From Science & Research
From Science & Research Novel Nanostructured Crosslinked hyperbranched polymer (HBP) Fig 1: Transmission electron photomicrograph of modified PLA showing nanoscale dimension of crosslinked HBP i.e. < 100nm (stained dark phase). Scale bar: 100 nm. 95 wt.% Modified PLA + 5 wt.% Talc 98 wt.% Modified PLA + 2 wt.% Organo-clay Modified PLA Unmodified PLA 3,2 3,2 3,2 3,5 4 37 83 104 Tensile Modulus (GPa) Elongation at break (%) 0 20 40 60 80 100 120 Fig 2: Tensile properties of hyperbranched polymer modified PLA, its organo-clay based nanocomposites and talc filled composites. Renewable resource based bioplastics are the next generation of materials, which are expected to play a major role in building of a sustainable bioeconomy. Polylactide (PLA) is a renewable resource based bioplastic. However, the inherent brittleness (poor elongation at break and impact strength) of PLA poses considerable scientific challenges and limits its large-scale commercial applications. Numerous approaches such as plasticization, blending with tough polymers and elastomers have been attempted to overcome its brittleness however with huge sacrifice of strength and modulus of the polylactides. At Michigan State University, recently new polylactide based materials having unique stiffness-toughness properties were invented by the authors. The research was focused on exploring the role of emerging hyperbranched polymers in modifying the PLA base resin. Hyperbranched polymers (HBP) are considered as mutant offspring of dendrimers. The nanoscale dimensions, unique physical and chemical properties of HBP make them a unique design tool for tailoring the material properties. Hydroxyl functional aliphatic polyesters are HBPs that consist of a polyalcohol core from which branches extend, forming a coreshell structure. These HBPs can have abundant hydroxyl groups on their periphery leading to their high surface functionalities . This research is based on creating new nanoscale hyperbranched organic particles in a PLA matrix (Biomer ® L9000 from Biomer, Germany) during industrially relevant melt processing. In this approach, a commercially 32 bioplastics MAGAZINE [02/07] Vol. 2
From Science & Research Polylactide Bioplastics for Multifarious Applications Article contributed by Dr. Amar K. Mohanty, associate professor and Rahul Bhardwaj, PhD student, both at School of Packaging, Michigan State University, East Lansing, MI, USA available hydroxyl functional hyperbranched polymer (BOLTORN TM H2004 from Perstorp, Sweden) was selectively in-situ crosslinked with a polyanhydride (PA-18, LV from Chevron- Phillips, USA) in the PLA matrix by reactive extrusion. There was formation of a novel nanostructured polylactide based two-phase system (Figure 1), in which crosslinked HBP particles were present in nano-domains (< 100 nm). The modified PLA, having 90-92 weight-% of pure PLA, exhibited an improvement in elongation at break of about 800-1000% with minimal sacrifice of tensile strength and modulus. The findings showed that such a modified PLA bioplastic material can act as an ideal matrix for nano-clay or talc as well as natural fiber reinforcements leading to the development of many PLA based materials with attractive properties. Figure 2 represents the tensile properties of such a modified PLA, its organoclay (Southern Clay Products, USA) reinforced nanocomposites and talc (Luzenac, USA) filled composites. The modified PLA surprisingly exhibited 20 and 25 fold improvement in elongation at break on specific loadings of nanoclay and talc particles. These findings also revealed that the modified PLA can act as an additive for the dispersion of nanoclay in polylactide based nanocomposites. The potential impact of this research on PLA can lead to the enhancement of its stiffness-toughness balance, improved melt strength, tailored melt viscosity and ease of processing, which can be exploited in a variety of products and processes. This research is financially supported by the US National Science Foundation- Division of Design, Manufacture, and Industrial Innovation (NSF-DMII) program. www.egr.msu.edu/cmsc/biomaterials 105x148_bioplastics www.msu.edu/~mohantya/ MAG_4c 16.05.2007 12:49 Uhr Seite 1 www.packaging.msu.edu/Mohanty.php Organizer NürnbergMesse Tel +49 (0) 9 11. 86 06-0 info@nuernbergmesse.de www.brau-beviale.de C M Y CM MY CY CMY K Note the date! Nuremberg, Germany 14 – 16.11.2007 47. European Trade Fair for the Beverage Industry 2007 Raw Materials – Technologies – Logistics – Marketing bioplastics MAGAZINE [02/07] Vol. 2 33
