Transcript Document
Thermal Degradation Of Carbon Fiber/Cyanate Ester Resin Composites Filled With Clay Silicate Nanoparticles
Dr. Shawn Doherty
Univ. of Delaware – Center for Composite Materials
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2006 University of Delaware, All rights reserved
Introduction
Polymer matrix composites are being used in extreme operating environments High temperature applications such as engine components and aircraft structures Long term use in extreme environments leads to decrease in composite properties Cyanate ester resins are promising thermosets for study due to excellent properties High glass transition temperature (T g ) Low moisture absorption Good thermal stability Low shrinkage
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2006 University of Delaware, All rights reserved
Introduction
Project Goal Use nanoclay additives to reduce the rate of thermo-oxidative decomposition and microcracking of high-temperature polymer resins Concept Dispersed nanoparticles in the matrix present a barrier to the diffusion of oxygen that would slow down the decomposition of the resin under long term exposure Inorganic nanoparticle additives would help overcome induced stresses during resin degradation preventing microcracking that accelerate thermo-oxidative degradation Inorganic nanoparticles help prevent rapid microcrack growth Addition of inorganic particles would reduce CTE of resin, minimizing mismatch between resin and carbon fibers
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2006 University of Delaware, All rights reserved
Outline of Work
Preparation of nanoclay/cyanate ester resin mixtures and composites Examination the effects of nanoclays on the cure behavior of the cyanate ester resin Examination of the effects of nanoclays on the structure and properties of the resin Analysis of changes in mechanical behavior of nanoclay/resin composites at high temperatures
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2006 University of Delaware, All rights reserved
Preparation of Materials
Base resin Modified cyanate ester resin (RS-9D) T g > 350 ºC Maximum service temperature of 280 ºC Nanoclays Organically modified montmorillonite clay Developed by Triton for high-temperature stability and solubility with cyanate ester resin
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2006 University of Delaware, All rights reserved
Preparation of Materials
Mixture of cyanate ester and clay High-shear mixing setup, 10,000 rpm at 110 ºC for 10 minutes Differerent weight percentages of nanoclay added 2.5 and 5 wt% of nanoclay for each resin system Cobalt-based catalyst added (1.5 wt%) to promote curing Used for cure behavior studies Composites made from resin mixtures and carbon fiber Prepreg made using IM7 carbon fiber and each clay/resin mixture Prepreg layers were pressed into ½” thick unidirectional panels Fiber volume fraction of 57% Used for mechanical testing and thermal aging studies
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2006 University of Delaware, All rights reserved
Effects on Cure Behavior - Rheological
Clay systems had lower cure temperatures and higher minimum viscosities than neat resin, which makes the resin less processable Cyclic Amine and Aromatic Phosphonium had best performance 3 2.5
2 Neat RS-9 resin Aliphitic Phosphonium (2.5 wt%) Aliphitic Phosphonium (5 wt%) Aromatic Phosphonium (2.5 wt%) Aromatic Phosphonium (5 wt%) Cyclic Amine (2.5 wt%) Cyclic Amine (5 wt%) Heterocyclic Amine (2.5 wt%) Heterocyclic Amine (5 wt%) Aliphatic Phosphonium had worst performance 1.5
1 Higher clay content = worse performance 0.5
0 70 80 90 100 110 120 Temperature (C)
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2006 University of Delaware, All rights reserved 130 140 150 160
10 9 8 7 2 1 0 0 4 3 6 5
Effects on Cure Behavior - Rheological
10 Working temperatures determined by isothermal heating Heterocyclic Amine had most accelerated cure, then Aromatic Phosphonium and Cyclic Amine
Clay acts like catalyst, curing at lower temperatures and shorter times
Neat Aromatic Phosphonium (2.5 wt%) Aromatic Phosphonium (5 wt%) Cyclic Amine (2.5 wt%) Cyclic Amine (5 wt%) Heterocyclic Amine (2.5 wt%) Heterocyclic Amine (5 wt%) 9 8 7 6 5 4 3 2 1 0 0 10 9 8 Neat Aromatic Phosphonium (2.5 wt%) Aromatic Phosphonium (5 wt%) Cyclic Amine (2.5 wt%) Cyclic Amine (5 wt%) Heterocyclic Amine (2.5 wt%) Heterocyclic Amine (5 wt%) 20 40 60 80 100 Time (min) 120 140 160 180 Neat Aromatic Phosphonium (2.5 wt%) Aromatic Phosphonium (5 wt%) Cyclic Amine (2.5 wt%) Cyclic Amine (5 wt%) Heterocyclic Amine (2.5 wt%) Heterocyclic Amine (5 wt%) 100 ºC 7 20 40 110 ºC 60 80 100 Time (min) 120 140 160 180 4 3 6 5 2 1 0 0 20 40 60 80
Time (min)
100 120 120 ºC 140 160 180
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2006 University of Delaware, All rights reserved
Effects on Cure Behavior - Calorimetric
Since nanoclay may be acting as a catalyst, measurements were taken for each system both with and without the cobalt-based catalyst In neat resin, catalyst lowered cure temperature and broadened peak Addition of clay to catalyzed system lowered initial cure temperature further and narrowed curing temperature range 0.3
0.4
Addition of clay to catalyst-free systems lowered the peak temperature
Neat Resin Aromatic Phosphonium
0.4
cyanateester76B_1.001
– – – – —— no catalysts - - - with catalysts 0.3
- - - no catalysts —— with catalysts 0.2
0.1
0.0
0.2
0.1
0.0
-0.1
50 Exo Up 100 150 Temperature (°C) 200 250 300 Universal V4.2E TA Instruments -0.1
50 Exo Up 100
