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A variety of companies manufacture boPET and other polyester films under different brand names. In the UK and US, the most well-known trade names are Mylar, Melinex, and Hostaphan.[1]
BoPET is used to create flexible types of packaging and lids used by many different industries such as the food, comic and archival storage industries. It is also commonly used as electrical and thermal insulation.[2]
History
Polyester (PET), a commonly recognized synthetic fiber made up of chemicals found in petroleum, uses Polyethylene Terephthalate as a basis of production. Polyester's large history of research led to the production of an extremely durable type of polyester, named BoPET (commonly known as Mylar), in the 1950's.
Original Patent
In 1941, an advancement upon the research of Wallace Carothers, an Organic Chemist, led to the creation and patent of the substance known as Polyethylene Terephthalate. This advancement is accredited to John Rex Whinfield and James Tennant Jackson, two chemists of the Calico's Printer Association of Manchester. This invention led to the creation of the first polyester fiber, laying down the stepping stones to the invention of BoPET, soon to be known as the strongest synthetic polyester film of it's time.
DuPont's Expansion
During the 1920's, DuPont, now known for the creation BoPET (Mylar), was heavily focused on nylon research, which at the time, was considered a very highly regarded up and coming synthetic fiber. It wasn't until 1945, DuPont's purchasing of Imperial Chemical Industries' (ICI) patent for Terylene polyester in hopes of further development of the invention, that DuPont began to re-initiate their research efforts towards the polyester industry. This new research initiative brought forth many trademarked polyester products, including the infamous Mylar, also known as BoPET.[3]
In 1955 Eastman Kodak used Mylar as a support for photographic film and called it "ESTAR Base".[5] The very thin and tough film allowed 6,000-foot (1,800 m) reels to be exposed on long-range U-2 reconnaissance flights.[6]
In 1964, NASA launched Echo II, a 40-metre (131 ft) diameter balloon constructed from a 9-micrometre (0.00035 in) thick mylar film sandwiched between two layers of 4.5-micrometre (0.00018 in) thick aluminum foil bonded together.[7]
Manufacture
Chemical structure of polyethylene terephthalate
Biaxial or Monaxial orientation methods are used in the production of BoPET since it is a thinner material, so that it can have properties such as tensile strength, toughness, heat stability, tear initiation resistance, and barrier.
Biaxial Orientation
The manufacturing process begins with a film of molten polyethylene terephthalate (PET) being extruded onto a chill roll, which quenches it into the amorphous state.[8] It is then biaxially oriented by drawing. The most common way of doing this is the sequential process, in which the film is first drawn in the machine direction using heated rollers and subsequently drawn in the transverse direction, i.e. orthogonally to the direction of travel, in a heated oven. It is also possible to draw the film in both directions simultaneously, although the equipment required for this is somewhat more elaborate. Draw ratios are typically around 3 to 4 in each direction.
Once the drawing is completed, the film is "heat set" or crystallized under tension in the oven at temperatures typically above 200 °C (392 °F). The heat setting step prevents the film from shrinking back to its original unstretched shape and locks in the molecular orientation in the film plane. The orientation of the polymer chains is responsible for the high strength and stiffness of biaxially oriented PET film, which has a typical Young's modulus of about 4 GPa (0.58×10^6 psi). Another important consequence of the molecular orientation is that it induces the formation of many crystal nuclei. The crystallites that grow rapidly reach the boundary of the neighboring crystallite and remain smaller than the wavelength of visible light. As a result, biaxially oriented PET film has excellent clarity, despite its semicrystalline structure.
If it were produced without any additives, the surface of the film would be so smooth that layers would adhere strongly to one another when the film is wound up, similar to the sticking of clean glass plates when stacked. To make handling possible, microscopic inert inorganic particles are usually embedded in the PET to roughen the surface of the film such as silicon dioxide.[9]
Biaxially oriented PET film can be metallized by vapor deposition of a thin film of evaporatedaluminium, gold, or other metal onto it. The result is much less permeable to gases (important in food packaging) and reflects up to 99% of light, including much of the infrared spectrum. For some applications like food packaging, the aluminized boPET film can be laminated with a layer of polyethylene, which provides sealability and improves puncture resistance. The polyethylene side of such a laminate appears dull and the PET side shiny.
