Blowing Agents and Foaming Processes 2011

232 Pages·2013·22.18 MB·English

by  iSmithers

Blowing Agents and
Foaming Processes 2011
13th International Conference
Radisson Blu Scandinavia Hotel Düsseldorf, Germany
10-11 May 2011
Conference Proceedings
Image courtesy of BASF - The Chemical Company
Supported by:
Organised by:
Journal of Cellular Polymers
Blowing Agents and Foaming
Processes 2011

Organised by

Düsseldorf, Germany
10-11 May 2011
eISBN: 978-1-84735-632-1
© Smithers Rapra Technology Ltd, 2011
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Blowing Agents and Foaming
Processes 2011
Contents
SESSION 1: BLOWING AGENTS, BLOWING GASES & SPECIALITIES
Paper 1 Chemical foaming of thermoplastics
Dr Thomas Mergenhagen, Tramaco GmbH, Germany
Paper 2 Further development of FEA-1100 -a zero ODP and low GWP foam expansion agent
Gary Loh, Dr Mark L Robin & Joseph A Creazzo, DuPont Co, USA
Paper 3 Composite and biocomposite foams based on polypropylene with reinforcements and
functional fillers prepared by supercritical CO dissolution
2
Dr Marcelo Antunes, V Realinho, M Ardanuy, M Ll Maspoch & J I Velasco, Universitat Politècnica
de Catalunya, Spain
Paper 4 Appliance PUR: Low climate change impact solution
James M Bowman, P E, Honeywell International, USA
Paper 5 A continued investigation of AFA-L1, a new low GWP blowing agent
Dr Laurent Abbas, Arkema, France & Ben Chen, Joseph Costa & Philippe Bonnet, Arkema Inc, USA
Paper 6 New formulations with methylal as a blowing agent for various rigid, flexible and integral skin
polyurethane foams
Henrique Bavoso, Arinos Quimica Ltda, Brazil & Michel Beaujean, Lambiotte SA, Belgium
SESSION 2: EXTRUSION: BIODEGRADABLES AND PARTICLE FOAMS
Paper 7 Foam (sheet) extrusion of externally plasticized cellulose acetate
Stefan Zepnik, S Kabasci & T Wodke, Fraunhofer Institute for Environmental Safety & Energy
Technology UMSICHT; K Berdel & T Hildebrand, Institute of Plastics Processing (IKV); H-J Radusch,
Martin Luther University Halle-Wittenburg & F van Lück, Inde Plastik Betriebsgesellschaft mbH,
Germany
Paper 8 Expanded polypropylene bead foams: process and characterisation
Mohamad Reza Barzegari, Yanting Guo, Raymond KM Chu,Chul B Park & Nan Q Zhou, University of
Toronto, Canada
Paper 9 Particle foam technology with bio based polymers: Processing and characterisation
Eva Potyra, Anja Schneider, Dr Jan Diemert, Dr Axel Kauffmann, Fraunhofer Institute for Chemical
Technology ICT, Germany +++ PAPER UNAVAILABLE +++
SESSION 3: LASER, FOAM BASICS & NEW FINDINGS
Paper 10 Laser induced foaming
Rüdiger Wissemborski, Chemische Fabrik Budenheim KG, Germany
+++ PAPER UNAVAILABLE +++
Paper 11 Advances in thermal insulation of extruded polystyrene foams
Dr Chau V Vo, Friedhelm Bunge & John Duffy, Dow Europe GmbH, Switzerland & Lawrence Hood,
Dow USA, USA
Paper 12 Foaming polystyrene using blends of HFC: solubility and processing behaviour
Michel F. Champagne and Richard Gendron, Industrial Materials Institute, National Research Council
Canada, Canada
Paper 13 Characterisation of polyolefins used for foaming via non-linear rheological methods
Elke Pachner & S Filipe, Borealis Polyolefine GmbH, Austria
Paper 14 Analysis of the expansions behaviour of cellular rubber materials
Prof Dr-Ing Dr-Ing E h Walter Michaeli, Prof Dr-Ing Christian Hopmann, Dipl-Gyml Sarah Sitz, Institut
für Kunststoffverarbeitung ( IKV), Germany
+++ PAPER UNAVAILABLE +++
Paper 15 Possibilities for the avoidance of surface defects on foamed components
Dipl-Ing Stefan Hins & Dipl-Ing Udo Hinzpeter,, Kunststoff-Institut Lüdenscheid, Germany
Paper 16 Implementation of the Mucell® process in commercial applications
Dr Hartmut Traut, Dipl-Ing, Uwe Kolshorn & Levi Kishbaugh, Trexel, Germany
Paper 17 Introducing two of KANEKA's structural design techniques for foamed products
Hiroshi Fujiwara, Kaneka Corporation, Japan +++PAPER UNAVAILABLE +++
SESSION 4: POLYOLEFIN FOAMS – NEW ASPECTS
Paper 18 Density graded linear medium density polyethylene foams produced under a temperature
gradient with expancel microbeads
Jiaolian Yao, Mohamad Reza Barzegari & Denis Rodrigue, Université Laval, Canada
Paper 19 Microwave enhanced foaming of carbon black filled polypropylene
Dr Aleksander Prociak, Sterzyński Tomasz & Michałowski Sławomir, Cracow University of
Technology, Poland
Paper 20 Thermoplastic processing behaviour of foamed polyolefin sheets for tank building applications
Dipl-Ing(FH) Dominic Müller, Dipl-Ing(FH) Marco Stallmann & Dr Marcus Hoffmann, Simona AG,
Germany
SESSION 5: EXTRUSION MACHINERY AND PRODUCTS
Paper 21 Advanced extrusion systems in the thermoplastic foam industry: Optimised twin screw
concepts
Jean P Strasser, Aixfotec GmbH, Germany
+++ PAPER UNAVAILABLE +++
Paper 22 PE foaming: foaming sustainability
Jérôme Gocyk & Paolo Mariani, Polimeri Europa, France
Paper 23 Development of foamed thermoplastic substrate materials for printed circuit boards
Clemens Keilholz, T Apeldorn, F Wolff-Fabris, V Altstädt, University of Bayreuth, Germany
Paper 24 Development of innovative and sustainable foam solutions
Dr Holger Ruckdaeschel, BASF SE, Germany
Blowing Agents and Foaming Processes 2011 10-11 May, 2011 – Düsseldorf, Germany

