From Bricks to Nanomaterials: The Evolution of Composites

What are composite materials? How can we significantly enhance the properties of fabric or metal? How are new materials created? Here, we explore recent discoveries and promising advancements in materials science.

Experts from diverse areas of materials science discuss the origins of composite materials, the connections between ancient bricks and modern nanotechnology, and the development of “smart” materials.

The First Composite Materials

The history of composite materials stretches back thousands of years. The earliest references date to around 5000 BCE in Mesopotamia, where people built boats by treating them with resin for added durability. Another ancient composite is adobe brick—a blend of clay and straw used in Egypt and Mesopotamia for building structures, some of which still stand today. Even then, people understood that combining two materials with different functions could create something more robust and resilient than each component.

The list of early composites should also include concrete and construction mixtures, which were well-known to ancient Romans. These mixtures were intuitively and deliberately created, combining components with specific roles. One part, like sand or gravel, provided reinforcement, while the other—a binding agent—held the reinforcing elements together, redistributed loads, and made the material solid and cohesive. The principles established by these early builders continue to underpin composite materials today.

The Modern Composite Materials

In modern terms, a composite material is a blend of two or more distinctly different materials, such as metals, carbon, ceramics, or polymers. These components must have at least one boundary separating them, and their proportions must be comparable—typically, the second component should make up at least 5% of the composition. While many mixtures of two polymers don’t qualify as composites, the lines defining these categories are often blurred.

The era of modern composites truly began in the 19th century, marking significant advancements in material science that have shaped our everyday lives. Inventions from that time in composite materials paved the way for those we rely on today. For instance, rubber was first developed in this period, and rubber-based products are considered classic examples of composite materials. Carbon black is added to rubber to enhance durability and resilience to repeated stress, which is crucial for products like car tyres.

The Polymer Composite Materials

Carbon fiber and fiberglass are the primary polymer-based materials that often come to mind when we think of “composite materials.” These composites consist of a fiber—either glass or carbon—and a polymer matrix, usually polyester or epoxy resin. The fiber imparts exceptional mechanical strength, while the resin distributes the load across the material.

The invention of fiberglass dates back to the latter half of the 19th century, with the first production of glass fibers occurring in the 1870s. Not long afterwards, it began to be combined with other materials. A breakthrough in polymer composite technology came in the early 1930s with the development of polyester resins, which were then combined with glass fibers. This innovation spurred rapid growth in fiberglass production.

One of the first major industries to adopt fiberglass was shipbuilding, where it became the preferred material for boat hulls. Owing to its strength and lightweight properties, fiberglass has also become widely used in aviation and automotive manufacturing.

Epoxy resin-based binders remain essential components of polymer composites. In 1909, Russian chemist Nikolai Prilezhaev discovered the epoxidation reaction, laying the foundation for the entire technology behind epoxy resin production. By the 1930s, research on epoxy resins was advancing rapidly, and they began to see widespread use in composite manufacturing.

The development and refinement of carbon fiber production technology also played a pivotal role in the evolution of composite materials. Carbon fibers are both lighter and stronger than glass fibers.  In 1880, Thomas Edison was among the first to produce carbon fiber, using heated carbon filaments derived from plant fibers for incandescent lamp filaments. More reliable tungsten filaments eventually replaced these, and Edison’s discovery was largely forgotten, though it served as a precursor to modern carbon fiber.

Today, advancements in carbon fiber technology have achieved remarkable results, with tensile strengths reaching up to 12 gigapascals and elastic moduli on the best samples reaching 1000 gigapascals. For a long time, carbon fiber composites were used exclusively in the space and aviation industries. It wasn’t until the 1980s, after a carbon-fiber race car won an international racing competition, that these materials entered the automotive industry, drawing significant resources and interest to the field of composite materials.

Carbon fiber and fiberglass composites are lightweight and robust but lack resistance to high temperatures. Epoxy resin composites typically function at temperatures above 100–120 °C. The theoretical limit for any polymer-based binder is around 400 °C, and in rare cases, up to 500 °C. Ceramics are used—lightweight, fire-resistant materials to make components that withstand higher temperatures. However, ceramics have a significant drawback: they are brittle. To increase their strength, reinforcement can be added to the ceramic matrix, such as extended metal or carbon fibers. Composite ceramics can withstand temperatures up to 2000 °C, making them ideal for aerospace and missile engineering refractory coatings.

These inventions fall under structural materials, but there’s also a field of functional materials. Functional materials incorporate a polymer component with a specific function, such as anti-friction, thermal conductivity, thermal insulation, or electrical conductivity. Sometimes, materials need to be both structural and functional. One example is syntactic foams, widely used in shipbuilding and aerospace to provide high strength and stiffness at a low weight. These foams consist of a polymer matrix filled with glass microspheres, which are sometimes metal-coated to absorb radio signals.

On the other hand, radio-transparent plastics are essential for applications like antennas. Some rooftops feature large white fiberglass domes housing antennas that must transmit or receive signals in all weather conditions. Fiberglass walls are ideal for these applications since they do not absorb radio waves.

Enhanced material properties

Enhanced material properties are crucial in aviation, aerospace, electrical engineering, and motor manufacturing, where materials must withstand high temperatures. For example, parts of the Sapsan train motor reach temperatures up to 250 °C at cruising speed. Materials must endure such temperatures over extended periods and remain effective insulators with low dielectric permittivity.

Radiation-resistant plastics are essential in nuclear energy. Using polyethylene or PVC cable sheaths like those found on regular desk lamps would quickly lead to equipment failure. This issue was notably severe during the Chernobyl disaster when electrical equipment malfunctioned due to plastics that couldn’t withstand high radiation doses.

