epoxy- allyl phenol- bismaleimide matrix system - property dependency on epoxy structure

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Epoxy- allyl phenol- bismaleimide matrix system - Property dependency on epoxy structure K. Ambika Devi, Bibin John, C. P Reghunadhan Nair and K.N Ninan Propellants, Polymers, Chemicals and Materials entity Vikram Sarabhai space Centre Trivandrum-695022 Abstract A ternary matrix system constituted by the reactive blending of epoxy- diallyl bisphenol and bismalemide (EPB) was found to be superior to the epoxy-phenol (EP) system in respect of its thermal and mechanical properties. The performance of the ternary blend system depends on the structure of its constituents, particularly the epoxy and bismaleimide. The influence of the structural variations of the epoxy resin on the thermal, physical and mechanical properties of the ternary blend was examined. EPB compositions were prepared using bismaleimide, diallyl bisphenol -A and three different epoxy resin systems viz. Novolac epoxy (E 1 ), bisphenol A diglycidyl ether (E 2 ) and tris (4-glycidyl oxyphenyl methane) (E 3 ), having different physical, chemical and functionality characteristics. The cure characterization of these reactive blends were carried out using techniques such as differential scanning calorimetry and rheological analysis. The thermograms showed that the temperature of onset of decomposition for the EPB systems with the above epoxies (identified as E 1 , E 2 and E 3 ) are in the order E 3 > E 2 > E 1 . The mechanical properties - compressive, flexural and interlaminar shear strength - of the glass composite were found to depend on the epoxy structure. The trend in these properties was E 1 > E 3 > E 2 . The higher crosslink density of the tri functional epoxy improved the thermal properties of the system. Highest strength values were obtained for the EPB system containing novolac epoxy. 1 Introduction The epoxy resin can be formulated in an infinite number of ways to manipulate characteristics such as system stability, cure kinetics, physical form, T g , mechanical performance and chemical resistance. The versatility in form, modification, properties, hardening methods, cure conditions and application is probably the most outstanding characteristic of epoxy resin. Its utility can be further widened by the modification of the same by 1

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Page 1: Epoxy- allyl phenol- bismaleimide matrix system - Property dependency on epoxy structure

Epoxy- allyl phenol- bismaleimide matrix system - Property dependency on epoxy structure

K. Ambika Devi, Bibin John, C. P Reghunadhan Nair and K.N NinanPropellants, Polymers, Chemicals and Materials entityVikram Sarabhai space CentreTrivandrum-695022

AbstractA ternary matrix system constituted by the reactive blending of epoxy- diallyl bisphenol and bismalemide (EPB) was found to be superior to the epoxy-phenol (EP) system in respect of its thermal and mechanical properties. The performance of the ternary blend system depends on the structure of its constituents, particularly the epoxy and bismaleimide. The influence of the structural variations of the epoxy resin on the thermal, physical and mechanical properties of the ternary blend was examined. EPB compositions were prepared using bismaleimide, diallyl bisphenol -A and three different epoxy resin systems viz. Novolac epoxy (E1), bisphenol A diglycidyl ether (E2) and tris (4-glycidyl oxyphenyl methane) (E3), having different physical, chemical and functionality characteristics. The cure characterization of these reactive blends were carried out using techniques such as differential scanning calorimetry and rheological analysis. The thermograms showed that the temperature of onset of decomposition for the EPB systems with the above epoxies (identified as E1, E2 and E3) are in the order E3 > E2 > E1. The mechanical properties - compressive, flexural and interlaminar shear strength - of the glass composite were found to depend on the epoxy structure. The trend in these properties was E1 > E3 > E2. The higher crosslink density of the tri functional epoxy improved the thermal properties of the system. Highest strength values were obtained for the EPB system containing novolac epoxy.

1 IntroductionThe epoxy resin can be formulated in an infinite number of ways to manipulate characteristics such as system stability, cure kinetics, physical form, Tg, mechanical performance and chemical resistance. The versatility in form, modification, properties, hardening methods, cure conditions and application is probably the most outstanding characteristic of epoxy resin. Its utility can be further widened by the modification of the same by suitable means to tailor its property to suit the different system requirements.

