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      Enhancing the melt stability of polylactide stereocomplexes using a solid-state cross-linking strategy during a melt-blending process

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          Abstract

          Selective cross-linking of PLLA and PDLA chain couples in the amorphous phase allows for the formation of stereocomplex (sc) crystallites in the continuous melting and recrystallization process to be perfectly reversible.

          Abstract

          Stereocomplexation between poly( l-lactide) (PLLA) and poly( d-lactide) (PDLA) provides a feasible route for improving the performance of polylactide (PLA), including mechanical strength, thermal stability and hydrolysis resistance. In recent years, several effective methods have been developed to prepare polylactide stereocomplexes (sc-PLA) from commercially available, linear, high-molecular-weight PLLA and PDLA. However, it is still a big challenge to attain pure sc-PLA in the melt-processed products because the prepared sc-PLA has a very poor melt stability, that is the ability to trigger the reformulation of stereocomplex (sc) crystallites after complete melting is significantly depressed, resulting in the formation of mixed homochiral (hc) and sc crystallites. Here we present a facile strategy to fabricate sc-PLA with good melt stability by low-temperature (180 °C) melt-blending of equimolar PLLA and PDLA in the presence of a trace amount (0.1–0.5 wt%) of a cross-linker. During the blending process, sc crystallites form rapidly, followed by a slight cross-linking of PLLA and PDLA chain couples in the mobile amorphous phase, whereas the chain couples in the crystalline phase hardly participate in the cross-linking reaction. The exclusive cross-linking of PLA chains in the amorphous phase not only allows for the introduction of abundant cross-linking points at the ends of the chain couples to prevent them from completely decoupling upon melting but also retains large amounts of long crystallizable PLA segments existing in the initially formed sc crystallites to impart the resulting sc-PLA with an excellent recrystallization ability upon cooling. The formation or reformulation of sc crystallites in the continuous melting and recrystallization process is found to be perfectly reversible, without any trace of hc crystallites.

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          Most cited references 38

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          Processing technologies for poly(lactic acid)

           L.-T. Lim,  R. Auras,  M Rubino (2008)
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            An overview of the recent developments in polylactide (PLA) research.

            The concept of biodegradable plastics is of considerable interest with respect to solid waste accumulation. Greater efforts have been made in developing degradable biological materials without any environmental pollution to replace oil-based traditional plastics. Among numerous kinds of degradable polymers, polylactic acid sometimes called polylactide, an aliphatic polyester and biocompatible thermoplastic, is currently a most promising and popular material with the brightest development prospect and was considered as the 'green' eco friendly material. Biodegradable plastics like polyglycolic acid, polylactic acid, polycaprolactone, polyhydroxybutyrate, etc. are commercially available for controlled drug releases, implantable composites, bone fixation parts, packaging and paper coatings, sustained release systems for pesticides and fertilizers and compost bags etc. This review will provide information on current PLA market, brief account on recent developments in the synthesis of lactic acid (monomer of PLA) through biological route, PLA synthesis, unique material properties of PLA and modification of those by making copolymers and composites, PLA degradation and its wide spectrum applications.
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              Poly(lactic acid) modifications

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                Author and article information

                Journal
                PCOHC2
                Polym. Chem.
                Polym. Chem.
                Royal Society of Chemistry (RSC)
                1759-9954
                1759-9962
                2014
                2014
                : 5
                : 20
                : 5985-5993
                Affiliations
                [1 ]College of Polymer Science and Engineering
                [2 ]State Key Laboratory of Polymer Materials Engineering
                [3 ]Chengdu 610065, P. R. China
                [4 ]College of Light Industry
                [5 ]Textile and Food Engineering
                10.1039/C4PY00700J
                © 2014
                Product
                Self URI (article page): http://xlink.rsc.org/?DOI=C4PY00700J

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