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Rings and stoppers are useful aids in the daily lab routine. Manufacturers like Bohlender, Deutsch&Neumann, Bürkle and Duran produce stoppers and rings for various types of vessels, flasks and valves. Stoppers are made of fluoroplastics (e.g. PTFE), silicone or glass. Further stoppers are available in numerous shapes with variable top and bottom diameter, with a middle hole or a lamella-like grinding.  

Here you find further information on fluoroplastics

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Rings & Stoppers

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Fluoroplastics: Rings & Stoppers made of PTFE, FEP, PFA etc.

Fluoroplastics belong to the family of thermoplastics. The higher the fluoric content, the better the chemical and thermal capacity of fluoropolymers. A number of characteristics makes fluoroplastics an ideal material for rings and stoppers. Unique properties are:

• universal chemical resistance,
• high thermal load capacity (-200 °C up to +260 °C),
• resistance to all sterilisation temperatures,
• resistance to environmental changes (weather, light),
• ultra-low friction coefficient and
• UV-resistance.

Further, accessories made of fluoroplastics are
• non-flammable,
• non-adhesive,
• unbreakable,
• physiologically safe and
• inert, without taste or odour.

In particular, the chemical and thermal resistance of PTFE is remarkable (-260°C up to +300°). The permanent temperature resistance depends on the load, so PTFE can be used from -200°C to +260°C at moderate mechanical load. PTFE lab equipment, e.g. hoses, magnetic stirring bars, bottles, or stirrer shafts, has a white appearance, a non-adhesive surface and extraordinary slip characteristics.

The chemical and mechanical properties of FEP are similar to those of PTFE. However, the upper limit of the permanent working temperature is lower (+205° C). FEP lab supply, e.g. hoses, is translucent to transparent and non-porous.

PFA has similar chemical and thermal characteristics to PTFE. PFA labware, e.g. hoses, bottles, or round-bottom flasks, is translucent to transparent, non-porous and particularly useful in high-purity work.

PP however does not belong to the family of fluoroplastics. PP is autoclavable (at +121° C) and has good mechanical and chemical properties almost up to its softening point. Lab supply made of PP, e.g. olives for stopcocks and valves or also lab furniture, is unbreakable and an economical alternative.

Cleaning of Fluoroplastics

Due to their smooth, non-wetting surface, all fluoroplastics (PTFE, PFA and FEP) can easily be cleaned. However, abrasive scouring agents might damage the surface and result in a milkiness of the vessels. All neutral detergents (pH 7) are suitable, for a stronger contamination an alkaline detergent up to pH 12 is recommended. Vessels should only be cleaned or dryed in laboratory washing machines when they are completely opened. Here you find a selection of cleaners and disinfectants as well as further information. Vessels made of PTFE, PFA or FEP can be autoclaved or sterilised at +121° C. To avoid deformation or destruction, all vessels with screw covers or stoppers have to be open while being autoclaved. Pressurisation (from inside) should be avoided, too due to the thin walls of standard PTFE, PFA or FEP bottles.

Duran Stoppers made of Borosilicate Glass

Stoppers made of borosilicate glass by Duran are an alternative to stoppers made of fluoroplastics. Borosilicate glass 3.3 is resistant to water, neutral and acid solutions, concentrated acids and acid mixtures, chlorine, bromine, iodine and organic substances. Further, borosilicate glass endures temperatures over 100° C and is universally applicable. Hence Duran glass is suitable ideally for the application in laboratories. Only HF-alkylation, concentrated phosphoric acid and strong alkali in combination with high temperatures (>100°C) lead to glass corrosion. For any other application areas e.g. Duran semi-hollow glass flat-head stoppers are available at Analytics-Shop.com.

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