Template for SPE ACCE Conference - SPE Automotive Division
NOVEL ISOCYANATE-BASED RESIN SYSTEMS WITH TUNABLE REACTION TIMES Dan Heberer and Michael Connolly Huntsman Polyurethanes, Auburn Hills, MI, USA Nick Limerkens, Eric Huygens, and Johan Derluyn Huntsman Polyurethanes, Everberg, Belgium
Abstract ®
The VITROX isocyanate-based resin system is a novel development that provides a unique combination of high thermal stability and toughness in a resin system that is easy to process and to cure. The low initial viscosity of the system, as low as 150 centipoise at room temperature, enables fast injection or infusion rates. Simultaneously, the stable viscosity profile at elevated temperatures yields long working times. At the end of a tunable induction period up to several hours long at room temperature, the „snap-cure‟ reaction profile reduces overall cycle times. This processing latitude has not been reported for urethane materials in the past and had previously limited this technology. The new resin chemistry can be formulated to yield a wide range of glass transition temperatures (up to 250 °C) while achieving the combination of high toughness in a high Tg system. The thermal stability is additionally enhanced by the inherent high fire, smoke and toxicity (FST) performance of the resin obtained without the use of added fire retardants. The benefits of the unique processing parameters, cure conditions, and high physical properties lead to it being used in a number of composite processes including pultrusion, RTM, resin infusion and filament winding. Data will be presented on resin cure and rheology as well as composite part processing and physical properties.
Introduction High-performance lightweight composites are routinely produced with state-of-the-art resin, fiber, and processing methods; they are generally however, only commercially viable in applications where the performance requirements justify the higher cost of these materials. This cost issue has limited composite usage to lower volume military and commercial aerospace applications, high-end sports equipment, and high performance passenger vehicles. State-of-the-art composites are cost prohibitive for high volume industries because part production is not scalable to high volumes as a result of constraints in cycle time and processing method. For these reasons, structural composite applications for mainstream automotive production have not yet been realized. Common aerospace grade epoxy resins require cure cycle times of 30 minutes or more which are well above the transportation industry‟s goal of five minute or less cycle times. Polyurethanes are a promising alternative to traditional epoxy-based matrix systems as they offer the potential for fast cycle times, high toughness, and exceptional durability. Polyurethanes are currently used in pultrusion applications where the polyurethane matrix has enabled new part design and production. In other composite processes such as RTM and VARTM, polyurethanes are traditionally limited to the production of smaller composite parts due to the short pot-life of the mixed resin. After mixing, the urethane system begins to react and the viscosity increases, hindering the infusion of the resin into larger parts.
Page 1
These viscosity and pot-life limitations of PU resins have been overcome through a major breakthrough in novel catalysis chemistry. In particular, this new system offers pot-lives of several hours at room temperature while maintaining a snap-cure during molding, hence reducing process cycle times. The development of the next generation thermoset composites based upon this advanced polyurethane chemistry offers a breakthrough for high volume composite production. In particular this chemistry offers the following advantages:
Significantly lower resin viscosity compared to epoxy resins which can reduce injection times in RTM processes.
Drastically increased pot-life for urethane-based resins.
A reduction in cycle time achieved by a snap-cure mechanism.
High mechanical property performance, particularly fracture toughness.
High Tg resins that enable in-line painting of automotive parts.
Excellent Fire, Smoke, and Toxicity performance without added flame retardants.
