Being a person nestled in the dark and humid recesses of industry, I find myself boggling at certain things out in the bright and sunny world. Truly, it boggles my mind how little appreciation people have for polyolefin resins. That is to say, polyethylene, polypropylene and all the myriad copolymers and formulations found thereto. Ok, let’s throw PVC and polystyrene in the mix as well.
Why do I boggle at this? What makes my head spin in puzzlement? I’m so glad someone asked. Polyolefin films look innocent enough to be ignored. In their uncompounded state they are clear and colorless or they may be white. Polyolefin films and extruded components are ubiquitous in packaging and thus are not normally an object of desire. They serve the object of desire. They occupy a lesser state interest in nearly all contexts. They are made inexpensively enough to be torn asunder from the desired object and tossed wantonly to the side for later clean up.
But if the uneducated user of polyolefins only knew the extent to which modern science and engineering had been carefully applied to the lowly stretch wrap or the roll of 1 mil PE film. If they only knew the scientists and engineers who carefully devised the ethylene crackers to produce high purity ethylene, or if they knew the highly educated people who devise the polymerization process, they might have heard an account of the long march to produce water white films with properties matched to the end use.
Puncture resistance, elongation, fish-eyes, haze, modulus, crystallinity, glass transition temperatures, melt points, low volatiles, melt viscosity and strength- all attributes carefully tended to so that the film appears invisible to the consumer. High gloss, low haze films to make the product look even better. Low volatiles and residues for food contact use. Polyolefins engineered for specific densities for the global market.
All of the attributes above to attend to with a continuous polymerization loop that spews 50,000 to 80,000 lbs per hour of pellets into silos and rail cars. Pellets that will eventually go to converters who will blow films and extrude widgets all day long. All so the consumer product can arrive at its destination wrapped unscuffed and free of dust.
Polyolefin materials are incredibly useful and amazing in their own right. We should have more appreciation for these materials and how they serve our needs.
Lamentations on Chemistry 
Wonderful write up, you pretty much captured it all.
But blowing as a film making process, … well… it ______.
The big boys have tenters. The resin is melted, extruded as a thick sheet which is then set upon a series of heated rollers. At one point, the roll speed suddenly increases 5x or more, drawing the film in the machine direction. The edges of the film are then attacked by clamps that are on a continous loop running through the tenter oven. The heated film is then drawn 10x in the cross direction before cooling down and being wound up.
My first job out of school was at a tenter plant. At that point in time we were working on machines that ran ~ 25 feet wide, ~ 150 fpm if I recall correctly. Management decided to double company output by putting in a machine that was ~ 75 feet wide and ran 300 fpm. That’s a lot of resin. You don’t get it delivered by truck, but you have a rail spur to the plant.
Then I found out that our competition was putting in 3 such machines and decided to leave the company. (Good choice. The division was sold to a new company in less than a year.)
Hi John,
I am pleased to defer to your greater knowledge on this matter. I was thinking of the blown film systems that I saw in operation at a polymer trade show a dozen years ago in Chicago. It was at the McCormick center and there were at least 4 machines blowing film on the trade show floor as well as extrusion units and other equipment. It left a big impression on me. People stood in line for an hour to get a freshly extruded lawn chair. How they got it on the plane I do not know.
Nice essay, gaussling. I wish more people would see and appreciate how technology has become such an integral part of their world that they don’t even stop to think about it.
I’m glad you did and I’m glad that you are sharing these thoughts.
Having been briefly involved in support of an olefins plant as well as a polyethlylene plant, I know where you are coming from. Climbing up a 7 story cracker, looking into the furnace (1500 deg F) was an amazing experience. The back end of the plant, where they need to separate the witches brew of materials from the cracker is a whole other matter. At the poly plant, seeing silos upon silos of poly pellets, railcars, etc…the capital put into these places…no wonder they need to be operated 24/7/365.
Wow. I’ve never been near a cracker. I have been in polymer plants in Sarnia, Freeport, and Thailand. I think that these facilities are wholly misunderstood by citizens who use their polymer products. It’s not so important that everyone understand the microscopic details of polymers. But more citizens should grasp the scale and impact of this industry and how the resins make their lives better.
While the polymer industry is happy that consumers are pleased to burn through X kg/person*yr of these materials, I think that some familiarity may lead to more conservation of resources. Hydrocarbons in the ground is like money in the bank. These resin products are important and we should not encourage wasteful consumption. Not a popular view, I suppose.