How Compostable Plastic Bags Are Made: The Science of Eco-Friendly Packaging

Production Process

1. Raw Material Preparation: The main raw materials are renewable biopolymers, such as corn starch, cassava starch, sugarcane derivatives, or plant - oil - based materials. To enhance the toughness and flexibility of the bags, plasticizers, fillers (such as calcium carbonate), and biodegradable auxiliaries are added. Before processing, the pellets need to be dried to remove excess moisture, which could affect the melting and subsequent forming processes.
2. Compounding & Pelletizing: The prepared biopolymers and additives are fed into a twin - screw extruder. They are thoroughly mixed and melted at high temperatures to ensure that the starch, plasticizers, and auxiliaries are evenly dispersed within the polymer matrix. The molten material is then cooled and cut into uniform pellets, which are convenient for subsequent processing.
3. Film Extrusion: The resin pellets are introduced into a blown - film extruder and heated to a molten state. The melt is extruded through an annular die to form a tube, which is then inflated with air to form a "bubble". The bubble is flattened into continuous film sheets, a process similar to that for conventional plastic bags.
4. Printing (Optional): If necessary, the film can be printed with branding or labels using eco - friendly inks to ensure that no harmful residues are left during composting.
5. Bag Conversion: The rolled - up film is fed into a bag - making machine. The machine first cuts the film to the specified dimensions and then creates the bottom and side seams by heat - sealing or ultrasonic sealing. If handles are required, a die - cutting process is used.
6. Quality Control: Rigorous quality control is carried out during production and on the finished products. This includes checking the film thickness uniformity, tensile strength, and tear resistance. More importantly, the products must meet international compostability standards, such as EN 13432 or ASTM D6400.

7、Packaging & Distribution: The qualified compostable plastic bags are collated, bundled, and packed into cartons with labels indicating compostability certification, usage instructions, and environmental marks. Then they are shipped to retailers, food businesses, or directly to consumers.
 

Science Behind Creation

• Material Science: The key raw materials for compostable plastic bags, such as PLA and PBAT, have unique chemical structures and properties. PLA is made from lactic acid obtained by fermenting corn, and it has certain strength and clarity. PBAT is a biodegradable polyester with good flexibility. By blending different biopolymers, such as combining the hard - brittle PLA with the soft PBAT and adding starch for adhesion, a composite material with balanced performance can be obtained.