Experimental Rheological tests were carried out on a Dynamic Stress Rheometer using disposable parallel plates with a 25-mm diameter. To measure the onset of cure as evident by a rapid rise in viscosity, the instrument was run in a dynamic (oscillating) stress mode with a peak stress of 4 Pa, a frequency of 1 rad/sec and a 1 mm gap separation. However, due to the low initial viscosity of these materials, it was necessary to revert to steady state (non-oscillating) tests to accurately determine the viscosity of the uncured material. All components were mixed together in a Flaktek mixer for 30 seconds before being placed in the rheometer. In order to perform full property testing on this system, it was necessary to find a way to produce void and bubble free samples by preventing out-gassing during the preparation of the neat resin plaques and the carbon fiber composites. The following scheme was developed. First the system components were degassed individually before being combined and further degassed after mixing in another container (the long room temperature pot-life of these samples makes this possible). The mixed components were transferred to a heated mold (with or without the carbon fiber) at 200-300 g/min. For the carbon fiber samples the total injection time was 12 minutes and the samples were cured 180°C for 2 hours. The DMA analysis on cured materials was conducted in oscillatory mode with a frequency of 1 Hz and a heating rate of 3°C/min in a torsion beam geometry. The Tg is described as the G‟ onset Tg, or the temperature at which the storage modulus G‟ begins to rapidly decrease with increasing temperature. The tensile properties of the neat resins were evaluated in accordance to ASTM D638-03 and the composite samples using ASTM D3039. Mode I Interlaminar Fracture Toughness was conducted according to ASTM D5528 and the Interlaminar Shear Strength (ILSS) was based upon the ISO 14130 standard. The Fire, Smoke, and Toxicity (FST) behavior was determined through two techniques. Fire Testing was conducted using NF P92-501 (1995) Exposure to Radiant Heat. Smoke and Toxicity performance was evaluated through NF F 16-101 Rolling Stock-Fire Behavior, Smoke Density NNFX 10-702-1 and 10-702-5, and Toxicity in accordance with NF X 70-100-1 and NF X 70-0200-2. Page 2
Results and Discussion The rheological performance of the novel urethane system was compared to two conventional amine cured epoxy resins (RTM EP and VARI EP). Figure 1 illustrates the viscosity as a function of temperature as the materials are heated at 3°C/min. The shape of the viscosity curves are determined by two competing processes: the decrease in viscosity that occurs as the resins are heated and the increase in viscosity as the materials begin to react. After reaching a minimum viscosity at approximately 50°C the epoxy resin ultimately surpasses its room temperature viscosity (at 65°C) and shows a continual, steady viscosity increase as the material begins to cure. The urethane system also displays a minimum viscosity (at 58°C), but in contrast to the epoxy system the viscosity remains below its room temperature viscosity until a critical temperature (77°C) is reached. The material then exhibits a snap-cure behavior with rapid conversion to a cured material. The ability to maintain a low viscosity for an extended time enables the infusion of large composite parts. Low Viscosity Region Novel Material
Figure 1. Viscosity Profiles During Heating. It is also desirable to understand the viscosity profile of the three resin systems under conditions simulating RTM molding operations. In this case the viscosity was determined as a function of time under isothermal temperature conditions. The viscosity profiles at 80°C, as shown in Figure 2, further illustrate the snap-cure behavior of the urethane system. Since the initial viscosity is very low and remains nearly constant until cure, the mold filling operations of infusion processes are enabled with these novel urethane systems relative to the epoxy materials. The rapid conversion to a fully cured system enables fast demolding of a composite part. Since the onset of cure can be adjusted through proper resin formulation, the gel time can be matched to a particular process leading to the lowest possible cycle times.
Page 3
Low Viscosity Region
Novel Material
Figure 2. Viscosity Profile Versus Time at 80°C. The thermal performance of the cured urethane system and the RTM epoxy is shown in Figure 3 which is a plot of the storage modulus G‟ of a composite sample as a function of temperature. The storage modulus curve is relatively independent of temperature up to 200°C and exhibits a G‟ onset Tg of approximately 240°C. For comparison the same curve is shown for the RTM Epoxy system in which an G‟ onset Tg of 118°C is observed.
35
Tg ~~ 240 240°C °C Storage Modulus [GPa]
Vitrox Material Novel
30
RTM - Epoxy
25
20
15
10
0
50
100
150
200
250
300
Temperature [°C]
Figure 3. DMA Storage Modulus versus Temperature. Table 1 lists the mechanical property data of the RTM epoxy resin and the two urethane formulations as measured on neat resin plaques. Urethane 1 exhibits a tensile strength, an elongation at break, and a Young‟s modulus similar to the RTM epoxy despite the significantly higher glass transition of the urethane. Urethane 2 sacrifices modulus and tensile strength to achieve a higher strain-at-break while maintaining a high Tg. The fracture toughness and fracture energy values are the most striking difference between the epoxy and urethane systems. The urethane systems have a G 1C values of 350 and 460 J/m2; significantly higher values than the 190 J/m 2 of the epoxy. These values, in combination with the high Tg values of 260 and 240°C, demonstrate that the urethane resin systems can achieve a high Tg without sacrificing toughness.
Page 4
Table 1. Mechanical Properties of the Neat Epoxy and Urethane Systems.
