POLY (TRIMETHYLENE CARBONATE) POLYOLS IN POLYURETHANE ELASTOMERS Alma Cámara-Hinojosa, M.S., Adisa Bajramovic, Aisa Sendijarevic, Ph.D., Kurt C. Frisch, Ph.D. Polymer Institute – College of Engineering and Science University of Detroit Mercy W.H. Boon, D.E. Gwyn, C.J. Smith Shell Chemical Company OBJECTIVE The objective of this project is to prepare and evaluate the properties of polyurethane elastomers based on poly (1,3-propanediol carbonate) polyols from Shell Chemical Co. as the soft segments. SUMMARY Shell Chemical Co. has developed a novel type of polycarbonate polyol, poly (1,3-propanediol carbonate) polyol (PTMC), with proprietary technology. In this study, polyurethane elastomers based on PTMC polyol of 2000MW were prepared and their properties evaluated. PTMC 2000 polyol sample was characterized by the hydroxyl content (OH number), glass transition temperature, and viscosity at different temperatures. The compatibility of PTMC 2000 with 1,3- propanediol (1,3-PDO) and 1,4-butanediol (1,4-BD) chain extenders in the temperature range from RT to 90°C was evaluated. Both aromatic and cycloaliphatic thermoplastic polyurethane elastomers (TPUs) based on PTMC polyols were prepared and evaluated. 4,4’-Diphenylmethane diisocyanate (MDI) was utilized to prepare aromatic TPUs and methylene-bis (4- cyclohexyl isocyanate) (H 12 MDI) to prepare aliphatic TPUs. The elastomers were prepared using the one-shot procedure. 1,3-PDO and 1,4-BD were used as chain extenders and the hard segment concentration was varied from 22 to 35%. As a reference, TPUs based on commercial poly (1,6-hexanediol carbonate) polyol (Desmophen C-200, Bayer Co.) were prepared and evaluated. The physico-mechanical properties (hardness, stress-strain properties, tear resistance, compression set, resilience and abrasion resistance) of TPUs were measured according to ASTM standard methods. The solvent resistance (oil, ethylene glycol and dilute acid/bases) was determined by measuring the weight change upon immersion. The water resistance was evaluated by measuring the
Transcript
POLY (TRIMETHYLENE CARBONATE)POLYOLS IN POLYURETHANE ELASTOMERS
Alma Cámara-Hinojosa, M.S., Adisa Bajramovic, Aisa Sendijarevic, Ph.D., Kurt C. Frisch, Ph.D.Polymer Institute – College of Engineering and Science
University of Detroit MercyW.H. Boon, D.E. Gwyn, C.J. Smith
Shell Chemical Company
OBJECTIVEThe objective of this project is to prepare and evaluate the properties ofpolyurethane elastomers based on poly (1,3-propanediol carbonate) polyols fromShell Chemical Co. as the soft segments.
SUMMARYShell Chemical Co. has developed a novel type of polycarbonate polyol, poly(1,3-propanediol carbonate) polyol (PTMC), with proprietary technology. In thisstudy, polyurethane elastomers based on PTMC polyol of 2000MW wereprepared and their properties evaluated. PTMC 2000 polyol sample wascharacterized by the hydroxyl content (OH number), glass transition temperature,and viscosity at different temperatures. The compatibility of PTMC 2000 with 1,3-propanediol (1,3-PDO) and 1,4-butanediol (1,4-BD) chain extenders in thetemperature range from RT to 90°C was evaluated.
Both aromatic and cycloaliphatic thermoplastic polyurethane elastomers (TPUs)based on PTMC polyols were prepared and evaluated. 4,4’-Diphenylmethanediisocyanate (MDI) was utilized to prepare aromatic TPUs and methylene-bis (4-cyclohexyl isocyanate) (H12MDI) to prepare aliphatic TPUs. The elastomers wereprepared using the one-shot procedure. 1,3-PDO and 1,4-BD were used as chainextenders and the hard segment concentration was varied from 22 to 35%. As areference, TPUs based on commercial poly (1,6-hexanediol carbonate) polyol(Desmophen C-200, Bayer Co.) were prepared and evaluated.
The physico-mechanical properties (hardness, stress-strain properties, tearresistance, compression set, resilience and abrasion resistance) of TPUs weremeasured according to ASTM standard methods. The solvent resistance (oil,ethylene glycol and dilute acid/bases) was determined by measuring the weightchange upon immersion. The water resistance was evaluated by measuring the
retention of stress-strain properties and the weight change upon immersion inwater at 70°C.
The morphology of the elastomers was studied by thermal analysis includingdifferential scanning calorimetry (DSC), thermo-mechanical analysis (TMA) anddynamic-mechanical analysis (DMA) as well as Fourier transform infra-redanalysis (FTIR). The elastomers transparency was also measured.