Monaxial Orientation is most commonly used when the BoPET material is being manufactured for the use of shrink-sleeve label films. This is due to the fact that this process allows for a high amount of shrinkage to occur when the film is exposed to relatively low temperatures, as well as increased stiffness, optical properties, barrier properties and increased tear strength, which is desired for this type of product. The process is extremely similar to that of Biaxial Orientation, but has differences towards the end of the production process. Once the thicker film of molten polyethylene terephthalate (PET) is laid onto a cooled surface, it is immediately temperature conditioned, and then is stretched between two rollers of differentiating speeds. These rollers are held extremely close to one another to lower the amount of unwanted gap where orientation normally takes place.[10]
Properties
BoPET has many properties that make it very useful in the commercial world. These properties include;
BoPET (Mylar), originally created in the 1950's, has since been used in many types of industrial areas, such as; electronics, magnetic media, imaging, graphics, industrial, and packaging fields.[11]
Uses for boPET polyester films include, but are not limited to:
Packaging
Laminates containing metallized boPET foil (In technical language called printin or laminate web substrate) protect food against oxidation and aroma loss due to its gas barrier properties, as well as its high durability., achieving long shelf life. Examples are coffee "foil" packaging and pouches for convenience foods.
BoPET is used in packaging that contains products which are irritable to moisture changes, such as pharmaceutical products.
White boPET web substrate is used as lidding for dairy goods such as yogurt.
Clear boPET web substrate is used as lidding for fresh or frozen ready meals. Due to its excellent heat resistance, it can remain on the package during microwave or oven heating.
boPET film is used in bagging comic books, in order to best protect them during storage from environmental conditions (moisture, heat, and cold) that would otherwise cause paper to slowly deteriorate over time. This material is used for archival quality storage of documents by the Library of Congress[12] (specifically Mylar® type D)[13] and several major library comic book research collections, including the Comic Art Collection at Michigan State University.[14] While boPET is widely (and effectively) used in this archival sense, it is not immune to the effects of fire and heat and could potentially melt, depending on the intensity of the heat source, causing further damage to the encased item.[15]
Similarly, trading card decks (such as Pokémon, Magic: The Gathering, and Yu-Gi-Oh!) are packaged in pouches or sleeves made of metallized boPET. It can also be used to make the holographic artwork featured on some cards, typically known as "holos", "foils", or "holofoils".
For protecting the spine of important documents, such as medical records.
Insulation for houses and tents, reflecting thermal radiation
One sided reflective BoPET is often used as insulation because of its metallic properties, allowing it to reflect 99% of light
When being used to increased warmth on the interior, the reflective side is placed facing inwards so that it will reflect the heat that would normally escape
When being used to keep cool, the reflective side is placed facing outward so that it reflects heat from the outside, which would otherwise penetrate into the interior
Five layers of metallized boPET film in NASA's spacesuits make them radiation resistant and help regulate temperature.
Metallized boPET solar curtains reflect sunlight and heat away from windows.
Aluminized, as an inexpensive solar eclipse viewer, although care must be taken, because invisible fissures can form in the metal film, reducing its effectiveness.
Amateur and professional visual and telescopic solar filters. BoPET films are often annealed to a glass element to improve thermal conductivity, and guarantee the necessary flat surface needed for even telescopic solar observation. Manufacturers will typically use films with thicknesses of 280–500 micrometres (0.011–0.020 in), in order to give the films better resilience. 250-micrometre (0.0098 in) thickness films with a heavy aluminium coating are generally preferred for naked-eye Solar observation during eclipses.
Films in annular ring mounts on gas-tight cells, will readily deform into spherical mirrors. Photomultipliercosmic-ray observatories often make use of these mirrors for inexpensive large (1.0 m and above), lightweight mirror surfaces for sky-sector low and medium energy cosmic ray research.
As a light diaphragm material separating gases in hypersonic shock and expansion tube facilities.
Insulating material for a cryocooler radiation shield.
As a window material to confine gas in detectors and targets in nuclear physics.
In CT scanners it acts as a physical barrier between the xray-tube, detector ring and the patient allowing negligible attenuation of the xray beam when active.
