A New Strategy for Recycling and Preparation of Poly(l-lactic acid):  Hydrolysis in the Melt

Abstract

Poly(L-lactide) [i.e., poly(L-lactic acid) (PLLA)] was hydrolyzed in the melt in high-temperature and high-pressure water at the temperature range of 180-350 degrees C for a period of 30 min, and formation, racemization, and decomposition of lactic acids and molecular weight change of PLLA were investigated. The highest maximum yield of l-lactic acid, ca. 90%, was attained at 250 degrees C in the hydrolysis periods of 10-20 min. Too-high hydrolysis temperatures such as 350 degrees C induce the dramatic racemization and decomposition of formed lactic acids, resulting in decreased maximum yield of L-lactic acid. The hydrolysis of PLLA proceeds homogeneously and randomly via a bulk erosion mechanism. The molecular weight of PLLA decreased exponentially without formation of low-molecular-weight specific peaks originating from crystalline residues. The activation energy for the hydrolysis (deltaE(h)) of PLLA in the melt (180-250 degrees C) was 12.2 kcal x mol(-1), which is lower than 20.0 kcal x mol(-1) for PLLA and 19.9 kcal x mol(-1) for poly(dl-lactide) [i.e., poly(DL-lactic acid)] as a solid in the temperature range below the glass-transition temperature (21-45 degrees C). This study reveals that hydrolysis of PLLA in the melt is an effective and simple method to obtain l-lactic acid and to prepare PLLA having different molecular weights without containing the specific low-molecular-weight chains, because of the removal of the effect caused by crystalline residues.

Hydrolytic Degradation

“…The obtained DE h of PLLA crystalline residues was 75.2 kJ/mol, which is significantly higher than the 50.9 kJ/mol obtained by us for PLLA in the melt in the temperature range of 180-250 C [70], but is slightly lower than the 83.7 and 83.3 kJ/mol reported by Makino et al [15] for PLLA and PDLLA microspheres, respectively, as solids in a temperature range below the glass transition temperature (T g ) (21-45 C).…”

Water vapor permeability of poly(lactide)s: Effects of molecular characteristics and crystallinity

“…16 The purpose of this article was to investigate in detail the effects of molecular characteristics and highly ordered structures of PLA specimens on their water vapor transmission behavior. For this purpose, we have prepared PLLA having different molecular weights by polymerization of l-lactide at different conditions and by hydrolysis of relatively low molecular weight PLLA in the melt 17 and synthesized or obtained PLA with different d-lactide contents (tacticities and optical purities). We have prepared films from these polymers by solution casting and the obtained films were made amorphous by melt-quenching or the melt-quenched films were crystallized for different times to have various X c values.…”

Economics and GHG emission reduction of a PLA bio-refinery system—Combining bottom-up analysis with price elasticity effects

“…Fan et al, 2003;Tsuji et al, 2003). PLA is converted into L-LA by a short hydrolysis at low temperatures, i.e.…”

“…PLA is converted into L-LA by a short hydrolysis at low temperatures, i.e. about 90% LA can be recovered at 250 • C in 10-20 min (Tsuji et al, 2003). The L-LA is then polymerised to PLA again.…”

“…About 90% l-lactic acid can be recovered by hydrolysis at 250 • C and a processing time of 10-20 min (Tsuji et al, 2003). kg biomass input.…”