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We investigated the recycling process of carbon fibre-reinforced polyimine vitrimer composites and compared composites made from virgin and recycled fibres. The vitrimer matrix consisted of a two-component polyimine-type vitrimer system, and as reinforcing materials, we used nonwoven felt and unidirectional carbon fibre. Various diethylenetriamine (DETA) and xylene solvent ratios were examined to find the optimal dissolution conditions. The 20:80 DETA–xylene ratio provided efficient dissolution, and the elevated temperature (80 °C) significantly accelerated the process. Scaling up to larger composite structures was demonstrated. Scanning electron microscopy (SEM) confirmed effective matrix removal, with minimal residue on carbon fibre surfaces and good adhesion in recycled composites. The recycled nonwoven composite exhibited a decreased glass transition temperature due to the residual solvents in the matrix, while the UD composite showed a slight increase. Dynamic mechanical analysis on the recycled composite showed an increased storage modulus for nonwoven composites at room temperature and greater resistance to deformation at elevated temperatures for the UD composites. Interlaminar shear tests indicated slightly reduced adhesion strength in the reprocessed composites. Overall, this study demonstrates the feasibility of recycling vitrimer composites, emphasising the need for further optimisation to ensure environmental and economic sustainability while mitigating residual solvent and matrix effects. [ABSTRACT FROM AUTHOR]

The continuous development of the industry of composite materials and epoxy resins requires the development of components that modify these systems. It is extremely beneficial to modify functionality by using one or two substances instead of modifying only one system parameter. Typically, this end-use will determine the key parameters of the resin system that should be modified and the modification systems designed as such. In this study, we introduce novel systems utilizing ionic liquids, strategically designed to concurrently alter multiple system parameters, including: (i) flexibility, (ii) crosslinking density, and (iii) fire resistance. The following techniques were used in the research: (i) Differential Scanning Calorimetry (DSC), (ii) Thermogravimetric Analysis (TGA), (iii) Dynamic Mechanical Analysis (DMA) and (iv) fire performance tests (UL-94, Limiting Oxygen Index and Mass loss type cone calorimetry (MLC)) to show as much dependence of material parameters on the type of modifying additive as possible. Both the cured resin and the curing process as well as a single-layer composite reinforced with carbon fiber were tested. The results show that properly designed ionic liquids are able to perform many functions in the composite material and simultaneously affect several parameters, both by lowering and increasing them. In addition, they can exhibit activity in the field of flame-retardant composites. [ABSTRACT FROM AUTHOR]

Due to strict safety regulations, the automotive industry requires an effective reduction of flammability in polymer components. Flame retardants are usually added to the polymer matrix, affecting the viscosity of the matrix. Another possible solution is the application of coatings containing flame retardants, which can additionally ensure good surface quality and protection against external influences. In our research, the flammability of reference and flame retarded gelcoat base materials was investigated using oxygen index (LOI), UL-94, and mass loss type cone calorimetry (MLC) tests. Based on the flammability tests, the best results were obtained with the gelcoat formulation containing 15%P ammonium polyphosphate (APP) and the mixed formulation containing 5%P APP and 5%P resorcinol bis(diphenyl phosphate) (RDP), with a 55% and 64% reduction in the total heat release compared to the reference gelcoat, respectively. The two best-performing coatings were applied to polypropylene (PP) samples. 15%P APP reduced the peak heat release rate of PP by 89% compared to the reference. The gelcoat formulation containing 15%P APP was applied to polyurethane (PUR) automotive components, where the coating reduced the maximum heat release rate by 53% and shifted the time to peak heat release rate by 447 s. [ABSTRACT FROM AUTHOR]

The flame retardancy of sorbitol-based epoxy resin is targeted. From the bioepoxy 3% phosphorus-containing matrix samples were prepared. Surprisingly, only HB classification of UL-94 test was reached with the application of ammonium polyphosphate (APP) and resorcinol bis(diphenylphosphate) (RDP). V-0 was reached in the case of red phosphorus (RP) and ammonium salt of DOPO (DXA), while the melamine salt resulted in HB rating, due to the lower P-content of the sample. In the meantime, the highest LOI value was reached in the case of APP. The V-0 red phosphorus composition, however, has an LOI of as low as 25 V/V%. In the case of the thermogravimetric analysis, the application of red phosphorus resulted in significantly increased thermal stability, but faster degradation than in the case of the reference. The RDP showed somewhat decreased stability, due to the less stable phosphorus ester bonds. The amount of the charred residues is increasing with the flame retardant content, but to different extents depending on the type of flame retardant. The highest values were reached with APP. Regarding the cone calorimeter results; the lowest heat release rate belongs to the APP-containing sample, while the V-0 compositions (RP and DXA) show poorer performance in this respect. [ABSTRACT FROM AUTHOR]

An editorial is presented on the role of polymer recycling in achieving the European Union's sustainability goals, focusing on the Circular Economy Action Plan and the European Green Deal. It emphasizes the need for innovative approaches in polymer design and recycling to reduce waste generation and lower the environmental impact. It further discusses the importance of upcycling secondary polymers to meet mandatory recycled content targets set by the European Union (EU).

