We work with a wide variety of resins and thermoplastics and have done extensive research on melt flow and behavior. There are several questions that will be helpful as you discover what materials you will need. Some questions include: What environmental conditions will the part need to operate under? Does it need to withstand solder reflow temperatures or other high-heat situations? Does it touch the human body or other bio-materials? Are there lubricity or hydroscopic properties to include or exclude? These are just some of the good questions we can help you navigate before you begin the process.
Polyethylene, first accidentally developed in 1898 by Hans von Pechmann, is considered the most “widely used” of the plastic resins available. It is estimated that 80 million metric tons of material are used annually. It’s most common use is for packaging, specifically plastic bags.
It wasn’t until the 1930s when it began production for commercial use when English scientists “accidentally” developed a standardized process for the basis. The initial synthesis, low-density polyethylene (LDPE), began production in 1939. Its common counterpart, high-density polyethylene (HDPE), another accidental discovery by scientists at Phillips Petroleum, began in 1953.
Both LDPE and HDPE are widely used in the packaging or containment industries. LDPE often finds itself in the form of film as the basis of plastic bags or coatings over paper for items like milk cartons. Other common uses include blow-molded containers for a variety of markets including medical and cosmetics. The injection-molded applications are also found in common household products like mop buckets or other kitchen containers.
HDPE is more common for injection-molded applications. While it can be processed as a film or extrusion, molded HDPE for bottles, shipping containers and other distribution or storage devices is widely used.
Polypropylene was first developed in the mid-1950s by scientists Paul Hogan and Robert L. Banks (the same two from Phillips Petroleum that discovered the HDPE). They were working with ethylene and propylene separately for a project and “accidentally” combined the two materials forming both crystalline polypropylene and liner polyethylene.
Polypropylene is considered a very durable and inexpensive material. It has a high tensile strength and can withstand high amounts of compression. It is also considered very resistant to many solvents, chemicals, and acids. Polypropylene has a large variety of industrial uses because of these properties. It is also widely used in the medical industry because of its chemical resistance and non-toxicity properties as well.
“PP is normally tough and flexible, especially when copolymerized with ethylene. This allows polypropylene to be used as an engineering plastic, competing with materials such as ABS.”
Nylon, or polyamide, is a highly engineered thermoplastic synthesized from ethylenediamine. The material was first introduced in 1938 by DuPont as a fiber and then as an injection moldable grade in 1941.
The most common variation of Nylon in the U.S. is Nylon 6/6, others like Nylon 6 and 12 are also very common. This family of resins is noted for excellent “weather and friction-resistant” properties. Common applications include gears, bearings, and mountings. It is also common to find the material blended with an additive such as glass for reinforcement. Moisture absorption can be an issue in some applications because of its hydroscopic nature.
Polycarbonate was first sold commercially in 1958 when both Bayer and GE scientists from across the globe independently “discovered” similar processes for producing the material earlier that decade. GE’s material, Lexan, and Bayer’s Makrolon are still very common brands of PC today.
Online plastics and elastomers portal, Omnexus.com, aptly describes polycarbonate. “Polycarbonate is a transparent amorphous polymer which exhibits outstanding physical properties such as outstanding impact resistance (almost unbreakable), heat resistance up to 125°C and excellent clarity, although opaque and translucent grades are also available. Polycarbonate is often used to replace glass or metal in demanding applications when the temperature does not exceed 125°C.” 
Delrin (Acetal / Polyoxymethylene / POM)
Polyoxymethylene, or Acetal, or its more common trade name, Delrin, was first developed in the 1920s but because it was not considered thermally stable it wasn’t initially commercialized. It wasn’t until 1952 when DuPont scientist stabilized the process, a patent was filed in 1956, and commercial production began in 1960. Today you can find a variety of other versions of the POM-based material from other vendors as well.
Acetal plastics are known to be fairly chemically resistant and are very hydrophobic in nature. However, it is not considered to have high strength resistance and has a “very high” coefficient of thermal expansion. It’s considered to have a low melt temperature as well. This, along with its resistance to water, has made it an ideal choice for applications where wear is an issue such as bearings, wheels, casters, etc. It also has common use within the food industry.
Polysulfone, known for its “toughness and stability at high temps,” was first introduced to the market in 1965 by Union Carbide. It is considered the “highest service temperature of all melt-processable thermoplastics.” It’s also used as a high-end replacement to Polycarbonate for specialty applications.
