How Are Thermoset Composites Used for Water Treatment Applications?

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Published on February 5, 2025

Water is integral to the survival of the human species. It covers about 80 percent of the human body and 75 percent of the Earth’s surface. However, just 3 percent of the planet’s water is potable, with two-thirds not readily accessible. In fact, over a quarter of the world’s population has limited access to drinkable water. As potable freshwater is so precious, scientists continue to research materials that make human communities’ collection, distribution, storage, transport, and treatment of water more efficient and cost-effective.

Thermosets are used to increase efficiency in water treatment facilities and reduce the waste of potable water resources. For water treatment, these thermoset resins are often combined with other materials to produce composites with properties that make them particularly useful for a variety of water treatment applications. Thermoset composites are increasingly used in systems for disinfecting, filtering, storing, and transporting water, along with their use as components within water treatment equipment.

Thermoset Composites in Water Treatment Applications

Treating water or wastewater involves various processes and equipment to remove contaminants and make water safe for humans to drink. Advanced materials like thermoset composites are used for components and structures within these water treatment systems. While other types of material are integrated into these composites, these advanced materials offer unique properties due to their inclusion of thermosets. Thermoset composites are particularly well-suited for water treatment applications, given their resistance to corrosion and water absorption, among other qualities. 

Other advantageous properties thermoset composites offer include: 

  • Chemical resistance: Keeps harsh contaminants within the water from degrading equipment and components.
  • Durability: Enables water treatment equipment to last longer without frequent maintenance or replacement of critical parts.
  • High mechanical strength: Allows equipment to handle high-pressure applications better.
  • Lightweight: Components with lower weights are more efficient, as they require less energy to put into motion, while enabling greater design flexibility. 
  • Thermal stability: Many thermosets maintain shape to ensure functionality even under extreme temperatures. 

Though thermoplastic resins are more venerable than their thermoset cousins, which only came into commercial use in the early 20th century, the latter have somewhat fallen out of favor. This is due to the relative ease with which thermoplastics can be recycled, giving them an advantage over thermosets. For water treatment, however, the properties of thermosets and thermoset composites often make them more appropriate for the application in which they’re used.

A Case for Using Thermosets for Water Treatment

For certain applications, the permanency of form after curing and limitations on recyclability are real shortcomings for thermosets. For water treatment, both thermoset composites and thermosets offer material qualities that make them preferable to other materials for water treatment applications. Additionally, thermosets are easier and less expensive to process than thermoplastic resins.

However, unlike thermoplastic resins, which can be melted down and easily reconstituted into new products, this is not the case with plastics classified as thermosets. This has contributed to their decreased use for water treatment and other applications. Thermoset composites must go through intricate chemical, mechanical and thermal processes to recover helpful material from them. However, advances in recycling techniques are leveling the playing field between thermoset and thermoplastic resins, paving the way for more advanced thermoset composites.

Properties of Thermosets Used for Water Treatment

Using thermosets for water treatment applications like piping and storage tanks reduces the need for metals, which are generally more prone to corrosion. Resistance to corrosion and chemicals is especially desirable, as water treatment often uses corrosive chemicals, including citric acid to remove mineral deposits, hydrochloric acid to balance pH, and sodium chlorite (bleach) to disinfect the water during treatment.

Thermoset composites for water treatment often use the following four resins: 

  • Epoxy resins offer superior adhesive, chemical resistance, and mechanical strength characteristics.
  • Phenolic resins are used in filter media due to their higher strength and thermal stability.
  • Polyester resins provide cost-efficient solutions for coating and otherwise protecting structural components.
  • Vinyl ester resins mix excellent corrosion resistance with durability.

As an example, thermoset composites like G-10 and G-11 are glass epoxy laminates that offer high mechanical strength in wet conditions while also preventing the absorption of water. This property is fundamental in water treatment applications, as when excessive water is absorbed, equipment will degrade more quickly.

Epoxy Resins

Coatings made from epoxy resins are used to rehabilitate water pipes due to the lower cost of material and the labor involved. In using these thermosets for water treatment, epoxy coatings allow water treatment facilities to continue using what would otherwise be considered deteriorated piping rather than replacing it.

Commonly, epoxy thermosets for water treatment are used to: 

  • Coat the insides of metal or concrete water tanks to avert adulteration and deterioration.
  • Line interiors of water pipes to inhibit leaks and guard against corrosion.
  • Restoring damaged surfaces of pumps and other water treatment machinery.
  • Sealing cracks in concrete structures within water treatment facilities.

While epoxy is used for repairing water piping, it’s also used to increase its lifespan, with the interiors of new pipes often coated with this thermoset. Composites for water treatment applications typically use epoxy resins for the matrices, usually reinforced with carbon or glass.

Phenolic Resins

Phenolic resins and their derivatives are considered potent pollutants that cause water to taste and smell unpleasant. The effluent produced by the chemical, paint, pesticide, petrochemical, pharmaceutical, and other industrial sectors often contains these thermosets. However, new disinfection methods have been developed for water treatment involving these resins in combination with ultraviolet light.

Phenolic formaldehyde has been shown to disinfect water when combined with radiation from sunlight or LED lighting, which works under static or continuous flow conditions. E. coli bacteria deactivate markedly when exposed to light in combination with coatings made with this thermoset. Composites that include phenolic resins thus show great promise for solar-based water purification and reducing dangerous bacteria in water treatment facilities. 

Polyester Resins 

Isophthalic and orthophthalic polyester resins are the two main categories of these thermosets. For water treatment, isophthalic polyester resins are most often used due to their superior resistance to water and corrosion and their durability. Often, isophthalic polyester resins are reinforced with fiberglass to make thermoset composites used for water pipes and storage tanks in various water treatment systems.