Well designed (multilayer, adaptive, reactive) interphases, being a key element of multicomponent structures, could be tailored to different requirements through controlled technologies. This is the link connecting various green, safe, healthy materials and innovative pharmaceuticals. Upgraded recycling could be performed by interfacial consolidation of self-reinforced composites, the flame retardancy of which is feasible with surprisingly low amount of flame retardant. Examples are shown how the reinforced and foamed forms of thermosetting and thermoplastic biopolymers can play a significant role (after flame retardant modification) in the development of airplanes and electric cars. Biopolymer nanofibres, such as polycaprolactone and polyhydroxybutyrate, could be formed with increased productivity for various medical uses. Raman-based control of the units of integrated continuous technologies has been elaborated including controlled formation of crystals with polymer interlayer for direct tableting. [ABSTRACT FROM AUTHOR]

Resin transfer moulding (RTM) is commonly used for the production of high-performance fibre-reinforced polymer composites. In numerous application areas, the addition of fillers is necessary to enhance some properties of the polymer matrix or provide it with additional properties, such as flame retardancy. As many of the applied additives are solid phase, the reinforcement layers may filter the solid phase additive particles during RTM, resulting in a non-uniform distribution and uneven performance. Consequently, the proper distribution of the solid phase additives in composites is of key importance. This review primarily aims at facilitating the production of flame retarded structural composites by RTM in cases where the required fire performance can only be achieved with solid additives. First, the parameters influencing the particle distribution, along with the models describing it, are reviewed. Then, analytical methods for determining the particle distribution in composites manufactured by RTM are presented. Finally, the possible solutions to improve the particle distribution of solid phase additives are outlined. [ABSTRACT FROM AUTHOR]

Carbon fibre reinforced flame-retarded bioepoxy composites were prepared from commercially available sorbitol polyglycidyl ether (SPE) cured with cycloaliphatic amine hardener. Samples containing 1, 2, and 3% phosphorus (P) were prepared using additive type flame retardants (FRs) resorcinol bis(diphenyl phosphate) (RDP), ammonium polyphosphate (APP), and their combinations. The fire performance of the composites was investigated by limiting oxygen index (LOI), UL-94 tests, and mass loss calorimetry. The effect of FRs on the glass transition temperature, and storage modulus was evaluated by dynamic mechanical analysis (DMA), while the mechanical performance was investigated by tensile, bending, and interlaminar shear measurements, as well as by Charpy impact test. In formulations containing both FRs, the presence of RDP, acting mainly in gas phase, ensured balanced gas and solid-phase mechanism leading to best overall fire performance. APP advantageously compensated the plasticizing (storage modulus and glass transition temperature decreasing) effect of RDP in combined formulations; furthermore, it led to increased tensile strength and Charpy impact energy. [ABSTRACT FROM AUTHOR]

A systematic study was performed to describe the effect of epoxidized soybean oil (ESO) on storage modulus, glass transition temperature ( Tg) and mechanical properties in epoxy resin composites reinforced by jute fabric. In addition to aromatic diglycidylether of bisphenol-A (DGEBA) resin, a glycerol (GER)-and a pentaerythritol (PER)-based aliphatic resin was applied as base resin, which can be also synthesized from renewable feedstock. Based on strip tensile test results, the usual alkali treatment of jute fabric was avoided. By increasing the ESO-content in aliphatic composites the Tg increases, whereas in case of DGEBA, it decreases. The results indicate that although ESO has a significant softening effect, the jute fiber-reinforced DGEBA composite can be replaced without significant compromise in mechanical properties by a potentially fully bio-based composite consisting of 25 mass% ESO-containing aliphatic PER-reinforced by jute fibers. POLYM. COMPOS., 38:884-892, 2017. © 2015 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Flame-retarded bioepoxy resins were prepared with the application of commercially available sorbitol polyglycidyl ether (SPE). The additive-type flame retardancy of the cycloaliphatic amine-cured SPE was investigated. Three-percent phosphorus (P)-containing samples were prepared with the application of the liquid resorcinol bis(diphenyl phosphate) (RDP), the solid ammonium polyphosphate (APP), and by combining them. Synergistic effect was found between the inorganic APP and the organophosphorus RDP, when applied in combination: formulations applying RDP or APP alone showed increased limiting oxygen index (LOI) values, however, their UL-94 standard ratings remained HB. When the same amount of P originated from the two additives, V-0, self-extinguishing rating and LOI value of 34% (v/v) was reached. By the combined approach the heat release rate of SPE could be lowered by approximately 60%. The assumed balanced solid and gas phase mechanism was confirmed by thermogravimetric analysis, Fourier transform infrared spectrometry (FTIR) analysis (of the gases formed during laser pyrolysis), attenuated total reflection-infrared spectrometry (ATR-IR) analysis (of the charred residues), as well as by mechanical testing (of the char obtained after combustion). [ABSTRACT FROM AUTHOR]