EXPERIMENTALMaterials
The materials utilized in this study are shown in Table 1. Prior to elastomerpreparation polyols and chain extenders were vacuum dried at 70°C for at least24 hours. The isocyanates were used as received from the suppliers. The NCO%was checked by titration utilizing the di-n-butylamine method (ASTM D1638-74).
The viscosity of the polyols at different temperatures was measured using aBrookfield viscometer. The glass transition temperature was determined bydifferential scanning calorimetry and dynamic-mechanical method. The hydroxylnumber of the polyols was determined by using the standard phthalic anhydrideesterification method (ASTM D4273). The compatibility of PTMC 2000 with chainextenders (1,4-BD and 1,3-PDO) was studied by mixing components at specifiedratios at different temperatures. Visual observation of the mixtures was recorded.
Preparation of polyurethane elastomersTPUs were prepared by the one-shot method at hard segment concentrations of22, 25, 28, and 35%. The isocyanate index (isocyanate to hydroxyl equivalentratio) was 1.02.
Polyol and chain extender were weighed in a plastic cup and heated at 100°C or135°C. Isocyanate, which was previously heated at the mixing temperature, wasadded to the mixture of polyol and chain extender and all components weremixed vigorously for 5-10 seconds. The mixture was then poured into a Teflon-coated mold, which was preheated at 105°C or 135°C. When gelation occurred(as determined by string formation), the mold was placed in a Carver press andthe resin was compression-molded at 24000 lbs at 105°C or 135°C. Afterwards,the polyurethane sheet was post-cured in an oven at 105°C or 135°C for 24hours (or 135°C for 20 hours and 150°C for 4 hours). The curing and postcuringconditions in the preparation of aromatic TPUs are shown in Table 2 and for thealiphatic TPUs in Tables 13 and 14. The polyurethane elastomers were testedone week after preparation.
Evaluation of Elastomer PropertiesThe following physical and mechanical properties were measured:
elasticity modulus and toughness) at RT and 70°C (ASTM D-412).
• Tear resistance, Graves die C (ASTM D-624) and Split tear (ASTM D-1938)•-Compression set (ASTM D-395)•-Resilience, Bashore Rebound (ASTM D-430)•-Abrasion resistance (Taber Abrader)•-Coefficient of thermal expansion (TMA)
The glass transition temperature (Tg) was measured by differential scanningcalorimetry (DSC) and dynamic-mechanical analysis (DMA) and the softeningpoint by the thermo-mechanical analysis (TMA).
The chemical resistance (weight change) was measured by immersion for oneweek in: oil, ethylene glycol, diluted acids (HCl 10% and H2SO4 10%) and NaOH10%.
The water resistance of elastomers was measured by immersion in water at 70°Cfor two weeks. The weight changes and tensile strength were measured afterimmersion.
FTIR spectra were prepared by scanning tiny films casted from the solution of thepolyurethane elastomer.
RESULTS AND DISCUSSIONPolyol propertiesThe viscosity of PTMC 2000 at RT was found to be higher than that ofDesmophen C-200, which is due to the higher concentration of stiff carbonategroups in PTMC 2000 (Table 3, Figure 1). The viscosity significantly decreasedwith temperature. The glass transition temperature of PTMC 2000 was found tobe –28.5°C.
PTMC 2000 was compatible with 1,4-butane diol (1,4-BD) and 1,3-propane diol(1,3-PDO) from RT to 90°C (Table 4). In this evaluation the weight ratio of polyolto chain extender corresponds to elastomers with hard segment concentration of22 to 35%. The compatibility of Desmophen C-200 with chain extenders at roomtemperature was limited.
TPUs BASED ON MDIThe code for sample designation is:
• SPM-22 to SPM-35 represents PTMC2000/1,3-PDO/MDI-formulations withthe hard segment concentration of 22 to 35%.
• SBM-22 to SBM-35 represents PTMC2000/1,4-BD/MDI• DPM-22 to DPM-35 represents Desmophen C-200/1,3-PDO/MDI• DBM-22 to DBM-35 represents Desmophen C-200/1,4-BD/MDI
Physico-mechanical propertiesThe formulations and properties of MDI-based TPUs based on PTMC 2000 andDesmophen C-2000 extended with 1,3-PDO are shown in Tables 5 and 6.Increasing the hard segment concentration from 22 to 35% resulted in thehardness of PTMC2000 TPUs increasing from 73 to 91 Shore A. In general, thetensile strength, elasticity modulus and Die C tear resistance of TPUs increasedwith the hard segment concentration, as expected. The abrasion resistance ofPTMC 2000 elastomers was very good, better than that obtained for DesmophenC-200. This could possibly be due to the reinforcing effect of hydrogen bonds inPTMC 2000 polyurethanes, which contain a high proportion of carbonate groupscapable of forming hydrogen bonds. The abrasion resistance of PTMC 2000TPUs was similar or even better than PTMO 2000 and polycaprolactone TPUs(Appendix A-1 and A-2). PTMC TPUs demonstrated relatively low compressionset (4 to 7%), lower than that of Desmophen C-200 TPUs (14.3 to 23.5%). It isinteresting to note that the resilience of 1,3-PDO extended polycarbonate TPUsincreased with increase of the hard segment concentration.
