A greener alternative to plastics: liquid wood

Bryn Nelson Columnist

Just in time for Christmas, German researchers are ramping up a manufacturing technique for making intricate Nativity figurines, toys, and even hi-fi speaker boxes from a renewable and surprisingly versatile source: liquid wood.

The bio-plastic dubbed Arboform, derived from wood pulp-based lignin, can be mixed with hemp, flax or wood fibers and other additives such as wax to create a strong, nontoxic alternative to petroleum-based plastics, according to its manufacturers.

Crude oil is the basis of the chemical for plastics, said Norbert Eisenreich, a senior researcher and deputy of the directors at the Fraunhofer Institute for Chemical Technology in Pfinztal, Germany. As the price of crude oil increases, he said, so does the price of plastics — and the interest in finding replacements.

The growing list of health concerns linked to plastic ingredients, such as heavy metals and softeners known as phthalates, also has increased the impetus to find a good substitute for manufacturing toys and other products.

The institute began looking for alternatives to oil-based products in the mid-'90s, said Eisenreich. To decrease the dependence on oil, however, any alternative material would need to be relatively abundant. Lignin, he said, offers an ideal candidate because tens of millions of tons are often discarded as a byproduct of the papermaking process.

The idea for liquid wood grew from this realization: “Why not compose material out of the waste of this paper-making?”

Liquid wood, Eisenreich said, combines the high stability and good acoustical properties of wood with the injection-molded capabilities of plastic.

Woodworking, by contrast, can yield intricate figurines but is an arduous, time-consuming process. “Now you make only one complex mold,” he said, “and you can do mass-production. You can make figures.”

In paper mills, wood is typically separated into its three main components: lignin, cellulose and hemicellulose.

Lignin, which tends to give paper a brownish hue, can be used for lower-quality newsprint but is most often separated out with a sulfite- or sulfate-based pulping process prior to the production of high-quality paper.

By mixing that discarded lignin with fibers and wax, Tecnaro, a spin-off German company, has refined a technique for producing plastic-like pellets. Under high-pressure conditions, Eisenreich said, the composite material behaves like melted plastic, allowing it to be injected through a nozzle into a mold and made into a wide range of forms.

Beyond the nine Nativity figurines crafted in collaboration with German toy manufacturer Schleich, the Arboform material has been fashioned into everything from loudspeaker boxes and car parts to golf tees and ballpoint pens.

Customers can even buy liquid wood watches on the company’s Web site, where it reports a current capacity of 300 tons annual output of its biomaterial, but adds that the amount “can be increased easily.”

To make the material more toy-friendly, researchers dramatically reduced the high sulfur content typically associated with the separation of lignin from wood’s other fibers. Eisenreich said a range of processes are widely available for separating lignins without the need for sulfur chemicals.

The institute’s solution, he said, was to use high-pressure hydrolysis (with nothing more than water, high temperature and high pressure) to yield water insoluble lignin. The resulting material maintains its stability even if exposed to water or saliva.

The Arboform material also can be broken into pieces and recycled as a filler. Though it can’t be re-melted, he said, it can be burned just like wood.

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