86908078 urethane science and technology

1.2.3.2e Pail Test Another test was devised to evaluate foam bulk stability in a free-rise mixed foam.Foams prepared from TDI formulations were poured directly from the machine headinto

Urethane Science

and Technology

Daniel Klempner

and Kurt Frisch

Rapra Technology Limited

Shawbury, Shrewsbury, Shropshire, SY4 4NR, United KingdomTelephone: +44 (0)1939 250383 Fax: +44 (0)1939 251118

http://www.rapra.net

Rapra Technology Limited

Shawbury, Shrewsbury, Shropshire, SY4 4NR, UK

©2001, Rapra Technology Limited

All rights reserved Except as permitted under current legislation no part

of this publication may be photocopied, reproduced or distributed in anyform or by any means or stored in a database or retrieval system, without

the prior permission from the copyright holder

A catalogue record for this book is available from the British Library

Typeset by Rapra Technology LimitedPrinted and bound by Lightning Source UK

ISBN: 1-85957-275-8

In memory of Kurt C Frisch

One of the founding Fathers of polyurethanes

January 15th 1919 to October 21st 2000

1 Dimensional Stabilising Additives for Flexible Polyurethane Foams 3

1.1 Introduction 3

1.2 Experimental Procedures 6

1.2.1 Materials 6

1.2.2 Handmix Evaluations 8

1.2.3 Machine Evaluation 9

1.3 TDI - Flexible Moulded Additives 15

1.3.1 Dimensional Stability Additives for TDI 16

1.3.2 Low Emission Dimensional Stability Additives 42

1.4 MDI Flexible Moulded Foam Additives 63

1.4.1 Dimensional Stability Additives for MDI 64

1.4.2 Low Emissions Dimensional Stability Additives in MDI 67

1.5 TDI Flexible Slabstock Low Emission Additives 73

1.5.1 Reactivity 74

1.5.2 Standard Physical Properties 74

1.5.3 TDI Flexible Slabstock Foam Review 74

1.6 Foam Model Tool Discussions 75

1.6.1 TDI and MDI Moulded Foam Model 75

1.6.2 TDI Flexible Slabstock Foam Model 78

1.7 Conclusions 81

2 Demands on Surfactants in Polyurethane Foam Production with Liquid Carbon Dioxide Blowing 85

2.1 History of Polyurethane Foams 85

2.1.1 Environmental Concerns in Relation to Flexible Foam Density 86

2.2 Current Liquid Carbon Dioxide Technologies for Flexible Slabstock

Polyether Foam Production 88

2.2.1 Machinery 88

2.2.2 The Foaming Process 90

2.2.3 Additional Tasks of Silicone Surfactants in Flexible Slabstock Foam Production 95

2.2.4 Chemistry of a Silicone Surfactant in Flexible Slabstock Foam Production 99

2.2.5 A Surfactant Development Example 101

3 Polyurethane Processing: Recent Developments 113

3.1 Industrial Solutions for the Production of Automotive Seats Using Polyurethane Multi-Component Formulations 113

3.1.1 Market Requirements 113

3.1.2 Dedicated Solutions: Metering Equipment 114

3.1.3 Dedicated Solutions: Mixing Heads 116

3.1.4 Dedicated Solutions 121

3.2 ‘Foam & Film’ Technology - An Innovative Solution to Fully Automate the Manufacture of Automotive Sound Deadening Parts 130

3.2.1 The Problem 131

3.2.2 The Approach to a Solution 131

3.2.3 The Film 133

3.2.4 Industrial Applications 135

3.2.5 Applications 137

3.2.6 Advantages 138

3.3 InterWet - Polyurethane Co-injection 138

3.3.1 Glass-Reinforced Polyurethanes, a Well-Known Technology 139

4 Recent Developments in Open Cell Polyurethane-Filled Vacuum Insulated Panels for Super Insulation Applications 157

4.1 Introduction 157 4.2 Some General Properties of Open Cell PU Foams for Vacuum

Insulated Panels 158

4.3 Vacuum Issues in the Selection of VIP Components 163

4.3.1 Vacuum Properties of the Open Cell Foams 163

4.3.2 Vacuum Properties of the Barrier Film 167

4.3.3 The Getter Device 179

4.4 Vacuum Panel Manufacturing Process and Characterisation 188

4.4.1 Some Manufacturing Issues 188

4.4.2 Characterisation of Vacuum Panels 191

4.5 Insulation Performances of Open Cell PU-Filled Vacuum Panels 196

4.6 Examples of VIP Applications and Related Issues 199

4.6.1 Household Appliances 199

4.6.2 Laboratory and Biomedical Refrigerators 203

4.6.3 Vending Machines 204

4.6.4 Refrigerated/Insulated Transportation 205

4.6.5 Other Applications 206

4.7 Near Term Perspectives and Conclusions 206

5 Modelling the Stabilising Behaviour of Silicone Surfactants During the Processing of Polyurethane Foam: The Use of Thin Liquid Films 213

5.1 Introduction 213

5.2 Film Drainage Rate: Reynold’s Model and Further Modifications 216

5.2.1 Rigid Film Surfaces 216

5.2.2 Mobile Film Surfaces 217

5.2.3 Surface Viscosity 217

5.2.4 Surface Tension Gradients 218

5.3 Experimental Investigation of Model, Thin Liquid Polyurethane Films and the Development of Qualitative and Semi-Quantitative Models of Film Drainage 219

