Transforming Plastic: Common Bioplastics

Consider widening your scope of bioplastics and delve into the world of biodegradability with this primer on common materials and their composition.

| August 2019

 polystyrene
Photo from Adobe Stock/Thanakon

These are some common bioplastics, with varying degrees of biodegradability:

Starch is cheap, abundant, and renewable and makes up about half of the bioplastics market. It is so simple it can be made at home, and if you ever made paper-mâché as a child, chances are you have already made some. Flexibilizers and plasticizers, such as sorbitol and glycerine, can also be added for a resulting bioplastic called thermo-plastic starch. Starch-based bioplastics can be blended to produce starch/polylactic acid, which has better water-shedding and mechanical properties. These blends are also compostable, but others, such as the starch/polyolefin blends, are not, although they do have a lower carbon footprint than petroleum-based plastic.

Cellulose is the original natural plastic and still the most abundant organic polymer on Earth. It’s the primary structural ingredient of the cell walls of green plants, many forms of algae, and the oomycetes (water molds). Some species of bacteria secrete it to form biofilms. The cellulose content of cotton fiber is 90 percent, wood 40-50 percent, and hemp approximately 57 percent. Cellulosic fibers added to starches can improve mechanical properties, permeability to gas, and water resistance due to being less hydrophilic (water loving) than starch.



Wheat gluten, soy protein, and casein (from milk) show promising properties as biodegradable polymers. Soy proteins have been used in plastic production for over one hundred years but lost out to fossil-based plastics due to their water sensitivity and relatively high cost. A new frontier lies in blends of soy with biodegradable polyesters to boost water resistance and lower cost.

Polylactic acid (PLA) is a transparent plastic produced from corn or dextrose. It is superficially similar to polystyrene but degrades to non-toxic products. Unfortunately, it is inferior to polystyrene in impact strength, heat and cold tolerance, and blocking air permeability com-pared to other blends in commercial use.






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