Extrusion of Plastic Foams - Fundamentals & Introduction

The production of plastic foams always involves an uncontrolled reaction inside the extruder. These reactions are either the production of a gas by a chemical decomposition, or the physical expansion of a compressed gas by a drop in pressure!

Therefore, it is important to know which parameters can have a greater influence on the final quality of the foam in order to be able to:

• Fine-tune properties
• Maximize performance of the extrusion process
• Excel troubleshooting

Before we get into the extrusion process, let's first discuss the reason behind choosing the plastic foams. that is, benefits of plastic foams:

Key Features of Plastic Foams

Plastic foams are widely used in many applications, where their inherent properties are most valued:

• Light weight
  The lower density of foams constitutes the driving factor for its use in applications, such as: Packaging, construction, automotive and other. Plastic foams can have densities ranging from 800 kg/m³ down to 20 kg/m³. Lighter packaging with reduced carbon footprint and lighter vehicles with reduced fuel consumption and CO₂-emissions can be manufactured with the use of foams.

Lightweight Extruded Polystyrene (XPS) for Food Packaging



• Insulation
  Foams have superior thermal and sound insulation properties. Therefore, these are the material of choice for many construction and automotive applications. Thermal and sound insulation in construction is one of the largest applications for very light foams. The automotive industry is also taken benefit of the sound damping features of foams to improve comfort in vehicle interiors.



Thermally Insulated XPS Boards (L); XPE Rolls (R)


• Impact damping
  The capability of soft light foams of damping an impact or a shock is seek in some industrial applications, such as: Protective packaging, cushioning, joints, floors, etc.



Polyolefin Foam for Damping application in Automotive



• Soft touch, floatability, easy-cleaning
  These features boost the use of foams in leisure and sports applications, such as: Floating vests, gym pads, protection gear, etc.

Technologies for Extrusion of Plastic Foams

There are different technologies for obtaining plastic foams by extrusion. Choosing one or the other will depend on material, extrusion technology available, range of density desired and main features seek.

Generally, we can distinguish between two different groups of technologies for foaming:

1. Physical foaming
   Involves the use of a compressed gas as blowing agent. Physical foaming is used for the production of light and very light foams, with densities between 20 and 200 kg/m³. Special equipment is needed for the injection of the gas in the extruder, the intimate mix of the gas with the molten polymer and the correct expansion of the foam.
   
   Key to produce functional foam with the featured properties are:
   
   
   • Rheological properties of the resin
   • Processing conditions
   • Chosen blowing agent
   • Equipment design
   • Formulation, and more


2. Chemical foaming
   Chemical foaming can be used to obtain light crosslinked polyolefinic foams, with very low densities. This technology requires the use of special equipment, a thorough control of the processing conditions and the formulation.
   
   On the other hand, chemical foaming can also be used to obtain heavy foams, with a reduction of density of around 20-30% compared to the solid polymeric resin. In this case, standard extrusion equipment can be used with minor adjustments, and only an adjustment of the processing conditions and the formulation is needed.

Market of Plastic Foams

Foams that are not produced by extrusion, such as PUR (polyurethane) and EPS (expanded polystyrene) foams represent, by far, the largest volumes of consumption on the global foam market.

Whereas, the largest volume in extrusion foams is taken up by XPS (extruded polystyrene), followed by PE foams (crosllinked and non-croslinked), PP foams and PET foams.

PET Foams for Light Weighting Applications

CrossLinked PP for Automotive Applications

XPE for Packaging Applications

• Packaging and construction are taking the largest share, especially due to the wide use of XPS in insulation panels and food trays.
• PE foams also have a considerable use in packaging and construction, and a growing share in automotive, together with PP foams.
• Other particular foams, such as PET foams, are increasingly being used in sandwich applications and also in light-weight packaging

Plastic Professionals: Stay Alert!

Stay updated on latest advances in foam extrusion practices to identify where the true potential & new opportunities exist for you and make better R&D decisions. Join the course: Extruding Plastic Foams to Meet Today’s Market Needs and learn the latest practices of the evolved art of foam extrusion.