EPOXY RESIN SYSTEMS FOR HIGH PERFORMANCE FRP MOULDS Dr Mahesh Soni * GM Research & Development - Polymers / Atul Ltd mahesh_soni@atul.co.in Dr Utkarsh Shukla Manager Research & Development - Polymers / Atul Ltd utkarsh_shukla@atul.co.in Himanshu Dhol Asst Manager Application Development Composites / Atul Ltd himanshu_dhol@atul.co.in Paresh Raiyani Executive Application Development Composites / Atul Ltd paresh_raiyani@atul.co.in ABSTRACT Three epoxy resin systems have been developed and studied for various properties from process and performance point of view. All three systems are versatile in nature and suitable for most of the process techniques including Resin Infusion (RI), Hand Molding and RTM. Process properties such as mix viscosity at different temperature, rise in viscosity with respect to time and temperature, pot life at working temperature have been determined and reported to ease the selection of a resin system for composite applications. Several performance properties in neat state and with reinforcement have also been studied at standard conditions. The epoxy systems developed and reported in this study has varying pot life from 7 minutes to more than 6 minutes. Mix viscosities of epoxy systems are suitably low to achieve faster impregnation of reinforcement. The cured systems are capable to achieve glass transition temperature from 4 to 6 C. results of physiochemical properties, reactivity, process and performance properties make these epoxy systems suitable for high performance composite tooling applications. Page of 7
INTRODUCTION Composite materials have emerged as a major class of structural elements and are either used or being considered as substitution for metals / traditional material in tooling for aerospace, automotive and other industries due to their high specific stiffness, high strength and controlled anisotropy which make them very attractive structural materials. Use of plastics in tooling applications was introduced during World War II to alleviate a critical shortage of tooling metals. Initial tooling plastics were Phenolic and later polyesters; however, these materials posed a number of disadvantages which limited their versatility. [] Epoxies are one of the most widely used engineering resins and are well know for their use in composites with high strength fibers. Epoxy resins form a glass network, exhibit excellent resistance to corrosion & solvents, good adhesion, reasonably high glass transition temperatures and adequate electrical properties. [] Epoxies were introduced as tooling resin in about 95 and with passage of time have gained wide acceptance. Currently, they are being employed in about 9 of all plastic tooling applications Use of epoxy formulations in tooling applications offers several advantages like speed and ease of manufacturing, dimensional stability, excellent strength by using anisotropy to advantage, high strength to wt ratio, and low shrinkage during cure which permits close tolerance reproduction. [] Epoxy tooling was initially introduced in aircraft and automobile production which continues to be one of the major applications. In aircraft, where production runs are short and often complicated by design changes, epoxies have proved of particular value. [] In automobile industry, epoxy metal forming tools are not suited for long production runs but such tools are useful as serving for prototypes for metal tooling and can be used to cut the time required by 5-5. [4] Tooling parts can be manufactured by various processing methods like castings, hand Lay up, resin infusion, RTM or various other traditional processing techniques. In the present study, we have selected three epoxy systems which are most suitable for different processing technique like resin infusion, hand molding and RTM. These systems are of varying viscosities, pot life / gel time, glass transition temperature and mechanical strength. EXPERIMENTAL WORK Materials Following three Lapox epoxy resins and suitable curing agents were selected: Resin Hardener - -4 49 - -8 - -8 Measurement and ing Viscosity and rise in viscosity measurement at different temperatures was done using rotational viscometer make Brookfield - model LVDV II+ Pro with software. Glass transition temperature was measured using Mettler Toledo DSC model 8e. Pot lives were determined using Gardco, USA pot life tester. Mechanical properties like tensile and flexural strength, modulus and elongation of bare and reinforced epoxy samples were determined by using Instron model -69, USA Universal ing Machine. The crosshead speed of mm.min - for tensile and mm.min - for flexural strength as per and 78 was used respectively. Sample Preparations Samples for tensile strength and flexural strength of casted epoxy systems were prepared by specimen moulds. Dimensions of specimens were as per and 78 standards respectively. Glass fiber reinforced samples were prepared by infusion process using two layers of UD glass fiber, gsm. Curing schedule for different epoxy systems are tabulated as below: Page of 7
