additives feature | Natural fi bres Natural elements
“If one understands the underlying causes for the damage to bio-fi llers one can design a twin-screw extruder process zone to achieve full capac- ity with little or no damage to the bio-fi ller”, says Robert Roden, head of global compounding technology at extruder maker Steer Engineering. He says that the primary cause of
damage to the fi llers, which includes crushing and burning, is from the shearing that occurs during compression of the fi llers. Particle-to-particle friction results in localized heating of the biomass, damage to the fi llers and/or reinforcements, and loss of product properties. Typical two-lobe kneading
blocks used for mixing will impart some degree of compression, irrespective of how wide or narrow the lobes are. Roden says that Steer has developed
technology that uses tensile forces for mixing rather than compressive forces. He described the company’s Dynamic Stirring Elements, or DSEs, as forward conveying elements with “pins and groves” within the root of the screw segment. These provide a combination of elongational mixing as well as a disruptive splitting and recombination of the melt pool, minimizing shear. Particles of biomass are pulled apart during elonga- tion and wetted with the recombination of melt pools. Particle-to-particle friction is said to be practically eliminated. Elongational mixing also consumes much less power than mixing with compressive forces. DSEs are fully self-wiping and intermeshing, so there is no opportunity for the stagnation of bio-fi ller. The aspect ratio of fi bre is well preserved. To support the higher throughput of an extruder incorporating this “mixing-by-tension” technology, Steer now provides its “Shovel” element (pictured above) for side feeders. This is claimed to be able to signifi - cantly increase throughput.
www.steerworld.com
MoveVirgo has injection moulded PP surfboard fi ns using hemp
reinforced PP produced by the Ultrafi bre project
year for unconnected reasons. According to the European Industrial Hemp Association (EIHA), which represents hemp processing companies within the EU, none of its other members have invested in the technology. Frank Rawson, the head of InControl Ultrasonics, says the equipment the company built is now moth- balled at Smithers Rapra, and without more major government funding no further development is likely. “We learned a lot [in the Ultrafi bre project] but we didn’t get the overwhelming technical improvements that would justify more work,” he says.
The project also demonstrated that fi bres
treated with plasma can increase fl exural strength in a PP compound by as much as 23%. The effect is similar to adding MAPP into the compound, and is said
22 COMPOUNDING WORLD | March 2014
www.compoundingworld.com
to be more cost-effective if treatment costs can be kept below €0.18/kg of fi bre. Unfortunately, in the short-term at least, it does not
look as if they can. “The techno-economic analysis suggests that, at present conditions, the costs of effective plasma treatment of refi ned fi bres for PP based injection moulding compounds will be signifi - cantly higher than costs for using commercial MAPP coupling agent,” says the Ultrafi bre report. Ultrafi bre participant GreenGran produces various
grades of compounds for injection moulding applications, most of them based on polypropylene/MAPP reinforced with bast fi bre coming from various plants. Bast is a collective term for plant fi bre collected from the “inner bark” of such plants as fl ax, hemp, jute and kenaf. The company is headquartered in the Netherlands,
but its production is in Hong Kong, where it partners with local company, Wearmax. GreenGran managing director Martin Snijder says that the Chinese market for its products had been expected to grow faster than in Europe, but he has found that much of the demand there is for production of products for export. “Bio- based plastics are still too expensive for much of the domestic market,” he says, adding that selling natural fi bre compounds for injection moulding anywhere is still tough going. The company’s PP-based compounds are priced similarly to low-end engineering thermoplastics. “Just like everywhere else, customers are mostly
only interested if you have something better and cheaper than what they are currently using. And with most injection moulding companies producing on a toll basis, it’s often not they who decide which material to use anyway. But we are still expecting that in one or two years we will have a breakthrough.” GreenGran produces compounds using jute, hemp and kenaf fi bres, which it sources from Asian suppliers. Snijder says that it has taken some time to obtain reliable sources of supply of materials with consistent quality. “This is a new market for them as well, so we
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