Flexible packaging bag

Soft LDPE film shaped and sealed into a bag.

Flexible packaging bag, illustrative image

Material

Bag film: LDPE

Material selection rationale

Flexible
Bends around the contents instead of behaving like a rigid box.
Heat-sealable
Allows film edges to be joined to form a bag.
Sealable contact surfaces
Heat softens touching polymer surfaces so they join on cooling; sealing depends on thickness, temperature history and contamination at the seam.

How it becomes a product

  1. Extrude film: Molten LDPE flows through a die. In blown-film processing, air expands it into a thin tube. A representative blown-film route stretches a hot tube, cools it and collapses it before cutting and sealing.
  2. Cut and seal: The cooled film is flattened, cut and heat-sealed into bags.

Preparation routes

Ethene route

Free-radical addition polymerisation. Ethene molecules join into long chains. The high-pressure radical process also creates branches, giving the material its characteristic low-density structure. Branch formation during radical growth changes packing without adding a different main-chain repeat unit. This connects reaction conditions to film flexibility.

A radical initiator, such as an organic peroxide, starts chain growth. It is not a second monomer. Film blowing, heat sealing and foam expansion happen after the chemical chains have formed.

  1. Poly(ethene): structure, manufacture and usesChemical Industry Education Centre, University of York

Sources

  1. Poly(ethene): structure, manufacture and usesChemical Industry Education Centre, University of York
  2. DOW LDPE 219M: film and bag applicationsDow