Additives for Polymer Composites Introduction Additives are those

Additives for Polymer Composites

Introduction �Additives are those substances which are added into the resin matrix during composite fabrication process. 2

Purpose �Additives are added to meet ◦ various end-use properties in the polymer and ◦ processing and handling needs of polymer. 3

Types of Additives �Monomer �Catalyst �Accelerators �Mould �Fillers Release agents �Pigments 4

Monomer �Monomer is the smallest unit of a polymer chain which has capability to form chain like structure. �Therefore monomer is used for linking polymer chains to get a 3 -dimentional network structure of polymer. 5

Monomer… �Such process is extensively utilized in curing of polyester resin during composite fabrication. �For the curing (cross-linking) of polyester resin, styrene (monomer) is added �The amount of styrene ranges at 3050 % by weight. 6

Monomer… �The carbon-carbon double bonds in unsaturated polyester molecules and the carbon double bonds in the styrene molecules work as the cross-linking site. 7

Catalyst �Catalysts are used for curing purpose. �Cure rates of a polymer can be controlled by the use of catalysts. �Catalysts are also used for curing polyesters with reduced quantity of styrene. 8

Catalyst… �Resin and catalyst mixing can take place inside a gun. �Gun mixing provides thorough mixing of resin and catalyst and it is preferred to minimize the health risk of the operator. 9

Release agent �A release agent is a liquid/soft semi-solid material which is applied to the mold for easy removal of the fabricated composite part from the mould. �Wax, and grease are widely used as release agent. 10

Release agent… �Sometimes, a gel coat is applied after the application of release agent. The purpose of the gel coat is to get a highly polished surface finish on the part. 11

Accelerators �Accelerator is used to promote the curing reaction. It is also known as hardener. �Lime or magnesium oxide increases the hardening rate of novolak-hexa compositions are sometimes called as accelerators. 12

Accelerators… �To obtain a sufficient rate of cure during moulding, accelerator is added about 0. 2 -2. 0 %. �Such accelerators are ammonium sulphamate, ammonium phenoxyacetate, ethylene sulphite and trimethyl phosphate. 13

Accelerators… �According to the concentration of catalyst and accelerator used, the resin will gel in any time from few minutes to many hours. 14

Accelerators… �When methyl ketone peroxide (MEKP) is added to a polyester resin containing vanadium naphthenate accelerator, the resin set almost immediately. 15

Composition of a typical Polyester composite 16