Paper - 10
INNOVEX® Polyolefin a novel foam enhancement technology for LDPE foams
Sergio Torres-Giner, Carlos Vázquez-Torner, José Luis Feijoo-Gómez
FERRO SPAIN, Specialty Plastic Division (PCEM), Almassora, Castellón, 12550, Spain
Nowadays foaming offers several benefits such as
weight reduction and efficient thermal insulation to
polyolefins processors. One of the most important
applications of flexible polymer foams is found in the
packaging industry acting as impact energy absorbers in
which the mechanical behavior in compression is one of
the most desired characteristics. Ferro, as a leader in the
technology for nucleation in the extruded polystyrene
(XPS) foams market, has recently developed a new foam
enhancement masterbatch that improves the mechanism of
nucleation and reinforcement in polyolefin foams.
This technical paper presents and describes the
benefits of the novel Ferro’s masterbatch INNOVEX®
LD-0392NU on extruded non-crosslinked low density
polyethylene (LDPE) foams. From a structural point of
view, the presence of this new nucleating agent made
possible to reduce the cell size and the open cell content
when compared to a typical talc masterbatch at same
process conditions. Furthermore, regarding the
mechanical properties, Ferro’s masterbatch produced an
overall improvement in the compression performance that
was achieved due to a severe reduction of the number of
cells that break during compression. The new masterbatch
is based on the Ferro’s proprietary technology that is
commercialized under the trade name of INNOVEX®.
Today the polyolefin foams represent a fast growing
segment within the polyolefin market. Polyolefin foams
can be produced in a great variety of densities, ranging
from a very few kg/m3
to solid polymer density. Low
density polyethylene (LDPE) foams habitually present a
closed-cell structure, which makes them suitable for
applications where flexibility is important as well as
provides certain chemical resistance, thermal and
electrical insulation. Such versatile properties make LDPE
foams ideal for packaging applications but also open up
new possibilities in weight and energy saving for other
industries such as construction, transportation, insulation,
sports and leisure, and agriculture (1). Additionally this
corresponds with the sustainable trend in modern society
to create new products with the consumption of fewer raw
The industrial process for non-crosslinked foams
consists basically on the direct extrusion in a tandem
extruder of a multicomponent formulation including a
LDPE resin, a physical gas and a chemical blowing agent
and/or nucleating agent. Colorants, stabilizers, and other
additives are frequently added to obtain the desired
properties. After the residence time required for
dissolving the gas in the polymer and cooling the melt, the
high-pressure drop at the extrusion die exit causes the
instantaneous expansion of the gas encapsulated inside the
polymer matrix that generates the foam.
Ultrathin mineral fillers, i.e. inorganic structures
below 1μm, represent a novel generation of functional
nucleating agents for producing a large number of
heterogeneous nucleation sites and retarding the bubble
growth in the early stage of the foaming process. The
combination of such low-sized particles with polymer
foaming technologies can lead to the achievement of
novel foams with improved cellular structure that at the
same time present an increase in the macroscopic
properties (2). Not only the particle size but also the
particle shape and the surface chemistry of the particles
play an important role on the bubble formation. Typically
non-crosslinked low density LDPE foams have a mean
cell size of ca. 1,500 microns by using conventional
nucleating agents such as micrometric lamellar talc.
However, the uniform dispersion of intercalated
organomodified montmorillonite has led to reduce cell
sizes and narrower the cell size distribution in LDPE
foams (3). A recent study (4) has also shown that the
addition of silica nanoparticles produced an improvement
of the cellular morphology in LDPE foams, not only in
achieving reduced cell sizes and increased cell densities
but also in cell size distribution homogeneity. In other
polyolefin foams, for instance polypropylene, the
incorporation of nanoparticles has not only improved the
cellular morphology but has also dramatically increased
the melt viscosity and melt strength, which lessened the
occurrence of cell coalescence (5).
The main objective of this work is to study the effect
of Ferro’s novel nucleating agent based on ultrathin
natural clays on the morphology, thermal and mechanical
properties of non-crosslinked LDPE foams. The
relationship between the cell morphology and the foam
mechanical properties was also considered.
INNOVEX® LD-0392NU masterbatch was
fabricated using a twin-screw technology extruder at
FERRO’s facilities. The proprietary composition consists
of ca. 50% cocktail of non-modified ultrathin clays pre-
dispersed in an olefinic-based carrier. The particles are
based on an optimal combination of fibrillar and lamellar
morphologies. The resin employed was a LDPE for foam
extrusion with a density of 0.92 g/cm3
and a melt flow
index of 1.9 g/10 min at 190ºC. A commercial 50% talc
masterbatch was also used.