The potential of carbonized electrospun nanofiber mats to render epoxy resin composites for aircraft applications electrically and thermally more conductive was investigated. The effect of carbon nanotube inclusion both inside the carbon nanofiber and in the epoxy resin matrix material was studied, in order to reveal any synergistic effects of multilevel presence of nanosized reinforcements on the conductivity and mechanical properties. The carbon nanotube inclusion into the carbonized nanofibers increased the electrical conductivity of the samples by 20-50% and the thermal conductivity by approximately three times leading to a higher value than that of the conventional composites. The preparation of layered composites with a conductive upper layer containing nonwoven carbon nanofabric and a load bearing lower layer with conventional unidirectional carbon fiber reinforcement can offer a cost-effective and weight-saving solution for the replacement of metal meshes in structural aircraft composites. [ABSTRACT FROM AUTHOR]

ABSTRACT The flame-retardant efficacy of phosphorus-containing reactive amine hardeners for epoxy resins is well-known; however their synthesis often applies hazardous, objectionable reagents. The aim of this work is to develop an effective synthesis method for the preparation of P-containing amines, which can act as flame-retardant crosslinking agent in epoxy resins. The syntheses and testing of an aliphatic and two aromatic amines are described: curing properties, glass transition temperature, thermal stability, and flame-retardant performance of the amines are studied. On the basis of these results, the scaling-up and the optimization of the synthesis of the phosphorus-containing aliphatic amine hardener in ReactIR™ in situ FTIR apparatus is discussed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40105. [ABSTRACT FROM AUTHOR]

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The mass of usage of secondary plastics are mostly determined by their quality and price. Therefore it was essentially to collect and evaluate the related aspects and expectations from the potential secondary-plastics users. To enable this in the frame of the W2Plastics EU7 project (Magnetic Sorting and Ultrasound Sensor Technologies for Production of High Purity Secondary Polyolefins from Waste) an adequate questionnaire was worked and sent out to automotive plastics end-product manufacturers. With the evaluation of these questionnaires basic parameters for the technology development in the frame of W2Plastics project were determined. [ABSTRACT FROM AUTHOR]

• Non-FR gelcoats significantly impair the fire performance of composites. • The pHRR of the composite was reduced by 67 % with 15 % P in the gelcoat. • Above 10 % P content the gelcoat outperformed the commercial FR gelcoat. • The use of RDP in the matrix further reduced the heat release of coated composites. • Thicker gelcoat led to lower pHRR, but the additional FR effect of RDP decreased. This research article focuses on the development of multifunctional, flame retarded epoxy gelcoat formulations based on phosphorus-containing, intumescent flame retardant (FR). We prepared epoxy resin-based gelcoats with 5 %, 10 % and 15 % phosphorus (P) content using ammonium polyphosphate (APP), and compared their thermal stability, glass transition temperature, crosslinking reaction enthalpy and fire performance to the non-flame retarded reference and a commercial FR gelcoat. We coated carbon fibre reinforced pentaerythritol (PER)-based epoxy composites (non-FR, and FR) with these gelcoats in two thicknesses (0.5 mm and 1.0 mm). The APP-based gelcoats outperformed both the commercial reference and FR gelcoat in terms of thermal stability. When the APP concentration in the gelcoat was increased, the thermal stability and the limiting oxygen index (LOI) increased. All FR gelcoats reached the self-extinguishing (V-0) classification during the UL-94 test and showed remarkable char formation during the mass loss calorimetry (MLC) test even at a lower heat flux (25 kW/m2). In terms of heat release rate, the gelcoat with 10 % P from APP behaved similarly, while the formulation with 15 % P from APP outperformed the commercial FR gelcoat. The tendency in the fire performance of the coated composites was similar to the behaviour of the gelcoat matrices: above 10 % P content, the coated sample outperformed the commercial FR gelcoat. The addition of a liquid, organophosphorus flame retardant (resorcinol bis(diphenyl phosphate) (RDP), acting mainly in the gas phase) to the epoxy matrix of the composite resulted in the further decrease of heat release rate. Non-FR gelcoats considerably deteriorated the fire performance of the fibre reinforced composites, even when applied in a thickness of 0.5 mm. If a gelcoat layer is necessary on the surface of the composite part, a substantial increase in heat release must be considered, or an FR multifunctional gelcoat should be used as an alternative. We reached a 67 % reduction in peak heat release rate when we replaced a 1 mm thick non-FR gelcoat with a gelcoat containing 15 % P on the PER reference composite. [ABSTRACT FROM AUTHOR]

