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1 0 OFFICE OF NAVAL RESEARCHC ontract N00014-76-C-02000 Task No. NR 356-504tTECHNICAL REPORT NO. 26 EFFECT OF THE EXTENT OF CURE ON THE MODULUS, GLASS TRANSITION,WATER absorption , AND density OF AN AMINE-CURED EPOXYbyJohn B. Enns and John K. Gillhamfor publication inJournal of Applied Polymer SciencePRINCETON UNIVERSITYP olymer Materials ProgramDepartment of Chemical EngineeringPrinceton, New Jersey 08544 April 1983 Reproduction in whole or in part is permitted forany purpose of the United States GovernmentThis document has been approved for public release and sale;its distribution is unlimitedCPrincipal InvestigatorLLJ John K. Gillham-(609) ,~!

2 GCUIIITY CLASSIF ICATION Of THIS PAGE (fts. DNSe SAt.,f_____REPORT DOCUMENTATION PAGE READR COMtITWIG ORMT echnical Report #26 1 0 V ACESIO W n~4. TITLE (and Subtitle) 5. TYPIE OF REPORT a PERIOD COVEREDE ffect of the Extent of Cure on the Transition, Water absorption , and density April 1981-April 1983of an AMine-Cured Epoxy *111G. REPORT NMB~ER7. AUTNOR(.) I. CONTRACT 0R GRANT NumUeR(s)John B. Enns and John K. Giliham N00014-76-C-02009. PERFORMING ORGANIZATION NME AND ADDRESS I0. PROGe0 RAM9 ELEMET. Materials ProgramDepartment of Chemical University, Princeton, NJ CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATEO ffice of Naval Research April 1983800 North Quincy St.)

3 I2. NUMBER OF PAGESA rlington, VA 22217 4014. MONITORING AGENCY NAME & ADDRESS(il difernt bass ConreIMin Office) 1S. SECURITY CLASS. (of miia report) ASSI FICATION/ DOWN GRADINGSCHEDULE16S DISTRIBUTION STATEMENT (of tis Report)Approved for Public Release; Distribution DISTRIBUTION STATEMENT (*(I% ah bstract eteredin Pleek 20, IIlifeei bes. Repo"1)IS. SUPPLEMENTARY NOTES .-I,It. KEY WORDS (Continue an reverse side Itotecesewat Mdflflfr by' Week nmm)Torsion Pendulum Water absorption of EpoxyTorsional Braid Analysis Free Volume of EpoxyTransitions Epoxy CureDensity of Epoxy Time-Temperature-Transformation Cure DiagramsModulus of EpoxyZqVDSTRACT (C.))

4 ,tlnsa an reveree alde It ReoosM -dsh0 M eek boo ernbe.)The modulus, density , glass transition (Tg), and water absorption charac-teristics of an amine-cured resin (diglycidyl ether of bisphenol A (Epon 828)/diaminodiphenyl sulfone (DDS)] were studied as a function of extent of glass transition Is a function of the extent of cure and reaches a maximumtemperature, TS .-een it is completely cured; specimens with different ex-tents of cure were formed by Isothermal cure below Tgso for different slowly cooling, the density at each extent of cure was obtained at roomDD 1473 EDITION OP I NO0V 6SI 1 SIS9 OLEYSSI@102LF04d6601 SCURITV CLAWSIICASOW OP T1418 PAGE (Uhe.)

5 , Dote omSICURITY CLASSIFICATION Of THIS PAGE (3leu Du. nierioEtemperature. Moisture absorption vas monitored gravimetrically at 250C fortwo months at several humidity levels. The room temperature density andmodulus decreased with increasing extent of conversion whereas the glasstransition temperature and equilibrium water absorption increased. Theequilibrium water absorption increased linearly with relative humidity, andthe absorptivity increased linearly with specific volume. An interpretationof these anomalous results is made in terms of the nonequilibrium nature ofthe glassy state. The glass transition temperature increases as the extentof cure increases resulting in a material that is further from equilibriumat room temperature and therefore having more free volume and a greaterpropensity to absorb CLASS PICATION @"WlS PA4 Sibm Doelam-1-EFFECT OF THE EXTENT OF CURE ON THE MODULUS,GLASS TRANSITION, WATER absorption , ANDDENSITY OF AN AMINE-CURED EPOXY*John B.)

