Wit Witkiewicz*, Andrzej Zieliński***Ship Design and Research Centre, Department of Materials Science, Corrosion andEnvironment Protection, Gdańsk, Poland,**Gdańsk University of Technology, Department of Materials Science and Engineering,Gdańsk, Poland,PROPERTIES OF THE POLYURETHANE (PU) LIGHT FOAMSABSTRACTThe report presents results of laboratory investigations made on the PU foams. Mechanical propertiesof foams have been measured in compression tests for two foams of 16 kg/m3 and 62 kg/m3 density, andin tension and shearing tests for foam of 62 kg/m3 density. PU foams have shown anisotropic propertiesas measured in parallel and perpendicular direction to the foam rise. Three directional values of Poisson’sratios in tension have been determined for foam of 62 kg/m3 density. The fatigue tests have been made forfoam of 62 kg/m3 density, at 10,000 cycles of loading and unloading of mass cargo barge. Reduction inbuoyancy for both foams after 7 and 30 days of immersion in water has been shown to occur to someextent. The burning tests were performed for foam of 62 kg/m3 density showing good behaviour.Key words: polyurethanes, propertiesINTRODUCTIONThe polyurethanes (PU) foams are widely used as insulating and core materials forfurniture, cooling and freezing systems, in housebuilding, shipbuilding etc. The use ofrigid foams is resulted from their low heat conduction coefficient, low density, lowwater absorption, relatively good mechanical strength [1,2]. The PU foams have beenapplied also as core materials of sandwich constructions with steel plates, in buildingthe industrial houses, warehouses, sport houses, fruit stores, carrying freezers and coldstores, where they have to fulfill both insulating and mechanical requirements [3,4].There is a number of references illustrating the effects of foam density on mechanicalproperties of PU foams [2,5]. The data are largely dependent on foam producer, as usedsubstrates and production technology decide on intrinsic structure and foam density, andin such a manner - on capacity to carry mechanical loads. The data on fatigue propertiesof PU foams are generally lacking.This project has been aimed at complex evaluation of various properties: static anddynamic mechanical properties, physical properties (density and water absorption) andchemical properties (flame spreading rate – burning test) of the foam EDULAN A/Sproduced by the Danish enterprise. Such foam is considered to be used as a corematerial in production of the light barges for shallow waters, designed in the frameworkof the UE INBAT project.
36ADVANCES IN MATERIALS SCIENCE, Vol. 6, No. 2 (10), October 2006The PU foam created in situ between steel plates will undergo the mechanical stressof different form and level. Therefore, the various tests have been performed, includingamong others: fatigue tests simulating loading and unloading of coal and ore; Tests ofwater absorption as to measure the change in mechanical properties after damage of sideand bottom plating of barge; burning tests to assess the danger for crew, resulting frompossible fire.EXPERIMENTALTwo kinds of foams were investigated: (a) polyurethane foam EW 045-45-20-Kdelivered as of 62 kg/m3 density, and (b) polyurethane foam EW 045-14-20-C deliveredas of 16 kg/m3 density. Apparent density of PU foams was determined according to ISO845 Standard.The compression, tensile, shearing and fatigue tests were performed with the MTS810.12 No. 1012 machine. The force/deformation relation were computer-recorded andprocessed using ExMTS software developed by the Ship Design and Research Centre.The linear regression procedure was applied for determination of elasticity modules.The compression tests were carried out according to ISO 844 Standard in parallel andperpendicular direction to the foam rise. Specimens’ dimensions were 100x100x50 mm.The used equipment is shown in Photo 1. The compression strength and rigiditymodulus were measured for both foams. For the foam of 62 kg/m3 density compressiveproperties were determined in a 10 kN force range, 15 mm displacement range and atesting speed of 5 mm/min. The modulus of elasticity was determined within the loadrange of 0.75 2. 5 kN. For the foam of 16 kg/m3 density compressive properties weredetermined in a 0.5 kN force range, 15 mm displacement range and at a testing speed of5 mm/min. Approximate modulus of elasticity was determined within the load range of0.004 0.01 kN.Photo 1. Equipment used in compression tests of foams
