The basic requirement of medical plastics is to have chemical stability and biological safety, the reason is to contact with drugs or contact with the human body. The components in the plastic material cannot precipitate into the drug or the human body, and 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.
The following are seven commonly used medical plastics:
I. Polyvinyl chloride (PVC)
PVC resin powder is white or light yellow powder, pure PVC is a random structure, hard and brittle, rarely used. According to different applications, different additives can be added to make PVC plastic parts present different physical and mechanical properties. A variety of hard, soft and transparent products can be made by adding the right amount of plasticizer to PVC resin.
Hard PVC contains no or a small amount of plasticizers and has good tensile, bending, compressive and impact resistance properties and can be used as a structural material alone. Soft PVC contains more plasticizers, and it has increased softness, elongation at break, and cold resistance, but reduced brittleness, hardness, and tensile strength. The density of pure PVC is 1.4g/cm3, and the density of PVC plastic parts with plasticizers and fillers, etc., is generally in the range of 1.15 to 2.00g/cm3.
According to incomplete estimates, about 25% of medical plastic products are PVC, mainly due to the resin's low cost, wide range of applications, and its ease of processing. PVC products for medical applications include: hemodialysis lines, breathing masks, oxygen tubes, etc.
Second, polyethylene (PE, Polyethylene)
PE plastic is the plastic industry in the production of large varieties, milky white, tasteless, odorless and non-toxic glossy waxy particles. Performance is better, can be widely used in industry, agriculture, packaging and daily industry.
PE mainly includes low density polyethylene (LDPE), high density polyethylene (HDPE) and high molecular weight polyethylene (UHDPE) and other varieties. HDPE has fewer branched chains on the polymer chain, higher relative molecular mass, crystallinity and density, higher hardness and strength, poor opacity, higher melting point, commonly used in injection molded parts. lDPE with many branched chains, thus smaller relative molecular mass LDPE has many branched chains and thus has a smaller relative molecular mass, lower crystallinity and density, better flexibility, impact resistance and transparency, and is often used in blown film, which is an optional substitute for the widely used PVC. UHDPE has high impact strength, low friction, stress cracking resistance and good energy absorption characteristics, making it an ideal material for artificial hip, knee and shoulder connectors.
III. Polypropylene (PP, polypropylene)
PP is colorless, odorless and non-toxic. Appearance like polyethylene, but 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, flexural resistance, etc.. It has a wide range of applications in daily life, including woven bags, films, crates, wire shielding materials, toys, car bumpers, fibers, washing machines, etc. Medical PP has high transparency, good barrier and radiation resistance, which makes it widely used in medical equipment and packaging industry. Non-PVC material with PP as the main body is a substitute for the widely used PVC material at present.
IV. Polystyrene (PS) and K-resins
PS is second only to polyvinyl chloride and polyethylene plastic species, usually as a single-component plastic processing and application, the main characteristics are light, transparent, easy to dye, molding and processing performance, so it is widely used in daily plastic, electrical parts, optical instruments and educational supplies. The texture is hard and brittle, and has a high coefficient of thermal expansion, thus limiting its application in engineering. In recent decades, modified polystyrene and styrene-based copolymers have been developed to overcome the shortcomings of polystyrene to some extent.
K resin is made of styrene and butadiene copolymer, it is an amorphous polymer, transparent, tasteless, non-toxic, density of about 1.01g/cm3 (lower than PS, AS), impact resistance than PS, transparency (80-90%) good, heat deflection temperature of 77 ℃, K material contains the number of butadiene components, its hardness is also different, due to the good fluidity of K material, processing temperature range Because of the good fluidity and wide processing temperature range of K material, its processing performance is good.
The main uses in daily life include cups, lids, bottles, cosmetic packaging, hangers, toys, PVC substitutes, food packaging and medical packaging products.
ABS, Acrylonitrile Butadiene Styrene copolymers (Acrylonitrile Butadiene Styrene copolymers)
ABS has certain rigidity, hardness, impact and chemical resistance, radiation resistance and ethylene oxide sterilization. ABS is mainly used in medical applications as surgical tools, roller clips, plastic needles, tool boxes, diagnostic devices and hearing aid shells, especially the shell of some large medical equipment.
Six, polycarbonate (PC, Polycarbonate)
PC's typical properties of toughness, strength, rigidity and heat-resistant steam sterilization, these characteristics make PC preferred as hemodialysis filters, surgical tool handles and oxygen tanks (when in surgical heart surgery, this instrument can remove carbon dioxide from the blood and increase oxygen);
Medical applications of PC also include needle-free injection systems, perfusion instruments, blood centrifuge bowls and pistons. Using its high transparency properties, the usual myopic glasses are made of PC.
VII. PTFE (polytetrafluoro ethylene)
PTFE resin is a white powder, waxy appearance, smooth and non-stick, is an important plastic. PTFE has excellent performance, non-generic thermoplastics can be compared, so there is a "plastic king" name. Its coefficient of friction is the lowest among plastics, and it has good biocompatibility, so it can be made into artificial blood vessels and other devices directly implanted in the human body.