Provided are methods for improving the melt strength of oriented thermoplastic polymer compositions comprising a polyvinyl chloride formulation, comprising adding an acrylic copolymer to the oriented thermoplastic polymer composition, wherein the acrylic copolymer comprises polymerized units derived from (i) 50 to 95 weight % of methyl methacrylate monomers, and (ii) 5 to 50 weight % of C2-C6 alkyl (meth)acrylate monomers, based on the total weight of monomers in the acrylic copolymer, wherein the acrylic copolymer has a M w /GPC-PS of 4 x 106 g/mol or more.