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2006 University of Delaware, All rights reserved 150 Temperature (°C) 200 250 300 Universal V4.2E TA Instruments
Effects on Cure Behavior - Calorimetric
Clay reduced heat of cure in catalyzed systems compared to neat resin, up to 24% for Heterocyclic Amine (no change in non-catalyzed) Polymerization initiated at lower T and occurs at faster rate, but prevented from reaching full conversion due to premature termination Changes in cure kinetics of resin systems may lead to reduction in mechanical properties for clay systems, due to reduced cross-linking With catalyst Without catalyst Organoclay type ΔH 0 (J/g) T max (C) ΔH 0 (J/g) T max (C) Neat Heterocyclic Amine Aromatic Phosphonium Cyclic Amine Aliphatic Phosphonium 519 395 468 498 164 147 187 196 442 174
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2006 University of Delaware, All rights reserved 458 420 429 438 437 254 195 192 215 187
Microscopic Analysis of Composite Structure
Some of the nanoclay resin systems were examined using transmission electron microscopy (TEM) to determine the distribution of particles in the resin Clay layers can be seen at higher magnification and agglomerates at low magnification which indicates minimal particle separation or exfoliation of the clay
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2006 University of Delaware, All rights reserved
Effects of Thermal Aging – Weight Loss
Composite samples of each clay/resin system were aged for 51 days at 260 ºC and the weight loss was measured.
After 3 days, each had lost 0.8% of initial weight After 1 month, neat resin had lost 5.6% while others had lost ~4.5% After 51 days: Neat: 12% Largest: 5 wt% Cyclic Amine (10.5%) Smallest: 2.5 wt% Aromatic Phosphonium (5.6 %) 12.00% 10.00% 8.00% 6.00% 4.00% 2.00% Neat Resin Cyclic Amine (2.5 wt%) Cyclic Amine (5 wt%) Aromatic Phosphonium (2.5 wt%) Aromatic Phosphonium (5 wt%) Heterocyclic Amine (2.5 wt%)
Nanoclay particles are reducing the amount of
0.00% 0 200 400 600 800
thermal degradation in the resin system Time (hours) ©
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Effects of Thermal Aging – Fracture Toughness
To measure the fracture toughness of the nanoclay composite systems, notched samples were cut according to ASTM D-5045 Each specimen was 3” x ½” x ¼” with fiber direction // to the short dimension and the notch ¼” deep sharpened to a crack at the tip Samples were tested in a 3 point bend test to measure displacement as a load was applied to the cracked region Fracture toughness (K IC ) was calculated for each of the systems using 5 replicates
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2006 University of Delaware, All rights reserved 1 Hansen, Gillespie; Journal of Composites Technology and Research ; Vol.20; 1998
Effects of Thermal Aging – Fracture Toughness
800 700 600 500 400 300 200 100 0
After 250 hours, Cyclic Amines had largest decrease (20%) Heterocyclic Amine had almost no change Neat resin had 16% loss of toughness After 500 hours, no significant change in fracture toughness compared to 250 hours
Neat resin Cyclic Amine (2.5 wt%) Cyclic Amine (5 wt%) Aromatic Phosphonium (2.5 wt%) Aromatic Phosphonium (5 wt%) Heterocyclic Amine (2.5 wt%)
Results consistent with weight loss: Largest weight loss corresponds to largest in fracture toughness loss (Neat and Cyclic Amine systems) Variation in toughness for the control samples is likely due to variation in cure behavior due to the nanoclay components.
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Effects of Thermal Aging - Microcracking
Study on effects of nanoclays on crack propagation currently underway Initial work examined the surface cracking of the aged composites to determine if the nanoclays had any visible difference Surface cracks in aged neat composite were more pronounced than aged composite with nanoclay particles Neat cyanate ester composite after Aromatic phosphonium / cyanate ester 500 hours of aging
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composite after 500 hours of aging 2006 University of Delaware, All rights reserved
Conclusions
Addition of organically modified nanoclay particles to cyanate ester resin will effect the properties and processability of the material Clay particles will decrease the processing window of the resin prior to curing Nanoclay decreases the cure temperature of the resin Nanoclay shrinks the amount of time before the resin cures at a fixed temperature Clay particles act as catalysts, increasing the rate of cure and decreasing the maximum cure temperature Nanoclay/resin composites are more thermally stable than neat systems Nanoclay composites had less weight loss after aging than neat system Nanoclay composites had higher fracture toughness than neat system
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2006 University of Delaware, All rights reserved
Future Work
Work to improve the distribution and exfoliation of the clay particles in the resin system, since increasing the resin-clay interaction should improve properties Continued study of the microcracking in order to quantify the penetration of cracks into the composite bulk. Factors to be considered: Aging time Nanoclay system Both in-plane and transverse direction
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2006 University of Delaware, All rights reserved
Acknowledgements
Dr. Joseph Deitzel – CCM Misaki Takemori – CCM Touy Thiravong – CCM Apoorva Shah – Triton Systems, Inc Dr. Arjan Giaya – Triton Systems, Inc Dr. Jack Gillespie – CCM Dr. Dirk Heider – CCM
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2006 University of Delaware, All rights reserved