A pre-preg is a semi-finished material used in the manufacture of high-performance composite parts. It refers to fibres “pre-impregnated” with a plastic or rubber resin system.
Making composite parts from pre-preg allows for a higher ratio of fibre vs resin when compared to other composite manufacturing methods, resulting in higher mechanical strength. It also allows consistent and repeatable parts to be manufactured, and is favoured for demanding applications such as aerospace and motor sport, as well as lightweight composite armour.
How are composite pre-pregs manufactured?
Composite pre-pregs can be manufactured from many types of fibre including glass, carbon and aramid but also natural plant-based fibres such as cotton or flax. The resin can be a range of thermoset, thermoplastic or rubber materials. The choice of fibre and resin allows a wide range of different properties to be achieved in the final part.
As an advanced material solution, Permali typically uses formulations based on epoxy resin for high-strength or electrical insulating applications, and phenolic resin for fire resistance or ballistic properties. In both cases, Permali develops its own proprietary resin blends by adding various additives or fillers to improve properties such as strength or flammability performance. By having full end-to-end control of the materials and manufacturing processes, Permali is able to optimise the performance of the final product. We can make to a maximum width of 1.9m and generally up to 840gsm, however we can be accommodating for bespoke requests. Most commonly we use the fibres; E-glass, S-glass, Aramid and Polyester. It is also possible to use Nylon, Basalt or Cotton in some cases. Our forms are yarn-based fabric, woven roving, tissue and stitched bi-axial.
The impregnation process involves taking rolls of fabric and passing them through a bath of the resin, and then rollers and scrapers that control the resin content. The wet fabric carrying the resin is then passed through an oven to evaporate solvent, and the solvent is then neutralised in the solvent abatement equipment. The resin may also be partially cured in the oven, in a process known as “B Staging”. The B Staging affects how much the resin flows during subsequent manufacturing processes.
Once the composite pre-preg is manufactured, the next step is to consolidate and cure one or more layers under heat and pressure. There are several ways of applying heat and pressure, including laminating in a heated platen press, or in an autoclave. Autoclaves operate at lower pressures than platen presses, and so require more resin flow during the cure cycle. For this reason, pre-pregs for autoclave manufacture have low levels of B Stage and are “tacky”. Pre-pregs for platen pressing under higher pressures generally have higher levels of B Stage and less flow, which gives the advantage of a longer shelf-life and less demanding storage conditions.
Applications of Pre-pregs
Pre-pregs are an important component in the manufacture of high-performance composite parts. They offer maximum strength, high quality and consistent performance and are the material of choice for applications such as aircraft interiors and racing car chassis. Use in other critical parts such as aircraft primary structures, automotive bodywork and train structures is expanding rapidly, and the increasing availability of natural fibres and bio-resins allow “green” composite parts to be manufactured.
A composite material, commonly shortened to composites, describes material that results from at least two other components, often to form one with superior properties. Yet, despite this bonding, in composites the constituent components are still distinctly identifiable. Traditional materials may serve a limited range of applications, whereas compositional materials are more suitably adapted to address various, often taxing, environments. More advanced than the constituents, composites take on new properties such as strength, stretch, durability, lightness, or resistance to moisture, or electricity, or corrosion.
The resulting composite creates a superior material that is tailored for more advanced applications. Composites can, for example, be engineered to answer the safety critical demands of high-speed motorsport. Another example of superior performance, barrier fabrics and textiles, subjected to hard compliance by the FAA, represents a more advanced application of composites to enhance aerospace activities.
Structure of composites
Composites can be identified based on their structures, or assembly, which can be engineered in different ways to result in unique properties. These commonly include:
Those reinforced with particles
Those reinforced with chopped strands
What are the common types of composite materials?
Though there are many, some more familiar examples of composites include:
Composites woods like plywood
Created from thin layers of overlapping wood, plywood is one of the earliest examples of a composite material. As a common application, these can appear in everyday scenarios from small DIY projects to larger structural ones.
Reinforced plastics like fibreglass
A common composite where a polymer matrix is reinforced with fibres. Due to its versatility, its applications can range from industries like aerospace to ballistics.
From adding in reinforcements, concrete can be strengthened through steel, polymers and other alternative composites. For more advanced applications, reinforced concrete nowadays feels necessary in building projects, like construction.
