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- Carbon filler (1)
- Charring (1)
- Dielectric spectroscopy (1)
- Epoxy (1)
- Flame retardancy (1)
- Graphene (1)
- Poly(butylene terephthalate) nanocomposites (1)
- Pyrolysis (1)
- Rheology (1)
- Thermal properties (1)
Condensed-phase mechanisms play a major role in fire-retardant polymers. Generations of development have followed the concept of charring to improve fire properties. Whereas the principal reactions are believed to be known, the specific description for multicomponent systems is lacking, as is the picture across different systems. A two-step approach is proposed in general, and also presented in greater detail. The second step covers the specific reactions controlling charring, whereas the actual reactants are provided in the preceding step. This model consistently incorporates the variety of structureproperty relationships reported. A comprehensive case study is presented on seven phosphorus flame retardants in two epoxy resins to breathe life into the two-step approach.
The influence of distinct carbon based nanofillers: expanded graphite (EG), conducting carbon black (CB), thermally reduced graphene oxide (TRGO) and multi-walled carbon nanotubes (CNT) on the thermal, dielectric, electrical and rheological properties of polybutylene terephthalate (PBT) was examined. The glass transition temperature (Tg) of PBT nanocomposites is independent of the filler type and content. The carbon particles act as nucleation agents and significantly affect the melting temperature (Tm), the crystallization temperature (Tc) and the degree of crystallinity of PBT composites. PBT composites with EG show insulating behaviour over the tested concentration range of 0.5 to 2 wt.-% and hardly changed rheological behaviour. CB, CNT and TRGO induce electrical conductivity to their particular PBT composites by forming a conducting particle network within the polymer matrix. CNT reached the percolation threshold at the lowest concentration (<0.5 wt.-%), followed by TRGO (<1 wt.-%) and CB (<2 wt.-%). With the formation of a particle network, the flow behaviour of composites with CB, CNT and TRGO is affected, i.e., a flow limit occurs and the melt viscosity increases. The degree of influence of the carbon nanofillers on the rheological properties of PBT composites follows the same order as for electrical conductivity. Electrical and rheological results suggest an influence attributed to the particle dispersion, which is proposed to follow the order of EG<< CB<TRGO<CNT.