While there are a wide variety of thermoplastics, these can be subdivided into groups based on chemistry and the imparting performance properties. We offer medical tubing solutions from the following polymers, and many more, for a wide range of applications. We also offer a wide range of flexible PVC compounds used throughout the medical device industry.
This group of crystalline polymers includes polyethylene and polypropylene. Polyethylenes include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE).
HDPE is highly crystalline and very inert. It absorbs very little water and is not attacked by most acids, bases or solvents. Polypropylene offers low density and low cost. It absorbs very little water and, due to its glass transition temperature which is below room temperature, it exhibits good impact strength.
In general, polystyrene has a low density, high modulus (a measure of rigidity), and virtually no water absorption. However, it is brittle and sensitive to solvent attack.
To improve its toughness, butadiene can be added to the polymer. To improve chemical resistance, acrylonitrile can be added. To achieve higher temperature performance, maleic anhydride is incorporated as a co-monomer. The result is the family of polymers. Examples include:
High-Impact Polystyrene (HIPS) – Includes a discrete amount of butadiene that can vary substantially, leading to wide variations in impact strength.
Acrylonitrile Butadiene Styrene (ABS) – The addition of acrylonitrile to styrene and butadiene creates a terpolymer known as ABS. Since the amounts of all three constituents can vary significantly, the range of properties among ABS grades is quite broad.
Styrene Acrolonitrile copolymers (SAN) – These have fairly low impact strength and their tensile and flexural properties exceed polystyrene.
Polyvinyl Chloride (PVC)
Polyvinyl chloride (PVC) is economical for many medical applications and can be readily extended with low cost fillers. Rigid PVC has tensile and flexural properties similar to many in the styrene family. Unless it is filled, it is inherently tough. It is also nonflammable.opic and arthroscopic procedures.
Flexible PVC, achieved by compounding plasticizers and other additives with rigid PVC, is a dominant material used for the storage of IV fluids, dialysis solutions, blood and blood products. This is because of its clarity, strength, ability to withstand a wide range of temperatures, and resistance to sterilization from steam, EtO and gamma radiation. PVC can also be joined together by solvent or high frequency welding, which offers the possibility of making containers with complex shapes and with various attachments.
The most common plasticizer for medical-grade PVC is DEHP (also known as DOP). DEHP-plasticized PVC containers have been used for the collection of blood and blood components for the last 45 years. DEHP has been shown to have very beneficial effects in maintaining the viability and long-term storage of red blood cells (RBCs). In some geographies, where legislation activity is curbing the used of DEHP in medical applications, other plasticizers are available to manufacture medical-grade compounds.
There are many types of polyesters which cover a wide range of properties. Most are crystalline with high melting temperatures. They have higher densities compared to polyolefins, but low densities compared to the fluorocarbons. They absorb a moderate amount of water. Their mechanical properties can vary substantially.
Polyethylene terephthalate (PET) is the lowest cost, highest volume polyester produced, even compared to thermosetting polyesters. Polybutylene terephthalate (PBT) is used frequently for injection molding applications. PBT absorbs less water and has better impact strength than PET.
There are a wide variety of nylons available commercially. Most nylons are crystalline and have relatively low melt viscosities. The primary nylons in use, nylon 6 and nylon 6/6, exhibit excellent strength, stiffness and toughness. These materials offer low friction, good abrasion resistance properties, and good chemical resistance. However, they are sensitive to absorption of water.
Nylon 11 and nylon 12 are significantly more flexible, tougher and absorb less water than nylon 6 and 6/6. These are materials of choice in tubing used for many interventional medical catheter applications.
Polyacetals, also known as polyoxymethylene (POM) or acetal, are polymerized from formaldehyde. POM is chemically resistant, rigid, strong and tough. It also has a low coefficient of friction and has been used for decades in Dunn™ polymer mandrels, which are used to support the inner diameter of diagnostic and interventional catheters during the manufacturing processes. These processes often include pressure extrusion and high-tension braiding, which would collapse the inner tube diameter without support of an acetal mandrel.
Polycarbonate (PC) is best known for its toughness and clarity. It also offers very good dimensional control and tolerances in molded or extruded parts. Compared to styrenics, polycarbonates offer higher mechanical properties, higher temperature resistance, and better sterilization resistance. These are often materials of choice for tubes and handles of many single-use medical instruments and devices, such as those used in laparoscopic and arthroscopic procedures.