Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 22, 2006
Publication Date: February 12, 2007
Citation: Evangelista, R.L. 2007. Milkweed seed wing removal to improve oil extraction. Industrial Crops and Products 25(2):210-217. Interpretive Summary: Milkweed is now grown commercially mainly for the production of floss used as hypoallergenic filler in comforters and pillows. The seeds obtained after separating the floss are currently sold, to a limited extent, as planting material for prairie restoration and highway beautification projects. New uses for the seeds are being developed to improve the economics of milkweed production. Issues related to seed processing must also be addressed. The shape of the seed, its light weight and the presence of paper-thin husk (wing) around its edges all contribute to its poor flow characteristics. Agitation is required to keep the seeds moving out of bins and hoppers. The light wing also breaks readily during handling, creating a dust problem that could be a safety issue. This study was conducted to explore the feasibility of removing the wings from the seeds as part of the seed cleaning step before oil extraction. Seed wings were effectively removed and separated using a simple process and employing inexpensive equipment. The dewinged seeds are 1.5 times heavier and have 11% higher oil content than the whole seeds. Removing the wings improved seed flow and minimized dust. The decrease in seed volume will consequently bring about a large increase in the output of the oil extraction equipment.
Technical Abstract: Milkweed is now being grown commercially, mainly for the production of floss used as hypoallergenic filters in pillows and comforters. More recently, the use of milkweed seed oil in soaps and personal care products is being explored. The oil used in this effort was obtained by screw pressing whole milkweed seeds. The milkweed seed has a considerable amount of paper-thin wing around the edge of the hull. The light wing contributes greatly to the low bulk density of the seeds and the efficiency of oil extraction. This study explored the feasibility of removing the wings from the seeds to reduce the amount of material going into oil extraction. Hand-fractionation of the seeds showed that the wings, hulls, and kernel accounted for 12.2%, 51.2% and 36.5% of the seed weight, respectively. The wing contained 1% of the total oil. Most of the oil is in the kernel (73%), but a significant amount is also found in the hulls (22.4%). Mechanical removal of seed wing was evaluated using an impact huller. Seeds (1 kg) with 4%, 7.2% and 10% moisture were passed through the huller running at 1250 and 1750 rpm impeller speeds. The seeds discharged from the huller were screened to separate the instact seeds and partially dewinged seeds, dewinged seeds and fines. Seed wings were effectively removed at seed moisture contents and impeller speed combinations of 7% and 1250 rpm or 10% and 1700 rpm. This was verified using 100 kg seeds. Removing the wings reduced the weight of the seeds by 13%, reduced the volume by 46% and increased the bulk density by 63% while losing less than 5% of the total oil. The oil content of the dewinged seeds was 16.6% higher than the whole seeds. These reductions in seed weight and volume can significantly increase the output of the oil extraction equipment.