Teats, rubber

Preservative availability may be appreciably reduced by interaction with packaging materials. Examples include the permeation of phenolic preservatives into the rubber wads and teats of multi-dose injection or eye-drop containers and by their interaction with flexible nylon tubes for creams. Quaternary ammonium preservative levels in formulations have been significantly reduced by adsorption onto the surfaces of plastic and glass containers. Volatile preservatives such as chloroform are so readily lost by the routine opening and closing of containers that their usefulness is somewhat restricted to preservation of medicines in sealed, impervious containers during storage, with quite short use lives once opened. 

The dropper shown in Figure 81, II, has a small bulb so that for maximum uptake liquid does not enter the rubber teat reagent solutions are then less likely to be contaminated. The capillary tube... 

Three groups of substances are regulated individually, i.e. vinyl chloride monomer in plastics (78/142/EEC), nitrosamines in rubber teats and soothers (93/11/EEC), and bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, and novolac glycidyl ethers in plastics and coatings (2002/16/EC). 

Draft directive on nitrosamines in rubber teats and soothers... 

On 15 March 1993 the Commission adopted Directive 93/11/EEC concerning the migration of N-nitrosamines and N-nitrosatable substances from elastomer or rubber teats and soothers. This Directive stipulates that these articles must not release any N-nitrosamine and N-nitrosatable substance detectable by a validated method able to... 

Nasal drops rely upon the instillation of one or more drops of drag solution, either from a dropper with a flexible (rubber) teat, or directly from a squeezable plastic container into the nasal cavity. 

Before use the droppers must be calibrated, i.e. the volume of the drop delivered must be known. Introduce some distilled water into the clean dropper by dipping the capillary end into some distilled water in a beaker and compressing and then releasing the rubber teat or bulb. Hold the dropper vertically over a clean dry 5 ml measuring cylinder, and gently press the rubber bulb. Count the number of drops until the meniscus reaches the 2 ml mark. Repeat the calibration until two results are obtained which do not differ by more than 2 drops. Calculate the volume of a single drop. The dropper should deliver between 30 and 40 drops per ml. Attach a small label to the upper part of the dropper giving the number of drops per ml. 

To remove the supernatant liquid, a capillary dropper is generally used. The centrifuge tube is held at an angle in the left hand, the rubber teat or nipple of the... 

For a 3 ml centrifuge tube or a 4 ml test-tube, the top part of the rubber teat (bulb) from a dropper makes a satisfactory stopper a small hole is made in the rubber bulb and the delivery tube is carefully pushed through it. 

In the 1980s it became evident that rubber teats and soothers may release carcinogenic nitrosamines, which are reaction and degradation products from accelerators and stabilisers used in the mbber. Legislation contained in Directive 93/11/EEC prescribes that nitrosamines and nitrosatable substances that can be transformed into nitrosamines in the stomach shall not be released from the teats and soothers in detectable quantities. Methods for the analysis are proposed with the detection limit set to 0.01 mg/kg rubber for nitrosamines and 0.1 mg/kg rubber for nitrosatable substances. 

Commission Directive 2004/14/EC of 29 January 2004 amending Commission Directive 93/10/EEC relating to materials and articles made of regenerated cellulose film intended to come into contact with foodstuffs. OJ L 27, 30.1.2004, p. 48. Commission Directive 93/11/EEC of 15 March 1993 concerning the release of the N-nitrosamines and N-nitrosatable substances from elastomer and rubber teats and soothers. OJ L93, 17.4.1993, p. 37. 

Special Category (test 24 hours at 40 °C). Rubber articles directly associated with the consumption of food and which are being, or are expected to be, taken into the mouth, e.g., toys according to Recommendation XLVll, teats, soothers, gum-shields, balloons. 