CHEMICAL FOAMING OF THERMOPLASTICS

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

BIOGRAPHICAL NOTE

Dr. Thomas Mergenhagen 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 of thermoplastics 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 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. 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 action of chemical foaming agents as nucleating agents in
physical foaming.

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

INTRODUCTION

Polymeric 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, polymers and production processes makes the foaming of thermoplastics a
very complex field. 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.

CHEMISTRY OF FOAMING AGENTS

Foaming agents in the context of the polymer industry are substances that are used to manufacture
polymeric foams. But the use of this term is often not stringent: it is used in the same way for the basic
chemicals that are used as well as for the formulated foaming agents which are made “ready-to-use” by the
polymer processor.

There are two big groups of foaming agents, the physical and the chemical foaming agents, and a relatively
new and smaller group of so-called microspheres.
Page 1 of 6 pages Paper 1 - Mergenhagen
10-11 May 2011- Düsseldorf, Germany Blowing Agents and Foaming Processes 2011

The physical foaming agents are either gases or low boiling liquids that are mixed into the polymer melt at
high pressure and evaporate to form voids in the polymer on decompression.

Chemical foaming agents are (in general solid) substances that are not stable at higher temperatures but
decompose to form gases and other decomposition products. The released gases then act in the same way
as physical foaming agents do.

The microspheres are small droplets of low boiling liquids covered with a polymeric shell. On heating the
shell softens and the liquid evaporates building a pressure that lets the softened shell expand in this way
again creating voids within the polymer matrix.

The chemical foaming agents which are the main topic of this paper are again 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 organic substances that, on reaching a certain temperature, decompose and
release gas and heat. Because of this the decomposition reaction is auto-catalytic, the released heat raises
the temperature and the reaction becomes even faster. This makes for a very fast decomposition of the
exothermic foaming agents but also for a point-of-no-return. Once started the reaction can no longer be
influenced.

