What is the expected mold shrinkage of polyester?
Molecular weight does not have a significant effect on mold shrinkage for Eastman™ PET based containers. Shrinkage is mainly thermal, related to the coefficient of linear thermal expansion of thermoplastic polyesters, so sheet temperature and mold temperature control the shrinkage. The CLTE of Eastman™ PET 9921 is 65xE-6 in/in/°F, so changing the delta between sheet and mold temperature is not effective to change the shrinkage. There is a further cooling segment from the mold temperature down to room temperature, but this is a small effect. Mold shrinkage is a property of the polymer, Eastman™ PET 9921 shrinks 0.2 to 0.3%. CLTE accounts for 0.16% of the shrinkage of Eastman™ PET 9921. Mold shrinkage can be affected by any mechanical advantage in the design of the part, such as ribs, turned flange, which can restrain the shrinkage. As you go up in CHDM content, the coefficient of linear thermal expansion is higher. The CLTE for polyesters is not significantly different for temperature r
