Fabricating plastics
for Medical Applications
by Paige Bowen

erformance plastics have been a part of the medical industry for decades, often replacing other materials for better durability, easier sanitation and patient comfort. Seen in applications that range from storage to prosthetics to hospital bed frames, performance plastics have played a role in saving people’s lives every day. But what does it mean to the performance plastics industry that our medical system depends on using plastics?

Prior to COVID, it’s likely that most people didn’t think about the use of performance plastics in the medical field. However, starting in April 2020, businesses throughout the world scrambled to purchase as much clear acrylic and polycarbonate as they could find to keep their employees and customers safe. Everything from face shields to barriers required clear plastic. Nurses and doctors went from wearing their usual masks to wearing masks and face shields. Large corporations ramped up their production of personal protective equipment (PPE) and cottage industries sprung up to meet the demand.

Materials for medical applications

Let’s start with the basic definition of medical-grade plastics: to be considered medical-grade, the plastics manufacturer must work under a physician’s license to pass the verification and validation requirements of regulatory agencies. Some of these requirements include having biocompatibility, temperature and impact and corrosion resistance and being able to withstand high wear and repeated sterilization. The most common thermoplastics used are polycarbonate (PC), polypropylene (PP) and polyethylene (PE).

Polycarbonates, because of their impact resistance properties and ability to withstand high-temperature ranges, are used frequently in the medical field. Everything from protective gear to medical devices can be manufactured out of polycarbonate. To help prevent the spread of COVID-19, hospitals and clinics had no choice but to increase their sterilization protocols. However, with these new protocols, the material started developing environmental stress cracks (ESC), resulting in premature device failures. Since learning this, manufacturers have started creating and testing new thermoplastic blends. One such blend that is showing promise is polycarbonate copolymers.

Polypropylene is a cost-effective choice for medical grade plastic where steam-sterilized medical devices are necessary. PP is also highly effective in durability for the number of cycles it can be reused, in addition to being recyclable. PP is slightly harder than polyethylene and more heat resistant. It also has a high chemical resistance; at room temperature, it is resistant to almost all organic solvents. The bottles pharmacies use for medication are typically made from PP. In hernia and pelvic organ prolapsed repairs, PP meshes have been used. One of the benefits of using this material for these sorts of procedures is that the body rarely rejects it. However, it has been noted that the PP mesh can erode the tissue surrounding the area, resulting in the FDA in 2012 to order dozens of manufacturers to study the side effects.

Polyethylene (PE) is the most used thermoplastic today. PE is typically used for packaging, bags, films, geomembranes, containers, etc. Ultra-high molecular weight polyethylene (UHMW) is used to make artificial joints. UHMW has excellent toughness, allowing for high levels of wear, this is the ideal material to manufacture joints.

Fabricating medical grade materials

When it comes to fabricating thermoplastics, whether you are dealing with medical grade or not, hot air plastic welding is a safe, structurally strong process. The most important aspect to welding thermoplastics is knowing the different temperature ranges each type of plastic requires to achieve a strong bond. What works for one type of plastic may not work for another type. This is extremely important especially when the item being fabricated requires being watertight.

Welding PC requires the welder to be set between 600°F/316°C – 675°F/357°C and PP requires 550°F/288°C – 625°F/329°C. The temperature required to weld PE ranges depending on the density. Low density PE (LDPE) requires 500°/260°C – 550°F/288°C, high density PE (HDPE) requires 500°/260°C – 600°F/316°C and ultra high molecular weight PE (UHMW) requires 900°F/482°C – 1000°F/538°C. These temperature ranges are based on using a 500-watt 120 volt heating element and welding approximately 2-3 feet per minute.

Additional considerations

As with all types of hot air welding, location, experience and thickness of the plastic can impact the temperature ranges required for welding. Those who live in a drier, cooler climate may find that they must set their temperature slightly higher than those who live in a more humid, hotter climate. The same goes for experience: those who have years’ worth of experience may be able to weld at a hotter temperature, enabling them to move faster than those who are beginners.

Thermoplastic welding is truly an art form and the more experience the user has, the faster and better welder the fabricator will become.

Paige Bowen is the president of Seelye Acquisitions, Inc. For more information, contact Seelye Acquisitions, Inc. at 946 Century Lane, Apopka, FL 32702-3709 USA; phone (407) 656-6677 or (800) 258-2936, fax (407) 656-5244, customerservice@seelyeinc-orl.com or www.seelyeinc-orl.com.