Test
Property Modulus
Neat Resin Tensile
Fracture Toughness
Epoxy Resin
Urethane 1
Urethane 2
MPa
2200
2250
1450
%
5
6
10
Strain to failure Strength
MPa
74
75
56
Fracture Energy (GIC)
J/m²
190
350
460
0.63
0.88
0.81
120
260
240
Fracture Toughness (KIC) Thermal
Units
MPa·m
Tg
°C
½
Table 2 lists mechanical property data for the carbon fiber composite samples including interlaminar shear strength (ILSS) measurements before and after exposure to various chemical solutions. The tensile strength of the epoxy system is approximately 21% higher than the two urethane systems while the tensile modulus and interlaminar shear strength are essentially equivalent. As seen for the neat resin samples, the fracture energy G1C of the urethane composite samples are nearly twice as high as that of the epoxy system. The chemical resistance of the composite systems was tested by exposure to HCl and NaOH solutions and toluene. The ILSS before and after exposure are equivalent for all materials, indicating a strong interface between the resin and the carbon fiber. There is some difference in the weight change after the 7 day exposure tests: the epoxy system had a lower weight increase in the HCl solution but the urethane systems performed better in the NaOH solution and in boiling water. The effect of toluene on the weight change for the three systems was minimal.
Page 5
Table 2. Mechanical Properties of Carbon Fiber Composite Made from Epoxy and Urethane Resin Systems. Test
Property
Units
Epoxy Resin
Urethane 1
Urethane 2
%
55
55
54
GPa
44
44
42
%
1.8
1.4
1.5
Fibre volume fraction (Vf) Composite Tensile
Modulus Strain to failure
Density Fracture Toughness ILSS
Chemical Resistance
Moisture uptake
FST
Thermal
Strength
MPa
690
570
560
Density
g/cm3
1.51
1.56
-
Mode-I Fracture Energy (GIC)
J/m²
186
340
450
Interlaminar Shear Stress (ILSS)
MPa
47
51
46
ILSS after 7 days in HCl solution
MPa
46
54
46
ILSS after 7 days in NaOH solution
MPa
47
50
44
ILSS after 7 days in Toluene
MPa
50
53
47
% weight gain (7 days in HCl)
%
0.9
1.7
2.2
% weight gain (7 days in NaOH)
%
3.1
1.9
2.4
% weight gain (7 days in Toluene)
%
0.2
0.1
0.4
% weight gain (3 days in boiling H2O)
%
1.1
0.4
-
Exposure to radiant heat
-
M1
-
Smoke Density
-
F1
-
Toxicity
-
F1
-
120
260
240
Tg
°C
(1) Composite made using RTM and Vf = 55% (0°, +/-45°, 90°) carbon textile
The FST performance was determined on Urethane 1 by a third party laboratory. The highest rating of M1 was assigned after testing in the fire test NF P92-501 “Exposure to Radiant Heat”. The smoke and toxicity classification was given the second highest rating of F1 with emission values of 0 mg/g of HCl, HBr, and HF and 2 mg/g of HCN. It should be noted that these fire and toxicity values were obtained on a carbon fiber composite made with the virgin resin system without the addition of external flame retardant additives.
Applications of the New Urethane Chemistry The unique cure profiles of the new urethane chemistry have opened up process applications that previously were not available to urethane resin systems. Figures 4 and 5 are pictures of two such applications. The first is the construction of a carbon fiber composite tube made via filament winding using 12K (Toray T700) carbon roving with a fiber direction of 90° followed by a +/- 45° over wrap. The resin system was post-cured with infra-red heating.
Page 6
Figure 4. Filament Winding with the Novel Urethane Chemistry. Figure 5 shows the equipment and resulting carbon fiber composite made by vacuum infusion with perimeter injection and a central outlet and degas point. The low viscosity and long open time of the novel urethane produced a 110 X 120 cm part with very good infusion of the resin into the fibers.
Figure 5. Vacuum Infusion Processing with the Novel Urethane Chemistry.
Conclusions Unique urethane catalysis has recently been developed, eliminating the pot-life issues of traditional urethane resins and replacing the normal, gradual viscosity increase with a snap-cure reaction profile. This advance has greatly expanded the ability to use urethane chemistry for composite applications and resulted in the formulation of new resin systems that offer a number of material attributes and processing advantages:
Page 7
High Tg materials with short-term exposure temperatures up to 250°C.