Vinyl Ester Resins

As with polyester, these thermosets for water treatment applications offer greater durability, along with excellent corrosion and water resistance. This is especially true with thermoset composites made from vinyl ester resins combined with fiberglass. Thermoset composites containing vinyl ester are the most common material for coatings in water storage tanks and water treatment facilities generally.

Thermoset composites made with vinyl ester resins are also used to construct lightweight components and other structural elements. In water treatment systems, such thermoset composites are often favored, as they absorb less water than other materials. Their ability to withstand corrosion also makes them more cost-effective and dependable than metals in such applications.

Water Treatment Applications for Thermoset Composites

One of the most common roles of thermosets for water treatment involves their function in piping systems. Thermoset composites are used in treatment plants that handle water in its various forms, including deionized water, domestic wastewater, industrial effluent, potable freshwater, seawater, sewage and stormwater.

Key considerations for the use of thermoset composites in water treatment include:

  • Capacity of system
  • Cost effectiveness
  • External environmental conditions
  • Placement of piping (whether aboveground or underground)
  • Stiffness of piping
  • System pressure
  • Temperatures of various processes

As an example, epoxy-based filament wound composites are often used for pump system fittings and pipes, as these thermoset composites provide the best physical qualities for this function. Piping systems benefit from the strength and toughness of such composites, along with the ability to maintain their form at higher temperatures.   

Corrosion-Resistant Equipment Made with Thermoset Composites

One of the prime benefits of using thermoset composites is their corrosion-resistance, making them particularly useful for storage tanks, pipes, filters, fittings, clarifiers and other components in water treatment equipment. Often, these composites replace metals that can corrode over time while also costing more than composites containing thermosets. For water treatment, a variety of thermoset composites are used because of their corrosion-resistance.

Corrosion-resistant thermoset composites used for water treatment include: 

  • Epoxy-based composites to coat concrete or metal structures in water treatment facilities to prevent corrosion.
  • Phenolic-based composites are used for filter housings, odor control covers, and similar applications.
  • Polyester-based composites for structures like walkways, smaller tanks for containing toxic chemicals and gratings, and piping in wastewater treatment plants.
  • Polyurethane-based composites are used for lining tanks, pumps and pipes, seals, gaskets, and other components of water treatment equipment.  
  • Fiberglass often reinforces Vinyl ester-based composites for applications like storing chemicals used in water treatment and piping systems for desalination plants.

Additionally, thermoset composites containing epoxy, polyester, or vinyl ester resins are used in biofilters, piping systems, scrubbers, and water tanks in these facilities. Thermosets for water treatment are also combined with carbon fiber for components that need to withstand higher pressures or for piping handling corrosive liquids. Additionally, thermoset composites sometimes incorporate thermoplastics for liners in piping systems, reactors and piping systems.

Thermoset Composites in Reverse Osmosis Processes

For applications like reverse osmosis, desalination plants use thermoset composites in housings for membranes, which are often made with fiberglass or carbon fiber combined with thermosets. For water treatment, epoxy-based composites tolerate high pressures and saltwater well, while their lighter weight makes them preferable to alternatives made from metals. This is especially the case with epoxy glass tubing, which is now standard in many municipal water treatment and desalination plants.

Since the 1970s, epoxy tubes have become increasingly common for purifying water, as they can handle higher pressures and remove more toxins than composites made from other thermosets. For water treatment, epoxy tubes provide more environmental benefits, longer lasting components and greater cost-efficiency. The reinforced fibers of epoxy glass tubes provide corrosion-resistance and strength for such applications, helping to minimize both maintenance and operational costs.

How Thermoset Composites are Used in Ion Exchange Systems

Ion exchange systems are primarily used for removing contaminants and softening water, which may involve various composites made from thermosets. For water treatment applications, softening the water involves removing minerals that cause scaling like. This entails replacing calcium and magnesium ions with sodium ions, less damaging to plumbing. While the resin beads in ion exchange systems are primarily made with thermoplastic resins, thermoset composites play an essential role in their structures. Epoxy, fiberglass, phenolic, polyester, vinyl ester, and certain thermosetting polyurethanes are often integrated into the thermoset composites utilized for ion exchange water treatment systems.  

Uses in ion exchange systems for thermoset composites include: 

  • Bases, skids, supports and other structural components.
  • Filters and strainers for prefiltering systems that remove suspended solids prior to ion exchange.
  • Gasket and seal connections between water tanks, valves and pipes.
  • High pressure containers for desalination or industrial water treatment systems.  
  • Internal components like collectors, distributors, and nozzles.
  • Linings for concrete tanks containing treated water or regenerants.
  • Piping that transports feed and treated water, as well as hydrochloric acid, sodium hydroxide sulfuric acid, or other regenerants.
  • Resin beds where ion exchange beads are housed for removing calcium, heavy metals, magnesium, and other contaminating ions.
  • Storage tanks for hydrochloric acid, sodium hydroxide sulfuric acid, or other regenerants are used to treat the water.
  • Tanks that hold highly noxious alkaline and acidic solutions.

Thermoset composites work well within ion exchange systems as they can handle the saline, alkali, and acid solutions used to regenerate water in these systems due to their chemical inertness. Their robust nature allows them to endure repeated ion exchange cycles, while their lighter weight makes them more customizable than metal components. Additionally, the corrosion and chemical resistance of thermoset composites lowers maintenance costs and increases uptime.

Thermoset Composites from Spaulding 

Among the thermosets for water treatment, Spaulding Composites Inc. makes glass epoxies. Used for reverse osmosis water purification, these thermoset composites are filament wound tubes that protect the semipermeable membranes used to remove contaminants. Spaulding can additionally offer injection molding services for interconnectors and assist with designing both these and core tubes. To learn more about thermosets for water treatment and other applications, contact the experts at Spaulding Composites.