Carbon-Fiber-Recycling Strategies: A Secondary Waste Stream Used for PA6,6 Thermoplastic Composite Applications

With a view to achieving sustainable development and a circular economy, this work focused on the possibility to valorize a secondary waste stream of recycled carbon fiber (rCF) to produce a 3D printing usable material with a PA6,6 polymer matrix. The reinforcing fibers implemented in the research are the result of a double-recovery action: starting with pyrolysis, long fibers are obtained, which are used to produce non-woven fabrics, and subsequently, fiber agglomerate wastes obtained from this last process are ground in a ball mill. The effect of different amounts of reinforcement at 5% and 10% by weight on the mechanical properties of 3D-printed thermoplastic composites was investigated. Although the recycled fraction was successfully integrated in the production of filaments for 3D printing and therefore in the production of specimens via the fused deposition modeling technique, the results showed that fibers did not improve the mechanical properties as expected, due to an unsuitable average size distribution and the presence of a predominant dusty fraction ascribed to the non-optimized ball milling process. PA6,6 + 10 wt.% rCF composites exhibited a tensile strength of 59.53 MPa and a tensile modulus of 2.24 GPa, which correspond to an improvement in mechanical behavior of 5% and 21% compared to the neat PA6,6 specimens, respectively. The printed composite specimens loaded with the lowest content of rCF provided the greatest improvement in strength (+9% over the neat sample). Next, a prediction of the "optimum" critical length of carbon fibers was proposed that could be used for future optimization of recycled fiber processing

Different Production Processes for Thermoplastic Composite Materials: Sustainability versus Mechanical Properties and Processes Parameter

Up to now, fiber-reinforced composites with thermoplastic matrix have seen limited fields of use in the structural scope due to their high viscosity in the molten state, which results in poor impregnability of the reinforcement, leading to mechanical properties of the finished product that are not comparable to those of thermosets. Although the latter still dominate the various sectors of automotive, aerospace, transportation and construction, new applications involving the production of thermoplastic composites are growing rapidly, offering new approaches to the solution of this problem. The aim of this work is to study and evaluate the state of the art on the manufacturing processes of thermoplastic matrix composite, analyzing the parameters that come into play and that most influence the process and material performance. The advantages of film stacking and powder impregnation techniques are contrasted by the versatility of hybrid fabrics and, at the same time, parameters such as pressure and temperature must be carefully considered. A description of different thermoplastic composite processes such as powder impregnation, film stacking molding, hybrid woven fabric, hybrid yarn and products follows, which represent the current possibilities to move from a thermosetting matrix composite to a thermoplastic one, upon which the concept of sustainability is based. This article wants to present an overview of research that has been done in manufacturing thermoplastic reinforced composites and will serve as a baseline and aid for further research and development efforts

Green2 composite: green resin for green composite

The present proposal is focused on the chemical recycling of the bioepoxy matrices for composite. The approach I propose in this article is aimed to bridge the gap between the industrial and academic development by focusing on those methods which are most relevant from a technological, sustainable and economic point of view. The project aims to develop, characterize and evaluate a possible use of an eco-friendly and recoverable chemically epoxy resin, used with a recycled reinforcing carbon fibres, with the aim of obtaining a mechanically performing and completely green composite. Differences between composite specimens made with classic epoxy resin matrix and bio-based epoxy resin formulation respectively, both reinforced with recycled carbon fibres, will be analysed. Then, it will be evaluated which mechanical properties can be achieved by the completely green composite. Several characterization techniques supported by mechanical testing and dynamic mechanical analysis (DMA) will be used

Thermoplastic Composite Materials Approach for More Circular Components: From Monomer to In Situ Polymerization, a Review

