There are several different material used for wind turbine blades. We will skim over the materials most commonly used.
Aluminum is not a suitable material for such conditions. It is light weight but cannot stand up to fatigue caused by repeated bending.
Wood has been used for some time in wind machines and is still a good material for small applications. It is relatively inexpensive and does not take extraordinary tools to machine. This currently makes it the material of choice for homebuilt wind turbines.
Moisture is a problem for wood. Wood blades can be sealed with various finishes, however, nicks and scratches in the surface coating will allow moisture to penetrate the wood. The blades will retain moisture at differing rates and causes blade imbalance.
Fiberglass is another suitable material used in blade construction. Different variations in the matrix can be used such as vinyl ester, polyester and epoxy. Fiberglass is reasonably stiff with good strength. The Bergey XL.1 blades are made of pultruded fiberglass.
Polypropylene blades are widely used by larger companies such as Southwest Wind Power and Proven Energy. SWWP list their's as Polypro/Carbon glass reinforced. Proven blades are shown as polypropylene composite. The carbon and the glass fibers are for reinforcement to provide a stiff blade with good fatigue levels.
The bottom line on blade material is a tough one to use as selection criteria. The more important issue in the blade department is the rotor diameter or swept area.