Case study 1
HEUR reactive extrusion
Structure-forming associative polymers (APs) are increasingly used to control the stability and rheology of dispersions. An important family of commercial APs are the so-called hydrophobically modified ethylene oxide urethane (HEUR) thickeners.
The main application of HEUR thickeners is as additives in water-based surface coatings. In addition to isocyanate, other linkers have been investigated, such as diisocyanate, esters and ethers. The latter yield hydrophobically modified polyethers (HMPE). The chemical structures of HEUR and HMPE are the result of the polycondensation reaction between a long and flexible diol (water-soluble polyethylene glycol, PEG), a small hydrophobic alcohol and a diisocyanate (HEUR) or dihaloalkane (HMPE).
In the classical chemical industry, HEUR and HMPE are produced in batches of several cubic meters. HEUR is produced in two phases. For the end user Coatex, the entire process can take up to 20 hours in total.
Objectives of SIMPLI-DEMO
Previous work in SIMPLIFY on HEUR has demonstrated the capabilities of reactive extruders (REX) using ultrasound and microwaves. The long reaction time required in the conventional batch process could be reduced to less than 10 minutes in the REX process, while the product conversion remained intact. In addition, the range of achievable Mw was increased up to 20000 g/mol compared to the commercial reference, resulting in HEUR grades with almost double the thickening efficiency.
It was found that processing the reaction mixture under intense thermal conditions for short periods of time, as enabled by microwaves, resulted in HEURs with molecular weights comparable to those of the industrial product, and with process times that were several times lower compared to conventional processing (5-15 min vs. 60 min for conventional heating).
SIMPLI-DEMO brings HEUR synthesis from TRL5 to TLR7 by introducing modularity and integrating PATs into the pilot device. Flexibility and adaptability are explored by performing HMPE synthesis in the same instrument.
HMPE is an environmentally interesting alternative to HEUR, leading to products that could replace isocyanate in some applications. The HMPE product range is comparable to HEUR in terms of viscosity. Previous work on the use of reactive extruders (REX), ultrasound and microwave for the Williamson ether reaction shows promising results in this regard. In the INNOREX project led by Fraunhofer, for example, the combination of REX and microwave led to an improvement in polymer conversion (from 62% to 80%) and molecular properties (increase of 13%), while the combination of REX and ultrasound led to an increase in conversion from 58% to 80% and Mw increase between 10 and 170%.