Industrial scale LDPE foamed rectangular sheets of
11 mm of thickness and an approximate density of 20
were obtained using a tandem single/single-screw
extruder at 650 Kg/h. Isobutane was used as physical
blowing agent. LDPE foams were obtained nucleating
with talc masterbatch and with INNOVEX® LD-0392NU
masterbatch, in both cases dosing at 1.0% and keeping the
same process conditions. LDPE planks of ca. 50 mm were
also produced by an industrial thermal welding process of
five LDPE sheets.
Density measurements of the LDPE foams were
performed by Archimedes principle using the density
determination kit for the AT261 Mettler-Toledo balance,
following the ASTM standard D1622-08. The open cell
content (OP) was measured with an Eijkelkamp 08.06
Lange air picnometer according to ASTM D6226-10.
Cellular structures were obtained by optical
microscopy. A Leica DM2500M optical microscope was
used. Cell size and anisotropy ratio were determined from
foams sections in the extrusion and wide direction using
an image processing tool based on the software Image J.
Thermal properties were analyzed by Differential
Scanning Calorimetry. Measurements were performed in
a Mettler-Toledo DSC 822e equipment. The thermal
program, under nitrogen atmosphere, consisted of: A
heating step from 40 to 200°C at a heating rate of
10°C/min, an isothermal step at 200°C for 3min to erase
thermal history, a cooling step (crystallization) from 200
to 40°C at 20°C/min and a heating step 40 to 200°C at
10°C/min. Samples mass was ca. 10 mg.
Compression tests were performed on LDPE planks
of 30 x 30 mm section using a universal testing machine
(Instron 5500R6025) at a strain rate of 10 mm/min and
maximum static strain of 75%. Collapse stress (σC) and
stress at maximum strain (σ-75%) were obtained from the
experiments following the standard ISO 604-2002.
All foam characterization was conducted at CellMat
Technologies SL (Valladolid, Spain).
Table 1 presents the density and the open cell content
for talc and INNOVEX®, respectively. This shows that
density is kept for both talc and INNOVEX® in the LDPE
foams and, more notably, foam samples nucleated with
INNOVEX® presented a reduction in the percentage of
open cells of ca. 47%.
Table 1. Cellular characterization of LDPE foams.
Sheets Density (Kg/m3
) OP (%)
Talc 19.31 ± 0.02 16.5 ± 0.9
INNOVEX® 19.55 ± 0.09 8.7 ± 2.6
Figure 1 shows the cellular images of the LDPE
foams nucleated with talc (left) and INNOVEX® (right),
respectively. In the figure it is possible to notice the lower
cell sizes obtained with INNOVEX® when compared to
talc. Besides it is worthy to mention that the distribution
of cell sizes seems to be much more regular.
Figure 1. Optical images, in the extrusion direction, of the
LDPE foams for: A. Talc; B. INNOVEX®.
Table 2 gathers the cell sizes in the three main
directions of the foams. This indicates that the influence
of the ultrathin clay particles used in INNOVEX®
produced a reduction of ca. 12% on the mean cell size for
the LDPE foams. Results also show that the cell
orientation was not modified by the presence of
INNOVEX®. In all cases cells were, to some extent,
oriented to the gravity.
Table 2. Cell morphology for LDPE foams.
Talc 1339 1379 1714 1477 1.26
INNOVEX® 1175 1226 1520 1307 1.27
* Cell Anisotropy Ratio: Dgrav / (Dext + Dwide)
The effect of INNOVEX® on the thermal properties
of the LDPE foams is summarized in Table 3. The similar
melting temperature (Tm), crystallization temperature
(TC), temperature difference between melting and
crystallization (ΔT) and crystallinity (C) of the foams
indicate comparable nucleating effect of INNOVEX® and
talc on the crystallization process of the LDPE matrix.
Table 3. Thermal characterization of LDPE foams.
Sheets Tm (ºC) TC (ºC) ΔT (ºC) C (%)
Talc 111.33 97.03 14.30 44.00
INNOVEX® 111.35 97.00 14.35 43.31
In Figure 2 the stress–strain curves of the LDPE
planks for talc and INNOVEX® are depicted. Both foams
presented a flexible behavior in the compressive test. The
observed response consists on a short period in which the
strain occurs immediately on applying the stress that,
above the collapse stress, is followed by a substantial
deformation as a function of the applied load.
