**7. Plasticisers**

Plasticisers are the additives added to polymeric materials to improve their flexibility and durability by spacing them apart. A plasticiser-polymer mix contains more free volume than a pure polymer, thus, the plasticised polymer need to be cooled to a lower temperature to reduce its free volume which defines glass transition temperature of the polymer. There are many types of plasticisers can be used to modify the thermoplastic elastomers and enhancing their utilities. Each of the plasticisers has a compatibility with a specific type of polymer. Among them, ester plasticisers have a well known function in the TPEs due to its exceptional ability to provide improved low-temperature by plasticising the soft phase while allow the hard phase to stay intact for strength and high temperature properties. Some examples of ester plasticisers are phthalate esters which are used in situations where good resistance to water and oil is required, adipic esters which are used for low temperature or resistance to UV light and trimellitic esters which are used in automobile interiors and where resistance to high temperature is required. TPU tend to be internally plasticised by choice of monomer combination. For polyolefin elastomers, it is important to identify plasticisers which have low glass transition temperature and high boiling temperature and which are compatible over a broad temperature range with both rubber and polyolefin plastic components.
