Industry News • Paul Murphy Plastics

Plastics.jpg

July 10, 2019

Thermoplastics are polymers, which soften (becomes pliable and plastic) and melt when heated. In the melted conditions thermoplastics may be formed by various methods (injection molding, extrusion, Thermoforming).

No new cross-links form (no chemical curing) when a thermoplastic cools and harden. Thermoplastics may be reprocessed (re-melt) many times.

Molecules of most of thermoplastics combine long polymer chains alternating with monomer units.

Thermoplastic materials may contain filler materials in form of powder or fibers, providing improvement of specific material properties (strength, stiffness, lubricity, color etc.).

Thermoplastic groups:

  • Polyolefins: Low Density Polyethylene (LDPE), High Density Polyethylene (HDPE), Polypropylene (PP).
  • Styrenics: Polystyrene (PS), Acrylonitrile-Butadiene-Styrene (ABS), Styrene-Acrylonitrile (SAN), Styrene/Acrylic (S/A), Styrene-Maleic Anhydride (SMA).
  • Vinyls: Polyvinyl Chloride (PVC), Chlorinated Polyvinyl Chloride (CPVC).
  • Acrylics: Polymethylmethacrylate (PMMA), Polyvinyl Chloride-Acrylic Blend (PVC/MA).
  • Fluoropolymers: Polychlorotrifluoroethylene (PCTFE), Polytetrafluoroethylene (PTFE), Polyvinylidene fluoride (PVDF), *Ethylene chlorotrifluoroethylene (ECTFE), Fluorinated ethylene propylene (FEP), Ethylene tetrafluoroethylene (ETFE), Perfluoroalkoxy (PFA).
  • Polyesters: Polyethylene Terephthalate (PET), Polyester PETG (PETG), Polybutylene Terephthalate (PBT), Polyarylate (PAR), Liquid Crystal Polyester (LCP).
  • Polyamides (Nylons): Nylon 6 (N6), Nylon 66 (N66), Nylon 11 (N11), Nylon 12 (N12), Polyphthalamide (PPA), Polyamide-imide (PAI).
  • Polyimides: Polyimide (PI), Polyetherimide (PEI).
  • Polyethers: Polyacetal (POM), Polycarbonate (PC), Polyphenylene Oxide Blend (PPO), Polyaryletherketone (PAEK), Polyetheretherketone.
  • Sulfur Containing Polymers: Polyphenylene Sulfide (PPS), Polysulfone (PSF), Polyethersulfone (PES), Polyarylsulfone (PAS).

Properties and applications of some thermoplastics

  • Thermoplastic Low Density Polyethylene (LDPE)
  • Thermoplastic High Density Polyethylene (HDPE)
  • Thermoplastic Polypropylene (PP)
  • Thermoplastic Acrylonitrile-Butadiene-Styrene (ABS)
  • Thermoplastic Polyvinyl Chloride (PVC)
  • Thermoplastic Polymethylmethacrylate (PMMA)
  • Thermoplastic Polytetrafluoroethylene (PTFE)
  • Polyvinylidene fluoride (PVDF)
  • Ethylene chlorotrifluoroethylene (ECTFE)
  • Polychlorotrifluoroethylene (PCTFE)
  • Fluorinated ethylene propylene (FEP)
  • Ethylene tetrafluoroethylene (ETFE)
  • Perfluoroalkoxy (PFA)
  • Thermoplastic Polyethylene Terephthalate (PET)
  • Thermoplastic Polyamide (Nylon 6)
  • Thermoplastic Polyimide (PI)
  • Thermoplastic Polycarbonate (PC)
  • Thermoplastic Polysulfone (PSF)
  • Thermoplastic Polyamide-imide (PAI), electrical grade
  • Thermoplastic Polyamide-imide (PAI), bearing grade

Original Source


Plastics.jpg

July 3, 2019

Bend me, shape me, anyway you want me. Those are the words of an old love song, but it could just as easily be a song about plastics—the most versatile materials in our modern world. Plastics are plastic, which means we can mold them into pretty much anything, from car bodies and washing-up bowls to toilet seats and toothbrushes. That’s partly because there are many different kinds of plastic but also because each kind can be used for many things. What exactly is plastic? How do we make it? How do we get rid of it when we no longer need it? Let’s take a closer look!

 

What are plastics?

We talk about “plastic” as though it’s a single material, but there are in fact many different plastics. What they have in common is that they’re plastic, which means they are soft and easy to turn into many different forms during manufacture. Plastics are (mostly) synthetic (human-made) materials, made from polymers, which are long molecules built around chains of carbon atoms, typically with hydrogen, oxygen, sulfur, and nitrogen filling in the spaces. You can think of a polymer as a big molecule made by repeating a small bit called a monomer over and over again; “poly” means many, so “polymer” is simply short for “many monomers.” If you think of how a long coal train is made from many trucks coupled together, that’s what polymers are like. The trucks are the monomers and the entire train, made from lots of identical trucks, is the polymer. Where a coal train might have a couple of dozen trucks, a polymer could be built from hundreds or even thousands of monomers. In other words, polymers typically have very large and heavy molecules.

How the polythene polymer molecule is made by endlessly repeating the ethene monomer.

Types of plastics

Sellotape sticky tape dispenser

 

There are many different plastics, so we need ways of making sense of them all by grouping similar ones together. Here are a few ways we can do that (and there are others I’ve not listed):

  • We can split them into natural (ones easily obtained from plants and animals) and synthetic (ones artificially made by complex chemical processes in a factory or lab). Cellulose is a natural polymer used for making sticky tape (among other things), whereas nylon is a synthetic polymer made in a factory.
  • We can group them according to the structure of the monomers that their polymers are made from. That’s why we talk about polyesters, polyethylenes, polyurethanes and so on—because they’re different polymers made by repeating different monomers.
  • When it comes to recycling, we need to separate plastics into different kinds that can be processed together without causing contamination. That depends on their chemical properties, physical properties, and the polymer types from which they’re made, and gives us seven main kinds. (You’ve probably noticed seven different recycling symbols numbered 1-6 and “null” on plastic packaging, if you’ve looked carefully.)
  • We can group by what they’re made from (say bioplastics—artificially made from natural ingredients) or how they behave when they’re buried in landfills (biodegradable, photodegradable, and so on).
  • We can split them into two broad kinds according to how they behave when they’re heated: thermoplastics (which soften when they’re heated) and thermosets(thermosetting plastics, which never soften after they’re initially molded).

