Beáta Szolnoki

Thermochemical stabilization and analysis of continuously electrospun nanofibers

Carbon nanotube (CNT)-loaded and neat polyacrylonitrile nanofibers were produced by a needleless continuous electrospinning method as carbon nanofiber precursors. The details of the stabilization, which is a crucial issue during carbon fiber production, were investigated as these nanofibers are especially sensitive to degradation. In order to determine the optimal parameters, the nanofibers were stabilized at different temperatures. The stabilized samples were analyzed by Fourier-transform infrared spectroscopic and differential scanning calorimetric (DSC) measurements and by the determination of the color changes. The chemical changes during the stabilization (the formation of the so-called ladder-polymer) can be followed by infrared spectrometry, while the conversion can be monitored by DSC. The formation of the ladder-polymer occurs according to the Gaussian distribution function, where the temperature of the stabilization is the statistical parameter, which was also determined. In the case of CNT-loaded samples, the range of stabilization temperature was wider, which provides better controllability of the process. Based on the established models, an appropriate multi-step heat-treatment program could be determined, which led to completely stabilized nanofibers, suitable for carbonization.

Flame retardancy of sorbitol based bioepoxy via combined solid and gas phase action

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).

Flame Retardancy of Carbon Fibre Reinforced Sorbitol Based Bioepoxy Composites with Phosphorus-Containing Additives

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.

Reactive and Additive Phosphorus-based Flame Retardants of Reduced Environmental Impact

Abstract Phosphorus-based flame retardants are environmentally favored owing to their lower environmental impact during their entire life-cycle—including production, use, and disposal—when compared to other conventional flame retardants. Phosphorus-containing flame retardant systems are reviewed in this chapter by presenting the most recent innovative approaches of environmentally friendly flame retardancy. Environment- and process-centered comparison of reactive and additive fire retardant types is presented on the example of thermoplastic polyurethanes. In the case of epoxy resins preferences are given to the novel reactive-type flame retardants, especially when these are synthesized according to the principles of green chemistry. In thermoplastics, where the additive-type flame retardants dominate, the environmental gain of interface/interphase modifications is highlighted. In order to achieve even more green flame retardant systems the use of recycled and renewable resources is proposed.

Fire-retardant recyclable and biobased polymer composites

Abstract This chapter reviews flame retardancy of recyclable and biobased polymer composites. Synthesis routes to obtain thermosetting biobased polymer matrices are discussed and environmentally friendly flame-retardancy solutions are proposed. Fire retardancy of thermoplastic biomatrices and fully recyclable self-reinforced composites made thereof are summarized. New methods to characterize flame-retardant biocomposites and understand their thermal degradation and flame-retardant mechanisms are presented. After reviewing chemical treatments to flame retard natural fibres, flame-retardancy results of thermosetting and thermoplastic biocomposites are discussed. Green solutions utilizing synergistic effects, multifunctionality and integrated approaches are highlighted. Finally, application possibilities and future trends in the field of flame-retarded biocomposites are indicated.

Flame Retardancy of Low-Viscosity Epoxy Resins and Their Carbon Fibre Reinforced Composites via a Combined Solid and Gas Phase Mechanism

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.

Investigating mechanical performance of PLA and CA biodegradable printed circuit boards

The paper presents a set of experiments investigating the mechanical performance of PCBs manufactured from biodegradable, sustainable polymers, compared to conventional materials. Cellulose Acetate (CA), Polylactic Acid (PLA) and Flame-Retardant Class 4 (FR-4) substrates were compared during the experiments. The methods involved dynamic mechanical analysis (DMA), three-point bending tests and UL 94 flammability tests. Preliminary results show that the overall performance of the basic biodegradable, sustainable PCBs are considerably weaker compared to FR4 boards, however further improvements with additives and use in special applications can point to practical purposes of the substrates.