Particle board is comprised of wood chips, saw dust and other small chunks of wood that are glued together. While the material is inexpensive, it is also unable to be used for many projects because it is not a solid wood. Particle board is good for shelves, however, and may be updated easily using paint. As long as you properly prepare your particle board, once you cover it with paint no one will ever know that engineered wood lies beneath.
Put your shelves on a drop cloth to protect your floors. Always work in a well ventilated area, such as an open garage or another room with open windows.
Sand the shelves lightly. The purpose of sanding is twofold: it will clean up any wood splinters and dirt on the shelves, and it will add more texture to the surface, which will better enable the primer to stick. Wipe down the shelves with a damp cloth after you sand to clean up the dust and debris.
Apply a coat of primer to the shelves using a paint roller. An oil-based primer will provide the strongest adhesion to your wood, but latex primer is also acceptable. Allow the primer to dry per the manufacturer's instructions, and then turn the shelves over to paint the other side. Let the shelves dry completely before you begin painting.
Apply two coats of paint using a paint roller. Remember that thin coats are better -- the paint will dry more quickly and be less likely to chip. Allow each coat to dry thoroughly, at least two hours, before applying the next coat.
Add a coat of clear water-based urethane after two days if you want to protect the shelves from scratches. Make sure that you purchase a non-yellowing urethane to maintain your original paint color over time.