Blowing Agents and Foaming Processes 2013

227 Pages·2013·22.41 MB·English

by  Smithers Rapra

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Conference Proceedings
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©Smithers Rapra 2013 r
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ISBN 978 1 909030 42 8
Organised by

14-15 May 2013
Mainz, Germany
ISBN: -978-1-909030-42-8
© Smithers Information Ltd, 2013
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CONTENTS

SESSION 1: CHEMICAL AND PHYSICAL FOAMING BASICS

Paper 1 Chemical foaming agents in thermoplastics and thermosets
Dr Thomas Mergenhagen, Tramaco GmbH, Germany

Paper 2 Chemical foaming of thermoplastic seals at ambient pressure
Matthias Gössi & Jürgen Finter, Sika Technology AG, Zürich/Switzerland

Paper 3 A zero ODP and low GWP foam expansion agent
Claus-Peter Keller, Dupont de Nemours (Deutschland) GmbH, Germany, Gary Loh, Joseph A. Creazzo,
Mark L. Robin, PhD & Saadat A. Ata, DuPont Company, USA

Paper 4 Shelf life evaluation of PU rigid spray foams
David Modray, Foam Supplies, Inc, USA

SESSION 2: CURED SYSTEMS (PUR AND SILICONE)

Paper 5 Foaming process and cellular structure analyses of bio-based flexible polyurethane foams
Piotr Rojek & Aleksander Prociak,, Cracow University of Technology, Poland

Paper 6 Foaming of silicone rubber with physical blowing agents in an extrusion process
Dipl.-Gyml. Sarah Sitz, Prof. Dr.-Ing. Christian Hopmann, Elena Göbel & Margareta Merke, Institut für
Kunststoffverarbeitung (IKV) an der RWTH Aachen, Germany

Paper 7 Silicone foams: how to expand the fastest crosslinking elastomer
Dr. Jürgen Weidinger, M+S Silicon GmbH & Co.KG, Germany - paper unavailable at time of print

SESSION 3: POLYMERS AND PROCESSES

Paper 8 Sustainability in foam created by rheological analysis and LDPE foam resins
John Krist & Emanuel van der Ven, SABIC Europe, The Netherlands

Paper 9 Retrofit concepts for foam extrusion with heat exchangers
Christian Schlummer, Promix Solutions AG, Switzerland

Paper 10 Foams and wood composite foams produced by rotomoulding
Alexandre Raymond & Denis Rodrigue, Université Laval, Canada

SESSION 4: INJECTION MOULDING

Paper 11 Molding large foamed plastic parts
Brian Read, Horizon Plastics International Inc, Canada

Paper 12 A mould filling simulation and validation data for microcellular foaming
Levi Kishbaugh, Trexel Inc, USA & Anthony Yang, Lloyd Shiu, Dan Chang, Moldex3D
Presenter: Martin Jacobi, Trexel GmbH, Germany
Paper 13 Light-weight potential of fiber reinforced foams
Dipl.-Ing Alexander Roch, Fraunhofer Institute for Chemical Technology ICT,Germany

SESSION 5: EXTRUSION DIRECT GASSING TRENDS AND MARKETS

Paper 14 Trends and potential of advanced insulating foams
Dr.-Ing. Maria-Kristin Sommer, P. Gutmann, C. Schröder, R. Hingmann, C. Däschlein, A. Löffler, BASF SE,
Germany

Paper 15 New class of brominated polymeric flame retardants for use in polystyrene foams
Heli Hollnagel2, Inken Beulich2*, J. Chris Bloom1, John W. Davis1, Bruce King1, Shari Kram1, Christine
Lukas3, Ted Morgan1, Bill Stobby1 1The Dow Chemical Company, USA,2 Dow Europe GmbH,
Switzerland,3Dow Chemicals UK Limited, United Kingdom

Paper 16 Japanese market situation for EPS and EPP: differences with European market
Hiroshi Fujiwara & Hidekazu Ohara, KANEKA Corp., Japan

SESSION 6: EXTRUSION DG NEW FINDINGS

Paper 17 Morphology, mechanical properties, and thermoforming behaviourof extrusion foamed organic
cellulose ester
S. Hendriks1, T. Hildebrand2, C. Hopmann1, S. Kabasci3, H.-J. Radusch4, F. van Lück5, S. Zepnik3,4
1Institute of Plastics Processing (IKV), RWTH Aachen University, Aachen, Germany
2Selit Dämmtechnik GmbH, Erbes-Büdesheim, Germany. 3Fraunhofer Institute for Environmental, Safety
and Energy Technology UMSICHT, Oberhausen, Germany. 4Martin Luther University Halle-Wittenberg,
Centre of Engineering Sciences, Chair Polymer Technology, Halle (Saale), Germany 5Inde Plastik
Betriebsgesellschaft mbH, Aldenhoven, Germany

