San Sebastian, Spain – Scientists at the University of the Basque Country have developed a new type of antimicrobial polyurethane foam. It was achieved by incorporating functional quaternary ammonium monomers within the polymer structure.
The most common technique for making antimicrobial polyurethane foam is to include a biocide additive within the formulation, such as silver nanoparticles. However, these can leach out. If the antimicrobial component were chemically bonded to the polymer, it is likely to be more stable, the researchers said.
The Spanish team chose to use antimicrobial active quaternary ammonium groups, which have the additional advantage of being cheap. Hydroxyl-functionalised quaternary ammonium triol and tetraol monomers were synthesised from triethanolamine, and used to make a polyurethane foam with PPG and either TDI or pHDI. The resulting open cell foams were cured at 50°C overnight.
Nine different foam compositions were synthesised, with varying concentrations of the components. NMR analysis showed there was almost no unreacted quaternary ammonium in the foams, and therefore the antimicrobial behaviour was down to the foam itself.
Antimicrobial activity was assessed with both E. coli and S. aureus bacteria. The foams made with TDI performed best for the latter, whereas both TDI and pHDI were effective against the former when the foam contained at least 15% of the quaternary ammonium monomer.
The amount of this monomer in the formulation also affected the foaming efficiency. They found that its presence in the mixture catalysed the blowing reaction, allowing a foam with good characteristics to be made without using additional blowing catalysts.
The team speculated that applications for the foam could include water purification, where it might prove a cheap and efficient alternative to more expensive technologies. ‘They could also have applications in cushions, for instance in the automotive area,’ says research associate Haritz Sardon. ‘These materials are really cheap.’
The team is now focusing on other antimicrobial applications, and looking at non-isocyanate chemistry. ‘We think that it is a new way to look for new applications in the area of polyurethanes,’ Sardon says. ‘Talking with companies, the use of isocyanate-based polyurethanes is highly stabilised, and it is difficult to change a production process for a company.’
Reference: E. Udabe et al. J. Appl. Polymer Sci. 2017, doi 10.1002.APP.45473