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Research Papers

Interlaminar Toughening of GFRP—Part II: Characterization and Numerical Simulation of Curing Kinetics

[+] Author and Article Information
Dakai Bian

Department of Mechanical Engineering,
Columbia University,
New York, NY 10027
e-mail: db2875@columbia.edu

Bradley R. Beeksma, Y. Lawrence Yao

Department of Mechanical Engineering,
Columbia University,
New York, NY 10027

D. J. Shim, Marshall Jones

GE Global Research,
Niskayuna, NY 12309

1Corresponding author.

Manuscript received November 21, 2016; final manuscript received February 14, 2017; published online March 24, 2017. Assoc. Editor: Donggang Yao.

J. Manuf. Sci. Eng 139(7), 071011 (Mar 24, 2017) (10 pages) Paper No: MANU-16-1610; doi: 10.1115/1.4036127 History: Received November 21, 2016; Revised February 14, 2017

Various methods of toughening the bonding between the interleaf and laminate glass fiber reinforced polymer (GFRP) have been developed due to the increasing applications in industries. A polystyrene (PS) additive modified epoxy is used to improve the diffusion and precipitation region between polysulfone (PSU) interleaf and epoxy due to its influence on the curing kinetics without changing glass transition temperature and viscosity of the curing epoxy. The temperature-dependent diffusivities of epoxy, amine hardener, and PSU are determined by using attenuated total reflection–Fourier transfer infrared spectroscopy (ATR–FTIR) through monitoring the changing absorbance of their characteristic peaks. Effects of PS additive on diffusivity in the epoxy system are investigated by comparing the diffusivity between nonmodified and PS modified epoxy. The consumption rate of the epoxide group in the curing epoxy reveals the curing reaction rate, and the influence of PS additive on the curing kinetics is also studied by determining the degree of curing with time. A diffusivity model coupled with curing kinetics is applied to simulate the diffusion and precipitation process between PSU and curing epoxy. The effect of geometry factor is considered to simulate the diffusion and precipitation process with and without the existence of fibers. The simulation results show the diffusion and precipitation depths which match those observed in the experiments.

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References

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Figures

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Fig. 1

The three main chemical reactions during curing process of the epoxy. (a)Primary amine from hardener has open-ring reaction with epoxide group and generates secondary amine. (b) Secondary amine reacts with the epoxide group and generates tertiary amine. (c) Etherification reaction [15].

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Fig. 2

ATR–FTIR spectra of RIMH 137 curing agent, RIMR 135 resin, and PSU. Peaksmonitored during diffusion experiments: 915 cm−1 (epoxide deformation) and 1036 cm−1 (aromatic deformation) in RIMR 135; 2916 cm–1 (C–H stretching of diamine) for RIMH 137; and 1151 cm−1 (S = O stretching) for PSU.

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Fig. 3

FTIR experiment setup for determination of diffusivity and curing kinetics

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Fig. 4

Typical FTIR spectra of 1151 cm−1 peak (S = O stretching) decreased with the increasing time observed in the experiment. The diffusivity and reaction rate are both obtained by monitoring the absorbance changes of characteristic peaks with time.

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Fig. 5

Diffusivity determination of PSU into epoxy from 60 °C to 120 °C. Normalized absorbance data were obtained from ATR–FTIR experiments. Least square fitting curves were based on Eq. (4) for each condition.

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Fig. 6

Diffusivity determination of epoxy into PSU from 60 °C to 120 °C. Normalized absorbance data were obtained from ATR–FTIR experiments. Least square fitting curves were based on Eq. (4) for each condition.

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Fig. 7

Diffusivity determination of PSU to hardener from 60 °C to 120 °C. Normalized absorbance data were obtained from ATR–FTIR experiments. Least square fitting curves were based on Eq. (4) for each condition.

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Fig. 8

Diffusivity determination of hardener to PSU from 60 °C to 120 °C. Normalized absorbance data were obtained from ATR–FTIR experiments. Least square fitting curves were based on Eq. (4) for each condition.

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Fig. 9

Diffusivity determination of PSU into 5% PS modified epoxy from 60 °C to 120 °C. Normalized absorbance data were obtained from ATR–FTIR experiments. Least square fitting curves were based on Eq. (4) for each condition.

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Fig. 10

Degree of curing versus curing time of modified and nonmodified epoxy curing at (a) 80 °C and (b) 120 °C

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Fig. 11

Diffusion and precipitation process simulation of the 5% PS modified epoxy cured at (a) 80 °C and (b) 120 °C. Concentration map of PSU is not shown. The line plots represent the concentration of epoxy and PSU along dashed line (I).

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Fig. 12

EDX line scan across the interface of 5% PS modified specimen without fibers cured at (a) 80 °C and (b) 120 °C. The dashed lines represent the width of the diffusion and precipitation region.

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Fig. 13

Diffusion and precipitation depth results from experiments and simulations from 25 °C to 120 °C. The error bars represent standard deviation.

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Fig. 14

Diffusion and precipitation simulation of the 5% PS modified epoxy with fibers cured at 80 °C. Concentration map of PSU is not shown. The line plots represent the concentration along line (I) and line (II) in the concentration map.

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Fig. 15

Diffusion and precipitation simulation of the 5% PS modified epoxy with fibers cured at 120 °C. Concentration map of PSU is not shown. The line plots represent the concentration along line (I) and line (II) in the concentration map.

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Fig. 16

EDX element mapping of the 5% PS modified specimen cured at 120 °C. Sulfur, nitrogen, and silicon were traced to represent PSU, cured epoxy, and fibers.

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Fig. 17

EDX element mapping of the 5% PS modified specimen cured at 80 °C. Sulfur, nitrogen, and silicon were traced to represent PSU, cured epoxy, and fibers.

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