We prepared reference and flame-retarded carbon fibre reinforced composites both by liquid composite moulding, in particular vacuum infusion, and by hand lamination followed by hot pressing (wet compression moulding) in order to study the effect of carbon fibre reinforcement and particle distribution of solid flame retardants (FRs) on fire performance. The flame-retarded matrix had 3% total phosphorus (P) content from ammonium polyphosphate (APP). When the infusion site of the composite produced by vacuum infusion faced the conical heater during the mass loss type cone calorimeter tests, the peak of heat release rate (pHRR) was lower, the time of pHRR became longer and the intumescence increased in comparison to the laminated sample, which supported our hypothesis about the filtration of solid APP during the vacuum infusion process. In order to model the suspected filtration, we prepared a laminated composite sample with an increasing amount of APP equivalent to 1%, 2%, 3%, 4%, 5% P content in each subsequent layer. The HRR curve of the composite produced by vacuum infusion with the infusion site facing the conical heater was basically identical with the curve of the model composite with the 5% P layer facing the conical heater in the early phase of the degradation, while in the main degradation phase, the lower burnable ratio of the composite prepared by vacuum infusion led to a further decrease in pHRR (184 kW/m2) and THR (15.5 MJ/m2), and the consequent best overall fire performance of the composite produced by vacuum infusion. The suspected accumulation of APP in the first layers of the composite caused by the carbon fibre reinforcement was proven by SEM-EDS elemental maps of the whole cross-section of the composite. • LCM composite overperformed the laminated one with same composition in fire tests. • Solid FR particles accumulated on the surface of composite during infusion process. • Particle filtration in fibre reinforced LCM composites was proven by SEM-EDS. • LCM composite was modelled by a laminated with increasing APP-amount in each layer. [ABSTRACT FROM AUTHOR]

Achieving special features in polymer composites, such as flame retardancy and thermal and electrical conductivity, often requires the application of different additives, which might negatively affect other properties of the polymer matrix and the composite structure. Furthermore, the application of solid additives in composites produced by liquid transfer moulding can lead to the filtration of the additive by the reinforcement, which causes a non-uniform particle distribution and an uneven performance. An evident solution to address these issues is to apply the additives in a separate layer on the surface of the composite. As in many applications, gelcoats are used to reach appropriate surface quality, a reasonable progression in the composite industry is the development of multifunctional gelcoats. In this article, after a short introduction to gelcoats and their main base materials (unsaturated polyester, epoxy, and others) multifunctional gelcoats are discussed according to their functionality, in particular water resistance, electric conductivity and flame retardancy. Classical and novel gelcoat preparation methods (application by brush and/or roller, spraying, UV-curing, in-mould gelcoating), as well as common defects that occur during gelcoating are discussed. Finally, the testing methods of multifunctional gelcoats are outlined. [ABSTRACT FROM AUTHOR]

We studied the effect of a multilevel presence of carbon-based reinforcements—a combination of conventional load-bearing unidirectional carbon fiber (CF) with multiwalled carbon nanotubes (CNT) and conductive CNT-containing nonwoven carbon nanofabric (CNF(CNT))—on the fire performance, thermal conductivity, and mechanical properties of reference and flame-retarded epoxy resin (EP) composites. The inclusion of carbon fibers and flame retardant reduced the peak heat release rate (pHRR) of the epoxy resins. The extent to which the nanoreinforcements reduced the pHRR depended on their influence on thermal conductivity. Specifically, high thermal conductivity is advantageous at the early stages of degradation, but after ignition it may lead to more intensive degradation and a higher pHRR; especially in the reference samples without flame retardant. The lowest pHRR (130 kW/m2) and self-extinguishing V-0 UL-94 rating was achieved in the flame-retarded composite containing all three levels of carbon reinforcement (EP + CNF(CNT) + CNT + CF FR). The plasticizing effect of the liquid flame retardant impaired both the tensile and flexural properties; however, it significantly enhanced the impact resistance of the epoxy resin and its composites. [ABSTRACT FROM AUTHOR]