Thermoplastics and thermosets

The last one on my list is such an important way of grouping plastics that we’d better look at it in a bit more detail. What’s the difference between thermoplastics and thermosets—and how can we explain it?

Thermoplastics

Toes inside brown nylon stockings.

 

You can make something like a plastic bottle by injecting hot, molten plastic into a mold, then letting it cool down. Your bottle stays solid, but if you heat it up again later, it’ll soften and melt. We say it’s made from a thermoplastic: something that becomes plastic (soft and flexible) when it meets thermal energy (heat). In a thermoplastic, the long polymer molecules are joined to one another by very weak bonds, which easily break apart when we heat them, and quickly reform again when we take the heat away. That’s why thermoplastics are easy to melt down and recycle. Some everyday examples you will have come across are polyethylene/polythene (plastic bottles and sheets), polystyrene (crumbly white packaging material), polypropylene (plastic ropes), polyvinyl chloride/PVC (toys and credit cards), polycarbonate (hard plastic windows and car headlamps), and polyamide (nylon—used in everything from stockings and swimming shorts to toothbrushes and umbrellas).

Thermosetting plastics (thermosets)

A frying pan coated with nonstick Teflon, a plastic polymer

 

Thermosets are usually made from much much bigger polymer chains than thermoplastics. When they’re initially manufactured, they’re heated or compressed to form a dense, hard, structure with strong cross-links binding each of these long molecular chains to its neighbors. That’s very different from thermoplastics, where the polymer chains are held to one another only by very weak bonds. And that’s why we can’t simply heat thermosets to remold or reform them. Once they’re “set” (cured) during manufacture, they stay that way. You’ll be less familiar with thermosets than with thermoplastics; even so, you may have come across examples like polyurethane (insulating material in buildings), polytetrafluoroethylene/PTFE (nonstick coatings on cooking pots and pans), melamine (hard plastic crockery), and epoxy resin (a tough plastic used in strong adhesives and wood fillers).

How do we make plastics?

We’ve already seen that plastics are made from polymers, but how are polymers made? They’re based on hydrocarbons (molecules built from hydrogen and carbon atoms) that we get mostly from things like petroleum, natural gas, or coal. Crude oil drilled from the land or sea is a thick gloopy mixture that contains thousands of different hydrocarbons, which have to be separated out before we can use them. That happens in an oil refinery, through a process called fractional distillation. It’s a more involved version of the distillation you might have used to purify water. If we heat water, it eventually turns into steam, which we can then collect, cool, and condense back to water; that’s distillation, and it produces highly purified or “distilled” water. We can heat and distill crude oil the same way, but all those many hydrocarbons it contains have molecules that are different sizes and weights, so they boil off and condense at different temperatures. Collecting and distilling the different parts of crude oil at different temperatures gives us a bunch of simpler mixtures of hydrocarbons, called fractions, which we can then use for making different types of plastics.

Plastic computer keyboard

 

Hydrocarbons made in this way are the raw materials for polymerization, the name we give to the chemical reactions that make polymers. Some polymers are made simply by fastening hydrocarbon monomers together, like daisy chains, which is a process called addition polymerization. Others are made by joining together two small hydrocarbon chains and removing a water molecule (two hydrogen atoms and one oxygen), making a bigger hydrocarbon chain in a process known as condensation polymerization. The more often you repeat this, the longer the polymer gets.

Typically, we need to use other chemicals called catalysts to kick-start polymerization. Catalysts are simply substances we can add that make a chemical reaction more likely to happen and, though they may change temporarily during the reaction, they re-emerge at the end in their original form; in other words, they’re not permanently changed as the reaction takes place. Ziegler-Natta catalysts, some of the most important for making polymers, were developed through the work of German chemist Karl Ziegler and Italian Giulio Natta, which won them a joint Nobel Prize in Chemistry in 1963.

Because we need plastics to do all sorts of things, we often have to add other ingredients to the basic hydrocarbons to produce a polymer with exactly the right chemical and physical properties. These extra ingredients include colorants (which, as the name suggests, turn plastics into all kinds of bright and happy colors), plasticizers (which make plastics more flexible, viscous, and easier to shape), stabilizers (to stop our plastics breaking apart in sunlight and heat), and fillers (typically low-cost minerals that mean we need less of the expensive, oil-based hydrocarbons to make our final plastic product—so we can make and sell it more cheaply).

A length of anti-static tubular hose pipe.

 

The plastic-making process doesn’t end there. What we’ve got at this point is a plastic polymer known as a resin, which can be used for making all kinds of plastic products. Resins are supplied as powders or grains that are loaded into a machine, heated, and then shaped by one or more processes to make our finished plastic product. The shaping processes include injection and blow molding (where we squirt hot plastic through a nozzle into a mold to make things like plastic bottles), calendering (squashing between heavy rollers, for example, to make plastic sheets or films), extruding (squeezing plastic through a nozzle, perhaps to make pipes or straws), and forcing plastics through a kind of microscopically small sieve, called a spinneret, to make thin fibers (which is how fibers are made for things like toothbrushes or nylon stockings). There are many other plastic-making processes as well.

What are plastics like?

The many kinds of plastics all have different properties (if they didn’t, we wouldn’t need so many of them in the first place). Having said that, they do have things in common. Generally, plastics are flexible and easy to shape in a variety of ways (remember, that’s why we call them plastics); easy to make in all different shapes, sizes, and colors; lightweight; electrically insulating; waterproof; and relatively inexpensive. Some of them are meant to be very strong and durable (car bits and prosthetic body parts are examples), while others are designed to fall apart in the environment relatively quickly (biodegradable plastic bags, for example). The properties of a plastic can also be deliberately engineered. Suppose we want plastics to be resistant to static electricity so they don’t pick up so much dust; then we can use anti-static additives during the manufacturing process to make them slightly electrically conducting.

