The use of Braskem’s PIB In Stretch Films

Stretch film is a plastic LLDPE film (linear low-density polyethylene film) which is elastic and can stretch well, for the purpose of binding together and protecting other materials. For example, agricultural and/or pallet packaging. To do this, the film must exhibit properties such as good tensile strength, elongation, high retention strength, adhesion and tear resistance. The film is wrapped around the material to be protected in several layers until adhesion and stability are guaranteed. Every layer has adherence over the other as the film has a tacky behavior. The tacky surface can be reached through the incorporation of Braskem’s PIB as a tack agent. 

How It’s made

The two most common methods for producing LLDPE plastic films are bubble (blown) extrusion in a ring die and extrusion through a cast die. Blown films is offering a higher tear resistance and a higher load and stretch capacity where cast films give higher clarity. Between 1% and 4% PIB is coextruded (This technique allows for multiple textures in one product stream), but since it is not miscible with polyethylene, it migrates in the roll to the surface within 48 hours. The adhesive strength increases over time and reaches a maximum after 2 weeks when stored at about 20'C. The main factors affecting migration are the molecular weight and level of the PIB used, the molecular structure of the LLDPE film, as well as the density, morphology and crystallinity of the LLDPE and therefore on the adhesive forces. Both mono and coextruded blown films generally have the same end properties, such as tensile strength and elongation. 

The impact of Molecular weight 

PIB with a higher molecular weight (e.g., 4200 g/mol) diffuses much more slowly through LLDPE films than PIB with a lower molecular weight (e.g., 1300 g/mol). PIB migrates immediately and more rapidly through the bulk of a lower density LLDPE (e.g., 0.900 g/cm3) versus one with a higher density (e.g., 0.930 g/cm3), resulting in higher adhesive films. PIB with a lower molecular weight (e.g., 1300 g/mol) will ultimately result in much higher adhesive forces compared to PIB with a higher molecular weight (e.g., 4200 g/mol ).
The adhesive strength increases when stored at higher temperatures, which is the reason why less PIB is used during production in summer. With migration, the pressure in the roll increases, so the tension of the film during winding is very important. In addition to the film's stickiness, PIB is also non-staining, non-toxic, improves the film's gas barrier, and increases gloss.

Want to know more about Braskem’s PIB?

You may be wondering how you can apply Braskem’s PIB to your products. Check out more about Braskem's PIB or contact our specialist James Meacock.