Paper 18 Continuous polymer foam extrusion with a physical blowing agent in the solid state
Dipl.-Ing Sven Hendriks & Daniel Sander, IKV - Institut für Kunststoffverarbeitung, Germany

Paper 19 In-line rheology of gas-loaded polymer melts –The key for understanding the foaming process
T. Köppl, D. Raps, V. Altstädt, University of Bayreuth, Germany

Paper 20 Effects of crystallinity on the foaming behaviours of extruded polypropylene blown with CO
2
Alireza Tabatabaei, M. Reza Barzegari, Mohammadreza Nofar, and Chul. B Park, University of Toronto,
Canada

SESSION 7: NANOFILLERS IN FOAMED EXTRUDED SUBSTRATES

Paper 21 Additives with strong thermodynamic affinity for supercritical carbon dioxide: effect on continuous
foam processing
Ali Rizvi, Alireza Tabatabaei, Reza Barzegari and Chul B. Park, University of Toronto, Canada

Paper 22 Influence of carbon-based nanoparticles on the thermal conductivity of extruded polystyrene foams
Chimezie Okolieocha, Thomas Köppl, Sabrina Kerling, Volker Altstädt, University of Bayreuth, Germany

SESSION 8: NEW FINDINGS AND R&D WORK

Paper 23 Possibilities and challenges of extrusion of foamed products at pilot plant level
Dr Ana Espert Bernia, Aimplas, Spain

Paper 24 Fatigue of sandwich composites and the impact on lightweight applications
Lars Massueger, Jean-Francois Koenig, Alain Sagnard & Fabio D’Ottaviano, DOW Europe GmbH,
Switzerland
Blowing Agents and Foaming Processes 2013 14-15 May, 2013 – Mainz, Germany
CHEMICAL FOAMING AGENTS IN
THERMOPLASTICS AND THERMOSETS

Dr. Thomas Mergenhagen
Tramaco GmbH
Siemensstraße 1-5, 25421 Pinneberg, Germany
Tel: [phone] Fax: [phone] email: [email protected]

BIOGRAPHICAL NOTE

Dr. Thomas Mergenhagen has worked for six years as a Technical Service
Engineer in the rubber industry, covering processing additives and release agents
after completing his Ph.D. in organic photochemistry at the University of Hamburg.

From there he shifted to the paint industry to work as Business Development
Manager for a paint manufacturer and as Application Engineer for a resin
manufacturer.

In 2008 he joined Tramaco GmbH as Technical Sales Manager for chemical
foaming agents.

ABSTRACT

Foaming is today widely used in the polymer industry, not only to reduce the weight of final products but also
to achieve certain properties. But producing thermoplastic and thermoset foams is a critical process and
processing windows tend to be very small.

This paper aims to give a better understanding of the mechanisms of foaming and the differences between
thermoplastic and thermoset foaming. This will give a better understanding of production problems and how
to avoid them. The basic chemical foaming agents and their chemistry will be discussed as well as the mode
of action of chemical foaming agents as nucleating agents in physical foaming.

Some examples of typical chemically foamed thermoplastics and thermosets produced by extrusion,
injection moulding, plastisol processes or even rotomoulding will be given.

INTRODUCTION

In the thermoplastic and thermoset (e.g. rubber, PVC plastisol and others) industry foams are today widely
used in many different applications, each utilizing on the specific advantages that foams can offer over
compact materials. The construction industry uses very low density foams for insulation, the automotive
industry focuses on sealing properties (e.g. rubber weatherstrips) and weight reduction for plastic parts and
producers of consumer goods look for material savings, just to name a few typical applications.

The multitude of applications and polymers makes the foaming of thermoplastics and thermosets a very
complex field with many different multi-step processes. But this complexity can be mastered by knowledge of
the basic principles governing the foaming of polymers.

With a good understanding of the chemistry of the foaming agents and the mechanisms involved in the
foaming of polymers one can optimize the design and the production process in order to achieve the best
possible foam in the finished article.

Page 1 of 6 pages Paper 1 - Mergenhagen
14-15 May, 2013 – Mainz, Germany Blowing Agents and Foaming Processes 2013

CHEMISTRY OF FOAMING AGENTS

In the polymer industry there are a number of different processes to create foams and all of these processes
use special substances referred to as foaming agents in the respective industry:

 The gases or low boiling liquids used in the physical foaming of thermoplastics.
 The liquids used in PU foaming.
 The surfactants used to stabilize entrapped air in latex and plastisol processes.
 The microspheres, hollow polymer shells filled with low boiling liquids.
 The heat-decomposing chemicals used in the thermoplastics, rubber and plastisol industry.

And in all these industries the term “foaming agent” is used for the pure chemicals as well as for the ready-
to-use preparations supplied by specialized formulators.

