Dow Specialty Elastomers for Thermoplastic Polyolefins - White Paper - Dow Elastomers
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White Paper
Dow Specialty Elastomers for
Thermoplastic Polyolefins
Updated: August, 2013
Author: Jim Hemphill, Senior R&D Manager, Dow Elastomers, The Dow Chemical Company
Dow ElastomersDow Specialty Elastomers for Thermoplastic Polyolefins
Abstract Introduction to Rigid TPOs are made with a majority
Thermoplastic Polyolefins polypropylene component, with added
The Dow Chemical Company (“Dow”) is a
ingredients to attain an overall balance of
global leader in science and technology, Thermoplastic polyolefins (TPOs) gener-
properties. Rigid TPO formulation devel-
providing innovative chemical, plastic, ally refers to a class of plastic used in
opment starts by selecting an appropriate
and agricultural products and services a variety of markets and applications –
PP, and adding just the minimum modi-
to many essential consumer markets. In especially in the transportation sector,
fier level to achieve acceptable ductility,
the arena of thermoplastic polyolefins including automotive exterior and inte-
while keeping rigidity (as measured by
(TPOs), Dow has developed a breadth of rior fascia. The TPOs are usually injection
flexural modulus) as high as possible.
specialty plastics and elastomers to help molded into the desired article, though
This toughness/stiffness balance is shown
our customers meet current and emerg- there is increasing use of sheet and pro-
in Figure 1.
ing specifications in a variety of markets, file extrusion/thermoforming and
applications, and processes. other processes. A typical rigid TPO compound starting
point would be composed of:
Advanced Dow elastomer technology, TPOs are generally produced by the blend-
coupled with our in-depth knowledge ing of polypropylene (PP) with elastic • 56% Polypropylene – generally an
of automotive TPO compound require- ethylene copolymers (polyolefin elasto- impact copolymer (ICP) or a homo-
ments, helps Dow to tailor solutions mers or POEs), and the addition of other polymer (hPP)
based on desired compounding and fillers and additives. The specific blending • 24% Elastomer
processing characteristics, as well as amounts are dependent upon the overall • 20% Talc
finished part performance and appear- balance of properties to meet performance • Plus stabilizer and additives, as needed
ance. Specialty elastomers from Dow are specifications and desired processing for the part’s durability
used as copolymers with polypropylene equipment used for an application.
This type of compound is often used for
to enhance impact resistance, improve
TPO ingredients generally include: injection molded automotive interior or
weatherability, minimize weight, and
• Polypropylene (including homopolymer, exterior fascia and generally targets duc-
contribute to the recyclability of parts.
impact copolymer, or others), which tility at -30°C and high part rigidity [1].
Dow materials can also improve
generally provides rigidity and tempera-
the processability of TPO compounds, In contrast, flexible TPOs contain a major-
ture stability
enhancing productivity and economy in ity phase of elastomer with PP added for
• Elastomers, which give flexibility and
injection molding, sheet extrusion/ther- improved temperature stability [2].
impact strength
moforming, and other processes.
• Talc or other mineral fillers, which A typical soft TPO compound starting
This paper will focus on TPO formulary, impart higher part stiffness and dimen- point would be composed of:
fabrication processes, means of elastomer sional stability • A base polymer matrix of:
incorporation, and recommendations for • Other additives (including antioxidants, ––70% High Melt Strength Elastomer
TPO elastomer selection. plasticizers, and additives for ignition ––30% Branched or Conventional
resistance, scratch and mar resistance) Polypropylene
for improving end-use performance • Plus stabilizer and filler addition (min-
and durability eral filler/plasticizer), as desired for cost
and performance
This type of compound can be extruded
Figure 1: Balancing TPO Properties
into a sheet and thermoformed for use in
F automotive interior skins that are com-
L I
E M petitive with products like vinyl, leather,
X Threshold Impact P and thermoplastic urethanes (TPUs).
A
C Other applications are growing through
M
O T the use of flexible extrusion profiles and
D blow molding applications mentioned in
Modifier Level the next section.
