7 commonly used medical plastics
Polyvinyl chloride (PVC)
Polyethylene (PE)
Polypropylene (PP)
Polystyrene (PS) and K resin
Acrylonitrile-butadiene-styrene (ABS)
Polycarbonate (PC)
Polytetrafluoroethylene (PTFE)
Main features of plastic compared to glass/metal materials:
• Low cost, can be reused without disinfection, and is suitable for use as a raw material for disposable medical devices;
• Simple processing, which can be processed into a variety of useful structures using its plasticity, while metal and glass are difficult to manufacture into complex structures;
• Tough, flexible, not as fragile as glass;
• Has good chemical inertness and biosafety.
These performance advantages make plastics widely used in medical equipment, including polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), polystyrene (PS), polycarbonate (PC), ABS, Polyurethane, polyamide, thermoplastic elastomer, polysulfone and polyetheretherketone. Blending can improve the properties of plastics and make the best performance of different resins, such as polycarbonate / ABS, polypropylene / elastomer and other blending modification.
After the general plastic synthesis, from the synthesis tower of the large petrochemical plant, it is a flour-like powder, which cannot be used to directly produce products. This is what people often say is the same as extracting the fat from the sap. It is called resin, also called powder. It is a kind of pure plastic. It has poor fluidity, low thermal stability, easy aging and decomposition, and is not resistant to environmental aging.
In order to improve the above defects, in the resin powder, a heat stabilizer, an anti-aging agent, an anti-ultraviolet agent, a plasticizer, etc. are added, and after granulation modification, the fluidity thereof is increased, and a variety of processing techniques are produced. There are special grades of different grades of plastics. Therefore, there are many grades of the same plastics, according to the processing method, there are injection molding grades, extrusion grades, blown film grades; according to performance, high rigidity, toughening, etc. .
Plastic materials commonly used by medical device manufacturers are plastic particles that can be directly modified by modification. For products with special properties not available in the market, the instrument factory can introduce granulation production lines and process plastic granules through different formula designs.
Due to contact with the drug solution or contact with the human body, the basic requirements of medical plastics are chemical stability and biosafety. Simply put, the composition of plastic materials can not be precipitated into the liquid or human body, does not cause toxicity and damage to tissues and organs, and is non-toxic and harmless to the human body. In order to ensure the biosafety of medical plastics, the medical plastics that are usually sold in the market are certified and tested by the medical authority, and the users are clearly informed which grades are medical grade.
Medical plastics in the United States usually pass FDA certification and USPVI bioassay. China's medical grade plastics are usually tested by Shandong Medical Device Testing Center. At present, there are still quite a few medical plastic materials in China that are not strictly biosafety certified, but these conditions will be improved with the gradual improvement of regulations.
Depending on the structural and strength requirements of the device, we choose the right type of plastic and the appropriate grade and determine the material's processing. These properties include processability, mechanical strength, cost of use, assembly, sterilizability, and the like. The processing properties and physical and chemical properties of several commonly used medical plastics are now introduced.
Polyvinyl chloride (PVC)
PVC is one of the largest varieties of plastics in the world. PVC resin is white or light yellow powder, pure PVC is atactic, hard and brittle, rarely used. Different additives can be added according to different purposes, so that the PVC plastic parts exhibit different physical properties and mechanical properties. A variety of hard, soft and transparent articles can be made by adding an appropriate amount of plasticizer to the PVC resin.
Hard PVC does not contain or contain a small amount of plasticizer, has good tensile, flexural, compressive and impact resistance properties and can be used alone as a structural material. Soft PVC contains a large amount of plasticizer, and its softness, elongation at break, and cold resistance increase, but brittleness, hardness, and tensile strength decrease. The density of pure PVC is 1.4 g/cm3, and the density of PVC plastic parts to which plasticizers and fillers are added is generally in the range of 1.15 to 2.00 g/cm3.
According to market estimates, about 25% of medical plastic products are PVC. Mainly due to the low cost, wide application range and easy processing of the resin. PVC products for medical applications include: hemodialysis tubing, breathing masks, and oxygen inhalers.
Processing conditions
It can be injection molded, extruded, blown, and calendered. Drying is usually not required. Melting temperature: 170-200 ° C, mold temperature: 20-50 ° C. Injection pressure: up to 1500 bar, holding pressure: up to 1000 bar. Injection speed: To avoid material degradation, a relatively low injection speed is generally used.
