NEXIMID® MHT-R in short
Nexam Chemical introduces a new ”easy to process” resin that is primarily intended for use within the aerospace industry. Other areas, such as machine, general industry and transport sectors will also benefit from this high property material. The new resin, NEXIMID® MHT-R, is intended for small to medium sized production volumes of high-temperature composites by Resin Transfer Moulding (RTM). Temperature properties such as Tg is superior to most other materials and polyimides on the market. Characterization of mechanical properties is ongoing and more results is expected within the coming 6 months.
NEXIMID® 100 (PEPA)
NEXIMID® 400 (EBPA)
NEXIMID® MHT-R is a polyimide resin which is based on Nexam Chemical’s crosslinkers NEXIMID® 100 (PEPA) and the Nexam Chemical unique NEXIMID® 400 (EBPA) in combination with 6-FDA.
The resin is a new product on the market and has a unique combination of advantages such as:
- Temperature performance, with a high softening temperature from 330°C and up to 420⁰C via post-curing.
- Very low melt viscosity at processing temperatures enables superior processing properties
The above unique combination of advantages makes it suitable for manufacturing of high-temperature composites with RTM, which is beneficial from both a time and cost perspective for the users.
The resin is provided as a Dark amber solid or light yellow coarse powder or solid in room temperature. Melting of the power occurs between 100-120°C and viscosity is below 1000 mPas. Curing onset is about 320°C and curing maximum is at 370°C. Safety Data Sheet (SDS) can be ordered here.
Processing of the resin in a Resin Transfer Moulding Process is illustrated in Figure 1. The NEXIMID® MHT-R resin is an easy processable resin due to low melt viscosity, ability to be exposed to melt temperatures below curing temperature for a very long time without forming a gel and a distinct curing behaviour at temperatures around 370°C.
Figure 1. Example of process cycle for NEXIMID® MHT-R resin
Temperatures for the resin during a production cycle:
- Resin melt temperature: 200-250°C
- Crosslinking onset: 320°C
- Crosslinking temperature 370°C
- Post curing temperature 390-440°C
The post curing is normally run as a discrete step in an oven after that the part has been demolded and taken out of the RTM process.
Viscosity as a function of temperature for the NEXIMID® MHT-R resin is showed in Figure 2. The viscosity continuously decreases with increasing temperature up to temperatures around 250°C and remains below 600 mPa s in the temperature interval between 250°C and 320°C. Above 320°C the viscosity increases due to chemical reaction/crosslinking.
Figure 2. Viscosity as a function of temperature for NEXIMID® MHT-R resin
Post curing (example):
The post curing cycle can be divided into two steps. The purpose with Step 1 is to finally cure all unreacted triple bonds that have not reacted in the initial curing during the process. In this step inert atmosphere N2 or vacuum is used together with a post curing temperature of 400-440°C.
In Step 2 the intention of a second post curing step is to improve performance and increase resistance towards degradation by blocking non reacted or partly reacted triple bonds by using oxygen containing atmosphere (air). Temperature should be the same as in Step 1.
Binders for fixation of fibre preforms:
Reactive binders for fixation of a fiber pre-form are available. The binders are NEXIMID® A57 and A58. A57 is a mono functional binder that reacts with the resin and A58 is a bi functional binder. Each binder melts at a specific temperature and upon cooling glues the pre-form together. During processing the binders react with the resin upon curing. The reaction is an addition reaction and no volatiles are formed during the process.
Viscosity at different temperatures
In Figure 2 the shear viscosity as function of temperature is shown. The temperature ramp is used in the characterisation was 5⁰C/min.
Gel time measurements of NEXIMID® MHT-R at 330°C
Figure 3. Determination of Gel Point
From the graph in Figure 3, gel time can be determined as the crossover point where the elastic component becomes larger than the viscous component. This occurs after about 18 min (1080s). Gelation, according to the definition given by the standard, thus occurs at this temperature. This also indicates that the curing reaction of the MHT-R resin starts slowly already at 330°C.
Glass temperature (Tg )for the non-post cured resin is about 330°C. After post curing the Tg increases from 330°C up to 420°C or above depending on the post curing cycle.
Example of the potential of the resin regarding Tg property:
Figure 4. Example of the potential of the resin regarding Tg property
Mechanical properties from molded parts
Results from first produced test plates (initial tests) where the fiber T650/35 3K 309NTGP2 from Cytec was used indicates that the mechanical performance regarding E-modulus and Strength from tension measurements is well in the level of other high temperature polyimide composites using the same fiber. The same is also valid from Short Beam shear characterization of Strength as well as for Modulus and Strength measured by Flexure testing.
 P Fernberg, G. Gong, P. Mannberg, Processing and properties of new polyimide composites with high temperature ability, June 2014.
 Process development, test plate manufacturing and mechanical testing has been made by Swerea SICOMP, Piteå, Sweden.