Making polylactide sheet by melting and extruding polylactide granules into or onto rollers

摘要

To form a sheet capable of crystallization, the internal temperature of the extruder is less than 220 deg C, the residence time of the polylactide in the extruder is at most 10 min. and the temperature of the smoothing roller pair (4,5) into which the sheet enters, or the temperature of the roller onto which the sheet is extruded, is maintained no higher than 70 deg C. Preferred features: The internal temperature of the extruder is at least 190 deg C. The temperature of the roller(s) is at least 20 deg C. The smoothing rollers (3) are at least three-high with S-shaped lacing of the sheet. The first roller (4) has a temperature of 20 deg C-50 deg C, the second (5) a temperature of up to 15 deg C higher, and the third (6) an up to 30 deg C higher temperature than the first. The sheet is extended by thermoforming. Before stretching in the thermoforming die, it is heated to 80 deg C at least, for 0.5 min. at least. Before stretching, heating continues for up to 5 min. It is heated at most to 180 deg C. During stretching in the thermoforming die, the sheet has a temperature of at least 60 deg C. Thermoforming is conducted using vacuum or pressure.