Investigation of Ageing Effects on Organic Binders used for Mineral Wool Products

Phenol-Urea-Formaldehyde (PUF) binder based mineral wool products’ mechanical properties
have been observed to degrade during ageing at elevated temperatures and humidity, while
mineral wool products based on a newly developed alkanol amine-acid anhydride binder
exhibited better ageing properties for the same duration of ageing. The main purpose of the
present work is to examine the chemical changes occurring in the phenol-urea-formaldehyde
binder based mineral fibres due to ageing, which cause deterioration of the mechanical properties
of mineral wool products. This has been done using surface analytical techniques such as x-ray
photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToFSIMS).
XPS and ToF-SIMS characterization of the PUF binder coated mineral fibres showed
that significant changes in the surface chemistry of the binder coated mineral fibres occurred
mainly due to hydrolyzation of urea containing groups. On the other hand, XPS and ToF-SIMS
characterization of alkanol amine-acid anhydride binder coated mineral fibres consistently
showed that the surface chemical composition of the organic components of these samples did
not change appreciably during ageing, which is relevant to the good retention of mechanical
strength for products formulated with the alkanol amine-acid anhydride binder.
Initial results on surface characterization of the mineral wool products based on PUF binder
showed that the main source of the degradation of the mechanical properties is the PUF binder,
therefore further research work was performed to the pure PUF binder coatings to directly
observe the ageing effects on the surface chemistry of the binder. High mass resolution ToFSIMS
spectra of the pure PUF binder coatings confirmed that the depolymerisation of the cured
binder occurred during ageing due to hydrolytic cleavage of amide bonds, methylene and
methylene ether linkages between urea groups in the binder network.
The ageing effects on the amino-propyl-silane (APS) and quaternary ammonium surfactant
(QACs) treated mineral fibres were also investigated by XPS and ToF-SIMS. In the production
of mineral wool insulation products, amino-propyl-silane (APS) is used as a coupling agent and
quaternary ammonium based surfactants (QACs) are used as a softener. If the degradation of
these coatings takes place, it will indirectly affect the ageing properties of the mineral wool
products. Both XPS and ToF-SIMS consistently showed a decrease in hydrocarbon groups due to
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removal of the cationic surfactant and mineral oil from the surface, which results in an increase
in the signals from the underlying silanized mineral fibres. This research work did not provide
any further information on the ageing mechanism of APS coating, thus pure amino-propyl-silane
coated silicon wafers were also investigated. Both XPS and ToF-SIMS demonstrated that the
accelerated ageing caused a significant decrease in the surface coverage of the APS coating. A
decrease in the surface concentration of the free amino groups was observed upon ageing, which
is probably due to partial removal of the physisorbed aminosilane layer from the substrate during
ageing. Meanwhile, an increase in the surface composition of amide bonds after ageing was
found in the C1s high resolution spectra, which could be related to incorporation of oxygen into
amino groups during ageing. This study provides a further insight into the extent of silane
degradation during ageing.