Polylactide, biodegradation

Polycaprolactones (see also Section 25.11), although available since 1969, have only recently been marketed for biodegradable purposes. Applications include degradable film, tree planting containers and slow-release matrices for pharmaceuticals, pesticides, herbieides and fertilisers. Its rate of biodegradability is said to be less than that of the polylactides. 

Sinha, R.S., Yamada, K., Okamoto, M. and Ueda, K. 2002. New polylactide/layered silicate nanocomposite A novel biodegradable material. Nano Betters 2 1093-1096. 

Arimura H, Ohya Y, Ouchi T (2005) Formation of core-shell type biodegradable polymeric micelles from amphiphilic poly(aspartic acid)-Wock-polylactide diblock copolymer. Biomacromolecules 6 720-725... 

The neutral fats used in the preparation of the hydrophobic core of the several liposphere-vaccine formulations described here included tricaprin and tristearin, stearic acid, and ethyl stearate. The phospholipids used to form the surrounding layer of lipospheres were egg phosphatidylcholine and dimyristoyl phosphatidylg-lycerol. Polymeric biodegradable lipospheres were prepared from low molecular weight polylactide (PLA) and polycaprolactone-diol (PCL). 

All liposphere formulations prepared remained stable during the 3-month period of the study, and no phase separation or appearance of aggregates were observed. The difference between polymeric lipospheres and the standard liposphere formulations is the composition of the internal core of the particles. Standard lipospheres, such as those previously described, consist of a solid hydrophobic fat core composed of neutral fats like tristearin, whereas, in the polymeric lipospheres, biodegradable polymers such as polylactide or polycaprolactone were substituted for the triglycerides. Both types of lipospheres are thought to be stabilized by one layer of phospholipid molecules embedded in their surface. 

Carboxylic Acids Obtained by Fermentation of Carbohydrates Lactic (2-hydroxy-propionic) acid obtained by fermentation of glucose and polysaccharides is used by NatureWorks (Cargill/Dow LLC) to prepare polylactide (PLA), a biodegradable or recyclable polymer with a potential production of 140000 t a-1 (Scheme 3.4) [23], This and other potential useful reactions from lactic acid have been reviewed by Datta and Henry [24],... 

Hu et al. showed a decrease in electrical resistivity of PVA by four orders of magnitude with a percolation threshold of 6 wt% [68], while biodegradable polylactide-graphene nanocomposites were prepared with a percolation threshold as low as 3 5wt% [46]. For polystyrene-graphene composites, percolation occurred at only 0.1 °/o of graphene filler, a value three times lower than those for other 2D-filler [69]. Figure 6.7(b) shows the variation of conductivity of the polystyrene-graphene composite with filler content. A sharp increase in conductivity occurs at 0.1 % (the percolation threshold) followed by a saturation. The inset shows the four probe set up for in-plane and trans-... 

One approach to compartmentalize hemoglobin is to encapsulate hemoglobin in biodegradable polymer-PEG-polylactide (30). These nanocapsules have a diameter of 80-150 nm and contain superoxide dismutase, catalase, carbonic anhydrase, and other enzymes of Embden-Meyerhof pathway that are needed for long-term function of an oxygen carrier (31,32). The polylactide capsules are metabolized in vivo to water and carbon... 

The use of biodegradable polymers, especially polylactic acid (PLA), in oral solid dosage forms has been reported in the literature. PLA has been used as a matrix for phenobarbital tablets (9). Similarly, the use of polylactide as a matrix for oral dosage form of naproxen has also been reported (10). 

DL-Polylactic acid, for the most part, was found to erode in about 12 months. Slow degradation of DL-polylactic acid often becomes a limitation on its use. This rate can be accelerated appreciably by copolymerizing with up to 50 mol% glycolide to yield complete erosion in as fast as 2 to 3 weeks. Incorporation of glycolide into the polylactide chain alters crystallinity, solubility, biodegradation rate, and water uptake of the polymer. 

Arshady, R. Preparation of biodegradable microspheres and microcapsules 2. Polylactides and related polyesters. J. Contr. Rel. 17 1—22, 1991. 

Following the recognition of polylactide as a promising biomedical polymer, attention was drawn to related polyesters in the search for new degradable polymers in similar applications. PCL was recognized as a biodegradable and nontoxic material. 

BMM623>, /3-valerolactone <2002JA15239>, and a-methyl-/3-pentylpropiolactone <2004T7177>. The polyester formed from the latter monomer was used in the formulation of immiscible blends or block copolymers with the biodegradable aliphatic polyester polylactide <2004T7177>. 

S. S. Ray, K. Yamada, M. Okamoto, and K. Ueda, New polylactide-layered silicate nanocomposites. 2. Concurrent improvements of material properties, biodegradability and melt rheology, Polymer 44, 857—866 (2003). 

Keywords biodegradable, biobased, polyester, polylactide, mechanical properties, dispersion, environmentally friendly. 

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