The threshold impact will generally dictate the modifier
level needed and the resulting compound stiffness.
™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow
®
2TPO Fabrication Processes Thermoformed TPOs There is further development of flex-
ible TPOs for use in thermoformed
Any TPO development must consider the In the past, TPO compounds have gener-
instrument panels, door panels, and non-
process that will be used to transform the ally not fared well in thermoforming
carpeted flooring. As noted earlier, a high
compound into its final form. The follow- applications because they could not be
melt strength elastomer is used as the
ing sections give a brief description of reliably processed after they reached
majority component and combined with
these processes and some of the consider- their softening point. Advances in both
a branched PP [7]. The high melt strength
ations for the application that may affect polypropylene and elastomer tech-
elastomer also gives the desired benefit
elastomer selection. nologies are now making this more of a
of a lower gloss (i.e.,There is no right or wrong way to intro- Elastomer Design and Selection ENGAGE™ Polyolefin Elastomers (POEs)
duce the elastomer to the TPO. However, that offered improved control of molecu-
The elastomer manufacturer has a variety
there are inherent benefits and risks lar architecture using metallocene
of catalysts, processes, and monomers to
which may influence the direction of the catalysis and processing capabilities.
create elastomers that are useful for TPOs.
manufacturer, compounder, or processor These novel elastomers combined several
(see Table 1). Dow’s use of INSITE™ Technology in benefits which led to improved TPO
the early 1990s enabled the creation of compound performance and their rapid
Furthermore, the selection of the elasto-
success as replacements for other ethylene
mer may be influenced by the capabilities
of the manufacturer (PP producer, com-
pounder, or molder/extruder), the other
TPO compound ingredients, and desired Figure 3: Low Temperature Ductility of Various Ethylene/Alpha-Olefin Elastomers(1)
end-use performance. In many instances, -35
the best cost/performance balance comes
Glass Transition Temperature (°C)
from compounding a lower-performing -40
PP with a high-performance elastomer Propylene
-45
versus use of a polypropylene impact
copolymer or reactor TPO (r-TPO). -50
Butene
-55
-60 Octene
-65
0 5 10 15 20 25
Crystallinity (%)
(1)
Data per tests conducted by Dow. Test protocols and additional information available upon request. Properties shown are typical, not to be
construed as specifications. Users should confirm results by their own tests.
Table 1: Elastomers Introduction for TPO Applications
Method Positives Deltas
PP In-Reactor
Adding ethylene to the PP reactor to create • Excellent dispersion of the ethylene comonomer • Often lower throughput on the PP train (higher cost)
ethylene-propylene (EP) elastomer segments for • Lower elastomer needs for compounding or • The reactor elastomer is generally not as efficient as higher
impact copolymer (ICP) or a reactor TPO (r-TPO) for at-press and in-line processing performance elastomers – especially for low temperature
impact strength
• Still likely need to compound filler/additives for TPO use
PP Post-Reactor
Feeding an elastomer into the PP compounding • Often higher manufacturing throughput of the • Capital may be needed for elastomer introduction
operations downstream from manufacturing base polypropylene • Still likely need to compound filler/additives for
• Increased flexibility in formulation versus TPO use
in-reactor addition
Compounding
Adding an elastomer to PP, fillers, and other • Greatest degree of flexibility • Capital requirements for compounding operations
additives in a compounding operation • Multiple sources of ingredients • Logistics/heat history
• Ability to optimize cost and performance
At-Press or In-Line
Adding an elastomer directly to the ingredients • Bypasses compounding operation and • Generally less efficient dispersion than with compounding
stream in an injection molding or extrusion reduces cost • Possible need for new capital and higher elastomer levels to
operation • Can modify elastomer levels as needed meet impact requirements
™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow
4copolymers like ethylene propylene diene Figure 4: Elastomer Dispersion in TPO(1)
monomer (EPDM):
EPDM
• Low glass transition temperature –
increasing alpha-olefin chain length
from propylene (C3) up to butene (C4)
and octene (C8) gives enhanced low
temperature impact performance (see
Figure 3, page 4) [11]
• Narrow molecular weight distribution
and low branching levels – contribute
to improved dispersion of the elastomer
in the polypropylene (see Figure 4)
• Pellet form – allows continuous
compounding and bulk handling of
the elastomer
POE
Further development of INSITE™
Technology has resulted in the ability to
modify branching and molecular weight
characteristics to produce high melt
strength grades of ENGAGE™ HM POEs.