To move toward eco-sustainable and circular composites, one of the most effective solutions is to create thermoplastic composites. The strong commitment of world organizations in the field of safeguarding the planet has directed the research of these materials toward production processes with a lower environmental impact and a strong propensity to recycle the polymeric part. Under its chemical properties, Nylon 6 is the polymer that best satisfies this specific trade-off. The most common production processes that use a thermosetting matrix are described. Subsequently, the work aimed at investigating the use of thermoplastics in the same processes to obtain comparable performances with the materials that are currently used. Particular attention was given to the in situ anionic polymerization process of Nylon 6, starting from the ε-caprolactam monomer. The dependencies of the process parameters, such as temperature, time, pressure, humidity, and concentration of initiators and activators, were therefore investigated with reference to the vacuum infusion technique, currently optimized only to produce thermosetting matrix composites, but promising for the realization of thermoplastic matrix composite; this is the reason why we chose to focus our attention on the vacuum infusion. Finally, three production processes of the polymeric matrix and glass fiber composites were compared in terms of carbon footprint and cumulative energy demand (CED) through life-cycle assessment (LCA)

Nickel intolerance disease: surface modification of a zeolite for direct human assumption and cultivation eco-sustainable strategy

The presence of nickel in environments dedicated to the cultivation of nickel-fixing fruit and vegetables determines non-negligible concentrations of this element in food. Furthermore, its widespread use in the metal and electronics industry makes human exposure to nickel practically inevitable. The toxicity of this metal is widely demonstrated, and in thousands of clinical cases and targeted tests, it has been possible to find a sensitivity to nickel by more than 5% of the population. This project proposes two solutions to the problem in which the use of zeolites is foreseen. The first consists of the intake of alimentary zeolite as a detoxifier from heavy metals, and the second is based on a nickel-free diet, possible thanks to the products of aeroponic agriculture. The properties of molecular sieve, together with those of a size and a chemical-physical composition compatible with the gastrointestinal tract, are present in a particular form of zeolite called clinoptilolite. The use of this substance, suitably modified to increase its ion-selectivity, as a food supplement prevents, through adsorption and ion exchange, the accumulation of toxins, free radicals, and heavy metals, including nickel. A definitive solution to the problem of nickel sensitivity lies in the upstream elimination of this metal from the fruit and vegetable production process thanks to the use of aeroponic cultivation systems. This system consists of the growth of plants in ideally isolated environments in which the water used can be treated with zeolite to remove nickel. These conditions allow for more controlled, efficient, and nutritionally safe growth of foods with a saving of water (90-95% less), nutrients and soil (80-90% less) compared to classic agriculture. In both cases, the adsorption efficiency of the zeolites strictly depends on the degree of crystallinity. According to the most recent studies, high purity clinoptilolite is synthesized through the sol-gel method, with structure directing agent (SDA), combined with the hydrothermal method where silica dioxide is the source of silicon and aluminium hydroxide is that of aluminium. The possibility of synthesizing clinoptilolite with a high degree of crystallinity and with specific adsorption functions within the gastrointestinal environment and in aeroponic cultivation plants would make an effective contribution to the goals of 2030 Agenda in terms of nutrition improvement, water saving, sustainable models of production and mitigation of climate change

Performing composite materials: thermoplastic matrix for more circular components, from monomer to in situ polimeryzation