Superior toughness (impact strength; strain at break; crack resistance; etc) compared to traditional thermoset resins with equivalent Tg.
Robust fire and smoke and toxicity (NF standards) without fillers or other additives.
Resistance to chemical and moisture exposure.
Compatible with glass, carbon, and other reinforcements yielding composite structures with high strength and toughness.
Wide range of resin viscosity (150-2,000 centipoise at room temperature) and a wide range of pot lives with a snap-cure reaction profile and short cycle times.
The unique chemical and physical properties of these urethane resins enable the production of composite using common thermoset composite processing operations. The result is new opportunities for material substitution (replacement of metals, expensive high-performance epoxies, phenolics, imides, etc.) and for applications that currently are restricted due to issues of scalability resultant from cycle and process times limits.
DISCLAIMER While the information and recommendations in this publication are, to the best of our knowledge, information and belief, accurate at the date of publication, NOTHING HEREIN IS TO BE CONSTRUED AS A WARRANTY, EXPRESS OR OTHERWISE. IN ALL CASES, IT IS THE RESPONSIBILITY OF THE USER TO DETERMINE THE APPLICABILITY OF SUCH INFORMATION AND RECOMMENDATIONS AND THE SUITABILITY OF ANY PRODUCT FOR ITS OWN PARTICULAR PURPOSE. NOTHING IN THIS PUBLICATION IS TO BE CONSTRUED AS RECOMMENDING THE INFRINGEMENT OF ANY PATENT OR OTHER INTELLECTUAL PROPERTY RIGHT, AND NO LIABILITY ARISING FROM ANY SUCH INFRINGEMENT IS ASSUMED. NOTHING IN THIS PUBLICATION IS TO BE VIEWED AS A LICENCE UNDER ANY INTELLECTUAL PROPERTY RIGHT. Except where explicitly agreed otherwise, the sale of products referred to in this publication is subject to the general terms and conditions of Huntsman International LLC or of its affiliated companies. Huntsman Polyurethanes is an international business unit of Huntsman International LLC. Huntsman Polyurethanes trades through Huntsman affiliated companies in different countries such as Huntsman International LLC in the USA and Huntsman Holland BV in Western Europe. VITROX® is a registered trademark of Huntsman LLC or any affiliate thereof, in one or more countries, but not all countries. Copyright © 2010 Huntsman LLC or an affiliate thereof. All rights reserved.
Page 8
Abstract ®
The VITROX isocyanate-based resin system is a novel development that provides a unique combination of high thermal stability and toughness in a resin system that is easy to process and to cure. The low initial viscosity of the system, as low as 150 centipoise at room temperature, enables fast injection or infusion rates. Simultaneously, the stable viscosity profile at elevated temperatures yields long working times. At the end of a tunable induction period up to several hours long at room temperature, the „snap-cure‟ reaction profile reduces overall cycle times. This processing latitude has not been reported for urethane materials in the past and had previously limited this technology. The new resin chemistry can be formulated to yield a wide range of glass transition temperatures (up to 250 °C) while achieving the combination of high toughness in a high Tg system. The thermal stability is additionally enhanced by the inherent high fire, smoke and toxicity (FST) performance of the resin obtained without the use of added fire retardants. The benefits of the unique processing parameters, cure conditions, and high physical properties lead to it being used in a number of composite processes including pultrusion, RTM, resin infusion and filament winding. Data will be presented on resin cure and rheology as well as composite part processing and physical properties.
Introduction High-performance lightweight composites are routinely produced with state-of-the-art resin, fiber, and processing methods; they are generally however, only commercially viable in applications where the performance requirements justify the higher cost of these materials. This cost issue has limited composite usage to lower volume military and commercial aerospace applications, high-end sports equipment, and high performance passenger vehicles. State-of-the-art composites are cost prohibitive for high volume industries because part production is not scalable to high volumes as a result of constraints in cycle time and processing method. For these reasons, structural composite applications for mainstream automotive production have not yet been realized. Common aerospace grade epoxy resins require cure cycle times of 30 minutes or more which are well above the transportation industry‟s goal of five minute or less cycle times. Polyurethanes are a promising alternative to traditional epoxy-based matrix systems as they offer the potential for fast cycle times, high toughness, and exceptional durability. Polyurethanes are currently used in pultrusion applications where the polyurethane matrix has enabled new part design and production. In other composite processes such as RTM and VARTM, polyurethanes are traditionally limited to the production of smaller composite parts due to the short pot-life of the mixed resin. After mixing, the urethane system begins to react and the viscosity increases, hindering the infusion of the resin into larger parts.