Tab. Details of mixing ratio and curing schedule for different system Sr No - - - RESULTS -4 / 49-8 / -8 / Physical properties Viscosity Resin: Hardener mixing ratio (pbw) :4 : :5 Curing Schedule 8ºC/h + ºC/h + 6ºC/h + ºC/4h 8 o C/h + o C/h + ºC/8h 8 o C/h + o C/h + 5ºC/8h Table- shows the initial mix viscosity at three different temperatures 5ºC, 5ºC and 45ºC. The viscosity decreases with increase in temperature. Values vary in the range of 4 cps to 6 cps at 5ºC. - shows the highest viscosity whereas system- has the lowest viscosity at 5ºC. Tab. Initial mix viscosity of epoxy resin systems at different temp. Syste m - - - -4 / 49-8 / -8 / Meth od 9 9 9 5ºC 5ºC 45ºC 6 84 76 5 79 978 485 95 Viscosity (cps) 5 5 5 Rise in Viscosity @ 5ºC -4/49 4 5 Time (Min) Fig. Rise in viscosity at 5ºC for different epoxy systems It was observed that system-, has higher reactivity compared to other two systems and about 55 rise in viscosity was observed within 5 min. - has lowest initial viscosity of 5 cps at 5ºC suitable for infusion process. - -4/49 has highest initial mix viscosity of 6 cps at 5ºC and at 5ºC it is cps which is reasonably low. Here rise in viscosity is slow which makes it suitable for infusion at temperature of 5ºC. Processing Properties Pot Life / working Life Reactivity of all systems was determined at standard temperature of 5ºC. Samples were conditioned for 4hr in incubator at 5ºC before test. Figure illustrates that system- has fastest reactivity and gels within 7 min. - has moderate reactivity whereas system- has very long pot life. Rise in Viscosity Figure shows rise in viscosity at 5ºC w.r.t time for different epoxy systems. Page of 7
Pot Life @ 5ºC 6 78.8.9. Time (min.) 7-8+ 4-8+ -4+ 49 Fig. Pot life of different epoxy system at 5ºC. Cured system Properties Three different epoxy resin systems with stoicheomatric ratio of resin:hardener were prepared and cured as per the schedule mentioned in Table. Table shows the properties of system in cured state. A wide range of Tg was achieved ranging from 4-6ºC for different systems. - shows very high modulus whereas system- shows highest tensile strength in neat resin system. Tab. properties of different casted unreinforced epoxy systems in cured state Descriptio n Glass Transition Temp Tg Strength Tension strength Unit ºC Meth od 7 5-78 78 4 / AH4 9-8 / 8 / 6 4 5 4 7 65.6 4.8.5.6.. 7. 7. 5 Strength () Modulus () 4 8 6 4 & Strength of epoxy systems Strength 4 strength 7 65 7 4/49 and modulus for epoxy systems Tension 4.5.5.5.5.6.8-4/ 49...9 Page 4 of 7
and elongation for epoxy systems & Strength of reinforced epoxy systems Tension Strength strength () 8 7 6 5 4.6 4.8 7..5 5 Strength () 8 6 4 74 7 6 6 64 98-4/49-8/AH -4/ 49 Tab. 4 Mechanical Properties of different reinforced epoxy system Descriptio n Strength Tension Strength Unit Metho d 45 45 45 4 / 49-8 / 8 / 74 6 64.4.5.5 4 4 4 7 6 98.5.6.8 4 Modulus () and modulus for reinforced epoxy systems Tension 45 4 5 5 5 5 4 4 4-4/ 49 4 Page 5 of 7
() Page 6 of 7 and elongation for reinforced epoxy systems 4.5.5.5.5.4.5 4/49 CONCLUSION Tension.5.8.5.6 The three systems developed and available commercially with Atul-Ltd, offer low to moderate mix viscosity, varying reactivity and pot life, and fast impregnation of reinforcement at ambient conditions. Their suitable mix viscosity and reactivity at processing conditions make them ideal for most of the composite processing techniques including Resin Infusion (RI), Hand Molding, and Resin Transfer Molding (RTM). The varying glass transition temperature of these systems, which is an important property for material selection, is ranging from 4 to 6ºC Therefore, a FRP composite can be fabricated from these resins which can work at extreme conditions of temperature. The mechanical properties obtained in tension and bending mode are excellent and suitable for most of the applications. More importantly elastic modulus of these systems are directly proportional to their Tg and have shown very high value in tension and bending mode. Easy processability due to appropriate viscosity, reactivity, high mechanical strength, and modulus, and high glass transition temperature (Tg) value of these versatile epoxy systems makes them most suitable for fabrication of FRP tools (molds) using various process techniques described above. Molds manufactured by these systems can be suitably used for manufacturing of FRP components for aerospace, automobile, wind turbine blades, sports articles, components for defense, recreation, general, and electrical engineering components. FUTURE WORK Further study can be done for shrinkage, impact strength, fracture toughness, dynamic properties in various modes, weight loss by TGA, and fatigue properties. REFERENCES. Henry Lee, Kris Neville, 98, Handbook of Epoxy resins, a Mcgraw-hill book company, USA,. Jeffery L Reynolds, Rajesh H Turakhia, George Chennakattu Jacob, Marty J Null, Nov 8, High Tg epoxy systems for composite applications, US, US /945 A. Mele, March 958, Cutting production costs and time with epoxy resins press dies, Plastics Technol. 4. AVRO, Dec 956, cuts cost with plastic tooling, Am. Aviation, 5. test standard for tensile strength, - for reinforced and neat epoxy system 6. test standard for strength, -78 for and neat epoxy system 7. test standard for strength, -78 for and composite epoxy system 8. 9 for measurement of initial mix viscosity. ABOUT THE AUTHORS Dr Mahesh Soni GM R&D and Business Development. He has a doctorate (Ph.D) in polymer composites. Dr Soni has years of rich experience in the field of polymeric resins, formulations and application development in the field of composites, electrical, civil and coatings. He has worked for 7 years outside the India and has rich experience of serving global customers for product development and technical services. Dr Utkarsh Shukla Manager R&D. He has a doctorate in Polymer Chemistry with 5 years of Research and Development experience in the field of Polymers. Himanshu Dhol Asst Manager Application Development. He has a bachelors degree in Plastic Engineering and has 8 yrs of experience in composites processing industry.
Paresh Raiyani Executive Application Development. He is masters in Science and has 5 years of experience in polymer and composite industry. Page 7 of 7