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Bayfomox - flame-retardant PU foam  #11(117), 2012

On the basis of Bayfomox system used for molding of polyurethane foam (PUF) products, the experts of the LANXESS concern have developed formulation for spraying coatings. Further on - apart from flame retardation issues – mechanical, acoustic and heat insulating properties of PUF coatings are described, data on their water and chemical resistance is presented, equipment characteristics and spraying modes are discussed, comparison of molding and spraying technologies is given

Otto MAUERER,
Business development manager of Phosphorus Chemicals section
of the Functional Chemicals business unit,
LANXESS Deutschland GmbH

Bayfomox system
The Bayfomox polyurethane system comprises the two main components, namely polyol and isocyanate, and proved itself especially perfect in construction – in terms of fire safety.

Obtained from Bayfomox PU foam articles when exposed to flame or high temperature are becoming swelled and carbonized (so-called intumescence effect), thus gaining enhanced fire resistance. Intumescent layer (Fig. 1) serves as flame retardant physical barrier, making the material hardly flammable and self-extinguishing.

By changing the ratio of polyol and isocyanate in original composition the properties of the finished material can be varied – from elasticity and viscoelasticity to rigidity and hardness. The material density lies in the range of 200 kg/m3 (for elastic PU foams) to 800 kg/m3 (for rigid ones). At a density above 350 kg/m3 it becomes necessary to use dehumidifiers (e.g., zeolites), which bind the moisture and slow down or prevent foaming.

One scope of the Bayfomox application is the protection of cable openings. The elastic blocks of PU foam easily take the form of uneven contacting surfaces, are easily mounted without the use of special tooling, and despite the fact that are made of polymer material have exceptional fire resistance (Fig. 2).

The rigid molded articles with heightened density and notable for stable sizes, are also manufactured from Bayfomox. Even in case of fire occurrence the electric circuits protected via such PU foam are continuing functioning for rather long time (Fig. 3).

Bayfomox system contains no halogens, asbestos, fibers, heavy metals, plasticizers and solvents. It is tested and approved by the German Institute of Civil Engineering (Deutsches Institut fuer Bautechnik, DIBt).

Molding or spraying?
Most products of PU foam having a simple geometric shape (“bricks” or “masonry blocks” (Fig. 2), plugs, profiles, housings and casings, air gates), are manufactured via stepwise technology with a foaming in a closed mold. First polyol and isocyanate are quickly but thoroughly stirred in a mixer and poured into a mold. After the latter is closed the reactive mixture is foamed and fills the mold cavity. After cleaning and surface treatment with release agent the mold is ready for the next cycle.

Such manufacturing process of PUF products is quite laborious, while duration of certain operations cannot be reduced. Such technology is difficult, if not to say impossible, to apply for production of parts having thin walls, large surface area or for production of coatings. It should be somehow obviously clear that efficient method of obtaining such products is the PUF spraying (Fig. 4).

When the spraying technique is used no time is wasted on waiting for completion of foaming and then curing of reactive composition, on extraction of article off the mold, on additional cleaning and treatment operations. Another indubitable advantage is that the mobile small-sized spraying sets can be used directly at a place of coating.

 

Table 1. Standard Bayfomox compositions


Component

Dedication

Content, mass fraction

Result of change

in components content

Bayfomox PA

Polyol

100

-

Bayfomox P

Isocyanate

40-60

Changing of PUF state from flexible and viscoelastic to rigid

Water

Foaming agent

0-0.6

Changing of PUF density within

350-200 kg/m3

Zeolites

Desiccant

0-2

Changing of PUF density within

350-800 kg/m3

Myritol (only for molded parts)

Cellularity regulator

0.1-0.6

Changing of cells size (from 0.5 to 4 mm) with increase of open cells fraction

Dimethylcyclohexylamine (only for sprayed coatings)

Catalyst

0-2

Acceleration of reaction if the temperature increase is not allowed



Table 2. Properties of elastic PUF


Factor

Value

Density (DIN 43420), kg/m3

210

Tensile strength (DIN 53571), кPа

150

Elongation (DIN 53571), %

65

Compressive stress at 40-percent deformation (DIN 53577), кPа

27

Residual deformation after 50-percent compressive strain (DIN 53572), %

<10

Ultimate oxygen index (ISO 4589), %

32.5

Fume density at combustion (ASTM E 662), Dm

96

Fume density at smoldering (ASTM E 662), Dm

204

Combustibility class (DIN 4102)

B-2



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