Designing Polyurethane Elastomers with Low Compression Sets

Ashok Sarpeshkar & Peter Markusch Specialty Business Group Polyurethanes Division

Robert Cline Research Department Polyurethanes Division

Objectives

l  Elastomer characteristics l  Elastomer production techniques l  Designing for low compression set l  Methods of testing & results l  Applications l  Summary Polyurethane Elastomers with Low Compression Sets

Elastomer Characteristics

l  Resistance to permanent deformation l  High elastic modulus & high rigidity l  Performance under varying temperatures and pressures l  Low coefficient of friction l  Resistance to oil and hydraulic fluids

Polyurethane Elastomers with Low Compression Sets

Elastomer Production Method

Raw Material Functionality

Hot-Cast

Difunctional

Thermoplastic PU

Difunctional

One-Shot Process

Di- and Trifunctional

Polyurethane Elastomers with Low Compression Sets

Hot-Cast Process Prepolymer

Extender

Meter & Mix

Cast Elastomer Polyurethane Elastomers with Low Compression Sets

Compression Set of MDI Cast Elastomers Product Name Baytec MS-041 Baytec MS-242 Baytec MS-061 Baytec MS-081 Baytec ME-050 Baytec ME-080 Baytec ME-090 Baytec MP-090 Baytec MP-100

Comp. Set (%) 20 24 18 20 16 18 17 45 35

Hardness Soft Segment (Shore) 72A 85A 87A 90A 85A 93A 95A 85A 90A

Polyester Polyester Polyester Polyester C-4 Polyether C-4 Polyether C-4 Polyether PO-Polyether PO-Polyether

Polyurethane Elastomers with Low Compression Sets

Hot-Cast Process Benefits:

Superior mechanical properties Low compression set

Limitations:

Difunctional raw materials High-melting prepolymers High-temp processing Prepol : extender ratio of 10:1 Accurate metering needed Require postcure

Polyurethane Elastomers with Low Compression Sets

Elastomer Production Method

Raw Material Functionality

Hot-Cast

Difunctional

Thermoplastic PU

Difunctional

One-Shot Process

Di- and Trifunctional

Polyurethane Elastomers with Low Compression Sets

Thermoplastic Polyurethanes Isocyanate

Polyol

Extender

Reaction Extruder TPU Polyurethane Elastomers with Low Compression Sets

Effect of Postcure on Comp. Set of TPUs TPU

Hardness

Comp. Set (%) Before Postcure

Comp. Set (%) After Postcure

Texin 285

85A

16

12

Texin 390

88A

65

35

Texin 250

52D

75

35

Texin 945U

50D

22

20

Texin 5265

65D

88

35

Elastomers postcured for 16 hours @ 110ºC

Polyurethane Elastomers with Low Compression Sets

Thermoplastic Polyurethanes Benefits:

Superior mechanical properties Low compression set Co-extrusion with other plastics Parts are mass produced

Limitations:

Difunctional raw materials High-melting raw materials High-temp reaction extrusion Specialized equipment Extrusion & injection molding

Polyurethane Elastomers with Low Compression Sets

Elastomer Production Method

Raw Material Functionality

Hot-Cast

Difunctional

Thermoplastic PU

Difunctional

One-Shot Process

Di- and Trifunctional

Polyurethane Elastomers with Low Compression Sets

One-Shot Process Isocyanate

Polyol Extender Filler Catalyst Additives Plasticizer

Meter / Mix Elastomer Polyurethane Elastomers with Low Compression Sets

One-Shot Process - Benefits

l  Di- & trifunctional liquid raw materials l  Vast raw material pool l  Room temperature processed l  Favorable mix ratios l  Post-curing is optional l  Very low compression set l  Variable hardness l  Good physical properties l  Attractive alternative to hot-cast process Polyurethane Elastomers with Low Compression Sets

Designing for Low Compression Set Hot-Cast & TPU

l  Difunctional raw materials l  Slightly over-indexed [1.05] l  Crosslinking via post-cure at 110ºC/16 hr.

