Q2. What is the dominant polymer in the advanced composites industry?
4.1 BMI/EpoxyEpoxy resins are the dominant polymers in the advanced composites industry, particularly in the commercial aerospace sector.
Q3. What is the way to improve the processability of a polymer?
Another route for improving the processability is to introduce bulky, soluble side groups into the monomer backbone to enable dissolution in industrially acceptable solvents and to lower the material’s melting point.
Q4. What is the main issue with using thermoplastics as toughening agents?
3.3 Low molecular weight thermoplasticsOne of the primary issues with using thermoplastics as toughening agents in advanced thermosets is that they inherently raise the viscosity of the uncured resin.
Q5. What is the effect of nanotubes on the mechanical performance of BMI resins?
The loss in conductivity can be partially accounted for by using nanotubes of a longer length, whilst having little to no impact on the mechanical performance [123].
Q6. What is the name of the family of high performance thermosetting polymers?
Bismaleimide (BMI) resins are a family of high performance thermosetting polymers that possess a range of attractive properties for industrial applications, particularly in the aerospace materials sector.
Q7. What solvents were found to be soluble in the BMI monomer?
A BMI monomer containing both fluorenyl cardo and aryl ether linkages was found to be soluble in a range of solvents including acetone, toluene and dichloromethane (DCM).
Q8. What is the challenge associated with the development of such materials?
The challenge associated with the development of such materials, particularly in an aerospace environment, is the balancing of a large, reversible strain capability, high activation temperature and sufficient mechanical properties.
Q9. What is the way to improve the mechanical properties of carbon nanotubes?
The interfacial bonding between a carbon nanotube and a matrix resin is typically poor due to the atomically smooth surface of the nanotubes [121]; however, it is possible to functionalise the surface of the nanotubes to introduce groups that can react with the curing resin to form strong covalent bonds.
Q10. What can be changed to improve the thermal performance of thermoplastics?
Factors that can be changed include thermoplastic loading, backbone structure, molecular weight, molecular weight distribution and end group functionality.
Q11. How much weight is needed to produce effective BMI prepregs?
The addition of a very low weight percentage of such a polymer (ca. 1 wt%) is sufficient to provide the necessary improvements in resin flow and thus enable the production of effective BMI prepregs [77].
Q12. What is the effect of particle toughening on the performance of BMI resins?
Particle toughening has also been shown to increase the compression after impact performance of BMI resins, with 60 MPa improvements being obtained [78].
Q13. What is the effect of the modifications on the impact strength of the polymer?
As expected these modifications lead to an increase in the energy absorbing ability of the materials due to a greater degree of molecular freedom, thus resulting in improved impact performance.
Q14. What is the effect of the new monomer on the char yield in air?
The new monomer improved the char yield in air when incorporated into a thermoset from 1.8 to 50 % at 700 °C, whilst maintaining a high Tg of over 300 °C.
Q15. What is the downside to functionalisation of carbon nanotubes?
The downside to this functionalisation is that it often leads to degradation in the mechanical and electrical performance of the nanotubes asthe delocalised system is disrupted.
Q16. What is the main reason for the high degree of crosslinking in bismaleimides?
The high degree ofcrosslinking is responsible for the excellent elevated temperature performance of these materials, however it is also the reason behind the biggest drawback associated with BMIs: the cured polymers are brittle, with low fracture toughness.
Q17. What is the obvious method for introducing new or refined properties into conventional BMI systems?
2. DEVELOPMENT OF NOVEL BMI MONOMERSPerhaps the most obvious method for introducing new or refined properties into conventional BMI systems is to alter the monomer’s chemical structure.
Q18. What is the common example of a molecule that can be used to improve processability?
A commonly used example of such a molecule is 4,4’-bis(2-(1-propenyl)phenoxy)-benzophenone (marketed by Evonik as Compimide TM123, Figure 8), which imparts improved processability and toughness at the cost of a decrease in Tg.
Q19. What is the way to reduce crosslink density of cured polymers?
as has been described previously, the crosslink density of the cured material can be decreased by increasing the molecular weight of the monomer, or the distance between the two functional end groups using chain extenders such as diamines [34].
Q20. What is the effect of the introduction of maleimide or amine groups on the particle surface?
In this case, the introduction of maleimide or amine groups to the particle surface lead to increases in Tg (up to 15 °C) and reductions in CTE (up to 8 °C/ppm) compared to unmodified particles.
Q21. What is the effect of graphene oxide on the thermal performance of the studied BMIs?
the thermal degradation of the studied BMIs has shown to be unaffected by the addition of graphene oxide, although the glass transition temperatures of the materials have not been investigated or reported.
Q22. What is the main reason why the cured composite is prone to bubbles?
this reaction leads to the evolution of water, increasing the risk of bubbles or voids forming in the cured material, which is particular problem in a reinforced composite.
Q23. What are the characteristics of BMI monomers?
BMI monomers (the general structure is outlined in Figure 1) are molecules that are terminated by two maleimide functional groups, often containing multiple aromatic moieties in order to enhance their cured properties.
Q24. What was the thermal decomposition temperature of the cured BMI monomer?
the thermal decomposition temperature of the cured material was over 400 °C, however no information was given with regards to the Tg or mechanical properties of the cured resin [41].
Q25. What are the different pathways through which BMI/epoxy blends can co-re?
There are a number of different pathways through which these two materials can co-react to form a single three dimensional network thanks to the varied reactivity of the two functional groups of interest; epoxies and maleimides.
Q26. What is the way to improve the thermal stability of a BMI?
This is a very exciting development as it offers the opportunity to introduce reactive toughening agents, albeit with a Tg penalty, without apparently compromising the thermal stability behaviour of the cured BMI blend.