Present Situation and Future Perspectives of Poly(lactic acid)

Of the biobased polymers developed to date, poly(l-lactide) (PLLA) is the most widely used in many application fields because of its excellent cost–property balance. However, PLLA is slightly inferior to conventional petroleum-based polymers in terms of thermal resistance and functionality. Various modified polylactides (PLAs consisting of enantiomeric d- and l-lactide units in different sequences and ratios) have recently been proposed and should expand the market for these polymers. The new developments involve polymers of high melting temperature (high-T _m polymers) based on stereocomplex-type PLAs (sc-PLA) and stereoblock-type PLAs (sb-PLA) as well as those of high glass transition temperature (high-T _g polymers) obtained by unit modification and polymer blending. Various specialty derivatives having excellent flexibility and functionality have also been developed by controlled crystallization, polymer blending, organic–inorganic hybridization, and copolymerization. The molecular weight, terminal groups, copolymer composition, and functionalities must be precisely controlled to enable control of the properties of these PLA polymers. Ordinary PLLA, being biodegradable, is widely used in commodity and agricultural fields as well as biomedical fields, mainly in the form of a film or as a non-woven fabric. The new specialty and high-performance PLA polymers can be used as functional and durable materials. Especially interesting is the applicability of PLLA polymers to 3D printing, particularly in fused deposition manufacturing (FDM).