Today, the manufacturing of composite materials is in full development and innovation with a view to the future of plastic.
The industry in this specific sector invests a large number of hours in manual processes, in which production costs are high and process repeatability is difficult to achieve. Therefore, finding advanced technological processes is key to achieving the production volumes, costs and characteristics of conventional materials.
Another of the main problems of composite materials is their recyclability. This is because the type of polymer used as resin in most applications is thermoset. This material degrades when it reaches a certain temperature, which makes it impossible to recycle by melting it.
On the contrary, thermoplastic materials are capable of melting without losing their mechanical properties; however, these are generally lower than those found in thermosets.
With respect to commonly used reinforcing materials such as fiberglass, carbon fiber or aramid, they have expensive and unecological production processes. Likewise, its recyclability is complex.
Below, we present the trends of processes and materials in development that respond to some of the questions proposed above and are a reference in innovation of composite materials.
But before delving into the future of composites, don’t forget to read the article on the “History and evolution of composite materials” to learn all the details of the evolution of these materials and gain a more complete perspective.
AUTOMATED FIBER PLACEMENT (AFP)
Automated fiber placement, known by its acronym in English as AFP, is an advanced, automated method of manufacturing composite materials.
This process consists of heating and compacting non-metallic fibers pre-impregnated with synthetic resin in generally complex tooling mandrels . The fiber is commonly found in the form of “tow” or cable, which is typically carbon fiber impregnated with epoxy resin. The threads are fed to a heater followed by a compaction roller in the head of the FPM and by movements exerted by a robot arm the threads are placed along the surface of the mold. Generally, carbon threads are placed in orientations of 0º, 45º, -45º and 90º to form layers that, in combination, have good properties in all directions.
Automated fiber placement machines are a recent development within composite manufacturing technologies. They aim to increase the ratio, precision and repeatability of the production of advanced composite parts.
AFP machines place fiber reinforcements on molds or mandrels in an automated manner and use a series of narrow threads (typically up to 8 mm) of thermoset or prepreg thermoplastic material to form different layups.
This technology allows for better precision and increased deposition rates compared to manual processes by experienced laminators. However, this rate does not reach the levels of ATL (automated tape laying) machines, which are only capable of producing composites with simpler geometries. In contrast, the level of complexity enabled by AFP technology is incredibly high.
CONTINUOUS FIBER 3D PRINTING
Additive manufacturing systems for composite materials have recently been developed. To achieve this, it has been necessary to integrate an FFF (fused filament manufacturing) machine together with a thermoplastic AFP machine.
In this case, the resin to be used is a thermoplastic polymer because it is necessary to melt the material to carry out this technology. Remembering that thermostables degrade at certain temperatures, while thermoplastic materials melt before degrading.
In this case, high-performance thermoplastics are used combined with different types of fiber reinforcement.
This machine is capable of printing soluble materials used to create supports or mold parts, continuous fiber ribbon and fiber in chopped format.
The first step consists of depositing the soluble material on the printing base, on which the robot will print the fiber reinforcement with the thermoplastic resin melt. The material is consolidated directly, compacting it in the process. In the case of the reinforcing tape, it is laser welded to the support material.
The properties achieved with this technology are very competitive and the porosity of the final piece can be compared with autoclave production.
CONTINUOUS FIBER INJECTION
The EURECAT company has developed a system in which the continuous fiber is injected at the same time as molten thermoplastic resin . To do this, it is necessary to create tubular cavities or hollow molds of small diameter to pass the material through them.
For this technology, it is important to know the curing parameters of the composite material, since it must be verified that it reaches all the designed points.
Once cured, the resin solidifies and unifies all the material together with the cavity in which it is located.
This allows the creation of highly optimized parts made of very light materials reinforced only at their critical points by high-performance composite material ribs.
ADDITION OF GRAPHENE IN PLASTIC MATERIALS
Graphene is composed purely of carbon molecules, with its atoms arranged in a regular hexagonal pattern. This material offers a very high resistance value, so adding a weight percentage of only 0.5% with plastic materials can improve the rigidity by up to 2.5 times and the tensile strength of these materials by 15%. .
VITRIMERS
In response to this major drawback, a material called Vitrimer has been developed. This material is highly cross-linked, like thermosets, offering the associated good characteristics.
However, unlike thermosets, which have a permanent fixed shape after curing, the chemistry of vitrimers results in a product that can be remolded.
Vitrimers consist of molecular chains linked by strong covalent bonds. The main difference with thermosets is that, thanks to exchange reaction processes, covalent bonds become reversible when heat is applied.
This means that at high temperatures the viscosity of the material decreases, making it capable of flowing. When it cools, the viscosity increases again, behaving like a soft solid with characteristics and properties similar to those of thermosets.
Therefore, this material allows them to be malleable after having been completely cured and remodeled by working at a specific temperature.
A very interesting application is that of pieces that can self-heal on their own. By applying a certain temperature to the area in question, the material will flow enough to harden again in its position.
MACRO FIBER COMPOSITES
These smart composite materials are not alive, but they are capable of “feeling” and moving. It is a material developed by NASA in 1999, which consists of a laminate of rectangular piezoelectric rods sandwiched between layers of adhesive, electrodes, polyamide films and structural epoxy.
The electrodes are adhered to the film in an interdigital pattern that transfers the applied voltage directly to and from the ribbon-like rods. So this set allows in-plane polarization, actuation and detection.
MFC can also be adhered (usually glued) as a thin film to the surface of various types of structures, or embedded in a composite structure. If tension is applied, it works as an actuator and will bend or distort materials, counteract vibrations or generate them. If no voltage is applied, it can function as a very sensitive strain gauge, detecting deformations, noise and vibrations.
The MFC is also an excellent device for harnessing the energy of vibrations; on a large scale it could be used as a useful electrical energy recuperator.
Using all the properties that these materials offer us, we can achieve intelligent parts and materials necessary for the emergence of industry 4.0 in the plastic materials sector.
NATURAL FIBERS
The use of natural fibers is growing significantly in the polymer industry due to the trend in the search for biocompatible, reusable and ecological materials.
The cost of processing this type of reinforcement is generally low, on the contrary, its mechanical properties are also low. However, hybrid fibers (understood as a mixture of synthetic and natural) can offer very competitive characteristics.
The most common fibers used in the manufacture of composite materials are: Hemp, Linseed, Jute, Agave, Coir and Gomuti.