Spacecraft are insulated with a metallized BoPET film.
The material for solar sails of spacecraft.
Biomedical
BoPET is one of the commonly employed polymers clinically for orthopedic applications, vascular grafts, ocular application, dentistry, tissue engineering, and drug delivery systems
boPET film has been used in the production of banjo & drumheads since 1958 due to its durability and acoustical properties when stretched over the bearing edge of the drum. They are made in single- and double-ply versions, with each ply being 2–10 mils (0.051–0.254 mm) in thickness, with a transparent or opaque surface, originally used by the company Evans.
The advantage's of BoPET film allow for a consistency in pitch and tone that is otherwise impossible
Clear and white boPET films are used as core layers and overlays in Smart Cards.
Hydroponic Gardening
BoPET can be used to reflect wasted light towards a desired target
Improves the usability of light within the plant when practicing Hydroponic Gardening
Advantages from BoPET use cause an increase in the speed of growth for the plant itself
Can increase light efficiency by 40%, or even more if the patterns of reflection overlap across multiple fixtures and reflectors
BoPET is popular for use in grow tents, where it is bonded to the interior walls, ceiling and floor, while a thick canvas fabric is used for the outer shell
Using patterned Mylar reduces instances of hot spots and broadcasts light the best[11]
Printing Mediums
Before the widespread adoption of CAD, engineering drawings or architectural drawings were plotted onto sheets of boPET film, known as drafting film. The boPET sheets become legal documents from which copies or blueprints are made. boPET sheets are more durable and can withstand more handling than bond paper. Although "blueprint" duplication has fallen out of use, mylar is still used for its archival properties, typically as a record set of plans for building departments to keep on file.
Used in dentistry when restoring teeth with composite.
In nail polish, as a coloured and finely shredded additive to create a glitter effect.
Numismatics - The product is used instead of PVC for safe coin storage. Chemical composition is more conducive to the metals coins are made of i.e Silver & Copper (Coins used to be stored in PVC sleeves which damage coins when exposed for longer periods due to chlorine being released.)
Technological Advancements
The plastic resin known as Polyethylene Terephthalate is the most commercially common polyester that is used today. Soon after being created, Polyethylene Terephthalate became the most wide spread synthetic fiber produced around the world. This technology today has advanced so greatly that it is now seen in almost every application imaginable.
Carbon Reinforcement
Looking to increase Polyethylene Terephthalate's already powerful electrical, chemical and physical-chemical properties, scientists nowadays have found that adding carbon based materials such as graphene, carbon fiber, and carbon nanotubes to the PET Polymer is the answer to creating a more powerful synthetic fiber. This is due to carbon based materials having extremely prominent thermal conductivity properties, as well as strong chemical and physical-chemical properties.
Nano-Composite Technology
Polyethylene Terephthalate's wide variety of applications and field of use made it an automatically assumed prospect for use within newly emerging technological advances now and in the future as well. Using brand new developments surrounding the synthesis of PET Nano-composites, Polyethylene Terephthalate is now able to see huge increases in highly desired properties such as mechanical strength, permeability, electrical conductivity, and thermal stability. This is accomplished by incorporating nano-fillers such as carbon nanotubes, nano-clays, and other inorganicnanoparticles. These new advancements suggest a very promising future of nano-composite PET technologies.[16]
^ abHelmenstine, Anne Marie, Ph D. Dr Helmenstine holds a Ph D. in biomedical sciences, Is a
Science Writer, educator, consultant She has taught science courses at the high school, college, and Graduate Levels. “What You Should Know About Mylar.” ThoughtCo. Accessed March 10, 2019. https://www.thoughtco.com/mylar-polyester-film-608929
^Eyes in the Sky, Dino A. Brugioni 2010, Naval Institute Press, ISBN978 1 59114 082 5, pp. 102, 115.
^Staugaitis, C. & Kobren, L. "Mechanical And Physical Properties of the Echo II Metal-Polymer Laminate (NASA TN D-3409)", NASA Goddard Space Flight Center (1966).
History of Polymers & Plastics for Teachers. by The American Chemistry Council (HTML format) or (PDF format) - 1.9MB, which includes the "chasing arrow" recycling symbols (PET is #1) and a description of plastics.
