[Image above] Basalt fiber is another material besides carbon and glass being considered to reinforce polymer composites. Credit: D. Nishio-Hamane, Flickr (CC BY-NC-SA 2.0)

Even though I spend a majority of my workday reading, it remains one of my favorite pastimes as well. The variety of books that I consume covers almost every genre, but one type in particular that I like are books by other science communicators on topics outside my purview—in other words, materials besides ceramics and glass.

One such book that I recently finished is “Science and Cooking,” a new book based on the popular Harvard University and edX course. The book approaches food from a materials science standpoint and offers a transformative appreciation for cooking from a molecular perspective.

For example, one point the authors emphasize is how much a food’s flavor and texture depends on how you break apart and combine chains of protein, carbohydrate, and fat molecules. Such reactions often are induced using heat, but you also can bring about changes in the molecular makeup by introducing new enzymes into the food to trigger or accelerate chemical reactions.

Reading the book made me realize that cooking is one of the best examples of composite materials in our everyday lives. A composite material is produced by combining two or more constituent materials with different physical and chemical properties; the resulting composite has properties unlike the individual elements.

While composite materials are all around us, we often are not familiar with the original elements used to make the composite and so cannot appreciate how the combination of materials changed the properties. But with cooking, you can experience the individual elements firsthand when combining them in a bowl—and then create a new dish that can taste very different from each of the original ingredients.

Cooking offers a clear example of how composite materials can be very different from the constituent elements. Credit: Marco Verch Professional Photographer, Flickr (CC BY 2.0)

Outside of the kitchen, carbon fiber reinforced polymer is one composite material that is poised to make a big difference in our daily lives. This composite material, often referred to as “carbon fiber,” has received much attention in recent decades because of its potential to replace steel. The combination of carbon fibers within a polymer matrix gives these polymer composites the desirable properties of high strength and light weight.

The high cost of carbon fiber reinforced polymers limits their widespread use, however, so lowering the cost is imperative for manufacturers. Research toward this end has yielded some success, but researchers also are considering other fibers besides carbon that may be useful to reinforce polymer composites.

Basalt fiber is another material being considered as reinforcement. This inorganic fiber, when used to reinforce polymers, has resulted in composites that demonstrate good strength, high operating temperature range, good chemical resistance, excellent heat and sound insulation properties, and low water absorption. In addition, basalt fibers are easily processed, eco-friendly, and—crucially—inexpensive.

To date, basalt fiber reinforced polymers have not achieved large-scale market acceptance because of several technical challenges, such as inconsistent raw material properties and regulatory standards. But progress on all the necessary fronts—manufacturing efficiency and capacity, global presence, product design and development, regulatory activity—have manufacturers confident that these materials will play a bigger role in the future.

The tribological performance of basalt fiber reinforced polymers under various working conditions is one question that manufacturers must answer to overcome regulatory challenges preventing these composites from entering certain markets. Tribology refers to the science of two interacting surfaces in relative motion and encompasses friction, wear, lubrication, and related design aspects.

Tribological performance depends on several factors, such as the manufacturing process, operating parameters, and characteristics of the polymer matrix and fiber. Thus, mapping out the tribological performance under various working conditions for these composites will require time and numerous studies.

A new open-access study by researchers in Malaysia and Brazil contributes to this effort. They aimed to compare the friction and wear characteristics of glass fiber or basalt fiber reinforced epoxy composites to reveal the effect of these different fibers on the tribological performance of epoxy-based composites.

The researchers used the epoxy resin Miracast 1517A, which is a low-viscosity laminating resin. They fabricated the composites using conventional filament winding and the hand layup method, and then they conducted testing in two stages:

  1. Fixed load, speed, and distance under adhesive, abrasive, and erosive wear conditions.
  2. Unidirectional and reciprocating adhesive sliding motions against steel counterpart, with the former varied at pressure–velocity factor (0.23 MPa·m/s vs. 0.93 MPa·m/s) and the latter varied at counterface configuration (ball-on-flat vs. cylinder-on-flat).

As seen in the figure, stage one testing revealed that the composite’s wear properties improved up to 60% when reinforced with either glass fiber or basalt fiber. However, performance of composites reinforced with basalt fiber compared to glass fiber was not consistent.

In adhesive and abrasive wear conditions, the glass fiber reinforced polymer showed better wear than the basalt fiber reinforced polymer, with differences of 18.33% and 22.75%, respectively. “This might be due to the higher hardness obtained by [glass fiber reinforced polymer] composite compared to [basalt fiber reinforced polymer] composite that prevents severe matrix removal from adhesive wear,” the researchers write. Or, the small diameter size of the basalt fibers (9–15 μm, compared to 10–17 μm for the glass fibers) may affect the fiber–matrix interface strength.

Wear volumes of pure epoxy (EP) and its glass fiber (GF) and basalt fiber (BF) reinforced composites at different wear conditions. Credit: Talib et al., Materials (CC BY 4.0)

Only in erosive wear condition did the basalt fiber reinforced polymer show better wear than the glass fiber reinforced polymer, with improvement of 9.93%. “This might attribute to thermal changes that occurred inside the erosive pot. The sand mixture eroding the surface creates higher friction as the distance increases. Therefore, the heating can cause changes to the thermal and mechanical properties of glass fiber reinforcement,” they write.

During stage two testing, the researchers drew several interesting conclusions, including

  • Low friction coefficient recorded during sliding does not always reflect a low wear rate of the composite,
  • Basalt fiber reinforced polymers showed better wear rate and friction coefficient than glass fiber reinforced polymers under unidirectional sliding only at high operating parameters, and
  • Basalt fiber reinforced polymers showed an inconsistent pattern of improvement between wear rate and friction coefficient compared to glass fiber reinforced polymers during reciprocating sliding.

Ultimately, they conclude that while friction and wear properties of composites are highly dependent on test conditions, “it can be said that [basalt fiber] can potentially replace [glass fiber] to be used in tribological applications as the differences between them are still comparable.”

The open-access paper, published in Materials, is “Effect of wear conditions, parameters and sliding motions on tribological characteristics of basalt and glass fibre reinforced epoxy composites” (DOI: 10.3390/ma14030701).