I have a molded electrical connector. The density is 1.30 g/cc. In the air, the inorganic residue in TGA or ASH test is 12-14%. The FTIR of inorganic residue shows silica (SiO2). XRF analysis indicated a small amount of Na but mostly Al and Si. The FTIR of the composition (attached) indicated it to be PP-based and having Al2SiO3. The part burns very slow and self extinguishes, so perhaps it is V0 rated. FTIR does indicate it not it o be halogenated or with APP type FR additive. Further, the residue is not black char but white powder, So it is unlikely to be APP or other intumescent FR additives which leave black char.
Having a density of 1.30 for filled PP indicates a large amount of FR additive. Al2SiO3 leaves 60% inorganic, ATH 67%, Silicon rubber nearly 80%. The density of most of the inorganic oxides is 2.4-2.6. So for PP (density 0.905) to have a density of 1.30 requires composition to have a large amount of additive, but the TGA indicates much less presence.
Hi Amit,
Al2SiO3 is not common but can use as talc filler for PP and if you calculate it you will end up with 20% in the original formula (in order to end up with 1.3 gr/cc). sound reasonable.
Talc is used as filler for PP in order to provide high stiffness and low deformation and increase temperature stability. it is also provide FR properties.
usually compounders use Magnesium silicate and not Aluminum silicate but it is an option.
As Yonatan said, it is quite common to use talc for flame retarded PP. However, you indicated the XRF composition is Al and Si. Since talc contains a large amount of Mg, it is likely not talc. On the other hand, using about 15% char yield, the true density of the inorganic filler needs to be about 3.3-3.4 g/cc, which is possible among many silicate (high end) but very unlikely to be used as a flame retardant additive. An inorganic additive using a physical flame retardation mechanism, such as production of nonflammable gas, absorption of heat, and others, requires at least about 30wt% of additives. One seldom sees only 15wt% additive without chemical mechanisms, such as halogenated or phosphonate. A more likely scenario is that the filler may contain a volatile component, such as carbonate or hydrate, so that during the TGA analysis, those small molecules decompose and evaporate. Thus, despite adding, say 30-40%, the TGA analysis after heating to about 800-900oC leaves only the none-volatile component. This is consistent with the small char yield, but addition of relatively large fraction of inorganic component at the room temperature value.
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