Polymer Matrix Composites

What is a Polymer Matrix Composite?

A polymer matrix composite (PMC) is a composite material composed of a variety of short or continuous fibers bound together by an organic polymer matrix. PMCs are designed to transfer loads between fibers of a matrix. Some of the advantages of PMCs include their lightweight, high stiffness, and their high strength along the direction of their reinforcements. Other advantages are good abrasion resistance and good corrosion resistance.

Polymers that are often used as composites are either thermoplastic polymers, thermosetting polymers, or elastomers. Polymers, which are a source of a wide variety of low-priced raw materials, offer many advantages. These include low specific weight, enhanced stability against corrosion, improved electrical and thermal insulation, ease of shaping and economic mass production, and attractive optical properties, e.g. fiber optics, glazing applications, etc. However, they suffer from some serious shortcomings:

• exhibiting, quite often, poor mechanical stiffness and strength, and poor resistance against heat

• being sensitive to aging i.e. change of the physical, chemical, and mechanical properties by light, heat, oxygen, and moisture

• being combustible

• exhibiting large values of coefficient of thermal expansion, which can generate high levels of internal frozen-in stresses.

Polymer matrix composites are classified based on their level of strength and stiffness into two distinct types:

• Reinforced plastics - confers additional strength by adding embedded fibrous matter into plastics

• Advanced Composites - consists of fiber and matrix combinations that facilitate strength and superior stiffness. They mostly contain high-performance continuous fibers such as high-stiffness glass (S-glass), graphite, aramid, or other organic fibers.

Properties of a polymer matrix composite

Compared with conventional materials, composites offer:

• lightweight

• high specific strength and stiffness

• high toughness (impact strength)

• damping ability (attenuates noise and vibrations/shocks)

• high fatigue resistance (improves fatigue life)

• corrosion resistance

• low and controllable coefficient of thermal expansion (CTE) (i.e. good dimensional stability)

• ablative shielding

• non or low conductivity

• thermal insulation

• visual attractiveness

• reduced machining

• part consolidation: allows a reduced number of assemblies and fasteners

• ability to manufacture complex shapes and one-offs from low-cost tooling

• damaged structures can be easily repaired

• potential to tailor mechanical and thermal properties, particularly by suitable fiber orientation/

• arrangement.

Polymer matrix materials

• Thermosets

The most common matrix for PMCs; is cheaper than thermoplastics. Higher stiffness is advantageous. In order of increasing performance, and cost:

• Polyesters

Unsaturated polyesters will cross-link in the presence of accelerators to form a rigid structure. Some restrictions on their use as styrene can be released during curing. Low cost means generally only used with cheaper reinforcement such as glass.

• Vinyl esters

Much better mechanical properties and environmental resistance than polyesters. More expensive.

• Epoxy resin

Usually made by mixing two liquid components resin + 'hardener'. Polymer cures by forming chemical cross-links between polymer chains. Good mechanical properties (strength, toughness, high modulus), good environmental resistance. Maybe more than twice as expensive as polyesters or vinyl esters. Used principally with carbon, glass and aramid fibres. 

• Thermoplastics

Advantages over thermosets: Short-fibre composites can be made by conventional thermoplastic processing Greater potential for high-grade recycling Tougher matrix Parts can be joined by welding (using heat and pressure) Examples: PEEK (poly-ether-ether ketone); PES (poly-ether-sulphone): High cost, high performance; used with carbon fibre or aramid. Polypropylene with chopped glass fibre, for low-load automotive applications. Nylon with chopped glass fibre: electrical, automotive parts

What is a PMC used for?

PMCs are regarded due to their low cost and straightforward fabrication methods. Applications for PMCs include :

Automotive industry - Body panels, leaf springs, driveshaft, bumpers, doors, racing car bodies, and so on.

Aircraft and aerospace industry - Used in the construction of structural parts for military aircraft, space shuttles, and satellite systems. The main purposes of using PMCs are to reduce aircraft weight, which can improve its performance, and to reduce its costs.

Marine - Fibreglass boat bodies, as well as canoes and kayaks.

Sports goods - Used in performance footwear, sports equipment, and other sporting goods because of their lightweight and high-strength properties.

Biomedical applications - Medical implants, orthopedic devices, MRI scanners, X-ray tables, and prosthetics.

Electrical - Panels, housing, switchgear, insulators, and connectors. It also covers electronic devices like capacitors, Li-ion, and flexible batteries and covers for digital portable equipment like headphones, etc.

Protective equipment - Since polymer matrix composites can withstand extreme hot or cold and other hazardous conditions, they are often made as raw materials for bulletproof vests and other armor.

Industrial - Chemical storage tanks, pressure vessels, pump housing, and valves. PMCs are also used in impellers, blades, blower and pump housings, and motor covers.

Structural - Polymer matrix composites are used to repair bridges and other construction materials and equipment like booms and cranes.

Conclusion 

Polymer Matrix Composites have revolutionized industries with their exceptional properties and applications. As technology continues to advance, PMCs will play an increasingly vital role in creating lightweight, durable, and cost-effective solutions for a wide range of sectors. Embracing the future of advanced materials means embracing the potential of Polymer Matrix Composites.

Frequently Asked Questions

Are PMCs environmentally friendly?

Yes, PMCs can be environmentally friendly when used in applications that reduce energy consumption and emissions, such as lightweight components in transportation.

Can PMCs replace traditional building materials?

While PMCs offer advantages like durability and weight reduction, they may not entirely replace traditional materials in all construction applications due to cost considerations.

Are PMCs recyclable?

Some PMCs can be recycled, especially those made with thermoplastic matrices. Recycling options are expanding as technology advances.

How are PMCs tested for safety?

PMCs undergo rigorous testing for various factors, including mechanical properties, heat resistance, and chemical compatibility, to ensure their safety in specific applications.

What is the future of PMCs in the aerospace industry?

PMCs will continue to play a pivotal role in aerospace, reducing aircraft weight and enhancing performance while lowering production costs. Advances in composite technology will further drive their adoption in this industry.