New Developments in Polyisocyanurate Laminate Foam - Huntsman

RESULTS AND DISCUSSIONS
As seen in Tables 2-4, the closed cell content of all foam boards produced in this study is high, >86% uncorrected, and
the cell size is in the range of 200-300 micron. Such numbers are typical of commercially produced polyiso boards and
validate our aim to evaluate each polyol for its true attributes using the formulation that is optimal for the given polyol or
polyol blend.
The properties of boards made with STEPANPOL ® PS-2352 polyol at the overall foam density of 1.75 pcf are deemed
as reference in this study. As seen in Table 2, properties of boards made using STEPANPOL ® PS-2352 polyol are good
and suggest that full size boards manufactured using this formulation at the 1.75 pcf overall density will meet the current
model building code requirements [5].
Ecopol 123 and Ecopol 124
Table 2 shows the formulations and properties of all boards made using these two polyols, along with those made using
STEPANPOL ® PS-2352 polyol. All boards made at an overall density of 1.75 pcf are marked “Ref. Dens.” (listed just
below the heading of the Table) whereas those made at a higher density are marked “High Dens.” The laydown with both
Ecopol polyols was essentially “solution or liquid” much like that with HCFC-141b and very different than “fine
emulsion” seen with STEPANPOL® PS-2352 polyol using blends of iso-pentane and n-pentane. Processing temperature
window with either Ecopol polyol was much higher as compared to that with STEPANPOL® PS-2352 polyol., i.e., there
was no rapid frothing even when mix-head chemical temperature was high. We noticed that the total blowing level
required to get to a given overall board density was about 7.5% higher for Ecopol 124 polyol than those for either
STEPANPOL® PS-2352 polyol or Ecopol 123 polyol.
Comparing properties of boards made with Ecopol 123 polyol at 1.75 pcf overall density with that of STEPANPOL ®
PS-2352 polyol, we can see that Ecopol 123 polyol board exhibits equivalent, if not slightly better, fire performance but the
thermal resistance and structural properties, in particular compressive strength and low temperature dimensional stability,
are poorer. The lower compressive strength value across the thickness for the laminate and of the geometric mean for the
core foam, as well as shrinkage under low temperature dimensional stability test conditions, as illustrated in Figure 3,
suggest that Ecopol 123 polyol based foam is weaker. The geometric mean compressive strength (MCS) of the core foam,
defined as the geometric mean of the compressive strength measured in each of the three principal axes of the foam (rise,
machine and cross-machine directions) is an indicator of polymer strength of the foam, without the vagaries of cell
orientation. The following relationship between MCS and core foam density has been observed historically for closed cell
polyurethane foam and was found to hold for foams made in this study [9].
MCS = Material Constant x Density 1.61 (1)
The value of the “Material Constant” remains the same as long as density is changed by varying the amount of blowing
agent while keeping the formulation and processing essentially the same. This relationship was used to calculate the core
foam density at which the MCS of board made using Ecopol 123 polyol would equal that for the reference. Foam was
made targeting the calculated density and is identified as “High Dens” in Table 2. We can see that the structural properties
of the Ecopol 123 foam at about 7% higher density are similar or better than the reference foam. The fire properties at this
higher density are, if anything, better than the reference.
Friability of foams made with Ecopol 123 polyol is higher than that for the reference but the facer adhesion, though not
experimentally measured, appeared to be extremely good.. The thermal resistance, both initial and more importantly,
LTTR, of the Ecopol 123 foam is lower than that for reference even at the higher density. We did not investigate the
underlying reasons for this but cell size numbers suggest that it is unlikely to be cell size related.
Foam boards made with Ecopol 124 polyol followed essentially the same trend as that with Ecopol 123 polyol. The
significantly higher PIR/PUR ratio and friability with Ecopol 124 is likely to be the result of much higher index associated
with lower hydroxyl number of the Ecopol 124 as we kept the % isocyanate the same in all the foams compared in Table 2.
PIR/PUR ratio is just a diagnostic tool and a higher number is generally desirable. Despite the high tumbling friability, the
facer adhesion did not appear to be an issue with Ecopol 124. Though we did not experimentally measure facer peel
adhesion, there was no visual appearance of foam-facer delamination and facer generally tore off rather than delaminate
when manually pulling using a finger-nail.