5.3.1 Experimental Details 221

5.3.2 Qualitative Description of Polyurethane Films 223

5.3.3 Quantitative Measurement of Film Drainage Rates:

Bulk and Surface Effects 226

5.4 The Development of Theoretical Models of Vertical, Draining Thin Liquid Model PU Films 236

5.4.1 Rigid-Surfaced Collapsing Wedge Model 236

5.4.2 Deforming Film Models 239

5.4.3 Tangentially-Immobile Films 242

5.4.4 Finite Surface Viscosity 245

5.4.5 Adding Surfactant Transport 249

5.5 Summary 254

6 Synthesis and Characterisation of Aqueous Hybrid Polyurethane-Urea-Acrylic/Styrene Polymer Dispersions 261

6.1 Preface 261

6.2 Introduction 261

6.2.1 General Considerations 261

6.2.2 Acrylic Dispersions and Polyurethane Dispersions (DPUR) 264

6.2.3 Hybrid Acrylic-Urethane Dispersions 266

6.3 Concept of the Study 268

6.3.1 Selection of Starting Materials 268

6.3.2 Assumptions for Synthesis of Hybrid Dispersions 269

6.4 Methods of Testing 276

6.4.1 Dispersions 276

6.4.2 Coatings 277

6.4.3 Films 278

6.5 Experimental results 279

6.5.1 Characterisation of Starting Dispersions Used for Synthesis of MDPUR 279

6.5.2 Synthesis of MDPUR and MDPUR-ASD 288

6.5.3 Investigation of the Effect of Various Factors on the Properties of Hybrid Dispersions 290

6.5.4 Additional Experiments 312

6.6 Discussion of results 320

6.6.1 Estimation of the Effect of Various Factors on the Properties of Hybrid Dispersions and Films and Coatings Made from Them 320

6.6.2 Mechanism of Hybrid Particle Formation 326

6.7 Summary 330

7 Adhesion Behaviour of Urethanes 335

7.1 Introduction 335

7.2 Surface Characteristics of PU Adhesive Formulations 335

7.2.1 Experimental 336

7.2.2 Results and Discussion 338

7.2.3 Conclusions 347

7.3 Acid/Base Interactions and the Adhesion of PUs to Polymer Substrates 347 7.3.1 Experimental 348

7.3.2 Results and Discussion 351

7.4 The Effectiveness of Silane Adhesion Promoters in the Performance of PU Adhesives 355

7.4.1 Experimental 356

7.4.2 Results and Discussion 358

7.4.3 Conclusions 364

8 HER Materials for Polyurethane Applications 369

8.1 Introduction 369

8.2 Experimental Conditions 370

8.2.1 Chain Extenders 370

8.2.2 Prepolymers 370

8.2.3 Preparation of Cast Elastomers 372

8.2.4 Physical and Mechanical Properties Determination 372

8.3 HER Materials Synthesis and Characterisation 373

8.4 Cast Poly(Ether Urethanes) 375

8.4.1 Pot Life Determination 375

8.4.2 Polyurethane Castings 376

8.4.3 Calculation of Hard and Soft Segment Contents 376

8.4.4 Hard Segment Versus Hardness 378

8.4.5 Tensile Properties 378

8.4.6 Tear, Compression Set and Rebound Properties 380

8.4.7 Differential Scanning Calorimetry 381

8.4.8 Dynamic Mechanical Analysis 383

8.5 Cast Poly(Ester Urethanes) 390

8.5.1 Pot Life Determination 390

8.5.2 Tensile Properties 390

8.5.3 Tear, Fracture Energy, Compression Set and Rebound Properties 390

8.5.4 Differential Scanning Calorimetry Analysis 393

8.5.5 Dynamic Mechanical Analysis 395

8.6 Cast Polyurethanes from HER/HQEE Blends 397

8.6.1 Freezing Point Determination of HER/HQEE Blends 397

8.6.2 Cast elastomers and Their Properties 398

8.7 High Hardness Cast Polyurethanes 401

8.7.1 Cast Elastomers and Their Hard and Soft Segment Contents 401

8.7.2 Hardness, Tensile, Tear, Compression Set and Rebound Properties 401

8.7.3 FT-IR Analysis of Cast Polyurethanes 403

8.7.4 Differential Scanning Calorimetric Analysis 405

8.7.5 Dynamic Mechanical Analysis 405

8.8 High Thermal Stability Polyurethane with Low Heat Generation 405

8.8.1 Hardness Measurements 408

8.8.2 Tensile Measurements 408

8.8.3 Differential Scanning Calorimetric Analysis 410

8.8.4 Dynamic Mechanical Analysis 412

8.9 Conclusions 416

9 Ultra-Low Monol PPG: High-Performance Polyether Polyols for Polyurethanes 421

9.1 Introduction 421

9.2 MDI/BDO Cured Elastomers Based on Ultra-Low Monol PPG Polyols 424 9.2.1 Effect of Monol Content on 4,4´-Methylene Diphenylmethane Diisocyanate (MDI)/1,4-Butanediol (BDO) Cured Elastomers 424

9.2.2 Processability and Property Latitude of Elastomers Based on Ultra-Low Monol PPG Polyols 429

9.2.3 Processing Latitude Improves by Incorporating Oxyethylene Moieties 434

9.3 One-Shot Elastomer System Based on EO-Capped, Ultra-Low Monol PPG Polyols 436

9.3.1 Effect of Primary Hydroxyl Concentration on One-Shot Elastomer Processability 436

9.3.2 Effect of Monol Content on One-Shot Elastomer Processability and Properties 438

9.3.3 Processability and Property Latitude of Elastomers Based on EO-Capped, Ultra-Low Monol Polyols 440

9.4.1 MDI/BDO Cured Elastomers: Acclaim Polyol 3205 Versus

PTMEG-2000 445

9.4.2 Enhanced Elastomer Properties Utilising Ultra-Low Monol PPG/PTMEG Blends 447

9.5 Polyol Molecular Weight Distribution Effect on Mechanical and Dynamic Properties of Polyurethanes 449

9.5.1 TDI Prepolymers Cured with Methylene Bis-(2-Chloroaniline) [MBOCA] 450

9.5.2 Moisture-Cured TDI Prepolymers 454

9.5.3 Aqueous Polyurethane/Urea Dispersion Coatings 456

9.5.4 MDI Prepolymers Cured with BDO 459

9.6 Conclusions 461

APPENDIX 465

Laboratory Preparation of 2,4-TDI and 4,4´-MDI Prepolymers 465

Laboratory Casting of 4,4´-MDI Prepolymers Cured with BDO 465

Laboratory Casting of One-Shot Elastomers Based on Carbodiimide-Modified MDI, Polyol, and BDO 465

