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Basic paths towards fully green flame retarded kenaf fiber reinforced polylactic acid (K-PLA) biocomposites are compared. Multicomponent flame retardant Systems are investigated using an amount of 20 wt% such as Mg(OH)2 (MH), ammonium polyphosphate (APP) and expandable graphite (EG), and combinations with Silicon dioxide or layered silicate (LS) nanofillers. Adding Kenaf fibers and flame retardants increases the E modulus up to a factor 2, although no compatibilizer was used at all. Thus, in particular adding EG and MH decreases the strength at maximum elongation, and kenaf fibers, MH, and EG are crucial for reducing the elongation to break. The Oxygen index is improved by up to 33 vol% compared to 17 vol% for K-PLA. The HB classification of K-PLA in the UL 94 test is outperformed. All flame retarded biocomposites show somewhat lower thermal stability and increased amounts of residue. MH decreases the fire load significantly, and the greatest reduction in peak heat release rate is obtained for K-PLA/15MH/5LS. Synergistic effects are observed between EG and APP (ratio 2:1) in flammability and fire properties. Synergistic multicomponent systems containing EG and APP, or MH with adjuvants offer a promising route to green flame retarded natural fiber reinforced PLA biocomposites.
The recently approved EU Construction Products Regulation (CPR) applies to cables as construction products.
The difficulty of predicting the fire performance of cables with respect to propagation of flame and contribution to fire hazards is well known. The new standard EN 50399 describes a full-scale test method for the classification of vertically mounted bunched cables according to CPR. Consideration of the material, time, and thus cost requires an alternative bench-scale fire test, which finds strong demand for Screening and development purposes. The development of such a bench-scale fire test to assess the fire Performance of multiple vertically mounted cables is described. A practical module for the cone calorimeter is proposed, simulating the fire scenario of the EN 50399 on the bench scale. The efficacy of this module in predicting full-scale CPR test results is shown for a set of 20 different optical cables. Key properties such as peak heat release rate (PHRR), fire growth rate (FIGRA), and flame spread are linked to each other by factors of around 5. In a case study, the bench-scale test designed was used to investigate the influence of the main components on the fire behaviour of a complex optical cable.
Nanocomposites of a charring polymer (like polyurethane foam) filled with aluminum phosphinate (AlPi) with or without melamine cyanurate (MelCy) have been prepared by microwave processing and their thermal stability and fire behavior have been studied. Results on the interaction between flame retardants and layered silicates were provided as well as detailed investigation of the char strength, which has been carried out using a suitably developed method based on dynamic-mechanic analysis.
Generally, the thermo-oxidative stability in presence of layered silicates was higher than the counterparts even if an additive rather than synergic effect took place; however, in some cases the interaction between clays and phosphinate led to a significant decrease of weight residue. In nitrogen the residue amounts were about the same but a higher amount of phosphorus was retained in the solid phase in presence of clays. Cone calorimeter results showed that the use of phosphinates led to a decrease of the PHRR; further addition of clays did not reduce the PHRR owing to the worse quality of char layer as demonstrated by the char strength test. However, it has been shown that the partial substitution of aluminum phosphinate with melamine cyanurate gave improved results: the AlPi–MelCy filled foams showed similar pHRR and THE but lower TSR and higher char strength than AlPi filled foams. It was also confirmed that phosphinate acted by flame inhibition but its action was depressed by the use of nanoclays owing to their interaction.
The use of coconut fiber (CF) agricultural waste was considered as an environmentally friendly and inexpensive alternative in flame retarded biocomposites. To decrease the high content of aluminum trihydrate (ATH) required, the thermal decomposition (thermogravimetry), flammability [oxygen index (LOI) and UL 94 test] and fire behavior (cone calorimeter) of a combination of CF and ATH were investigated in a commercial blend of thermoplastic starch (TPS) and cellulose derivatives. CF induced some charring activity, slightly decreasing the fire load and burning propensity in cone calorimeter test. ATH decomposes endothermically into water and inorganic residue. Significant fuel dilution as well as a pronounced residual protection layer reduces the fire hazards. Replacing a part of ATH with coconut fibers resulted in improved flame retardancy in terms of ignition, reaction to small flame, and flame-spread characteristics [heat release rate (HRR), fire growth rate (FIGRA), etc.]. The observed ATH and CF synergy opens the door to significant reduction of the ATH contents and thus to interesting flame retarded biocomposites.
