[ACS Symposium Series] Polymeric Foams Volume 669 (Science and Technology) || Polyisocyanurate Foams Modified by Thermally Stable Linkages

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<ul><li><p>Chapter 6 </p><p>Polyisocyanurate Foams Modified by Thermally Stable Linkages </p><p>K . Ashida1, K . Saiki2, J. Goto2, and K . Sasaki2 </p><p>1Polymer Institute, University of Detroit Mercy, 4001 West McNichols Road, P.O. Box 19900, Detroit M I 48219 </p><p>2Nippon Polyurethane Industries Company, Limited, 440 Akiba-cho, Totsuka-ku, Yokohama 245, Japan </p><p>Urethane-modified polyisocyanurate foams have inherentiy higher flame retardation and thermal stability than those of urethane foams. However, they still have disadvantages of relatively high flammability , low thermal stability, and high smoke generation due to the labile urethane linkages. In this study, thermally more stable linkages than the urethane linkages, e.g., amide, imide and carbodiimide linkages were examined for improving these disadvantages. The resulting foams exhibited significant improvement in the above properties. In addition, zero ODP physical blowing agents consisting of halogen-free azeotropes were examined. </p><p>The isocyanurate linkage ( Figure 1) is formed by the cyclotrimerizaon of isocyanate groups, and has inherently higher thermal stability than that of the urethane linkage. However, unmodified polyisocyanurate foams have inherent disadvantage by being extremely friable. In particular, their high friability makes it impossible to handle them in practical applications.Therefore, the crosslink density of the foams should be reduced by incorporating urethane linkages by the addition of polyols as modifiers [1 ]. A general formula of modified isocyanurate foams is illustrated in Figure 2. Since 1966, a number of R &amp; D efforts were focused on urethane-modified isocyanurate foams. Two primers of isocyanurate foams have been published [2, 3 ]. The modifiers which appeared in the literature are summarized in Table I, in which " X " represents modifiers The linkages for modification include urethane [1 ], amide [1,9JO ] , imide [4,9 ], carbodiimide </p><p> 1997 American Chemical Society 81 </p><p>Dow</p><p>nloa</p><p>ded </p><p>by S</p><p>TAN</p><p>FORD</p><p> UN</p><p>IV G</p><p>REEN</p><p> LIB</p><p>R on</p><p> Aug</p><p>ust 1</p><p>9, 2</p><p>012 </p><p>| http:</p><p>//pubs</p><p>.acs.o</p><p>rg Pu</p><p>blic</p><p>atio</p><p>n D</p><p>ate:</p><p> June</p><p> 1, 1</p><p>997 </p><p>| doi: 1</p><p>0.1021</p><p>/bk-19</p><p>97-066</p><p>9.ch00</p><p>6</p><p>In Polymeric Foams; Khemani, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997. </p></li><li><p>POLYMERIC FOAMS </p><p>0 I! </p><p>- R - ^ N - R _ </p><p>0=C , C = 0 R </p><p>Figure 1. Isocyanurate Linkage. </p><p> 0 0 </p><p>-R-N ^ N - R - X - R - l T N-R N-R-</p><p>1 I I R R R I ' </p><p>oc I </p><p>2 -</p><p>( &lt; </p><p>I </p><p>Figure 2. Modif ied Isocyanurate Foams, </p><p>heat &lt; </p><p> I </p><p>Polymer ----&gt; Flammable Decomposition Products &gt; </p><p>air 4- heat I </p><p> &gt; Combustion Products + Heat &gt; </p><p>Figure 3. Combustion Mechanism. </p><p>Dow</p><p>nloa</p><p>ded </p><p>by S</p><p>TAN</p><p>FORD</p><p> UN</p><p>IV G</p><p>REEN</p><p> LIB</p><p>R on</p><p> Aug</p><p>ust 1</p><p>9, 2</p><p>012 </p><p>| http:</p><p>//pubs</p><p>.acs.o</p><p>rg Pu</p><p>blic</p><p>atio</p><p>n D</p><p>ate:</p><p> June</p><p> 1, 1</p><p>997 </p><p>| doi: 1</p><p>0.1021</p><p>/bk-19</p><p>97-066</p><p>9.ch00</p><p>6</p><p>In