Investigation of the ageing effects on phenol-urea-formaldehyde binder and alkanol amine-acid anhydride binder coated mineral fibres

Phenol-Urea-Formaldehyde (PUF) binder coated mineral fibres' mechanical properties have been observed to degrade during ageing at elevated temperatures and humidity, while alkanol amine-acid anhydride binder based mineral fibres exhibited better ageing properties for same duration of ageing. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were employed to identify the chemical changes occurring in the PUF binder coated mineral fibres and alkanol amine-acid anhydride binder coated mineral fibres during that ageing. The samples were aged in a climate chamber for 7 days at 70 °C and 95% relative humidity. In the case of the PUF binder coated fibres, quantitative XPS measurements showed some significant changes in the atomic composition of the PUF binder coated mineral fibres after ageing, including decreased urea and carbonyl groups concentrations. Principal Component Analysis (PCA) was applied on the positive and negative ToF-SIMS spectra of the PUF binder coated mineral fibres, showing a decrease in the concentration of the nitrogen containing peaks during ageing. This decrease was attributed to the depolymerisation of the binder due to hydrolysis of amide, methylene ether and methylene linkages between urea groups present in the PUF binder. In the case of the alkanol amine-acid anhydride binder coated mineral fibres, both XPS and ToF-SIMS techniques consistently showed that the surface chemical composition of the organic components of the alkanol amine-acid anhydride binder coated mineral fibres did not change appreciably after 7 days of climate ageing, which is relevant to the good retention of mechanical strength for products formulated with the alkanol amine-acid anhydride binder.