Effect of well dispersed amorphous silicon dioxide in flame retarded styrene butadiene rubber
(2013)
Spherically shaped amorphous silicon dioxide with broad size particle distribution was used in combination with aluminium trihydroxide (ATH) in styrene butadiene rubber composites. The pyrolysis, flammability, fire properties, flame spread and gas diffusion were investigated. The kind and amount of ATH, but in particular the fine silicon dioxide chosen as an additive, influenced the thermal decomposition and fire behaviour of styrene butadiene rubber composites. Gravimetric gas sorption measurements showed that the gas diffusion was systematically lower with silicon dioxide. The initial pyrolysis gas release was hindered, increasing the temperature at which decomposition begins as well as the ignition time in fire tests. During combustion, ATH and silicon dioxide accumulate on the surface of the specimen, forming a residual protective layer. A reduced peak heat release rate and fire spread were observed. The addition of a special kind of silicon dioxide is proposed to play a key role in optimising fire retardancy.
The potential of a multi-component laminate composite material in terms of improved flame retardancy and adequate mechanical performance is discussed. A double-layer system based on a biodegradable polyhydroxyalkanoates blend was obtained by compression molding. A thin halogen-free flame-retarded layer was located at the top of a kenaf-fiber-reinforced core. Kenaf fibers acted as a carbonization compound promoting charring and building up a superficial insulating layer that protected the material throughout combustion. The impact of different skin/core thickness on the thermal and fire properties was investigated. Synergistic flame retardancy occurs in the cone calorimeter. Chemical and fire investigations confirmed a changed pyrolysis behavior in multicomponent materials. Promising results are obtained in terms of mechanical performance: higher flexural and impact properties were observed in the single fiber-reinforced layer.
Both alkylphosphinates and inorganic phosphinates (based on sodium, calcium, magnesium or zinc) have been recently proposed as flame retardants for polyesters, polyamides and polyurethane foams as well. The main aim of this work was to compare the flame retardant effectiveness of inorganic (already proofed in PU foams) and organic phosphinates in PU foams which have never been used in polyurethane (PU) foams. The thermal stability in nitrogen and air as well as limiting oxygen index and cone calorimeter behaviour have been studied to assess the effectiveness of such flame retardants in PU foams.
The results obtained showed that both inorganic and organic phosphinates are effective in enhancing fire behaviour of PU foams since they improve thermal stability, LOI and fire performance. Cone calorimetry highlighted the flame inhibition action in the gas phase due to the release of phosphorus-containing molecules. The better results obtained for inorganic phosphinate are probably related to the better quality of the char layer developed during burning, but may also be related to the higher phosphorus content of such flame retardant with respect the other ones. It was also verified that both inorganic and organic phosphinate containing N-synergic compound showed a fuel dilution effect, deriving from water and/or ammonia release in the gas phase.
The synthesis of a disiloxane-functionalized [2.2]paracyclophane and its polymerization to the corresponding siloxane-substituted poly(p-xylylene) via chemical vapor deposition (CVD) has been described. Because of the enhanced solubility of the siloxane substituted poly(p-xylylene) analysis of the molecular structure by NMR, molecular weight, and polydispersity by gel permeation chromatography (GPC), and processing by film casting as well as nanofiber formation by electrospinning was possible. Structural isomers were found by NMR which was expected due to the isomeric mixture of the precursor. High molecular weights at moderate polydispersities were found by GPC which was unexpected for a vapor phase deposition polymerization. The amorphous morphology in combination with a low glass transition temperature led to high elongation at break for the siloxane substituted poly(p-xylylene). Significant difference for the wetting versus water was found for as-deposited films, solution cast films, and nanofibers obtained by electrospinning with contact angles up to 135° close to superhydrophobic behavior.
The pyrolysis and the flame retardancy of poly(butylene terephthalate) (PBT) containing aluminum diethylphosphinate (AlPi) and nanometric Fe2O3 were investigated using thermal analysis, evolved gas analysis (Thermogravimetry-FTIR), flammability tests (LOI, UL 94), cone calorimeter measurements and chemical analysis of residue (FTIR). AlPi mainly acts as a flame inhibitor in the gas phase, through the release of diethylphosphinic acid. A small amount of Fe2O3 in PBT promotes the formation of a carbonaceous char in the condensed phase. The combination of 5 and 8 wt% AlPi, respectively, with 2 wt% metal oxides achieves V-0 classification in the UL 94 test thanks to complementary action mechanisms. Using PBT/metal oxide nanocomposites shows a significant increase in the flame retardancy efficiency of AlPi in PBT and thus opens the route to surprisingly sufficient additive contents as low as 7 wt%.