Polymeric Foams; Khemani, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997. </p></li><li><p>6. ASHIDA E T A L . Polyisocyanurate Foams 83 </p><p>[5,8 ] , oxazolidone [6 ] and substituted urea [7 ] linkages in which urethane linkages are most widely employed for producing commercial products. </p><p>Urethane-modified isocyanurate foams have better flame retardance and thermal stability than urethane foams. </p><p>The thermal stability and smoke generation of the urethane-modified isocyanurate foams are not quite satisfactory because the urethane linkage has a labile hydrogen atom, and therefore the linkage dissociates easily at about 200 C to the original components, i.e., polyisocyanates and polyols .,These monomers can be ignited at elevated temperature in the presence of air , according to the combustion mechanism shown in Figure 3. </p><p>The research philosophy in this study is based on a hypothesis that the higher the thermal stability of polymeric linkages, the less the generation of flammable gases which result in low combustibility, and that the higher the thermal stability, the lower the smoke generation. </p><p>This paper , therefore, will present an evaluation of thermally stable modifiers, such as carbodiimide , imide , and amide linkages. In this study, the following abbreviation will be used. U-PIR : Urethane-modified isocyanurate foams, CD-PIR: carbodiimide-modified isocyanurate foams, I-PIR: imide-modified isocyanurate foams, A-PIR : amide-modified isocyanurate foams, and PUR : urethane foams. </p><p>Experimental </p><p>1. ) Carbodiimide-ModiOed Polyisocyanurate Foams ( CD-PIR) . 1.1. Raw Materials A polymeric isocyanate ( polymeric M D I , NCO% : 31.2% ), carbodiimide-</p><p>forming catalyst [ 1 -phenyl-3-methyl-2-phospholene-1 -oxide, (PMPO)], isocyanate trimerization catalysts, [ quaternary ammonium carboxylate, ( DABCO TMR-2)], potassium 2-ethylhexanoate, ( DABCO K-15), and 1,3-5,-tris(dimethylaminopropyl)sym-hexahydrotriazine, ( Toyocat TRC ) ], silicone surfactant, [ poly(dimethyl siloxane-oxyalkylene- block copolymer , DC-137 ], and a physical blowing agent, C C I 2 F - C H 3 , (HCFC-141b) , were used. </p><p>1.2. Foaming Procedures The one step process employed for preparing modified polyisocyanurate </p><p>foams was as follows; Into a paper cup, a polymeric MDI and a silicone surfactant were charged and then a carbodiimdie-forming catalyst and an isocyanate trimerization catalyst were added using microsyringes. After the catalysts were added, the mixture was immediately stirred for 7-10 seconds at about 2000 rpm. using a high shear stirring paddle, and allowed to foam in the paper cup. The foams </p><p>Dow</p><p>nloa</p><p>ded </p><p>by S</p><p>TAN</p><p>FORD</p><p> UN</p><p>IV G</p><p>REEN</p><p> LIB</p><p>R on</p><p> Aug</p><p>ust 1</p><p>9, 2</p><p>012 </p><p>| http:</p><p>//pubs</p><p>.acs.o</p><p>rg Pu</p><p>blic</p><p>atio</p><p>n D</p><p>ate:</p><p> June</p><p> 1, 1</p><p>997 </p><p>| doi: 1</p><p>0.1021</p><p>/bk-19</p><p>97-066</p><p>9.ch00</p><p>6</p><p>In Polymeric Foams; Khemani, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997. </p></li><li><p>84 POLYMERIC FOAMS </p><p>Table I. Modifiers for Isocyanurate Foams </p><p>Modifier Resulting Linkage </p><p>Urethane </p><p>Amide </p><p>Imide </p><p>Carbodiimide </p><p>Oxazolidone </p><p>Urea </p><p>Structure </p><p>- N H - C O - O -</p><p>- N H - C O -</p><p>C O -R N-</p><p>C O -N=C=N-</p><p>- N H - C H 2 - C H -o = c R </p><p>- N - C O - N H -</p><p>Polyol Polycarboxylic acid Carboxylic dianhydride </p><p>( catalyst only) </p><p>Polyepoxide </p><p>Poly-sec.amine </p><p>Table IL Comparison Between Unmodified Polycarbodiimide Foam and Unmodified Polyisocyanurate Foam </p><p>Formulation (pbw) 1 2 </p><p>Polymeric M D I 2 5 . 