Plastové materiály - základní popis - PDF

Plastové materiály - základní popis PS: Polystyrene Polystyrene is glass-clear, hard, brittle, and dimensionally stable due to its amorphous structure. PS has good chemical resistance to aqueous solutions

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Plastové materiály - základní popis PS: Polystyrene Polystyrene is glass-clear, hard, brittle, and dimensionally stable due to its amorphous structure. PS has good chemical resistance to aqueous solutions but limited resistance to solvents. Disadvantages include low thermal stability and its tendency to suffer from stress-cracks. SAN: Styrene-acrylonitrile This is a glass-clear material with good resistance to stress-cracking. It has slightly better chemical resistance than PS. PC: Polycarbonate These are thermoplastic linear carboxylic acid polyesters combining many of the properties of metals, glass and plastics. The materials are transparent and have good thermal properties between -130 to +130 C. Note: PC may be weakened by autoclaving or exposure to alkaline detergents. PMMA: Polymethyl methacrylate Rigid, glass-clear ( organic glass ). Resistant to atmospheric agents. Replaces glass in many applications where temperatures are below 90 C and low chemical resistance is required. PMMA has excellent UV radiation stability. PA: Polyamide Polyamides are linear polymers with repeating amide chain linkages. With their favorable strength characteristics and high durability, polyamides can often be used as structural materials and for surface coating metals. They have good chemical resistance against organic solvents, but are easily attacked by acids and oxidizing agents. PVC: Vinyl chloride polymers The vinyl chloride polymers are mainly amorphous thermoplastics with very good chemical resistance. Their combination with plasticizers opens up many useful applications, ranging from artificial leather to injection molding components. PVC has good chemical resistance, especially with oils. POM: Polyoxymethylene POM has superior properties with regard to hardness, rigidity, strength, durability, chemical resistance and favorable slip and abrasion characteristics. It can replace metals in many applications. POM can withstand temperatures up to 130 C. PP: Polypropylene PP has a similar structure to Polyethylene, but with methyl groups at every second carbon atom of the chain. The major advantage, compared with PE, is its higher temperature resistance. It can be repeatedly autoclaved at 121 C. Like the above men tioned polyolefins, PP has good mechanical properties and good chemical resistance but is sligthly more susceptible to be attacked by strong oxidizing agents than PE-HD. PMP: Polymethylpentene PMP is similar to PP but has isobutyl groups instead of the methyl groups. Chemical resistance is comparable to PP but tends to suffer from tension cracks when exposed to ketones or chlorinated solvents. The most important qualities of PMP are its excellent transparency and good mechanical properties at temperatures up to 150 C. PE-LD: Low Density Polyethylene The polymerization of ethylene under high-pressure results in a certain number of branches in the chain. PE-HD exhibits a less compact molecular structure than PE-HD, with very good flexibility and good chemical resistance, but less chemical resistance to organic solvents than PE-HD. Use is limited to temperatures below 80 C. PE-HD: High Density Polyethylene If the polymerization of ethylene is controlled by a catalytic process, a very small number of branches in the chain are obtained. The result is a more rigid and compact structure with enhanced chemical resistance and usability up to 105 C. ECTFE: Ethylene-Chlorotrifluoroethylene ETFE: Ethylene-Tetrafluoroethylene These are ethylene s of chlortrifluoroethylene and tetrafluoroethylene respectively. Both are plastics of high chemical inertness, but lower temperature resistance than PTFE. PTFE: Polytetrafluoroethylene PTFE is a fluorinated carbon with a high-molecular, partly crystalline structure. PTFE is resistant to virtually all chemicals. It offers the widest working temperature range, from -200 to +300 C. Its sur face is adhesion resistant. The slip properties and electrical insulation capacity of the material are better than those of FEP and PFA. The only disadvantage is that it can only be molded by sintering processes. PTFE is opaque. It is suitable for use in microwave ovens. FEP: Perfluoroethylene-propylene PFA: Perfluoroalkoxy These are fluorinated carbons