Elevated temperature base resins are those that cure to yield somewhat inflexible molecular structures. Rigidity can be built in to the cured matrix in several ways: through the incorporation of aromatic groups, an increase in the number of reaction sites (epoxy groups) per molecule or a reduction in the distance between the reaction sites. The three primary classes of epoxy resins used in composite application are phenolic glycidyl ethers, aromatic glycidyl amines and cycloaliphatics [1]. In order to improve the thermal and mechanical properties of epoxy resin, modifying the molecular backbone and /or increasing the number of epoxide group functionality are employed by many researchers [2,3]. The introduction of epoxy in to bismaleimide increases the fracture toughness and fracture energy of epoxy system with modest reduction in both modulus and glass transition temperature. A modest improvement in lap shear properties is possible, but the most important benefits will accrue at higher temperatures. The cure reactions of reactive blends of bismaleimides and epoxies has been studied and reported [4].

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Page 2: Epoxy- allyl phenol- bismaleimide matrix system - Property dependency on epoxy structure

We have reported a ternary polymer blend of epoxy- allyl phenol and bismaleimide with improved high temperature performance and comparable mechanical properties in comparison with epoxy-phenol system [5]. The structural changes and the resulting property variations of the epoxy and the BMI systems can influence the performance of the ternary EPB blend. In the present study, the effect of structural variations of epoxy resin on the performance of EPB co- curing system is presented.

2.Experimental2.1 Materials The materials used in the study are Diallyl bisphenol A (DABA)- synthesized from bisphenol A, Epoxy resin-1- EPN 1139- supplied by M/S Ciba Geigy, Mumbai, Epoxy resin-2-Ly-556 -supplied by M/S Ciba Geigy, Mumbai, Epoxy resin-3-Tri epoxy- supplied by M/s Aldrich, USA, Triphenyl phosphine (TPP)-Supplied by E-Merck, 2, 2 –bis 4-(4 maleimidophenoxy) phenyl] propane-BMIP-synthesized in VSSC by a reported procedure [6], E-Glass cloth- Plain weave, silane treated fabric of thickness 0.25mm from Unnathi Corporation, India.2.2 Preparation and characterization of Ternary blend

The preparation and characterization of EPB reactive blend of novolac epoxy diallyl bisphenol and bismaleimide was reported by us [7]. The same was repeated for the EPB systems with epoxies E2 and E3.The ternary EPB blends were characterized using Nicolet 510 P FTIR spectrophotometer, Mettler TA 3000 Thermal analysis system in conjunction with TC -10A TA processor and standard DSC-2920 analyser, SDT-2960 simultaneous TGA-DTA and Reologica Stress Tech Rheometer.The curing of the polymer blend was achieved by following the time temperature cure schedule optimized for the EPB system [7].

2.3 Preparation of Laminates and characterization of composites

Laminates were prepared using the three EPB systems and plane weave glass cloth. The mechanical properties of the composites were evaluated by determining their flexural strength, compressive strength and interlaminar shear strength (ILSS) following the ASTM standard test procedures. The resin content was determined by matrix digestion method using a muffle furnace.

3 Results and discussion

3.1 Cure characterization of the ternary polymer blend

The IR spectrum of the EPB systems with different epoxies E1, E2 and E3 recorded before and after cure reaction confirmed the cure completion. The DSC cure thermograms of the EPB systems with different epoxies is given in Fig.1. The epoxy –phenol reaction (100 -150 oC) was found to be not prominent in the case of Tri epoxy. The phenol-epoxy, Ene reaction and Diel-Alder reaction all occur more or less in the same temperature regions. The curing of the unsaturated groups of the adduct occur beyond 250 oC.

