Highly Flame Retardant and Bio-Based Rigid Polyurethane Foams Derived from Orange Peel Oil.
Polyurethanes are widely used among various polymeric products due to extensive options available in selection of polyols and isocyanates to form products with wide range of different properties such as tunable density, flexibility, and rigidity (foams, castings, elastomers, adhesives, and many more) [1-9]. It had a huge market of ~54 billion dollars in 2015, which is expected to continuously grow at the rate of about 7% . About half of the polyurethane market focuses on construction, interior, and furniture which majorly consists of rigid polyurethane foams . Second, considering environmental factors, European Chemicals Agency (ECHA) and U.S. Environmental Protection Agency (EPA) has attracted major attention toward greener approach for majority of applications [11, 12].
Green-based approach for foams has initiated wide research over bio-based polyols using vegetable oils . Polyols, which are organic compounds with multiple hydroxyl groups possessing ability to readily react with isocyanate and form polymeric compounds . Polyols were synthesized by generation of multiple hydroxyl groups at the double bonds of vegetable oils creating higher degree of crosslinking and making for rigid structural foams . Soybean oil, castor oil, canola oil, corn oil, sunflower oil, cashew-based derivatives and many other sources used for bio-based polyols were reported [5-7, 15-31].
Another of such bio-based derivative is dipentene dimercaptan also called as limonene dimercaptan which is in fact mercaptenized limonene, a major component of orange peel. Thiol or mercaptan group (--SH) presents advantage of higher reactivity toward double bonded organic compound and can be added in single step thiol-ene reaction [6, 18, 25]. Thiol-ene reaction provides an advantage of faster reaction, higher purity of obtained product, narrow molecular weight distribution and above 90% conversion yield with efficient stirring [32, 33].
Seeing the market application of polyurethane as rigid foams for various applications, it is essential that they perform physically well during their on-field applications. Especially, polyurethane foams suffer from disadvantage of high flammability which amplified due to higher surface with respect to mass density of the product. Moreover, high oxygen, carbon, and hydrogen content due to aliphatic chains readily allows ignition even with small glint of fire [8, 25]. Thus, for any practical applications, it is essential to prepare flame retardant polyurethanes.
Flame retardant polyurethanes foams have been prepared by addition of various flame retardant compounds such as compounds containing phosphorus and/or nitrogen groups, expendable graphite, MgO, and [Al.sub.2][O.sub.3] [8, 9, 25, 34-40]. It was observed that expandable graphite and nitrogen-based derivatives require higher loading as additive to achieve decent flame retardancy [8, 9]. While, phosphorus-based additives such as dimethyl methyl phosphonate showed higher flame retardant properties at lower weigh loading [25, 40] Therefore, in this work, we explored the flame retardant characteristics of bio-based polyurethanes using dimethyl methyl phosphonate as flame retardant additive. However, study suggests that additive approach does provide excellent flame retardancy but inversely affects the mechanical properties of the foam due to poor compatibility with the substrate . Moreover, possibility of migration of additive over a period of time and compromising the flame retarding ability could be a serious concern . Thus, our secondary approach turned in to synthesis of a novel bromine-based reactive polyol which could exhibit sustainable flame retardancy and enhance the mechanical properties of the foam.
Here, we report synthesis and characterization of a bio-based polyol using mercaptenized limonene and glycerol-1-allyl ether using thiol-ene reaction under UV radiation to obtain high quality dimercaptan-glycerol-1-allyl ether polyol. Further, the flame retardant properties of rigid foams from as prepared polyol with addition of DMMP as an additive flame retardant and novel bromine-based reactive polyol as a reactive flame retardant were studied. DMMP with phosphorus loading of 0, 0.23, 0.45, 0.9, 1.3, and 1.7 wt% and bromine polyol with bromine content of 0, 4, 4.5, 5, 5.5, and 6 wt% within the foams were prepared and analyzed. Results suggest outstanding reduction in burning time from 75 to 7.5 sec with weight loss of 4.7% after burning by addition of only 0.9% phosphorus in the foam. Bromine-based polyurethanes form showed inferior flame retardancy but improved the mechanical strength of the polyurethane foams. Our results suggest excellent flame retardancy for both additive-and reactive-based compounded foams with high mechanical strength.
