Barbara Gerard

Recent Posts

Creep in Plastic Materials

Posted by Barbara Gerard on 12.12.2016

Creep is the tendency of a solid material to move slowly or deform permanently under a mechanical load. In material sciences, creep is sometimes referred to as cold flow. In this regard, the difference between plastics and other materials is that plastics display time-dependent viscoelastic behavior. Viscoelastic behavior is the property of a material to display both viscous and elastic characteristics when undergoing deformation. It can result from long-term exposure to high levels of stress that are still beneath the yield strength or yield point of the material. The yield strength or yield point of a material is the property defined as the stress at which that material begins to deform permanently. Deformation refers to any change in the shape of an object due to an applied force or a change in temperature. The first instance can be the result of tensile forces, sometimes called pulling forces, compressive forces (pushing forces), or shear, bending or torsion (twisting). Deformation is often described as “strain”. Prior to the yield point, the material will deform elastically and will return to its original shape when the applied stress is removed. Once the yield point is passed, some fraction of the deformation will be permanent and non-reversible.

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Metal Detectable Plastics in the Food Industry

Posted by Barbara Gerard on 10.10.2016

You are eating a hot dog or digging into a carton of your favorite ice cream. You don’t even think there could be a piece of plastic or metal or just small particles of these materials in there- broken or worn off from the machinery and tools used to get your favorite foods to your grocers’ shelves. But many of the food processing machines and tools used to provide food products have plastic parts in them or are made of plastics. For example, foods like melons, peaches, carrots, strawberries or apples can pick up plastic particulates from plastic tote bins or containers that are damaged or worn. Such foods as olives in a vat can mix with tiny particles from a plastic shovel or scraper as they wear. Metal parts from machinery can break off or wear and enter the food supply. So how can food processers know if there are plastics, metals or other foreign bodies in the foods they sell?

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Plastic Materials Close Up: Polyoxymethylene (POM), Acetal, Delrin®, and Celcon®

Posted by Barbara Gerard on 08.30.2016

Polyoxymethylene (POM) is a thermoplastic materialalso known as acetal.  It is a molecule containing the functional group of carbon bonded to two –OR groups. POM was first discovered by German chemist Hermann Staudinger who won the 1953 Nobel Prize in Chemistry. He had studied it in the 1920s but found it to be thermally unstable. DuPont synthesized a version and filed for patent protection of the homopolymer crediting R.N. MacDonald as the inventor. This material had the same problem as Staudinger’s POM, in that it was also thermally unstable and therefore not useful commercially. A heat-stable POM homopolymer was finally discovered by Dal Nagore. He realized that by reacting the hemiacetal ends with acetic anhydride he could readily depolymerize hemiacetal into a thermally stable and melt processable thermoplastic. In 1960, Du Pont built a manufacturing plant to produce Delrin®, its version of the POM homopolymer, while in the same year Celanese completed its study of the copolymer and in 1962 started production of Celcon®. Other manufacturers followed with their own versions of these materials.

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Rubik’s Cube: How It’s Made and Solution Clues

Posted by Barbara Gerard on 08.22.2016

Emo Rubik, a professor at the University of Budapest in Hungary, designed the now famous Rubik’s Cube in the mid-1970’s. It is made up of 26 smaller cubes and has six faces, each made up of nine different colors: red, yellow, blue, white, green and orange. His intention in designing it was to demonstrate to his students three-dimensional relationships. When he showed the prototype to his students, it was an instant hit not so much as a teaching tool but as a game.

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How to Identify a Plastic Material Using the Burn Test

Posted by Barbara Gerard on 08.05.2016

So you have a plastic part and you need to know what it is made of but you have no idea what plastic it is. This can be a challenging task. Many plastics look and feel alike but we will take a closer look here at some of the ways using a burn test. Please note, this test should be done in an industrial setting and not at home since proper safety protocol must be observed. Burning plastics can give off toxic fumes and plastic drips are very hot.

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A Technical Look at Polymer Synthesis and Additives

Posted by Barbara Gerard on 07.25.2016

Originally, plastic resins were made from vegetable matter including cellulose from cotton, furfural from oat hulls, oils from seeds and various starch derivatives. Bakelite (phenol formaldehyde resin), one of the first plastics made from synthetic components, was developed by Belgian born chemist Leo Backeland in New York in 1907. Bakelite is made through an elimination reaction of phenol with formaldehyde. It was originally lused for its electrical non-conductivity and heat-resistant properties in electrical insulators, radio and telephone casings. As it has a pleasing appearance, it was also used to make consumer products such as jewelry. Today, however, most plastics are made from petrochemicals including natural gas.

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How Is Nylon Made?

Posted by Barbara Gerard on 07.11.2016

For centuries, inventors tried to create a “synthetic silk.” In the early 1880’s, Sir Joseph Swan experimented with forming threads by dissolving the inner bark of mulberry trees. Although Swan did realize that fabric could be woven from this material, he never pursued this application as he was mainly interested in finding a filament for Thomas Edison’s light bulbs. It was not until 1889 that the French chemist Count Hilaire de Chardonnet developed rayon or “artificial silk,” which he introduced at the Paris Exhibition. He is known as the “father of the rayon industry.”

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3 Top Plastic Bearing Materials:  Vespel®, Torlon® and Flourosint®

Posted by Barbara Gerard on 05.31.2016

Here at Craftech, we make plastic bearings in a wide variety of materials, some of which perform better than others. For a high performance bearing, three of the best materials to use are Vespel®, Torlon and Flourosint®, mica filled PTFE. Let’s take a closer look at these three to see what makes them ideal bearing materials.

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Acetal, Delrin AF and PTFE: Plastic Bearing Materials

Posted by Barbara Gerard on 04.19.2016

Three of the most useful plastics for making bearings are Acetal, Delrin AF® and PTFE.  Acetal and Delrin AF® are both thermoplastics; meaning that these materials can be heated into a liquid form and then cooled into a solid retaining the shape of either the extrusion nozzle or the mold used to shape it. PTFE has the lowest friction constant of any plastic material. It is not a thermoplastic but it can be extruded. These materials are ideal for use in applications where the sliding action of the parts is needed for things such as plain bearings, gears, and slide plates.

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Special Plastic Material Highlight: TPU

Posted by Barbara Gerard on 03.23.2016

Thermoplastic polyurethane* is a fully thermoplastic elastomer. It is elastic and melt-processable. TPU can be extruded, injection molded, and compression molded. Because TPU is a linear segmented block copolymer made up of hard and soft segments, it allows for a considerable number of physical property combinations. This diversity makes TPU an extremely flexible material, adaptable to dozens of uses. For even greater utility, the molecular weight, ratio, and chemical type of the hard and soft segments can be varied. The hard segment is either aromatic or aliphatic. Aromatic segments can be made up of organic compounds containing aromatic rings with six carbons as their backbones. Isocyanates are built in such a way as to have toluene, benzene or other aromatic solvents as some of their possible precursors. The precursors are used to produce MDI—(MDI is a blend of 2,2’, 2,4’ and 4,4’ methylene diphenyl diisocyanates) which is one of thermoplastic’s key constituents. They also have to have at least two linear OH functionals. Such compounds are typified by benzene and its derivatives and are based on isocyanates. Wet environments generally require a polyether based TPU. Generally speaking, thermoplastic TPU remains stable when it comes into contact with greases, lubricants and test oils even at high temperatures up to 100°c and over a period of several weeks. However, some oil-based fluids may damage TPU, so compatibility testing is recommended. For example, oil and hydrocarbons resistance often demands a polyester-based TPU.

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Categories: TPU