10.2417/spepro.005830
New impact-modified
polycarbonate/polyester blends
Huanbing Wang and Hongtao Shi
A refractive index matching approach can be used to develop
transparent/translucent materials with improved impact strength and
transmittance properties.
Polycarbonate (PC) materials are a group of thermoplastic polymers
that contain carbonate groups. PC materials generally have good
impact strengths, as well as high levels of optical transparency and heat
resistance. PC substances, however, do have several deficiencies. For
example, PC has a relatively limited range of chemical resistance, and
the high melt viscosities of PC make it difficult to mold. Furthermore,
PC formulations that contain visual-effect additives (e.g., metallic pigments or mineral flakes) are often—even at room temperature—very
brittle. The addition of impact modifiers (IMs) to PC compositions is
a widely used approach for increasing the low-temperature impact
resistance of these materials. For instance, the ductile–brittle transition
temperature of PC can be lowered by adding polymers such as
acrylonitrile butadiene styrene (ABS) or methyl methacrylatebutadiene-styrene (MBS). With addition levels of only 1%, however,
these modifications cause significant decreases in the transparency (i.e.,
one of the key properties) of PC.
In a previous study, it was shown that the optical clarity from a blend
of two transparent and immiscible polymers can be improved by the
addition of a third polymer (which is selectively miscible with one of
the two original polymers).1 Through this work—based on matching
refractive index (RI) values—formulations for materials with good
transparency, improved chemical resistance, high flow, and lowtemperature ductility characteristics have been derived. In addition, it
has been demonstrated that by adjusting the ratio of immiscible PC and
polyester, the RI of the blends can be made to match well with the RI
of clear MBS or ABS.2
At SABIC, we have developed a new set of transparent or translucent impact-modified polycarbonate/polyester (PC/PE) blends, such as
our XYLEX resin.3 The transparency, low-temperature ductility, and
improved chemical resistance of XYLEX means that it is commonly
used in several applications (e.g., doors of washing machines, glasses
frames, and in-mold decorations). We have also been investigating
ways to improve the physical properties (i.e., strength and
Figure 1. Photographs of color chips molded from blends of
polycarbonate (PC), polyester (PE), and impact modifier materials.
A visual check is used to determine the transparency of each chip.
Photographs of PC/PE/K-resin (K-resin is a styrene-butadiene copolymer) chips were not obtained. Therefore, their images shown (on the
right) are of yellow panes. The transmittance and haze properties of
each chip are indicated. The rubber type and loading of each blend is
given in the orange boxes. TABS: Transparent acrylonitrile butadiene
styrene. MBS: Methyl methacrylate-butadiene-styrene. SBS: Styrenebutadiene-styrene. B: Rubber content of each impact modifier. F6855,
ST-100, F6843, F4050, and KR01 refer to commercially available
impact modifiers. PCCD: Poly(1,4-cyclohexylene dimethylene
terephthalate).
Continued on next page
10.2417/spepro.005830 Page 2/3
transmittance) of our PC/PE blends. We have learned that the opacity of PC blends is caused by the relatively high RI of aromatic PC
(about 1.58), which is higher than for most immiscible IM materials (e.g., aliphatic rubbery and/or siloxane components with values of
1.48–1.56). To prepare our transparent PC/IM blends, it is therefore
necessary to include a third phase that must meet two requirements.
First, this phase must be miscible with PC. Second, the RI of the third
phase must be much lower than both the IMs and the PC. We find that
materials—used as the third phase—with the lowest RI values require
the least amount of the material to be used in our blends. In addition,
we observe that the lower RI materials allow the PC properties to be
better maintained.
To create transparent blend materials with the use of our RI
approach, we require accurate RI measurements. For most transparent resins, this information can be obtained from their accompanying handbooks. For some transparent IMs, however, we must calculate
the RI based on the constituent components, because their structure is
complex and their composition can vary between different commercial
grades and suppliers. In cases where the IM is obviously opaque (e.g.,
for ABS), we estimate its RI so that we can blend the materials with
PC and/or polyesters. Furthermore, we can easily calculate the RI values of copolymers (i.e., two or more polymerized monomers) from the
contribution of each constituent component in the material.