All chemicals were used as received without any further purification. Limonene dimercaptan (dipentene dimercaptan) from Chevron Philips and glycerol-1-allyl ether from Acros Organic were obtained. Jeffol SG-360, a sucrose-based polyether polyol (OH content of 360 mg KOH/g), Rubinate M isocyanate (methylene diphenyl diisocyanate, NCO content of 31%) were purchased from Huntsman. Catalysts DAB CO T-12 and NIAX A-1 were received from Air Products and OSi Specialties, respectively. Silicone-based surfactant (Tegostab B-8404) was purchased from Evonik. Distilled water was used as blowing agent. Dimethyl methyl phosphonate (DMMP), 2,4,6-tribromophenol (2,4,6-TBP), glycidol (GLY), tetramethylguanidine (TMG), and 2-hydroxy-2-methylpropiophenone was purchased from Sigma-Aldrich, USA. Ethylene oxide (EO) was purchased from ARC specialist products, USA.
Synthesis of Limonene Dimercaptan-Based Polyol. LDM-GAE polyol was synthesized by thiol-ene click chemistry using UV irradiation. Limonene dimercaptan and glycerol-1-allyl ether were added in molar ratio of 1:2 along with 2.5 wt% of a photo initiator, 2-hydroxy-2-methylpropiophenone. The thiol-ene reaction was carried out at room temperature for 6 h under ultraviolet radiation. The reaction mixture was stirred constantly using magnetic stirrer at 300 rpm during entire reaction period. The Schematic of overall setup for thiol-ene reaction is given in Fig. la and their corresponding reactions are shown in Fig. 1b.
Synthesis of Bromine-Based Polyol. Bromine-based polyol was synthesized by reacting 0.2 mol of 2,4,6-tribromophenol with 0.4 mol of glycidol in the presence of 0.5 wt% tetramethylguanidine as a catalyst in a 450 ml Parr reactor. Reactor was purged with nitrogen at 50-60 psi in-pressure and 10 psi outpressure several times followed by a steady pressure flow of 10-15 psi. The reaction mixture was heated at 105-110[degrees]C resulting in an exothermic reaction assisted with constant water cooling maintaining temperature range between 120 and 140[degrees]C. After 1.5 h of reaction, when exothermicity of the reaction reduces and temperature approached ~110-115[degrees]C, 0.4 mol of ethylene oxide was added in to the mixture with a constant pressure of 50-55 psi. Reaction was continued for further 2 h to ensure completion of reaction. The compound was purified using vacuum distillation in at 90-100[degrees]C under vacuum of 60-65 mm Hg. The resulting bromine polyol was light brown and highly viscous liquid. The reaction and the structure of bromine-based polyol are given in Fig. 1c.
Characterization of Polyols
Synthesized polyols were characterized using various techniques. The hydroxyl number (OH number) of the polyols was determined by the phthalic anhydride/pyridine (PAP) method (ASTM-D 4274). Acid value was determined according to IUP AC 2.201 standard using indicator method. The molecular weight of the polyols was analyzed using gel permeation chromatography (GPC) using a system by Waters (Milford, MA, USA) which was composed of four 300 x 7.8 mm phenogel 5 [mu] columns with different pore sizes of 50, 102, 103, and 104 [Angstrom]. Eluent solvent was tetrahydrofuran and eluent rate was 1 ml/min at 30[degrees]C. Shimadzu IR Affinity-1 spectrophotometer was used to record the FT-IR spectrum of the polyol at room temperature. Viscosity of polyol was measured using an AR 2000 dynamic stress rheometer (TA Instruments, USA) at 25[degrees]C with shear stress increasing from 1 to 2,000 Pa linearly. The rheometer has a cone plate with an angle between 2[degrees] and a cone diameter of 25 mm.
Preparation of Flame Retardant Rigid Polyurethane Foam
Additive Flame Retardant Polyurethane Foams. Equivalent weight of all polyols was calculated as described in previous study . All the ingredients were added according to Table 1 to prepare polyurethane foams with different concentration of phosphorus and were designated accordingly. All the ingredients except MDI were added into a 500 ml cup and stirred vigorously (3,000 rpm) to mix completely. After complete mixing, 32.07 g of MDI was added in to the mixture and stirred at 3,000 rpm to make AFR-polyurethane foams designated as P0%, P-0.2%, P-0.45%, P-0.9%, P-1.3%, and P-l.7% respective to percentage of phosphorus added.
