Pankaj Pandey, NDSU Department of Agricultural and Biosystems Engineering
Dilpreet Bajwa, NDSU Department of Mechanical Engineering
Sreekala Bajwa, NDSU Department of Agricultural and Biosystems Engineering

This project investigates the application of fibers from Distiller’s Dried Grains with Solubles (DDGS) and corn hull as alternate raw materials in natural fiber filled polymer composites used in the building and landscaping industries. These sectors are currently served by wood plastic composites (WPC) that use wood fiber as the filler. Fibers separated from corn grain hull, and DDGS were compared against oak, a wood fiber, as control. Composite samples were manufactured at both laboratory and commercial scales. Lab samples used two fiber loadings of 30 and 50%, and two types of HDPE, Braskem, a bio-based HDPE made from sugarcane, and Marlex, a petro-chemical. Commercial samples used a fiber loadings of 50%, and Petrothane as the HDPE since Marlex did not work well with its high melt flow index. The samples were tested for several physical and mechanical properties including water absorption, specific gravity, flexural strength, and compressive strength based on appropriate ASTM standards.

All lab-scale samples exhibited specific gravities slightly over one. However, the samples with 30% corn hull or DDGS fiber had significantly lower specific gravity than the oak samples. The DDGS fibers resulted in high water absorption compared to other samples. The samples made with Marlex HDPE absorbed more moisture than samples made with bio-based HDPE, with the highest moisture gain of 22.4% exhibited by samples with 50% corn hull, followed by 15.2% for samples with 50% DDGS fiber. The Braskem composite samples showed the highest water absorption of 9.1% for 30% DDGS fiber, and lowest water absorption of 2.8% for 50% corn fiber. The flexural strength of samples decreased when fiber loading increased from 30 to 50% with Marlex. Braskem composites did not show a change in the flexural strength with fiber loading or fiber type. The impact resistance and linear thermal expansion were significantly higher for samples containing 30% DDGS fiber and Braskem HDPE than all other samples.

The commercial samples containing corn fiber at 50% loading exhibited the highest water absorption of 18.39% followed by samples with 25% corn fiber. All the formulations exhibited specific gravities more than one, with 50% fiber loading showing the lowest values. Samples with 50% DDGS, 50% oak, and 25% oak + 25% DDGS showed high stiffness. Composite samples containing 50% oak and 25% oak + 25% DDGS showed the highest strength.

This study indicates that both DDGS and corn fibers have great potential to be used as a fiber filler in thermoplastic composites, especially in combination with bio-based plastics. While strength properties were comparable or better, moisture affinity of the fibers seemed to be a major problem. Issues of moisture affinity may be addressed with the use of coupling agents in future research as coupling agents have reported to reduce moisture absorption by composite materials.