2 5 . DC-193 0.4 0.4 P M P O 1.0 0 . Dabco T M R - 2 0 . 0.4 H C F C - 1 4 1 b 0 . 5.0 </p><p>Reaction Profile Cream time, sec. 6 0 . 70 . Gel time, sec. 1,400. no. Rise time, sec. &gt;3,600. 185. </p><p>Foam Properties Density, kg/m^ 19.4 28.5 Cell size coarse fine Closed cell content, % 5.0 90.0 Friability, % wt. loss 20.0 100. </p><p>Dow</p><p>nloa</p><p>ded </p><p>by S</p><p>TAN</p><p>FORD</p><p> UN</p><p>IV G</p><p>REEN</p><p> LIB</p><p>R on</p><p> Aug</p><p>ust 1</p><p>9, 2</p><p>012 </p><p>| http:</p><p>//pubs</p><p>.acs.o</p><p>rg Pu</p><p>blic</p><p>atio</p><p>n D</p><p>ate:</p><p> June</p><p> 1, 1</p><p>997 </p><p>| doi: 1</p><p>0.1021</p><p>/bk-19</p><p>97-066</p><p>9.ch00</p><p>6</p><p>In Polymeric Foams; Khemani, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997. </p></li><li><p>6. ASHIDA E T A L . PolyisocyanurateFoams 85 </p><p>were post cured for 2 days under ambient conditions before testing. Similar procedures were used for preparing other types of modified polyisocyanurate foams. </p><p>The two step process consists of the first step of prepolymer preparation and the second process of mixing foaming ingredients . The prepolymers were prepared by the reaction of a modifier with an excess amount of polyisocyanate. The preparation conditions are described in respective chapters. </p><p>This process was preferably used for preparing CD-PIR foams and adipic acid modified A-PIR foams. </p><p>1.3. Foam Testing The smoke density was determined by the A S T M D-2843-70 using the </p><p>XP-2 smoke chamber. The Butler chimney test was used for determining surface flammability according to A S T M D-3014-76. The friability test was conducted according to A S T M C-421, and the oxygen index was determined by A S T M D-2863-77. The flame penetration test was conducted by the method according to the Bureau of Mines Report of Investigation # 6366 ( 1964). </p><p>1.4. Results and Discussion A comparison of an unmodified carbodiimide foam (Formulation #1) and </p><p>an unmodified isocyanurate foam ( Formulation #2) are shown in Table II. The unmodified carbodiimide foam exhibited a low closed cell content and a low friability. In comparison, the unmodified polyisocyanurate foam exhibited a high closed cell content and extremely high friability. </p><p>CD-PIR foams were prepared by both the one step and the two step processes. A one step process formulation and the foam properties obtained are listed in Tables III and IV. Table III shows a comparison of various catalysts. In the one step process, low density foams were obtained without the addition of blowing agents, because the carbodiimide linkage formation is accompanied by the simultaneous generation of carbon dioxide gas. Table IV exhibits the effect of component temperature of CD-PIR by the one step process. A component temperature of 40 -60 C gave a desirable foaming profile, and the resulting foams exhibited outstanding flame retardance in terms of the Butler Chimney test and superior low-friability, but the closed cell content was low due to the generation of carbon dioxide gas in the low viscosity components. Therefore, the prepolymer (two step) process was attempted to solve this disadvantage. </p><p>A