MIL-HDBK-17-1F Volume 1,Chapter 5 Prepreg Materials Characterization Specimen: Prepreg(10 to 30 mg)in an aluminum sample pan Reference: Empty sample pan Heating Rate: 10°C/min Temperature Range: Room temperature to 350C Atmosphere: Dry nitrogen gas purge Data Handling: Data is stored on a computer disk and a plot of heat flow dH/dt(uw/sec)vs temperature(C)is produced. Heat of Reaction: The calibration routine and integration program provided with the thermal analyzer is used to calculate heats of reaction AH of thermoset prepreg resins. Glass Transition: A cooling device attached to the DSC cell may be needed to facilitate glass transition temperature T measurements of thermoset prepreg resins;i.e.,it is often necessary to initiate temperature scans at-50C or lower since such resins typically have T values below room temperature.The thermal ana- lyzer may have a software routine to assist in determining T:values. 5.5.5 Procedure for dynamic mechanical analysis(DMA) A single ply of prepreg is cut into a 1.1 cm x 1.7 cm strip and the strip is mounted in a DuPont model 982 or 983 DMA accessory.A DuPont 9900 or 1090 controller is used to run the test and plot the results Equivalent instruments may also be used. Heating Rate: 5°C/min Temperature Range: Room temperature to 350C Atmosphere: Dry,nitrogen gas purge Data Handling: Data is stored on a computer disk and a plot of storage modulus and tan 8 is plotted as a function of temperature. Glass Transition: The temperature of the damping peak maximum is assigned as the T value. Gelation: Gelation occurs when the Young's modulus starts increasing rapidly(several orders of magnitude)over a narrow temperature range.Gelation temperature depends upon heating rate and mechanical frequency.Therefore,both heating rate and frequency should be included when DMA gelation temperatures are reported. Gelation Time: In the isothermal mode,the time to gelation is determined by rapidly heating a sample to the desired temperature,holding the temperature constant and monitoring the change in Young's modulus with time.Gelation time is defined as the time it takes for the modulus to start rapidly increasing (several orders of magnitude). 5.5.6 Procedure for rheological characterization A Rheometrics Dynamic Spectrometer(RDS)or equivalent system is used for this test.Samples are prepared by cutting three 25-mm diameter circles from a single ply of prepreg.The three plies are stacked and placed between the rheometer's parallel plates. Heating Rate: 2C/min Temperature Range: Room temperature to the onset of gelation(for thermosets) Atmosphere: Air or a blanket of nitrogen gas Geometry: 25-mm diameter parallel plate Gap: Typically 0.8 mm,but may be adjusted according to sample characteristics. Data Reporting: Shear moduli(storage and loss)and complex viscosity are plotted as a function of temperature. 5-8MIL-HDBK-17-1F Volume 1, Chapter 5 Prepreg Materials Characterization 5-8 Specimen: Prepreg (10 to 30 mg) in an aluminum sample pan Reference: Empty sample pan Heating Rate: 10°C/min Temperature Range: Room temperature to 350°C Atmosphere: Dry nitrogen gas purge Data Handling: Data is stored on a computer disk and a plot of heat flow dH/dt (µW/sec) vs temperature (°C) is produced. Heat of Reaction: The calibration routine and integration program provided with the thermal analyzer is used to calculate heats of reaction ∆H of thermoset prepreg resins. Glass Transition: A cooling device attached to the DSC cell may be needed to facilitate glass transition temperature Tg measurements of thermoset prepreg resins; i.e., it is often necessary to initiate temperature scans at -50°C or lower since such resins typically have Tg values below room temperature. The thermal ana￾lyzer may have a software routine to assist in determining Tg values. 5.5.5 Procedure for dynamic mechanical analysis (DMA) A single ply of prepreg is cut into a 1.1 cm x 1.7 cm strip and the strip is mounted in a DuPont model 982 or 983 DMA accessory. A DuPont 9900 or 1090 controller is used to run the test and plot the results. Equivalent instruments may also be used. Heating Rate: 5°C/min Temperature Range: Room temperature to 350°C Atmosphere: Dry, nitrogen gas purge Data Handling: Data is stored on a computer disk and a plot of storage modulus and tan δ is plotted as a function of temperature. Glass Transition: The temperature of the damping peak maximum is assigned as the Tg value. Gelation: Gelation occurs when the Young's modulus starts increasing rapidly (several orders of magnitude) over a narrow temperature range. Gelation temperature depends upon heating rate and mechanical frequency. Therefore, both heating rate and frequency should be included when DMA gelation temperatures are reported. Gelation Time: In the isothermal mode, the time to gelation is determined by rapidly heating a sample to the desired temperature, holding the temperature constant and monitoring the change in Young's modulus with time. Gelation time is defined as the time it takes for the modulus to start rapidly increasing (several orders of magnitude). 5.5.6 Procedure for rheological characterization A Rheometrics Dynamic Spectrometer (RDS) or equivalent system is used for this test. Samples are prepared by cutting three 25-mm diameter circles from a single ply of prepreg. The three plies are stacked and placed between the rheometer's parallel plates. Heating Rate: 2°C/min Temperature Range: Room temperature to the onset of gelation (for thermosets) Atmosphere: Air or a blanket of nitrogen gas Geometry: 25-mm diameter parallel plate Gap: Typically 0.8 mm, but may be adjusted according to sample characteristics. Data Reporting: Shear moduli (storage and loss) and complex viscosity are plotted as a function of temperature