b'Steep SlopeContinued from page 7spread. The confinement of the adhesive with the glass plates was representative of the confinement of adhesive that occurs when adhesive ribbons are dispensed and weighted by overlying rigid insulation board(s). Confinement of the adhesive significantly influences the size, shape, and lateral spread of the low-rise foam bubbles and therefore, likely impacts the tensile strength of the adhesive.In addition to this, we found that elongation and stiffnessareimportantpropertiesthatcould be factors in identifying desirable performance behaviors in adhered roof assemblies. A discussion of elongation and stiffness is included in the full report. Figure4.LowmagnificationimagesofManufacturerABE(topleft),Manufacturer B BE (top right), Manufacturer A AE (bottom left), and Manufacturer B AE (bottom right). Microscopical Evaluation and Chemical Testing. Specific studies of the adhesive were performed to better understand the effect of various conditions (i.e., curing time, temperature) on the polyurethane reaction and cellular foam formation (Figure 4). An understanding of the chemical reactions occurring Temperature Effect. Temperature plays a very provides an understanding of any changes in thesignificant and important role in the final cure, resulting cured low-rise foam adhesive, as well asspread, and tensile strength of adhesive ribbons. provides context for manufacturers requirementsThese adhesive properties can be affected and for storage and use. retarded by applications that include condensationEvaluation of Results. Data from the physical andmoisture and cold temperatures, either separately or chemical testing was compiled to show similaritiesin combination. An increase in curing temperature and/or differences between the two materials useddecreases foam bubble void size thereby increasing and their performance when application and curingtensile strength, and cold temperatures limit polymer conditions are considered. formation and reduce ultimate tensile strength of Key Findings of the Test Program the foam. See Figure 5 below. Shelf-Life Effect. Tensile strength of AE adhesive Ambient temperature (70F), BE and AE - The was greater in some instances than BE adhesivemeasured tensile strength of AE adhesive for the (Table 1); however, the spread of the foam is anseven-day cure puck specimens is significantly important factor. The BE foam spread for bothhigher than the BE adhesive. Average tensile Manufacturers A and B exhibited a wider spreadstrength at ambient temperature for seven-day when confined by the glass plates than did thespecimens was 13.09 psi for Manufacturer A and AE adhesive, creating a larger surface area for6.03 psi for Manufacturer B. After fourteen days contact of the adhesive ribbons. The larger surfacecure the average tensile strength for Manufacturer area results in an overall higher tensile strengthB increased by 26%. Thus, an increase in cure time compared to a ribbon with a smaller spread aspositively impacts tensile strength for Manufacturer observed on the AE specimens. In addition, thereB. Both Manufacturer A and Manufacturer B had is a correlation between adhesive expiration statusincreased tensile strength for AE adhesive. (BE: and adhesive spread when rise of the foam isA - 13.09 psi, B - 6.03 psi; AE: A - 29.57 psi, B - restrained. BE adhesive provides an increase in18.36 psi).the amount and size of COgas bubbles compared 35F temperature (BE) - Both Manufacturer A and 2 Manufacturer B puck specimens conditioned at to AE adhesive, which results in greater adhesive35F had low and variable tensile strengths. Cold 8 www.mrca.orgMidwest Roofer'