Inventory of seven commonly used medical plastics

June 24, 2022

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The basic requirements for medical plastics are chemical stability and biosafety due to contact with drugs or with the human body. The components in the plastic material cannot be precipitated into the liquid or the human body, will not cause toxicity and damage to tissues and organs, and are non-toxic and harmless to the human body. In order to ensure the biosafety of medical plastics, the medical plastics usually sold in the market are certified and tested by medical authorities, and users are clearly informed which grades are medical grade.

Here are the seven commonly used medical plastics:

1. Polyvinyl chloride (PVC, Polyvinyl chloride)

PVC resin powder is white or light yellow powder. Pure PVC is atactic, hard and brittle, and is rarely used. According to different uses, different additives can be added to make PVC plastic parts show different physical and mechanical properties. Adding an appropriate amount of plasticizer to PVC resin can make a variety of hard, soft and transparent products.

Hard PVC does not contain or contains a small amount of plasticizers, has good tensile, flexural, compressive and impact resistance properties, and can be used alone as a structural material. Soft PVC contains more plasticizers, and its flexibility, elongation at break, and cold resistance increase, but brittleness, hardness, and tensile strength decrease. The density of pure PVC is 1.4g/cm3, and the density of PVC plastic parts with plasticizers and fillers is generally in the range of 1.15~2.00g/cm3.

According to incomplete estimates, approximately 25% of medical plastic products are PVC. This is mainly due to the low cost of the resin, its wide application range, and its ease of processing. PVC products for medical applications include: hemodialysis tubing, breathing masks, oxygen inhalation tubes, etc.

medical plastics

2. Polyethylene (PE, Polyethylene)

PE plastic is the most productive variety in the plastics industry, milky white, tasteless, odorless and non-toxic glossy waxy particles. It has good performance and can be widely used in industry, agriculture, packaging and daily industry.

PE mainly includes low density polyethylene (LDPE), high density polyethylene (HDPE) and ultra-high molecular weight polyethylene (UHDPE). HDPE has fewer branches on the polymer chain, higher relative molecular mass, crystallinity and density, higher hardness and strength, poor opacity, and higher melting point. It is often used in injection molding parts. LDPE has many branches, so the relative molecular weight is small, the crystallinity and density are low, and it has good softness, impact resistance and transparency. . It is also possible to mix HDPE and LDPE materials according to the performance requirements. UHDPE has high impact strength, low friction, stress crack resistance and good energy absorption properties, making it an ideal material for artificial hip, knee and shoulder connectors.

medical plastics

3. Polypropylene (PP, polypropylene)

PP is colorless, odorless and non-toxic. Looks like polyethylene, but is more transparent and lighter than PE. PP is a thermoplastic with excellent performance, with the advantages of small specific gravity (0.9g/cm3), non-toxic, easy processing, impact resistance, and flex resistance. It has a wide range of applications in daily life, including woven bags, films, turnover boxes, wire shielding materials, toys, car bumpers, fibers, washing machines, etc. Medical PP has high transparency, good barrier properties and radiation resistance, making it widely used in medical equipment and packaging industries. Non-PVC material with PP as the main body is a substitute for the widely used PVC material.

medical plastics

4. Polystyrene (PS) and K resin

PS is second only to polyvinyl chloride and polyethylene. It is usually processed and applied as a one-component plastic. The main features are light weight, transparency, easy dyeing, and good molding performance. Therefore, it is widely used in daily plastics, Electrical parts, optical instruments and stationery. The texture is hard and brittle, and has a high coefficient of thermal expansion, which limits its application in engineering. In recent decades, modified polystyrene and styrene-based copolymers have been developed to overcome the shortcomings of polystyrene to a certain extent. K resin is one of them.

K resin is made of styrene and butadiene copolymerized. It is an amorphous polymer, transparent, odorless, non-toxic, with a density of about 1.01g/cm3 (lower than that of PS and AS), and its impact resistance is higher than that of PS. , good transparency (80-90%), thermal deformation temperature of 77 ° C, the amount of butadiene contained in the K material, the hardness is also different, because the K material has good fluidity and a wide processing temperature range, so its Good processing performance.

The main uses in daily life include cups, lids, bottles, cosmetic packaging, hangers, toys, PVC substitute products, food packaging and medical packaging supplies.

medical plastics

5. ABS, Acrylonitrile Butadiene Styrene copolymers

ABS has certain rigidity, hardness, impact and chemical resistance, radiation resistance and ethylene oxide sterilization resistance. The medical application of ABS is mainly used as surgical tools, roller clips, plastic needles, tool boxes, diagnostic devices and hearing aid shells, especially the shells of some large medical equipment.

medical plastics

6. Polycarbonate (PC, Polycarbonate)

The typical properties of PC are toughness, strength, rigidity, and heat-resistant steam sterilization, which make PC the preferred choice for hemodialysis filters, surgical tool handles, and oxygen tanks (when in surgical heart surgery, this device can remove blood carbon dioxide, increasing oxygen);

Medical applications of PC also include needle-free injection systems, perfusion instruments, blood centrifuge bowls and pistons. Taking advantage of its high transparency, the usual myopia glasses are made of PC.

medical plastics

7.PTFE (polytetrafluoroethylene, Polytetrafluoro ethylene)

PTFE resin is a white powder with waxy appearance, smooth and non-sticky, and is the most important plastic. PTFE has excellent performance, which is beyond the comparison of ordinary thermoplastics, so it is known as "the king of plastics". Its friction coefficient is the lowest among plastics, and it has good biocompatibility. It can be made into artificial blood vessels and other devices that are directly implanted into the human body.

medical plastics