What do we use plastics for?

Selection of plastic household articles

 

In the early 20th century, plastics were quite a novelty; there were only a handful of plastics and very few uses. Zoom the clock forward 100 years and it’s hard to find things that we don’t use plastics for. Materials science means understanding the properties of different materials so we can use them to best advantage in the world around us. Given what we’ve just learned about the properties of plastics, it comes as no surprise to find them helping us out in building construction, clothing, packaging, transport, and in many other parts of everyday life.

In buildings, you’ll find plastics in things like secondary glazing, roofs, heat insulation and soundproofing, and even in the paints you slap on your walls. There are plastics insulating your electrical cables and carrying water and waste-water in and out of your home. Look around you now and you’ll see plastics everywhere, from picture frames and lamp shades to the clothes on your back and the shoes on your feet. How do all these things get into your life? Up to a third of all the plastic we use finds its way into the packaging we use to protect products (sometimes even plastic products) on the journey from factory to home.

Photo of plastic plane by NASA

 

Because plastic means flexible, by definition, we tend to think plastics are relatively weak materials. Yet some are incredibly strong and long-lasting. If you have a rotten wooden door or window, for example, you might chisel out the rot and replace it with epoxy resin filler, a very strong thermosetting plastic that will turn rock hard in a matter of minutes and stay that way for years. Car fenders are now mostly made of plastic—and lightweight car and boat bodies are often made from composites such as fiberglass (glass-reinforced plastic), which are plastics mixed with other materials for added strength. Some plastics are soft or hard as the mood suits them. An amazing plastic called D3O® has an astonishing ability to absorb impacts: normally it’s soft and squishy, but if you hit it very suddenly, it hardens instantly and cushions the blow. (Find out more about it in our article on energy-absorbing materials.)

Plastics and the environment

Most plastics are synthetic, so they’re carefully designed by chemists and laboriously engineered under very artificial conditions. They’d never spontaneously appear in the natural world and they’re still a relatively new technology, so animals and other organisms haven’t really had chance to evolve so they can feed on them or break them down. Since a lot of the plastic items we use are meant to be low-cost and disposable, we create an awful lot of plastic trash. Put these two things together and you get problems like the Great Pacific Garbage Patch, a giant “lake” of floating plastic in the middle of the North Pacific Ocean made from things like waste plastic bottles. How can we solve horrible problems like this? One solution is better public education. If people are aware of the problem, they might think twice about littering the environment or maybe they’ll choose to buy things that use less plastic packaging. Another solution is to recycle more plastic, but that also involves better public education, and it presents practical problems too (the need to sort plastics so they can be recycled effectively without contamination). A third solution is to develop bioplastics and biodegradable plastics that can break down more quickly in the environment.

It’s easy to dismiss plastics as cheap and nasty materials that wreck the planet, but if you look around you, the reality is different. If you want cars, toys, replacement body parts, medical adhesives, paints, computers, water pipes, fiber-optic cables, and a million other things, you’ll need plastics as well. Maybe you think we struggle to live with plastics? Try imagining for a moment how we’d live without them. Plastic is pretty fantastic—we just need to be smarter and more sensible about how we make it, use it, and recycle it when we’re done.

A brief history of plastics

A typical bakelite electric power adapter from the 1950s or 1960s.

 

  • Ancient people start using plastics (natural materials like rubber, animal horn, and tortoiseshell are made from polymers).
  • 1838: Injection molding is developed for diecast metal products (a technology that will later revolutionize plastic-making).
  • 1839: Charles Goodyear develops vulcanized (heat and sulfur treated) rubber—an example of a tough, durable cross-linked polymer.
  • 1855: Georges Audemars, a Swiss chemist, makes the first synthetic plastic silk fibers using mulberry bark and rubber gum.
  • 1856: Alexander Parkes develops the first artificial plastic, Parkesine, by making nitrocellulose from cellulose and nitric acid.
  • 1875: Alfred Nobel invents gelignite, a plastic explosive also based on nitrocellulose.
  • 1885: George Eastman (of Kodak camera fame) revolutionizes photography by making plastic photographic film from cellulose.
  • 1894: Viscose, the first commercially successful artificial silk (a form of rayon), is produced by Charles Cross, Edward Bevan, and Clayton Beadle.
  • 1907: Belgian-born chemist Leo Baekeland makes the first fully synthetic thermosetting plastic, Bakelite, from phenol and formaldehyde. He experiments with injection molding around the same time.
  • 1920: American John Wesley Hyatt develops the first injection molding machine for plastics.
  • 1930: American chemist Wallace Carothers and his team at DuPont accidentally discover a weird new material. It soon becomes nylon, a wildly successful plastic that revolutionizes textile manufacture.
  • 1930: Transparent, “Scotch” sticky tape is invented by Richard G. Drew of 3M.
  • 1930s: German chemist Eduard Simon accidentally makes polystyrene, initially called styrol oxide and, later, metastyrol.
  • 1938: Roy Plunkett of DuPont accidentally discovers PTFE (Teflon).
  • 1942: Harry Coover of Eastman Kodak invents plastic superglue (methyl cyanoacrylate).
  • 1949: Lycra (a type of polyurethane) is invented by DuPont.
  • 1949: American Bill Tritt builds the Glasspar G2, the first production sports car with a body made entirely from fiberglass (a plastic composite).
  • 1953: Karl Ziegler develops aluminum catalysts for speeding up polymerization.
  • 1954: Giulio Natta develops polypropylene, first made by Italian chemical company, Montecatini.
  • 1955: Building on earlier work by Karl Ziegler, Natta perfects Ziegler-Natta catalysts.
  • 1954: Dow Corning invents expanded polystyrene.
  • 1958: George de Mestral files a patent for VELCRO®, the reusable plastic hook-and-loop fastener.
  • 1966: Stephanie Kwolek and Paul Morgan of DuPont are granted a patent for Kevlar®, a super-tough plastic similar to nylon. It’s commercially introduced in 1971. Also in 1966, another DuPont chemist, Wilfred Sweeny, is granted a patent for a chemically similar nylon-relative called Nomex®, a revolutionary fireproof material.
  • 1982–1983: Various countries (and regions with their own currencies), including Costa Rica, Haiti, Ecuador, El Salvador, and Britain’s Isle of Man, experiment with banknotes made from a flexible, paper-like plastic called Tyvek®.
  • 1982: The Jarvik 7, a complete artificial heart, made from plastic polyurethane, is first implanted in a human.
  • 1988: Australia becomes the first country to issue high-security plastic banknotes properly (not as part of a temporary trial). It switches all its notes to polymer versions by 1996.
  • 1990s: The first modern 3D-printers are developed. They can make realistic models of objects by squirting out layers of hot ABS (acrylonitrile butadiene styrene) plastic.
  • 1997: Captain Charles Moore discovers the Great Pacific Garbage Patch.
  • 1998: Smart cars made from composites enter production.
  • 2001: Scott White, Nancy Sottos, and collaborators at the University of Illinois at Urbana-Champaign develop remarkable self-healing materials from plastics.
  • 2002: British inventor Richard Palmer files a patent for a revolutionary energy-absorbing plastic, which he calls D3O, that can soak up the force from impacts.
  • 2016: Japanese scientists report the discovery of bacteria that can eat plastic bottles.

