a$)$ Propose, with supporting justification, a processing route which would be suitable for making an isotropic hybrid material comprising polystyrene as a matrix in which a $25\%$ volume fraction of particles of zirconia toughened alumina are dispersed.

b$)$ During prolonged service in a moist atmosphere $(95\%$ relative humidity$),$ at $65\backslash$deg C in the dark, what ageing mechanisms is polystyrene likely to be susceptible to$?$