polyester polyols in rigid polyurethane and polyisocyanurate foams for structural building panels

601

Polyester Polyols in RigidPolyurethane and PolyisocyanurateFoams for Structural Building Panels

W. W REICHMANN

Mobay CorporationMobay Road

Pittsburgh, PA 15205-9741

B. A. PHILLIPS

Bayer, AGLeverkusen

Federal Republic of Germany

INTRODUCTION

n the United States, polyester polyols are used in rigid polyurethanefoams for structural building panels. The polyester polyols reducethe cost and improve the fire resistance of building panels. The foamused in these panels must meet high standards. The standards for thefoam cover four basic aspects: physical, structural, thermal insulationand combustion properties. The important physical properties of thefoam are dimensional stability, compressive and tensile strength. Thestructural properties are more complex; both the core and surface fria-bility of the foam must be minimized so that the building panels aredurable, strong and responsive to the specific demands of each applica-tion. Another critical structural problem is blister formation anddelamination between foam and metal facings. The standards require

This paper was presented at Polyurethanes World Congress 1987, Proceedings of theSPI/FSK, Aachen, Federal Republic of Germany, September 29-October 2, 1987. Thepaper is being published herein from the conference proceedings after review by theEditorial Board, but without the customary peer review process.

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602 W. W REICHMANN AND B. A PHILLIPS

excellent adhesion of the foam especially to the exterior metal facing sothat the building panels can withstand long-term temperature changesand environmental stresses. Good foam firmness is also important. Thequick build-up of foam firmness during manufacture permits bothshort demold times in discontinuous operations and high line speeds incontinuous processing. The next aspect, thermal insulation, is linked tothe proper foam formation during manufacture. The right reaction pro-file gives the foam a fine and uniform cell structure. This kind of cellstructure and the chlorofluorocarbon gas trapped within the cells givethe foam good insulating properties.Perhaps the most critical requirements for rigid foam are the com-

bustibility standards imposed by the Building Codes in the UnitedStates. Various tests are required; however, the basic combustibilitytest for the foam is ASTM E-84. Rigid foam used in metal-faced build-ing panels is required to pass ASTM E-84 with a Class 1 * rating,Flamespread :525* and Smoke < 450 *. In metal building panels, thefoam density should be approximately 50 kg/m3 for structural reasons.In non-structural applications, such as roof and wall insulating panels,the density can be about 32 kg/m3. The 32 kg/m3 foams get Class 1 *ratings more easily because they have less mass to burn than the 50kg/m3 foams. The polyester polyols influence the properties of the foamsin all aspects that have been mentioned.

OBJECTIVES

This paper discusses the advantages of polyester polyols in rigidpolyurethane (PUR) and polyisocyanurate (PIR) foams for structuralbuilding panels, putting most of the emphasis on the PIR foams. Ittouches on the processing performance, the physical and insulatingproperties of the foams and focus on their ASTM E-84 performance. Thefoams must have an in-place density in the metal panel of approx-imately 50 kg/m3 for structural reasons and must have Class 1 * ASTME-84 ratings for the American Building Codes. The relationshipbetween the key variables of the polyester polyols (Table 1) and the keyproperties of the foams (Tables 2 and 3) are discussed.The key variables of each polyester polyol affecting the ASTM E-84

classification are aromatic content, functionality, free glycol contentand hydroxyl number. The polyester polyols used are based on refinedor recycled raw materials and on residue products.

*This numerical flamespread rating is not intended to reflect hazards presented by thisor any other material under actual fire conditions.



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607Polyester Polyols in Rigid PUR and PIR Foams

In general, PIR foams perform better than PUR foams in the ASTME-84 test. PIR foams have better fire resistance because the isocyanateindex can be varied over a wide range and can be raised to high levels.The isocyanate index determines the number of cyclic isocyanurategroups, which improve the combustibility performance of the foam.However, the improved fire resistance of PIR foams is offset by certaindisadvantages-less processing latitude, higher foam friability andpoorer foam adhesion to metal. The use of polyester polyols in the PIRfoams allows us to reduce the isocyanate index without affecting theircombustibility performance. This lower isocyanate index level is advan-tageous because it improves foam processing and foam adhesion tometal; and decreases foam friability. The polyester polyols also improvethe fire resistance of PUR foams. For both foams, the polyester polyolsthemselves are cost effective and have the additional benefit of sig-nificantly reducing the need for expensive flame retardants.

Foaming parameters for PIR and PUR foams

RESULTS

Tables 2 and 3 show the processing performance, the physical, in-sulating and ASTM E-84 properties for PIR and PUR foams. Looking atthe PIR foams (Table 2), you find foam A to be the best. It has excellentClass 1* ratings: Flamespread 25*, Smoke 200*. Foam A has the lowestfriability, good physical and insulating properties as well as very goodprocessing performance. Foam E also has well-balanced properties and



608 W. W. REICHMANN AND B. A. PHILLIPS

the lowest Smoke* value of all the foams. Among the PUR foams (Table3), only foam L has both acceptable dimensional stability and fire re-sistance.

