Extrusion International 4-2017

34 Extrusion International 4/2017 COMPOUNDING Compounding experts meet in Wuerzburg In one of 14 presentations at the 12th Compounding Conference, organised by SKZ Süddeutsches Kunststoffzentrum in Würzburg, Germany, SKZ researcher Dr Nikola Kocic reviewed investigations made into biobased alternatives for plasticised PVC, compounded on a Leistritz ZSE27 Maxx co-rotating extruder and injection moulded into test pieces on a Wittmann Battenfeld TM 1300 injection moulding machine. The work resulted in selection of a close alternative with a formulation consisting of 57 wt% PHB (polyhy- droxybutyrate), 19.5wt% biobased plasticiser, 16wt% filler, 5wt% elasto- mer, 2wt% compatibiliser and 0.5wt% lubricant, resulting in 64% renewable content. The PHB based compound was per- ceiveed as suitable for children’s toys. This was due to lower Shore D harness of 35 (plasticised PVC 44) and almost three times higher elongation at break of 307% (PVC 97%), offset however by lower tensile strength (9 MPa) com- pared with PVC (17 MPa) and slightly higher price of €3.0/kg compared with €2.5/kg for PVC. Migration was still low at 0.3% after seven days at 70°C, even though higher than 0.1% for plasticised PVC. As Manager of the Hexpol TPE Central Technology & Development Centre, Dr Thomas Köppl spoke about Dryflex Green biobased thermoplastic elasto- mer (TPE) compounds sourced from re- newable resources such as plant & veg- etable crops. These TPE compounds range in hardness between Shore A 20 and Shore D 50 and in renewable con- tent from 20% to above 90% Köppl said Hexpol faced a challenge in combining high mechanical properties with high renewable content. In order to perform as well as or as close as pos- sible to conventional fossil-based TPEs, renewable alternatives should have good adhesion to various fossil-based polymers and to PLA (polylactide acid) as a biodegradable bioplastic. He showed how renewable content for Dryflex Green compounds increases with hardness, fromover 20%for Shore A55 through to above 60% for Shore A 80 and above 70% for Shore D 55, with corresponding reductions in carbon di- oxide footprint of 1.0, 2.5 (Shore A 85) and 3.5 kg CO 2 equivalent per kg TPE. Köppl said Dryflex Green is a whole range of materials based on combina- tions of “building blocks”, resulting in “thousands of possible materials and possibilities that make sustainability in daily life a reality”. Further oppor- tunities will arise as high renewable content is extended to also include low hardness versions of Dryflex Green, Köppl stated. He likened this with the TPE product development life cycles of observed for conventional TPEs by consultants Robert Eller Associates. Max Guntern, process engineer at Swiss compounding machinery producer Buss, talked about efficiently com- pounding highly filled masterbatches with Buss MX Kneader extruders. MX kneading action extruders are charac- terised by gentler processing than con- ventional twin screw extruders, result- ing in less fibre length reduction and opening up of filler agglomerates with- out destroying structural properties. This gentle yet effective processing is achieved with features such as dual ro- tational and oscillating screw motion to obtain both axial and transverse mixing action, interaction of kneading flights in the mixing screw, station- In SKZ technology center