The basis of a natural polymer is a renewable raw material that is refined into a compound. The compound is a fine, grainy substance that can be further processed. Depending on its intended use, either corn starch or lactic acid will be the source.
However, bioplastics cannot be created using only these two base substances; in the course of the handling process, several additives have to be introduced to complete the product. NaKu typically uses minerals, resins, oils and sunflower waste for this procedure. Sunflower husks contain natural oils that can be used as an internal lubricant.
Extraction of starch (NaKu primarily uses corn starch):
Starch is an organic compound that is present in various plants. In our region, corn starch and potato starch are mainly used as raw materials. But there are also a lot of other plants that produce starch, such as rice or Jerusalem artichokes.
Starch is a polysaccharide; this means that on a chemical level it resembles a long chain of sugar molecules. Corn starch is attained by elution: All parts of the plant that contain starch are crushed, and the starch is drained out of the cells through filtration and centrifugation until pure corn starch is obtained. This is then dried to produce native corn starch powder. In industrial-scale production, starch is used as a source material for print paper, adhesives, glue and similar products.
Extraction of lactic acid:
Lactic acid is a natural substance that can be found in yogurt, sauerkraut, and even in parts of the human body, such as the muscles. The human digestive system can easily break down lactic acid, so it is completely safe to use as natural polymer.
The raw material from which lactic acid is derived is, in fact, also corn starch. With the help of bacteria, corn starch is fermented to produce lactic acid. Other products of our daily life like cottage cheese or yogurt are produced similarly.
Polymerization to PLA:
To obtain a stronger material that can be reshaped, the lactic acid has to be polymerized. Lactide, a short chain of lactic acid, gets transformed into polylactide or polylactic acid (PLA), a longer chain. This happens at high temperatures between 140 and 180 degrees Celsius under the influence of catalytic tin compounds. This procedure results in a thermoplastic material with high stability.
Thermoplastic material is too sticky to be processed. To put it to use, it must first undergo a compounding process. In this procedure, all the components (thermoplastic material and additives like minerals or oils) are mixed in an extruder. The extruder produces a long “sausage” of natural polymer that is cut and ground into granulate. This can be made from starch, PLA or any other raw material base for natural polymers.