fiber.

[0026] In embodiments glass fibers used in the invention are electrically and chemically resistant glass fiber, commonly referred to as ECR glass fibers, generally composed of alumino-lime silicate and having low alkali oxide content, ECR fibers are resistant to acid and alkali.

[0027] Fig. 2 depicts a substantially linear variation of tensile strength and tensile modulus with increasing content of glass in a homogeneous blend of glass and polyester in a felt. In embodiments, reinforcing fibers are provided at a ratio in a range of 5:95 to 95:5 percent by weight with respect to the carrier fibers. In embodiments, reinforcing fibers are present in a range of 50:50 percent by weight to 95:5 percent by weight with respect to the carrier fibers.

[0028] In embodiments, a hybrid felt comprising a blend of reinforcing fibers and carrier fibers inverts with the same level of force as standard felts whereas a stiffer fiberglass layer is more difficult to invert. Moreover, the hybrid felt requires less material (in some cases half the material) to reach the same composite properties as standard felt. Inversion of the hybrid felt requires less force because the thickness is less. The density of the reinforcing layer often makes it more difficult to invert the liner.

[0029] The most common reinforcement fibers in composite manufacture are fiberglass and carbon fiber, which have very high strengths and stiffnesses compared to the commonly used resins, for example more than twice the modulus of the resin, and in embodiments at least ten times the modulus of the resin. In general terms, a reinforcement fiber may have a modulus an order of magnitude greater than the resin. For instance, resins commonly have a modulus, of 2-3 GPa, similar to most polymer-based fibers, whereas fiberglass is 70-90 GPa, and carbon fiber is 230-500 GPa or more. With a high difference in modulus, a relatively small percentage of reinforcing fibers, for example as low as 5% can offer a large improvement in material stiffness (as can be approximated by the rule of mixtures). This puts typical composite properties with 50% volume fraction of unidirectional glass or carbon at approximately 50 GPa and 105 GPa, and a balanced composite around 25 GPa and 60 GPa, respectively. This is a 10-fold increase and 24-fold increase, respectively, in stiffness compared with the neat resin for balanced fabrics.

[0030] In embodiments, the hybrid felt can also be used with ultraviolet (UV) curable resins, in contrast to the more standard heat curable resins. The standard polyester carrier web does not work well with UV curable resin, because the polyester blocks the UV light and leaves the interior portions of resin uncured. Glass fibers result in a transparent infusion and allow the UV light to fully cure the resin. The more glass in the hybrid felt the better it is for UV cure. Higher glass content also results in a lower thickness of felt required to reach the specified strength thresholds. This saves additional resin costs, which may be higher for

UV resin systems. [0031] The hybrid liner may be manufactured by blending the carrier fibers and the reinforcing fibers together until the mixture is uniform throughout. The degree of uniformity is largely dependent on the processing step to produce an homogenous web. Fiber diameter and length can be adjusted depending on the particular method of blending and processing. In embodiments, a reinforcing fiber is selected to have 0.5-4 inches in length. Fiber lengths greater than 1 inch tend to afford optimal composite properties. Blending can be performed by traditional textile processing methods including mechanical agitation, carding, and/or turbulent air flow.

[0032] Once the fibers are blended in the preferred ratio, they may be processed with a carding line. The carding line may be a wire card, with or without a cross-lapper, or an air laid line. These systems will form the fibers into a web, or batting, which is then needlepunched, hydroentangled, or thermally/ultrasonically bonded for stability. Needlepunching uses barbed needles to transfer fibers through the thickness of the batting to create mechanical entanglements that strengthen the material. Hydroentangling also creates mechanical entanglement between the fibers, but it uses waterjets in place of needles to transfer fibers. Thermal bonding uses heat to melt thermoplastic fibers in the batting causing them to fuse. This could be a uniform application of heat or at specific points and intervals over the surface of the batting. RF/Ultrasonic welding may also be used in a similar way. Hot air may similarly be used to uniformly fuse the web structure together with thermoplastic fibers. Once bonding is complete the batting can be termed a felt. This felt can be used as an uncoated resin carrier, or it can be coated. The rolled good is then seamed into a tube using CIPP processing known in the art.

[0033] It is also possible to process the fibers into a homogenous web using a wet-laid process. In the process fibers are dispersed into a liquid, usually water, then mixed and formed onto a porous belt. Typically, this is used for shorter fiber lengths and lighter areal weight fabrics, but the process may be adapted for longer fiber lengths, and multiple layers of wet-laid batting may be bonded together using needlepunching or hydroentangling to build up to the desired fabric weights. Fabric weights may be in a range of 3-30 ounces per square yard in some embodiments of the invention. In embodiments, the fabric weight for a particular carrier web may range between 10 and 14 ounces per square yard.

[0034] Resin is conventionally loaded into a carrier fiber layer at a weight of about 80%. With the hybrid carrier fiber layer of the present invention, lower resin loading may be employed: less than 80%, in embodiments less than 70%, and in some embodiments less than 60%.

EXAMPLE 1

[0035] A 6 denier polyester fiber was blended with 50% by weight ECR glass fiber for most resins and up to 90-95% glass fibers for UV cured resins. Fibers may be processed using either a carding line or an air-laid line to form a web and needlepunched to form a felt.

[0036] Different blends of carrier fibers may be used to optimize specific felt properties, such as density and thickness. For instance, it may be beneficial to use a larger denier carrier fiber with greater crimp to add extra thickness to a felt with a high percentage of reinforcing fibers. This keeps the felt from compressing as much and allow for thickness retention during cure. The carrier fiber could also be a blend of different fibers or different deniers of the same fiber, similarly for reinforcing fibers. Creating a blend for the carrier component or the reinforcing component may add functionality, or may simply be used as a cost saving measure. As an example, a small amount of reclaimed glass could be added to virgin glass fibers as a cost savings measure with negligible impact on performance. Basalt fibers could also be a cost saving measure, compared with ECR glass. Carbon fibers have a high performance boost, but are costly. Using a small percentage of carbon with a larger percentage of glass would offer a performance boost at an acceptable cost increase.

[0037] The felt itself can be produced in various thicknesses and densities to achieve the desired properties of the end use. Similarly, reinforcing fiber ratio and type can be adjusted to tailor composite properties at a given thickness. This keeps the installation procedure constant for different repair requirements, that otherwise might be impacted by the different handling characteristics of multi-layered materials.

[0038] The improvement in tensile strength and modulus means that compared with a standard CIPP felt composed of polyester, a felt with 50% glass blended in with the carrier fiber will require as much as half the thickness and half the resin in order to meet the requirements listed in ASTM F1216-08. The performance of different fiber blends, including the performance in accordance with ASTM standards, in each case using the same resin is shown in Table 1.

TABLE 1

[0039] Reference to American Society for Testing of Materials Standards referenced herein refer to the ASTM standards in effect on the filing date of this application. ASTM D790 supplies an art-recognized measure of mean flexural strength, and the threshold for CIPP applications is 4500 psi. ASTM D 790 also provides a measure of flexural modulus and the threshold requirement for CIPP applications is 250,000 psi. ASTM D 638 provides a mean tensile strength requirement of 3000 psi. These methods of testing and measurement are consistent with the skill level in the art and are incorporated by reference.

[0040] In the foregoing, a hybrid resin-carrier layer containing glass reinforcement fiber and polyester carrier fiber is compared with a conventional application in which a nonwoven in layer of unblended glass fibers is layered with a polyester carrier fiber layer. It is also within the scope of the invention to layer an unblended glass reinforcement layer with the hybrid layer, infused separately or together with resin.

[0041 ] While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.