The sight of large pieces of plastic debris on coastlines and beaches is all too familiar, says marine biologist Richard C. Thompson of the University of Plymouth, ...
RESEARCH NEWS
Plastics break down on the beach POLYMERS
Plastic bottles together with coconut seeds washed up on the shoreline in St Lucia, Caribbean. (Courtesy of Richard C. Thompson.)
Ever wondered where some of the millions of tons of plastic produced annually end up? According to new research from the Universities of Southampton and Plymouth and Sir Alister Hardy Foundation for Ocean Science in the UK, some of that plastic debris ends up as microscopic fragments and fibers in marine habitats [Thompson et al., Science (2004) 304, 838]. The sight of large pieces of plastic debris on coastlines and beaches is all too familiar, says marine biologist Richard C. Thompson of the University of Plymouth, but less obvious is
the presence of microscopic plastic fragments in oceans and beach sediment. Most plastics are not biodegradable and persist for long periods of time, during which they break down into smaller and smaller fragments, probably through mechanical action. However, the abundance of microscopic plastic debris in marine systems was largely unknown until now. Thompson and colleagues collected sediment from beaches and estuaries around the UK and identified particulates of unnatural appearance using Fourier Transform infrared (FTIR) spectroscopy. Some of this material could not be identified, but about one third consists of synthetic polymers (including acrylic, alkyd, poly(ethylene:propylene), polyamide, polyester, polyethylene, polymethylacrylate, polypropylene, and polyvinyl-alcohol). The researchers also looked at plankton samples collected over the last 40 years in the North Atlantic. Plastic debris captured at the same time provides a record of its abundance over recent decades. The amount of debris in samples from the 1980s and 1990s is significantly higher than in the 1960s and 1970s. The microscopic fragments are also sufficiently small to be ingested by marine organisms such as amphipods, lugworms, and barnacles, which all feed in different ways. The effects of plastic particulate ingestion are not known as yet and further work is needed. “Our team is now working to identify the possible environmental consequences of this new form of contamination,” says Thompson. If it is found that the toxic chemicals used in plastic fabrication (e.g. plasticizers, colorings, etc.) can be transferred along the food chain, then this would be a cause for concern, he says. “Given the durability of plastics and the disposable nature of many plastic items, this type of contamination is likely to increase,” says Thompson. “There is a challenge here to all of us to dispose of our waste appropriately and wherever possible to reuse or recycle plastic items.” Cordelia Sealy
Using carbon nanotubes to reduce polypropylene flammability POLYMERS Researchers from the National Institute for Science and Technology and the University of Kentucky have studied the thermal and flammability properties of polypropylene filled with multiwalled carbon nanotubes (MWNT) (Kashiwagi et al., Polymer (2004), 45 (12), 4227). Polypropylene pellets were melted and placed in a mixer. MWNTs were added and mixing continued for 30 minutes. MWNT dispersion in the polypropylene was examined using both scanning electron and optical microscopy. Both
analyses indicate that the MWNTs vary considerably in diameter and length, but are well dispersed in the polypropylene. The MWNT content varies from 0.5 wt.% to 4 wt.%. Flammability properties were measured with a cone calorimeter in air and a gasification device in a nitrogen atmosphere. More than 2 wt.% MWNT content was required to increase the ignition delay time of the nanocomposite. MWNTs significantly reduce the peak heat release rate, with
the greatest reduction at 1 wt.% MWNT. Residual Fe particles and defects in the MWNTs have a negligible effect on the heat release rate of the polypropylene/MWNT nanocomposite. The researchers suggest that a relatively uniform network-structured layer covers the entire sample surface without any cracks or gaps forming during heating. This layer re-emits much of the incident radiation back into the gas phase from its hot surface, thereby reducing the heat transmitted
to the polypropylene layers below. In contrast, carbon black filled polypropylene did not form this network-structured layer and its heat release rate does not significantly differ from that of unfilled polypropylene. The reduction in polypropylene flammability, therefore, is dependent upon the size and shape of filler carbon particles. Thermal conductivity increases with increasing MWNT content, with the effect greatest above 160°C. John K. Borchardt
July/August 2004
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