Density and Crystallinity Correlations: Enhancing Moisture Barrier Properties in Poly(<scp>l</scp>‐Lactic Acid), Poly(<scp>d</scp>‐Lactic Acid), and Stereocomplex‐Poly(<scp>l,d</scp>‐Lactic Acid) Films
James F. Macnamara, Richard S. Vallery, David Gidley, Rafael Auras
Abstract
ABSTRACT This study examines the relationship among the density, crystallinity, and moisture barrier properties of poly( l ‐lactic acid) (PLLA), poly( d ‐lactic acid) films (PDLA), and their PLLA/PDLA blends (85/15, 70/30, 50/50, and 30/70). Amorphous film samples display densities between 1,230 ± 6 and 1,243 ± 2 kg m −3 , while semi‐crystalline samples show higher densities of 1,250 ± 8 to 1,257 ± 9 kg m −3 . A notable finding is an inverse relationship between density and moisture barrier performance, 2.308 ± 0.207 to 0.713 ± 0.128 × 10 −14 (kg m) (m −2 s −1 Pa −1 ) as density increases. The analysis confirms a correlation between increased density and crystallinity, with fully crystalline PLLA and a 50/50 PLLA/PDLA blend achieving densities of 1,270 and 1,285 kg m −3 , respectively. The impact of annealing time on 50/50 PLLA/PDLA blends is explored, demonstrating that as annealing time increases, so does the stereocomplex‐PLA crystallinity and rigid amorphous fraction, impacting the overall density. Higher densities are observed at shorter annealing times (5 and 15 min) when homocomplex structures dominate over stereocomplex structures. In contrast, longer annealing times (30 and 60 min) favor stereocomplex structures and exhibit lower densities due to the competition between increased rigid amorphous formation and homocomplex and stereocomplex PLA ratio. This study provides crucial insights and experimental data on stereocomplex PLA.