Unique Microstructure and Mechanical Properties from Melt Processing Poly(Lactide- co -Glycolide)/Poly(Trimethylene Carb
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Unique Microstructure and Mechanical Properties from Melt Processing Poly(Lactide-coGlycolide)/Poly(Trimethylene Carbonate) Jianbin Zhang, Lian Luo, Suping Lyu, Bryant Pudil, Jim Schley, Mike Benz, Adam Buckalew, Kim Chaffin, Chris Hobot, and Randy Sparer Medtronic Strategy and Innovation, Medtronic, Inc., 710 Medtronic Parkway, Minneapolis, MN, 55432, USA ABSTRACT Poly(lactide) (PLA) and its copolymers degrade through hydrolysis into non-toxic and water soluble metabolic products in vivo. They are ideal materials for resorbable biomedical applications such as drug delivery and tissue engineering. However, these polymers are brittle and often need to be toughened. One of the most effective toughening methods is reactive blending, in which additives are dispersed into polymer matrices as small particles with strong bonding between the two materials. In this paper, we studied toughening poly(lactide-coglycolide) (PLGA) through reactive blending with poly(trimethylene carbonate) (PTMC). We observed warm-like micelle or swollen warm-like micelle structures created during the reactive blending process with a twin screw extruder at high temperature. The micelle structures were orientated along the extrusion direction with their length ranging from 50 to 1000 nm and diameters about 50 nm. This structure could be produced only with a twin screw extruder. When a batch mixer was used, the PTMC additive (10 to 30 wt%) formed spheres with diameters on the order of 100-500 nm. The PLGA/PTMC copolymers formed in situ were responsible to this microstructure. The mechanical properties of this blend were significantly improved over the pure PLGA. INTRODUCTION PLA and its copolymers for example PLGA have been extensively studied for biomedical applications such as controlled drug delivery, engineered tissue replacements, and other implantable medical devices.1-5 They are strong and rigid, but brittle. It has been demonstrated that a brittle polymer can be converted into a ductile one by blending with a rubbery dispersed component that has small domain sizes, high aspect ratios, and strong interfacial boding.6,7 Various additives, including polycaprolactone, polyethylene and etc., have been studied for this purpose and proved effective to certain extent.8 However, in order for these additives to work more effectively, premade copolymers often were used for compatibilization.8,9 A more effective blending method is reactive blending. In a previous study, it was discovered that spontaneous transesterification reactions happened between PLGA and PTMC at elevated temperature and resulted in the formation of copolymers (PLGA-co-PTMC).10 In the current study, we explored the microstructure formed during melt blending PLGA and PTMC. Two methods, batch mixing vs. twin-screw extrusion, were compared. The blend morphologies were studied by both scanning and transmission electron microscopy. The mechanical properties were also investigated.
EXPERIMENT Materials Characteristics of the polymers used in this study are listed in Table
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