There, corn kernels are milled, a chemical substance called dextrose is extracted, and dextrose is fermented by bacteria or yeast in big vats. . The result is lactic acid which acts as a repeating unit to make PLA.
But lactic acid cannot be directly polymerized into PLA because the chemical reaction that bonds two molecules of lactic acid together also generates water. The water molecules prevent the growing chain of lactic acid molecules from stay together.
So, instead of a long chain of lactic acid molecules, many small chains are formed. They are called polylactic acid oligomers in which “oligomer” means “small chain.” These small chains are processed in a chemical reaction that leads to smaller lactide molecules.
The chemical reaction also produces water, which is later eliminated. The lactide molecules act as monomers that are polymerized into PLA in a process similar to the polymerization of ethylene into polyethylene.
The other common bioplastic, PHA, is a polymer produced naturally by bacteria. Different PHA molecules are made by the bacteria. These molecules can consist of more than 150 different types of monomers, leading to materials with very different properties from one another.
Two types of PHA polymers are formed in polymerization reactions that combine more than 150 different types of monomers, leading to materials with very different properties.