Processing, polylactic acids

Polylactic acid (PLA) has been produced for many years as a high-value material for use in medical applications such as dissolvable stitches and controlled release devices, because of the high production costs. The very low toxicity and biodegradability within the body made PLA the polymer of choice for such applications. In theory PLA should be relatively simple to produce by simple condensation polymerization of lactic acid. Unfortunately, in practice, a competing depolymerization process takes place to produce the cyclic lactide (Scheme 6.10). As the degree of polymerization increases the rate slows down until the rates of depolymerization and polymerization are the same. This equilibrium is achieved before commercially useful molecular weights of PLA have been formed. 

The first step will be to separate the seed from the straw (collection will obviously occur simultaneously, to minimise energy use and labour cost). The seeds may then be processed to produce starch and a wide variety of products, including ethanol and bioplastics (e.g. polylactic acid). The straw can be processed to products via various conversion processes, as described above for a lignocellulosic feedstock biorefinery. 

The 3-stage process involves utilisation of plant sugars derived from photosynthetically fixed C02 as carbon sources in the fermentation of organic acids, alcohols and amino acids. These substances are then used as building blocks for the chemical synthesis of polymers. Examples of polymers using the 3-stage process include polylactic acid and polybutylene succinate. 

The starting material for polylactic acid is starch from a renewable resource such as corn. Corn is milled, which separates starch from the raw material. Unrefined dextrose is then processed from the starch. Dextrose is turned into lactic acid using fermentation, similar to that used by beer and wine producers. 

Polylactic acid has been around for many decades. In 1932, Wallace Carothers, a scientist for DuPont, produced a low molecular weight product by heating lactic acid under a vacuum. In 1954, after further refinements, DuPont patented Carothers process. 

Polylactic acid also has many potential uses in fibres and non-wovens. It is easily converted into a variety of fibre forms using conventional melt-spinning processes. Spunbound and meltblown non-wovens as well as monocomponent, bicomponent, continuous (flat and textured) and stable fibres are all easily produced. 

Polylactic acid was first discovered in the 1930s when a DuPont scientist, Wallace Caruthers, produced a low molecular weight PLA product. In 1954, DuPont patented Carothers process. Initially the focus was on the manufacture of medical grade applications due to the high cost of the polymer, but advances in fermentation of glucose, which forms lactic acid, has dramatically lowered the cost of producing lactic acid and significantly increased interest in the polymer. 

In 2005, Japanese company Kaneka developed the first beads-process, foamed resin moulded product, which is based on polylactic acid. The new KanePearl product has the strength and shock-absorbing properties of existing beads-process, foamed polystyrene products. 

Nodax can be blended with other biodegradable polymers such as polylactic acid and thermoplastic starch for improved processing performance. 

Polylactic acid is a biodegradable polymer. It can be made from lactic acid, which can be produced by fermentation of glucose. Because it is biodegradable and can be manufactured from agricultural products, polylactic acid is potentially a renewable material. US 6,326,458 assigned to Cargill Inc. describes a process for making polylactic acid from lactic acid. Estimate the cost of production of the purified polymer. 

Abbreviations A, acetone ASES, aerosol solvent extraction system DM, dichloromethane DMF, A/,A/-dimethyl-formamide E, ethanol GAS, gas antisolvent process H, hexane HYAFF-11, hyaluronic acid benzylic ester I, isopropanol PAN, polyacrylonitrile PCA, precipitation with compressed antisolvent PCL, polycaprolactone PHB, poly(p-hydroxybutyric acid) PLA, polylactic acid PLGA, poly(lactic-co-glycolic acid) SAS, supercritical antisolvent process SEDS, solution enhanced dispersion by supercritical fluids TFE, 2,2,2-trifluoroethanol Triblock polymer, p poly(L-lactide-CO-D,L-lactide-co-glycolide)(62.5 1 2.5 25). 

High density (HDPE), 52 Irregularities, 52 Linear low density (LLDPE), 52 Low density (LDPE), 52 Molecular weight, 52 Melt flow index, 53 Melting temperature, 51 Moisture absorption, 51 Polymeric forms, 52 Resistance to chemicals, 52 Resistance to oxidation, 52 Shrinkage, 54 Unsaturations, 54 a-transition, 51 P-transition, 51 y-transition, 51 Polyisocyanate, 79 Polylactic acid, 79, 91 Polymer alloys, 48 Polymer processing additives, 646 Polymer rheology, 619 Polymeric forms, 52 Polyphase PlOO, 451 polypropylene (PP), 2, 11 Polypropylene homopolymer, 70... 

From the perspective of biocompatibility, degradability, and process-ability, synthetic polymers have many advantages over complex natural polymers such as collagen. One class of polymers in particular, polyesters in the family of polylactic acid (PLA), polyglycolic acid (PGA), and copolymers of lactic and glycolic acids (PLGAs), most closely meets the listed criteria. These polymers have been approved by the FDA for in vivo... 

In an early study by Lin et al., insulin-loaded polylactic acid (PLA) microcapsules were synthesized by an emulsification-solvent evaporation process originally reported by Beck et al. Several parameters in the synthesis process were modified with the intention of optimizing the insulin release profile. Such modifications included variations in types, concentrations, and viscosities of protective colloids used in the emulsification process. Polyvinyl alcohol (PVA), when used as the protective colloid in the fabrication process, was found to produce the PLA microparticles in reproducible quality. Further studies revealed that the concentration PVA directly affects the PLA particle size and the surface characteristics of the microcapsules. With higher concentrations of PVA, microparticles tended to be smaller and to have a smoother surface. When the release profiles of the microcapsules were stud-... 

Lactic acid can be produced chemically, or biologically, by fermentation of carbohydrate by lactobacillus, for example [SOD 02]. There are a number of ways to produce PLA [JAC99], also written as polylactic acid . The industrial and conventionally used means of obtaining high-molar-mass PLA is presented in Figure 9.5. This process is based on several steps ... 

Oksman, K., et al., 2006. Manufacturing process of cellulose whiskers/polylactic acid nanocomposites. Composites Science and Technology 66 (15), 2776—2784. 

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