Original Source


Plastics.jpg

May 28, 2019

Thermoplastics are polymers, which soften (becomes pliable and plastic) and melt when heated. In the melted conditions thermoplastics may be formed by various methods (injection molding, extrusion, Thermoforming).

No new cross-links form (no chemical curing) when a thermoplastic cools and harden. Thermoplastics may be reprocessed (re-melt) many times.

Molecules of most of thermoplastics combine long polymer chains alternating with monomer units.

Thermoplastic materials may contain filler materials in form of powder or fibers, providing improvement of specific material properties (strength, stiffness, lubricity, color etc.).

Thermoplastic groups:

  • Polyolefins: Low Density Polyethylene (LDPE), High Density Polyethylene (HDPE), Polypropylene (PP).
  • Styrenics: Polystyrene (PS), Acrylonitrile-Butadiene-Styrene (ABS), Styrene-Acrylonitrile (SAN), Styrene/Acrylic (S/A), Styrene-Maleic Anhydride (SMA).
  • Vinyls: Polyvinyl Chloride (PVC), Chlorinated Polyvinyl Chloride (CPVC).
  • Acrylics: Polymethylmethacrylate (PMMA), Polyvinyl Chloride-Acrylic Blend (PVC/MA).
  • Fluoropolymers: Polychlorotrifluoroethylene (PCTFE), Polytetrafluoroethylene (PTFE), Polyvinylidene fluoride (PVDF), *Ethylene chlorotrifluoroethylene (ECTFE), Fluorinated ethylene propylene (FEP), Ethylene tetrafluoroethylene (ETFE), Perfluoroalkoxy (PFA).
  • Polyesters: Polyethylene Terephthalate (PET), Polyester PETG (PETG), Polybutylene Terephthalate (PBT), Polyarylate (PAR), Liquid Crystal Polyester (LCP).
  • Polyamides (Nylons): Nylon 6 (N6), Nylon 66 (N66), Nylon 11 (N11), Nylon 12 (N12), Polyphthalamide (PPA), Polyamide-imide (PAI).
  • Polyimides: Polyimide (PI), Polyetherimide (PEI).
  • Polyethers: Polyacetal (POM), Polycarbonate (PC), Polyphenylene Oxide Blend (PPO), Polyaryletherketone (PAEK), Polyetheretherketone.
  • Sulfur Containing Polymers: Polyphenylene Sulfide (PPS), Polysulfone (PSF), Polyethersulfone (PES), Polyarylsulfone (PAS).

Original Source


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May 23, 2019

One major characteristic that’s useful to understand when it comes to plastic prototype production and/or plastic part manufacturing is the distinction between thermoplastic and thermoset materials. To make a long story short, thermoplastic materials can be melted, cured (cooled down such that they become solid), melted again, cured again, and so forth. There is a limit to the number of times this process can be repeated depending on the particulars of the given material but the point is that thermoplastic materials can be melted multiple times without significantly degrading the material. Thermoset materials, by contrast can only be melted once. After a thermoset material cures, attempting to heat it again to its melting point would cause it to burn (rather than melt) the material. It is useful to think of a 2-part epoxy when trying to understand thermoset plastics. An epoxy, like a thermoset material, is liquid prior to setting. Once the resin dries, however, it is not possible to melt it again.

When it comes to injection molding it’s easy to misunderstand the relevancy of thermoset and thermoplastic materials. For starters, both thermoset and thermoplastic polymers can be injection molded. The primary difference applies after the injection mold cycle (typically only a few seconds in duration) when the molded plastic cures (solidifies). During injection molding plastic is heated and then injected into a metal “tool” (think of a cube with an internal cavity in the shape of your final part). In order to physically get to the cavity the molten plastic must first pass through a series of tunnels and entry points known as sprues, runners, and gates. Plastic cools every cycle within the mold cavity as well as within these channels that lead to the cavity. The material that solidifies in the sprues, runners, and gates is not part of the final product. It is essentially waste.

So what happens to this “waste” material during injection molding?

1. Thermoplastics:

In the event that a thermoplastic material is being used for injection molding, it can be recycled and used again (oftentimes this occurs right on the factory floor). Solid material left over after each cycle in the sprues, runners, and gate locations can frequently be combined with the raw material that originally goes into the injection molding press. The same is true with material from rejected parts or the overflow material on the edges of parts where the mold tool was not 100% airtight. All of this plastic (called “regrind”) can be ground up and recycled back into the beginning of the process. This all translates into higher efficiency and ultimately means lower costs for the end consumer and a more competitive or higher margin product for the producer. Of note, that does not mean that a precisely designed mold tool is unnecessary for injection molding with thermoplastics. To the contrary, oftentimes quality control measures limit the amount of regrind that can be reused as a percentage of total plastic to prevent potential degradation of material properties.