Polyurethane Elastomers with Low Compression Sets

Designing for Low Compression Set One-Shot Process - Method 1

Isocyanate [high 2,4’-MDI] with functionality = 2.0 Polyol blend with average functionality > 2.0

Polyurethane Elastomers with Low Compression Sets

Designing for Low Compression Set One-Shot Process - Method 2

Polyisocyanates [high 2,4’-MDI] with functionality > 2.0 Polyol blend with average functionality = 2.0

Polyurethane Elastomers with Low Compression Sets

Polyol Formulation - A [Funct. > 2.0] Raw Material

PBW

Multranol 3900 Multranol 4012 1,4-Butanediol Baylith L Paste Antifoam DC-1400 Dabco T-12

63.53 18.18 9.09 9.09 0.10 0.005

Polyurethane Elastomers with Low Compression Sets

Elastomers from Difunctional Prepolymers and Polyol A Isocyanate

% NCO

Mondur PF Mondur PF/1455 [1:1] Mondur 1455 Mondur ML Mondur 1437

23.0 23.0 23.0 33.6 10.0

Hardness 90A 91A 89A 62A 51A

Elastomers postcured for 16 hours @ 110ºC

Polyurethane Elastomers with Low Compression Sets

Comp. Set (%) 9 4 2 5 0.4

Polyol Formulation - B [Funct. = 2.0] Raw Material

PBW

Multranol 9111 Diethylene Glycol Baylith L Paste Antifoam DC 1400 Dabco T-12

85.25 12.74 1.96 0.05 0.02 - 0.05%

Polyurethane Elastomers with Low Compression Sets

Elastomers from Polyisocyanates & Polyol B Isocyanate

Functionality Hardness

Mondur MRS Mondur MRS-5 Mondur MRS-2 Mondur MR-5 Mondurs MR + PF [1:1] Mondurs MR + 1455 [1:1]

2.7 - 2.8 2.4 2.2 2.4 2.4 2.4

80A 77A 77A 81A 87A 77A

Elastomers processed at 25ºC

Polyurethane Elastomers with Low Compression Sets

Comp. Set (%) 6 8 10 22 16 4

Soft Elastomers with Low Comp. Set & Improved Temperature Resistance Isocyanate

Polyol1

Mondur 743 Mondur 1437 Mondur MRS Mondur MRS-4 Mondurs MR

ENC-140P ENC-140P ENC-120P ENC-120P ENC-120P

Hardness2

Comp. Set (%)2

60A 63A 49A 46A 43A

1Epoxy-modified

polyols 2postcured for 16 hours @ 80ºC

Polyurethane Elastomers with Low Compression Sets

3 8 3 7 9

Compression Testing Methods ASTM D-395

Measure ability of elastomer to maintain elastic properties after extended exposure to compressive forces

ASTM D-575B

Compare ability of elastomers to resist compressive stress

Polyurethane Elastomers with Low Compression Sets

Compression Set [ASTM D-395]

Polyurethane Elastomers with Low Compression Sets

Low Compression Set 6.0 ft

Polyurethane Elastomers with Low Compression Sets

High Compression Set 4.5 ft

Polyurethane Elastomers with Low Compression Sets

Compression Load Deflection [ASTM D-575B]

Polyurethane Elastomers with Low Compression Sets

Stress-Strain Relationship - Cast Elastomers Compressive Stress, MPa

1600 Baytec MS-090

1400 1200 1000

MS-081

800

MS-242

600

MS-052

400

MS-041

200 0 0

5

10

15 20 Deflection, %

25

Polyurethane Elastomers with Low Compression Sets

30

Stress-Strain Relationship - TPUs Compressive Stress, Mpa

1600

Texin 250

1400 1200

Texin 390

1000 800

Texin 285

600 400 200 0 0

5

10

15

20

25

Deflection, %

Polyurethane Elastomers with Low Compression Sets

30

Polyurethane O-Rings

Polyurethane Elastomers with Low Compression Sets

Octagonal O-Ring

Polyurethane Elastomers with Low Compression Sets

Polyurethane Seal for Pumps

Polyurethane Elastomers with Low Compression Sets

Seals & Gaskets

Polyurethane Elastomers with Low Compression Sets

Summary

l  Elastomers with excellent compression set properties from one-shot systems

Polyurethane Elastomers with Low Compression Sets

Summary

l  Elastomers with excellent compression set properties from one-shot systems

l  Crosslinking achieved by varying functionality of either isocyanate or polyol component produces low compression sets

Polyurethane Elastomers with Low Compression Sets

Summary

l  Elastomers with excellent compression set properties from one-shot systems

l  Crosslinking achieved by varying functionality of either isocyanate or polyol component produces low compression sets

l  Addition of 2,4’-MDI rich isocyanate enhances compression set properties Polyurethane Elastomers with Low Compression Sets

Summary ●  Elastomers with excellent compression set properties from one-shot systems

●  Crosslinking achieved by varying functionality of either isocyanate or polyol component produces low compression sets

●  Addition of 2,4’-MDI rich isocyanate enhances compression set properties

●  Attractive alternative to hot-cast elastomers with good physical properties Polyurethane Elastomers with Low Compression Sets

Acknowledgements

Robert L. Cline Peter H. Markusch Nicole Stamper

Polyurethane Elastomers with Low Compression Sets