JEC COMPOSITES MAGAZINE - Issue #133 - March/April 2020 - 140

TECHNOLOGY resin

Fig.1: Cross-section of a vertically-infused transfer-moulded laminate demonstrating a uniform distribution of nanocalcite after infusion processing [4, 5].
Nanocalcite appears as small white dots

ed for composite processing and the polymer/particle interactions
needed for superior mechanical properties; and
- Particle size distribution enabling impregnation of the fibre reinforcement without filtration.
To illustrate the latter capability, Figure 1 shows a cross-section of a
cured laminate from a through-thickness infusion process [4, 5]. The
concentration is uniform from the top of the laminate to the bottom,
confirming that the nanoscale particles were not filtered out during
infusion. The particles are seen to be well-distributed even between
individual fibres.

Development of formulated and
masterbatch nanocalcite resin systems
The desirability of highly loading matrix materials for fibre composites with surface-modified inorganic nanoparticles was established
previously using amorphous spherical silica. Prepreg, pultrusion,
resin transfer moulding (RTM), and winding were used to produce
materials and parts with enhanced performance [e.g., 2-4, 6-11]. The
extensibility of the technology was demonstrated through successful implementation in various epoxy and bismaleimide formulations
and through use with various curatives.

Previous work examined the effect of nanocalcite particle concentration on the properties of a bisphenol-A epoxy resin [4]. This study
demonstrated the range and balance of properties that are achievable as a function of particle loading and synergies with various cure
chemistries. Important properties for composite matrix applications
were reported including modulus, fracture toughness, coefficient of
thermal expansion, cure exotherm, cure shrinkage, and hardness.
Based on this initial work, 3M recently developed a series of low-viscosity nanocalcite-modified thermoset resins in order to provide
differentiated resin solutions for use in composite processes such
as filament winding, pultrusion, resin transfer moulding (RTM),
high-pressure RTM (HP RTM), vacuum-assisted resin transfer
moulding (VARTM) and solvent-based prepregging [5]. Table 1 lists
the selected resin formulations featured in this discussion. A range
of important attributes are addressed in this material set: viscosity,
toughness, service temperature, and processability. From the standpoint of material development, each of these presents challenges of
maintaining particle stabilization, controlling particle-particle interactions, and balancing cured resin properties. The final nanocalcite
particle loading for these resins depends on the curative type and the
epoxy/curative ratio used. The matrix resins listed in Table 1 allow
loadings of 35 wt% for typical anhydride cures (8831, 8832, 8834)
and amine curatives (8833, 8836). For typical catalytic curing, 57
wt% can be achieved with MR 8830.

Nanocalcite-modified epoxy neat resin properties
Tables 2 summarizes neat resin data for selected nanocalcite-modified epoxy resins spanning a glass transition range of 120-220°C and
epoxy structures (i.e., Bis-A, Bis-F, cycloaliphatic) versus suitable
control systems. The neat resin properties of matrix resins 883X (X=
0-5) and the effect of nanocalcite concentration were reported previously [4, 5]. Summarizing Table 2, the inclusion of nanocalcite leads
to resin systems with a high modulus, high hardness, increased fracture resistance, low coefficient of thermal expansion (CTE), reduced
cure shrinkage, and reduced cure exotherm.
A unique feature of the nanocalcite-modified epoxy systems is the simultaneous improvement in modulus and fracture toughness. Stiffness
and toughness are competing properties in thermosets. Strategies to
increase modulus can result in the creation of a brittle, lower toughness
resin system. Alternatively, traditional toughening strategies, such as
the incorporation of core-shell rubber materials, can cause a decrease

Tab.1: Calcite resin portfolio

140

Matrix resin

Description

Processing/attributes

8830

Bis-A epoxy

Masterbatch form of material in [4]

8831

Epoxy formulated for low viscosity

Low viscosity facilitates winding, pultrusion for anhydride cures

8832

Epoxy with toughening agent

Significantly increased toughness for anhydride cures

8833

Epoxy formulated for low viscosity with lower particle size

Formulated for RTM, VARTM, HP-RTM and winding with amine curatives

8834

Cycloaliphatic epoxy

Low viscosity for vacuum infusion; capable of very high service temperature; high particle
loading

8835

Epoxy with solvent (acetone)

Suitable for solvent prepregging processes

8836

Bis F epoxy with lower particle size

Formulated for RTM, VARTM, and HP-RTM with amine curatives

jec composites magazine / N°133 March - April 2020
JEC COMPOSITES MAGAZINE - Issue #133 - March/April 2020

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