To move towards eco-sustainable and circular materials, one of the most effective solutions is to create thermoplastic composites. The strong commitment of world organizations in the field of safeguarding the planet has directed the research of these materials towards production processes with a lower environmental impact and strong propensity to recycle the polymeric part. The will to produce a composite with a thermoplastic matrix lies in its intrinsic value nature, which is the òpposite of thermosetting one, that is the possibility of recycling the material: the thermosetting polymer, such as epoxy resin, certainly guarantees the best mechanical characteristics, but once that the material has finished its function, it cannot be reworked and reused for other pùrposes. Up to now, indeed, incineration and landfilling are the main approaches for disposing of composite wastes. These routes, however, are not viable tools in view of the strong expected growth in waste production because they completely discard the related environmental impact, the waste accumulation of composites and they especially imply the loss of all the high-added value. On the other hand, the thermoplastic polymer can undergo a softening process which allows to obtain again a melt capable of being subjected to a new type of processing with a new purpose. What is being studied in recent times is the search for the application and implementation of impregnation processes used for thermosetting matrix composites towards thermoplastic matrix ones. The attempted infusion methods involved the use of an already polymerized thermoplastic matrix which was brought back to the molten state by applying heat, subsequently proceeding with the impregnation of the fiber fabrics. The problem encountered, however, lies in the difficulty of the actual impregnation due to the high viscosities of the thermoplastic polymers in the molten state. Under its chemical properties, Nylon 6 is the polymer that best satisfies this specific trade-off above all thanks to its precursor, Ɛ-caprolactam, a molecule that melts at about 70 °C which allows to obtain a liquid phase characterized by similar water viscosity. With this low viscosity it is possible to obtain a potentially optimal impregnation of the fibers, with subsequent reaction activated by the increase in temperature. The solution, therefore, lies in in-situ polymerization precisely because it no longer allows starting from a polymer, in which macromolecules are already formed, which results in high viscosity and process temperatures from 170 °C up to 200 °C, but from monomers which therefore allow a process not too far from those already known for thermosetting. However, it will be necessary to move towards an optimization of the process parameters and, consequently, of the impregnation phase, guaranteeing a greater homogeneity of dispersion of the reactive mixture and a better adhesion between fiber and matrix, aiming at the study of sizing compatible with thermoplastics matrices. These resolutions will lead to the real goal, which is the production of performing composite materials with a thermoplastic matrix, with increasing volumetric quantities of reinforcement, up to values equal to 40%, allowing a true comparison, in terms of both the quantity of filling and mechanical properties, with composite materials with a thermosetting matrix. It is a fact that, when taking into account factors such as climate change, global warming, environmental sustainability and circular economy, the landfill or incineration of composites wastes must be avoided. The future research studies must be focused on the following points: the production process and the chemistry of the matrices to obtain a performing thermoplastic matrix composite, with mechanical–functional characteristics suitable for completely replacing thermosetting agents; the use, recovery, and disposal of thermosetting and thermoplastic composites which re-enter the circulation to obtain manufactured articles; evaluation of the potential to close the life cycle loop of composites and reducing energy consumption and recycling cost. Thanks to the intelligent reaction and research of different groups around the world, the future looks bright for new possibilities

Valorization of a secondary stream of recycled carbon fibres in concrete application: compatibility, performance, and compounding optimization

Downcycling synthetic fibre waste for reinforced concrete in the construction sector can provide mutual benefits for both industries due to not only alleviating the strain on the environment and socio-economic impact but also enhancing the properties of the cementitious material. Incorporating carbon fibres to develop fibre-reinforced concrete (FRC) is an attractive route in enhancing some engineering performance for better applicability of the material, including mechanical strength, post-cracking behaviour, shrinkage mitigation, and thermal resistance. In the framework of eco-sustainable design of construction materials, this work dealt with the viability of engineering cementitious mixtures with scrap carbon fibres (sCF) deriving from an industrial thermal recycling processing of waste carbon-fibre composites. Due to the agglomerate-like structure of the recycled fraction, the main criticality that emerged in the manufacturing stage was to ensure adequate dispersion of the reinforcement in the matrix. Therefore, in this work, a de-agglomeration treatment of the fibres by nanoclay slurry was developed. Nanoclay-based functionalization aimed to ensure a more homogeneous distribution of the reinforcement while providing pozzolanic activity for concrete improving its microstructural characteristics. In the present research, different contents of sCF were implemented (from 0.25 w/w% to 1 w/w%) with respect to the amount of cement binder, studying FRC mix designs with and without nanoceramic treatment. The influence of the reinforcing fibres as well as the compatibilizing effect of nanoclay were investigated by a multi-methodological experimental analysis including, rheological tests, mechanical characterization, and microstructural assessment. The graphical abstract in Figure 1 illustrates the main phases of the research activity proposed in this study