WATER-BLOWN POLYURETHANE RIGID FOAMS MODIFIED BY CHEMICAL PLASTICATION

Chinese Journal of Reactive Polymers2006, 15(1): 23~ 28Article: 1004 7646(2006)01-0023-06WATER-BLOWN POLYURETHANE RIGID FOAMSMODIFIED BY CHEMICAL PLASTICATION*YU Ming XU QiangSchool of Materials Science and Engineering, East China University ofScience and Technology, Shanghai 200237, ChinaAbstract: Water-blown polyurethane rigid foams are getting more and more attention, because thetraditional blowing agent HCFCI4Ib has already been abolished to prevent the ozone layer fromdestruction. However the polyurethane rigid foams blown by water have serious defects, i.e. friabilityand resulting lower adhesion strength. Thus, the purpose of this study is to resolve the problems bychemical plastication. The maleate was added to polyol-premix containing water or to polyisocyanate,with both of which maleate does not react. To prove the reaction when polyol-premix andpolyisocyanate were mixed, the model composite was synthesized and analyed by IR, NMR and ESI(MS). Furthermore, a series of water-blown polyurethane rigid foams added different amount maleatewere sccessfully prepared. By testing impact strength and adhesion strength of the foams, the actualeffect of adding maleate was obtained.Key words: Water-blown; Rigid foams; Chemical plastication.Library Classification No.: 0631Literature Mark: A1. INTRODUCTIONThese years, HCFC-141b may be the most used blowing agent for its useful properties. But,because of its high global warming effect leading to the destruction of the ozone layer,production of HCFC141b has been forbidden. However, there are some promising alternativeblowing agents for polyurethane rigid foams manufacture, such as hydrofluorocarbons (HFCs),hydrocarbons (HCs) and water. Nevertheless, compared with HCFC-141b, all of these blowingagents have disadvantages. For example, HFCs costs more and has higher thermal conductivitycoefficient; and HCs is combustible and lower dissolubility in polyol [1.2].Polyurethane rigid foams used water as blowing agent has serious disadvantages, especially,friability and resulting lower adhesion strength. On the other side, water has many advantages,such as zero ODP value, incombustibility, easy handling and low cost. Consequently, if thedefects are improved by an easy or an inexpensive solution, water would be the best blowingagent for polyurethane rigid foams.中国煤化工MYHCNMHG* Received: 12 June, 2006First Author: YU Ming (1981~), Male, Bom in Shangdong Province, Graduate student.●24.Chinese Jourmal of Reactive PolymersJune 20, 2006The friability of water: -blown polyurethane rigid foams is usually eminent at surface layer andprone to bring about destruction of the surface layer. The reaction of isocynanate and watercreates the urea linkage, which has immoderate cohesion leading to friability of the surface layer.Thus, the purpose of this study is to resolve the problems by chemical plastication- a simple,easy approach by adding maleate additives which is inexpensive.2. MODEL COMPOUND2.1 PreparationIf maleate reacts with primary amine after polyol-premix and polyisocyanate were mixed, itwould decrease the urea linkage to improve the friability. In order to conform whether maleatereacts with primary amine and what resultant is created, the model compound reacted by Dibutylmaleate (DBM) and aniline was synthesized.Dibutyl maleate and aniline, with mole ratio of 1:1, was mixed with catalyst in a flask.Temperature was adjusted at 60C~70C, and the reaction lasted for a while until the mixedliquid turned its color from yellow to absolutely blood red. Then after the resultant was purifiedby dstillation, it was tested by IR, NMR, and MS (ESI).2.2 Spectral2.2.1 IkFigure 1 shows the FT-IR absorbance of the DBM and the resultant. One peak can be detectedin the range of 1600cm:1 to 1680cm:' on the bottom of Figure 2. The absorption band centered at1643cm:' is assigned to C=C stretching vibration of DBM. And, it is obvious that the absorptionband centered at 1643cm' disappears in the spectra of the resultant. The result of FT-IR suggeststhat C=C reacted with aniline, and became C -C. .ResultatANIUNE?WM /rVDBMww.LLRutanNyi4000300020001000987654321Wavenumber (cm")PPmFig.1 The IR Spectral of DBM and the Resultant中国煤化工DBM.AninenMHCNMHGntVol. 15 No. 1Chinese Journal of Reactive Polymers●25●2.2.2 NMRThe DBM, aniline, and the resultant's NMR spectral is shown in Fig 2. H band for CH=CHof DBM is 6.2ppm and 'H band for NH2 is 3.6ppm. However, both of them disappear in theNMR spectra of the resultant. And the NMR spectra of the resultant has new 'H band at 2.8ppmfor NH. Thus, from NMR spectral we can conclude that the group NH2 reacted with the groupCH=CH, and created the group NH.2.2.3MS0In order to get more information what theresultant is, the resultant was tested by Mass的4Spectrometry. By estimating the molecular massof the resultant, we used electrosprayionization(ESD). Figure 3 shows the ESI spectral of themsresultant. We use Mre standing for the molecular6034mass of the resultant. As shown in Figure 3, the.