What we know as polyethylene pipe, poly pipe or pe pipe, would not be what it is today were it not for our obsession with the hula hoop in the 1950s. When Paul Hogan and Robert Banks discovered crystalline polypropylene, and that a similar plastic could be produced using ethylene, a new world of plastic appeared on the horizon. Using the new resin to create products such as polyethylene pipe, however, proved to be much harder than anyone imagined. The production process was unrefined and even after investing millions in the production process, the Phillips Petroleum Company still couldn’t convince manufacturers to buy the resin.
Thankfully, by 1959, having finally mastered the production process, polyethylene manufacturers found a receptive market for their new plastic. Polyethylene’s ability to handle high temperatures made it a perfect replacement for glass used in baby and liquid detergent bottles. Household product manufacturers were quick to follow, and with the success of the hula hoop, tubing and pipe applications of polyethylene skyrocketed. Always on the look out for cost effective alternative piping materials, the electrical, gas, potable water and mining industries were quick to use polyethylene for everything from insulating electrical cables to transporting waste water and mineral slurries.
What is Polyethylene?
When Hogan and Banks first created a reaction between ethylene and benzaldehyde using two thousand atmospheres of internal pressure, their experiment went askew when all the pressure escaped due to a leak in the testing container. On opening the tube they were stunned to find a white waxy substance that looked a lot like some form of plastic. After repeating the experiment, they discovered that the loss of pressure was not due to a leak at all, but was a result of the polymerization process. The residue polyethylene (PE) resin was a milky white, translucent substance derived from ethylene (CH2=CH2). Polyethylene was produced with either a low or high density.
Low-density polyethylene (LDPE) has a density ranging from 0.91 to 0.93 g/cm3 (0.60 to 0.61 oz/cu in). The molecules of LDPE have a carbon backbone with side groups of four to six carbon atoms attached randomly along the main backbone. LDPE is the most widely used of all plastics, because it is inexpensive, flexible, extremely tough, and chemical-resistant. LDPE is molded into bottles, garment bags, frozen food packages, and plastic toys.
High-density polyethylene (HDPE) has a density that ranges from 0.94 to 0.97 g/cm3 (0.62 to 0.64 oz/cu in). Its molecules have an extremely long carbon backbone with no side groups. As a result, these molecules align into more compact arrangements, accounting for the higher density of HDPE. HDPE is stiffer, stronger, and less translucent than low-density polyethylene. HDPE is formed into grocery bags, car fuel tanks, packaging, and, of course, piping.
Polyethylene Time Line
1862 – Parkesine, the first synthetic plastic
1866 – Celluloid by John Wesley Hyatt
1891 – Rayon is used to make Cellophane
1900 – Celluloid is used for Film
1907 – Bakelite, the first thermosetting synthetic resin.
1918 – Polystyrene
1926 – PVC or Vinyl
1927 – Nylon – synthetic silk for stockings in 1939
1933 – Polyethylene
1935 – Low Density Polyethylene
1938 – Teflon
1951 – High Density Polyethylene
1957 – Velcro and Silly Putty
The history of the polyethylene (PE) pipe begins with early civilization’s attempts to find a suitable transport medium that could move water and other fluids from one place to another. It is no secret that plastic is relatively a new kid on the block as a piping material. Concrete has, in some form or another, been around since the Assyrians, Babylonians and Egyptians, while steel was first patented in 1855. Plastic piping, on the other hand, beginning with polyvinyl chloride or PVC in 1926, dates back to the 1930s, when it was utilized for sanitary drainage. Polyethylene was first developed in 1933 as a flexible, low density coating and insulating material for electrical cables. It played a key role during World War II — first as an underwater cable coating and then as a critical insulating material for such vital military applications as radar insulation. Because of its light weight, radar equipment was easier to carry on a plane, which allowed the out-numbered Allied aircraft to detect German bombers under difficult conditions such as nightfall and thunderstorms.
High density polyethylene, however, is quite a bit different from the polyethylene used in the 1930s. Low density polyethylene was discovered in 1935 and it wasn’t until sixteen years later in 1951 that high density polyethylene appeared on the scene. As a relatively newcomer in the piping industry, polyethylene is constantly making its way into applications normally reserved for the older piping technologies. It was not until after the war, though, that the material became a tremendous hit with consumers and from that point on, its rise in popularity has been almost unprecedented. Since the late 1950s and early 1960s, polyethylene has made its way into every corner of our lives launching a multi-billion dollar industry. It became the first plastic in the United States to sell more than a billion pounds a year and it is currently the largest volume plastic in the world. This is partly due to the fact that there are certain characteristics (or combinations of characteristics) of high density polyethylene that make it an attractive alternative. Whether it is an issue of installing a new piping system or rehabilitating an existing system, there are certain requirements placed on the piping material: that it be simple to install, that it doesn’t leak or cost a lot to maintain, and will last a very long time. As long as polyethylene can satisfy these demands better than any other material, it will continue its gain in popularity.