expect to understand the chemistry, physics, engineering, and manufacturing of
stratospheric balloon films. Although plastics such as polyethylene are used in
thousands of roles, the one application that resembles a balloon envelope is the
plastic wrap in your kitchen. That is the kind of wrap typically sold on rolls in
boxes with a cutting edge. It clings to many smooth surfaces and can stay tight
over the opening of a food container without adhesive. Common plastic wrap is
roughly 12.5 μm (0.0005 in) thick. A human hair is thicker at 75 μm (0.003 in).
Thus it is difficult to conceive of a balloon made of such thin material that is as tall
as a 25-40 story building.
But wait; there’s more! Or should I say less? The Balloon Facility of the Tata
Institute of Fundamental Research (TIFR) in Hyderabad, India has created thin
films that have a thickness of 5-6 μm (0.0002-0.00024 in) for the fabrication of
sounding balloons for probing the stratosphere up to 42 km (137,800 ft). They
have also carried out R&D on films of various thickness not only for that type of
balloon but also for other scientific applications. In 2011, they started work on
balloon grade ultra-thin polyethylene film that had a thicknesses of 2.8-3.8 μm
(0.0001-0.00015 in) for fabrication of balloons which would penetrate into the
mesosphere to meet the needs of scientists working in the area of atmospheric
dynamics. Tests continued through 2014. While these were very small balloons
with only 10-30 kg (22-66 lb) payloads, the tests yielded useful data. One of the
2014 flights reached the mesosphere with an altitude of 51.666 km (169,464 ft).
The altitude record is held by the Japanese Institute of Space and Astronautical
Science (ISAS) which, in 2002, built and launched a 60,000 m
3
(2.12 million ft
3
)
balloon using an ultra-thin film with a thickness of only 3.4 μm (0.000136 in). It
ascended to 53.0 km (173,840 ft), the highest altitude yet achieved by a balloon.
This opened a new era for scientific observations in the mesosphere.
The Blown Film Process
But first a clarification. A polymer is a substance that has a very large molecular
structure consisting chiefly (or entirely) of a great many repeating similar units
bonded together; for example, many synthetic organic materials used as plastics
and resins. These ought not to be confused with natural polymers such as cotton,
wool, and wood. The definition relates to the repeating nature of large molecules.
Blown film extrusion is one of many polymer manufacturing techniques and it
is used to make commodity and specialized polymer films that are typically used
in packaging such as shrink, stretch, barrier films (used to protect deli meat), frozen food packaging, and shopping bags. The process for balloon films is similar
but further processing is necessary to achieve an envelope the size of a stadium.
There are many types of polymers that can be used in blown film extrusion (the
most common being polypropylene and polyethylene) to make low density, high
density, and linear low density polyethylene (LDPE, HDPE and LLDPE). This
method can manufacture monolayer films as well as more complex multi-layer
films that involve co-extrusion in order to combine more than one plastic into a
3.1 Balloon Envelopes 35
stratospheric balloon films. Although plastics such as polyethylene are used in
thousands of roles, the one application that resembles a balloon envelope is the
plastic wrap in your kitchen. That is the kind of wrap typically sold on rolls in
boxes with a cutting edge. It clings to many smooth surfaces and can stay tight
over the opening of a food container without adhesive. Common plastic wrap is
roughly 12.5 μm (0.0005 in) thick. A human hair is thicker at 75 μm (0.003 in).
Thus it is difficult to conceive of a balloon made of such thin material that is as tall
as a 25-40 story building.
But wait; there’s more! Or should I say less? The Balloon Facility of the Tata
Institute of Fundamental Research (TIFR) in Hyderabad, India has created thin
films that have a thickness of 5-6 μm (0.0002-0.00024 in) for the fabrication of
sounding balloons for probing the stratosphere up to 42 km (137,800 ft). They
have also carried out R&D on films of various thickness not only for that type of
balloon but also for other scientific applications. In 2011, they started work on
balloon grade ultra-thin polyethylene film that had a thicknesses of 2.8-3.8 μm
(0.0001-0.00015 in) for fabrication of balloons which would penetrate into the
mesosphere to meet the needs of scientists working in the area of atmospheric
dynamics. Tests continued through 2014. While these were very small balloons
with only 10-30 kg (22-66 lb) payloads, the tests yielded useful data. One of the
2014 flights reached the mesosphere with an altitude of 51.666 km (169,464 ft).
The altitude record is held by the Japanese Institute of Space and Astronautical
Science (ISAS) which, in 2002, built and launched a 60,000 m
3
(2.12 million ft
3
)
balloon using an ultra-thin film with a thickness of only 3.4 μm (0.000136 in). It
ascended to 53.0 km (173,840 ft), the highest altitude yet achieved by a balloon.
This opened a new era for scientific observations in the mesosphere.
The Blown Film Process
But first a clarification. A polymer is a substance that has a very large molecular
structure consisting chiefly (or entirely) of a great many repeating similar units
bonded together; for example, many synthetic organic materials used as plastics
and resins. These ought not to be confused with natural polymers such as cotton,
wool, and wood. The definition relates to the repeating nature of large molecules.
Blown film extrusion is one of many polymer manufacturing techniques and it
is used to make commodity and specialized polymer films that are typically used
in packaging such as shrink, stretch, barrier films (used to protect deli meat), frozen food packaging, and shopping bags. The process for balloon films is similar
but further processing is necessary to achieve an envelope the size of a stadium.
There are many types of polymers that can be used in blown film extrusion (the
most common being polypropylene and polyethylene) to make low density, high
density, and linear low density polyethylene (LDPE, HDPE and LLDPE). This
method can manufacture monolayer films as well as more complex multi-layer
films that involve co-extrusion in order to combine more than one plastic into a
3.1 Balloon Envelopes 35