Mineral Wool Insulation Binders

Abstract

Mineral wool is considered the best known insulation type among the wide variety of insulation materials. There are three types of mineral wool, and these consist of glass, stone (rock), and slag wool. The overall manufacturing processes, along with features such as specifications and characteristics for each of these types, as well as the role of the binder within the process are described.

Of the variety of mineral wool binders such as sodium silicates, polyesters, melamine urea formaldehyde, polyamides, furane-based resins, and others, phenolic resin-based binders continue to enjoy prominence as the preferred binder for mineral wool.

Optimum conditions are presented for preparing a low viscosity (<50 mPas) resole, infinite water dilutability, solids content (SC) between 45 and 55%, low tetradimer content (≤18%), lowfree phenol (<0.4%), and adequate storage stability by using a molar ratio of F/P of ∼4:1. Various inorganic and organic base catalysts are described along with the strengths and weaknesses of these catalysts. The resulting resole binder contains a high amount of free unreacted formaldehyde and is reduced to zero within a temperature range of 20–40°C by the addition of urea prior to use as a binder. The resulting PFU (phenol-formaldehyde-urea) resin is called “premix” or “prereact.”

The formation of the undesirable tetradimer [bis(4-hydroxy-3,5-dimethylolphenol) methane] and several methods to minimize it from crystallizing within the resole are listed. Even some selective base catalysts that are used to prepare the resole binder provide some enhanced stability against tetradimer precipitation.

Gel times or B-Stage of the resole binder is within 5–20 min and is adjusted to coincide with the overall process (from binder spraying to oven cure). A correct set B-stage enables the binder to flow to the junction points of the mineral wool fibers as the material enters the curing oven and cures within the residence time of the oven to provide the necessary product properties such as recovery, tensile strength, and resistance against ageing.

The emission of various volatile organic components (VOCs) such as monomethylol phenols, trimethyl amine, ammonia, phenol, and formaldehyde occurs at the site of mineral wool production. The generation of the latter three VOCs is shown to occur by resin cure (formaldehyde), the urea responsible for the generation of ammonia, and free phenol due to an unreacted amount within the resin.

The roles of some of the other components (ammonium hydroxide, ammonium sulfate, silane, emulsifier, de-dusting oil, extenders, and water) that are introduced into the final binder mixture are discussed. Ammonium hydroxide brings the pH of the premix binder to a 9–10 pH value at the site of mineral wool production and “temporarily” stabilizes the higher oligomeric species such as dimers and tetramers from precipitating by maintaining them in solution. Ammonium sulfate (AS) is involved in a multiplicity of roles such as release of acidity only at elevated temperature to facilitate resole cure within the curing oven, regulation of the gel time of the resole by pH change (guided by a plot of gel time vs pH on the thermal hardening of the resole from the initial spraying, to binder-coated fibers into the collecting chamber, and finally the curing oven), and provides the mineral wool with its characteristic color from white to yellow, with an intensity of yellow, due to the amount of AS that is present.. The amount of AS can be 1.03–1.3 mol/mol of the basic catalyst used in resin preparation, and this amount contributes to maximum burst strengths.