Soybean, one of the most abundant plants, has been cultivated around the world as a familiar crop. Especially, most of the soybean is globally used as a crop to obtain the oil. The degreased soybean contains a lot of protein in it. The part of the degreased soybean is used for the food of human consumption and livestock feed, however most of this are discarded as industrial waste throughout the world.
Therefore, we demonstrated the preparation of bioplastics consisting of soy protein. Although the soy protein without the cross-linking reaction by formaldehyde (HCHO) was collapsed in water, bioplastics were stable in water. Additionally, the bending strength of the bioplastic increased with the HCHO concentration and showed the maximum value of approximately 35 MPa at a 1% HCHO concentration. Surprisingly, this bending strength value was the same as that of polyethylene. In contrast, the infrared spectra indicated the formation of methylene cross-linking between the basic amino acids, such as lysine and arginine. Finally, we estimated the biodegradable property of the bioplastic by pronase, one of the proteolytic enzymes.
As a result, this bioplastic showed the weight loss of approximately 30% after the incubation time of 6 days. These results suggested that the bioplastic consisting of soy protein possesses a biodegradable property. Therefore, the bioplastic consisting of soybean may have the potential to be used as a biodegradable material, such as agricultural materials, industrial parts, and disposable items.
The SeaCleaners’ View :
The first plastics were made by chemical modification of natural substances.
The manufacture of bioplastics from proteins has been known for a very long time. For example, the milk protein casein, in reaction with formaldehyde, was used to produce galalite, a plastic widely used in the manufacture of buttons, electrical equipment, jewellery, etc. at the beginning of the 20th century. Various sources of proteins were tested: eggs, blood, vegetable… but no application was economically resistant to the development of plastics of petrochemical origin. Even carbochemistry, derived from coal, used to produce nylon and PVC at their beginnings, only lasted for a short period of time.
Soya production became a global issue.
Along with wheat, soybeans represent a major agricultural production with a considerable impact on the agri-food industries. The quantities produced increased by 750% between 1968 and 2017 due to the introduction of soybeans in animal food, a sector that is also growing rapidly. Over the same period, the production of poultry meat increased by 890% and that of pork by 250% at world level.
As an oilseed, its original use was in the production of oil, second in volume after palm oil. Today, however, almost 75% of soybean production is used for protein cake to feed livestock. China is the main producing country.
Formaldehyde is a reagent very present in the soybean industry.
The authors of the study presented here have developed the manufacture of bioplastics from the waste products of soybean production. The process is not new, the proteins present in these wastes are modified by the action of formaldehyde and become a biopolymer with the properties of a plastic material. Strongly cross-linked by formaldehyde, its mechanical properties are those of polyethylene (PE). It may seem strange to favour a process based on formaldehyde, a product reputed to be carcinogenic that Western countries have “officially” banned from food processes, but it is in fact a very common reagent in the soybean industry, as cakes for animal feed are often formalized to improve their mechanical properties. The same is true for the refining of white sugar and alginates, hence our use of the quotation marks to “officially”.
Food or chemistry?
The major component of this bioplastic is soy protein. The waste envisaged as raw material is therefore unsold soybean meal, linked to falling prices or overproduction. In order to develop a replacement market for petrochemical plastics, the quantities needed will largely exceed these availabilities which, moreover, fluctuate from year to year. In the event of regular production of this bioplastic, the question will therefore arise as to the priorities for the use of agricultural land for food or chemical purposes. The Food and Agriculture Organization (FAO) has already warned of the risk of shortages in the short term, as the world’s agricultural land area has not increased for several years, despite intense deforestation. It therefore recommends reserving cropland for food production and strongly advises against growing crops for biofuels or chemicals.
Preparation of bioplastic using soy protein (2020)
Yamada, Masanori; Morimitsu, Sakura; Hosono, Eiji; Yamada, Tetsuya.
Int. nation. J. of biol. Macromol. : 149, 1077–1083. – DOI-Link : https://doi.org/10.1016/j.ijbiomac.2020.02.025