Abstract: A novel biaxially oriented polystrene sheet product and process for making the sheet. Oriented polystyrene sheet is prepared by melt extruding a polymer, such as styrenic resin having average molecular weight of at least 270,000, blended with a processing agent, such as mineral oil, to lower glass transition temperature of the resin by at least 10.degree. C. The cooled extruded sheet is biaxially oriented under reduced orientation load conditions and orientation temperature. In a preferred embodiment styrenic resin is blended with about 3-10 wt % paraffinic hydrocarbon oil, such as mineral white oil or the like, in the substantial absence of other additives to provide a clear, oriented polystyrene sheet product having high modulus and low haze.

Abstract: A novel biaxially oriented polystrene sheet product and process for making the sheet. Oriented polystyrene sheet is prepared by melt extruding a polymer, such as styrenic resin having average molecular weight of at least 270,000, blended with a processing agent, such as mineral oil, to lower glass transition temperature of the resin by at least 10.degree. C. The cooled extruded sheet is biaxially oriented under reduced orientation load conditions and orientation temperature. In a preferred embodiment styrenic resin is blended with about 3-10 wt % paraffinic hydrocarbon oil, such as mineral white oil or the like, in the substantial absence of other additives to provide a clear, oriented polystyrene sheet product having high modulus and low haze.

Abstract: A nucleonic thickness gauge measures the total electron density of a pigmented thermoplastic film from which a product density and thickness may be derived. The amount of pigment admixed with the thermoplastic film resin in an extruder is controlled in response to a comparison between the thickness measured with the nucleonic gauge and the thickness determined from the actual product weight.