山peaks 322.2m/z, 344.2m/z, 643.4m/z, 665.4m/z100200300400 500 600 700 800were associated with the resultant, each standsm/Zfor [Mre+H]*， [Mre+Na]*， [2Mre+H]*, andFig.3 ESI Spectra of the Resultant[2Mre+Na]. Therefore, we can obtain that themolecular mass of the resultant is 321. However, the molecular mass sum of aniline and DBM is321. Thus, it should be the addition reaction.3. DISCUSSIONFrom the IR, NMR and ESI spectral, the reaction equation between DBM and aniline shouldbeCnH2n+L。CnH20+)Catalyst-NH2 + CnH2m+CnH2n+1-NHThus, the polyol-premix and the polyisocyanate were mixed after maleate was added topolyol-premix or polyisocyanate. The reaction of isocynanate and water generated primaryamine, which reacted quickly with maleate to secondary amine. Then, the secondary aminereacted with another isocynanate to“substituted-urea linkage", which acts as inhibiter for theexcess coagulation of the ordinary urea linkage because of its moderate cohesive propertyrelated with bulky maleate residue.中国煤化工3.1 FOAMSMHCNMHG3.1.1 PreparationIn this paper we added maleate to polyol-premix. If necessary, maleate can be added to●26●Chinese Joumnal of Reactive PolymersJune 20, 2006polyisocyanate, because it does not react with polyol or polyisocyanate. Thus, polyol-premixwas prepared by mixing of polyol 41 10 (OHV=440, Sinopec Shanghai Gaoqiao PetrochemicalCorporation), water as blowing agent, surfactant, and catalyst. Maleate was chosen both diethylmaleate (DEM) and dibutyl maleate (DBM). A polymeric-MDI (44V20, NCO=31%, BayerCorporation) was used as polyisocyanate.Table 1 FormulationPolyol-premix4110(0HV=440)100 pbwWater3 pbwSurfactant1.5 pbwCatalyst1.2 pbwDEM or DBM0~10 pbwPolyisocyanate44V20Index=100The polyol-premix and polyisocyanate were mixed and vigorously stirred for 10 sec with handmixer. The reaction paths of the water -blown polyurethane rigid foams modified by maleatewere shown in scheme 1. Then, the mixer was quickly pored into an aluminum mold(width=7cm, length=13cm, height=6cm). After about 25 minutes of curing period at temperature45"C, polyurethane foam prepared was taken out of the mold.3.1.2 Impact Strengthwco. 4110。URETHANEPRIMARY AMINE(Blow ing)UREACgH2a+h、CH2a+1 Maleate =(DEM)n=(DBM)CnH2a+lNH0SUBSTITUTED UREAr ~oC.H2o1Scheme 1 Reaction Paths of the Water -blown Polyure中国煤化iy MaleateTH.CNMH GThe sample for impact strength test was cut to recrangle (unckness= icm, width=1 .5cm,length=12cm). The test result was shown in Fig. 4 and Fig. 5. Thus, it is obvious that whenVol.15 No.1Chinese Journal of Reactive Polymers●27●increasing of DEM or DBM content, the impact strength increases; and the effect of addingDEM is better than that of adding DBM in this system.1.0. 0.40-; 0.8-0.35昌0.6-0.300.40.25i230.2-0DBM mass content (%)DEM mass content (%)Fig. 4 Effect of DBM Content onFig.5 Effect of DEM Content onthe Impact Strength of Foarmsthe Impact Strength of Foams3.1.3 Adhesion strengthStel plate (25mmx100mm) was previously.4put to the inner face of the aluminum mold in.3-order to measure adhesion strength, and itattached to the polyurethane foam surface during昏0.2-the formation of the foam. The adhesion strengthwas defined as the peeling strength betweensteel plate and the foam. Fig 6 shows effect of.0-DBM content on the adhesion strength. The0.00 0.02 0.04 0.06 0.08surface layer of foam without maleate was quitefriable, resulting the foams did not adhere to theFig.6 Effect of DBM Content on the Adhesionsteel plate. Thus， measuring the adhesionStrength of Foamsstrength is impossible. From Fig 6, within theDBM mass content 3% of the foam, theadhesion strength increases while DBM mass content increasing. However, the adhesion strengthwas spoiled by excess amount of DBM. Therefore, it appears that the moderate amount of DBMis appropriate. Furthermore, when the foams adding DEM were tested, the steel plate couldn't bepeeled from the foams until the foam samples were destructed. Thus, the adhesion strength ofthe foams adding DEM is stronger than the strength of the foams, and it is impossible tomeasure.中国煤化工4. CONCLUSsMYHCNMHG.The water-blown polyurethane rigid foams modified by chemical plastication was●28.Chinese Joural of Reactive PolymersJune 20, 2006successfully prepared. By adding maleate (DBM and DEM) the friability of the foam surfaceand adhesion was considerably improved, which was shown in the impact strength and adhesionstrength test. Moreover, the effect of adding DEM is better than DBM.Synthesis and spectral studies suggest that the reaction of isocynanate and water generatedprimary amine, which reacted quickly with maleate to secondary amine. Then, the secondaryamine reacted with another isocynanate to“substituted-urea linkage", which acts as inhibiter forthe excess coagulation of the ordinary urea linkage because of its moderate cohesive propertyrelated with bulky maleate residue.Thus, using inexpensive maleate to solve the friability and the lower adhesiveness ofwater-blown PUR rigid foams is available.REFERENCE[1] Prociak Aleksander, Pielichowski Jan, Sterzynski Tomasz, Polymer Testing [], 2000, 19(6):705~712.[2] Modesti M., Baldoin N., Simioni F., European Polymer Jourmal [J], 1998, 34(9): 1233~1241.中国煤化工MYHCNMHG