Figure 2. Compression test carried out on the LDPE
planks for talc and INNOVEX®.
The compressive values obtained from the stress-
strain curves are reported in Table 4. This shows that the
cellular structure of the LDPE foamed samples reinforced
with INNOVEX® presented higher compression
resistance and lower residual strain. In particular, the
collapse stress (σC) and the stress at maximum strain (σ-
75%) were increased ca. 9 and 11%, respectively. The
increase in compressive strength is connected to the better
cellular structure in terms of cell size and open cell
Table 4. Mechanical characterization of LDPE foams.
Talc 4.2 ± 0.2 155.0 ± 3.9 17.4 ± 0.4
INNOVEX® 4.6 ± 0.3 173.9 ± 2.1 15.1 ± 1.6
The following equation (Eq. 1) can predict the stress
(σ) – strain (ԑ) relationship in compression for low density
flexible foams, considering isothermal conditions with
short timescales (6):
Where σC is the collapse stress, P0 is the pressure of
gas enclosed in cells and ρR is the relative density of the
foam, i.e. the foam density (ρf) divided by the density of
the solid polymer (ρs). This considers that, in the post-
collapse zone, load is supported partially by the cellular
structure and partially by the gas enclosed on the cells.
The gas contribution is directly related to the closed cells
fraction )1( OP . The lower the percentage of open cells
the higher is the stress needed to compress the foam.
From Eq. 1 the following term can be detached:
This is named ‘gas volumetric strain’ and it is related
to the contribution of the gas to the foam compressive
response. Curves for the LDPE foams were obtained from
the experimental data plotting the compressive stress
applied as a function of the ‘gas volumetric strain’ (see
Figure 3). According to this isothermal compression
model, the slope of the curve represents the effective
pressure of the gas contained in the cells and its axis
cross-point corresponds to the collapse stress value.
Figure 3. Stress vs ‘gas volumetric strain’ for the LDPE
Table 5 shows the value of the effective gas pressure
inside the LDPE foams obtained from the curves for talc
and INNOVEX®. This shows that, during compression,
the amount of pressure in the foams reinforced with
INNOVEX® was ca. 21% higher. This suggests that the
overall improvement in compression performance for the
LDPE foamed with INNOVEX® is achieved due to the
initial low fraction of open cells and, predominantly, to
the reduction of the number of cells that break during
The same reasons explain the lower residual strain
for the foams containing INNOVEX®. As the amount of
gas enclosed in the cells after the compressive cycle is
higher for these materials the recovery is quicker and
Table 5. Effective gas pressure enclosed in the cells.
Planks )1(0 OPP (KPa)
Talc 42.8 ± 0.9
INNOVEX® 54.0 ± 1.7
The current paper describes the main benefits of new
Ferro’s masterbatch INNOVEX® LD-0392NU for LDPE
foams. The ultrathin particles included in INNOVEX®
act as a novel nucleating agent that contributes to the
creation of a very regular celled LDPE foam with low cell
sizes and reduced open cell content. From a mechanical
point of view, the presence of INNOVEX® significantly
induces an improvement in the compression and recovery
performance which is achieved due to the generation of an
enhanced and reinforced cellular structure that reduces the
number of cells that break during compression.
On account of the above, the INNOVEX®
technology for polyolefins can be regarded as novel foam
enhancement platform to replace conventional foaming
additives such as talc and chemical blowing agents. The
technology can be successfully applied to the industrial
production of low density polyethylene foams with
enhanced mechanical performance or, alternatively, to
obtain same foams with lower densities without inducing
a mechanical impairment. Results can be extended to
polypropylene foams as well as other foams in flexible
and semi-flexible packaging applications.
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Hosseini, Sh. Khelgati Sh. Polymer Composites, 32,
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J.A. de Saja. Composites: Part B, 48, 40 (2013).
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Barcelona, Spain (2012).
Keywords: LDPE foams, INNOVEX®, ultrathin
particles, flexible packaging.
CellMat Technologies SL (University of
Valladolid) is acknowledged for all the foam samples
characterization. In particular we would like to thank
Dr. Miguel A. Rodríguez-Pérez and Dr. Cristina Saiz-
Arroyo for their technical support and helpful
discussion about the experimental results.