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Polcarb™ SB in uPVC Extrusions

Polcarb SB is widely used in unplasticised PVC extrusions. Its very fine particle size and stearate coating gives good processability and increases impact strength significantly.

The benefits of fine, controlled particle size are demonstrated in Figure 1. where impact strengths are shown for a lead stabilised uPVC extrusion, filled with different particle size calcium carbonates.

As the filler gets finer not only does impact strength increase but so does ductility (the difference between yield and fail energies)

Levels at which Polcarb SB is used in uPVC are both application and formulation dependant; typical loadings for soil or waste pipe are in the range 7 phr to 15 phr but higher loadings are not uncommon. For profile and thin walled pipe sections, loadings of 4 to 10 phr are normally chosen.

A good low temperature impact strength is an essential property requirement of corrugated drainage pipe. In this and other critical applications, only fine particle size natural calcium carbonates such as Polcarb SB can be used.

In Table 1, Polcarb SB is compared with a competitive ultrafine calcium carbonate. A dry blend was prepared with a commercial stabiliser/lubricant one pack formulated for soil pipe. Process data was obtained using a Brabender Torque Rheometer and twin screw extruder. uPVC properties were measured on a 60mm x 1.5 mm extruded strip.

Table 1
			Polcarb SB 10 phr	Competitive Filler 10 phr
Processing Behaviour
Brabender Fusion Time		mins	2.8	2.7
Brabender Fusion Torque		Nm	41.7	44.7
Extruder Torque		Nm	160	160
Extrusion Die Pressure		MPa	6.9	5.9
uPVC Properties
Falling Weight Impact Strength		J/mm	12.2	13.3
Tensile Strength		MPa	62.4	64.3
Elongation at Break		%	173	160
Extrudate colour	(L value)	-	73.7	73.6
	(a value)	-	-0.2	0.4
	(b value)	-	19.2	18.9
Congo Red Heat Stability		mins at 200°C	27	28

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