I use turpentine too clean my brushes...will turpentine stiffens the hog bristle of an oil painting brush?

After you get most of the turps and paint out, wash your brushes in a liquid dish detergent and rinse well with cool water. Lay the brushes flat to dry, never stand them upright with the bristles up. Never, never allow your brushes to soak in soapy water. Water soaking under the ferrule will ruin brushes.