In this paper we will focus on the chemical foaming agents which are (in general solid) substances that are
not stable at higher temperatures but decompose to form gases and other decomposition products. This
decomposition is initiated deliberately in the polymer processing and the resulting gases create the desired
polymer foam.

The chemical foaming agents can be divided into two groups, the endothermic and the exothermic foaming
agents. Endothermic foaming agents are substances that require heat for the decomposition reaction. This
makes the decomposition reaction rather slow and allows the reaction to be regulated by heat transfer.
Endothermic foaming agents are mostly inorganic chemicals like carbonates, hydrogen phosphates, tartrates
and organic acid derivatives. The economically most important endothermic foaming agents are sodium
bicarbonate and citric acid derivatives.

Under current EU regulations the endothermic foaming agents are the only possibility to chemically foam
polymers for food contact applications.

Exothermic foaming agents are mostly
organic substances that, on reaching a Foaming reaction Decomposition gas volume
certain temperature, decompose and agent temperature [°C] [ml/g]
release gas and heat. Because of this the Azo (ADC) exo 220 220
decomposition reaction is auto-catalytic,
OBSH exo 160 125
the released heat raises the temperature
TSH exo 145 110
and the reaction becomes even faster. This
BSH exo 140 110
makes for a very fast decomposition of the
exothermic foaming agents but also for a TSS exo 230 120
point-of-no-return. Once started the 5PT exo 240 175
reaction can no longer be influenced.
NaHCO endo 135-190 120
3
Citric acid
Materials mainly used as exothermic endo 190-220 120
derivates
foaming agents in Europe are Azodi-
carbonamide (Azo or ADC), 4,4´-Oxybis- Table 1: Important chemical foaming agents
(benzenesulfonylhydrazide) (OBSH), para-
Toluenesulfonylhydrazide (TSH), Benzenesulfonylhydrazide (BSH), para-Toluenesemicarbazide (TSS) and
5-Phenyltetrazole (5PT). Of these Azo and OBSH are economically by far the most important.

Table 1 lists the most important chemical foaming agents and their key properties as the decomposition
temperature and the gas volume released on decomposition.

Especially for the exothermic chemical foaming agents but also for the citric acid derivatives the reaction
pathways of the decomposition reaction are quite complex. And they can be greatly influenced by the applied
temperature and by accelerating substances, either added intentionally to modify the reaction or present in
the polymer matrix (fillers, stabilizers or other additives).

As an example Table 2 shows how the reaction temperature can influence the efficiency and the resulting
gaseous products of the azodicarbonamide decomposition reaction.

Paper 1 - Mergenhagen Page 2 of 6 pages
Blowing Agents and Foaming Processes 2013 14-15 May, 2013 – Mainz, Germany
APPLICATION OF CHEMICAL FOAMING AGENTS

Chemical foaming agents are used for a number of reasons in the polymer industry. The most important
reason is the weight reduction of finished parts with the focus either on material savings or on weight savings
as in the automotive and aviation industries.

Other big applications are the insulating properties like in crosslinked PE foam, reduction of sink marks and
warpage in injection moulding, sealing properties in cellular rubber or the nucleation needed for physically
foamed polmers. But also decorative (wallpapers) and haptic effects (soft touch), impact protection
(packaging) or sound damping are reasons for using chemical foaming agents.

Which of the chemical foaming agents discussed above is the best choice depends on many parameters:
The polymer used, the production process (injection, extrusion, rotomoulding etc.), the temperature profile of
the process, the part geometry, the goal sought for by foaming and others.

The production processes in the polymer industry are rather complex and it is only rarely possible to use the
pure chemical foaming agents. In most cases it is necessary to modify the foaming agent and formulate it
with additives to make it applicable in the individual production process and to achieve optimum
performance.

In many production processes the powder form cannot be used directly, either for technical reasons or
because of workplace hygiene and safety. It is necessary to modify the product form to make it applicable:
classical masterbatches in most extrusion and injection operations, oil-treated powders for reduced dust and
improved dispersion, and also liquid, pumpable formulations are in use in the industry today.

MECHANISM OF CHEMICAL FOAMING OF THERMOPLASTICS

The mechanism of foaming polymers with chemical foaming agents is a multi-
Mix of polymer and
step process. The understanding of these steps allows the polymer processor
chemical foaming agent
to adjust the production process in such a way that the foaming works well and

that the finally resulting foam shows optimum performance.
In the first step the formulated foaming agent (masterbatch) is mixed with the
bulk polymer and a homogenous blend should result.

Polymer melt with
In the next step the polymer is plastified and the chemical foaming agent (yet
evenly
unreacted) must now be evenly dispersed in the polymer melt.
distributed foaming

agent
It is important that before the chemical foaming agents start to decompose the

polymer melt is under pressure so that the gases evolving in the reaction are
solved in the polymer melt.