These elastomers demonstrate benefits
in extrusion, thermoforming, and blow
molding applications, as well as improv-
ing aesthetics (reductions in gloss and
flow lines) in injection molded parts [12].
(4.5 mm = 1 micron)
Table 2: Summary of Elastomer Design Effects on TPO Performance [13]
Low Heat
Flexural TPO Injection TPO
Elastomer Effects on TPO Performance(1) Temperature Distortion Melt Strength Gloss
Modulus Molding Flow Shrinkage
Impact Temperature
Decreasing Comonomer Chain Length ↓ ↔ ↔ ↔ ↔ ↔ ↔
Decreasing Elastomer Crystallinity
(lower density) ↑ ↔ ↔ ↔ ↓ ↔ ↓
Decreasing Melt Index (increasing
Molecular Weight [MW]) ↑ ↔ ↔ ↓ ↑ ↑ ↑
Decreasing Elastomer Content ↓ ↑ ↑ ↑ ↑ ↔ ↑
Decreasing Molecular Weight
Distribution (MWD) ↑ ↔ ↔ ↓ ↔ ↓ ↑
Decreasing Branching ↑ ↔ ↔ ↓ ↔ ↓ ↑
(1)
Data per tests conducted by Dow. Test protocols and additional information available upon request. Properties shown are typical, not to be construed as specifications. Users should confirm results by their own tests.
™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow
5Table 3 demonstrates Dow’s breadth of Using this selection guide, Dow recom- Summary
specialty elastomers that can be used for mends starting TPO injection molding
Elastomer technologies continue to
TPO modification to achieve a desired formulations with the desired PP and
evolve to meet the cost/performance
balance of properties and processing. filler/additives and adding progressively
needs for TPO applications. The elasto-
higher levels of the “Better” elastomers
Beyond these products, there are other mers evolution will need to continue to
until the desired ductility is achieved.
innovative materials that are beginning coincide with advances in materials (poly-
Further optimization of the TPO com-
to enter the marketplace, including propylene, fillers, and additives), and
pound can then be made to achieve the
propylene-ethylene elastomers [14] and process technologies. Many of the trends
desired balance of performance. Likewise,
olefin block copolymers [15, 16]. for performance are well established for
TPOs for extrusion, thermoforming, or
existing applications and processes, and
The Dow specialty elastomers are further blow molding can be formulated with
further development is being focused on
divided into TPO performance levels and high melt strength elastomers (usually
emerging technologies.
processing subsets as shown in Table 4 an elastomer havingReferences [5] K.W. Walton, et al., “The Role of [9] R. Leaversuch, “Blow Molding Gets
Impact Modifiers on TPOs Requiring Green Light in Detroit,” Plastics
[1] J.J. Hemphill, et al., “Expanding
High Melt Strength,” Proceedings Technology Online Article: www.
the Product Portfolio of Ethylene
of the SPE-Automotive TPO Global ptonline.com/articles/blow-molding-
Elastomers – ENGAGE™ Polyolefin
Conference (2004). gets-green-light-in-detroit
Elastomers for Large Volume TPO
Applications,” Proceedings of the SPE- [6] B.W. Walther, et al., “Novel [10] S. Patel, et al., “Development of
Automotive TPO Global Conference (2005). Thermoforming TPO Compound a Slush Molded TPO Instrument
Developed Using Advanced Panel Skin,” 2005 SAE World Congress,
[2] Dow Publication 774-01501-1006AMS,
Material Science,” Proceedings of the SPE- Detroit, Michigan (April 2005).
