Publisher’s version / Version de l'éditeur:
Technical Note (National Research Council of Canada. Division of Building Research), 1974-10-01
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Comments on Polyurethane Insulation
Shirtliffe, C. J.
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NATIONAL RESEARCH COUNCIL OF CANADA
No.
DIVISION OF BUILDING RESEARCH
587
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PREPARED BY PREPARED FOR C. J. Shirtliffe Inquiry reply CHECKED BY D. G. S. APPROVED BY L. W. G. M!.!.. October 1974SUBJECT COMMENTS ON POLYURETHANE INSULATION
Urethane or polyurethane is the second most widely used rigid plastic in the construction industry. One of its unique properties - - its high strength to weight ratio - - makes it the strongest of all the common foam plastics. It comes in a variety of forms including, rigid or flexible, low or high density, open or closed celled. It is normally used in a rigid closed celled form for building insulation. Both factory-made board stock and spray-on types are becoming more common in construction.
Urethane is made from two components: a polyisocyanul'ate and a polyhydroxyl. The components also contain catalysts, a surface-active agent, and a blOWing agent, which is normally a flurocarbon refrigerant. The refrigerant gases have large molecules that do not transfer heat readily, and are easier to hold in the plastic material. Normally refri-gerants R-ll and R-12 are used.
The reaction of the two components produces a large amount of heat which expands the gas, thus producing the cells. The catalyst
controls the speed of reaction. The surface-active agent acts in control-ling the cell structure and allows production of a foam with a fine cell structure, which is necessary for a good ther mal ins ulation.
There are two basic types of isocyanurates used in the production of commercial urethane insulation. These are termed TDI and MDI; chemical names and details could be found in any reference book on urethane. In addition, a wide variety of polyols are used. These are generally selected according to cost or the foam properties desired. In general, the more expensive the polyol used, the better the properties, although this can be influenced to some ･ｾｴ･ｮｴ by the equipment used in mixing the components.
Z
-Mixing of the components is done either in spray nozzles
,or
py a number of more or less secret processes. The mixing ratio of the two components must be maintained constant to within about I per cent to maintain a uniform product. The temperature of the components greatly affects the dispensing of the material. Normally the mixing is best if it is done in a factory where control of conditions and careful supervision of the equipment is possible. On-site, spray-on equipment must be carefully designed to ensure proper mixing.After mixing, the urethane expands 30 to 40 times in volume. This can be accomplished in one or two rises. When both R-II and R-IZ are used as the blowing agent in the foam, the material rises as the R-IZ vaporizes and then rises a second time when the R-ll vaporizes. From 80 to 90 per cent of the cells are closed in a well-controlled, single-rise factory application. This means that the blowing agent does not
escape immediately and the foam will maintain its high thermal resistance for a considerable time. There is little information on the closed cell content for spray-on urethane. I t could be expected to be lower on
average than for factory-made foam. In most factories an upper platent compresses the foam and prevents it from rising freely. This causes cells to be ellipsoid in shape. As a result, the thermal resistance and vapour transfer resistance are increased and the material will age more slowly. Spray-on urethane has spherical cells or the cells are elongated in the direction of rise. This reduces the thermal resistance and vapour transfer resistance, and increases the rate of ageing.
In both factory-made and spray-on urethane the open cells can form long chains in the direction of rise. Such a poor material has a "worm eatenl l
appearance. These openings drastically reduce the vapour-transfer resistance and increase the rate of ageing. I t is more
difficult to eliminate this type of structure in spray-on material than in factory-made material.
The density of urethanes can vary from 1. 5 to 30 Ib/ft3. Most spray-on material is made in densities of Z to 3 1b/ft3• Newer spraying
equipment can produce lower densities but the conditions of the surface and the environment become more critical. Since material cost is directly proportional to density, the applicator normally prefers to apply a low density material. The structural and thermal properties are generally better at the intermediate densities.
Urethane foam has good chemical resistaace. This helps to avoid problems in selecting adhesives and coatings. I t also increases its
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-present. Like all plastics, urethane is not resistant to all chemicals, so some caution is necessary. It is also not resistant to ultra-violet radiation. The temperature of the material may affect its chemical resistance as well.