Polycarbonate TPUs were also prepared with 1,4-BD chain extender at ahardness range from 22 to 35% (Tables 7 and 8). The strength properties (tensilestrength, 100% and 300% elasticity modulus, Young’modulus and toughness)and Die C tear strength of PTMC 2000 and Desmophen C-200 TPUs changedquite uniformly with increase in the hard segment concentration. The tensilestrength of the PTMC-TPUs was found to be somewhat lower as compared toDesmophen C-200, but modulus values were somewhat higher (Figs. 2 and 3).The elongation at break, modulus and resilience indicate that 1,4-BD extendedTPUs are more flexible than those extended with 1,3-PDO. It was foundrepeatedly that the resilience of PTMC TPUs increased with increasing hardsegment concentration.
Heat resistanceThe heat resistance of the elastomers was evaluated by measuring the stress-strain properties at 70°C (Tables 5 and 6). The retention of the tensile strengthwas found to be higher for PTMC 2000/1,3PDO/MDI TPUs than for DesmophenC-200/1,3-PDO/MDI TPU (Fig. 4.) The elongation at break of PTMC 2000increased significantly upon heating and the elasticity modulus decreased. Thecoefficient of thermal expansion, as measured by TMA, was found to be lower for
PTMC TPUs than Desmophen C-200 (Tables 8 and 9). The softeningtemperature of the TPUs, as measured by TMA, was in the range of 160 to209°C for PTMC 2000 and 160 to 175°C for the corresponding Desmophen C-200 polyurethanes.
MorphologyThe glass transition temperature of PTMC TPUs was about 0°C and shiftedabout 10°C when measured by DMA. The Tg defines these polyurethanes moreas elastoplastic materials with very good elasticity above room temperature. Theglass transition temperature of Desmophen C200 TPUs was about 30 degreeslower.
An insight into the morphology was also obtained by FTIR spectroscopy. TheFTIR spectra (Appendix I) of the elastomers exhibited the bands typical forpolycarbonate aromatic polyurethanes: -NH, (free and bonded) at 3300-3400 cm-
1; CH2-at 2900-2970 cm-1; C=O in carbonate and bonded urethane group at
1740-1759 cm-1; C=O free urethane group at 1706 cm-1; aromatic group at 1600cm-1 and -C-O-C- in ester group at 1033 cm-1. The ratio of absorbance 1705cm-
1/1745cm-1 increased with an increase of the hard segment concentrationsuggesting an increase in the proportion of unbonded urethane groups. This ratiowas found to be higher with the PTMC TPUs. The hydrogen bonds in thepolycarbonate polyurethanes are formed between urethane groups, and bybridging carbonate and urethane groups.
Water resistanceThe water resistance was evaluated by measuring the weight gain and change instress-strain properties upon immersion in water at 70°C for two weeks. Theresults are shown in Tables 10 and 11 and Figures 5 and 6. The weight gain ofPTMC TPUs was 1.2 to 1.6%. These results correlate well with the change intensile strength, which was 8 to 57% for PTMC 2000 (depending on the hardsegment concentration).
The relative transparency was measured by determining the light transmission(%) in the visible range of 474 to 630 nanometers. The degree of transparencydecreased with increase of the hard segment concentration. PTMC 2000 TPUsexhibited significantly higher transparency at different hard segmentconcentrations as compared to Desmophen C-200. This could be due to the lessordered structure of PTMC backbone or the higher degree of the phase mixing offlexible and hard segment.
Chemical resistanceThe chemical resistance of TPUs was measured in various media including oil(100% neutral paraffinic oil, Fisher Brand 19), ethylene glycol, diluted acids (10%H2SO4 and 10% HCl) and sodium hydroxide (Table 12 and Fig. 7). The weightgain in hydraulic oil was low while in inorganic acids, it was higher. Unexpectedly,the weight gain in ethylene glycol was much lower with PTMC than withDesmophen C-200 TPUs. Overall the resistance of TPU in this media was good.
The PTMC TPUs were much more resistant to all of these materials than poly(oxytetramethylene) polyols (Appendix B).
