Starch expandable beads

Figure 4. Foam density as function of die processing temperature for potato starch expandable beads with a water content of 10% at constant injection speed.

Starch is one of these renewable resources. Starch is widely available and is especially suited for the production of foamed thermoplastic materials due to the intrinsic presence of a blowing agent. Destructurization of starch by means of extrusion compounding will facilitate the formation of expandable beads or foams of thermoplastic starch. 

As an alternative to these materials the objective in this research will be to produce starch based resilient thermoplastic foams based totally on native potato starch. This is done in two steps the production of expandable thermoplastic starch beads by extrusion and foaming of the expandable beads after conditioning in a successive foaming step. The properties of these foams will be studied as a function of processing parameters and material composition. A further objective is to determine the ultimate properties of pure starch based foams. 

Within a certain processing window it is possible to foam the expandable beads. The resulting foam properties depend strongly on the actual processing conditions during foaming. The correct parameters enable the production of a resilient diermoplastic foam from pure potato starch. Material freeze up due to a fast drop in Tg is the predominant mechanism for cell growth and stabilization of these foams. 

An important use of PS is in foams and beads which are widely used as impact absorbing materials in packaging. Because of its very low bulk density, expanded PS is a very visible component of plastics litter and is often seen floating on the surface of water. For the same reasons it is particularly expensive to collect and reprocess. Biodegradable foamed plastics based on starch are being developed which promise to be an ecologically acceptable alternative to PS (Chapter 5). 

The objective of extrusion compoimding is to produce amorphous expandable starch beads with a defined glass transition temperature. Extrusion is done on a Clextral BC45 co-rotating twin screw extruder... 

---