Reactive Flame Retardant Polyurethane Foams. Reactive flame retardant polyurethane foams were synthesized using the above method but having various concentration of bromine-based polyol along with LDM-GAE polyol. The formulation is given in Table 2. The obtained foams were designated as Br4%, Br-4.5%, Br-5%, Br-5.5%, and Br-6% representing the bromine content in overall foams. All as prepared foams were kept for 7 days to complete curing process.
Characterization of Polyurethane Foams
Foams were cut in to required size of the specimen for further characterization. Foams in cylindrical shape of 45 mm x 30 mm (diameter x height) were cut to obtain both density and closed-cell content of the prepared foams. The apparent density of foams was measured using the standard test method for apparent density of rigid cellular plastics (ASTM D 1622). Closed-cell content of the foams was measured using Ultrapycnometer, Ultrafoam 1000 according to ASTM 2856 standard method. Compression strength of the foams was determined using a foam with dimension of 50 mm x 50 mm x 25 mm (length x width x height). The compressive strength at 10% strain was determined by using a Q-Test 2-tensile machine (MTS, USA) according to ASTM 1621 standard method. The compressive force rising with a strain rate of 30 mm/min was applied parallel to the direction of the foam. Microstructure and cell size distribution of the rigid polyurethane foams were studied using a Phenom G2 Pro scanning electron microscope (Netherlands). Before imaging, foam samples with sharp-blade shape were attached with conductive carbon tape and gold sputtered to avoid the charging effect during imaging. A TA instrument (TGA Q500) was used to study the thermal behavior of the foams. Thermogravimetric analysis was performed under nitrogen atmosphere by heating the foams from room temperature to 600[degrees]C with heating rate of 10[degrees]C/min. Fire-retardant properties were examined using the test method for horizontal burning characteristics of cellular polymeric materials (ASTM D 4986-98). After exposing specimens of 150 mm x 50 mm x 12.5 mm to flame for 10 s, burning time and weight difference (before and after the burn) were recorded.
RESULTS AND DISCUSSION
Characteristics of LDM-GAE Polyol
LDM-GAE polyol showed hydroxyl number of 470 mg KOH/g, acid value of 0.7 mg KOH/g, and viscosity of 6.5 Pa*s. Higher hydroxyl number and lower acid value ensures higher degree of reactivity of the polyol during foaming. The overall reaction mechanism for the reacting species was analyzed using infrared-spectroscopy and gel permeation chromatography to confirm the desired structure of the LDM-GAE polyol. Figure 2a and b shows the FT-IR spectra and GPC curves of starting materials and obtained product. As seen in the graphs, double bond of glycerol allyl ether near 1,700 [cm.sup.-1] reacts with--SH group of LDM at 2,550 [cm.sup.-1] to obtain LDM-GAE polyol containing hydroxyl group around 3,400 [cm.sup.-1]. There is clear indication of C--S bond formation as desired by the reaction near 1,086 [cm.sup.-1], this ensures that reaction has proceeded as desired. Similar behavior was observed in other resources . Thus, using thiol-ene reaction, it can be assumed that obtained products were pure and without any side reactions.
Gel permeation chromatography graph provides the molecular weight distribution behavior of the reacting species and the product. It can be clearly observed that retention time for obtained LDM-GAE polyol reduced to 35 min with respect to LDM (39 min) and GAE (38 min) individually. This indicates that higher molecular weight product has been obtained. The sharp peak in GPC graph of LDM-GAE indicates the narrow molecular weight distribution (polydispersity index of 1.07) of the obtained polyol and completeness of the reaction. It can be observed from the GPC of other resources that nonmercaptenized limonene showed minor unreacted double bond within aromatic structure . This problem seems to be resolved due to introduced S--H group in limonene allowing easy reaction with double bond of GAE.
Characteristics of Bromine Polyol
Br-polyol showed hydroxyl number and acid value of 398 and 0.28 mg KOH/g, respectively. The proceedings of reaction can be analyzed using FT-IR and GPC analysis. Figure 2c and d shows the curves for raw materials and final product for Br-polyol. As reaction proceeds between 2,4,6-TBP and GLY, the phenol group represented by sharp peak at 1,159 [cm.sup.-1] is converted in to--(C--O--C)--bond observed by strong broad peak from 1,000 to 1,300 [cm.sup.-1]. Further, peak between 2,937 and 2,873 [cm.sup.-1] represents--(C[H.sub.2])--bond as observed in GLY and final polyol. Peak at 3,070 [cm.sup.-1] which is characteristic peak of aromatic [sp.sup.2]--CH stretch can be observed in 2,4,6-TBP and final Br-polyol. 856, 738, 702, and 667 [cm.sup.-1] are representative peak for substituted benzene group followed by peak at 675 [cm.sup.-1] which represents C--Br bond. This represents that the compound contains aromatic ring with bromine substitution. Lastly, the peak at around 3,400 [cm.sup.-1] represents the OH group which can be observed in 2,4,6-TBP, GLY, and in Br-polyol. Hydroxyl group is most important functional group taking part in urethane reaction. Hence, FT-IR curves represent the effective proceedings for expected reaction.