A significant challenge for polymer composites is adhesion strength—the ability of dissimilar surfaces to bond. If fibers don’t adhere well to the matrix, the material will fracture along the boundary, weakening the entire component. When the material carries heavy loads, maximum adhesion is crucial. Chemical and physical methods are available to activate surfaces and improve the bond between matrix and fiber.

A promising development in composites is the creation of fire-resistant materials. Coatings that prevent entire buildings from igniting in a fire, even under high thermal loads, are essential. Many traditional interior polymers—like PVC paint, linoleum, or furniture made from polyurethane foam—emit toxic gases when burned, which can be a lethal hazard in fires. Fire-resistant composite coatings are already used in the new Vityaz metro cars. The transportation and construction industries are set to undergo a significant revolution by introducing fire-resistant polymer materials, which must be prioritized in sectors with a high risk of man-made disasters.

Nanocomposites 

One of the most promising directions in materials science today is the development of smaller-scale structures, the search for environmentally compatible materials, and adapting natural resources. Composites have also followed this trend, giving rise to nanocomposites.

In a nanocomposite, one of the material components—either the matrix or the filler—contains particles measuring less than 100 nanometers. When this scale is achieved, the material qualifies as a nanocomposite. Fillers are often various nanoparticles, both organic and inorganic, such as carbon, metal, and oxide nanoparticles, nanotubes, graphene-like structures, and even biostructures, ranging from biofibers to DNA or RNA chains, which measure just a few nanometers when folded.

The final material’s properties can change significantly thanks to the nanostructured component’s ratio of surface atoms to volume atoms. In addition to enhanced physical and mechanical properties, nanocomposites can offer improved electrical, thermal, optical, electrochemical, and other attributes, including biocompatibility.

While the physical-mechanical properties of traditional composites are crucial for creating large parts or structural elements, such as airplane wings, adding nanostructures to these composites can help enhance their properties. Nanofibers, metal nanorods, and carbon or boron nitride nanotubes can reinforce polymer composites. If evenly dispersed and not clumped together, nanoparticles mixed into resin can dramatically improve the composite’s physical-mechanical properties, making it significantly more robust. Nanoscale particles also have a large surface area, positively affecting adhesion to other materials. Even with a small percentage of nanoparticles, physical and mechanical properties can improve considerably.

There is also the concept of the “percolation threshold.” When this threshold is reached, a network of interlinked nanorods forms. If all technical processes are carefully controlled to reach the percolation threshold, the nanorods bond with the resin and interconnect, acting as an additional reinforcing component.

Polymers and metals can be enhanced with nanotubes, nanofibers, or other nanoparticles. In metals, nanoparticles disperse well and create reinforcing networks, enhancing material strength, corrosion resistance, and electrical conductivity. Such materials are primarily used for military applications, including armor production.

Shortly, nanocomposites will likely see broad use in medicine for targeted drug delivery, sensors, implants, and more. For instance, a composite system of polymer and nanoparticle could carry a drug, releasing it when it reaches a targeted area in the body; an external stimulus breaks down the polymer, delivering a high dose to the specific location, such as a tumor. This therapeutic nanocomposite could access parts of the body that conventional drugs cannot reach.

There’s also a significant trend toward biodegradable materials, including eco-friendly packaging and wound-healing materials. With nanostructuring, it’s possible to develop environmentally safe, fire-resistant materials, addressing key challenges in construction.

Smart materials 

Another important direction in the future of materials science is “smart” materials, which can controllably change their properties in response to external stimuli like pressure, heat, or electrical signals. Modern innovative materials can change shape and even “heal” cracks—self-repairing after damage.

Smart materials have been around for quite some time. For example, piezoelectrics, used in lighters, are a type of smart material: piezoceramics generate an electric spark under pressure.

Since the 1970s-1980s, smart materials have been used in medicine, particularly shape-memory alloys like Nitinol. These alloys are used in surgical tools and minimally invasive procedures, where they can expand or contract blood vessel walls or help extract a stone from the ureter. Wire shaped in any form will return to its original shape at a specific temperature. A cooled wire can be inserted into a blood vessel, and the body’s warmth will cause it to expand, opening the vessel and restoring blood flow.

Smart materials have also enabled self-adjusting implants, which can be inserted through a small incision and then unfolded to fit perfectly into a bone defect.

Thanks to aerospace funding to develop aircraft surfaces that can be repaired after damage, self-healing materials have advanced rapidly. This technology is also valuable for military applications; for instance, if a fuel tank is punctured, self-healing materials could seal the hole and prevent fuel leakage. Self-healing paints could prevent rust from forming on small scratches in the automotive industry. Current applications of self-healing materials include surfaces for electronic devices, such as phone screens, that can “heal” scratches and cracks.

Smart materials also include strain-sensitive sensors that detect overloads and adjust the material’s properties accordingly, which is especially useful for load-bearing structures.

The future of smart materials lies heavily in aerospace. This includes self-deploying modules that can be transported to orbit in a compact form and then unfold in space without complex mechanisms. Organizations like NASA and DARPA are heavily invested in these developments.

Civilian aircraft could also benefit from adaptive components, like wing sections with variable aerodynamics. Flaps can move up and down via mechanical systems, but smart materials could dynamically adjust the entire wing configuration.

Flexible polymer robots, a concept on the cutting edge of science that is gradually becoming practical, can change their shape and be used in rescue operations. They fit into tight spaces and then unfold to locate survivors. Smart materials represent a vast and long-standing field of research with an even broader future ahead.