Ceramic matrix composites
Commonly a subgroup of both ceramics and composites, these consist of ceramic fibres in a ceramic matrix.
Metal matrix composites
A composite that is composed of at least two constituents: one is a metal, and the other can be another metal, ceramic, or other compound.
Advanced Applications of Composites
From motorsport to aircraft, aerospace and military application, composites have grown in popularity to answer to the demands of a modern world transitioning into the future. As progressive characteristics are engineered, a composite material becomes uniquely custom to address the pressures and demands of new and exciting industries, which are often those pushing boundaries.
Though it takes an engineer’s trained eye to spot, the applications of a composite are broad and varied, including:
Land defence applications: popular ballistic technology has been historically serving the safety of deployed troops and other ground military activities.
Energy provision: mission critical to the cultivation of high energy resources, composites provide safety and protection amidst these demanding environments.
Automotive: similar to other applications, composites fortify safety protocol, but also enhance performance.
What are the constituents of a composite?
Reinforcement fibres can either be classified as a natural fibre (a mineral, for example) or a synthetic one (such as glass). Comparatively, glass fibres are the most popular reinforcement fibre. Its common applications usually target larger, if cost-effective, constructions, such as ships and wind turbines. An example of modern composites – and widely known as the original fibre reinforcement – fibreglass was largely embraced as a textile reinforcement. After continued innovation, fibreglass grew in recognition in the larger global composites market in the US and beyond.
Examples of fibres
The outcome of a fibres properties is shaped not only by the manufacturing process, but the constituent materials and chemistries used.
Other natural fibres
When thin strands of silica-based material, lime, alumina and magnesia are heated in a furnace at about 800oC, imparting a viscosity-like consistency into the paste. As the temperature rises, the impurities disappear from the glass, which is then passed along as a transparent mass. Pressured through dies, or platinum plates with small holes, fibres are extruded with small diameters of 5-24μm (the thinner the diameter, the less irritant the product feels against skin). This is produced as glass thread, which is ‘sized’ and dried. This is known to be particularly useful for its insulated and resilient properties, especially to high temperatures.
Other types of glass include:
AR glass (alkali resistant)
Glass fibres that are textile-grade are produced from silica (SiO2) sand that’s put under high heat and then cooled. The dynamic between quick cooling rates and risen temperatures, essentially applied heat, results in glass. SiO2 brought to 1720oC, then cooled off, prevents crystallisation which is essential in the formation of glass.
Unlike the lower-costing glass fibres, carbon fibres are engineered to bolster performance-based activities. Progressively more everyday in automotive use, carbon fibres have been used in aerospace applications too. Carbon fibre, also known as graphite fibre, is made form thin crystalline filaments of carbon, twisted and strengthened. It has a greater strength and stiffness than steel, though is lighter weight.
Aramid fibres (aromatic polyamide) is a strong contender for any activity where impact resistance is desired, such as armour and defence. It has a specific type of strength, owed to a low density.
Resins found in composites
Resins, as in composites, are polymers and come in two major groups: thermosets and thermoplastics.
Thermoset resins – They feature in the majority of composites, and go through a process called polymerization (sometimes cross-linking), moving from a liquid state into a solid. Thermosetting resins are, then, ‘cured’ through a catalyst or heat. Common examples include polyester, vinyl, and epoxy. They exhibit a useful chemical resistance, amongst other mechanical properties.
Thermoplastics – Known for their malleability, thermoplastic resins are recognised for being able to be shaped and reshaped whilst semi-fluid, before returning to a rigid form upon cooling. Common examples range from nylon, PP, and PET – whilst higher performing include PEI or PEEK.
Unsaturated polyester resins (known as UPR) are the most applied in the composites industry. Yet, epoxy resins have a reputation for yielding a variety of performances to match its demand. Resins exist across a variety of systems.
Improving composites with Fillers, Additives & Reinforcements
Fillers materials can improve certain properties, often enhancing a material, whilst reducing its cost (as fewer resins are required). Popularly, fillers are used in everyday applications, or recipes, such as plastics, rubber, paints and even coatings. Balancing additives and filers, material can be engineered with agents that introduce strength and toughness or UV absorption.
What are Intermediate Materials?