Increase in molecular weight can be observed by reduction in retention time for Br-polyol compared to other raw material as seen from GPC curves. GLY shows multiple peaks around 36, 38, and 42 min could be due to formation of oligomers by GLY due to active monomeric nature [42, 43]. Due to hydroxyl group attached to each glycidol molecule, activated monomer mechanism results in probability of higher amorphous structure . Hence, broad molecular weight distribution is observed for Br-polyol. Moreover, the peak observed around 37 for 2,4,6-TBP is completely disappeared in final Br-polyol suggesting completeness of reaction.
Characteristics of Flame Retardant Polyurethane Foams
The average density of the polyurethane foams was calculated using the average density from cylindrical--and square-shaped test specimen and is shown in Fig. 3a and d. The average density of 35 kg/[m.sup.3] for AFR-foams and 45 kg/[m.sup.3] for RFR-foams displays that obtained foams maintained industrial weight standards  Addition of DMMP showed no significant change in density of the final AFR-foams. However, average density of RFR-foams was higher compared to AFR-foams which could be due to higher bromine-polyol amount in the foams.
Close cell content is another property measurement tool to define thermal insulation characteristics of the foams. The overall foams showed close cell content higher than 95% which displays excellent thermal insulating characteristics of the foam. Figure 3b and e shows the percentage close cell graph for all synthesized flame retardant polyurethanes. Higher close cell prevents the air flow within the cellular structure preventing easy heat transfer from one cell to another resulting in higher insulation properties as well as restricts easy access to oxygen when subjected to burning. Furthermore, after comparing foams without DMMP and with DMMP, there is no change observed in close-cell content of the foams. Similar behavior was observed for Br-based foams. Obtained results seem to have highest close cell content compared to most of other results [5, 6, 25, 46].
The compression strength of all the foams is displayed in Fig. 3c and f. Results suggest gradual depreciation in compression strength properties with addition of DMMP. Foams without DMMP showed strength of 170 kPa which reduced to 120 kPa when DMMP was added to make high phosphorus content of 1.7%. Obtained results are comparatively higher than some cardanol-and castor-based foams [27, 47]. The observed decrease in mechanical properties could be due to incompatibility of DMMP within the substrate. Similar behavior was observed in other reports . To overcome this problem generally noticed in additive-based FR approach, bromine-based RFR-foams were synthesized. As the concentration of Br-polyol increases in the composition, there is respective increase in compression strength of the RFR-foams. The compression strength increased from 170 kPa to 325 kPa when concentration of Br in foams increased from 0 to 6%. This improvement can be due to cross-linking effect supported by Br-polyol within the foam structure providing sufficient rigidity to the foams. It was observed that foams from limonene with almost similar density and having higher hydroxyl number improved the number of crosslinking sites within the foams and showed higher results for ideal non-FR foams . Similarly, bromine-based polyol with higher hydroxyl number of 296 mg KOH/g would have supported in providing sufficient degree of crosslinking within the foams after being added in increased concentration. This suggests rigidity of the foams is directly dependent upon the hydroxyl number of synthesized polyols and type of additives used for exhibiting the flame retardancy. Hence, obtained foams have considerable amount of strength with respect to density and hydroxyl number for rigid foam application.
Scanning electron microscope was used to analyze the microcellular structure and its corresponding distribution within the foam. SEM images of all the foams are displayed in Fig. 4a and b. Overall cell size of LDM-GAE foam showed around 250 [micro]m size. On addition of DMMP, there was gradual increase observed in the cell size from ~250 to 320 [micro]m. This could be due to plasticizing effect of DMMP increasing the cell size of the foams. However, this problem is nullified in RFR-foams. Due to higher degree of crosslinking provided by reactive Br-polyol, the average cell size of RFR-foams is maintained to an average of 225 [micro]m thereby eliminating any possible plasticizing behavior as provided by DMMP. Overall all prepared AFR-foams and RFR-foams showed uniformly distributed cell structure with excellent close cell content above 95%.
