F. López-Serrano

Semicontinuous Heterophase Polymerization of Methyl and Hexyl Methacrylates to Produce Latexes with High Nanoparticles Content

The semi-continuous heterophase polymerization (SHP) under monomer-starved conditions of methyl methacrylate and hexyl methacrylate is reported, at various monomer addition rates to elucidate the effect of monomer solubility on the mechanism of particle nucleation and growth. Polymer particles in the nanometer range from both monomers were obtained, which decreased in size as monomer addition rate was decreased. Molar masses of both polymers also diminished as monomer addition rate was slowed down. The propagation rate constant dictates how fast the starved condition is achieved rather than the monomer solubility in the aqueous phase. A slow particle rate of growth helps to obtain a narrower PSD.

Pickering emulsion polymerization kinetics of styrene: Comparison of bare and surface modified SiO2 nanoparticles

ABSTRACT A step towards the understanding of some mechanistic events occurring in the styrene Pickering emulsions, using a SiO2 dispersion, is presented. Polymerizations at 80°C with different levels of a water soluble initiator were performed. The emulsion polymer content was ca. 15% with conversions close to 90%. With conversion and particle size measurements, the particle density was estimated for bare and surface modified SiO2 particles. Then, the average number of radicals per particle was inferred, yielding a pseudo-bulk type polymerization. It was found that bare SiO2 nanoparticles do not participate in the nucleation mechanism; however, they, along with the initiator, promote an enhanced oligomer coagulation. On the other hand, the hexadecyltrimethylammonium bromide modified SiO2 nanoparticles do participate in the nucleation and coagulation mechanisms, yielding more stable and smaller poorly-covered polymer particles. This approach allowed untangling some events such as: particle nucleation, radical entry to particles, particle density, coagulation and vitreous and Trommsdorff effects.

Monitoring styrene Pickering SiO2-supported emulsion polymerization kinetics by Raman spectroscopy: Elucidating mechanisms interpreting the silanol/phenyl π-interactions

ABSTRACT A different internal reference band in Raman spectroscopy, to monitor SiO2-supported styrene Pickering emulsion polymerizations, is postulated. Raman spectroscopy allowed detecting silanol/styrene-aromatic-ring interactions yielding a deviation, against conversion, in the 1630/1000 wave number ratio, commonly used for monitoring styrene polymerizations. The detection of silanol/aromatic-ring interactions permitted supporting a previous proposal for the continuous nucleation during Pickering polymerization, without requiring a more sophisticated analysis such as NMR.

Modeling, Simulation and Scale-up of a Batch Reactor

A simple model for the batch emulsion polymerization of styrene, considering different size reactors has been studied. The resulting differential equation-set was solved for the temperature (jacket and reactor) and conversion profiles as a function of time. The fundamental dimensionless numbers, appearing in the different terms of the reaction equation-set, involving the physics of the process, were compared for different size reactors allowing the basic description of scaling and its difficulties.

A Simple-to-Implement Simulator for the Reactive Extrusion of Poly(Lactic Acid) in a Corotating Uniform Twin-Screw Extruder

The present paper deals with the poly(lactic acid) (PLA) reactive processing simulation in a uniform corotating twin-screw extruder that can be readily turned into practical applications in pilot and industrial equipment. The simulator provides a cause-effect guide that can be useful for starting an experimental setup in a reactive screw extruder for a biopolymer in a growing industry. The proposed model considers a free radical ring-opening mechanism involving the main characteristic flows inside the extruder and the non-Newtonian behavior of PLA. The characteristic behavior relating reaction rate, average molecular weights, and polydispersity against chamber number are described by S-shaped and monotonically decreasing curves, for the equipment. Numerical predictions show that this simple and easy to implement model accurately reproduces previously reported data and that the impurity concentration exhibits a marked effect over all the variables, except conversion.