“High Melt Strength Materials Expand
Automotive TPO Global Conference (2006).
Thermoforming Possibilities for TPOs” [11] Laughner, et. al., “Modification
[7] L.B. Weaver, et al., “Novel of Polypropylene by Ethylene/
[3] R. Leaversuch, “Thermoforming
Ethylene/Alpha-Olefin Copolymers Alpha-Olefin Elastomers Produced
Shines in Exterior Vehicle Panels,”
– Polypropylene Blends for by Single-Site Constrained Geometry
Plastics Technology Online Article: www.
Thermoforming, Blow Molding, and Catalyst,” Proceedings of the SPE-
ptonline.com/articles/thermoforming-
Extruded Profiles,” Proceedings of SPE Automotive TPO Global Conference (1999).
shines-in-exterior-vehicle-panels
Polyolefins, Houston, Texas (2006).
[12] J.J. Hemphill, et al, “Continued TPO
[4] J.J. Hemphill, et al., “New Advances
[8] L.B. Weaver, et al., “Novel Ethylene/ Elastomer Development,” Proceedings
in Elastomer Technology,” Proceedings
Alpha-Olefin Copolymers – Propylene of the SPE-Automotive TPO Global
of the SPE-Automotive TPO Global
Blends for Extruded Profiles,” Conference (2007).
Conference (2003).
Proceedings of AMI Profiles (2007).
[13] J.J. Hemphill, et al., “Expanding
the Elastomer Portfolio for TPO
Applications,” Proceedings of the SPE-
Table 4: TPO Elastomer Selection(1)
Automotive TPO Global Conference (2006).
Injection Molding
[14] VERSIFY™ Plastomers and
Good Better Best
Elastomers, along with ENGAGE™
Balance of analogs that provide superior melt
Cost Effective Superior Impact High Flow Low Gloss
Properties
strength for thermoforming and
ENR 7380/ blow molding applications.
ENGAGE™ ENGAGE™ ENGAGE™ XLT ENGAGE™
ENGAGE™ HM
7270/7277 8100/8107 8677 8130/8137
7387(2) [15] INFUSE™ Olefin Block Copolymers
ENGAGE ™
ENGAGE ™
ENGAGE HM ™
ENGAGE™ 8003
8150/8157
ENGAGE™ 7467
8400/8407(3) 7487
[16] L.B. Weaver, et al., “A New Class of
Higher Melting Polyolefin Elastomers
DOW™ VLDPE ENGAGE™ ENGAGE™ 8180/
for Automotive Applications,”
1085 8200/8207 ENR 8187(2)
Proceedings of the SPE-Automotive TPO
DOW™ VLDPE
ENGAGE™ 8842 Global Conference (2006).
1095
NORDEL™ IP ENGAGE™ HM
3720P or 3745P 7487
Extrusion/Thermoforming & Blow Molding Other Considerations
High Melt Strength Elastomers Compatibilizer/Other
ENR 7380/ENGAGE™ HM 7387(2) AMPLIFY™ GR 216
ENGAGE HM 7487
™
VERSIFY™ Product Series
ENGAGE™ HM 7280 INFUSE™ Product Series
ENGAGE HM 7289
™
(1)
Data per tests conducted by Dow. Test protocols and additional information available upon request. Properties shown are typical, not to be
construed as specifications. Users should confirm results by their own tests.
(2)
ENR designates a developmental grade. When using developmental products, customers are reminded that: (1) product specifications may not
be fully determined; (2) analysis of hazards and caution in handling and use are required; (3) there is greater potential for Dow to change speci-
fications and/or discontinue production; and (4) although Dow may from time to time provide samples of such products, Dow is not obligated to
supply or otherwise commercialize such products for any use or application whatsoever.
(3)
ENGAGE™ 8400 POE is available in the European region. ENGAGE™ 8407 POE is available globally.
™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow
7North America Europe/Middle East + 800 3694 6367 dow.com
U.S. & Canada 1 800 441 4369 + 31 115 672626 dowelastomers.com
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Published August, 2013.
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