Thermal properties of foams were analyzed using thermo-gravimetric analysis (TGA). The TGA curves in Fig. 5a for AFR-foams suggest that multiple transitions were observed with the addition of DMMP leading to change in thermal behavior of the foams. As temperature escalates around 130[degrees]C, first transition starts to occur which continues until around 250[degrees]C. Higher amount of DMMP reduced the weight loss. This behavior was due to increased amount of volatilization of DMMP with its addition at the elevated temperature and thereby forming better char layer which inhibits fire consequently, reducing the weight loss [48, 49]. Moreover, observation suggests that major degradation of the foams occurred between 300-400[degrees]C leading to chain cleavage and substantial depolymerization of polyurethanes. Similar behavior was observed in other results [5, 6, 25]. While, TGA curves from Fig. 5b for RFR-foams showed no such thermal transitions below 300[degrees]C which suggests no prior release of any volatile compound as seen in AFR-foams. Actual degradation of the foam occurs between 300 and 400[degrees]C, during which bromine activates its flame retarding ability in air. There were no major weight loss transitions in overall foams up to 250[degrees]C, suggesting that RFR-foams showed thermal stability without releasing any volatiles like DMMP as in AFR-foams, until thermal temperature reaches to actual degradation phase.
Lastly, to analyze the on-field flame retardant characteristics of the foams, horizontal burning test was performed as per standards (ASTM D 4986-98). Results of burning test and respective weight loss are shown in Fig. 6a-d. Foams without DMMP resulted in burning time of 75 sec with around 48% weight loss. This time was significantly reduced to 12 sec when phosphorus content in AFR-foam was 0.2%. Figure 7a shows some actual photographs of various AFR-foams comparing the burning behavior with increased phosphorus content. The optimum burning time was reported to be 7.5 sec with minimum weight loss of 4.7% when the phosphorus content of polyol was as low as 0.9%. All the reported results are among lowest of the overall observed results for the burning test . Schematic of test, shown in Fig. 8, explains in detail about the overall test and flame retardant mechanism for AFR and RFR-Foams. This significant improvement in flame retardancy was due to two way active contribution of DMMP in condensed as well as in vapor phase . First, formation of intumescent barrier layer of char over the surface of the foams prevents the combustible media, oxygen and thermal energy to propagate. Second, radical phosphorus species such as PO*, P[O.sub.2.sup.*], and OHPO* helps in inhibition of H* and OH* . Hence, addition of very small amount of DMMP has led to effective flame retardancy to the polyurethane foams. For RFR-foams, the burning time was reduced from 75 to 12.8 sec and weight-loss decreased from 48% to 12.6% when bromine content in the foam was 4.5%. Figure 7b shows the actual images of burnt samples for RFR-foams. Further, with increasing concentration of bromine to 6% the self-extinguishing time went down to merely 7.2 sec with 6.3% weight loss. Even with lower concentration of bromine (around 4.5%) significant improvement in flame retardancy was observed which is comparable to higher preferred concentrations explained in other previously reported descriptions about bromine-based FR-compounds [51, 52]. This could be due to effective flame retardancy mechanism of bromine in air. During combustion, polymers undergo bond scission producing diffused polymer fragments in air creating combustible fuel which ignites above auto-ignition temperature liberating heat and maintaining the fire triangle . Various different radicals are produced including very reactive species H* and HO*. These radicals are likely to react with [O.sub.2] in air and promote the chain reaction producing more number of radicals . Exothermicity promotes with this chain reaction, for example, OH* reacts with CO molecule and forms C[O.sub.2] giving exothermic reaction. Hence, Br* released from RFR-foams reacts with active OH* and H* to form less reactive and sometimes inert molecules inhibiting the burning process. Previous reports suggest similar behavior for Br-based compound .
From the overall study, it was concluded that high purity polyol can be obtained by single-step thiol-ene reaction between limonene dimercaptan and glycerol-l-allyl-ether with low polydispersity index of 1.07. The synthesized polyol was used to prepare polyurethanes which showed moderate density, high mechanical strength, and high close cell content. Flame retardancy was introduced in the foams by addition different concentration of phosphorus- and bromine-based compounds. It was concluded that, 0.9 wt% phosphorus in AFR polyurethanes and 4.5% bromine in RFR polyurethanes resulted in optimum extinguishing time of 7.5 and 12.8 sec. By addition of RFR i.e. bromine polyol, the mechanical properties of the foams improved significantly which in contrast depreciated with addition of AFR, that is, phosphorous-based compound. Highest compression strength of 325 kPa was observed with 6 wt% of bromine in foam while a reduced compression strength of 120 kPa was observed for foam containing 1.7 wt% of phosphorus. From the overall observation, the reported polyurethane foams showed efficient flame retardant properties and can be used for rigid flame retardant foam application.
