Plastic injection molding is a leading and diverse additive manufacturing method that offers many benefits over other conventional techniques including design flexibility, suitability with multiple kinds of plastic resins, affordability, and accuracy in product creation. This method has yet to be matched in the field of plastics. Although it has been widely used, the variety of plastic polymers that are accessible is a challenge for mold manufacturers and designers when it comes to choosing the best material for a medical use product.
This blog post covers the essential material selection factors and provides a brief overview of widely used plastic resins and their advantages.
Top Plastic Resins Used For Injection Molding
Let’s figure out widely used plastic materials used in medical injection molding.
Polymethyl Methacrylate
Polymethyl methacrylate or PMMA, the acrylic as a common name, is a transparent and hard thermoplastic, which is easily transmitted by light. Acrylic plastics are strong, lightweight, and non-shatterable, hence a good alternative to glass. They can effectively bear weight and they are ideal for outdoor use because they endure sunlight and weather.
Besides, acrylic doesn’t belong to the category of porous materials, but it can be stained by greases and oils, and it’s very prone to scratching. It also has a low heat tolerance for heavy-duty industrial works and may also fracture under very heavy loads. In many cases, acrylic is used as a window panel, greenhouse panel, solar panels, and clear materials in construction and lighting projects.
Acrylonitrile Butadiene Styrene (ABS)
ABS, which is an abbreviation for, is a type of engineering thermoplastic that is rigid and opaque. It’s advantageous to withstand high-impact resistances. Abs plastic is popular for being tough, low cost, and providing good resistance against heat, grease, acids, and alkalis. ABS plastics are frequently present in many products like keyboard keys, enclosures of outlets, and headgear, among others. ABS is widely adopted for in interior, and exterior automobiles, consumer goods, sports equipment, and industrial fittings parts or products.
Nyon or Polyamides
Nylon or polyimide is a synthetic material that can shrink during the injection molding process, so it is not filled properly. Nylon possesses peculiar characteristics including exceptional toughness, heat resistance, abrasion resistance, fatigue resistance, and noise-dampening. It is especially useful for those applications which need high friction. Besides these, nylon is not flame resistant and may burn rapidly unless a fire retardant treatment is applied. This material is also vulnerable to degradation from sunlight. However, adding a UV stabilizer in nylon improves its performance.
Nylon is an extensively applied material for the manufacturing of mechanical parts that are robust, casings, snap-fit closures, and threaded inserts. It is used for this purpose in the production of toothbrushes, medical implants, and electrical connectors.
Polycarbonate
Polycarbonate (PC) plastics are strong and hardy, and somehow have a similar range of properties as acrylic, but with a wider temperature range.
They have a memory effect that allows them to keep the color for a long time and they are very resistant, which is around 250 times stronger than glass. PC plastics have a predictable and uniform shrinkage rate which is why they are the best in cases where precision in dimensional control is required. Besides, they are lightweight and have good optical quality too.
As polycarbonates contain BPA, so can not be effective for food-related applications. In addition, they are typically costly to manufacture medical products.
Globally, HDPE and LDPE are both good in chemical and moisture resistance with hardness, optical clarity, melting point, and flexibility are the other properties that differ. These types are mostly picked for their transparency, but they are vulnerable to sunlight damage and high temperatures. HDPE may be difficult to form into thin shapes, while LDPE may not meet the necessary tolerance. There is a wide range of PE plastic products that include milk and water bottles, toys, electronic cables, and some medical device parts.
Polyoxymethylene (POM)
Polyoxymethylene (POM), commonly identified as acetal, is a type of engineering plastic known for its low friction, high stiffness, and strong mechanical integrity due to its well-ordered crystalline structure. Usually opaque and white, POM resins are good for cases when it is necessary to have these characteristics.
With injection molding, POM is characterized by high rigidity, thermal resistance, and low friction. Nevertheless, POM resins suffer from severe mold shrinkage and low UV resistance, which restricts their outdoor applications and fire safety. Globally, polypropylene (PP), is the second most widely used medical-grade plastic similar to polyethylene (PE) in terms of hardness and heat resistance but does not have the lowest density like polyethylene, which can be modified by adding fillers.
PP plastics are characterized by their excellent chemical resistance, high melting point, and torsion and bending resistance, as well as their inherent waterproof quality, which guarantees their durability. Another great advantage of PET is that it can be recycled up to 4 times. Therefore, polyethylene is widely used in consumer, commercial, and industrial sectors, it includes storage containers, plastic packaging, appliance parts, and power tool casings.
Polystyrene
PS can be found in clear or opaque versions, which allow it to be used for different purposes. The material is the best choice for the injection molding process because of its uniform shrinkage rate. Moreover, PS is cheaper, lightweight, and resistant to moisture and bacteria growth, which makes it the best choice for different uses.
Nevertheless, PS is combustible, is weak against ultraviolet (UV) light exposure, degrades upon contact with hydrocarbon solvents, and is not biodegradable. On the other hand, its brittleness makes it more likely to be cracked.
PS is utilized in various areas of medical, optical, and electrical products. Additives mixed with it make it useful for appliances and equipment as well.
Thermoplastic Elastomer (TPE)
Thermoplastic Elastomer (TPE), is composed of of plastic and rubber characteristics. It is elastic like rubber while it is processed as plastic, having the capability to stretch without permanent deformation and shorter molding cycles compared to liquid silicone rubbers.
Unlike TPE, creeping is a major issue since it causes permanent deformation over time, and also it loses its rubbery properties at extreme temperatures. Furthermore, TPE is a versatile material that finds extensive applications in footwear, medical supplies (like breathing tubes and valves), automotive components (including weather seals), and pet products.
Conclusion
The most frequently used plastic material in medical injection molding is polypropylene (PP). It is used for its chemical resistance, flexibility, and sterilization compatibility. Moreover, polypropylene is widely adopted for the fabrication of stringent medical devices such as disposable syringes, enclosures, housings, and transplant tubing due to its biocompatibility and the ability to mold it into complex shapes with relative ease. This article contains the key details about compatible medical use plastics for injection molding. The provided information helps you make appropriate choices by figuring out the critical sides of each material and its intended application use.
FAQ’s:
Q1. Why is medical injection molding using polypropylene more popular?
Polypropylene is preferred for its chemical resistance, flexibility, and compatibility with sterilization techniques, which makes it a perfect material for medical applications.
Q2. What medical devices are usually manufactured by polypropylene?
Syringes, containers, tubing, and other disposable medical products are usually made of polypropylene because of their biocompatibility and molding characteristics.
Q3. Is polypropylene safe for medical use?
Yes, polypropylene is considered as safe for medical use because it is biocompatible, non-toxic, and resistant to chemicals, which makes it suitable for contact with body fluids and tissues.