Its resistance to water vapour absorption and its dimensional stability are ｡ｦｦ･｣ｾ･､ by temperature. Although the material usually is dimensionally stable (under 5 per cent in each direction and under
15 per cent by volume) up to 220°F i f dry and at a low relative humidity,
it becomes dimensionally unstable (changes of 5 to 20 per cent in each direction and 15 to 60 per cent by volume) once the temperature exceeds
l20°F to l50°F with the relative humidity over 90 per cent. There is relatively little information on this important characteristic, making it difficult for designers to compensate for this shortcoming.
Urethanes can have a high flame-spread rating relative to other building materials. When burning they can give off large amounts of smoke and dangerous fumes. The flame -spread rating can be reduced by adding ｰｨｯｳｰｨｯｲｯｵｳｾ chlorine. bromine or combination of these to the basic components. In ｡､､ｩｴｩｯｮｾ the basic chemistry can be changed
to produce an isocyanurate structure that is inherently more fire resistant.
This
increases the cost of the material and introducesundesirable characteristics such as friability and brittleness.
Materials intermediate between urethanes and isocyanurates are being produced with a more acceptable mix of properties.
All urethanes have quite a high resistance to water vapour transfer. They must be covered, however, with coatings and vapour barriers to protect them because of the problems with water absorption and dimen-sional instability. Although spray-on material has a skin which increase s the re sistance to water vapour transfer, the quality of the skin is not
controllable. As well, the properties of the skin have not been established well enough to allow designers to make use of it in system design.
Other characteristics of urethane insulation
Polyurethane is an expensive insulation. On the basis of cents per unit resistance for a square foot area, the current cost of fully aged urethane runs from five to seven times that of glass fiber insulation and two to three times the cost of polystyrene insulation.
Spray-on urethane does have some advantages over other insulations. The cost of labour for applying the material is low, nullifying to some extent the high cost of the material. This is of
.. 4 ..
particular advantage in structures that are difficult to insulate. There is very little possibility for saving, however, in a standard frame house where the installation of glas s fiber blankets or board -type insulation is relatively inexpensive.
Spray-on polyurethane can provide an excellent air barrier (and thus noise barrier) at the same time as it provides thermal insulation. Almost all cracks :..nd openings can be sealed by the foam. In a frame house where relative movements between structural members are not large. the seal is likely to remain intact for some time. Many older houses and some newer ones show evidence that there have been relative movements that are so large that had urethane been applied, it could not have maintained a seal. The effectiveness of urethane foam as an air barrier has not been proved except over a short term.
The ability of urethane foam to absorb acoustical energy is low. much lower than glass fiber insulation. The advantage provided by the air seal in reducing noise transmission is offset to some extent by this inability to absorb acoustical energy.
Polyurethane foam is basically a dimensionally unstable
material. This is because the gas pressure in the cells increas es to as much as 12 psi above atmospheric pressure as air permeates into the cells. Thus there is a large potential for an expansion or a releas e of large forces when restrained. Air penetration also leads to a
reduction in the thermal resistance of the foam. so is termed llageing. " At low relative humidities and temperatures well below 1500
F. instability is usually not important. At temperatures above 1500
F, or even 1200 F, ｾｲ at relative humidities approaching 90 or 95 per cent and temperatures above normal ambient, the material begins to lIgrow"
i f unrestrained. The cell walls stretch and the material expands.
High humidity has a detrimental effect on the material at high temperatures. Polyurethane is plasticized by the water vapour causing it to lose its strength and allowing the gas in the closed cells to expand.
I f expansion is restrained in one or two directions, larger expansions occur in the unrestrained directions. If it is completely confined, the
material applies a force to the surrounding structure. This can be large enough to cause damage even to such strong structures as
prefabricated concrete panels.
Polyurethane is best used where it can be kept in a cool. dry environment. A good design will ensure its protection from extremes in temperature and especially from wetting. I t will also keep the foam
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-from. entering the m.aterial and condensing or freezing in the colder parts of the foam.. Polyurethane does not have good freeze -thaw resistance. If the m.aterial is wet and is subjected to freeze-thaw cycles it will disintegrate after only a few cycles.
