A comparative study of the tensile properties of compression molded and 3D printed PLA specimens in dry and water saturated conditions

Abstract

This research work presents a comparative study of the tensile properties of polylactic acid (PLA) specimens per ASTM D638-14 fabricated by compression molding and 3D printing. PLA pellets from one batch are used in compression molding and filament extrusion for 3D printing. The compression molding process parameters are optimized to obtain an upper limit for mechanical properties of PLA specimens. Design of experiments (DoE) is used to evaluate the effect of processing temperature, pressure, and dwell time on the tensile properties of the specimens. The optimum compression molding trial resulted in slightly higher modulus for tensile specimens compared to 3D printing (3.33 GPa versus 3.22 GPa), while the average tensile strength was almost identical (59.9 MPa). Water absorption test is performed to evaluate moisture absorption of tensile specimens and compare their tensile properties in water saturated condition to the properties of dry specimens. 3D printed specimens showed a significant degradation of their tensile strength and modulus in water saturated condition by 28.4 % and 7.2 %, respectively. On the other hand, the tensile strength of the optimum compression molded specimens was decreased by only 12.0 %, while there was an increase of 14.1 % in tensile modulus.