two step process formulation and the foam properties obtained are shown in Table V. In the two step process, HCFC 141b was added as physical blowing agent Both the carbodiimide linkage and the isocyanurate linkage are thermally stable, and therefore, modification by these linkages provides more thermally stable </p><p>Dow</p><p>nloa</p><p>ded </p><p>by S</p><p>TAN</p><p>FORD</p><p> UN</p><p>IV G</p><p>REEN</p><p> LIB</p><p>R on</p><p> Aug</p><p>ust 1</p><p>9, 2</p><p>012 </p><p>| http:</p><p>//pubs</p><p>.acs.o</p><p>rg Pu</p><p>blic</p><p>atio</p><p>n D</p><p>ate:</p><p> June</p><p> 1, 1</p><p>997 </p><p>| doi: 1</p><p>0.1021</p><p>/bk-19</p><p>97-066</p><p>9.ch00</p><p>6</p><p>In Polymeric Foams; Khemani, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997. </p></li><li><p>86 POLYMERIC FOAMS </p><p>Table III. Effect of P M P O &amp; Cyclotrimerization Catalysts on Physical Properties of CD-PIR ** Foams, </p><p>( One Step Process ) </p><p>Formulation (pbw) 1. 2. 3. 4. 5. </p><p>Polymeric M D I (1) 25. 25. 25. 2 5 . 25. P M P O (2) 0.36 0.67 1.44 1.44 1.44 DC-193 (3) 0.4 0.4 0.4 0.4 0.4 Dabco T M R - 2 (4) 0.12 0.12 0.12 0 . 0 . Dabco K-15 (5) 0 . 0 . 0 . 0.12 0 . Toyocat T R C (6) 0 . 0 . 0 . 0 . 1.0 </p><p>Reaction Profile Cream time,sec. 6 0 . 3 5 . 18 . 14. 14. Gel time, sec. 120. 115. 110. 8 0 . 9 0 . Rise time, sec. 172. 155. 135. 120 155 </p><p>Foam Properties Density, kg/nr*. 47.3 33.3 27.2 30.6 27.4 Cell size fine fine fine fine fine Closed cell, % 6.9 6.8 14.7 29.3 15.3 Friability, % wt. loss </p><p>52.5 42.6 14.4 29.3 15.3 Butler Chimney, </p><p>% wt.retained 96.4 96.0 91.8 93.1 85.7 Oxygen index 28.5 28.0 27.5 27.5 25.0 Oxygen index </p><p>(1) % N C O : 31.2 , (2) l-Phenyl-3-methyl-2-phosphorene-loxide (3) Silicone surfactant, (4) Quaternary ammonium carboxylate (5) Potassium 2-ethylhexanoate (6) 1,3,5-tris(dimethy laminopropyl)sym-hexahydrotriazine </p><p>** Carbodiimide-modified polyisocyanurate </p><p>Dow</p><p>nloa</p><p>ded </p><p>by S</p><p>TAN</p><p>FORD</p><p> UN</p><p>IV G</p><p>REEN</p><p> LIB</p><p>R on</p><p> Aug</p><p>ust 1</p><p>9, 2</p><p>012 </p><p>| http:</p><p>//pubs</p><p>.acs.o</p><p>rg Pu</p><p>blic</p><p>atio</p><p>n D</p><p>ate:</p><p> June</p><p> 1, 1</p><p>997 </p><p>| doi: 1</p><p>0.1021</p><p>/bk-19</p><p>97-066</p><p>9.ch00</p><p>6</p><p>In Polymeric Foams; Khemani, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997. </p></li><li><p>6. ASHIDA E T A L . Polyisocyanurate Foams 87 </p><p>Table IV. Effect of Component Temperature of CD-PIR * Foams on Foam Properties ( One Step Process) </p><p>Formulation (pbw) 1 2 3 </p><p>Polymeric M D I 2 5 . 2 5 . 25 . P M P O 0.25 0.25 0.25 DC-193 0.4 0.4 0.4 Dabco K-15 ** 0.12 0.12 0.12 Component -</p><p>Temperature, 0 C 2 5 . 4 0 . 60 . </p><p>Reaction Profile Cream time, sec. 8 6 . 16 . 10. Gel time, sec. 100. 3 0 . 20 . Rise time,sec. 120. 3 6 . 28 . </p><p>Foam Properties Density, kg/m^ 44.4 41.1 34.0 Cel l size fine fine fine Friabil i ty, % wt.loss 33.3 24.0 20.0 Butler Chimney, </p><p>% wt. retained 97.6 97.9 97.7 </p><p>* Carbodiimide-modified polyisocyanurate ** Potassium 2-ethylhexanoate </p><p>Table V . CD-PIR * Foams by the Two Step Process </p><p>Formulation (pbw) 1 2 3 4 </p><p>% N C O , Prepolymer 29.2 26.7 23 .2 19.3 </p><p>Polymeric M D I , 25. 25. 2 5 . 