At tem.peratures below +500
F the refrigerant gas in the cells, norm.ally R -II, will condense causing som.e sm.all shrinkage of the
m.aterial and reducing its resistance to heat flow. This becom.es progres-sively worse as the tem.perature is reduced to _500
F, where the gas is alm.o st all condensed. The effect of this decrease in resistance is to reduce the econom.ic attractiveness of urethane as an insulation for cold
ｳｴｯｲ｡ｧｾ buildings. The exact extent of the effect on aged urethane foam.
is unclear. Air -filled foam. plastics can be much m.ore econom.ical for these applications and can take little or no extra space.
Spray-on urethane is a m.aterial that is m.anufactured on site. As such the applicator must take the responsibility for the very im.portant job of quality control. This usually involves inspection by a trained individual who understands the process thoroughly and can m.ake adjust-m.ents in the proces s to m.aintain a good quality product.
The quality of spray-on urethane depends on m.any factors. These include: the ratio of the two com.ponents used, the tem.perature of the
com.ponents in the tank, the tem.perature and relative hum.idity of the surrounding air, the type of equipm.ent used, the operator's skill, conta-m.inants on the surface to which the m.aterial is applied (substrate), and even therm.al conductivity of the surface m.aterial and tem.perature on the other side of the substrate.
The quality of the bond between the foam. and the substrate depends on m.any of these factors as well. If the first layer does not rise properly it will probably not adhere very well. This layer can also rob som.e of the constituents from. the next layer of foam. leaving it weak and friable. A failure in "ad hesion" m.ay occur at this next layer rather than right at the surface.
Polyurethane foam. can also be sprayed on surfaces in the form. of a froth, which is a partially expanded foam.. A froth is norm.ally produced by using both R-12 and R-ll refrigerant in the m.aterial. R-12 boils at a lower tem.perature, partially expanding the liquid. This is then sprayed against the surface, where the heat of reaction of the two com.ponents heats the froth causing the R -11 to boil and finish the foam.ing. It is claim.ed that the surface and atm.ospheric conditions have less effect on urethane applied in this way. The type of equipm.ent necessary to produce a froth is not yet commonly available nor is much known about the problem.s of this kind of operation.
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6
-This and other new spray equipm.ent will likely reduce the difficulty in producing good quality spray-on urethane in future. For exam.ple, in the past, m.any m.achines had adjustm.ents to control the m.ixing ratio and the m.achines tended to go out of adjustm.ent. The newer m.achines, however, are set to a fixed ratio which suits the com.ponents selected; they cannot be adjusted nor go out of adjustm.ent. This has reduced the amount of on-site supervision necessary to assure a good quality foam..
There are a large num.ber of m.anufacturers producing one or both of the com.ponents used in m.aking urethane foam.. The quality of these com.ponents is continually being im.proved. In addition, special
form.ul-ations are being developed to allow spraying under less favourable conditions. In particular, cold weather form.ulations are being developed.
Wind is a constant problem. when spraying on the outside of a structure. The resulting overspray can cause a m.ess, which m.ay result in expensive clean-up charges and a health hazard; it also greatly reduces or elim.inates the profit of the applicator. When spraying urethane, the overspray and fum.es are dangerous to the operators and persons in the im.m.ediate area.
I t is recom.nlended that the operators use fresh-air m.asks. Surrounding
areas should be well ventilated and cleared of all personnel. Nearby fur-niture and finished surfaces m.ay require protection.
A num.ber of large com.panies use spray-on urethane to insulate their own structures and equipm.ent. Som.e of these control the quality of the product they are receiving by constant inspection, sam.pling, and testing. If the m.aterial is substandard it m.ust be removed and replaced. This is not feasible for an individual or sm.all contractor. The reputation of the applicator m.ust, therefore, be relied upon. I tis not easy to determ.ine
this reputation without an extensive investigation. The individual or sm.all contractor is therefore gam.bling when he uses a spray-on urethane. A long-term. guarantee from. the applicator would not likely help as the cost to replace spray-on urethane, once it is built into a structure, is so great that the applicator m.ight be forced to declare bankruptcy i f forced to
disassem.ble the structure and replace the m.aterial.
This note has pointed out the negative aspects of spray-on insulation. The positive aspects are well covered in m.ost m.anufacturers' brochures and are not covered here. As with m.o st m.aterials, the m.aterial itself is an acceptable m.aterial as long as it is used properly for the correct applica-tion.
