Thermoplastic elastomer (TPE) compounds are used in hundreds of different applications, including consumer goods (think footwear soles and soft-touch grips); skin contact (such as dental devices or bracelets); food contact (food container lids or beverage tubing, for example); automotive parts (interior, such as grab handles and window extrusion); wire and cable jacketing; and a variety of appliance and industrial parts such as seals, tubes, connectors, valves, and stoppers for a range of uses.
TPEs can be used in so many ways because they can be formulated to have a wide range of properties designed for the intended application. Although there are many different types of TPEs, a thermoplastic elastomer compound supplier can give advice and make it easy to select the right TPE for your product. This article explains what you should consider when choosing a TPE compound.
How to choose a TPE compound for your product
One thing to consider is whether your product will contact food or beverages. If so, the material you choose should have food-contact approval for the country where it will be used and for the conditions under which it will be used. In the US, the Food and Drug Administration (FDA) under Title 21 CFR specifies raw materials suitable for use in food contact products. In Europe, food capable ingredients are according to EU 1935/2004, 10/2011. In both cases, additional testing such as migration resistance in contact with various ingredients (such as olive oil) or in-home use cases such as repeated dishwasher and microwave cycles may need to be conducted based on the requirements of the application.
The softness and spring-back qualities of TPE make them an ideal candidate for food container lids where seals act to preserve food and prevent spills. TPE compounds can chemically bond to harder substrates such a polypropylene to achieve an over-molded soft-touch feature to enhance comfort and gripping ability. In applications such as mats, TPEs can be brightly colored to create an aesthetically pleasing article while offering non-slip functions much needed in kitchen environments.
Processes such as hot fill or retort may require TPEs designed to withstand these extreme conditions. In addition, TPEs can be designed to be used with acidic foods or fatty or oily foods. It is important to understand how the material will be used before you choose it.
Medical, dental and healthcare
Materials used in medical and healthcare applications must also comply with regulations for specific countries and specific uses. Because they are inherently latex free and plasticizer free, TPE compounds that are designed to be biocompatible have low levels of extractable ingredients. Common sterilization methods such as gamma/ebeam irradiation, autoclave and ETO can be used on TPE compounds with little to no discoloration.
Indoor vs. outdoor
If a product will be used outdoors, the material will need to withstand all kinds of weather, and particularly exposure to sunlight. Black colors are often used to provide protection from UV rays in sunlight. Additives can also be used to make a material resistant to degradation by UV light even if the material is light in color.
Flame retardant wire and cable
TPEs offer enhanced flexibility and toughness as jacketing materials in applications such as flexible cord and industrial cables. Formulations with enhanced flame retardancy, UV resistance and oil resistance are available with a wide range of operating temperatures. TPEs offer great low temperature flexibility and are available with matte or glossy finishes.
Consumer goods, soft-touch applications
From cushiony footwear soles to dog chew toys, TPE compounds offer flexibility, strength, high surface quality, and the ability to easily modify color and feel, such as adding a soft touch to a product.
The softness of a TPE is measured by its durometer or “Shore A hardness”—the lower the durometer, the softer the polymer. TPE compounds can be as soft as 10 Shore A, all the way up to as hard as 95 Shore A. TPEs used for soft-touch grips, for example, typically have a durometer of around 60 to 75.
Manufacturing using TPE: molding vs. extrusion
In addition to a wide range of properties that can be designed into a thermoplastic elastomer compound to meet product specifications, TPEs are also versatile in how they can be formed into a final (or semi-finished) product, typically by extrusion (into a flat film or sheet or a round tube or rod, for example) or injection molding (into a solid shape, such as a cap or valve).
In all thermoplastic processes, a solid polymer compound is melted, shaped, and then cooled into the final part. But because the shaping process in molding and extrusion are very different, you must choose a TPE that is designed to flow in the process you are using.
In injection molding, the molten polymer is injected at high flow rates into a three-dimensional mold. In extrusion, the molten polymer is pushed through a two-dimensional die and then pulled into the shaping process. Thus, a TPE for injection molding must flow more easily and be more “liquid” than a TPE designed for extrusion. A compound supplier can help determine melt flow properties that will ensure optimum processing.
What is co-extrusion or co-molding?
TPEs are often co-extruded or co-molded in a process that bonds them to another thermoplastic polymer, such as a polystyrene (PS), polyethylene (PE), polypropylene (PP), polycarbonate (PC), polyamide (PA), or acrylonitrile butadiene styrene (ABS).
For a soft-touch grip, for example, a soft TPE is co-molded or over-molded over a harder thermoplastic, such as PP. The key benefit provided by thermoplastics is that the two materials are bonded in one manufacturing step, rather than in a separate post-processing step as would be required for thermoset rubbers. The co-molding process is more efficient and offers design freedom.
A plastic compound supplier can help identify a compound that is compatible and can bond to a substrate in a co-molding process.
Why choose a TPE?
Thermoplastic elastomers are a good choice for a wide variety of products, especially when you need a soft or flexible but strong material. Because TPE compounds do not contain plasticizers, they are readily compliant with regulations such as REACH, RoHS, and California Prop 65. TPEs are recyclable—they can be melted and formed again into a new product, unlike thermoset polymers (such as latex or synthetic rubber), which cannot be re-melted. Parts made with TPEs can have a good surface finish and can be made in a wide range of colors. TPEs can be formulated to have special properties, such as flame retardancy or UV stability.
When choosing a TPE, it is important to understand how it is going to be used and to seek a plastic compound manufacturer that can help you find the right material. Mexichem Specialty Compounds is a leading polymer compound manufacturing company supplying specialty plastics to customers across the globe.