Page 1
These viscosity and pot-life limitations of PU resins have been overcome through a major breakthrough in novel catalysis chemistry. In particular, this new system offers pot-lives of several hours at room temperature while maintaining a snap-cure during molding, hence reducing process cycle times. The development of the next generation thermoset composites based upon this advanced polyurethane chemistry offers a breakthrough for high volume composite production. In particular this chemistry offers the following advantages:
Significantly lower resin viscosity compared to epoxy resins which can reduce injection times in RTM processes.
Drastically increased pot-life for urethane-based resins.
A reduction in cycle time achieved by a snap-cure mechanism.
High mechanical property performance, particularly fracture toughness.
High Tg resins that enable in-line painting of automotive parts.
Excellent Fire, Smoke, and Toxicity performance without added flame retardants.
Experimental Rheological tests were carried out on a Dynamic Stress Rheometer using disposable parallel plates with a 25-mm diameter. To measure the onset of cure as evident by a rapid rise in viscosity, the instrument was run in a dynamic (oscillating) stress mode with a peak stress of 4 Pa, a frequency of 1 rad/sec and a 1 mm gap separation. However, due to the low initial viscosity of these materials, it was necessary to revert to steady state (non-oscillating) tests to accurately determine the viscosity of the uncured material. All components were mixed together in a Flaktek mixer for 30 seconds before being placed in the rheometer. In order to perform full property testing on this system, it was necessary to find a way to produce void and bubble free samples by preventing out-gassing during the preparation of the neat resin plaques and the carbon fiber composites. The following scheme was developed. First the system components were degassed individually before being combined and further degassed after mixing in another container (the long room temperature pot-life of these samples makes this possible). The mixed components were transferred to a heated mold (with or without the carbon fiber) at 200-300 g/min. For the carbon fiber samples the total injection time was 12 minutes and the samples were cured 180°C for 2 hours. The DMA analysis on cured materials was conducted in oscillatory mode with a frequency of 1 Hz and a heating rate of 3°C/min in a torsion beam geometry. The Tg is described as the G‟ onset Tg, or the temperature at which the storage modulus G‟ begins to rapidly decrease with increasing temperature. The tensile properties of the neat resins were evaluated in accordance to ASTM D638-03 and the composite samples using ASTM D3039. Mode I Interlaminar Fracture Toughness was conducted according to ASTM D5528 and the Interlaminar Shear Strength (ILSS) was based upon the ISO 14130 standard. The Fire, Smoke, and Toxicity (FST) behavior was determined through two techniques. Fire Testing was conducted using NF P92-501 (1995) Exposure to Radiant Heat. Smoke and Toxicity performance was evaluated through NF F 16-101 Rolling Stock-Fire Behavior, Smoke Density NNFX 10-702-1 and 10-702-5, and Toxicity in accordance with NF X 70-100-1 and NF X 70-0200-2. Page 2
Results and Discussion The rheological performance of the novel urethane system was compared to two conventional amine cured epoxy resins (RTM EP and VARI EP). Figure 1 illustrates the viscosity as a function of temperature as the materials are heated at 3°C/min. The shape of the viscosity curves are determined by two competing processes: the decrease in viscosity that occurs as the resins are heated and the increase in viscosity as the materials begin to react. After reaching a minimum viscosity at approximately 50°C the epoxy resin ultimately surpasses its room temperature viscosity (at 65°C) and shows a continual, steady viscosity increase as the material begins to cure. The urethane system also displays a minimum viscosity (at 58°C), but in contrast to the epoxy system the viscosity remains below its room temperature viscosity until a critical temperature (77°C) is reached. The material then exhibits a snap-cure behavior with rapid conversion to a cured material. The ability to maintain a low viscosity for an extended time enables the infusion of large composite parts. Low Viscosity Region Novel Material
Figure 1. Viscosity Profiles During Heating. It is also desirable to understand the viscosity profile of the three resin systems under conditions simulating RTM molding operations. In this case the viscosity was determined as a function of time under isothermal temperature conditions. The viscosity profiles at 80°C, as shown in Figure 2, further illustrate the snap-cure behavior of the urethane system. Since the initial viscosity is very low and remains nearly constant until cure, the mold filling operations of infusion processes are enabled with these novel urethane systems relative to the epoxy materials. The rapid conversion to a fully cured system enables fast demolding of a composite part. Since the onset of cure can be adjusted through proper resin formulation, the gel time can be matched to a particular process leading to the lowest possible cycle times.
