Disclosed herein is a process for preparing a composite material comprising mixing at least one natural fiber, at least one polyolefin resin, and at least one functionalized polyolefin coupling agent to provide said composite material; wherein said functionalized polyolefin coupling agent possesses a molecular weight distribution of greater than 2.5 (Mw/Mn by GPC) and comprises a base polyolefin resin that is grafted with a total of more than about 1 mmole of at least one polar monomer per 100 grams of functionalized polyolefin coupling agent.