Because of its heat resistance, it has taken on a role as a flame retardant for some applications. It is also a good candidate for some medical devices because it can withstand some of the re-sterilization processes demanded by that industry. Some variations of Polysulfone can have a heat-deflection rating of 345°F (174°C).
Polysulfone is considered a high-cost engineered resin. Along with the previously mentioned attributes it also has advantages for transparency, low moisture absorption and chemical/solvent resistance.
Polybutylene terephthalate (PBT)
Polybutylene Terephthalate was first marketed in 1970 by the company now known as Ticona. PBT is a semi-crystalline resin with “excellent” mechanical and electrical properties. It is also considered highly resistant to chemicals. The material tends to shrink very little during forming and is mechanically very strong.
Other common properties are high heat resistance, low moisture absorption and it makes a great insulator in electronic applications. This material also has a flame-retardant grade that is also commonly used. Other PBT applications include automotive, industrial, consumer goods and medical.
Acrylic (Polymethylmethacrylate / PMMA)
Acrylic, developed in the 1930’s as a coating, commercialized in 1937 as a moldable resin. Although it comes in many other variations it is probably best known by the name of Plexiglas and has played an important role in safety and glass replacements. Its extremely high durability and transparency make it a perfect candidate for long life applications.
Acrylic is also commonly used where light transmission is a necessary trait such as in taillights, display screens or windows. Plastics web portal IDES.com adds: “Acrylics are widely used in lighting fixtures because they are slow-burning or even self-extinguishing, and they do not produce harmful smoke or gases in the presence of flame.”
PEEK (Polyether ether ketone)
British chemical company, Imperial Chemical Industries (ICI), first patented the PEEK formulation in 1978 under the trade name Vitrex. The PEEK polymerization is considered an “organic polymer thermoplastic” and is resistant to thermal breakdown and is mechanically and chemically very stable.
PEEK is also considered an “advanced biomaterial” and is sought after in the medical device manufacturing world, especially implantables. Besides medical, the PEEK properties are also good for other demanding applications such as, aerospace, automotive and chemical diagnostic industries.
Ultem (Polyetherimide / PEI)
Polyetherimide, otherwise known by its trade name Ultem, was introduced by General Electric (now SABIC) in 1982. PEI is considered to be a relative to PEEK. It’s typically cheaper than PEEK, it’s also clear (or amber) but is less resistant to heat and strength when compared to its cousin. It can withstand continuous use temperatures of 340°F (170°C).
Typical applications for Ultem are Medical, Automotive, Electronics and Aerospace. While not necessarily considered an optical grade material Ultem is also highly used in the telecommunications market for fiber optic connectors. Its clarity is within the light transmission ranges for the fiber products and the natural heat deflection and low coefficient of thermal expansion make it an optimal resin for these tight tolerance applications.
Manufacture, SABIC, says: “The Ultem Resin family of amorphous thermoplastic polyetherimide (PEI) resins offers outstanding elevated thermal resistance, high strength and stiffness, and broad chemical resistance. Ultem is available in transparent and opaque custom colors, as well as glass filled grades. Plus, Ultem copolymers are available for even higher heat, chemical and elasticity needs. Ultem resins uniquely balance both mechanical properties and processability, offering design engineers exceptional flexibility and freedom.”
LCP (Liquid Crystal Polymer)
LCP, or Liquid Crystal Polymer, as a moldable resin is fairly new even though the components and research that ultimately lead to the resin we know today happened as early as 1888. It wasn’t till 1980, almost 100 years later, that the injection moldable version was available to the market. 
LCP is in a unique class of highly-engineered thermoplastic because of its base formulation that’s capable of forming “regions of highly ordered structure.” The material is considered very strong but expensive as a resin. It has good heat-deflection properties and can handle most solder reflow processes. It’s also a great candidate for thin-wall applications.
Plastics compounder and supplier RTP says this about LCP: “LCP can replace such materials as ceramics, metals, composites and other plastics because of its outstanding strength at extreme temperatures and resistance to virtually all chemicals, weathering, radiation and burning.”
There are 1000’s of material choices, and we have processed many of them. If there is a specific material that you’d like to know about for use in micro mold applications please let us know.
References available in downloadable PDF.