Project Report on Unsaturated Polyester Resins

Polyester resins are unsaturated resins formed by the reaction of dibasic  organic acids and polyhydric alcohols. Polyester  resins are  used in sheet moulding compound, bulk moulding compound  and the  toner  of  laser printers.  Wall  panels  fabricated from polyester resins reinforced with fiberglass so-called  fiberglass reinforced  plastic  (FRP)  are typically  used  in  restaurants, kitchens,  restrooms and other areas that require  washable low-maintenance walls. polyesters are condensation polymers formed by the  reaction  of polyols (also known  as  polyhydric  alcohols), organic  compounds  with multiple alcohol or  hydroxy  functional groups,  with  saturated or unsaturated  dibasic  acids.  Typical polyols used are glycols such as ethylene glycol; acids used  are phthalic   acid   and  maleic  acid.  Water,  a   by-product   of esterification  reactions, is continuously removed,  driving  the reaction  to  completion. The use of unsaturated  polyesters  and additives such as styrene lowers the viscosity of the resin.  The initially  liquid resin is converted to a solid by  cross-linking chains.  This  is done by creating free radicals  at  unsaturated bonds,  which propagate in a chain reaction to other  unsaturated bonds  in  adjacent molecules, linking them in the  process. The initial  free  radicals  are induced by adding  a  compound  that easily  decomposes into free radicals. This compound  is  usually and   incorrectly   known  as  the   catalyst[citation needed]. Substances  used are generally organic peroxides such as  benzoyl peroxide.