**8. Additives**

146 Thermoplastic Elastomers

blow molding where the molten plastic is injection molded around the core pin and then the core pin is transferred to a blow molding station to be inflated. There are two stretch molding techniques. In one-stage process, the preform is injection molded which is then transferred to the blow mold where it is blown and ejected from the machine. In the twostage process, preform is injection-molded, stored for a short period of time, and blown into

Thermoforming is a process which uses heat and pressure or vacuum to transform thermoplastic flat sheet into a desired three-dimensional parts. The sheet is drawn from large rolls or from an extruder and then transferred to an oven for heating to its softening temperature. The heated sheet is then transferred to a preheated, temperature-controlled mold. Vacuum is applied to remove the trapped air and deform the sheet into the mold cavity, where it is cooled to retain the formed shape. After that, a burst of reverse air pressure is applied to break the vacuum and assist the formed part out of the mold. The principal factors in this process include the forming force, mold type, sheet prestretching, the material input form and the process phase condition. These factors have a critical effect

Calendaring is a process where a large amount of molten plastic is fashioned into sheets by passing the polymer between a set of rollers. The rollers are hot and keep the polymer in its semi-molten state. This allows the molten to be rolled many times until the desired thickness is reached. The sheet is then rolled through cold rollers to enable it to go hard and then wound up into rolls. Calendar for thermoplastics generally operates in four-roll units made up of three banks, each bank being wider than the preceding one. The advantages of calendar over extruder are the possibility of calendar to produce embossed films, sheets and laminates and the higher output than extruder. Examples of the final products are cling film, shrink film, clear, translucent rigid sheets for blister packaging and opaque flexible film.

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

container using a reheat blow machine.

on the quality and properties of the final products.

**6.6 Thermoforming** 

**6.7 Calendaring** 

**7. Plasticisers** 

Common additives in TPEs include those materials added during or after polymerization to prevent their degradation, during monomer recovery, drying and compounding, and also storage.
