Medical Design Briefs - March 2023 - 18

TECHNOLOGY LEADERS Tubing/Extrusion
High-Performance
Crosslinkable
Thermoplastic Elastomers
for Medical Applications
A
family of thermoplastic elastomers
(TPEs) crosslinked by irradiation
improve thermomechanical
properties and chemical
resistance at elevated temperatures. These
materials can be easily injection molded
and extruded into thin wall parts and tubing
as well as wire and cable coatings.
This article presents an overview of
these TPE families and markets and
where they are used. It reviews the advantages
of the irradiation crosslinking
process and the improvements imparted
to plastics and elastomers, particularly to
the COPA family of thermoplastic.
TPE Overview
TPEs are unique synthetic compounds
that combine some of the properties of
rubber with the processing advantages
of thermoplastics. They consist of a number
of families, the majority of which are
listed in Table I.
Property
Specific gravity
Hardness (Shore)
SBCs
0.90-1.2
Compression set @ 100°C Poor
High temperature (°C)
Low temperature (°C)
Fluid resistance
100
-70
Poor
Like rubbers, the TPE key properties
are hardness and stiffness or flexibility.
The families overlap each other in these
characteristics. The TPUs, COPEs, and
COPAs offer the hardest and stiffest
grades available. Because of this, they are
sometimes referred to as the engineering
TPEs. This group is also the more expensive
and are often used in high-end
markets.
The TPO Family. Thermoplastic polyolefin
(TPO) elastomers are comprised
of various mechanical blends of polyolefin
resins. The components for these
blends are readily available and are relatively
inexpensive. They have found
application in less demanding large-volume
areas, such as wire and cable jacketing.
More
recently, a group of flexible polyolefins
has been added to this group.
They are sometimes called the FPOs or
POEs. These flexomers are made in-situ
TPOs
0.89-1.0
TPVs
0.90-1.0
30A-75D 60A-75D 40A-50D
Poor
120
-60
Poor
-60
Excellent
Table I. Performance characteristics of different TPE families.
Good/ excellent
135
TPUs
1.1-1.3
70A-75D
Fair/good
135
-50
Fair/ excellent
and, unlike the physical blends, these
materials come directly from the reactor
ready to be extruded or molded.
A number of these POEs are based on
metallocene catalyst technology. They
have been finding application in flexible
packaging, resin modification, medical
tubing, and blood bags.
The SBC Family. The SBC family, or
styrenic thermoplastic elastomers, represent
a class of elastomers introduced
in the mid I960s. The most noted of
the SBC elastomers are the SBS and
the SEBS. The SIS elastomers are also
a member of this family. Styrenic thermoplastic
elastomers obtain their thermoplastic
properties because of their
structure. This is due to the multiphase
composition in which the phases are
chemically bonded by block polymerization.
In all cases, at least one phase is
a styrenic polymer that is a hard phase
at room temperature. The other phase
COPEs
1.1-1.3
40A-82D
Fair
160
-65
COPAs
1.1-1.2
75A-72D
Fair/good
150
-65
Good/excellent Good/excellent
18
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Medical Design Briefs - March 2023

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