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Page 3: Epoxy- allyl phenol- bismaleimide matrix system - Property dependency on epoxy structure

The rheological cure characterization of the different blends enabled the determination of gel point and gave a better insight in to the temperature dependence of their cure profile with change in epoxy structural variations. The dynamic rheograms obtained for the EPB system with different epoxies showed that the temperatures corresponding to the gelation and crosslinking are differing slightly with change in epoxy type. The storage shear modulus vs temperature curves obtained for the three EPB systems are given in Fig.2.

50 100 150 200 250 300

1E-6

0.01

100

1000000

EPB-E3

EPB-E2

EPB-E1

Stor

age

shea

r mod

ulus

(KPa

)

Temperature(oC)Fig.1 DSC thermograms showing the cure Fig.2 Temperature dependence of Storage and lossreaction of EPB systems with different epoxies shear modulus of EPB system with different epoxies

The TGA thermograms recorded for the cured DABA-EPN–BMI blends with different types of epoxies showed that the temperature of initiation (Ti), peak (Tm) and completion (Ts) of decomposition for the EPB systems with epoxies E1, E2 & E3 are in the order E3 > E1 >E2 showing that their thermal stabilities are in the same order.

Table 1 Thermal decomposition characteristics of EPB systems with epoxy variation

Temperature Sample reference

EPB- E1 EPB-E2 EPB- E3

Ti (oC) 240 225 275

Tm (oC) 430 426 431

Ts (oC) 680 657 671

3. 2 Characterization of the composite The glass laminates prepared using the three component EPB resin systems containing different epoxies were characterized for their mechanical and physical properties and the results are summarized in Table 2.The mechanical properties (compressive, flexural and interlaminar shear strength) of the composite samples were found to be different for the

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Page 4: Epoxy- allyl phenol- bismaleimide matrix system - Property dependency on epoxy structure

systems with different epoxies. The trend in these properties were E1 > E3 > E2. The reduction in strength of the tri epoxy may be due to its very low flexibility caused by the higher crosslink density while the least strength values reported for the LY-556 may be due to its increased flexibility resulting from its molecular structure, which caused comparatively reduced cosslinkages in the system.

Table 2 Mechanical and physical properties of EPB systems with different epoxies

Property

Sample reference

EPB-E1 EPB-E2 EPB-E3

ILSS (kg/cm2) 450 380 410

Compressive strength (kg/cm2) 2780 2130 2380

Flexural strength (kg/cm2) 5600 5000 4800

Resin content (%) 20.4 21.4 21.6

The resin content in these composites determined by matrix digestion showed a variation from 20.4 - 21.6 for EPB systems with different epoxies.

4. Conclusion

The structural variation of epoxy was found to influence the properties of the Epoxy-phenol-bismaleimide composites. The tri epoxy having more crosslinking sites was found to have improved thermal properties. Their ILSS was found to be higher compared to the LY-556 based system, while its flexural properties were minimum among the three systems studied. The resin content was found to be with in a narrow range. All the strength properties showed maximum value for the EPB system containing novolac epoxy. 5. Acknowledgements

The authors thank Director VSSC for granting permission to present this paper. The analytical support given by our colleagues in Analytical and Spectroscopic Division (ASD) is also acknowledged.

6. Reference

1 ASM Hand Book Vol.-21, 79

2 T. Y.Murata, Y. Nakanishi, US patent 1997, 5623031.

3 C.S Wang, M.C Lee, J. Appl. Poly.Sci.70, 1998, 1907

4 C. Gouri, C.P Reghunadhan Nair and R. Ramaswamy, Polym Int. 50, 2001, 403-411

5 K.Ambika Devi, C.P Reghunadhan Nair, G.Viswanadhan Asari, K.N Ninan “Effect of bimaleimide on the thermal characteristics of Epoxy- Phenolic- Bismaleimide matrix system” International conference Thermans -2006 Feb.2006

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6 C. P. Reghunadhan Nair, Tania Francis, J Appl. Polym. Sci.74, 1999, 3366

7. K. Ambika Devi, Bibin John, C.P. Reghunadhan Nair, K.N Ninan, “Bismaleimide- co- cured di allyl bisphenol A – epoxy novolac system- Cure and thermal properties”

(communicated to J. Appl. Poly. Sci.)

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