Laboratory Casting of 2,4-TDI Prepolymers Cured with MBOCA 466

Laboratory Moisture-Curing of 2,4-TDI Prepolymers 466

Laboratory Preparation of Aqueous Polyurethane/Urea Dispersions using the Prepolymer Mixing Process 466

Abbreviations 469

Contributors 473

Author Index 477

Main Index 483

This is a landmark issue of ‘Advances in Urethane Science and Technology’ Notonly is this the first volume of the new millennium, but it is the first to be published

by Rapra Technology

On a more solemn note, one of the editors, Kurt C Frisch, passed away shortlybefore publication Dr Frisch, founder of the University of Detroit Mercy’s PolymerInstitute, was one of the pioneers of polyurethanes and was responsible for thesuccessful introduction of polyether polyurethane flexible foams into commerce inthe mid-1950s Let us not only mourn the loss of, but also celebrate the life of thisgreat scholar by continuing to further the frontiers of urethane science and

technology This volume is a good example of this progress

Polyurethanes continue to be one of the most versatile of all polymers, findingapplications in foams (flexible, rigid, and in-between), elastomers, coatings, sealants,adhesives, paints, textiles, and films This volume presents some of the major

advances in polyurethanes, both from the materials and research side of things aswell as processing and applications, and includes studies on foams (additives,

vacuum panel applications, blowing and processing), elastomers, adhesion

behaviour and new urethane raw materials

I would like to take this opportunity to express my gratitude to the authors whocontributed to this book and to the University of Detroit Mercy for its

encouragement of this effort

I would also like to thank the staff of Rapra, in particular, Frances Powers, ClaireGriffiths and Steve Barnfield

Daniel Klempner, Ph D.

Polymer Institute,University of Detroit Mercy

July, 2001

1.1 Introduction

The issues that an automotive seat manufacturer faces when formulating and producingseats are escalating Physical properties such as tensile and tear strengths, compressionset and wet set are critical when meeting specific mechanical performance requirements

as defined by the original equipment manufacturer (OEM) As new requirements forcomfort and durability are instituted, tests such as dynamic creep testing, long termvibration characterisation and repeated compression tests under various atmosphericand load conditions have been used to characterise foam performance for comfort.Comfort properties are best controlled by the polyols used to produce the polyurethanefoam cushion Significant changes in polyol technology to meet these dynamic comfortproperties have had an impact on the processing of polyurethane foam and on physicalproperties Increased tightness of the foam article resulting from changes in these rawmaterials has focused more attention by foam producers on crushing methods Flexiblemoulded polyurethane foam requires some type of mechanical crushing to preventshrinkage and ultimately maintain part stability

With recent changes made to polyol technology, mechanical methods of crushing do notalways provide the consistency required to produce a part that is dimensionally stable.Additionally, producers of polyurethane articles are continually building more complexityinto their seat designs to meet the aesthetic values required by today’s consumers Thesecomplex seat designs place more emphasis on crushing capability due to the nature ofthe designs With all these changes, additives needed to be developed which provide awider processing latitude and increased breathability to the polyurethane article Widerprocessing latitudes should reduce scrap and repair rates on the foam production lineand improve economics for the polyurethane producer [1]

The formation of moulded foam is a complicated chemical process which involves severalreactions occurring simultaneously There are rapid volume and temperature increasesand the concurrent development of phase separated polymer networks To understandhow foam properties can be affected by catalyst and surfactant chemistries severaltechniques are used to identify key performance benefits and issues A force to crush

Gary D Andrew, Jane G Kniss, Mark L Listemann, Lisa A Mercando, James D Tobias and Stephan Wendel

(FTC) detection device was used to measure the force required to crush a part to 50% ofits thickness for determination of cell openness Mass-loss/rate-of-rise was run tounderstand rate of rise and height measurements, weight loss from carbon dioxidegeneration and temperature profiles A scanning electron microscope (SEM) was used todetermine differences in cell structure and cell distribution caused by changes in thecatalyst and surfactant chemistries Physical properties were also tested using ASTM testmethods for flexible cellular polyurethane A novel chemical reaction foam modellingtechnique was also used to determine the selectivity of the catalyst packages, compared

to industrial standard controls [2]

In the past it was thought that the cell structure of polyurethane foam is controlled bythe type and amount of surfactant used Dabco DC5043 (Air Products and Chemicals,Inc.) was developed to enhance cell wall drainage to better enable cell opening duringcrushing cycles It was also thought that surfactant technology was the best way toprovide improved crushing techniques; therefore, catalyst technology was ignored [3]

As mentioned earlier, with new polyol technology development more emphasis was placed

on crushing New additive technology needed to be developed that would open cellsduring the foam formation and reduce the requirement and criticality of the crushingprocesses The technology had to go beyond providing easier cell opening at crush toproviding more open cells during the polyurethane formation

The real challenge in polyurethane foam formation is to control the chemical andphysiochemical processes up to the point where the material finally sets The sequenceand the rate of the chemical reactions are predominately a function of the catalyst andthe reactivity of the basic raw materials, polyol and isocyanate The physiochemicalcontribution to the overall stability and processability of a system is provided by thesilicone surfactants Optimum foaming results will be achieved only if the correctrelationship between chemistry and physics exists [4]

Another rapidly increasing environmental concern is over the emission of volatileorganic compounds (VOC) during and following the production of industrial andconsumer goods This has stimulated a great deal of effort within the chemical industry

to reduce and/or control the ways in which such emissions may occur In thepolyurethane foam industry, efforts to reduce VOC emissions have greatly impactedthe technologies used in manufacturing processes, especially for the use of organicauxilliary blowing agents such as chlorofluorocarbons In addition, the ultimate fate

of additional foaming additives, including surfactants and catalysts, is now comingunder increased global scrutiny As a result, foam manufacturers have expressed adesire for polyurethane additives that, among other things, do not exhibit the degrees

of fugitivity common to many of the additives that are currently used in polyurethanefoam production today

