THE FLAMMABILITY OF HYBRID VISCOSE BLENDS

Visil (manufactured by Kemira Fibres Oy, Finland) is a hybrid of organ ic-inorganic components to give a cellulosic fibre containing polysili cic acid produced by a modified viscose process. Viscose on its own wi ll burn, but non-flammable polysilicic acid which is present in Visil, when heated causes the cellulose to char and the silica formed to pro vide a flame and heat barrier. Thus the fibre is only partly combustib le and reduced volatiles from the cellulose emit only minor amounts of smoke along with some carbon monoxide and carbon dioxide. When blende d with other fibres which have low flammabilities themselves, non-addi tive levels of flame retardance may be observed compared with those ex pected from averaging of individual component properties. Initial resu lts of a larger research programme show that blends of Visil and modac rylic in yarn form show either higher or lower-than-expected Limiting Oxygen Index (LOI) values depending upon the yam structure. These effe cts are corroborated by char length studies following vertical strip t esting which show that either synergistic or more additive effects are possible depending on yarn physical structure. (C) 1996 Elsevier Scie nce Limited