The instant invention is directed to the use of lignin in thermoplastics (such as: ultra-high molecular weight polyethylene (UHMWPE)). In the first aspect of the invention, lignins are added to a lead acid battery separator comprising a microporous membrane including an ultra-high molecular weight polyethylene, a filler, and a processing oil. In the second aspect of the invention, lignins are used as a processing aid in thermoplastics.