Polyurethane foams are prepared from the simultaneous reactions of diisocyanate withwater and with polymeric diols and/or triols to form hydrogen-bonded urea (hard)segments and polyurethane networks (soft segments) The commercial production ofpolyurethanes via isocyanate poly-addition reactions requires the use of one or morecatalysts Tertiary amines are widely accepted in the industry as versatile polyurethanecatalysts Amine catalysts are generally stable in the presence of standard polyurethaneformulation components and can have an impact on both the blowing (water-isocyanate)and gelling (polyol-isocyanate) reactions Although the use of catalysts in themanufacturing of polyurethane foam both speeds the production of the foamed articleand, through the judicious choice of catalyst package, allows control of the physicalproperties of the product, there are some problems associated with the use of theseadditives A number of commonly used tertiary amine catalysts can volatilise under certainconditions Release of tertiary amines during foam processing and from consumer products

is generally undesirable Therefore, identifying alternatives to standard tertiary aminecatalysts which have no or low volatility, yet exhibit the same type of activity in isocyanatepoly-addition reactions, is desirable

The non-fugitive catalysts reported in this chapter address the problems associated withthe use of polyurethane catalysts by reducing the odour and volatility of these materialsand by eliminating the ability of these additives to escape from finished foam products.One strategy has involved functionalising the catalysts to render the species reactivetoward isocyanates, thereby covalently attaching the catalysts to the polymer network.This strategy not only renders the catalytic material non-fugitive in the final product, butalso reduces the odour and volatility of the catalyst through increases in molecular weightand polarity These non-fugitive catalysts also provide equivalent or improved physicalproperties when compared to industry standards, whereas conventional reactive aminecatalysts as well as metal catalysts cannot always meet todays ever increasing manufacturerand consumer performance requirements

These increasingly evolving requirements have led to the development of both novelnon-fugitive catalysts and new cell-opening non-fugitive catalysts for flexible foam Thesenew low emission additives have been developed to meet the challenge of optimisedfoaming and result in little or no emissions Several of the non-fugitive catalysts possesscell-opening capability This new technology allows the manufacturer of polyurethanefoam to optimise their system to achieve the best processing latitude for their foam process.These new additives maintain, or in some cases, improve key physical properties whileproviding a more open foam

1.2 Experimental Procedures

Data presented herein was derived from a combination of handmix and high pressureimpingement-mixing machine produced foam Foams were prepared using several generaltypes of formulations for toluene diisocyanate (TDI) and two general types of formulationsfor methylenediphenyl diisocyanate (MDI) which are representative of currently utilisedformulations in the automotive interior component industry In addition, an all waterblown formulation was used to represent the flexible slabstock industry

1.2.1 Materials

The materials used are shown in Table 1.1.

k r o w l a t n e m i r e p e n i d e s u s l a i r e t a M 1 e l b a T e

ICPA6

ICPA5

ICPA0

ICPA0

.snitacipa

ICPA

.snitacipa

ICPA

1 e l b a

ICPA9

ICPA5

ICPA7

ICPA7

ICPAF

)retaw

%5:AOED

%5(

ICPA8

6

-C

N olyolwithanOH#of 1.4 DowChemical0

1.2.2 Handmix Evaluations

1.2.2.1 Flexible Moulded Foam Handmix Procedure

Handmix experiments were carried out using the following procedure Formulationswere blended together for approximately 10 minutes using a mechanical mixerequipped with a 7.6 cm diameter, high shear, mixing blade, rotating at 5000 rpms.Premixed formulations were maintained at 23 ± 1 °C using a low temperatureincubator Mondur TD-80 (Bayer; a blend of 2,4-TDI and 2,6-TDI isomers in theratio of 4:1) or modified MDI was added to the premix at the correct stoichiometricamount for the reported index for each foam The mixture was blended togetherwith a Premier Mill Corporation Series 2000, Model 89, dispersator for approximatelyfive seconds The foaming mixture was transferred to an Imperial Bondware #GDR-

170 food container or ‘chicken’ bucket and allowed to free rise in order to obtain theprocessing data

1.2.2.2 Flexible Slabstock Foam Handmix Procedure

Handmix experiments were carried out using the following procedure A premixconsisting of polyol, surfactant and water was prepared by blending the components

in a shaker for approximately 20 minutes The premix was allowed to stand for 2hours prior to making the foam to allow for degassing of the mixture A measuredamount of premix was poured into a 1.9 litre paper cup; the required stoichiometricamounts of amine and tin catalysts were added to the contents of the cup and mixedfor 20 seconds using a Premier Mill Corporation dispersator equipped with a 5.5 cmdiameter, high shear, mixing blade, rotating at 6,000 rpm The corresponding amount

of Mondur TD-80 to provide for a 110 index (isocyanate index, which is the amount

of isocyanate used relative to the theoretical equivalent amount [5]) was measuredinto a 400 cm3 beaker Methylene chloride in the correct proportion was added tothe beaker containing the Mondur TD-80; the beaker was carefully swirled for 4 or

5 seconds and the contents poured into the paper cup The mixture was blendedtogether for 6-7 seconds and the foaming mixture poured into a paper bucket for up

to 12 seconds and allowed to free rise with the processing data being recorded.Reactivity profiles were determined from hand-mix foams prepared in 5.68 litre paperbuckets Foams for physical properties were prepared in 35.6 x 35.6 x 25.4 cmcardboard boxes Identical procedures were followed for both reactivity and physicalproperty experiments

1.2.3 Machine Evaluation

1.2.3.1 TDI Flexible Moulded Foam Procedure

Machine runs for the TDI flexible moulded foam were carried out on a Hi Tech SureShotMHR-50 (Hi-Tech Industries, Inc.), cylinder displacement series, high pressure machine.Fresh premixes, consisting of the appropriate polyols, water, crosslinker, surfactants andcatalysts for each formulation were charged to the machine Mondur TD-80 was usedthroughout the entire study All chemical temperatures were held at 23 ± 2 °C via themachine’s internal temperature control units The foam was poured into an isothermallycontrolled, heated aluminium mould maintained at 71 ± 2 °C The mould was a typicalphysical property tool designed with internal dimensions of 40.6 cm x 40.6 cm x 10.2

cm The mould has five vents, each approximately 1.5 mm in diameter, centred 10.0 cmfrom each edge and the geometric centre of the lid The mould was sprayed with asolvent-based release agent, Chem-Trend PRC-798, prior to every pour and allowed todry for one minute before pouring The foam premix was puddle poured into the centre

of the mould with a wet chemical charge weight capable of completely filling the mouldand obtaining the desired core density Minimum fill requirements were established foreach formulation evaluated The foam article was demoulded at 240 seconds after theinitial pour After demoulding, the foam was placed through a mechanical crusher, testedfor FTC measurements, or left uncrushed and set aside for 24 hour shrinkagemeasurements described in Section 1.2.3.2c

