Lactide polymer grade

Typically, polymer-grade l-LA with high chemical purity and optical purity (i.e., over 98-99% l-LA and less than 1-2% d-LA) is used for commercial PLA production. When l-LA is dehydrated at high temperature into L-lactide, some l-LA may be converted into d-LA. d-LA mixed with l-LA contributes to meso-lactide (the cyclic dimer of one d-LA and one l-LA) and heteropolymer PLA (with both d-LA and l-LA units). Heteropolymer PLA exhibits slower crystallization kinetics and lower melting points than homopolymer PLA (of pure l-LA units or pure d-LA units). 

As mentioned, there is not a specific level of purity for the polymers used for MDs. Purity level is easier to determine for drugs because the required degree of purity is pharma grade. However, there are ASTM standards that give the specific conditions for which a polymer can be used in different areas. For example, the ASTM F1925-09 Standard Specification for Semi-Crystalline Poly (lactide) Polymer and Copolymer Resins for Surgical Implants outlines the chemical-physical characteristics so that the poly(lactic acid) or a copolymer thereof can be used in a specified field. ASTM standards are available for purchase on the web. 

PLA can be produced by condensation polymerization directly from its basic building block lactic acid, which is derived by fermentation of sugars from carbohydrate sources such as com, sugarcane, or tapioca, as will be discussed later in this chapter. Most commercial routes, however, utilize the more efficient conversion of lactide—the cyclic dimer of lactic acid— to PLA via ring-opening polymerization (ROP) catalyzed by a Sn(ll)-based catalyst rather than polycondensation [2-6]. Both polymerization concepts rely on highly concentrated polymer-grade lactic acid of excellent quality... 

PURAC has been producing pharmaceutical-grade lactic acid based polymers for medical applications during the last 30 years. These medical applications (e.g., sutures, bone screws) are not the focus of this chapter, which covers only the large-scale industrial applications of PLA. In 2008, PURAC started a d-LA program and produced L-lactide and D-lactide for its PLA partners, such as Synbra. Synbra plans to introduce small volumes of expandable PLA (BioFoam ) to extend its range of expanded polystyrene (PS)-based foam products, before building a 50,000 ton per year expanded-PLA production facility (Schut 2008). 

There are many kinds of bio-based and biodegradable polymers, among which one of the most promising is poly(lactic acid) (PLA), a biocompatible thermoplastic aliphatic polyester. PLA is a linear thermoplastic polyester produced by the ring-opening polymerization of lactide. Ln general, commercial PLA grades are copolymers of poly(L-lactic acid) and poly(D,L-lactic acid), which are produced from L-lactides and D,L-lactides, respectively. The ratio of L-enantiomers to o,L-enantiomers is known to affect the properties of PLA, i.e. if the materials are semicrystalline or amorphous. Until now, most of the efforts reported in order to improve the properties of PLA have been focused on the semicrystalline material. ... 

In comnoercial PLA grades, the polymer is obtained by ring opening polymerization of Lactide, a dimer of Lactic acid. The maximum attainable crystalinity level is obtained by minimizing the amount of Z>-Lactide isomers and of Z Z -Lactide (i.e. mesolactide) to the Z-Lactide used as the major monomer. The PLA becomes completely amorphous the D-LA content reaches 7%. The crystallization speed is also strongly dependent on the L-LA content. For example, the crystallization half-time was found to increases by roughly 40% for every 1 wt % increase in the mesolactide content of the polymerization mixture [3]. 

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