September 11th, 2012Top StoryHow Duct Tape Fixes the WorldBy Andrew Tarantola
Duct Tape's War StoryRichard Drew, a 3M engineer working in St. Paul MN, is credited with inventing adhesive tape. While testing 3M's new "Wetordry" brand sandpaper at a local auto body shop in 1923, Drew noticed that workers there were having a hell of a time achieving sharp, clean lines on their two-tone paint jobs. His solution—Scotch Brand Cellulose Tape, the world's first adhesive-backed masking tape—debuted five years later and made 3M a household name. Fast forward to the 1940s, with America fighting in WWII. As part of the domestic war effort, Johnson and Johnson's Permacell division devised and perfected a military-grade adhesive tape to seal ammo boxes against moisture during transport. Permacell researchers found a way to insert fine-mesh duck cloth between the Scotch tape's polyethelene backing and rubber-based adhesive. This created a strong, durable tape that repelled water like a duck's feathers—with that ability, and the duck cloth construction, it had to be called "Duck Tape." Servicemen quickly found uses for this versatile material beyond just keeping ammo dry. They slapped duck tape on everything from tents to Jeeps as a quick, temporary fix. Air Force flight crews even covered their aircraft's gun ports with the stuff to cut down on drag during takeoff. At the end of the war, manufacturers replaced the Army Green backing with the now-familiar silver, and marketed it as a fix-all solution for repairing leaks in a home's forced-air heating system. Thus, duck tape became duct tape. What It's Made OfDuct tape is still made much in the same way it was in the Permacell labs. A cotton mesh constitutes the tape's core, giving it strength as it's stretched, along with an ability to be torn along its length or width. A tighter weave grants greater tear resistance, and different grades of duct tape are determined by the type of cotton mesh. Military grade tape, for example, has a tear rating of 40 pounds, while most consumer tapes are rated to only half that. The outer polyethylene coating protects the mesh from moisture and abrasion while remaining flexible enough to allow the tape to stick to irregular surfaces. The adhesive is formulated with natural rubber compounds to provide solid long-term adhesion. The process of actually making duct tape begins with the adhesive. Large blocks of the natural rubber base are first broken down and mixed with pellets of plastic resin (which add the tackiness that natural rubber lacks) within a Banbury mixer. These industrial mixers use a pair of rotating spiral-shaped blades to process the rubber and resin mix to the consistency of pizza dough. This compound is then fed into a sigma kneader, which heats and further processes the rubber/resin mixture. From there, the polyethene and cloth layers are simultaneously fed into a countering unit. That applies a generous layer of the adhesive through the cloth and onto the poly film, sticking everything toghter. From there, the single large roll of tape is unwrapped, sliced to length, and then rerolled, packaged and shipped. How It WorksDuct tape relies on what's known as a pressure-sensitive adhesive (PSA) for its inherent stickiness. PSAs are soft polymer blends that exploit van der Waals forces to join two objects together. The strength of the bond is due to the fact that the adhesive is hard enough and its viscoelastic properties are powerful enough to resist flow when stressed. This is not the same as the mechanics of structural adhesives like, say, Elmer's glue. Those adhesvies require the evaporation of a solvent to create the chemical bond. "Other adhesives, like glues and epoxies, are liquid when you apply them, but they react chemically and harden," says Costantino Creton, a materials scientist at the School of Industrial Physics & Chemistry in Paris. "PSAs have no chemical reaction. They don't change at all. They are in the solid state when you apply them, and they stick in their solid state." That is, of course, until the adhesive stops sticking. But when that problem arises, and the duct tape peels free, you already have just the thing to fix it. [Made How - Duck Brand Duct Tape - eHow - ACS - Wikipedia - Image: Ronald Sumners / Shutterstock]  | From Our SponsorTop Stories
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