how is plastic wrap made?

2 Answers

Relevance
  • 1 decade ago
    Favorite Answer

    Plastic wrap, known as cling-film in the United Kingdom, is a thin polymer material, approximately 0.13mm (0.003in) thick, typically used for sealing food items in containers to keep them fresh. The wrap, typically sold on rolls in boxes with a cutting edge, clings to many smooth surfaces and can thus remain tight over the opening of a container with no adhesive or other devices.

    Commonly known brands of plastic wrap, in the United States, include Saran wrap and Stretch-Tite. In Australia and New Zealand, Glad wrap is the leading brand, known well enough to make its manufacturer concerned about its trademark becoming genericized.[1] In Hong Kong, a company named Fine Vantage Limited is the major private label LDPE plastic wrap manufacturer.

    A similar material can also be made at home by spreading clear glue on a smooth flat surface and allowing it to dry. Depending on the thickness of the layer of glue, it may tear easily, or it may be tougher and more difficult to stretch.

    Materials used

    Plastic wrap was first made from PVC, which remains the most common material, but non-PVC alternatives are now being sold because of concerns about the transfer of plasticizers from PVC into food. It is also problematic to achieve full polymerization of the material, which can contain remains of vinyl chloride. For food catering applications, PVC is the most common. For household use, LDPE is gaining market share because it is purportedly safer.

    More and more countries over the world are concerned about the environmental impact of PVC, as the material is toxic and is hard to recycle. PVC is still used because its stretching properties offer excellent food catering presentation on the shelf, and it clings well to more kinds of surfaces. Some countries are starting to ban the use of PVC in toys for infants and food contact applications.

    Saran Wrap is made of polyvinylidene chloride (PVdC).

    The PVC-based films contain plasticizers, most often bis(2-ethylhexyl) adipate (DEHA), but phthalates (most often dibutyl phthalate (DBP) and bis(2-ethylhexyl) phthalate (DEHP) also cause concern. The plasticizers were found to migrate to some foods, for example cheeses or fatty fish and meat. In the UK, polymerized plasticizers replaced DEHP in this application, largely eliminating the problem. [2]

    A common alternative to PVC is low density polyethylene (LDPE), which is less clingy than PVC, but also does not contain traces of potentially toxic additives. Newer production processes are closing the clingy gap between PVC and LDPE. Linear low density polyethylene (LLDPE) is sometimes added to the material, as it increases the clinginess and the tensile strength of the film. [3] Brands like Glad Cling Wrap or Handi-Wrap are LDPE-based. Saran Premium Wrap, a newer version of Saran Wrap, is based on LDPE as well.

    Glad Press'n Seal has its surface covered by microscopic spikes, preventing direct contact of the polymer surfaces, preventing it from sticking to other materials, including itself. To achieve the adhesion, the material has to be subjected to mechanical force, crushing the spikes.

    PVdC has better barrier properties than the more-permeable LDPE, making the foods wrapped in it less subject to freezer burn. However, LDPE is substantially cheaper to make.

    LDPE nor PVdC are insufficiently clingy on their own, and they do not adhere to themselves. To achieve the desired clinginess, certain polymers with lower molecular weight have to be added; the most common two are polyisobutene (PIB), and poly[ethylene-vinylacetate] (EVA) copolymer. Their chains readily interact with each other and their lower molecular weight makes them more mobile within the host polymer matrix. [4]

    You could get more information from the link below...

    • Commenter avatarLogin to reply the answers
  • 1 decade ago

    Most plastic films like plastic wrap, photographic film, and the like are made by a process called "wheel doping." a large wheel or drum with a smoothly machined surface is suspended over a pan of liquid plastic that is often called "dope." The wheel is lowered or the pan raised until the wheel or drum just touches the surface of the dope, and the drum is rotated at a speed that picks up just the right thickness of dope from the pan.

    Heat lamps or a spray of catalyst may be used to cause the film to "kick over" or transition from liquid to solid as the drum or wheel revolves, so that it can be lifted off the drum at or near the top, and wound onto a smaller drum or a mandrel with a cardboard tube on it.

    There are many variations on this process and a number of alternative processes, which you can read about in the library or on the internet.

    • Commenter avatarLogin to reply the answers
Still have questions? Get your answers by asking now.