A literature review is presented regarding the synthesis, and physicochemical, chemical, and mechanical properties of poly(lactic acid)(PLA). Poly(lactic acid) exists as a polymeric helix, with an orthorhombic unit cell. The tensile properties of PLA can vary widely, depending on whether or not it is annealed or oriented or what its degree of crystallinity is. Also discussed are the effects of processing on PLA. Crystallization and crystallization kinetics of PLA are also investigated. Solution and melt rheology of PLA is also discussed. Four different power-law equations and 14 different Mark–Houwink equations are presented for PLA. Nuclear magnetic resonance, UV–VIS, and FTIR spectroscopy of PLA are briefly discussed. Finally, research conducted on starch–PLA composites is introduced.

/pdf/a-literature-review-of-poly-lactic-acid-559pd7jgnc.pdf

A Literature Review of Poly(Lactic Acid)

Polylactide polymers have gained enormous attention as a replacement for conventional synthetic packaging materials in the last decade. By being truly biodegradable, derived from renewable resources and by providing consumers with extra end-use benefits such as avoiding paying the "green tax" in Germany or meeting environmental regulations in Japan, polylactides (PLAs) are a growing alternative as a packaging material for demanding markets. The aim of this paper is to review the production techniques for PLAs, summarize the main properties of PLA and to delineate the main advantages and disadvantages of PLA as a polymeric packaging material. PLA films have better ultraviolet light barrier properties than low density polyethylene (LDPE), but they are slightly worse than those of cellophane, polystyrene (PS) and poly(ethylene terephthalate) (PET). PLA films have mechanical properties comparable to those of PET and better than those of PS. PLA also has lower melting and glass transition temperatures than PET and PS. The glass transition temperature of PLA changes with time. Humidity between 10 and 95% and storage temperatures of 5 to 40 degrees C do not have an effect on the transition temperature of PLA, which can be explained by its low water sorption values (i.e. <100 ppm at Aw = 1). PLA seals well at temperatures below the melting temperature but an appreciable shrinking of the films has been noted when the material is sealed near its melting temperature. Solubility parameter predictions indicate that PLA will interact with nitrogen compounds, anhydrides and some alcohols and that it will not interact with aromatic hydrocarbons, ketones, esters, sulfur compounds or water. The CO2, O2 and water permeability coefficients of PLA are lower than those of PS and higher than those of PET. Its barrier to ethyl acetate and D-limonene is comparable to PET. The amount of lactic acid and its derivatives that migrate to food simulant solutions from PLA is much lower than any of the current average dietary lactic acid intake values allowed by several governmental agencies. Thus, PLA is safe for use in fabricating articles for contact with food.

An Overview of Polylactides as Packaging Materials

Physical and mechanical properties of PLA, and their functions in widespread applications - A comprehensive review.

Poly(lactic acid) modifications

Poly(lactic acid) (PLA), so far, is the most extensively researched and utilized biodegradable aliphatic polyester in human history. Due to its merits, PLA is a leading biomaterial for numerous applications in medicine as well as in industry replacing conventional petrochemical-based polymers. The main purpose of this review is to elaborate the mechanical and physical properties that affect its stability, processability, degradation, PLA-other polymers immiscibility, aging and recyclability, and therefore its potential suitability to fulfill specific application requirements. This review also summarizes variations in these properties during PLA processing (i.e. thermal degradation and recyclability), biodegradation, packaging and sterilization, and aging (i.e. weathering and hygrothermal). In addition, we discuss up-to-date strategies for PLA properties improvements including components and plasticizer blending, nucleation agent addition, and PLA modifications and nanoformulations. Incorporating better understanding of the role of these properties with available improvement strategies is the key for successful utilization of PLA and its copolymers/composites/blends to maximize their fit with worldwide application needs.

pdf/physical-and-mechanical-properties-of-pla-and-their-3so4y8c0xi.pdf

Physical and mechanical properties of PLA, and their functions in widespread applications — A comprehensive review

Small-angle X-ray scattering (SAXS), optical microscopy and differential scanning calorimetry were used to establish relationships between crystallization, microstructure, and equilibrium melting temperature (Tm0) for random copolymers of poly(l-lactide-co-meso-lactide). Tm0s derived using the Gibbs−Thomson and data-fitting23 approaches were found to be in excellent agreement and decreased significantly with increasing meso-lactide concentration. Analysis of these equilibrium melting temperatures using models for copolymer crystallization leads to the conclusion that the meso defects are rejected from the crystalline regions. From analysis of the SAXS data, it was concluded that the copolymers contained significant interfibrillar regions whose concentration increased with higher comonomer content. Spherulitic growth rates were strongly dependent on meso content and were analyzed using the Lauritzen−Hoffman kinetic theory of crystal growth.

Crystallization and microstructure of poly (L-lactide-co-meso-lactide) copolymers

Solid-state 13C CP-MAS NMR spectroscopy has been used to investigate highly crystalline, partially crystalline, and amorphous poly(l-lactide) (PLLA). The amorphous domains have broad resonances with Gaussian line shapes, while the crystalline domains have narrower resonances with a high degree of Lorentzian character. Spectra of highly crystalline PLLA have at least five distinct resonances for the carbonyl and methine functional groups in the polymer, indicating five or more crystallographically inequivalent sites in the crystalline domains of the polymer. For the amorphous polymer, broad Gaussian peaks are observed for each of the methyl, methine, and carbonyl functional groups. Spectra of partially crystalline PLLA contains spectral features of both domains, and furthermore, the spectra appear to be sensitive to both short range (nanometer) and long range (micrometer) order within the polymer. A method to extract the information of crystallinity and morphology from the solid-state CP-MAS NMR spectra of...

Solid State 13C CP-MAS NMR Studies of the Crystallinity and Morphology of Poly(l-lactide)

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Crystallization and microstructure of poly (L-lactide-co-meso-lactide) copolymers

Solid State 13C CP-MAS NMR Studies of the Crystallinity and Morphology of Poly(l-lactide)