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Virtually all plastic goods pose a significant threat to the environment because they don't break down in the environment. Soybean plastics were created as a way to address this threat. These plastics have different qualities than conventional plastics, some of which are beneficial, and some of which are not.
The abundance and accessibility of soy, its usage potential, thermoplastic qualities, low cost, and biodegradability have made it very appealing for extensive use in the plastics industry. Since the functional qualities of the manufactured products are directly associated with the physical and chemical qualities of the raw material used to make them, a comprehensive understanding of soy-based materials is crucial for manipulating for various applications.
Moreover, the use of soybeans, when they are grown by sustainable techniques, lead to reduced greenhouse gas emissions, while biodegradable soybean plastics can replace petroleum-based products for a "greener" product lifecycle.
The polymers found in soybean protein closely resemble the desirable qualities in petroleum-based plastics. However, soy plastic must be meticulously formulated to be useful in commercial plastic processing processes, like extrusion and injection molding.
Two Varieties of Soy Bean Plastics
The two main kinds of soy-based plastics are polyurethane and polyester thermoset products. Soy polyols, produced from soybean oil, are used to make adhesives, coatings, sealants, inks, vehicle panels and urethane foam, including rigid foam insulation. When formulated with the proper chemicals, soy polyols can compete with their petroleum-based counterparts in stability, durability, and cost.
Some soy-based plastics are not biodegradable because they are comprised of nonbiodegradable polymer substances, which are used to give final products durability and strength. Many soybean plastics are biodegradable, however, and made to be disposable.
Most biodegradable soy-based plastics include food service items, tableware products, packaging, and plastic bags. The integrity of these products is susceptible to high temperatures and water. Soy protein plastics are made at considerably lower temperatures than conventional plastics, which results in energy savings. Soybean plastics appear and feel like petroleum-based plastics. They are generally are freezer safe and may tolerate hot foods and liquids up to around 90 degrees Celsius (200 degrees Fahrenheit).
Soy-based plastics that do biodegrade do so at a rate similar to that of paper. The products of soy plastic decomposition are carbon, oxygen, water, and bio-products, known as "biomass." Bacteria, fungi and other microorganisms can break down these plastics.
Biodegradable plastics designed to be compostable must break down within a certain period of time and should leave any residual toxicity. There is currently a big push to develop more soybean plastics that are not just biodegradable but also compostable.
Case study: Reducing Microbead Pollution
Recently, plastic microbeads used primarily in exfoliating soaps have been cited as a major source of plastic pollution. Found in waterways and in even in the open ocean, these tiny bits of plastic can injure animals and cause all kinds of environmental damage.
Addressing this issue, a team of student researchers at Purdue University announced the development of an environmentally-safe soybean plastic alternative to the plastic commonly used to make plastic microbeads.
To create this alternative, the research team milled down larger pieces of soybean plastic to the desired sizes. As with conventional plastic microbeads, the soy-based beads are very stiff and capable of safely exfoliating skin with a bit of rubbing action.
Plastic microbeads don't absorb water, but soy-based plastics can after a while. To minimize this issue, the team combined their beads with small quantities of oil to keep water from saturating the beads and decreasing their rigidity. The Rice team said they are studying the way to boost shelf-stability while making certain the product environmentally-friendly.