Main performance characteristics PVC material is a non-crystalline material, soluble in organic solvents such as cyclohexanone and tetrahydrofuran. Therefore, cyclohexanone is usually used to bond PVC parts. PVC materials are often added with additives such as stabilizers, lubricants, and dyes in actual use. Lead-bismuth additives are the most effective heat stabilizer for PVC, but they are forbidden to be used in medicine. Calcium-zinc additives are often used as stabilizers for medical grade PVC. Phthalate (DEHP) is a plasticizer for medical PVC. The precipitation of this plasticizer will cause toxicity to the human body and has attracted the attention of health organizations in Europe and North America. The drug regulatory department of China has begun to pay attention to this problem. PVC has poor thermal stability. Prolonged heating will cause decomposition and release hydrogen chloride gas to discolor PVC. The application temperature range is narrow, generally between -15-5 °C. The shrinkage of PVC is low, generally 0.2-0.6%. PVC is a polar material that is easily adsorbed with some polar drugs. Soft PVC film can be processed into bags using high frequency welding, such as bag infusion sets and urine bags.
Polyethylene (PE)
Polyethylene plastic is the most productive variety in the plastics industry, milky white, odorless, odorless and non-toxic glossy waxy granules. It is characterized by low price and good performance, and can be widely used in industrial, agricultural, packaging and daily industries, and plays a pivotal role in the plastics 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 molecular weight, crystallinity and density, higher hardness and strength, poor opacity and higher melting point, and is often used in injection molded parts.
LDPE has many branches, so it has relatively low molecular weight, low crystallinity and density, good flexibility, impact resistance and transparency. It is often used for blown film and is an alternative to PVC which is widely used at present. . 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.
Processing conditions
Drying: low water absorption, generally does not require drying, melting temperature 170-260 ° C, mold temperature 20-40 ° C. Injection pressure: up to 1500 bar, holding pressure: up to 750 bar, injection speed: fast injection speed is recommended. Runners and gates: Various types of runners and gates can be used. LDPE is particularly suitable for use with hot runner molds.
Main performance characteristics
The most notable feature of PE parts is that the molding shrinkage rate is large, which is prone to shrinkage and deformation. PE has a wide processing temperature range and is not easy to decompose (decomposition temperature is about 300 ° C), and the processing temperature is preferably 180 to 220 ° C. If the injection pressure is large, the product density is high and the shrinkage rate is small.
PE has medium fluidity, and the holding time needs to be long, and the mold temperature is kept constant (40 to 70 ° C). The degree of crystallization of PE is related to the molding process conditions. It has a higher solidification temperature and a lower mold temperature and a lower crystallinity.
During the molding process, the material temperature and mold temperature are higher, and the injection pressure should be as low as possible on the premise of ensuring the quality of the part.
Like PP, PE is a non-polar material, it is not easy to bond, and the amount of drug adsorption is small. It cannot be processed into a bag by high-frequency welding, and the heat sealing process is used for welding.
Polypropylene (PP)
Polypropylene is colorless, odorless and non-toxic. It looks like polyethylene but is more transparent and lighter than polyethylene. PP is a kind of thermoplastic with excellent performance, which has the advantages of small specific gravity (0.9g/cm3), non-toxicity, easy processing, impact resistance and flex resistance. It has a wide range of applications in daily life, including woven bags, films, turnover boxes, wire covering materials, toys, car bumpers, fibers, washing machines, and the like.
Medical PP has high transparency, good barrier properties and radiation resistance, making it widely used in medical equipment and packaging. Non-PVC materials based on PP are substitutes for PVC materials that are widely used today.
Processing conditions
It can be injection molded, extruded, blow molded or made into a film drying process: it has low water absorption and does not require drying treatment. Melting temperature: 220-270 ° C, be careful not to exceed 275 ° C. Mold temperature: 40-80 ° C, 50 ° C is recommended. Injection pressure: up to 1800 bar, injection speed: high-speed injection molding can be used to minimize internal pressure. If defects appear on the surface of the product, low speed injection at higher temperatures should be used. Runners and gates: For cold runners, typical runner diameters range from 4-7 mm. It is recommended to use a round inlet and flow path. All types of gates can be used. Typical gate diameters range from 1 to 1.5 mm, but gates as small as 0.7 mm can also be used. For edge gates, the minimum gate depth should be half the wall thickness; the minimum gate width should be at least twice the wall thickness. The hot runner system is fully available for PP materials.
Main performance characteristics
PP is a semi-crystalline material with high melting point, good heat resistance and can be sterilized at temperatures above 100 °C.
Yield strength, tensile strength, compressive strength, hardness and elasticity are higher than polyethylene (PE).
