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Cost-competitive solutions are key to the further penetration of composites in the aerospace industry. To help its customers meet this challenge, Huntsman has developed new advanced materials based on new chemistries for “direct process” technologies.
(Published on June-July 2005 – JEC Magazine #18)
BY PHILIPPE CHRISTOU, PRODUCT CREATION MANAGER, HUNTSMAN ADVANCED MATERIALS (BASEL)
Manufacturing of structural parts through direct process is now one of the major technologies currently used in aerospace applications. Its development has been slowed down by two characteristics generally encountered with available resin systems: lack of toughness and processing conditions (viscosity/ temperature/open time).
Taking those facts into consideration, Huntsman Advanced Materials Product Creation Department propose new solutions to the market based on new and patented chemistries.
A new RTM system based on patented benzoxazine/epoxy chemistry is proposed. The chemistry of LMB 6458 RTM solution involves the homopolymerisation of benzoxazine ring-forming oligomers containing hydroxyl and tertiary amine groups. Those oligomers can act as hardener for epoxy resins to form a thermosetting resin without releasing volatiles (fig.1). The use of a unique and patented benzoxazine building block makes this new RTM system to combine superior toughness, high glass transition temperature and modulus under dry and wet conditions because of very low moisture absorption, superior thermal oxidative stability. Benzoxazine/epoxy chemistry for structural parts is in its infancy. Research at Huntsman is still ongoing on order to improve processing to improve the processing conditions of LMB 6248, which are still a little bit less “friendly” than current qualified but brittle aerospace RTM epoxy/amine resin systems. Standard epoxy/amine chemistry novelties are also in development.
Very high levels of toughness can be reached using a new proprietary toughner. The one component LMB 6285 system has been developed mainly for the RFI process, but it can also be processed through RTM if adapted conditions are accepted (see figures). High glass transition temperature is associated to very high fracture energy (2.5 times higher than the level of current aerospace RTM epoxy/amine resin systems), one of the main characteristics of this new system.
Injection at room temperature is the key characteristic of the LMB 15X RTM system: it is a three-component epoxy-hybrid system (patentability procedure running) presenting a very low viscosity at room temperature (less than 100mPa.s) with a very long open time (up to 6 hours). Fracture energy is not reduced compared to currently used RTM systems processed at much higher temperature (100±20°C). This system would facilitate the production of large parts.
The charts (fig.2) present some of the key characteristics of the new systems compared to two commercial epoxy systems currently qualified for the aerospace market. In most cases, these new advanced materials solutions show superior performance. Their stringent properties are in line with the current and anticipated future requirements of the aerospace industry and will continue to impact manufacturing costs in a way.