All foams to be tested in each catalyst set were mechanically crushed 1 minute afterdemoulding using a Black Brothers Roller crusher set to a gap of 2.54 cm Crushing wascarried out three times on each part, rotating the foam 90 degrees after each pass throughthe roller All parts produced for physical testing were allowed to condition for at leastseven days in a constant temperature and humidity room (23 ± 2 °C, 50 ± 2% relativehumidity)

Three to four specimens were produced for any given set of conditions Four test specimenswere die-cut from each foam pad and evaluated for each physical property listed insubsequent data tables All results were included in calculating averages and standarddeviation Each test was carried out as specified in ASTM D3574 [5]

For each formulation evaluated, duplicate free rise ‘chicken’ buckets were poured at thesame shot size to determine overall reactivities and foam shrinkage Data recorded werecream time (the time between the discharge of the foam ingredients from the mixinghead and the beginning of the foam rise [5]), top-of-cup (TOC; the time between thedischarge of the foam ingredients from the mixing head and when the centre of the foamreaches the same height as the top of the chicken bucket), string gel (the time between

pouring of the mixed liquids and the time that strings of viscous material can be pulledaway from the surface of the foam when it is touched with a tool [5]), full rise time andfinal height The free rise buckets were again tested for final heights after 24 hours.Measurements of height were made using a Mitutoyo height gauge In addition to all thestandard tests, several more unique tests were performed where indicated, and aredescribed in Section 1.2.3.2.

1.2.3.2 Tests

1.2.3.2a Maze Flow Mould Test Description

A common type of isothermally heated mould was used to determine the flowability of

formulations with each of the catalyst candidates This maze mould is shown in Figure 1.1.

Machine foam was poured into the mould at the top left corner of the open cavity asindicated by ‘pour spot’ on the figure The lid was then closed and clamped tightly Foamwas allowed to free flow consecutively through each of the five gates for the standard 4

Figure 1.1 Diagram of Maze Flow Mould (Top View)

minutes prior to demould Minimum fill was first determined by completely filling thecavity with little or no extrusion through the vent at the end of the fifth gate Mathematicalreduction of the shot size was performed to obtain the first of three systematically scaleddown foam fill weights This first foam should have a fifth leg (the foam in gate 5 of the

maze flow mould, see Figure 1.1) which barely touches the front cavity wall The second

reduction in foam fill weight produced a foam that flowed approximately halfway throughthe fifth gate The third reduction in foam fill weight was equivalent to the step changefrom foam 1 to foam 2 Shot times were held constant for each of the three foam fillweights as compared to the control determined standard shot time in any given solidslevel formulation These three foams were weighed for total foam pad and fifth leg weight,and measured for fifth leg length to obtain a range of flow values for each of theexperimental catalysts compared to the control additives

1.2.3.2b Dimensional Stability Test

Foam dimensional stability is essentially the result of a balance between external andinternal forces The external forces are defined as the ambient pressure along with anyadditional applied loads The internal forces are the strength of the polymer matrix andthe internal cell pressure [6] Basically, if the sum of the internal forces is greater than theexternal forces, the foam will expand Consequently, if the sum of the external forces isgreater than the internal forces the foam will shrink Any expansion or shrinkage willimpact on the internal and/or external forces until an equilibrium is obtained It is theinternal forces, i.e., cell pressure and strength of the polymer matrix as defined by ‘greenstrength’ or cure, which will have an impact on the dimensional stability performance ofthe moulded polyurethane

Dimensional stability can be measured on a freshly demoulded part by determining theamount of force required to open cells, as measured by FTC FTC measurements weremade thirty seconds after demoulding The foam pad was removed from the mould,weighed and placed in the FTC apparatus The force detection device is equipped with a2.2 kg capacity pressure transducer mounted between the 323 cm2 circular plate crosshead and the drive shaft The actual force is shown on a digital display This devicemimics the ASTM D3574, Indentation Force Deflection Test [6] and provides a numericalvalue of the freshly demoulded foam’s initial hardness or softness The foam pad wascompressed to 50 percent of its original thickness at a cross head velocity of 275 mm perminute with the force necessary to achieve the highest compression cycle recorded inwhole Newtons Several compression cycles were completed A cycle takes approximately

30 seconds to complete Values are reported as the FTC value for the foam based on theassumption that the lower the FTC values the better the dimensional stability of thefoam This test requires the foam to be fully cured at demould A dimensionally stable

foam will exhibit little or no tendency to shrink after demoulding Poor dimensionalstability can result in numerous defects of the polyurethane article, such as lack of fit of

a polyurethane piece to the substrate These defects will ultimately cause loss of revenue

to the polyurethane manufacturers because of increased repair and/or scrap rates.Additionally the degree of cell openness of polyurethane foam can be measured directly

by the air flow physical properties of the polyurethane part Higher air flow valuesmeasured for a particular foam would indicate that the foam has less of a tendency toshrink and therefore be more dimensionally stable as compared to a foam with lower airflows Additionally, higher air flows may also indicate that the foam was much easier tocrush-out thereby breaking many of the cell windows Dimensionally stable foam shouldreduce scrap and rework by allowing the foam to conform to near its original mouldedshape or at least return to its original shape after being crushed

It was designed to measure the average foam pad shrinkage of an uncrushed foam Thisapparatus consists of two 432 mm long x 432 mm wide x 6.35 mm thick, plexiglassplates, mechanically pinned in each corner with threaded bolts to maintain the plates at

a constant 102 mm spacing The single uncrushed foam from each of the catalyst setswas aged 24 hours prior to being placed between the two plates Both top and bottomplates each contain 5 mm diameter holes evenly spaced, diagonally from corner to corner,