Low viscosity, potentially renewable aliphatic epoxy resins, appropriate for processing with injection techniques were flame retarded with the use of resorcinol bis(diphenyl phosphate) (RDP), acting predominantly in the gas phase, ammonium polyphosphate (APP), acting in the solid phase, and their combination. Samples of gradually increasing phosphorus (P) content (1%, 2%, 3%, 4%, and 5%) and mixed formulations with 2% P from APP and 2% P from RDP were prepared. The fire retardancy of matrix and carbon fibre reinforced samples was examined by limiting oxygen index (LOI), UL-94 tests, and mass loss calorimetry. The thermal stability of the matrices was investigated by thermogravimetric analysis, whereas the effect of flame retardants (FRs) on the crosslinking process and glass transition temperature was evaluated by differential scanning calorimetry in matrices and by dynamic mechanical analysis in composites. According to the results, although the trifunctional glycerol -based (GER) and the tetrafunctional pentaerythritol-based (PER) epoxy resins have a similar initial LOI and horizontal burning rate, GER has an approximately 1.5 times higher peak of heat release rate (pHRR) than PER. At least 4% P content is necessary to reach a reasonable improvement in fire performance in these resin transfer molding (RTM)-compatible systems and with the same FR-content PER reaches better fire performance. RDP has an early gas phase effect at the beginning of degradation, while later on the solid phase action of APP prevails, although in composites hindered by the reinforcing carbon fibres. In PER composites, the combination of APP and RDP had a synergistic effect, leading to a pHRR of 218 kW/m2 and total heat release of 18.2 MJ/m2. [ABSTRACT FROM AUTHOR]

Examines the optimum conditions of the monophosphorylation and the monophosphinylation. Kind of phosphate that form a traditional group of organophosphate flame retardants; Functions of the reactive sites of the phosphates and phosphinates.

• Thermoplastic in-situ polymerisable matrices gain ground in reinforced composites. • Flame retardancy of ε-caprolactam-based PA6 is essential and feasible. • Solubility and the effect on the polymerisation of flame retardants is a key issue. • Flame retardant structure and polymerisability correlations are evaluated. • Suitable composite processing and coating technologies are reviewed. The complexity of recycling crosslinked polymer composites has promoted the use of thermoplastic in situ polymerisable matrices, including ε-caprolactam-based polyamide 6 (PA6) in long-fibre reinforced composites. Their uptake by the automotive industry has created a need for adequate flame retardancy, which poses several challenges: flame retardants may hinder the in situ polymerisation reaction; moreover, the fibre reinforcement can filter out the additives not soluble in ε-caprolactam during liquid moulding composite processing, such as thermoplastic resin transfer moulding (T-RTM). We discussed the feasibility of the flame retardancy of ε-caprolactam-based PA6 and its composites, including the solubility of the additives in ε-caprolactam and their effect on the polymerisation reaction and fire performance. We evaluated the correlations between the flame retardant structure and the inhibition of polymerisation. Finally, we briefly summarised the composite processing and coating technologies suitable for preparing flame retarded ε-caprolactam-based PA6 matrix and composite systems, as well as the most often used tests for their characterisation. [Display omitted] [ABSTRACT FROM AUTHOR]

Natural hemp fabric reinforced epoxy resin composites were prepared in flame retarded form. Fabrics were treated in three ways: the first method involved the immersion of preheated fabric into cold phosphoric acid solution (allowing penetration into the capillaries of the fibres) and subsequent neutralization, the second way was a reactive modification carried out with an aminosilane-type coupling agent, while the third treatment combined the sol–gel surface coating with the first method. The introduction of phosphorus into the reinforcing fibres decreased the flammability not only of the hemp fabrics, but also of the epoxy composites made thereof. By applying amine-type phosphorus-containing curing agent (TEDAP) in combination with the treated fabrics, V-0 UL-94 rating was achieved. Composites of unexpectedly improved static and dynamic mechanical properties could be prepared only when the simple phosphorous fibre treatment and reactive flame retardancy was combined. [ABSTRACT FROM AUTHOR]