The present invention provides a thermoplastic composite comprising: a polyolefin; a cellulosic filler; a carboxylic acid and/or carboxylic acid anhydride graft polyolefin having an acid number greater than 15 mgKOH/g; and, a basic reactive filler present in an amount of 5-25 wt %, based on the weight of the composite. Such composites may be used in structural and non-structural applications and exhibit improved mechanical properties, thermal properties and/or resistance to biological degradation.