Optimisation of a flexible polyurethane foam formulation for use as soilless growing media

Increasing pressure for controlled environmental agriculture (CEA) using hydroponic
techniques to reduce their environmental impact as well as the rapid growth of this
sector has led to research into more environmentally friendly growing media. Flexible
polyurethane foams (fPUF) are a possible alternative to current growing media,
however there is little literature reporting the development and optimisation of fPUF
for horticultural applications. The aim of this thesis is to use design of experiment
(DoE) techniques to understand the influence of the fPUF formulation on select
physical and chemical foam properties and optimise these properties for plant growth
using hydroponic techniques.
Fast, easy to measure techniques were developed or adapted from literature for
screening select foam physical properties (density, cell size, water holding capacity,
water drop penetration and airflow) and chemical properties (cation exchange
capacity) to allow for rapid formulation development. Complete conversion of
isocyanate was ensured by using adiabatic temperature rise techniques during the
foam reaction.
A combination of polyols with a high ethylene oxide polyol composition (58.2 %)
composed of a 75:25 ratio of Voranol 1447: Voranol 3322 was selected to make
hydrophilic foams. 30 part per hundred polyol (PPHP) of sodium bentonite was used
to increase the water holding capacity of the foam. Carefully selected reactive
catalysts, dimethylethanolamine (DMEA) and Specflex Activ 2306, a catalytically
active polyol reduced the likelihood of reagents leaching out of the foam. Models for
fPUF physical properties and reaction responses were developed and verified using
DoE techniques. These models used the catalyst and surfactant loadings as factors
influencing the responses. Spring onions (Allium cepa) were grown in a set of foams
with varying physical properties and growth and nutrition responses were modelled.
Cell size and water holding capacity were the most important factors in predicting plant
growth and nutrient uptake, with a small cell size and high water holding capacity
preferred. An optimised set of physical properties was predicted using these modelsii
and an optimum foam formulation was selected. This foam was made its physical
properties matched the predicted optimum properties.