6 Enns and John K. GillhamPolymer Materials ProgramDepartment of Chemical EngineeringPrinceton UniversityPrinceton, New Jersey 08544 SynopsisThe modulus, density , glass transition (Tg), and water absorptioncharacteristics of an amine-cured resin [diglycidyl ether of bisphenol A(Epon 828)/diaminodiphenyl sulfone (DDS)] were studied as a function ofextent of cure. The glass transition is a function of the extent of cureand reaches a maximum temperature, Tg, when it is completely cured;specimens with different extents of cure were formed by isothermal curebelow Tg. for different times. After slowly cooling, the density at eachextent of cure was obtained at room temperature.

7 Moisture absorption wasmonitored gravimetrically at 25*C for two months at several humidity room temperature density and modulus decreased with increasing extent ofconversion whereas the glass transition temperature and equilibrium waterabsorption increased. The equilibrium water absorption increased linearlywith relative humidity, and the absorptivity increased linearly with specificvolume. An interpretation of these anomalous results is made in terms of thenonequilibrium nature of the glassy state. The glass transition temperatureincreases as the extent of cure increases resulting in a material that isfurther from equilibrium at room temperature and therefore having more freevolume and a greater propensity to absorb water.

8 *Present address: Bell Laboratories, Whippany, NJ curing phenomena of a thermosetting epoxy resin can be understoodin terms of a time-temperature-transformation (TTT) cure diagram (1) in whichthe times to gelation and vitrification are plotted versus the isothermal curetemperature. As can be seen in Figure 1, the "S"-shaped vitrification curveand the gelation curve divide the time-temperature plot into four distinctstates of matter: liquid, gelled rubber, ungelled glass, and gelled is the glass transition temperature of the unreacted resin mixture, the glass transition of the fully cured resin, and gelTg is the glasstransition of the resin at its gel times to gelation and vitrification can be determined from the losspeaks of an isothermal dynamic mechanical spectrum obtained using the torsionalbraid analysis (TBA) technique (2).

9 At cure temperatures sufficiently below reaction will not go to completion because, as the viscosity increases (a resultof the increasing molecular weight), the reaction becomes diffusion controlled andeventually is quenched as the material vitrifies (3). The extent of conversionattained when the reaction is quenched increases as the cure temperature israised, as evidenced by a corresponding increase in the glass transition addition to the increase in glass transition temperature, otherparameters can be monitored as a function of the extent of cure in an attemptto understand the changes that occur during cure. These include the shearmodulus (of a film which can be measured with a torsion pendulum), the roomtemperature density , and the room temperature equilibrium water this paper, the above mentioned techniques, as well as gel fractionexperiments to identify the gel time in the dynamic mechanical spectra (4), havebeen used to monitor the changes in physical properties that occur during preliminary report from this laboratory has been published (5).

10 EXPERIMENTALM aterialsA stoichiometric mixture of the diglycidyl ether of bisphenol A (Epon 828:Shell) and 4,4'-diaminodiphenyl sulfone (DDS: Aldrich) was prepared for theinvestigation (see Figure 2). For the TBA experiments each of the componentswas dissolved in methylethylketone (MEK) before mixing. For the other experi-ments the amine was added after the epoxy had been heated to 130 C; the mixturewas stirred until the amine dissolved in the epoxy (< 5 min). Equal amounts(by weight) of the neat resin were poured into aluminum foil-lined aluminummolds (2" x 1/2" x 1/16"), degassed in a vacuum oven (, I Torr) at 800C for20 min (until the bubbles disappeared), and placed in a heated oven (purgedwith nitrogen) at 175 C to cure.