Some polyesters are totally miscible with PC. In addition, it is possible to vary the components of their diol (i.e., two hydroxyl groups)
and diacid (i.e., two carboxyl groups) monomers to a large extent. As
such, the mechanical properties of polyesters can be widely
different. This characteristic of polyesters therefore provides us
with the opportunity to adjust the properties of our transparent/
translucent blends. Polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) are semi-crystalline polyesters, but
blends of these materials with PC are obviously not transparent.
We find, however that a number of other polyesters meet
our requirements. These include poly(1,4-cyclohexanedimethyl1,4-cyclohexanedicarboxylate), or PCCD, poly(1,4-cyclohexylene
dimethylene terephthalate), or PCT, glycol-modified PCT (PCTG),
and TRITAN4 (a copolyester—a modified polyester—manufactured by
Eastman). The merged glass transition temperatures of these materials
indicate to us that they are all miscible with PC. The RI of PCTG is
1.56, whereas the RI of its blend with PC ranges from 1.56 to 1.586
(which exceeds the values of most IMs). The application of this copolyester is therefore limited, and the properties of its blend are very different from those of PC. Although the RI of PCT is lower than PCTG,
we find that its heat deflection temperature (i.e., the point at which
a polymer deforms under a specific load) and impact properties are
far inferior to those of PC. The addition of PCT would therefore
decrease the heat resistance and impact strength of our PC blends. We
find that TRITAN displays the best balance between heat resistance
and impact strength among all the polyesters we considered. We performed a notched Izod impact strength test on this material. Our results
indicate that its ductile–brittle transition temperature is about 10◦C,
which is similar to that of PC. With the introduction of TRITAN to our
PC blends, we can therefore expect to maintain the desirable properties
of PC. In addition, we routinely use PCCD within our XYLEX product. The low RI of PCCD makes it a good candidate for blending with
PC, and we can use it to achieve clear blends with a wide range of RI
values (1.516 to 1.586).
We have also obtained the RI values of butadiene, styrene, acrylonitrile, and methyl methacrylate homopolymers as 1.515, 1.591,
1.515, and 1.491, respectively. We are thus able to calculate the RI
values of methacrylate-acrylonitrile-butadiene-styrene (MABS), MBS,
styrene-butadiene-styrene (SBS), and K-resin (a styrene-butadiene
copolymer made by Chevron Phillips) with different components
and compositions. In this way, we can use different pairings of
materials to prepare our transparent/translucent blends. These include PC/PCCD/MABS, TRITAN/PCCD/MABS, TRITAN/SBS, TRITAN/PCCD/SBS, and PC/TRITAN/K-resin. Images of color chips
molded from our PC/PE/IM blends are shown in Figure 1.
We have developed and prepared a new set of transparent/translucent
impact-modified polycarbonate/polyester blends that have improved
physical properties.5 We have used PCCD and/or the TRITAN
copolyester—blended with PC—as these substances are all miscible
with each other. In addition, we find that MABS, MBS, SBS, and Kresin can be used to toughen our PC/PE blends. We adjust the ratio
of the two resins so that the combined RI matches that of the impactmodifier material and to improve the overall transmittance of the final
blend. In our future efforts we will work on transparent blends with
reinforced glass fibers. We will also introduce some reactive building
blocks that will improve the compatibility, and thus transparency, of
our blends. It is therefore our aim to develop applicable blends with
balanced transparency, toughness, and strength characteristics.
Author Information
Huanbing Wang and Hongtao Shi
SABIC Technology Center
Shanghai, China
References
1. M. D. Hanes, Polymer blend clarity, US Patent 6040382, 2000.
2. J. B. Schlenoff, Compacted polyelectrolyte complexes and articles, US Patent 8114918,
2012.
Continued on next page
10.2417/spepro.005830 Page 3/3
3. https://www.sabic-ip.com/gep/Plastics/en/ProductsAndServices/ProductLine/xylex.html
Product webpage for XYLEX resin made by SABIC. Accessed 6 August 2015.
4. http://www.eastman.com/Brands/Eastman˙Tritan/Pages/Overview.aspx Product webpage for TRITAN copolyester made by Eastman Chemical Company. Accessed 6 August
2015.
5. H. Wang and H. Shi, New transparent/translucent impact modified polycarbonate/polyesters blends, Proc. SPE ANTEC, p. 2094805, 2015.
c 2014 Society of Plastics Engineers (SPE)