JEC COMPOSITES MAGAZINE - Issue #103 - March 2016 - 82

impact resistance

uniquely and specially adapted to produce exceptionally
lightweight, high-quality thermoplastic nonwovens. Unfortunately, due to commercial sensitivities, it is not possible to
discuss the details of these adaptations. The process (shown
in figure 1) used to produce all lightweight thermoplastic
nonwovens consists of three main stages: dispersion, forming and drying.
In the first stage, a dilute aqueous dispersion of shortchopped fibre (and other raw materials as appropriate) is
prepared. It is important to note that the "art" of dispersing
fibre is critical to both the quality and consistency of the
nonwoven. It is influenced by factors such as fibre type, fibre
dimensions (particularly the length-to-diameter ratio), fibre
cross-sectional shape, fibre surface chemistry, agitation and
processing conditions. Once the material is dispersed, it is
transferred to the forming section where the architecture
of the nonwoven is developed and a continuous fibre sheet
formed. The nonwoven is carried on a porous belt from the
forming section to the dryer ovens, where moisture is driven
off and any organic binder is dried and cured. An organic
binder can be added either at the dispersion stage or via a
coater. The resulting nonwoven can be prepared with an
areal weight ranging from 2 g/m2 (approx. 25 µm thickness)
to 2000 g/m2 (approx. 10 mm thickness) depending on the
selected operating conditions and machine configuration. A
typical short-chopped fibre nonwoven is shown in figure 2.
Until relatively recently, it was extremely challenging to
produce materials with an areal weight of <8 g/m2 but recent
process improvements have resulted in the ability to produce
high-quality materials at <4 g/m2.

Thermoplastic nonwovens
for mode I & II fracture toughness
The unique wet-laid process is exceptionally flexible and,
by careful selection of both raw material(s) and processing
conditions, a range of lightweight thermoplastic veils was

Fig. 2: Scanning electron micrograph (SEM) of a short-chopped fibre veil

82 jec composites magazine / No103 March 2016

More information
Key benefits of TFP's new Optiveil® lightweight thermoplastic
veils include:
- Delivering a proven increase in mode I and II fracture toughness of CFRP composites:
-Mode I - up to 160% improvement in GIC (initiation) and
up to 60% increase in GI PROP (propagation),
- Mode II - up to 350% improvement in GIIC (initiation)
and up to 430% increase in GII PROP (propagation).
- Ease of use due to the conformability and high porosity of
Optiveil® nonwovens.
- Lightweight for minimum weight addition.
- A broad choice of thermoplastic veils is available to ensure the
required performance and system compatibility. These include
polyimide, PEEK, PPS, PEI, polyamide and polyester.
- Providing a means to improve fracture toughness using
standard commercial manufacturing processes.

prepared for incorporation into fracture toughness studies
including those by Kuwata and Hogg [6, 7] and Sampson et
al. [8]. All the fibres used to form the veils were obtained
from commercial sources. The full fabrication details of
the composite laminates for the fracture toughness studies
can be found in the corresponding references and selected
details are highlighted here for clarity.
In the study by Sampson et al. [8], symmetrical unidirectional (UD) carbon fibre-epoxy laminates, each with a
nonwoven at the mid-point of the laminate, were prepared
using resin infusion. PPS veils with areal weights from 7 to
35 g/m2 along with an 11 g/m2 PEEK veil were investigated.
CFRP laminates with veil interleaves were then subjected to
mode I fracture toughness measurements according to the
ISO 15024:2001 methodology (i.e. a vertical tensile load was
applied to a pre-cracked double cantilever beam sample to
initiate in-plane propagation as shown in figure 3).
The laminates were also subjected to mode II fracture toughness testing using an end-notched 4-point bending method

Fig. 3: Diagram showing mode I fracture toughness opening mode testing

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #103 - March 2016