Polilactida

http://patentados.com/patente/poliester-alifatico-aromatico-biodegradable/

http://www.eis.uva.es/~macromol/curso05-06/medicina/polimeros_biodegradables.htm





Poly(lactide), PLA, polymershave been used as packaging materials in the last few years, meanly as containers for deli/convenience, dairy, bakery and fresh food products. As modern technologies are lowering the productioncosts, PLA has becoming an increasing alternative for a broad array of products and is available for new packaging applications.[1-3] Currently commercial PLA polymers are fabricated by polymerizing lacticacid monomer (LA). Polymerization through lactide (L) formation is by and
large the current method use for producing massive quantities of PLA polymers. In this method, either D-lactic acid (DLA),L-lactic acid (LLA), or a mixture of the two are pre-polymerized to obtain an intermediate low molecular mass PLA), which is then depolymerized into a mixture of lactide stereoisomers. Lactide (L) isformed by the condensation of two lactic acid molecules as follows: L-lactide (two L-Lactic acid molecules) (LLL), D-lactide (two D-Lactic acid molecules) (DDL), and meso-lactide (an L-lactic acid anda D-lactic acid molecule) (LDL). After purification the lactides are polymerized into high molecular mass PLA with a constitutional unit of –OCH(CH3)CO-O-
CH(CH3)-CO]-.[4]

Properties of PLA suchas melting point, mechanical strength, and crystallinity are determined by the polymer architecture (i.e., proportions of LLL, DLL or LDL) and the molecular mass (i.e., proper addition of hydroxyliccompounds). As for other plastics, final user properties of PLA also depend on compounding and processing conditions. The proportion of D and L lactides determines polymer morphology, and PLA can
beproduced totally amorphous or up to 40% crystalline. This results in PLA polymers with a wide range of hardness and stiffness values. The glass transition temperature of PLA (Tg) ranges from 50ºC to...