25 mm apart in an X-shaped pattern Nineteen holes are contained in each leg of the X,for a total of 37 holes per plate Measurements were made with a digital caliper byinserting the end down through each hole to just touch the foam surface with the indicatedvalue being recorded All measurements were normalised to discount the plexiglass platethickness and subsequently averaged to a single mould cavity and lid value

1.2.3.2d Time Pressure Release Test

Time Pressure Release (TPR) is the opening of the mould during the curing cycle torelease the internal pressure and then re-closing for the duration of the cure time [8] Thesudden release of the internally generated pressure bursts the cell windows, therebyimproving the crushability of the foam The tool is opened only a few millimetres andfor a specific time TPR can be applied at any time during the curing cycle, however, caremust be taken not to perform the operation too early or too late since surface qualityissues may occur

A ‘simulated’ TPR process was carried out during this study, whereby the tool lid wasopened approximately 1.5 mm for a three second duration TPR was applied at varioustime intervals throughout the evaluation Two mechanical clasps affixed to the top andbottom halves of the tool precisely controlled the gap opening These clasps were manuallyopened and closed at the desired TPR time interval

1.2.3.2e Pail Test

Another test was devised to evaluate foam bulk stability in a free-rise mixed foam.Foams prepared from TDI formulations were poured directly from the machine headinto a large open pail (the pail is a common high density polyethylene plastic withapproximate dimensions of 365 mm high and 290 mm in diameter) at a targeted mass.Several pours were carried out to ensure equivalent catalyst activity amongst eachformulation Foams were allowed to stand for 24 hours prior to removal from the pail.Each foam was weighed to obtain total individual mass Subsequently, a 25 mm slicewas cut directly through the geometric vertical centre of the foam Foam slices wereexamined for cell structure

1.2.3.2f Dynamic Fatigue Test

Dynamic Fatigue Constant Pounding testing was carried out using standard testingprocedures outlined in ASTM D3574-95 [6] A 60 minute recovery time and 80,000cycles were used for each test sample

1.2.3.2g Fogging Test

Gaseous foam emissions were compared in the standard fogging test procedure outlined

in SAE J1756 [9] A standard 7.6 cm thick piece of foam was preconditioned for 48hours, then tested in the Hart fogging apparatus at 100 °C for 3 hours Glossmeterreadings of the foam were taken after 60 minutes at room temperature

1.2.3.2h Headspace Analysis Test

Foam emissions were also evaluated by cutting equivalent portions, approximately 1 gram,

of foam from the geometric centre of the moulded foam articles 60 minutes after demoulding.Each sample was inserted into a 20 cm3 Kimble glass crimp top vial with a Teflon seal.Several vials were sealed without foam to be used as blanks to ensure all emissions hadeluted through the gas chromatograph prior to the injection of a second gas sample Allvials were loaded into a Tekmar 7000 Headspace Autosampler tray for sequential heatingfor 1 hour at 54 °C After heating and temperature equilibration, the headspace of the vialwas sampled and directly injected within a closed loop system onto a Hewlett Packard

5890 Series II Plus gas chromatograph containing a HP-5 dimethylsiloxane copolymer) stationary phase column (30 m, 0.25 mm internal diameter,1.00 mm film thickness) A standard oven heating profile was used to separate the gascomponents for detection with a Hewlett Packard 5972 Series Mass Selective Detector.Elution peaks were individually identified by comparison to standard libraries

(5%-diphenyl/95%-1.2.3.3 MDI Flexible Moulded Foam Procedure

Machine runs for the MDI flexible moulded foam were conducted on a Krauss-Maffei,cylinder displacement series, high pressure machine Fresh premixes, consisting of theappropriate polyols, water, crosslinker, surfactants and catalysts for each formulation werecharged to the machine Modified MDI was used throughout the entire study All chemicaltemperatures were held at 25 °C ± 2 °C via the machine’s internal temperature controlunits Foam pours were made into an isothermally controlled heated aluminium mouldmaintained at 60 °C ± 2 °C The mould was a typical physical property tool designed with

internal dimensions of 40.6 cm x 40.6 cm x 10.2 cm The mould has two vents eachapproximately 1.0 mm in diameter centred 10.0 cm from each edge and the geometriccentre of the lid The mould was sprayed with a solvent-based release agent prior to everypour and allowed to dry for one minute before pouring The foam premix was puddlepoured 15 cm away from the geometric centre of the mould with a wet chemical chargeweight capable of completely filling the mould with the appropriate core density Minimumfill requirements were established for each formulation evaluated The foam article wasdemoulded at 300 seconds after the initial pour Upon demoulding, the foam was placedthrough a mechanical crusher or tested for FTC measurements.

The foams were mechanically crushed 1 minute after demoulding using a roller crusher set to

a gap of 3.0 cm Crushing was carried out three times on each part All parts produced forphysical testing were allowed to condition for at least seven days in a constant temperatureand humidity room (23 °C ± 2 °C, 50% ± 2% relative humidity) Three to four parts wereproduced for any given set of conditions Four test specimens were die-cut from each padand evaluated for each physical property listed All results were included in calculating theaverages and standard deviation Each test was conducted as specified in ASTM D3574 [5].For each formulation evaluated, free rise cup foams (see Section 1.2.2.1) were poured todetermine reactivities and foam shrinkage Data recorded were gel time, full rise time andfinal height The free rise cup foams were tested for final heights and free rise density after 24hours Height measurements were carried out using a Mitutoyo height gauge All experimentalformulations reported in this work were matched by rise profile to each control formulation.FTC measurements were conducted 90 seconds after demoulding The foam pad was removedfrom the mould, weighed and placed in the FTC apparatus (Instron 4502) The force detectiondevice is equipped with a 5.0 kN capacity pressure transducer The actual force is shown on

a digital display This device mimics the ASTM D3574, Indentation Force Deflection Testand provides a numerical value of freshly demoulded foams initial hardness or softness Thepad was compressed to 70 percent of its original thickness at a cross head velocity of 380 mmper minute with the force necessary to achieve the highest compression cycle recorded inNewtons Values are reported as the FTC value for the foam based on the assumption thatthe lower the FTC values the better the dimensional stability of the foam

1.3 TDI - Flexible Moulded Additives

The automotive industry has placed increased pressures on OEM suppliers to improvetheir productivity, quality and cost of the polyurethane articles which they produce.Styling changes, complex designs and OEM productivity demands for automotive seatshave necessitated the need to produce more open foam in all-water blown TDI- and

MDI-based systems Furthermore, changes in polyol technologies designed to improveseat comfort factors can have a negative impact on foam openness and dimensionalstability Specifically, the comfort of high resilience foam may be related to the degree ofdimensional stability or foam openness.