Materials mainly used as exothermic
Foaming reaction Decomposition gas volume
foaming agents in Europe are Azodi-
agent temperature [°C] [ml/g]
carbonamide (Azo or ADC), 4,4´-Oxybis-
Azo (ADC) exo 220 220
(benzenesulfonylhydrazide) (OBSH), para-
Toluenesulfonylhydrazide (TSH), Ben- OBSH exo 160 125
zenesulfonylhydrazide, para-Toluenesemi- TSH exo 145 110
carbazide (TSS) and 5-Phenyltetrazole. Of
BSH exo 140 110
these Azo and OBSH are economically by
TSS exo 230 120
far the most important.
5PT exo 240 175
Table 1 lists the most important chemical NaHCO endo 135-190 120
3
foaming agents and their key properties as Citric acid
endo 190-220 120
there is the decomposition temperature derivates
and the gas volume that is released on
Table 1: Important chemical foaming agents
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 temperature [°C] 180-200 210-220 250-280
modify the reaction or present in the
gas volume [ml/g] 185-215 260-320 355-455
polymer matrix (fillers, stabilizers or other
residues [%] 72-77 61-68 47-57
additives).
gaseous products [%] 23-28 32-39 43-53
As an example Table 2 shows how the N ~72 ~57 ~46
2
reaction temperature can influence the
CO ~26 ~33 ~38
efficiency and the resulting gaseous
NH <1 7-12 8-19
products of the azodicarbonamide de- 3
CO ~1.5 ~1 ~2
composition reaction. 2
Table 2: Decomposition products of azodicabonamide
Source: Dongjin Semichem Co. Ltd.
Paper 1- Mergenhagen Page 2 of 6 pages
Blowing Agents and Foaming Processes 2011 10-11 May, 2011 – Düsseldorf, 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.

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.

And in many processes the powder form cannot be used. 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 even liquid, pumpable formulations are in use in the industry
today.

MECHANISM OF CHEMICAL FOAMING

The mechanism of foaming polymers with chemical foaming agents is a

multi-step process. The understanding of these steps allows the polymer
Mix of polymer and
processor to adjust the production process in such a way that the foaming
chemical foaming agent
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.

In the next step the polymer is plastified and the chemical foaming agent (yet
Polymer melt with 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.

Polymer melt with
The pressure is critical in this part of the process. If not maintained at
dissolved gas
sufficient high level the material will start to foam prematurely leading to very

inhomogeneous foams with very big cells and very bad mechanical
properties and rough surfaces.

In the following step the pressurized, gas rich polymer melt is decompressed,
Nucleation
for example when leaving the extruder die or when injected into a mould.

Immediately with the decompression the nucleation process starts forming
the 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
Diffusion, cell growth
be.

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 temperature, and with it the viscosity, control is critical. The
Cell stabilisation
viscosity of the polymer as determined by the temperature must not be too

high as then the pressure in the cells is not high enough to make them
Figure 1: Mechanism
expand. But if the viscosity is too low the thinning cell walls will not be stable
of polymer foaming
enough anymore and the cells will start to collapse. So in this part of the
foaming process it is necessary to find the optimum processing window
balancing the polymer viscosity for cell formation and stabilisation.
Page 3 of 6 pages Paper 1 - Mergenhagen
10-11 May 2011- Düsseldorf, Germany Blowing Agents and Foaming Processes 2011

In the last step of foaming the cell walls are hardened to support the foam structure. In thermoplastic
polymers this is done simply by cooling, in rubber by curing (crosslinking).

The figure 1 shows the different steps involved in the mechanism of foaming.

EXAMPLES OF CHEMICALLY FOAMED POLYMERS

A typical example of chemically foamed products
are PVC foam core pipes as shown in figure 2.
The pipes are mainly used for sewage lines and
are produced by extrusion. The formulated
foaming agent used in this application are almost
entirely masterbatches of exothermic foaming
agents that are dosed directly to the extruder.

Figure 2: PVC foam core pipes

PVC foam boards are also produced by extrusion using
blends of exothermic and endothermic foaming agents either
as free foam boards with slightly structured surface or in a
Celuka-process with smooth surface.

The boards are used in the construction industry, for
advertising, for the production of furniture and many other
applications. The latest trend are PVC foam boards that can
be decorated by digital printing with industrial ink jet
equipment.

Figure 3: PVC foam boards

Synthetic wine corks (and corks for all kinds of other liquids) are
produced either by injection moulding or by extrusion. Main polymers
used are PE and SEBS or PE/SEBS blends.

The corks are foamed using endothermic foaming agent compounds or
blends of endothermic foaming agents and special microspheres for
food contact applications.

Figure 4: Synthetic wine corks

Foamed rubber products are again produced by injection
moulding and extrusion and some are even produced in
compression moulding.

For closed cell rubber foaming agent compounds based mainly
on Azo and OBSH are used, for the open cell sponge rubbers
TSH and BSH are the foaming agents of choice.

Figure 5: Foamed rubber products
Paper 1- Mergenhagen Page 4 of 6 pages