Flexible polyurethane foams with nanocomposite coatings

: Enhanced mechanical properties and dye adsorption applications

Abstract

In this work, sepiolite nanoclay / flexible polyurethane (PU) foam composites were
prepared by coating pre-made foams, resulting in superior mechanical performance and
dye adsorption capability.
First, PU foam composites were reinforced by chitosan / sepiolite via a convenient
layer-by-layer assembly approach. The PU foam composites were characterised using
thermogravimetry analysis, infrared spectroscopy, scanning electron microscopy,
elemental analysis and μ-CT scanning. The foams coated with 6 bilayers (6 bls) showed
a 200% increase in the stiffness and a 33% enhancement in the damping loss factor
compared to the uncoated pristine foam. Remarkably, impact tests exhibited a 50%
decrease in the transmitted impact force of the 6 bls samples, demonstrating their
improved energy dissipation capability.
Secondly, a PU foam / polymer / clay (PUF / PAASep) composite was prepared via a
simple dip-coating method. The sepiolite (Sep) dispersion in a polyacrylate acid (PAA)
solution was first homogenised, evaluated using microscopy, and the obtained PAASep
solution was used to coat the PU foam uniformly for optimisation of the mechanical
performance. The PU foam struts coated with 1 wt% PAA and 3 wt% sepiolite were
strengthened, resulting in an eight-fold improvement of the stiffness and three-times
increase of the impact force resistance compared to the uncoated PU foams. More
importantly, the PU foam composites showed a remarkable vibration damping capability,
with the loss modulus 57 times that of the uncoated PU foams, enabled by micro
friction and stick-slip effects mediated by the PAASep coatings. This convenient route
for preparing PAASep-coated PU foams has significant potential for cushioning,
packaging and broad engineering applications involving energy absorption.
Thirdly, the prepared sepiolite-coated PU foam composites were used as monolithic
adsorbents to adsorb dye molecules from water. The methylene blue (MB) adsorption
ii
rate was tested under different conditions, and optimised with stirring on a roller mixer
at room temperature. Coated with 1 wt% PAA and 5% sepiolite, the foam composites
achieved a 98% of MB removal at an initial concentration of 1150 mg L-1
. This foam
composite also exhibited great reusability with a facile ethanol washing process. In
terms of adsorption mechanism, both physical and chemical dye-composite interactions
were much improved by the PAA / sepiolite coatings. This attempt to produce a
recyclable foam absorbent with excellent adsorption capability has potential to address
environmental challenge of dyed industrial effluents purification.

Date of Award	24 Jul 2024
Original language	English
Awarding Institution	University of Bristol
Supervisor	Fabrizio Scarpa (Supervisor) & Wuge H Briscoe (Supervisor)