The homopolymer PP has a high brittleness, and the random copolymer PP synthesized with ethylene has better toughness and stronger impact strength. Generally, products used under low temperature conditions should be modified with PP as much as possible, or by adding thermoplastic rubber to increase the flexibility and low temperature impact resistance. The Non-PVC large infusion bag is made of copolymerized PP and elastomer blended modified material.
It is easily depolymerized and aged under the action of oxygen, heat and light, so it is necessary to add an anti-aging agent.
PP products are not easy to bond, need to be treated before bonding, and special adhesives are used. The cyclohexanone used in the equipment factory cannot meet the requirements.
Poor coloring, large shrinkage (generally 1.6-2.5%), poor burn resistance, easy to catch fire.
PP is a non-polar material and has a low adsorption capacity for drugs.
The PP film is usually welded into a bag by heat sealing, and the processing process is more complicated than the process of welding the PVC bag with high frequency. Non-PVC large infusion bags are produced using fully automated equipment to ensure process stability and reliable quality.
Polystyrene (PS) and K resin
PS is the third largest plastic product after PVC and polyethylene. It is usually processed and applied as a one-component plastic. Its main features are light weight, transparency, easy dyeing and good molding and processing properties. Use plastics, electrical parts, optical instruments and stationery. The texture is hard and brittle and has a high coefficient of thermal expansion, thus limiting its application in engineering.
In recent decades, the development of modified polystyrene and styrene-based copolymers has overcome the disadvantages of polystyrene to some extent. K resin is one of them.
K resin is a copolymer of styrene and butadiene. It is an amorphous polymer. It is transparent, odorless, non-toxic, has a density of about 1.01g/cm3 (lower than PS and AS), and has higher impact resistance than PS. The transparency (80-90%) is good, the heat distortion temperature is 77 ° C, the amount of butadiene component in the K material is different, and the hardness is also different. Because of the good fluidity of the K material and the wide processing temperature range, Good processing performance.
The main uses in daily life include cups, lids, bottles, cosmetic packaging, hangers, toys, PVC substitutes, food packaging and pharmaceutical packaging products.
Processing characteristics
By using injection molding, generally, the water absorption of the extruded tube and the blown film K is low, and it is not necessary to dry before processing. If the K material is stored in an open environment for a long time, it needs to be dried (below 65 ° C).
It has good fluidity and is easy to process. Its processing temperature range is wide, generally between 170 and 250 °C.
When the K material is above 260 ° C, if the molten material stays in the barrel for a long time (more than 20 minutes), it will cause thermal degradation, affect its transparency, and even become discolored and become brittle. It should be formed under the conditions of “low pressure, medium speed and medium temperatureâ€, and the mold temperature should be between 20 and 60 °C.
Thicker products can be cooled in water after removal to achieve uniform cooling to avoid voids.
The main performance characteristics are extremely high transparency and surface gloss; low shrinkage (0.4 to 0.7%). K resin has superior toughness compared to ordinary PS. For some thicker samples, K resin still has the problem of gravitational cracking. Careful selection of grades is required before use. However, the heat resistance is low, and the heat distortion temperature is generally 70 to 98 ° C, and can only be used at a low temperature. Poor chemical resistance, easily eroded by oil, acid, alkali and strong organic solvents.
Acrylonitrile-butadiene-styrene copolymer (ABS)
ABS has a certain degree of rigidity, hardness, impact resistance and chemical resistance, radiation resistance and ethylene oxide sterilization. The medical applications of ABS are mainly used as surgical tools, roller clips, plastic needles, tool boxes, diagnostic devices and hearing aid housings, especially for large medical devices.
Processing conditions
In the medical field, ABS is usually processed by injection molding, and there are few blown film and squeeze tube applications.
Drying treatment: ABS materials are hygroscopic and require drying treatment before processing. Dry conditions of at least 80 hours at 80-90 ° C are recommended. The material temperature should be guaranteed to be less than 0.1%.
Melting temperature: 210-280 ° C; recommended temperature: 245 ° C.
Mold temperature: 25-70 ° C. (The mold temperature will affect the finish of the plastic part, and the lower temperature will result in a lower finish). Injection pressure: 500-1000 bar, injection speed: medium to high speed.
Main performance characteristics
ABS is synthesized from three chemical monomers of acrylonitrile, butadiene and styrene. The respective characteristics of these three components make ABS have good comprehensive mechanical properties. Acrylonitrile gives ABS good chemical resistance and surface hardness. Butadiene makes ABS tough, and styrene makes it have good processability and dyeing properties.
The properties of ABS are mainly determined by the ratio of the three monomers and the molecular structure in the two phases. This allows for great flexibility in product design and results in hundreds of different quality ABS materials on the market.