INTERPRETATION OF THE RESULTS

The key variables of the polyester polyols are correlated in (Table 1)with the properties of the PIR foams (Table 2). The best PIR foam con-tains polyester polyol 1. This polyester polyol is based on refined rawmaterials, which provide consistency in foam processing and foamproperties. Because of the linear molecular structure of polyester polyol1, the friability of foam A is very low for a PIR foam. The relativelyhigh aromatic content and especially the low free glycol content of thispolyester polyol give foam A its excellent ASTM E-84 performance. Thelower Smoke* value for foam E is caused by the still higher aromaticcontent of polyester polyol 5. The higher functionality of polyesterpolyol 5 slightly increases the friability of foam E. The chlorofluorocar-bon gas in the fine and uniform cell structure of foams A and E givesboth foams good insulating properties.Foams C and D don’t have Class 1 * ratings. The reasons are high free

glycol content and low aromatic content of the polyester polyols 3and 4.

Higher functionality and hydroxyl number of the polyester polyols 2and 6 increase the cross-link density in foam. This higher cross-linkdensity earns foams B and F Class 1 * ratings. The drawback is that thefoam friability increases dramatically.Compared to PIR foams, the properties of PUR foams are affected

even more by the key variables of polyester polyols. Only foam L, whichcontains polyester polyol 5, passes the in-house screening test forASTM E-84, Class 1 * and has satisfactory dimensional stability (Table3). This positive result is produced by the good combination of key vari-ables in polyester polyol 5, especially its high aromatic content and lowfree glycol content. The functionality and hydroxyl number of polyesterpolyol 5 build up enough cross-linking in foam L for acceptable dimen-sional stability. Foams H and M have better dimensional stabilitybecause of the higher functionality and hydroxyl number of polyesterpolyols 2 and 6. The increased cross-link density in foams H and M doesnot help in passing the screening test for ASTM E-84, Class 1 * becausethe aromatic content of polyester polyol 2 is too low and the free glycolcontent of polyester polyol 6 is too high. Like the PIR foams C and D,which also contain the polyester polyols 3 and 4, the PUR foams J andK don’t pass the Class 1 * screening test. In addition, foams J and K



609Polyester Polyols in Rigid PUR and PIR Foams

have unacceptable dimensional stability. The poor combination of keyvariables in polyester polyols 3 and 4 does not lead to foams withsatisfactory properties. The thermal conductivity of the PUR foamsdoesn’t seem to be affected by the polyester polyols evaluated. Perhapsthis is due to air entrapment in the foam caused by the handmix foamtechnique which was used to compare polyester polyols in the PURfoam series.

CONCLUSIONS

Aromatic content, functionality, free glycol content and hydroxyl Inumber are the four key variables of polyester polyols affecting theASTM E-84 classification of PIR and PUR foams for structural buildingpanels. Looking at all foam properties, PUR foams are more affected bythe polyester polyol structure than PIR foams. In both foam types, aro-matic and free glycol content affect the fire resistance most. Increasedfunctionality and hydroxyl number of polyester polyols improve thecombustibility performance of PIR foam, but also make the foam morefriable. Higher cross-link density brought about by higher functional-ity and hydroxyl number of polyester polyols is necessary in PUR foamfor better dimensional stability.

ACKNOWLEDGEMENTS

The authors would like to express their thanks to W. J. Nicola, Chem-ist with Mobay Corporation for all the experimental work he completedfor this special project. They would also like to thank the people fromthe Analytical Group at Mobay who have done an exceptional job inanalyzing the structure of the polyester polyols. Finally, they wouldlike to thank all those people in the polyurethane industry who haveprovided their expert advice, in particular, J. M. Trowell with HerculesIncorporated.

BIOGRAPHIES

Wolfgang W. Reichmann

Dr. Wolfgang W. Reichmann is currently employed by Mobay Corpo-ration, a Bayer USA, Inc. Company. He is a Group Leader in the RigidFoam Group of the Applications Development Department, Polyure-thane Division.

Dr. Reichmann received his Dr. rer. nat. in Organic Chemistry in



610 W. W. REICHMANN AND B. A. PHILLIPS

1974 from the University of Cologne, West Germany. He has been withBayer AG, Leverkusen, West Germany for eleven years. He began inthe Research Department of the Polyurethane Business Group in 1974and was transferred to the Applications Development Department in1979. He worked as a Group Leader in the Non-automotive RIM Groupuntil his transfer to Mobay Corporation in 1985.

Barry A. Phillips

Dr. Barry A. Phillips is currently on a three year assignment withBayer AG, Leverkusen, West Germany working in the Rigid FoamGroup of the Applications Development Department.He received his Ph.D. in Organic Chemistry in 1972 from West Vir-

ginia University. He served one year as a Post-doctoral Fellow at theUniversity of Nebraska, followed by four years of teaching at FortValley State College in Georgia.

Dr. Phillips has been employed by Mobay Corporation for ten years.He started in the Research Department and transferred to Applica-tions Development in 1979. He worked as a Research Specialist in theAutomotive RIM Group, followed by positions as Group Leader, SectionManager and finally Manager in the Rigid Foam Group before his cur-rent assignment in Germany.



polyester polyols in rigid polyurethane and polyisocyanurate foams for structural building panels

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