with a high-molecular, partly crystalline structure. Their surface is adhesion-resistant. Mechanical properties and chemical inertness are comparable with those of PTFE. Temperature use is restricted to range -100 to +200 C. The water absorption of FEP is extremely low. FEP and PFA are translucent. PFA is manufactured without the additionof catalysts or plasticizers, and can be molded to produce an extremely smooth, readily cleanable surface, and is therefore particularly well suited for trace analysis. Fyzikální vlastnosti Physical and chemical properties of plastics vary greatly according to their composition. The kind of application determines which plastic to select. Many factors have to be taken into consideration: exposure time and concentration of chemicals, thermal stress (e.g., autoclaving), exertion of force, exposure to UV radiation, and aging, which may be caused by the action of detergents, or other environmental factors. A careful evaluation of the necessary properties by the user is of prime importance. The recommendations listed here are based on technical literature and information provided by the manufacturers of raw materials. They were prepared carefully and are intended as general guidance. However, they cannot replace suitability testing performed by the user under actual working conditions. Max. operating temperature ( C) Brittle temperature ( C) Micro wave suitability* Density (g/cm 3 ) Flexibility Transparency PS no 1.05 rigid transparent SAN no 1.03 rigid transparent PMMA 65 to no 1.18 rigid transparent PC yes 1.20 rigid transparent PVC no 1.35 rigid transparent POM no 1.42 good opaque PE-LD 80 to yes 0.92 very good translucent PE-HD yes 0.95 good translucent PP yes 0.90 moderate translucent PMP yes 0.83 moderate transparent ECTFE/ETFE yes 1.70 moderate translucent PTFE yes 2.17 very good opaque FEP/PFA 205/ /-200 yes 2.15 moderate translucent FKM very good - EPDM very good - NR no 1.20 very good opaque SI no 1.10 very good translucent *Observe chemical and temperature resistance Sterilizace* Autoclaving* at 121 C, t o 20 min to DIN β/γ-radiation 25 kgy Gas (ethylene oxide) PS no yes no yes SAN no no yes yes PMMA no yes no yes PC yes 1) yes yes yes PVC no 2) no yes yes POM yes 1) yes (restricted) yes yes PE-LD no yes yes yes PE-HD no yes yes yes PP yes yes (restricted) yes yes PMP yes yes yes yes ECTFE/ETFE yes no yes yes PTFE yes no yes yes FEP/PFA yes no yes yes FKM yes - yes yes EPDM yes - yes yes NR no no yes yes SI yes no yes yes Chemical (formalin, ethanol) * Before autoclaving, labware must be carefully cleaned and rinsed with destilled water. Always remove covers from containers! 1) Frequent autoclaving may reduce mechanical stability. PC centrifuge tubes may become unusable. 2) With the exception of PVC tubing, which is autoclavable up to 121 C. Chemická odolnost With regard to chemical resistance, plastics are classified as follows: + = Excellent chemical resistance Continuous exposure to the substance does not cause damage within 30 days. The plastic may remain resistant for years. o = Good to limited chemical resistance Continuous exposure to the substance causes minor damages, some of which is reversible, within 7-30 days (e.g., swelling, softening, decrease of mechanical strength, discoloration). = Poor chemical resistance Not suitable for continuous exposure to the substance. Immediate(!) damage may occur (loss of mechanical strength, deformation, discoloration, cracking, dissolution). Classes of substances at 20 C PS SAN PMMA PC PVC POM PE- LD PE- HD PP PMP ECTFE ETFE PTFE FEP PFA FKM EPDM NR Acids, weak or diluted o o - o o o Acids, strong or concentrated o o Oxidizing acids, oxidizing agents o o - - Alkalis o + + o Alcohols, aliphatic Ketones o o o o o + - o - - Aldehydes - - o o - o o + + o o o Esters - - o o o o o o o o Hydrocarbons, aliphatic o + + o + + o + + o Hydrocarbons, aromatic o + o o Hydrocarbons, halogenated o o o o Ether o o o SI Abbreviations of the described plastics (to DIN 7728) PS Polystyrene SAN Styrene-acrylonitrile PMMA Polymethyl methacrylate PC Polycarbonate PVC Polyvinyl chloride POM Polyoxymethylene PE-LD Low-density polyethylene PE-HD High-density polyethylene PP Polypropylene PMP Polymethylpentene ECTFE Ethylene-chlorotrifluoroethylene ETFE Ethylene-tetrafluoroethylene PTFE Polytetrafluoroethylene FEP Perfluoroethylenepropylene PFA Perfluoroalkoxy FKM Fluoro elastomer EPDM Ethylene-propylenediene-rubber NR Natural rubber SI Silicone rubber
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