Electrospinning of Poly(L-lactide-co-DL-lactide) Copolymers: Effect of Chemical Structures and Spinning Conditions Chakrit Thammawong, 1 Sutawan Buchatip, 2 Atitsa Petchsuk, 2 Pramuan Tangboriboonrat, 3 Noppavan Chanunpanich, 4 Mantana Opaprakasit, 5 Paiboon Sreearunothai, 1 Pakorn Opaprakasit 1 1 School of Bio-Chemical Engineering and Technology, Sirindhorn International Institute of Technology (SIIT), Thammasat University, Pathum Thani 12121, Thailand 2 National Metal and Materials Technology Center (MTEC), Thailand Science Park, Pathum Thani 12120, Thailand 3 Department of Chemistry, Faculty of Science, Mahidol University, Bangkok 10400, Thailand 4 Industrial Chemistry Department, Faculty of Applied Science, King Mongkut’s University of Technology North Bangkok, Bangkok 10800, Thailand 5 Department of Materials Science, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand Nanofibers of poly(L-lactide-co-DL-Lactide) (PDLLA x ) copolymers with DL-lactate (DLLA) contents of 0, 2.5, 7.5, and 50%, which exhibit strong structure/properties correlation, were fabricated by electrospinning. Effect of the copolymer structure and electrospinning condi- tions on morphology and properties of the fibers were examined by SEM, DSC, XRD, and tensile measure- ments. Bead-free fibers of PDLLA x prepared from a DMF/CHCl 3 mixed solvent are roughly 10-times smaller in size (600–800 nm), with lower degree of surface po- rosity, compared to those of CHCl 3 . When CHCl 3 is employed, an increase in size (2.4–5.5 lm) and surface porosity (0–45%) with relative humidity value is observed in crystallizable copolymers, whereas an amorphous copolymer shows a reverse trend. Thermal properties and chain arrangements of the electrospun fibers are critically affected by DLLA content of the copolymers and electrospinning conditions, as a result from interplay between intermolecular and intramolec- ular hydrogen bonding. Contents of crystalline domains and ‘physical crosslinks’ generated from DL lactate segments are proposed as the origin of this phenom- enon. Fiber mats of PDLLA with 50% DLLA content show a large improvement in all aspects of mechanical properties, which are suitable for various biomedical applications. POLYM. ENG. SCI., 00:000–000, 2013. ª 2013 Society of Plastics Engineers INTRODUCTION Polylactide (PLA) is a thermoplastic aliphatic polyes- ter, which is widely used in packaging, medical, and agricultural applications, due to its degradability, biocom- patibility, and renewability [1–3]. PLA can be synthesized by polycondensation of lactic acid, derived from starch fermentation, or ring-opening polymerization of its cyclic lactide (LA) dimer, where the latter approach is common for producing high molecular weight (MW) products. LA is present in three forms, that is, L-lactide (LLA), D-lac- tide (DLA), and DL-lactide (DLLA). The chain structure and properties of PLA can be optimized by employing different LA forms [4]. Because of the LLA abundance, poly(L-lactide), (PLLA), is widely used in commercial applications. Although the polymer has good mechanical properties, comparable to other commodity plastics [5], it is too rigid and brittle to be used in certain applica- tions [6], Copolymerization of LLA and DLLA at vari- ous compositions produces poly(L-lactide-co-DL-Lactide) Correspondence to: Pakorn Opaprakasit; e-mail: pakorn@siit.tu.ac.th Contract grant sponsor: National Research University Project of Thai- land, Office of Higher Education Commission; contract grant sponsor: Thailand Research Fund (TRF)/Thailand Office of Higher Education Commission; contract grant number: RTA5480007; contract grant spon- sor: SIIT, Thammasat University. DOI 10.1002/pen.23576 Published online in Wiley Online Library (wileyonlinelibrary.com). V V C 2013 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—-2013