2. Thermosets:

In the event that a thermoset material is being used, the solid material from the sprues, runners, and gates is virtually guaranteed to be thrown away as waste. That means that all other things being equal (disclaimer: this is a bad assumption) that the end product will cost more.

Why else does the distinction between thermoplastics and thermoset materials matter?

As you might imagine, the same characteristics are relevant at the end of a plastic part’s lifecycle when it comes time to either throw away or recycle the material. Consider the plastic water bottles sold millions of times everyday. The 500mL of water inside is consumed in a matter of minutes while the bottle, if thrown into a landfill, would take hundreds of years to biodegrade. The number of plastic bottles in landfills eventually becomes an environmental issue if recycling is not a player in the process. Consequently most plastic bottles are made in whole or at least in part from recycled material. Take a look for yourself. The resin identification code on your plastic bottle is likely to read “1” which identifies materials made from polyethylene terephthalate (PET), a thermoplastic material.

In conclusion, thermoplastics provide some major advantages to manufacturers, consumers, and society in general. The fact that they can be easily recycled means that we are more responsibly stewarding our natural resources while the fact that manufacturing waste can be reused (thus preventing it from becoming “waste” in the first place) makes them a favorable choice if specific material properties aren’t exclusively available with a thermoset material.

Original Source


Plastics.jpg

May 15, 2019

Thermoplastic polymer resins are extremely common, and we come in contact with thermoplastic resins constantly. Thermoplastic resins are most commonly unreinforced, meaning, the resin is formed into shapes and have no reinforcement providing strength.

Examples of common thermoplastic resins used today, and products manufactured by them include:

  • PET – Water and soda bottles
  • Polypropylene – Packaging containers
  • Polycarbonate – Safety glass lenses
  • PBT – Children’s toys
  • Vinyl – Window frames
  • Polyethylene – Grocery bags
  • PVC – Piping
  • PEI – Airplane armrests
  • Nylon – Footwear

Many thermoplastic products use short discontinuous fibers as a reinforcement. Most commonly fiberglass, but carbon fiber too. This increases the mechanical properties and is technically considered a fiber reinforced composite, however, the strength is not nearly as comparable to continuous fiber reinforced composites.

In general, FRP composites refers to the use of reinforcing fibers with a length of 1/4″ or greater. Recently, thermoplastic resins have been used with continuous fiber creating structural composite products. There are a few distinct advantages and disadvantages thermoplastic composites have against thermoset composites.​

Advantages of Thermoplastic Composites

There are two major advantages of thermoplastic composites. The first is that many thermoplastic resins have an increased impact resistance of comparable thermoset composites. In some instances, the difference is as high as 10 times the impact resistance.

The other major advantage of thermoplastic composites is the ability reform. See, raw thermoplastic composites, at room temperature, are in a solid state. When heat and pressure impregnate a reinforcing fiber, a physical change occurs; not a chemical reaction as with a thermoset.

This allows thermoplastic composites to be reformed and reshaped. For example, a pultruded thermoplastic composite rod could be heated and remolded to have a curvature. This is not possible with thermosetting resins. This also allows for the recycling of the thermoplastic composite at end of life. (In theory, not yet commercial).

Properties and Benefits of Thermoset Resins

Traditional Fiber Reinforced Polymer Composites, or FRP Composites for short, use a thermosetting resin as the matrix, which holds the structural fiber firmly in place. Common thermosetting resin includes:

  • Polyester Resin
  • Vinyl Ester Resin
  • Epoxy
  • Phenolic
  • Urethane

The most common thermosetting resin used today is a polyester resin, followed by vinyl ester and epoxy. Thermosetting resins are popular because of uncured, at room temperature, they are in a liquid state. This allows for convenient impregnation of reinforcing fibers such as fiberglass, carbon fiber, or Kevlar.

As mentioned, a room temperature liquid resin is easy to work with. Laminators can easily remove all air during manufacturing, and it also allows the ability to rapidly manufacture products using a vacuum or positive pressure pump. (Closed Molds Manufacturing) Beyond ease of manufacturing, thermosetting resins can exhibit excellent properties at a low raw material cost.

Properties of thermoset resins include:

  • Excellent resistance to solvents and corrosives
  • Resistance to heat and high temperature
  • Fatigue strength
  • Tailored elasticity
  • Excellent adhesion
  • Excellent finishing (polishing, painting, etc.)

In a thermoset resin, the raw uncured resin molecules are crossed linked through a catalytic chemical reaction. Through this chemical reaction, most often exothermic, the resin creates extremely strong bonds with one another, and the resin changes state from a liquid to a solid.

A thermosetting resin, once catalyzed, it can not be reversed or reformed. Meaning, once a thermoset composite is formed, it cannot be remolded or reshaped. Because of this, the recycling of thermoset composites is extremely difficult. The thermoset resin itself is not recyclable, however, there are a few new companies who have successfully removed the resin through pyrolization and are able to reclaim the reinforcing fiber.

Disadvantages of Thermoplastics

Because thermoplastic resin is naturally in a solid state, it is much more difficult to impersonate reinforcing fiber. The resin must be heated to the melting point, and pressure is required to impregnate fibers, and the composite must then be cooled under this pressure. This is complex and far different from traditional thermoset composite manufacturing. Special tooling, technique, and equipment must be used, many of which are expensive. This is the major disadvantage of thermoplastic composites.

Advances in thermoset and thermoplastic technology are happening constantly. There is a place and a use for both, and the future of composites does not favor one over the other.

Original Source


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May 9, 2019

There are thousands of plastics on the market that can be used for rapid prototyping or low-volume manufacturing—choosing the right one for a given project can be overwhelming, especially for first-time inventors or new entrepreneurs. Each material has trade-offs when it comes to cost, strength, flexibility and surface finish. Consideration must be given not only to the application of the part or product, but also to the environment in which it will be used.

