ChemMatCARS Nuggets - Materials Science

Plastic Wrap for Fields: X-ray Studies Help Optimize Film Strength

Accomplishment
Some farmers use degradable plastic films to control humidity, light, and temperature around crops. With this aid, crops can be planted earlier and grow faster, thus expanding the viability of marginal growing regions. Important factors are how fast the film degrades, its thinness, and its strength.

X-ray studies characterized how the film’s crystalline microstructure changes when the film is stretched, as occurs during manufacturing. The results will help optimize the tricky manufacturing process that produces field-size sheets of film.

In the manufacturing process, the polyolefin films are first blown to a thickness of 100-200 µm (shown), then stretched to 10-30 µm (not shown).

Impact
Agricultural films help control humidty, but must be thin enough that plants can poke through at the right time as the film degrades. The films can be customized to retain desirable properties for local conditions, types of agricultural chemicals used, and required durability and lifetime.

However, producing square-mile quantities of micron-thick plastic is a significant manufacturing challenge. Film thickness is also a factor in cost.

The studies at ChemMatCARS helped determine that small- and wide-angle X-ray scattering are effective in determining the crystalline structure of the film as it is being stretched. The results can guide adjustments in the composition and manufacturing process so that high-quality films can be produced economically in bulk.

X-TEND films, developed by the Cooperative Research Centre for Polymers (Australia) and manufactured by Integrated Packaging (Australia) are currently being been tested on wheat, cotton, lentils, maize and sorghum by the Birchip Cropping Group in several Australian states.

At ChemMatCARS, films 15 to 30 µm thick were stretched to breaking in an X-ray beam (left) to study strain. Changes in the x-ray scattering (right) correspond to changing orientation in the crystal structure of the polymer as it is stretched.

September 2007

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