Dr. Ram K. Gupta expresses his sincere acknowledgment to the Polymer Chemistry Program, Pittsburg State University for providing financial and research support.
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C. Zhang, (1) Sanket Bhoyate, (1) M. lonescu, (2) P. K. Kahol, (3) Ram K. Gupta (iD) (1,2)
(1) Department of Chemistry, Pittsburg State University, Pittsburg, Kansas, 66762
(2) Kansas Polymer Research Center, Pittsburg State University, Pittsburg, Kansas, 66762
(3) Department of Physics, Pittsburg State University, Pittsburg, Kansas, 66762
Correspondence to: R. K. Gupta; e-mail: firstname.lastname@example.org
Published online in Wiley Online Library (wileyonlinelibrary.com).
Caption: FIG. 1. (a) Schematic of overall setup of reactor for synthesis of polyol using thiol-ene reaction, (b) Reaction showing synthesis of polyol using thiol-ene chemistry, (c) Reaction showing synthesis of bromine-based polyol. [Color figure can be viewed at wileyonlinelibrary.com]
Caption: FIG. 2. FT-IR and GPC graphs for: (a,b) LDM, GAE and LDM-GAE polyol; (c,d) 2,4,6-TBP, GLY and Br-polyol. [Color figure can be viewed at wileyonlinelibrary.com]
Caption: FIG. 3. Density, close cell content, and compression strength for: (a, b, c) AFR-polyurethane foams and (d, e, f) RFR-polyurethane foams. [Color figure can be viewed at wileyonlinelibrary.com]
Caption: FIG. 4. SEM images of the AFR-polyurethane foams containing various amount of phosphorus (a-f) and RFRpolyurethane foams containing various amount of bromine ([g.sup.-1]). [Color figure can be viewed at wileyonlinelibrary.com]
Caption: FIG. 5. TGA curves for (a) AFR-Foams and (b) RFR-foams. [Color figure can be viewed at wileyonlinelibrary.com]
Caption: FIG. 6. Burning time and percentage weight loss for: a, b) AFR-Foams and c,d) RFR-Foams. [Color figure can be viewed at wileyonlinelibrary.com]
Caption: FIG. 7. Photographs of the foams after burring test: a) ARF-Foams; b) RFR-Foams. [Color figure can be viewed at wileyonlinelibrary.com]
Caption: FIG. 8. Schematic of burning mechanism and flame retarding action by AFR and RFR. [Color figure can be viewed at wileyonlinelibrary.com]
TABLE 1. Formulation for preparation of phosphorus containing polyurethane foams. Compounds P-0% P-0.2% P-0.45% P-0.9% P-1.3% P-1.7% Jeffol-360 10 10 10 10 10 10 LDM-GAE 10 10 10 10 10 10 DMMP 0 0.5 1 2 3 4 Tegostab B-8404 0.4 0.4 0.4 0.4 0.4 0.4 Niax-A1 0.12 0.12 0.12 0.12 0.12 0.12 T-12 0.04 0.04 0.04 0.04 0.04 0.04 Water 0.8 0.8 0.8 0.8 0.8 0.8 MDI 32.07 32.07 32.07 32.07 32.07 32.07 TABLE 2. Formulation for preparation of bromine containing polyurethane foams. Compounds Br-4% Br-4.5% Br-5% Br-5.5% Br-6% Jeffol-360 10 10 10 10 10 LDM-GAE 10 10 10 10 10 Br-Polyol 6.8 7.85 9 10.2 11.57 Tegostab B-8404 0.56 0.56 0.56 0.56 0.56 Niax-Al 0.16 0.16 0.16 0.16 0.16 T-12 0.06 0.06 0.06 0.06 0.06 Water 1.01 1.01 1.01 1.01 1.01 MDI 42.84 43.82 44.9 46.02 47.55
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|Author:||Zhang, C.; Bhoyate, Sanket; Ionescu, M.; Kahol, P.K.; Gupta, Ram K.|
|Publication:||Polymer Engineering and Science|
|Date:||Nov 1, 2018|
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