The pressure is critical in this part of the process. If not maintained at sufficient
high level the material will start to foam prematurely leading to very Polymer melt with
inhomogeneous foams with very big cells and very bad mechanical properties dissolved gas
and rough surfaces.

In the following step the pressurized, gas rich polymer melt is decompressed,
for example when leaving the extruder die or when injected into a mould.
Immediately with the decompression the nucleation process starts forming the Nucleation
nuclei which will later become the cells of the foam. The number of nuclei that
form is dependent on the rate of pressure drop. The higher the rate of
pressure drop the more nuclei are formed and the finer the resulting foam will
be.
Diffusion, cell growth
The gas dissolved in the polymer now diffuses into the nuclei building pressure
that lets the nuclei expand leading to the cells of the polymer foam. In this
phase the viscosity control is critical (and of course the viscosity is controlled
by the temperature). The viscosity of the polymer must not be too high as then
the pressure in the cells is not sufficient to make them expand. But if the Cell stabilisation
viscosity is too low the thinning cell walls will not be stable enough anymore
and the cells will start to collapse (coalescence). So in this part of the foaming Figure 1: Mechanism
process it is necessary to find the optimum processing window balancing the of polymer foaming
Page 3 of 6 pages Paper 1 - Mergenhagen
14-15 May, 2013 – Mainz, Germany Blowing Agents and Foaming Processes 2013

polymer viscosity for cell formation and
Temperature [°C] 180-200 210-220 250-280
stabilisation.
Gas volume [ml/g] 185-215 260-320 355-455
In the last step of foaming the cell walls are Residues [%] 72-77 61-68 47-57
hardened to support the foam structure. In
Gaseous products [%] 23-28 32-39 43-53
thermoplastic polymers this is done simply by
N ~72 ~57 ~46
cooling. 2
CO ~26 ~33 ~38
This mechanism also works for the physical NH <1 7-12 8-19
3
foaming of thermoplastics, as applied for instance CO ~1.5 ~1 ~2
2
in very low density PS foamed sheets for
Table 2: Decomposition products of azodicabonamide
packaging and insulation. Of course in this
Source: Dongjin Semichem Co. Ltd.
process the gas is directly injected into the
extruder instead of being created by the
decomposition reaction, but the idea is that this gas is dissolved in the polymer melt as well and from there
on the process is the same. Only that chemical foaming agents are used in physical foaming as nucleating
agents to achieve a greater number and more uniform cells.

MECHANISM OF CHEMICAL FOAMING OF THERMOSETS

The first step of foaming thermosets is of course similar to the foaming of thermoplastics, it starts with the
mixing of foaming agent and polymer compound. But this mixing and the plastification of the polymer only
takes place to a point (temperature) where the foaming agent does not yet decompose. Typically the
foaming of thermosets is done in two-step processes. In the first mixing step a homogenous compound is
produced that will be cured and foamed in a second production step.

Typically the thermoset compound is either formed to a final shape at the end of the mixing step (e.g. in the
extrusion of crosslinked PE foam sheet) or it is “batched off” and shaped in a consecutive step (as in normal
rubber production).

In a following production step the thermoset is heated again to a temperature where the crosslinking (curing)
system starts to react and the foaming agent decomposes. So contrary to the foaming of thermoplastics the
gas of the foaming agent is not dissolved in the polymer melt but (ideally) every single particle of foaming
agent creates a void in the polymer compound.

This makes it very clear that in foaming of thermosets the particle size, reactivity and particle distribution play
an even stronger role in defining the resulting foam characteristics than in the foaming of thermoplastics.

Another very critical point is the balance between the decomposition reaction of the foaming agent and the
crosslinking reaction. If the crosslinking sets in too early or too fast the viscosity of the partly crosslinked
polymer will be too high as that a good foam can be achieved. On the other hand, if the crosslinking is too
late or too slow, the cells will grow too big and the strength of the polymer is sufficient to keep the cell walls
from rupturing which results in gas loss and a collapse of the foam.

The crosslinking or curing of the polymer of course stabilizes the cell walls and hence the foam structure.

MECHANISM OF CHEMICAL FOAMING OF PVC PLASTISOLS

A material that is somewhere between thermoplastics and thermosets is the PVC plastisol. Although the final
soft PVC does not have a crosslinked polymer structure and could be reformed, so it is a thermoplastic, the
foaming mechanism is very similar to that of thermosets.

The chemical foaming agent is dispersed in the plastisol and on heating the decomposition starts in parallel
to the gelling. So instead of the curing/crosslinking as in thermosets the gelling reaction increases the
viscosity of the polymer to stabilize the cell walls of the growing cells.

Paper 1 - Mergenhagen Page 4 of 6 pages