Overall, engineering plastics have advanced mechanical properties that offer greater durability and that won’t be compromised during the manufacturing process. Modifications also can be made to some types of plastics to improve their strength as well as their impact and heat resistance. Let’s delve into the different plastic materials to consider depending on the final part or product’s function.

Mechanical parts

One of the most common resins used to make mechanical parts is nylon, aka polyamide (PA). When PA is mixed with molybdenum it has a slippery surface for easy motion. However, using nylon-to-nylon gear trains is not recommended, as similar plastics tend to stick together. PA is highly resistant to wear and abrasion and has good mechanical properties at elevated temperatures. Nylon is ideal as a filament for 3D plastic printing, but it absorbs water over time.

Polyoxymethylene (POM) is also a great option for mechanical parts. POM is a type of acetal resin, used to make Dupont’s Delrin, a valuable plastic for gears, screws, wheels and more. POM has high flexural and tensile strength, stiffness and hardness. However, POM can degrade with alkali, chlorine and hot water and can be difficult to bond together.

Plastic containers

If your project is a vessel of sorts, polypropylene (PP) is best. PP is used for food-storage containers because it is heat resistant, is impervious to oils and solvents and doesn’t leach chemicals, making it food safe. PP also has a superior balance of stiffness and impact strength and can be easily formed into a hinge that can be bent repeatedly without breaking. It can also be used for applications in pipes and hoses.

Another option is polyethylene (PE). The most common plastic in the world, PE has low strength, hardness and rigidity. It usually has a milky white color and is the plastic found in medicine bottles and milk and detergent containers. PE is highly resistant to various chemicals, but has a low melting point.

Tool cases and hardware

For any project needing high impact resistance and strong resilience to tearing and breaking, acrylonitrile butadiene styrene (ABS) is ideal. ABS is lightweight and can be strengthened by adding glass fibers. It is more expensive than styrene, but lasts much longer due to its hardness and toughness. ABS is used for 3D fused deposition modeling of rapid prototypes.

Given its properties, ABS is a good option for wearable devices. At Star Rapid, we created a smart watch case for E3design with black, pre-colored ABS/PC plastic resin using plastic injection molding. This material choice allows the overall device to stay relatively light, while also providing a shell that can endure accidental impacts, such as when the watch hits a hard surface. If you need something that is versatile and impact resistant, high-impact polystyrene (HIPS) is a good option. This material is suitable for creating tough cases for power tools and tool boxes. While HIPS is economical, it is not considered environmentally friendly.

Rubber

Many projects call for injection molding of resins that have the soft, elastic properties of rubber. Thermoplastic polyurethane (TPU) is a great option, as it comes in many special formulas to achieve high elasticity, low-temperature performance and durability. TPU is also used in power tools, caster wheels, cable insulation and sporting goods. As it is solvent resistant, TPU can be found in many industrial environments due to its high abrasion resistance and shear strength. However, it is notorious for absorbing moisture from the atmosphere, so it can be difficult to process during manufacturing. For over-molding, there’s thermoplastic rubber (TPR), which is inexpensive and easy to handle for applications like cushioned rubber grips.

Transparent parts

If your part requires clear lenses or windows, acrylic (PMMA) is best. This material is used to make shatterproof windows like Plexiglass because of its rigidity and abrasion resistance. PMMA also takes a high polish, has good tensile strength and is economical in large volumes. However, it is not as impact or chemical resistant as polycarbonate (PC).

If you need something stronger for your project, PC is more durable than PMMA and has excellent optical properties, making it an appropriate choice for lenses and bulletproof windows. PC also can be bent and formed at room temperature without shattering. It’s useful for prototyping work, since it does not require expensive mold tools to shape. PC is more expensive than acrylic and may release harmful chemicals when exposed to hot water for extended periods of time, so it’s not food safe. Due to its impact strength and resistance to scratches, PC is ideal for a variety of applications. At Star Rapid, we used this material to create covers for handheld point-of-sale terminals for Muller Commercial Solutions. The part was CNC machined from solid blocks of PC; since it needed to be completely transparent, it was then hand sanded and vapor polished.

This is just a quick look at some of the most commonly used plastics for manufacturing. Most can be altered with various glass fibers, UV stabilizers, lubricants or other resins to achieve specific engineering properties based on the needs of the project and the manufacturing process being used—whether it’s injection molding, vacuum casting or 3D printing.

Original Source


fundamentals-of-extrusion.jpg

May 1, 2019

In the plastics extrusion process, raw thermoplastic material, or resin, is gravity fed from a top mounted hopper into the barrel of an extruder. Additives, such as colorants and UV inhibitors, in either liquid or pellet form are often used and can be introduced into the resin below arriving at the hopper. The process has much in common with plastics injection molding though differs in that the process is usually continual. While injection molding can offer many similar profiles in continuous lengths, usually with added reinforcing, the finished product is pulled out of a die instead of extruding the fluid resin through a die.

As the material enters the feed throat near the rear of the barrel it comes in contact with the screw. The rotating screw forces the plastic resin forward into the barrel that is heated to the desired melt temperature depending on the resin. In most processes, a heating profile is set for the barrel utilizing three or more independent PID (proportional-integral-derivative controller) controlled heat zones that gradually increase the temperature of the barrel from the rear where the resin has entered to the front. This allows the plastic resin to melt gradually as it is pushed through the barrel and lowers the risk of overheating which may cause degradation in the polymer.

At the front of the barrel, the resin leaves the screw and travels through a reinforced screen to remove any contaminants.  A breaker plate generally reinforces screens because the pressure at this point can exceed 5000 psi (34 MPa).

After passing through the breaker plate resin enters the die. The die is what gives the final product its profile or shape and must be designed so that the molten plastic evenly flows from a cylindrical profile, to the product’s profile shape. Uneven flow at this stage would produce a product with unwanted stresses at certain points in the profile. These stresses can cause warping upon cooling. Almost any shape imaginable can be created so long as it is a continuous profile.