Some manufactured commodities require further processing, such as fibres which are engineered into fabrics – whether through knitting, braiding, or needle punched, or woven. Composites, through the likes of textile engineering and other manufacturing, can become more deliberate, if precise, in how they are optimised.
A prepreg is shorthand for a (reinforcing) fabric that has been impregnated with a resin system, such as carbon fibre. Prepregs come ready for curing as tape, cloth, or mat sheets. Typically, prepregs have thermostats that can severely shortened, or limit, the shelf life when exposed to room temperature.
Composites can be expertly engineered and manufactured to address the demands and challenges of many advanced industries. Delivering bespoke material solutions, Permali has a history and reputation for making composites that protect, perform, and are precise.
A composite material is the permanent combination of at least two contributory materials, often with different or competing physical or chemical qualities. A composite combines these materials to form a more superior material with improved properties.
Importantly, a composite doesn’t forfeit its original identity, but carries through its useful characteristics into the new compositional material. Where traditional materials have a defined purpose, composites can introduce new properties, such as strength, durability, reduced density, or resistance to moisture, electricity or corrosion.
Typically, the resulting composites are improved, or performance tailored versions of their constituent materials, designed to better suit their end application.
A Short History of Composite Materials
Learning from the past, composite materials have a long history of helping civilisations transform the ways they work and the outcomes of their labour. Early artisans, engineers, and ancient builders alike throughout human history have embraced composites for smarter, more efficient applications.
The earliest recorded use of composites came from the Mesopotamians in 3400 B.C. Through a small, though significant, feat of engineering, they glued thin veneers in layers to form plywood. As a brilliant example of early construction techniques improved through composites, this era was ripe for developments in the way settlements and dwellings were built.
Throughout the 12th century, Mongol warriors succeeded in crafting swifter, more precise weaponry, specifically archery, in order to defeat their enemies. A clever craft of bamboo, pine resin silk and a few other materials meant that the Mongolians were able to fortify their instruments to heighten performance and precision.
The Industrial Revolution
Not limited to construction or instrument-design, later societies experimented with composites throughout the 1800s (including a particularly curious episode with canoes). During the late 1800s, synthetic resins were introduced on the market through a chemical process referred to as “polymerisation”.
At the dawn of the 1900s, a chemist by the name of Hendrik Baekeland modernised composites through Bakelite, an early synthetic resin that found commercial use in gearshifts for Rolls-Royce. It wasn’t until the 1930s, however, that composites heralded substantial shifts. A series of breakthroughs defined the era: Owens Corning, an early engineer, helmed a process of commercially producing fiberglass, not long after launching the FRP (Fibre Reinforced Polymers) industry. This helped transition construction and other areas alike away from an era of plastics.
Throughout the later 1930s and early 1960s, experiments with composites pushed the boundaries for change within manufacturing and construction, introducing cheaper and higher performing materials and processes. Formerly experimental, composites were accelerated into commercial settings by World War II.
Not long after, there was a popular and widespread demand for composites, which grew out rapidly into an industry, touching on the likes of transport and infrastructure. Ever evolving, the composite industry, long after the Space Age of the 1970s, was launched into a constant growth, advancing on its own limits.
What are Composite Materials Used For?
Often a composite material will be created as a solution to improve the performance, functionality, or design of something. The applications of composites are wide-reaching and varied, and have been incorporated across a multitude of markets.
Composite materials, in a variety of industry-wide applications, are often bespoke in how they adapt for heightened properties of protection, performance or precision.
Composite materials for performance:
With customisable properties, the engineering of materials will often focus on how performance can be boosted, heightened or refined. The kind of sought-after properties range from agility to lighter weight, softer materials to tougher, more strengthened resistance to unpredictable environments. For example, military aircraft, especially for transport, are often subject to tough conditions. As such, they can be fortified with ballistic solutions for an added skin of armour. Cargo Lining is also a popular application of FRP Composites used in both civil and military aircraft to protect the cargo bay from damage as a result of daily loading as well as fire and smoke.
Composite materials for precision:
One of the great benefits of composite materials is how they can answer to evolving regulations. For example, aircraft are designed with custom barrier fabrics and textiles that must satisfy tough FAA safety regulation.
What are the Advantages of Composites?