Wit Witkiewicz, Andrzej Zieliński: Properties of the polyurethane (PU) light foams37The tensile tests were performed according to ISO 1926 Standard in parallel andperpendicular direction to the foam rise. The equipment used and shape of specimenscut out from foam blocks are shown in Photo 2. The tensile strength and Youngmodulus were measured for foam of 62 kg/m3 density only. Tensile properties weredetermined in a 0.5 kN force range and at a testing speed of 5 mm/min. The strain wasmeasured with an extensometer MTS 632.12C-20 of a 50 mm gauge length and a 12.5mm strain range. The modulus of elasticity was determined within the strain range of0.1 0.5%.Photo 2. Equipment (left) and specimens (right) used in tension testsShearing tests were performed according to ASTM C 273-94 Standard in parallel andperpendicular planes to the foam rise. Dimensions of specimens were 300x50x25 mm.The used equipment is shown in Photo 3. The shear strength and shear modulus weremeasured only for foam of 62 kg/m3 density. The test specimens were rigidly supportedby steel plates bound to the foam with epoxy resin adhesive. The shear properties weredetermined at a 10 kN force range and a testing speed of 1 mm/min. The displacementof steel plates was measured with an extensometer MTS 632.12C-20 of a 50 mm gaugelength and 1.25 mm strain range. The shear modulus was determined within the travelof an extensometer of 0.1 0.5 mm. The extensometer was taken off when thedisplacement of plates had reached 1 mm and test was continued up to the moment offoam rupture, registering the force and displacement of piston of a testing machine(stroke).The Poisson’s ratios were performed for foam of 62 kg/m3 density, on the basis ofEN ISO 527-1:1996 Standard. The specimens of dimensions 75x50x50 mm in paralleland perpendicular planes to the foam rise were cut out. The used flat-wise tension testsetup according to the ASTM C 297-94 Standard is shown in Photo 5. The facings ofthe test specimen were bound to the loading blocks with epoxy resin adhesive. ThePoisson’s ratios were determined at a testing speed of 1 mm/min. The directional
38ADVANCES IN MATERIALS SCIENCE, Vol. 6, No. 2 (10), October 2006deformations of PU foam during tensile were measured simultaneously by means of twoextensometers fixed on the sides of specimen at the following parametrs: ext.l - travel of the extensometer 1, in a longitudinal direction, measured with anextensometer MTS 632.12C-20 of a 50 mm gauge length and a 1.25 mm strain range. ext.t - travel of the extensometer 2, in a transverse direction, measured with anextensometer MTS 632.11C-20 of a 25 mm gauge length and a 1.00 mm strain range.The relation of ext.l / ext.t was directly determined within strain range of 0.03 0.15mm, using the linear regression method and taking into account the data registeredduring the test by the extensometer 1 and 2. The following factors were determined for:ν12 - longitudinal direction parallel to the foam rise and transverse directionperpendicular to the foam rise,ν22 - longitudinal direction perpendicular to the foam rise and transverse directionperpendicular to the foam rise,ν21 - longitudinal direction perpendicular to the foam rise and transverse directionparallel to the foam rise.Photo 3. Equipment used in shearing tests (left) and for determining the Poisson’s ratio (right)The tests of reduction in buoyancy of foams after immersion in fresh water for aperiod of 7 and 30 days, 1 m under water level, were made according to IMOrecommendations (IMO DE 41/11/11 Section 6.4 „Evaluation And Test Report ForBuoyancy Material”). The dimensions of the specimens were 150x150x150 mm. Thesamples buoyancy was determined using an electronic balance having the 0.5 gaccuracy of reading. The balance was equipped with a specimen clamping setup,designed in accordance with the ISO 2896 Standard. The setup was hung under thebalance. The balance was calibrated after immersion in water. The foam specimenbuoyancy was measured directly after placing it in the set.The fatigue (loading – unloading) tests were carried out only for foam of 62 kg/m3density. The dimensions of the specimens were 100x100x50 mm, and test temperature26 2oC. It was assumed that specimens be loaded in the direction perpendicular to thefoam rise, in the least beneficial direction concerning the strength aspect. Eachspecimen was subjected to the test at 10,000 load cycles number. The time of the fatiguetest for one specimen approached ca 28 hrs.The one-sided haversquare compressive cycles are applied: cycle duration 10 s, σmin 0.005 MPa, σmax 0.15 0.35 MPa. The fatigue properties were determined at a 10 kNforce range and 15 mm displacement range. During the test, modulus of elasticity wasautomatically measured at compression before 1 cycle and after 2,000, 4,000, 6,000,