ABS material has superior processability, good appearance characteristics, low creep and excellent dimensional stability.
Various ABS materials are easily accepted for common secondary processing such as machining, bonding, fastening, plating, painting, and ultrasonic welding.
ABS has excellent impact strength and does not drop rapidly at low temperatures. Has good mechanical strength, hardness and a certain degree of wear resistance.
Has good cold resistance, oil resistance, water resistance, chemical stability, water, inorganic salts, alkalis, acids have almost no effect on ABS, in ketones, aldehydes, esters, chlorinated hydrocarbons will dissolve or form an emulsion, It is insoluble in most alcohols and hydrocarbon solvents, but it will soften and swell when exposed to hydrocarbons for a long time.
Polycarbonate (PC)
Typical properties of PCs are toughness, strength, rigidity and heat-resistant steam sterilization. These characteristics make PCs preferred as blood dialysis filters, surgical tool handles and oxygen tanks (when surgical heart surgery, this instrument can remove blood from the blood) Carbon dioxide, increase oxygen). The medical applications of PCs also include needle-free injection systems, perfusion instruments, blood centrifuge bowls and pistons. With its high transparency, the usual glasses are made of PC.
Processing conditions
In the medical field, PCs are mostly injection molded, with few tubes and blown films. Drying treatment: PC materials are hygroscopic, and drying before processing is important. The recommended drying conditions are 100 °C. -160 ° C, 3-4 hours. The humidity before processing must be less than 0.02%. Melting temperature: 260-340 ° C. Mold temperature: 70-120 ° C. Injection pressure: Use high injection pressure as much as possible. Injection speed: low speed injection for smaller gates and high speed injection for other types of gates.
Main performance characteristics
PC is a non-crystalline engineering material with particularly good impact strength, thermal stability, transparency, gloss, inhibition of bacterial properties, flame retardant properties and stain resistance.
The impact strength of PC is very high, and the shrinkage rate is low, generally 0.4% to 0.8%, and the dimensional stability is good.
PC has good mechanical properties and high temperature resistance. It is resistant to creep, abrasion, heat and cold. The embrittlement temperature is below -100 °C and the long-term working temperature is 120 °C.
Molded parts achieve good dimensional accuracy and maintain dimensional stability over a wide temperature range.
However, the flow characteristics are poor, the processing temperature is high (above 300 ° C), and the injection molding process is difficult.
The cost is higher, and its price is 2-3 times that of PE and PP materials.
It has good weather resistance, water resistance at room temperature, dilute acid, oxidant, reducing agent, salt, oil, aliphatic hydrocarbon, but not alkali, amine, ketone, fat, aromatic hydrocarbon.
The biggest disadvantage is that the plastic parts are easy to crack and the fatigue resistance is poor.
Polytetrafluoroethylene (PTFE)
The polytetrafluoroethylene resin is a white powder and has a waxy appearance and is smooth and non-sticky. PTFE has excellent performance and is comparable to ordinary thermoplastics, so it is known as the “Plastic Kingâ€. Its friction coefficient is the lowest in plastics, and it has good biocompatibility. It can be made into instruments such as artificial blood vessels that are directly implanted into the human body.
Molding performance
The processing is difficult, and the powder is generally cold pressed into a billet, and then sintered or extruded. It is not recommended that the device manufacturer produce this product. If the quantity is not large, the direct purchase is better.
Poor fluidity, easy to decompose, and corrosive gases when decomposed. The molding temperature should not be strictly controlled to exceed 350 ° C, and the mold should be heated to 100-150 ° C.
Transparent pellets, injection molding, extrusion molding. The molding temperature is 300-330 ° C, and it is easy to cause discoloration or bubble generation at 350 ° C or higher. It is suitable for high-speed low-pressure molding, and it is difficult to take off the mold.
Specific gravity: 1.7 g/cm3, molding shrinkage: 3.1-7.7%, molding temperature: 300-330 °C.
Main performance characteristics
Chemical resistance and chemical stability are the most superior ones among the currently known plastics. They are completely stable to highly corrosive media such as strong acids, strong alkalis and various oxidants, and even boiling "Aqua regia". .
It has good creep resistance and compressive strength, high tensile strength, elongation of 100-300%, and excellent radiation resistance.
It has excellent heat and cold resistance and can be used for a long time in the range of -195-250 °C without performance changes.
The disadvantage of polytetrafluoroethylene is that the coefficient of thermal expansion is large, the wear resistance and mechanical strength are poor, the rigidity is insufficient, and the molding is difficult.
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