Flexible moulded polyurethane foam requires mechanical crushing to open foam cells,which in turn prevents shrinkage and improves overall dimensional stability Currentmechanical methods for cell opening consist mainly of roller crushing, vacuum ruptureand TPR However, mechanical methods do not always result in complete or consistentcell opening and require a flexible moulded foam producer to invest in additionalmachinery Additionally, if the polyurethane article is not crushed properly, dimensionalstability suffers which can cause an increase in repair and scrap rates resulting in a negativeimpact on the cost of production A chemical method for cell opening would be preferred

1.3.1 Dimensional Stability Additives for TDI

When producing flexible high resilience foam, it is important to provide a wider TPRwindow to expand processing latitude and at the same time maintain or improve physicalproperties This should result in reduced scrap and/or repair rates, providing improvedeconomics for the polyurethane producer

The most commonly used catalyst and surfactant package for all water blown based moulded foam production is a blend of Dabco 33-LV and Dabco BL-11, coupledwith Dabco DC5043 silicone surfactant Additionally, the acid-blocked counterparts ofthese two catalysts, Dabco 8154 and Dabco BL-17, can also be used for the production

TDI-of high resilience moulded foam A combination TDI-of Dabco 33LV and Dabco BL-17 isused to facilitate a short delay in the reactivity of the polyurethane foaming process Acombination of silicone surfactants, Dabco DC5043 and Dabco DC5169, are utilised toprovide good foam stabilisation, improve cell regulation and cell wall drainage Thesecombinations of catalysts and surfactants served as the control additives to which theexperimental additives were compared and contrasted

A newly developed cell opening catalyst, Dabco BL-53, was evaluated to determine itsimpact on dimensional stability and general processability Dabco BL-53 affords all thebenefits of Dabco BL-11 or Dabco BL-17, with the added advantage of cell opening andslightly delayed initiation times Dabco BL-53 is not a chemical equivalent for DabcoBL-11 or Dabco BL-17; however, it will provide similar performance For rapiddemoulding systems, it is recommend that Dabco BL-53 be used at 0.12 to 0.22 pphp,with the optimum level at 0.16 to 0.19 pphp, in combination with a Dabco 33-LV level

at 0.30 to 0.32 pphp

As polyurethane seating design changed from the relatively simple configurations ofthe early 1990s to the more complex designs of today, the need to improve cell opening

or dimensional stability has intensified Accordingly, silicone surfactants providingimproved foam stabilisation, cell regulation and cell wall drainage were needed toenable polyurethane manufacturers to achieve their production goals Two experimentalsilicone surfactants, X-N1586 and X-N1587, were developed to provide open foamand promote dimensional stability

A TDI cushion formulation, with a density of 45 kg/m3 and a TDI back formulation,with a density of 35 kg/m3 were used in the TDI automotive study All of theseformulations were modified accordingly with the appropriate crosslinker, water, andadditive levels for the chosen density range These formulations are shown in

Tables 1.2 and 1.3.

m / g k 5

~ 2 1 e l b a

T 3 c u s h i n f o r m u l a i n n

1.3.1.1 Reactivity

1.3.1.1a Handmix Mass-Loss/Rate-of-Rise

Formulations used in the mass-loss/rate-of-rise are summarised in Tables 1.2 and 1.3.

Surfactant and catalyst additives were changed according to the formulation being studied.Foams were run at the optimum index as they were during the machine study All experimentswere duplicated Each mixed formulation was poured into a ‘chicken’ bucket equipped with

a thermocouple positioned at the centre of the bucket resting on a Mettler PM 30,000 balance.The centre height of the rising foam was recorded every second using a DAPS QA Model

#2500 rate-of-rise apparatus Knowing the foam mass, the rate-of-rise and using the idealgas law, it is possible to calculate the carbon dioxide generated or trapped over time [10, 11]

Figures 1.3 and 1.4 show height versus time achieved for the cushion and back formulations using the control formulations I and V, as well as the experimental formulations II, III, IV,

VI, VII and VIII The foam height versus time graphs clearly indicate higher rates for control formulations I and V in both cushion and back formulations Cushion and back

m / g k 5 3 3 1 e l b a

T 3 b a c k f o r m u l a i n n

formulations, which contained the new additives in formulations II, III, IV, VI, VII and VIII did not achieve the same foam height when compared to the control formulations.

Several things could cause the differences observed in the foam heights First, reactivityrates for control formulations might be faster than the experimental catalyst or surfactants.Second, overall foam stability could be compromised for the experimental catalyst andsurfactants Lastly, carbon dioxide might be diffusing from the reacting polyurethane foam

Figure 1.3 Foam Height versus Time - Cushion Formulation

Figure 1.4 Foam Height versus Time - Back Formulation

at an accelerated rate All of these possibilities were explored Data generated andobservations will be reported which demonstrate how these new additives promotedimensional stability through increased carbon dioxide diffusion.

Temperature profiles for control formulations I and V indicate reaction temperatures

which fall in the middle of the temperature profiles compared to the new additives denoted

in Figures 1.5 and 1.6 These temperature profiles clearly demonstrate that carbon dioxide

Figure 1.5 Temperature versus Time - Cushion Formulation

Figure 1.6 Temperature versus Time - Back Formulation

conversion is occurring at the same rate in the control as in the experimental formulations.The fact that carbon dioxideconversion is occurring at the same rates would not account

for the lower foam heights observed in Figures 1.3 and 1.4.