The product must now be cooled which is usually achieved by pulling the extrudate through a water bath. Plastics are excellent thermal insulators and are therefore very difficult to cool quickly. Compared with steel, plastic conducts its heat away 2000 times more slowly. In a tube or pipe extrusion line, a sealed water bath utilizes a carefully controlled vacuum to keep the newly formed and still molten tube or pipe from collapsing. A set of cooling rollers is generally used in the sheet extrusion process to cool sheet as it exits the extruder.

Sometimes, on the same line, a secondary process may occur before the product has finished its run. In the manufacture of adhesive tape, a second extruder melts adhesive and applies this to the plastic sheet while it’s still hot. Once the product has cooled, it can be spooled, or cut into lengths for later use.

Plastic extruders are also extensively used to prepare recycled plastic waste and/or raw materials after cleaning, sorting and/or blending into filaments suitable for blending into the resin pellet stock used by the plastics industry at large.

Original Source


Polyethylene-.jpg

April 17, 2019

The model above is an image of the pdb model you can view
by clicking here or you can just click on the image itself.
Either way, be sure to close the new window that opens up
with the 3D model in it when you are ready to come back here.


Polyethylene is probably the polymer you see most in daily life. It is one of the polymers called polyolefins, which is an odd name. Many names from the past have nothing to do with the actual chemical compositions of the molecules, but that’s a story for another time.
Polyethylene is the most popular plastic in the world. This is the polymer that makes grocery bags, shampoo bottles, children’s toys, and even bullet proof vests. For such a versatile material, it has a very simple structure, the simplest of all commercial polymers. A molecule of polyethylene is nothing more than a long chain of carbon atoms, with two hydrogen atoms attached to each carbon atom. That’s what the picture at the top of the page shows, but it might be easier to draw it like the picture below, only with the chain of carbon atoms being many thousands of atoms long:

Sometimes it’s a little more complicated. Sometimes some of the carbons, instead of having hydrogens attached to them, will have long chains or branches of polyethylene attached to them. This is called branched, or low-density polyethylene, or LDPE. When there is no branching, it is called linear polyethylene, or HDPE. Linear polyethylene is much stronger than branched polyethylene, but branched polyethylene is cheaper and easier to make. It is also more flexible and works great for sandwich wrap.

Linear polyethylene is normally produced with molecular weights in the range of 200,000 to 500,000, but it can be made even higher. Polyethylene with molecular weights of three to six million is referred to as ultra-high molecular weight polyethylene, or UHMWPE. UHMWPE can be used to make fibers which are so strong they replaced Kevlar for use in bullet proof vests. Large sheets of it can be used instead of ice for skating rinks.

Polyethylene is vinyl polymer, made from the monomer ethylene. Here’s a model of the ethylene monomer. It looks like some sort of four-legged headless animal if you ask me.

The model above is an image of the pdb model you can view by
clicking here or you can just click on the image itself.
Either way, be sure to close the new window that opens up
with the 3D model in it when you are ready to come back here.

Branched polyethylene is often made by free radical vinyl polymerization. Linear polyethylene is made by a more complicated procedure called Ziegler-Natta polymerization.UHMWPE is made using metallocene catalysis polymerization.

But Ziegler-Natta polymerization can be used to make LDPE, too. By copolymerization ethylene monomer with a alkyl-branched comonomer one gets a copolymer which has short hydrocarbon branches. Copolymers like this are called linear low-density polyethylene, or LLDPE. BP produces LLDPE using a comonomer with the catchy name 4-methyl-1-pentene, and sells it under the trade name Innovex¨. LLDPE is often used to make things like plastic films.


Other plastic polymers include: Other fiber polymers include:
Polypropylene Polypropylene
Polyesters Polyesters
Polystyrene Nylon
Polycarbonate Kevlar and Nomex
PVC Polyacrylonitrile
Nylon Cellulose
Poly(methyl methacrylate) Polyurethanes

Original Source


Plastics.jpg

April 3, 2019

Plastics extrusion is a high volume manufacturing process that melts and forms raw plastic material into a continuous profile. Plastic extrusion is a process that creates two-dimensional shapes on length providing the third dimension tubing, edging, moldings fence, deck railing, window frames, weather stripping, adhesive tape and wire insulation and similar products in continuous lengths or short sections. Extruded products can be utilized as it is, or may be transforming into more complex assemblies by punching, molding, forming and other techniques. The extruded products can provide a cost effective solution to your product fabrication and assembly needs.

The two different fundamental methods of extruding film are below extrusion and slit die extrusion. While the design and operation of the extruder during die is the similar in both methods.

In the form of small beads known for gravity, raw thermoplastic material fed from a top mounted hopper into the barrel of the extruder. Also in the extrusion of plastics additives such as colorants and UV inhibitors either in liquid or in pellet form are often used and can be mixed into the resin prior to arriving at the hopper. Through the feed throat and rotating screw plastic beads are forced forward into the barrel where it is heated to the desired melt temperature of the molten plastic. This leads plastic beads to melt gradually as they are pushed through the barrel and lowers the risk of overheating which may cause degradation in the polymer.

Innovative Extrusion Pvt Ltd is a specialist manufacturer and supplier of products like rigid PVC profiles, thermal breaker, injection moulded components, Dies and Moulds and dies and moulds.

Vinayak Plastic Industries is engaged in Manufacturing and Exporting of HDPE / PP Solid Extruded Sheets and PP Corflute Sheet / PP Corrugated Sheets / PP Hollow Profile Sheets & HDPE Pipes. The sound infrastructure furnished with Hi-Tech Machinery that facilitates bulk production of the products that includes extrusion process.

In the recent days, plastics extrusion has seen conventional and unconventional ideas those made lot of difference to the process and the sector. It is not only about process and machinery involved, but also the market demand for it. As per a research report, US demand for extruded plastics is forecast to expand 2.6% annually through 2013.