Page 3
Low Viscosity Region
Novel Material
Figure 2. Viscosity Profile Versus Time at 80°C. The thermal performance of the cured urethane system and the RTM epoxy is shown in Figure 3 which is a plot of the storage modulus G‟ of a composite sample as a function of temperature. The storage modulus curve is relatively independent of temperature up to 200°C and exhibits a G‟ onset Tg of approximately 240°C. For comparison the same curve is shown for the RTM Epoxy system in which an G‟ onset Tg of 118°C is observed.
35
Tg ~~ 240 240°C °C Storage Modulus [GPa]
Vitrox Material Novel
30
RTM - Epoxy
25
20
15
10
0
50
100
150
200
250
300
Temperature [°C]
Figure 3. DMA Storage Modulus versus Temperature. Table 1 lists the mechanical property data of the RTM epoxy resin and the two urethane formulations as measured on neat resin plaques. Urethane 1 exhibits a tensile strength, an elongation at break, and a Young‟s modulus similar to the RTM epoxy despite the significantly higher glass transition of the urethane. Urethane 2 sacrifices modulus and tensile strength to achieve a higher strain-at-break while maintaining a high Tg. The fracture toughness and fracture energy values are the most striking difference between the epoxy and urethane systems. The urethane systems have a G 1C values of 350 and 460 J/m2; significantly higher values than the 190 J/m 2 of the epoxy. These values, in combination with the high Tg values of 260 and 240°C, demonstrate that the urethane resin systems can achieve a high Tg without sacrificing toughness.
Page 4
Table 1. Mechanical Properties of the Neat Epoxy and Urethane Systems.
Test
Property Modulus
Neat Resin Tensile
Fracture Toughness
Epoxy Resin
Urethane 1
Urethane 2
MPa
2200
2250
1450
%
5
6
10
Strain to failure Strength
MPa
74
75
56
Fracture Energy (GIC)
J/m²
190
350
460
0.63
0.88
0.81
120
260
240
Fracture Toughness (KIC) Thermal
Units
MPa·m
Tg
°C
½
Table 2 lists mechanical property data for the carbon fiber composite samples including interlaminar shear strength (ILSS) measurements before and after exposure to various chemical solutions. The tensile strength of the epoxy system is approximately 21% higher than the two urethane systems while the tensile modulus and interlaminar shear strength are essentially equivalent. As seen for the neat resin samples, the fracture energy G1C of the urethane composite samples are nearly twice as high as that of the epoxy system. The chemical resistance of the composite systems was tested by exposure to HCl and NaOH solutions and toluene. The ILSS before and after exposure are equivalent for all materials, indicating a strong interface between the resin and the carbon fiber. There is some difference in the weight change after the 7 day exposure tests: the epoxy system had a lower weight increase in the HCl solution but the urethane systems performed better in the NaOH solution and in boiling water. The effect of toluene on the weight change for the three systems was minimal.
Page 5
Table 2. Mechanical Properties of Carbon Fiber Composite Made from Epoxy and Urethane Resin Systems. Test
Property
Units
Epoxy Resin
Urethane 1
Urethane 2
%
55
55
54
GPa
44
44
42
%
1.8
1.4
1.5
Fibre volume fraction (Vf) Composite Tensile
Modulus Strain to failure
Density Fracture Toughness ILSS
Chemical Resistance
Moisture uptake
FST
Thermal
Strength
MPa
690
570
560
Density
g/cm3
1.51
1.56
-
Mode-I Fracture Energy (GIC)
J/m²
186
340
450
Interlaminar Shear Stress (ILSS)
MPa
47
51
46
ILSS after 7 days in HCl solution
MPa
46
54
46
ILSS after 7 days in NaOH solution
MPa
47
50
44
ILSS after 7 days in Toluene
MPa
50
53
47
% weight gain (7 days in HCl)
%
0.9
1.7
2.2
% weight gain (7 days in NaOH)
%
3.1
1.9
2.4
% weight gain (7 days in Toluene)
%
0.2
0.1
0.4
% weight gain (3 days in boiling H2O)
%
1.1
0.4
-
Exposure to radiant heat
-
M1
-
Smoke Density
-
F1
-
Toxicity
-
F1
-
120
260
240
Tg
°C
(1) Composite made using RTM and Vf = 55% (0°, +/-45°, 90°) carbon textile
The FST performance was determined on Urethane 1 by a third party laboratory. The highest rating of M1 was assigned after testing in the fire test NF P92-501 “Exposure to Radiant Heat”. The smoke and toxicity classification was given the second highest rating of F1 with emission values of 0 mg/g of HCl, HBr, and HF and 2 mg/g of HCN. It should be noted that these fire and toxicity values were obtained on a carbon fiber composite made with the virgin resin system without the addition of external flame retardant additives.
