Biochar to the rescue: Balancing the fire performance and mechanical properties of polypropylene composites

Biochar based wood/polypropylene (PP) composites were manufactured with two flame retardants (FRs): ammonium polyphosphate/APP and magnesium hydroxide/Mg(OH)2. The amounts of wood and biochar were alternated for accommodating the FRs in each blend. Flammability and mechanical characterisation for both the batches containing different FRs were done. Having higher proportion of biochar and less wood is beneficial to reduce flammability. The thermally stable biochar contributes to formation of effective char to restrict O2 transfer into PP. The higher weight ratio of biochar than wood in the composites compromised the tensile and flexural strengths to some extent as the APP and Mg(OH)2 particles were trapped inside biochar pores consequently reducing the effectiveness of biochar pore infiltration by PP. In general, addition of biochar with a woody biomass (with FRs) to neat PP significantly impedes its flammability while enhancing certain mechanical properties, such as flexural strength and tensile/flexural moduli and preserving the tensile strength.