Effect of Plasticizer on Mechanical Loss

How much butyl acetate must be added to poly(methyl acrylate) to produce maximum damping (loss tangent or logarithmic decrement of free vibrations) at 60 Hz at 25 C  

From Table 12-1, the maximum in tan d occurs at 0.5 Hz at 298 K in the pure polymer the molecular weight does not enter, if sufficiently high. Enough diluent must be added to give log Oc = —2.1, shifting the frequency from 0.5 to 60. In equation 13 of Chapter 17, / for butyl acetate may be taken as 0.23 Fujita lists values of 0.22 and 0.24 for this diluent in polystyrene and poly(methyl methacrylate) respectively. The fractional free volume of the polymer,/2, is/ + a/ T — Tg) taking the values of the coefficients from Table 11 -II, we obtain/2 = 0.037. Equation 13 of Chapter 17 then takes the form 

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