BASF’s plastics extrusion technology has manufacturing of films, fibers, monofilaments, profiles, sheets, semi-finished products and a wide range of plastic materials plays important role in this process. The mechanical, thermal, chemical and electrical properties are information on fields of use on applications, which as well process information by extrusion or other processing techniques.

Custom Complex Profile Plastic Extrusions

Creating and generating custom plastic extrusions needs unique skills and talents, while it adds value and innovation to the current product.

Plastic Extrusion Technologies is recognized for its products and services in custom plastic profile and plastic tubing needs. Here over 25,000 square feet of plastic extrusions facility is filled with the most state-of-the-art production machinery. Plastic Extrusion Technologies has the technology, and more importantly, the knowledge to help you get your extruded plastic product into your customers’ hands. The clientele is from window manufacturers to adhesives producers, use Plastic Extrusion Technologies custom extrusions. The applications are prevalent in brush products, refrigeration, HVAC, cable and wire, safety products, point of purchase displays and commercial construction.

Eaton’s industrial plastics business provides custom complex profile plastic extrusions for a wide variety of customers and industries. The company’s value-added fabrication such as length cutting, hole punching, texture, and tape backing for mounting applications provide customers with the capabilities to complete any production. Custom profile extrusion products and solutions for a variety of applications and industries.

Crafted Plastics Inc has new approaches to the plastics extrusion process of making the specialized extruded plastic product. The approaches include

  • Co-Extrusion process is used when two materials and colors must be joined into one part.
  • Dual Durometer provides the making of a plastic extrusion where the same family of plastics, but with different hardness, is combined in various combinations-flexible and rigid, flexible and flexible, rigid and rigid. The term also applies when two different opaques are used in combination to make a part.
  • The Tri-Extrusion is a process that involves combining three materials or colors when needed in one plastic extrusion.
  • Value Added Operations after a plastic profile is extruded, additional work can be done. This work includes drilling, punching, notching, creating round or oval holes, cutting mitres, and doing precise tolerance cutting.

In the process, profile extrusion can be completed followed by adding tape like, film, foam, or magnetic, printing, or close tolerance cutting. Every year many events, exhibitions and conferences take place on plastics extrusion. An ongoing research and development has brought in improved applications and approaches to the plastics extrusion process. A lot of production lines via plastics extrusion machineries already lined up and this is the evidence of the demand for plastics extrusion technologies and the raw material.

Original Source


Polypropylene-.jpg

March 20, 2019

The model above is an image of the isotactic polymer you can view
by clicking here or you can just click on the image itself.
The image below is of the atactic version with random backbone stereochemistry.
Either way, be sure to close the new window that opens up
with the 3D model in it when you are ready to come back here.

Polypropylene is one of those rather versatile polymers out there. It serves double duty, both as a plastic and as a fiber. As a plastic it’s used to make things like dishwasher-safe food containers. It can do this because it doesn’t melt below 160oC, or 320oF. Polyethylene, a more common plastic, will anneal at around 100oC, which means that polyethylene dishes will warp in the dishwasher. As a fiber, polypropylene is used to make indoor-outdoor carpeting, the kind that you always find around swimming pools and miniature golf courses. It works well for outdoor carpet because it is easy to make colored polypropylene, and because polypropylene doesn’t absorb water, like nylon does.

Structurally, it’s a vinyl polymer, and is similar to polyethylene, only that on every other carbon atom in the backbone chain has a methyl group attached to it. Polypropylene can be made from the monomer propylene by Ziegler-Natta polymerization and by metallocene catalysis polymerization.

This is what the monomer propylene really looks like:

The model above is an image of the pdb model you can view
by clicking here or you can just click on the image itself.
Either way, be sure to close the new window that opens up with
the 3D model in it when you are ready to come back here.


Wanna know more?

Research is being conducted on using metallocene catalysis polymerization to synthesize polypropylene. Metallocene catalysis polymerization can do some pretty amazing things for polyolefins like polypropylene. Specifically, it allows polypropylene to be made with different tacticities. Most polypropylene we use is isotactic. This means that all the methyl groups are on the same side of the chain, like this:

Isotactic polypropylene has a high enough melting point that you can put it in your dishwasher and it won’t come out as a new form of plastic art. But sometimes we use atactic polypropylene. Atactic means that the methyl groups are placed randomly on both sides of the chain like the 3D image above or the figure below:

Atactic polypropylene has no commercial application because it’s pretty much a gooey, messy blob. However, by using special metallocene catalysts, it’s believed that we can make polymers that contain blocks of isotactic polypropylene and blocks of atactic polypropylene in the same polymer chain, as is shown in the picture:

This polymer is rubbery, and makes a good elastomer. This is because the isotactic blocks will form crystals by themselves, acting as physical crosslinkers. But because the isotactic blocks are joined to the atactic blocks, the little hard clumps of crystalline isotactic polypropylene are tied together by soft rubbery segments of atactic polypropylene, as you can see in the picture on the right.

To be honest, atactic polypropylene would be a very soft rubber without help from the isotactic blocks, but it wouldn’t be very strong. The hard isotactic blocks hold the rubbery isotactic material together, to give the material more strength. Most kinds of rubber have to be chemically crosslinked to give them strength, but not polypropylene elastomers.

Elastomeric polypropylene, as this copolymer is called, is a kind of thermoplastic elastomer. However, until the research is completed, this type of polypropylene will not be commercially available.

The polypropylene that you can buy off the shelf at the store today has about 50 – 60% crystallinity, but this is too much for it to behave as an elastomer. It does make it an excellent polymer for applications in plastic storage containers and bottles. Take a look on the bottom of what you use to store leftovers in the fridge. If it has a recycle number of “5,” it’s isotactic polypropylene.


Other polymers used as plastics include: Other polymers used as fibers include:
Polyethylene Polyethylene
Polyesters Polyesters
Polystyrene Nylon
Polycarbonate Kevlar and Nomex
PVC Polyacrylonitrile
Nylon Cellulose
Poly(methyl methacrylate) Polyurethanes

Original Source

 


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