Wit Witkiewicz, Andrzej Zieliński: Properties of the polyurethane (PU) light foams397,000, 8,000 and 10,000 cycles number. The modules of elasticity were determinedwithin the load range of 0.75 1.40 kN. After 99, 1,000, 2,000, 3,000, 4,000, 5,000,6,000, 7,000, 8,000, 9,000 and 10,000 cycles number, minimum and maximumspecimens deformations were determined as well as the data necessary to draw therelationships for full loading/deformation relation (hysteresis loops) were registered.The used equipment was shown in Photo 1. Scheme of fatigue tests is shown in Photo 4.Photo 4. Scheme of fatigue (loading – unloading) testsThe burning characteristics were tested according to the ISO 9772 standard. Thisstandard specifies a small-scale laboratory screening procedure for comparing therelative burning characteristics of horizontally oriented, small plastic specimens havingdensity lower than 250 kg/m3. Specimens of dimensions 150x150x13mm were cut outfrom block of PU foam in plane parallel to the foam rise.RESULTS AND DISCUSSIONThe results of compression tests for foam of 62 kg/m3 density are shown in Figs. 1 2, and for foam of 16 kg/m3 density in Figs. 3 4. The carried force is about one halfgreater for heavier foam.The results of tension tests are given in Figs 5 6. The maximum tensile strength isvery low, and scarcely depends on tension direction vs. foam rise direction. In the caseof specimens cut out from foam where no bonding of two layers existed, almost allspecimens fractured correctly at the necking of the section. In the case where border of
40ADVANCES IN MATERIALS SCIENCE, Vol. 6, No. 2 (10), October 2006layers ran even at the wider part of specimen, fracture occurred at the foam interfaceboundary.In Photo 5 two specimens are shown, before and after tension tests. As was here andgenerally observed, the specimens broke at the interface boundary, between twoportions of foam, which solidified at different time.Fig. 1. Results of compression tests of the foam of 62 kg/m3 density, parallel to the foam rise
Wit Witkiewicz, Andrzej Zieliński: Properties of the polyurethane (PU) light foamsFig. 2. Results of compression tests of the foam of 62 kg/m3 density, perpendicular to the foam riseFig. 3. Results of compression tests of the foam of 16 kg/m3 density, parallel to the foam rise41
42ADVANCES IN MATERIALS SCIENCE, Vol. 6, No. 2 (10), October 2006Fig. 4. Results of compression test of the foam of 16 kg/m3 density, perpendicular to the foam riseFig. 5. Results of tension tests of the foam of 62 kg/m3 density, parallel to the foam rise
Wit Witkiewicz, Andrzej Zieliński: Properties of the polyurethane (PU) light foams43Fig. 6. Results of tension tests of the foam of 62 kg/m3 density, perpendicular to the foam risePhoto 5. Specimens before (left) and after (right) tension test. The foam of 62 kg/m3 densityThe results of shearing tests for foam of 62 kg/m3 density are demonstrated in Figs.7 9. Fig. 7 shows dependence of the force on displacement of steel plates measured withan extensometer and illustrates the way of shear modulus determining. At thedisplacement ca 1 mm, the extensometer was removed to avoid its destruction duringshearing of the foam. Figs. 8 and 9 show dependence of the force on the displacementof a piston of a testing machine.The Poisson’s ratio data for the foam of 62 kg/m3 density are demonstrated inFig.10.
44ADVANCES IN MATERIALS SCIENCE, Vol. 6, No. 2 (10), October 2006Fig. 7. Results of shearing tests on the foam of 62 kg/m3 density, in perpendicular plane to the foam rise.Shear modulus determinationFig. 8. Results of shearing tests on the foam of 62 kg/m3 density. Shear strength determination inperpendicular plane to the foam rise
Wit Witkiewicz, Andrzej Zieliński: Properties of the polyurethane (PU) light foams45Fig. 9. Results of shearing test on the foam of 62 kg/m3 density. Shear strength determination in parallelplane to the foam risePU foam type EW 045-45-20-K (EDULAN)pss02-012003.05.22CTOPoisson's ratio testGdańsk No. 10.200Travel of the Extensometer 1 .1800.200Travel of the Extensometer 2 [mm] x -1Fig. 10. Relationship used to determine the Poisson’s ratioThe results of fatigue (loading – unloading) tests are demonstrated in Figs. 11-15.The relationships obtained under fatigue conditions at two values of maximum stress
46ADVANCES IN MATERIALS SCIENCE, Vol. 6, No. 2 (10), October 2006are presented in Figs. 11 and 12. Fig. 13 presents the force – deformation relationshipsrecorded periodically before and d