Blow Film Extrusion

The Blown film extrusion process is used in the production of continuous films for packaging application. During the process, the bioplastic is melted in the extruder. The molten polymer enters the die head to form plastic tubes. In the case of multilayer films, there is a need for one extruder per material. A plastic tube with concentric layers is formed as the melt strands are combined in the die head. Once it comes out of the die, the film tube is pulled up by a nip roller. At this time, the compressed air is blown to reach the desired thickness and width. Later cool air is blown, and the bubble is flattened to form a tube.

Bioplastics like polylactic acid (PLA), and polybutylene adipate terephthalate (PBAT) are also used in blow film extrusion applications. Though these come with different properties in comparison with PE they are used in applications that require high performance, residue-free and transparency.

The blown film process converts polymer and its blends into films. First, the physical properties are studied. When considering blown film processing of neat PLA, PBAT, and a reactive blend of PLA or PBAT, it was found that the neat PLA blown process was difficult as it was unstable because PLA has a low melting point. This can lead to changes in the thickness and size. PLA has a low crystallisation rate so the film will be transparent. On the contrary, PBAT filmmaking was easier as the PBAT bubble comes with a long neck. The film can be processed easily in PLA/PBAT blends. The PBAT/PLA blends come with good melting properties making them an ideal choice for plastic processing methods like blown film extrusion.