In recent years, more and more plastic injection parts have been used in medical treatment. Due to the need to have contact with liquid medicine or human body, the basic requirements of medical plastics are chemical stability and biological safety.
(1) Polyvinyl chloride (PVC)
PVC is one of the largest plastic varieties in the world. PVC resin is white or light yellow powder. Pure PVC is atactic, hard and brittle, and is rarely used. According to different purposes, different additives can be added to make PVC plastic parts present different physical and mechanical properties. Adding an appropriate amount of plasticizer to the PVC resin can make a variety of hard, soft and transparent products.
According to market estimates, approximately 25% of medical plastic products are PVC, mainly because of the low cost of the resin, wide application range, and easy processing. Medical PVC products include: hemodialysis tubing, breathing mask, oxygen tube, etc.
(2) Polyethylene (PE)
Polyethylene plastic is the most produced variety in the plastic industry. It is milky white, tasteless, odorless, and non-toxic glossy waxy particle. It is characterized by low price and good performance. It can be widely used in industry, agriculture, packaging and daily industries, and it occupies a pivotal position in the plastics industry.
PE mainly includes low-density polyethylene (LDPE), high-density polyethylene (HDPE), and ultra-high molecular weight polyethylene (UHDPE). HDPE has few branches on the polymer chain, high relative molecular weight, crystallinity and density, high hardness and strength, poor opacity, and high melting point. It is often used in plastic injection parts. LDPE has many branches, so the relative molecular weight is small, and the crystallinity and density are low. It has good flexibility, impact resistance and transparency. It is often used in blown film and is an alternative to the widely used PVC. It is also possible to mix HDPE and LDPE according to performance requirements. UHDPE has high impact strength, low friction, stress crack resistance and good energy absorption characteristics, making it an ideal material for artificial hip, knee and shoulder connectors.
(3) Polypropylene (PP)
Polypropylene is colorless, odorless and non-toxic. It looks like polyethylene, but it is more transparent and lighter than polyethylene. PP is a kind of thermoplastic with excellent performance. It has the advantages of small specific gravity (0.9g/cm3), non-toxic, easy processing, impact resistance, flexural resistance and so on. 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.
(4) Polystyrene (PS) and K resin
PS is the third largest plastic species after polyvinyl chloride and polyethylene. It is usually processed and applied as single-component plastics. Its main characteristics are light weight, transparency, easy dyeing, and good molding and processing properties, so it is widely used in daily plastics, electrical parts, optical instruments and cultural and educational supplies. It’s texture is hard and brittle, and it has a high coefficient of thermal expansion, which limits its application in engineering. In recent decades, the development of modified polystyrene and styrene-based copolymers has overcome the shortcomings of polystyrene to a certain extent. K resin is one of them.
K resin is a copolymer of styrene and butadiene. It is an amorphous polymer, which is transparent, odorless, and non-toxic, with a density of about 1.01g/cm3 (lower than PS and AS), and higher impact resistance than PS. It boasts a good transparency (80 to 90%), with the heat distortion temperature of 77℃. And the hardness is also different, depending on the content of butadiene in the K material. Because the K material has good fluidity and a wide processing temperature range, it is good at 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.
(5) Acrylonitrile Butadiene Styrene copolymers (ABS)
ABS has advantages of a certain rigidity and hardness, impact resistance and chemical resistance, radiation resistance and resistance to ethylene oxide disinfection. The medical application of ABS is mainly surgical tools, roller clamps, plastic needles, tool boxes, diagnostic devices and hearing aid housings, especially the housings of some large-scale medical equipment.
(6) Polycarbonate (PC)
The typical characteristics of PC are toughness, strength, rigidity and resistance to hot steam sterilization. These characteristics make PC a priority choice for blood dialysis filters, surgical tool handles and oxygen tanks (when in surgical heart surgery, this instrument can remove carbon dioxide from the blood, and increase oxygen); The applications of PC in medicine 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.
(7) Polytetrafluoro ethylene (PTFE)
PTFE resin is white powder, waxy in appearance, smooth and non-sticky, and is the most important plastic. PTFE has excellent performance, which is not comparable to ordinary thermoplastics, so it is known as the "the King of Plastic". Its friction coefficient is the lowest among plastics, and it has good biocompatibility. It can be made into artificial blood vessels and other devices directly implanted in the human body.