In the control formulations, I and V, the amount of carbon dioxide diffused was less than the amount of carbon dioxide diffused using the new additives Figures 1.7 and 1.8 were generated

using the ideal gas law from data generated with the mass-loss/rate-of-rise apparatus Diffusion

Figure 1.8 Carbon Dioxide Trapped versus Time: Back Formulation

Figure 1.7 Carbon Dioxide Trapped versus Time - Cushion Formulation

of carbon dioxide from cells as they form in the free rise reaction apparently keeps thereacting foam from reaching the same foam height when using these experimental additives.Reactivity profiles for these three new additives are essentially the same Data discussed

later in Section 9.3.1.1b, Tables 1.4 and 1.5, further supports the fact that there is no

n i a l u m r o f n i h s u c g n i s u n s i r a p m o c y t v i c a e r e s i r e r f x i m e n i h c a M

significant change in reactivity when comparing the control formulations to theexperimental formulations.

1.3.1.1b Machine Free Rise Reactivity

The machine mix free rise reactivity comparison of all formulations are shown in

Tables 1.4 and 1.5 This experimental data illustrates that the overall free rise foam

reactivity for both the cushion and back formulations remains relatively the same for

the beginning of the reaction The full rise reactivities in cushion formulations II, III and IV and back formulations VII and VIII start to deviate slightly from the control reference formulations I and V.

Percent shrinkage remains fairly consistent within the cushion formulations, I, II, III and

IV Increased foam shrinkage was observed with back formulations VII and VIII This

could be attributed to better cell wall drainage efficiency, providing more open foamand/or an overall increased carbon dioxide diffusion through the polymer network

1.3.1.2 Foam Physical Properties

1.3.1.2a TPR Effect on Machine Run Moulded Foam FTC

When producing polyurethane, manufacturers use some type of mechanical crushing to opencells and insure the polyurethane article does not lose dimensional stability Several techniquescan be used to provide the needed mechanical cell opening Manufacturers will use TPR,which has been described in Section 1.2.3.2d, along with mechanical roller crushing Someproducers will rely exclusively on the roller crushing and vacuum crushing techniques toprovide the mechanical cell opening required In both cases reducing FTC values and improvingfoam openness is important for producing polyurethane articles that are dimensionally stable

If TPR is carried out too soon during the polyurethane moulding cycle, the article will

collapse (blowout) as indicated in Figure 1.9 This is indicative of the foam being

insufficiently cured or lacking enough green strength when TPR was applied If TPR isconducted too late in the manufacturing process scalloping (concave surface areas on thefoam article) and tight foam (insufficient number of open cells within the foam articlethat causes the hot gas to be trapped and upon cooling forces the entire foam part toshrink) may also occur When scalloping occurs the foam article must be repaired orscrapped When tight foam occurs dimensional stability will suffer and there will be a

negative impact on physical properties as denoted in Figure 1.10 The foam pad in Figure

1.10 was produced at a 140 second TPR without crushing using formulation V

Figure 1.9 Example of a Collapse/Blowout Moulded Foam

(Reproduced with permission from APCI)

Figure 1.10 Example of Tight Foam with Shrinkage

(Reproduced with permission from APCI)

To understand the benefits of these new additive technologies that provide reduced FTCvalues, a TPR range from 70 to 150 seconds was run for each of the formulations inTables 1.2 and 1.3 At a 70 second TPR all formulations suffered blowout since the foamwas not sufficiently cured and thus lacked green strength At an 80 second TPR, noformulations evaluated experienced blowouts or collapse; however, slight distortionsand imperfections were evident on the foam surfaces to varying degrees of severity Tocomplete the TPR window, TPR cycle times were continually ramped up in this fashion

to determine the upper limit at which TPR could be applied for each formulation Theupper limit is reached for a given formulation when the foam displays the obvious signs

of scalloping and/or ‘dishing’ (concave surface areas of the foam) When this occurs thefoam is usually very tight and cannot be used as a functional part Additionally, partswere produced without utilising TPR during the production cycle in order to comparethe difference in foam crushability when TPR is used

1.3.1.2b Cushion Formulation Machine Evaluation Utilising TPR

Cushion control formulation I, which is listed in Table 1.2, was evaluated at a 90-100

second TPR Initial FTC values of 156 N/323 cm2 for a 90 second TPR and 165 N/323

cm2 for an 100 second TPR were observed These values were acceptable and produced

foam parts of good quality The new additives in formulations II, III and IV produced

maximum initial FTC values of 160 N/323 cm2 at TPR of 90 to 100 seconds Foam

produced at an 80 second TPR for the control formulation I and formulations II, III and

IV containing the new additives resulted in minor problems with foam quality, i.e.,

scalloping At a 70 second TPR, control and experimental formulations failed because of

severe blowout Figures 1.11 and 1.12 show no significant difference of FTC for all

formulations evaluated

When TPR values were increased to 120 seconds for control formulation I, initial valuesincreased to 623 N/323 cm2 and scalloping or foam quality suffered (Figure 1.13) However, increasing the TPR time for cushion formulations II, III and IV to 120 seconds,

produced maximum initial FTC values of 205 N/323 cm2 (Figure 1.13) Foam surface

quality was very good Increasing the TPR to 140 seconds increased initial FTC values to

a maximum of 543 N/323 cm2 and 534 N/323 cm2 for formulations II and III, respectively (Figure 1.14) Foam quality was still very good Formulation IV, which utilises a

combination of both surfactant and catalyst technologies, achieved a lower initial FTCvalue at a 140 second TPR of 191 N/323 cm2 This was only slightly higher than the FTC

values of the control formulation at a 90 second TPR Figures 1.11, 1.12, 1.13, and 1.14

show the results of FTC through the entire TPR range applied in this study These figuresclearly demonstrate that use of the new additives can reduce FTC values and maintaindimensional stability over the applied TPR range

Figure 1.11 FTC at 90 TPR - Cushion Formulation

Figure 1.12 FTC at 100 TPR - Cushion Formulation