Applications of the New Urethane Chemistry The unique cure profiles of the new urethane chemistry have opened up process applications that previously were not available to urethane resin systems. Figures 4 and 5 are pictures of two such applications. The first is the construction of a carbon fiber composite tube made via filament winding using 12K (Toray T700) carbon roving with a fiber direction of 90° followed by a +/- 45° over wrap. The resin system was post-cured with infra-red heating.
Page 6
Figure 4. Filament Winding with the Novel Urethane Chemistry. Figure 5 shows the equipment and resulting carbon fiber composite made by vacuum infusion with perimeter injection and a central outlet and degas point. The low viscosity and long open time of the novel urethane produced a 110 X 120 cm part with very good infusion of the resin into the fibers.
Figure 5. Vacuum Infusion Processing with the Novel Urethane Chemistry.
Conclusions Unique urethane catalysis has recently been developed, eliminating the pot-life issues of traditional urethane resins and replacing the normal, gradual viscosity increase with a snap-cure reaction profile. This advance has greatly expanded the ability to use urethane chemistry for composite applications and resulted in the formulation of new resin systems that offer a number of material attributes and processing advantages:
Page 7
High Tg materials with short-term exposure temperatures up to 250°C.
Superior toughness (impact strength; strain at break; crack resistance; etc) compared to traditional thermoset resins with equivalent Tg.
Robust fire and smoke and toxicity (NF standards) without fillers or other additives.
Resistance to chemical and moisture exposure.
Compatible with glass, carbon, and other reinforcements yielding composite structures with high strength and toughness.
Wide range of resin viscosity (150-2,000 centipoise at room temperature) and a wide range of pot lives with a snap-cure reaction profile and short cycle times.
The unique chemical and physical properties of these urethane resins enable the production of composite using common thermoset composite processing operations. The result is new opportunities for material substitution (replacement of metals, expensive high-performance epoxies, phenolics, imides, etc.) and for applications that currently are restricted due to issues of scalability resultant from cycle and process times limits.
DISCLAIMER While the information and recommendations in this publication are, to the best of our knowledge, information and belief, accurate at the date of publication, NOTHING HEREIN IS TO BE CONSTRUED AS A WARRANTY, EXPRESS OR OTHERWISE. IN ALL CASES, IT IS THE RESPONSIBILITY OF THE USER TO DETERMINE THE APPLICABILITY OF SUCH INFORMATION AND RECOMMENDATIONS AND THE SUITABILITY OF ANY PRODUCT FOR ITS OWN PARTICULAR PURPOSE. NOTHING IN THIS PUBLICATION IS TO BE CONSTRUED AS RECOMMENDING THE INFRINGEMENT OF ANY PATENT OR OTHER INTELLECTUAL PROPERTY RIGHT, AND NO LIABILITY ARISING FROM ANY SUCH INFRINGEMENT IS ASSUMED. NOTHING IN THIS PUBLICATION IS TO BE VIEWED AS A LICENCE UNDER ANY INTELLECTUAL PROPERTY RIGHT. Except where explicitly agreed otherwise, the sale of products referred to in this publication is subject to the general terms and conditions of Huntsman International LLC or of its affiliated companies. Huntsman Polyurethanes is an international business unit of Huntsman International LLC. Huntsman Polyurethanes trades through Huntsman affiliated companies in different countries such as Huntsman International LLC in the USA and Huntsman Holland BV in Western Europe. VITROX® is a registered trademark of Huntsman LLC or any affiliate thereof, in one or more countries, but not all countries. Copyright © 2010 Huntsman LLC or an affiliate thereof. All rights reserved.
Page 8