Wide-ranging and varied, the beneficial properties of composites can include anything from performance modification, such as changes in the weight of materials, to the strengths and durability of a product. Typically, a composite will be customised to its application – and this will explain the benefits of a composite material.
There are many advantages to using composites, including:
Design-modifiers: improved, high performing designs.
Various tolerances: can be toughened against harsh conditions.
Weight changes: more agile, lighter weight construction.
Resistance training: ward off hurtful factors that weather materials such as water, moisture, or corrosion.
Strength: similar to resistance, composites can be customised to fortify products against harsh, tough environments.
Cost reductions: not all materials are created the same, and composites are mindful of their job more than commonplace materials like steel.
Properties of composite materials
The properties of a chosen composite will vary depending on the job it’s designed for. It could, for example, be a material reinforced to offer better strength, toughness, or resilience. Another popular example is weight reduction.
Other common properties include:
Fire or water resistance
Why Use Composite Materials?
Conventional materials have their limitations, whereas composites can focus on heightening, often superior properties to offer a bespoke solution. The goal of lighter weight, added resilience, or precision is often an attraction to many industries wanting to improve their products or processes.
A continued innovation in composites is vital to the elevation of other industries that thrive on refining how they operate. Not merely is the world a changing force, but the complexity of legislation and compliance is a challenge that composites can meaningfully address – sustainability, ethics and a changing social and cultural attitude is a pressure that shapes the materials we use.
Types of Composite Materials
Many composites inherit their new properties from a tactful and precise bonding process that teases out a greater result. For example, many composites are preceded by reinforcements, which testifies to a process of strengthening materials. These have taken common materials and engineered a stronger, more resilient sibling material.
Nowadays, common composites are abundant, if sometimes invisible, within our built settings. Reinforced plastics, woods, and metals – these processes have advanced traditional materials for better, easier, and sometimes cheaper application. Fibreglass, as an everyday composite, is the result from a careful, deliberate bonding of glass fibre with fibre-reinforced plastics. It benefits from being cheaper and with greater flexibility. Plywood, familiar with construction tasks, is another example of a reinforced material. Engineered from thin piles of wood, plywood is known for its greater strength and compositional stability.
Yet, custom solutions provide answers to more strenuous, and commercial, uses of composite materials. These are often more technically aware, such as designing materials for precise environments, or applying composites to the high pressured, unpredictable circumstances of the sea and air as well as for land use.
An expert blend of technologists, engineers, and processing specialists, Permali’s standard and bespoke prepreg grades are targeted at markets using local resin formulations. In consulting the design of materials for markets, for example, Permali’s prepregs are printed on sheets, either as a roll or determined by size.
Certain composites are more commonly engineered, depending on the demand and urgency of their application into the modern, material world. Designed to remedy weaknesses in our built environment, these composites are everyday examples of how materials evolve to answer to challenges in various industries and settings.
Composite woods like plywood are created from multi-layered wood strips glued together at angles.
Fibreglass and fibre-reinforced polymer are examples of reinforced plastics in common, everyday use that serve a greater strength and elasticity.
Reinforced concrete is the result of fortifying concrete with a higher strength material like steel.
Improved ceramic materials can be engineered, known as ceramic matrix composites. This assumes additional properties of thermal shock absorption and are fracture resistant.
Examples of Composite Applications
Custom composites are tailored to specific applications or tasks that require vital properties of strength, resilience, insulation, and many more. It takes an expert hand to apply the right knowledge and expertise to get the job done.
Practical examples include, but are not limited to:
Anti-ballistic solutions for sea, air, and ground military vehicles.
How to Choose the Right Composite Material
Composites can offer bespoke solutions for material choices that might serve to enhance the performance, precision, or protection of a product.
It’s important to understand the various goals and desires of your materials – are you, for example, looking for a stronger alternative to traditional materials? The suitability of its role is going to guide the kinds of composites you might need, which is where a custom process can be the best direction forward. There is a variety of applications that can inform the suitability of composites.
Lastly, the economics of materials is another aera to consider. More often, composites are cost-effective alternatives to traditional materials, which may not be as sustainable.
Trusted Material Solutions from the Experts
With an 80+ year history of delivering efficient and practical material solutions, Permali has an industry-leading presence across industries such as Automotive, Medical, Textile, Construction and beyond. Offering custom composites, we’re experts in extracting and refining the superior qualities from the materials we use.