In the excitement of seeing the ‘bio’ industry grow, people are using terms that have more than one definition, which can confuse lay people. Dr. Ramani Narayan, University Distinguished Professor at Michigan State University, proposed that ‘bio-based’, ‘biomass-based’, or  renewably-based’ be used to describe plastics containing biogenic carbon that is derived from non-fossil, biological resources. He noted that the term ‘biomaterials’ has long been used in the biomedical industry to describe all material types implanted in the body, such as metals, ceramics, and plastics. ‘Biopolymer’ can be used, but this describes all classes of polymers produced by living organisms, which includes proteins and DNA as well as starch and polylactic acid (PLA). Speaker Dr. Jason Zhu from PolyOne said that people continue to be confused by the terms ‘bio-based’ and ‘biodegradable’, because biodegradable plastics may be based on either biomass or petrochemical resources. Dr. Narayan proposed that ‘biodegradable’ be clearly defined as complete removal from the environment in a short, defined time (180 days or maximum of one year), using microorganisms, in a defined disposal environment (composting, soil, marine or anaerobic). He says this definition is critical because partially degraded materials have the potential to cause environmental harm. While clear definition is not yet widespread in the United States, the state of California’s law (since 2005) requires plastic bags to meet ASTM standards for labeled terms such as biodegradable or  compostable.

 

Additives may or may not be bio-based or biodegradable themselves, although some examples are ‘biofillers’ such as wood flour and cornhusks and ‘biofibres’ like hemp and flax. More bio-based additives are being developed, and PolyOnerecently announced a joint programme with ADM to develop bio-based plasticizers for use in PVC formulations. Dr. Zhu sees great opportunity for compounders to add functionality to bio-based plastics, saying that additives can meet current technical challenges for bioplastics such as poor impact, low melt viscosity, slow crystallization rates, degradation, odour, and heat resistance. For example, PHBV  (polyhydroxybutyratepolyhydroxyvalerate) has a very slow crystallization rate, causing properties of a finished part to change over time. Poly- One has investigated various nucleating agents to increase  the crystallization rate of PHBV and the company recently filed a patent for an additive that is a more cost effective alternative to boron nitride, the industry standard.

 

NatureWorks LLC’s Richard Bopp presented work on improving the impact resistance of Ingeo™ Polylactide through biaxial orientation, rubber impact modifiers, and a mineral modifier. He said that no one impact modifier meets all of PLA’s needs; degradable polyester rubber impact modifiers  improve impact modestly, while core shell rubber impact modifiers yield greater impact but are not biodegradable. Dr. Bopp reported that, while not usable in transparent applications, Specialty Minerals’ EMforce® Bio High Aspect Ratio (HAR) calcium carbonate is successful in significantly improving fracture energy and producing ductile failures. Maximum improvement is shown with 20-25 per cent of the mineral modifier.

 

Dr. Jurron Bradley, senior analyst with Lux Research Inc., described the breadth of nanotechnology that is already commercial, noting what while nanotechnology is growing in use, the word ‘nano’ is becoming less publicized. Bradley reports that the initial entry of nanotechnology, from 2004-2007, was driven by coatings and composites, mainly in sporting goods, clothing and automotive. He predicts that in the next few years, all types of nanotechnology will grow at an estimated 54 per cent CAGR (compound annual growth rate) in widening application areas, including aerospace and medical. In the long term, through 2015, Bradley predicts that nanotechnology in electronics applications will have a high growth rate, and that other product areas will continue to deepen.

 

Dr. Karen Winey from the University of Pennsylvania presented studies of the electrical conductivity in composites containing single-wall carbon nanotubes (SWCNT), and described a model that captures the experimental trends. As expected, conductivity increases dramatically with SWCNT volume fraction at the percolation threshold, and the model calculates this critical volume fraction for cylindrical fillers of finite aspect ratio (L/D). The experimental and modeling studies demonstrate the importance of filler orientation on electrical conductivity and at fixed loadings define the ‘critical orientation’ necessary to create a conductive pathway. The highest electrical conductivity is found in nanocomposites having slightly aligned nanotubes, which highlights the importance of controlling filler orientation.

 

Dr. Al Berzinis and Norimitsu Yamaguchi from SABIC Innovative Plastics presented scoping projects investigating nanoclays in engineering resins like polyetherimide (PEI) and PPE/PS blends. They noted industry’s ongoing difficulties in completely exfoliating nanoclays, with melt compounding of commercial organoclays typically resulting in intercalation or partial exfoliation. Their research looked at characterizing and improving exfoliation, but concluded that more work needs to be done in order to determine if nanoclays have a real advantage over other modifiers such as glass fibres.

 

Dr. Joseph Lichtenhan, president of Hybrid Plastics, Inc., proposed that for nanotechnology to make a big impact in plastics, industry should look for problems that have no other material or engineering solution, as well as where nanotechnology could save time or money. He described Hybrid’s POSS® Nanostructured® Chemicals, which are nano-sized molecules derived from polyhedral oligomeric silsesquioxanes and polyhedral oligomeric silicates, and detailed some of the applications where POSS® is finding success. For example, in food packaging, replacing cellulose with a POSS-PA film allows the packager to achieve a specific permeation rate of carbon dioxide, water, and smoke; improves printability; and allows the processor to run the film 35 per cent faster. In medical applications, POSS copolymers are being used for implants and invasive medical devices like heart stents. POSS is being used as a flow aid for reducing viscosity in difficult-to-mould polymers like PPO.

 

In one application, POSS increased the MFI by almost 350 per cent without degrading mechanical properties, and also reduced colour formation, reported Dr. Lichtenhan. He emphasized thatHybrid Plastics is not trying to market the ‘nano’ name or simply replace existing additives with something a little better, but is seeking to ‘solve unsolvable problems’. He noted that other key success factors include having defensible intellectual property and appropriate safety testing. As with other nano- additives, dispersion is critical, and Hybrid typically provides POSS molecules in a pre-dispersed compound.