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Silicone Surfactants

Flexible polyurethane foams are made with the aid of non-ionic silicone based surfactants. Different grades of silicone are produced to meet the specific needs of the manufactures by adjusting the length and composition of the polysiloxane backbone and the number, length and composition of the polyoxyalkylene polymer present as pendant chains.

Silicone oil surfactant performs the following functions

  • *   reduction  of  surface  tension  for  an  improved  chemical  affinity  with  polyol
  • *   provision  of  film  resilience  known  as  self  healing  in  the  bubbles.  It  is  the  film  resilience  that  prevents  the  collapse  of  the  foam  during  rise  until  chain  extension  and  cross  linking  reactions  of  the  polymer  have  progressed  sufficiently  for  the  foam  to  be  self  supporting.
  • *   Silicone  surfactants  provide  cell  size  control  through  the  promotion  of  homogeneous  fine  cells.  This phenomenon is known as emulsification.
  • *   Silicone promotes bubble breakage at full rise.  If  this  action  does  not  take  place,  the  foam  is  bound  to  shrink  during  cure.  In  this  case  the  resulting  foam  product  is  said  to  be  dead  or  closed.
  • *   Silicone  counteracts  the  deforming  effect  of  any  solid  added to  the  reacting  system  or  formed  in  process.

Of  all  these  roles,  stabilization  of  the  cell  walls  is  the  most  important. Surfactants prevent the coalescence of rapidly growing cells until those cells have attained sufficient strength through polymerisation to become self supporting.
 
The following grades of silicone are available;

  • *   Niax L – 620 (High reactive general purpose silicone for flexible polyurethane foams)
  • *   Niax L – 580 (medium reactive silicone for low density foam formulations)