Ageing is known in the ROCKWOOL Group to cause deterioration of the stone wool products mechanical properties. The exact mechanism of ageing is unknown, but hydrolysis of the chemical bonds at the phenol-urea-formaldehyde, PUF, binder and coupling agent, 3-aminopropylsilane, APS, interfaces is assumed to be the main factor because ageing rates accelerate with increase of temperature and humidity.

Project objective: elucidate the effect of aging on mineral wools with different types of binders/coupling agents using surface sensitive techniques.

Project goal: to identify the mechanism of degradation and develop ways of preventing it and hence make a better product.

The project was aimed on understanding of mineral wool mechanical properties degradation during ageing at elevated temperatures and humidity and developing strategy to prevent loosing mechanical properties by strengthen the fiber-binder interface. The project was done in collaboration with University of Copenhagen and supported by Innovation Foundation, Denmark. The purpose of the project was to elucidate, using nanotechniques, the effect of ageing on mineral wool/binder interface with the focus at the single fiber scale. At nanometer scale, one can see detailed changes after ageing and make conclusions about chemical processes that result in product failure.

In Figure 1, the joint between two mineral fibers composed of cured PUF binder is shown before and after ageing in water bath at 80 °C. These joints create necessary shape and mechanical strength of the final wool product.

Figure 1. SEM images of mineral wool fiber samples before and after ageing for 4 hours at 80 °C in water bath. The circle marks the fibers joint where removal of the PUF binder occurred.

Their possible chemical structure is shown in Figure 2. The coupling agent, APS, reacts with the mineral fiber surface through silanol groups and with PUF matrix via amino groups. This leads to a strong adhesion between fibers after curing. However, after ageing it was shown that the PUF joints can reduce in size caused by reaction/dissolution with water (Figure 1 right). This process will lead to the decrease of joint’s strength and thus to the reduction of the mechanical properties of the wool material.

Figure 2. The hypothetical structure of PUF binder attached to mineral surface with APS coupling agent. Two mineral fibers are bonded together with PUF and APS. The circles showed bonds that are suspected for hydrolytic decomposition.

D.V. Okhrimenko, A. Budi, M. Ceccato, D.B. Johansson, D. Lybye, K. Bechgaard, S.L.S. Stipp (2017) Wettability and its influence on hydrolytic stability of silicate surfaces treated with 3-aminopropylsilane coupling agent and phenol-urea-formaldehyde binder. to be submitted to Composites A.

D.V. Okhrimenko, A.B. Thomssen, M. Ceccato, D.B. Johansson, D. Lybye, K. Bechgaard, S.L.S. Stipp (2017) Impact of curing degree on ageing and degradation of phenol-urea-formaldehyde binder. to be submitted to Polym. Degrad. Stab.

D.V. Okhrimenko, A. Budi, M. Ceccato, M. Cardenas, D.B. Johansson, D. Lybye, K. Bechgaard, S.L.S. Stipp (2017) Hydrolytic stability of 3-aminopropylsilane coupling agent on silica and silicate surfaces at elevated temperatures. Appl. Mater. Interfaces, 9(9), 8344–8353.