In the last decades bioresorbable and biodegradable polymers have gained a very good reputation both in research and in industry thanks to their unique characteristics. They are able to ensure high performance and biocompatibility, at the same time avoiding post-healing surgical interventions for device removal. In the medical device industry, it is widely known that product formulation and manufacturing need to follow specific procedures in order to ensure both the proper mechanical properties and desired degradation profile. Moreover, the sterilization method is crucial and its impact on physical properties is generally underestimated. In this work we focused our attention on the effect of different terminal sterilization methods on two commercially available poly(l-lactide-co-ε-caprolactone) with equivalent chemical composition (70% PLA and 30% PCL) and relatively similar initial molecular weights, but different chain arrangements and crystallinity. Results obtained show that crystallinity plays a key role in helping preserve the narrow distribution of chains and, as a consequence, defined physical properties. These statements can be used as guidelines for a better choice of the most adequate biodegradable polymers in the production of resorbable medical devices.
In Ziegler–Natta catalysis, the catalyst particle size has a strong influence not only on catalyst performance but also on the morphology and particle size distribution of the final polymer particles. Fundamental insight into the catalyst particle formation process is therefore of industrial importance when addressing specific requirements in the final products. In the present work, we fully characterize a single-step catalyst preparation process, which comprises a reactive precipitation of a MgCl2-supported Ziegler–Natta catalyst, through decomposition of the hetero-bimetallic complex, Mg(OR)2·Ti(OR)4, by addition of ethyl aluminum dichloride (EADC). We track the evolution of both of the concentrations of the metals (Mg, Ti, Al) as well as Cl in the liquid phase and the size of the formed catalyst particles. It is observed that the liquid-phase composition is governed by the EADC feed rate under fully Cl-starved conditions. The process can be divided into two stages: The first stage is dominated by the precipitation of the Mg-based support, and the second stage involves complex adsorption–precipitation of the Ti species. The growth of the catalyst particle size occurs only in the first stage and is controlled by the aggregation and breakage events during the MgCl2 precipitation. It follows that the hydrodynamic stress in the reactor plays the essential role in controlling the catalyst size. In the second stage, no further particle growth occurs, not only because of the depletion of Mg in the liquid phase but also because the adsorbed Ti complex stabilizes the particles against aggregation. Finally, we have performed polymerization tests with the prepared catalysts and found that the size distribution of the polymer particles indeed closely replicates the one of the used catalyst particles.
The production of porous clusters by controlled aggregation of polyacrylonitrile nanoparticles and thermal treatment, and their application to CO2 capture are reported. The synthesis of the primary particles by emulsion polymerization exhibits good reproducibility and is easy to scale up. The subsequent gelation of the produced latexes (controlled destabilization by salt addition) results in the formation of macroporous monoliths of nanoparticles with a mean pore diameter of 100 nm. A carefully assessed thermal treatment is applied to the dried monolith after grinding. The produced porous clusters are processed with three high‐temperature steps: oxidation, stabilization, and pyrolysis. The latter allows for the creation of micropores in the initially non‐porous nanoparticles, thus enabling access to the remaining nitrogen‐bearing species present in the pyrolyzed polymer. The relative contributions of the remaining nitrogen‐bearing species and of the micropores are elucidated by applying different oxidation temperatures. In particular, the fraction of the pores with diameter smaller than 0.7 nm is decisive in determining the final capture ability. After a treatment including oxidation at 240 °C, stabilization at 350 °C, and pyrolysis at 900 °C, the best reported material shows an average CO2 adsorption capacity of 3.56±0.17 mol (CO2) kg−1 at 0 °C and 1 atm.
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