Polyurethane particle size distribution and stability in a multistep industrial reactor and dispersion system (sponsored by Pidilite Industries, Mumbai)

This project is in collaboration with Pidilite Industries. There will be possible visits to the industry and their R&D centre in Mumbai, and even learn and have the opportunity to do some work at Pidilite (including using their experimental set-ups), in discussion with their scientists and R&D personnel. Also, the student may be permitted some honorarium in addition to the regular M. Tech. fellowship, as this project is sponsored by industry.

The objective of the research is to increase the stability and loading (in wt.%) of solid, polyurethane (PU) particles, in a solid-liquid (water) dispersion of pre-polymeric PU in water. This concentrated dispersion is expected to have a controlled, unimodal particle size distribution (of 400 micro-meter modal diameter) and higher stability in the aqueous dispersion, to facilitate subsequent existing applications of PU as a film-forming/coating material. To achieve the higher percentage loading of PU in a stable, aqueous dispersion:

(i) one may have to partially modify the beginning reaction process leading to pre-polymeric PU synthesis, in acetone as a solvent, or,

(ii) one may have to study the follow-up dispersion method of the PU-in-acetone by water, presently conducted in a semi-batch stirred tank, under slow addition of the former. 

Towards the above end, one may introduce a suitable functional group within the PU pre-polymer chain, during the first PU synthesis step:

(i) by selecting different raw materials for polyol or isocyanate (e.g. 1,6-hexamethylene diisocyanate for carboxylic groups), or,

(ii) by attaching different groups after synthesis of PU prepolymer (such as sodium sulfonate, a hydrophilic group, which will aid hydrophilicity and will likely produce a more stable aqueous dispersion, with higher particle loading). For water-soluble PU polymers to have hydrophilic segment, one can use different raw materials or chain extenders (e. g. carboxylate, sulfonate, ammonium etc.) for a better dispersion.

One major issue of PU colloidal dispersion is its viscosity and therefore, it may be one reason why it is difficult to increase the loading of the PU solids beyond the present 30-35% by wt. So, once the PU prepolymer synthesis step is finalized (after alteration, if any), further changes in various unit operation steps can be one of the ways to increase PU loading. This can be achieved by altering one or more of the following: the controlled addition rate (flow rate) of PU prepolymer in the water containing reactor, stirring speed for mixing, reactor configuration (introducing baffles and changing the impeller type etc.), addition of emulsifier, addition/removal of solvent (acetone) to control the viscosity of the solution. These parameters might help to achieve the high loading of PU. While fine-tuning these conditions, it is important to maintain the size of PU nanoparticles and its stability, for which a design of experiment approach can be pursued.

Simultaneously, the experiments can be supplemented and down-the-line validated by simulating combined models, which couple computational fluid dynamics (CFD) of the reactor-mixer flow-field, with kinetic Monte Carlo or population balance equation (PBE) based models, to calculate the size distribution of PU particles or their clustering to the currently undesirable, bimodal 800 micro-meter peak in the size distribution.

Thus, the student can start with experiments and later even combine modelling and simulation, with regular industry mentoring and interaction, in addition to guidance by IITB faculty.

One can do mostly experimental work or a combination of experiment and simulation.