SummaryPolylactic acid (PLA) is a 100 % bio‐based polyester with strong market growth potential in commodity applications as a substitute of fossil‐based polymers such as PET, PE and PS. The successful commercialization of this material relies on the possibility to devolatilize efficiently the unreacted monomer, which, in turn, requires an effective quenching of the polymerization catalyst. In this contribution we report an experimental screening of potential catalyst deactivators performed in small scale batch reactions. The best performing deactivator was then tested on a continuous PLA production plant of 1 kta to prove the reliability of the experimental approach. The plant data confirmed that the use of the selected deactivator improves the efficiency of the devolatilization process and leads to PLA with superior optical properties.

The hydrolysis of lactic acid oligomers involves several different reactions, acid-catalyzed, base-catalyzed as well as non-catalyzed. In the present paper a pH-dependent kinetic model has been developed and its kinetic constants evaluated by fitting to experimental data of degrading lactic acid oligomers at 37 °C in aqueous solution at pH = 1, 2, 3.5, 5.7 and 7.4. The model was able to properly describe the experimental data with an average error of about 5%. The estimated values of the kinetic constants at the selected temperature are: kDα=4.44×10−3 L2mol−2h−1, kDβ=9.29×10−4 L2mol−2h−1 (acid-catalyzed), kRH=1.56×103 L2mol−2h−1, kBB=2.88×106 Lmol−1h−1 (base-catalyzed) and kW=2.49×10−5 Lmol−1h−1 (non-catalyzed).

Nanoclusters (NCs) composed of nanoparticles (NPs) with different functionalities and having final size in the sub-micrometer range are of great interest for biomedical imaging, drug delivery, sensors, etc. Because some of the functionalities cannot be incorporated into a single NP, e.g., high drug loading combined with strong magnetic properties, here, we present a proof of the concept using an alternative way to combine these properties using different NPs. In particular, starting from polymer and magnetite nanoparticles (MNPs), we produce NCs made out of a statistical distribution of the two components through a process based on aggregation and breakup. The effect of all involved operating parameters, i.e., primary NP size and composition, surfactant type and concentration, and applied hydrodynamic stress on the NC size and internal structure, was systematically investigated using dynamic light scattering (DLS), static light scattering (SLS), and transmission electron microscopy (TEM) analyses. It was found that, by properly tuning the balance between attractive and steric repulsive forces on one side and hydrodynamic stress on the other, NCs as small as 100 nm can be produced. In all cases, the produced NCs have a very compact internal structure characterized by fractal dimension around 2.6. The proposed production strategy to synthesize hetero-NCs composed of mixtures of various primary particles is suitable for the production of multifunctional devices of nanometer size (i.e., approximately 100 nm) for material and biomedical applications.

The hydrolysis of water soluble PLA oligomers of different chain lengths and chirality was investigated at acidic pH and temperatures in the range from 40 to 120 degrees C. The time evolution of the concentrations of all oligomers was measured by HPLC and the corresponding degradation rates were evaluated for each specific chain length. In agreement with the preferential chain end scission mechanism suggested in the literature, the ester groups were classified as alpha (chain end esters) and beta (backbone esters). A kinetic model was developed from the resulting kinetic scheme and it was found to well reproduce the concentration values of all different oligomers during degradation as a function of time. The corresponding rate constants k(d)(alpha) and k(d)(beta) were estimated over the whole temperature range, with activation energies of 73 and 58 kJ/mol and pre-exponential factors of 8.21 . 10(7) and 1.77 . 10(5) l/mol/h, respectively. It is seen that the faster hydrolysis of the ester groups close to the carboxylic and hydroxyl chain end groups (alpha) with respect to those inside the polymer chain (beta) is mainly due to the largely different pre-exponential factors. This steric effect can be explained considering that the water approach is favoured by the hydrophilic nature of the chain end groups compared to the hydrophobic character of the polymer backbone. No dependence of k(d)(alpha) and k(d)(beta) on chiral composition was found, suggesting that the differences reported earlier in the literature are due to the effect of crystallinity on diffusion phenomena rather than to different reactivity of the two stereoisomers. (C) 2012 Elsevier Ltd. All rights reserved.

Estimating the colloidal stability of polymeric nanoparticles (NPs) in biological environments is critical for designing optimal preparations and to clarify the fate of these devices after administration. To characterize and quantify the physical stability of nanodevices suitable for biomedical applications, spherical NPs composed of poly-lactic acid (PLA) and poly-methyl-methacrylate (PMMA), in the range 100-200 nm, were prepared. Their stability in salt solutions, biological fluids, serum and tissue homogenates was analyzed by dynamic light scattering (DLS). The PMMA NPs remained stable in all fluids, while PLA NPs aggregated in gastric juice and spleen homogenate. The proposed stability test is therefore useful to see in advance whether NPs might aggregate when administered in vivo. To assess colloidal stability ex vivo as well, spectrophotofluorimetric analysis was employed, giving comparable results to DLS.

HPLC is applied and assessed as an effective tool to investigate both the production of PLA by polycondensation and its corresponding degradation. A new HPLC calibration procedure, through which it is possible to fully characterize LMW PLA samples by determining the concentration of each individual oligomer, is developed. A comparison between HPLC, H-1 NMR spectroscopy and non-aqueous solution titration is also reported in order to confirm the reliability of the proposed method. Finally, the proposed analytical technique is applied to monitor the development of a polycondensation reaction performed at 150 degrees C and 133.3 mbar for 12 h.