2 5 . DC-193 0.4 0.4 0.4 0.4 Dabco T M R - 2 0.4 0.4 0.4 0.4 H C F C - 1 4 1 b 4.5 4.5 4.5 4.5 </p><p>Foam Properties Density, kg/m^ 28.5 28.0 27.3 29.8 Cel l size coarse fine fine fine Closed cell ,% 56.1 93.4 82.4 15.8 Friabi l i ty , % wt.loss 100 50.0 45.5 41.5 Butler Chimney, </p><p>% wt. retained 98.6 94.1 95.3 95.7 Oxygen index, % 29.5 27.5 27.5 27.0 </p><p>* Carbodiimide-modified polyisocyanurate </p><p>Dow</p><p>nloa</p><p>ded </p><p>by S</p><p>TAN</p><p>FORD</p><p> UN</p><p>IV G</p><p>REEN</p><p> LIB</p><p>R on</p><p> Aug</p><p>ust 1</p><p>9, 2</p><p>012 </p><p>| http:</p><p>//pubs</p><p>.acs.o</p><p>rg Pu</p><p>blic</p><p>atio</p><p>n D</p><p>ate:</p><p> June</p><p> 1, 1</p><p>997 </p><p>| doi: 1</p><p>0.1021</p><p>/bk-19</p><p>97-066</p><p>9.ch00</p><p>6</p><p>In Polymeric Foams; Khemani, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997. </p></li><li><p>88 POLYMERIC FOAMS </p><p>100 </p><p>20 </p><p>A: CD-PIR B: Unmodified PIR C: Carbodiimide Foam D: U-PIR E: PUR </p><p>300 400 Temperature (eC) </p><p>500 700 </p><p>Figure 4. T G A Profiles of Various Foams ( Reproduced with permission from K.Saiki, K.Sasaki and K. Ashida, J. Cellular Plastics, Vol.30, No.5, Figure 1 ) </p><p>100 </p><p>1 80 I f eo </p><p>o 40 </p><p>11120 5 = O t. 3 ti. II. ID </p><p>15 </p><p>Butler chimney test </p><p>17 </p><p>Friability </p><p>19 21 23 25 27 NCO content (wt%) </p><p>31 </p><p>60 </p><p>60 - * c 1 </p><p>40 </p><p>30 &amp; 3 </p><p>20 I C m 10 </p><p>33 </p><p>Figure 5. Relationship Between NCO% vs. Foam Properties. ( Reproduced with permission from K.Saiki, K.Sasaki and K. Ashida, ibid: Vol.30, No.5, Figure 2 ) </p><p>Dow</p><p>nloa</p><p>ded </p><p>by S</p><p>TAN</p><p>FORD</p><p> UN</p><p>IV G</p><p>REEN</p><p> LIB</p><p>R on</p><p> Aug</p><p>ust 1</p><p>9, 2</p><p>012 </p><p>| http:</p><p>//pubs</p><p>.acs.o</p><p>rg Pu</p><p>blic</p><p>atio</p><p>n D</p><p>ate:</p><p> June</p><p> 1, 1</p><p>997 </p><p>| doi: 1</p><p>0.1021</p><p>/bk-19</p><p>97-066</p><p>9.ch00</p><p>6</p><p>In Polymeric Foams; Khemani, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997. </p></li><li><p>6. ASHIDA E T A L . Polyisocyanurate Foams 89 </p><p>foams than the U-PIR foams. Figure 4 shows a thermal stability comparison of CD-PIR foam, unmodified PIR foam, U-PIR foam (NCO / OH equivalent ratio = 30) and a PUR foam by means of TGA. The four kinds of modified foams, </p><p>except PUR foam, exhibited superior thermal stability. Figure 5 shows the relationship between NCO% of prepolymers vs. foam </p><p>properties. The foams were prepared with the addition of carbodiimide-forming catalyst and without the addition of a physical blowing agent, i.e. the foams were blown by the carbon dioxide generated in the simultaneous formation of carbodiimide linkages by the condensation reaction of isocyanate groups. Therefore, the higher the NCO content of the prepolymers , the higher the C O 2 generation , and therefore,the lower the foam density. It should be noted that the resulting foams exhibited outstanding weight retention determined by the Butler chimney test, according to A S T M D-3614, and low flame penetration ( burn through) time.according to Bureau of Mines test (Report # 6366) </p><p>Figure 6 shows a significant difference in smoke density between the CD-PIR foam and the U-PIR foam. </p><p>2 ) Amide-Modified Isocyanurate Foams.(A-PIR Foams) 2 - 1 . Raw Materials: The modifiers used in this study are adipic acid, </p><p>dimer acid ( Hystrene 3695, Witco Chemical) and a ketimine prepared by the reaction of 2-heptanone and hexamethylenediamine. The trimerization catalysts employed were...</p></li></ul>

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