Pad Materials and Properties

In general, polishing pads are composed of either a matrix of cast polyurethane foam with filler material to control hardness or polyurediane impregnated felts. Polyurethane is utilized because urethane chemistry allows the pad characteristics to be tailored to meet specific mechanical properties needs. Jairath et al. describe the manufacture of pad material as follows  

Polyurethane is a condensation polymer generally formed by the reaction between a di-isocyanate and a hydroxylated-terminated resin known as polyol in the presence of a catalyst and a foaming agent The urethane foam formed as a result of this reaction is a cellular polymer that derives its mechanical properties in part from the cell matrix formed during its manufacture and in part from the intrinsic polymer properties. Choice of the di-isocyanate and polyol dictates the inherent polymer properties in addition filler materials may be added to the polymer to improve its mechanical properties. 

F ure 4.11 Response of an elastic material to stress taxation occur instantaneously. 

F ure 4.12 Response of a viscous material to stress strain increases linearly with time and remains after stress is removed. 

F re 4.13 Response of a viscoelastic material to stress strain increases exponentially with time according to Equation (4.12). 

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