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This work investigates the fire phenomena of rigid polyurethane foams (RPUF) in detail. To elucidate structure-property relationships systematically varied sets of foams were prepared. RPUF were synthesized with different densities using water and pentane as blowing agent. What is more, a flame retarded RPUF and rigid polyisocyanurate-polyurethane foams were examined. The comprehensive understanding of the processes taking place during combustion is the foundation of customized development of successful flame retardant approaches.
Advanced cone calorimeter investigations provide insight into the fire behavior under forced flaming conditions. Thermocouples in the inside of specimens give information about the temperature gradient and temperature of the pyrolysis zone during combustion. Furthermore, fire phenomena were characterized using SEM, LOI and thermal analysis. By using a multi-methodological approach and systematically varied sets of foam materials, new insights into the burning of RPUF were won. The detailed knowledge of fire phenomena is essential for future development of tailored flame retardant strategies for RPUF.
The potential of nanocomposites, i.e. mixtures of nanoobjects with acceptable distribution in a polymer matrix, with respect to flame retardancy was discovered in an already early stage of nanocomposite reseach. Since then, a variety of nanocomposites often in combination with conventional flame retardants (FRs) and their effect on the burning behavior has been described.
Here, we show the application of this concept to enhance the flame retardancy of poly(butylene terephthalate) (PBT) and poly(butylene succinate) (PBS) using suitable phosphorus-containing polyesters as FR. The materials studied were prepared by melt compounding in a twin screw extruder using either a mixture of polymer matrix, phosphorus polymer and nanomaterial (direct compounding) or a mixture of a pre-formed batch of phosphorus polymer with nanomaterial and the polymer matrix (batch compounding). The second method has been shown to be very effective if batches prepared by in-situ nanocomposite synthesis via melt transesterification polycondensation were employed. Modified organoclay (montmorillonite, OMMT) as well as multiwalled carbon nanotubes were used as nanoobjects.
Organic modification of MMT resulted in better exfoliation and distribution within the poylmer matrix than observed with pure sodium MMT. However, modification with phosphorus-containing modifiers dis not support exfoliation due to high interaction between modifier and clay.
Analysis of the in-situ prepared nanocomposites of OMMT (Cloisite 30B) with the phosphorus polyester PET-P-DOPO by thermogravimetry, FTIR and pyrolysis-GC/MS showed that OMMT did not alter the principal decomposition pathway of the polyester, but shifted the onset of decomposition to lower temperature (due to the fast decomposition of the tertiary ammonium compound) and increased the amount of char. The fire behavir as observed by microscale combustion calorimetry (MCC) was altered and resulted in significant decrease of heat release capacity.
In-situ prepared batches of the phosphorus polyester PET-P-DOPO with 20 wt.-% OMMT and with MWCNT (1 wt.-%) were blended with PBT in the ratio 25/75 wt/wt to achieve a phosphorus concentration of 1.5 wt.-%. The nanocomposites were injection molded into plates for cone calorimeter measurements and examined using 50 kW/m2. In all samples, a reduction of toral heat evolved and total heat evolved/total mass loss (THE/TML) was observed. Addition of OMMT improved the char, which was even more pronounced in combination with PET-P-DOPO as illustrated in Figure 1. Blends containing PET-P-DOPO additionally showed intumescence. In all cases, a significant reduction of FIGRAmax was obtained. The addition of nanomaterials (both OMMT and MWCNT) to PBT/PET-P-DOPO reduced the effective heat of combustion (THE/TML) from 1.7 to 1.5 MJ/m2.
Carbon fibre (CF) and glass fibre (GF) reinforced polymers are used for diverse applications demaning flame and fire retardancy in the fire scenarios ignition, developing fire and fully developed fire. The fire behaviour of composites differs from polymers, since fibres behave often inert with respect to pyrolysis, change the melt flow / dripping behaviour, the heat absorption and transfer, the amount and properties of the fire residue. Concepts are needed suitable for the different fire protection goals, but also tailored for composites. The field is illuminated by examples carried out in the group of the author in the recent years. Approaches to halogen-free flame retardancy in GF reinforced thermoplastics and CF reinforced thermosets are presented as well as building up a bench and intermediate scale testing of composites in fire applying mechanical load and direct flame exposure simultaneously. The understanding of fire behaviour and flame retardancy modes of action in composites is a promising basis for target-oriented development.
Solid-state NMR Identifying the Chemistry in Multicomponent Flame-retarded Polyolefin Systems
(2017)
Understanding of the interaction in multicomponent flame-retarded polymeric system is crucial to obtain the best performance at the possible lowest load of additives. In this work, polyolefine based systems are investigated by solid state NMR and cone calorimetry. As a polymer matrix thermoplastic elastomer based on styrene (TPE-S) was chosen. Different combination of additives was investigated in order to identify the chemistry occurring during the pyrolysis. As additives aluminium diethylphosphinate (AlPi), ammonium polyphosphate, zinc borate (ZB), poly(phenylene oxide) (PPO), magnesium hydroxide (MH) and dimethyl- methylvinyl siloxane (Si) were used. Fire residues remained after the cone calorimeter test were analyzed by solid state NMR (31P, 27Al, 13C, 11B, 29Si). The formation of different phosphates and aluminates was identified, indicating the chemical interaction between the additives. Detailed investigation delivered meaningful insights into the chemistry controlling flame retardancy.