Plant Containers in the Greenhouse
Thousands of biobased and petroleum-based plant containers will be tested in largest-ever bioplastics program.

Greenhouse Trials Underway for Biobased Plant Containers Project

Biopolymers and Biocomposites Research Team (BBRT) members have started the first round of plant container development and greenhouse testing for their five-year Bioplastic Container Cropping Systems project. This research, funded in part by the U.S. Department of Agriculture, will develop biorenewable and biodegradable containers for the specialty crop industry. The $3.9 million project is led by BBRT faculty members William Graves, professor of horticulture; David Grewell, associate professor of agricultural and biosystems engineering; Michael Kessler, associate professor of materials science and engineering; and James Schrader, assistant scientist in horticulture.

Thirty-four different types of biorenewable polymers and composites are being screened to evaluate their potential for use in container crop production and to determine the rate of biodegradation in soil under landscape conditions.

The containers include commercially available pots that are marketed as biodegradable and containers developed by BBRT researchers. The biobased containers will be evaluated alongside conventional petroleum-based plastic containers in the greenhouse and in the landscape.

“One of the goals of this project is to develop and evaluate new bioplastic materials for use in plant containers that will fulfill all of the functions of petroleum-based plastic containers without the drawbacks,” said Grewell.

Biobased Materials

The 34 types of containers are made from a variety of biobased materials including soy protein, wheat starch, two commercially available plant starch-based plastics PHA (polyhydroxyalkanoates) and PLA (polylactic acid), and natural fibers (wood, paper, and coconut husk). PHA and PLA were also blended with dried distillers grains with solubles (DDGS), corn stover, and nano-clay to form biocomposite materials.

Dip Coating
Kenny McCabe dip coats the fiber-based plant containers.

The researchers are also testing some of the fiber and soy containers with thin coatings of biobased polyurethane, tung oil, PLA, and polyamide (a polymer produced from oil of pine trees). “These biobased coatings have potential to improve water use efficiency of fiber containers during plant production and preserve the integrity and appearance of the containers for improved marketability when sold to the consumer,” said Schrader.

“The first round of trials will provide information that will help eliminate materials with little success as plant containers,” said Schrader. “It will also provide data for improving the materials that show potential.”

Developing New Materials

BBRT researchers Gowrishanker Srinivasan, postdoctoral research associate; Samy Madbouly, postdoctoral research associate; and Kyle Haubrich, research associate, developed 25 of the 34 types of biobased containers. Madbouly generated the formulations and procedures for dip coating with biobased resins. Srinivasan and Haubrich developed two types of soy plastics and the procedures for processing them. They also created the methods for blending soy protein with PLA and DDGS, corn stover, and nano-clay with PHA and PLA. 

The non-commercial materials for injection-molded containers were prepared, extruded, and pelletized at the Center for Crops Utilization Research’s Technology Transfer Pilot Plant. The mixtures were extruded using a co-rotating twin screw extruder and then cut into pieces using a pelletizer.

The pellets were shipped to R&D/Leverage in Lee’s Summit, Missouri, and, under the technical guidance of Srinivasan and Haubrich, were formed into containers using injection-molding equipment. A total of 3,400 containers were injection molded for the greenhouse and biodegradation trials at Iowa State University.

Greenhouse Trials

McCabe prepares the 40 types of containers.
McCabe prepares the 40 types of containers for the greenhouse trials by planting a variety of plants.

A total of 40 types of plant containers including controls are being evaluated in two trials at the Horticulture greenhouses under the direction of Schrader and Kenny McCabe, research associate. In the first trial that is currently underway, five species of plants are being grown in the containers for four weeks. The container-plant units are monitored for plant growth and health and container function and durability.

“Several of the bioplastic and coated-fiber containers are performing quite well,” said McCabe. “Many appear to be producing plants as large and as healthy as controls, with no observable difference in water use efficiency. We’re anxious to see what the data show. ”

Plants from this trial will be transplanted in a garden plot at the Horticulture Research Station at the beginning of July to assess the long-term growth and health of plants produced in biobased containers. “The landscape trial will allow us to evaluate the biodegradation rate of containers and to quantify the plant growth benefit from containers as they degrade in the soil near the plant roots,” Schrader added.

In the second greenhouse trial to begin later this summer, two species of plants will be grown in containers for eight weeks. “During this trial, we will be looking more closely at water use efficiency and the fertilizer effect provided by container degradation during greenhouse production,” said Schrader.

The greenhouse trials will conclude this fall, and the favorable materials will be improved and tested in a second round of development and evaluation to take place in 2013.

For more information about the project, visit: http://bioplastic.public.iastate.edu.

Greenhouse Photos
Left: McCabe inspects the plants in the containers. Right: Jim Schrader (left) shows Gowrishanker Srinivasan the root system of one of the plants grown in a PLA container.