TPUs BASED ON H12MDI
The curing conditions of TPUs based on the cycloaliphatic diisocyanate H12MDIand PTMC 2000 and their properties are shown in Tables 13 and 14.
The following is the code for the sample designation:
• SPH-25 to SPH-35 corresponds to PTMC2000/1,3-PDO/H12MDI) with thehard segment concentration from 25 to 35%
• SBH-25 to SBH-35 correspond to PTMC2000/1,4-BD/H12MDI with the hardsegment concentration from 25 to 35%.
The tensile strength, which increased with hard segment concentration, exhibitedmoderate values, somewhat higher with 1,3-PDO than with 1,4-BD chainextender. PTMC 2000 TPUs exhibited better properties with 1,3-PDO than with1,4-BD chain extender, with both MDI and H12MDI. It should be noted that H12MDITPUs were cured at lower temperatures than MDI TPUs, due to their lower greenstrength.
The DSC glass transition temperature of H12MDI TPUs was below 0°C, lowerthan that of MDI TPUs, indicating less interaction of the flexible segment withH12MDI. The softening temperature of H12MDI TPUs was typically in the range of175 to 193°C. 1,3-PDO extended TPUs were transparent at 25% hard segmentconcentration and translucent at 28 to 35% hard segment concentrations. TPUswith 1,4-BD extended were translucent at 25% hard segment and hazy at higherhard segment concentrations.
The weight change of SPH-TPUs upon immersion in water at 70°C for two weekswas 1.2 to 1.73%, similar to MDI-TPUs (Table 15).
The resistance of H12MDI-TPUs in hydraulic oil, ethylene glycol, 10% HCl, 10%H2SO4 and 10% NaOH, as measured by the weight gain is shown in Table 16.The resistance to oil was excellent (no weight increase). The weight gain in acid,sodium hydroxide and ethylene glycol was moderate.
CONCLUSIONSTPUs were successfully prepared using PTMC 2000 diol, developed by ShellChemical Co. Both aromatic (MDI) and cycloaliphatic (H12MDI) elastomers wereprepared using the one-shot method.
Due to the rigid nature of PTMC diol, the elastomers exhibited Tgs around 0°C.Their hardness was somewhat higher than that of the corresponding TPUs basedon Desmophen C-200, PTMO 2000 or caprolactone polyols (Appendix C and D). PTMC 2000 TPUs exhibited good physico-mechanical properties. Their tensilestrength was somewhat lower but the elasticity modulus was higher thanDesmophen C-200 TPUs. The abrasion resistance and compression set ofPTMC 2000 TPUs was very good, comparable to that of polyether TPUs.
The heat stability of PTMC 2000 TPUs, as indicated by the properties at elevatedtemperature, the softening temperature and the coefficient of the thermalexpansion was found to be improved over that of Desmophen C-200 TPUs.
By using PTMC 2000 it is possible to improve the clarity of TPUs and even obtaincompletely clear material with H12MDI.
The resistance of PTMC 2000 TPUs to oil was excellent and good to other mediasuch as diluted inorganic acids, bases and ethylene glycol.
For more information, please contact:Shell Chemical CompanyManager, CORTERRA®* Polymers CommunicationP.O. Box 2463Houston, Texas 77252-24631-713-246-8230Fax: 1-713-241-1606
For literature assistance and technical referral, call toll free:1-888-CORTERRA
(1-888-267-8377)
For literature via fax, call toll free:1-800-990-8737
For customer service, including orderplacement, call toll free:
WarrantyAll products purchased from or supplied by Shell are subject to terms andconditions set out in the contract, order acknowledgement and/or bill of lading.Shell warrants only that its product will meet those specifications designated assuch herein or in other publications. All other information, including that herein,supplied by Shell is considered accurate but is furnished upon the expresscondition that the customer shall make its own assessment to determine theproduct's suitability for a particular purpose. Shell makes no other warrantyeither express or implied, regarding such other information, the data uponwhich the same is based, or the results to be obtained from the usethereof; that any products shall be merchantable or fit for any particularpurpose; or that the use of such other information or product will notinfringe any patent.
Health & Safety ConsiderationsRead and follow all information presented in the Material Safety Data Sheet(MSDS) for this product. Also refer to all safety information provided withprocessing equipment.
Shell Chemical Company is a Chemical Manufacturers Association ResponsibleCareTM Partner Company and strongly supports product stewardship.
The expression “Shell Chemicals” refers to the companies of the Royal Dutch/Shell Group which are engaged in thechemical businesses. Each of the companies which make up the Royal Dutch/Shell Group of companies is anindependent entity and has its own separate identity.
*CORTERRA is a registered trademark of the Royal Dutch/Shell Group of companies.
