Abstract
Fabrics from commingled natural (flax) –thermoplastic (polypropylene (PP) / poly lactic acid
(PLA) polymeric fibres were fire retarded with an oragnophosphonate flame retardant (FR). The
fire retarded flax/PP and flax/PLA fabrics were melt pressed to prepare respective thermoplastic
composites. The effect of FR concentration on the fire and mechanical properties of composites
were studied and the results analysed in terms of concentration of FR elements in the composites.
While the UL-94 test was used as a benchmark to achieve a V-0 rating, cone calorimetric
parameters were used for in-depth analysis of fire performance. The results show that flax/PP and
flax/PLA composites require a minimum 0.9 and 0.6 % phosphorus (P), respectively to achieve a
V-0 rating in the UL-94 test. Mechanical properties, evaluated in tensile and flexural modes are
however slightly impaired, most probably due to the acidity of the FR solution (pH = 3.2). In
order to improve the mechanical properties, a buffer solution was used to change the pH to 6.0,
which while having a minimal effect on mechanical properties of flax/PP, significantly reduced
those of flax/PLA, and increased flammability of both composites and hence overall showed no
benefit.