A survey of the extractables present in rubber teats was published in 1991. The samples were extracted with diethyl ether or acetone and the extracts analysed by GC and GC-MS. Data was obtained on 49 rubber teats commercially available in Holland and a number of compounds not permitted in the Dutch regulations were identified, including dibenzylamine, acetophenone, zinc dibenzyldithiocarbamate, 4,4 -thio-bis(2-tert-butyl 5-methyl)phenol and bis(2-hydroxy-3-tert-butyl 5-ethylphenyl)methane. 

A more recent Dutch retail survey looked at the migration of A-nitrosamines, A-nitrosatable substances and 2-mercaptobenzothiazole (MET) from 19 samples of teats and soothers. In addition to these species, screening work was also carried out for any other potential migrants. The majority of the teats and soothers were found to be based on sihcone mbber, and the extractable substances were found to be siloxanes. The remaining samples were natural rubber and only one was found to be above the permissible limits, and that was for nitrosatable substances at 0.23 mg/kg. MET was found in only one of the natural rubber products and this was below the migration limit of 0.3 mg/teat. 

A study in Japan looked at the migration of dimethylamine (DMA) into water and hydrochloric acid from 25 rubber articles (including stoppers, chopping boards, spatulas and teats). After one hour of refluxing, the water extracts contained 3 to 1280 mg of DMA per kg of rubber. The study also showed that the thiuram accelerators that were present (TMTD and TMTM) were almost totally decomposed to DMA (a nitrosatable substance). However, in the case of dimethyl dithiocarbamate salts (sodium, zinc, copper and lead examples were included), the decomposition to DMA depended on the solvent used and the salt compound. 

The physiological inertness of silicone rubber enables its use in the manufacture and packaging of food, as disposable articles for contact with the body e.g. teats for babies and implants in the human body, e.g. artificial heart valves. 

Examples of preservatives are phenylmercuric nitrate or acetate (0.002% w/v), chlorhexidine acetate (0.01% w/v), thiomersal (0.01% w/v) and benzalkonium chloride (0.01% w/v). Chlorocresol is too toxic to the corneal epithelium, but 8-hydroxy-quinoline and thiomersal may be used in specific instances. The principal consideration in relation to antimicrobial properties is the activity of the bactericide against Pseudomonas aeruginosa, a major source of serious nosocomial eye infections. Although benzalkonium chloride is probably the most active of the recommended preservatives, it cannot always be used because of its incompatibility with many compounds commonly used to treat eye diseases, nor should it be used to preserve eye-drops containing anaesthetics. As benzalkonium chloride reacts with natural rubbers, silicone or butyl rubber teats should be substituted and products should not be stored for more than 3 months after manufacture because silicone rubber is permeable to water vapour. As with all rubber components, the rubber teat should be pre-equilibrated with the preservative before use. Thermostable eye-drops and lotions are sterilized at 121 °C for 15 minutes. For thermolabile drugs, filtration sterilization followed by aseptic filling into sterile containers is necessary. Eye-drops in plastic bottles are prepared aseptically. 

Traditionally, ophthalmic liquid products were packed in glass containers fitted with rubber teats for the eye dropper. Glass containers have (limited) use today when there are product stability or compatibility issues which exclude the use of flexible plastic containers made of polyethylene or polypropylene. Most liquid eye products on the market are plastic containers fitted with nozzles from which, by gentle squeezing, the contents may be expressed as drops. 

Dick, John S., and R. A. Annicelli, eds. Rubber Technology Compounding and TeAting for Performance. Cincinnati, OH Hanser Gardner Publications, 2001. 

Before use the droppers must be calibrated, i.e. the volume of the drop delivered must be known. Introduce some distilled water into the clean dropper by dipping the capillary end into some distilled water in a beaker and compressing and then releasing the rubber teat or bulb. Hold the dropper vertically over a clean dry 5 ml measuring cylinder, and gently press the... 

To remove the supernatant liquid, a capillary dropper is generally used. The centrifuge tube is held at an angle in the left hand, the rubber teat or nipple of the capillary dropper, held in the right hand, is compressed to expel the air and the capillary end is lowered into the tube until it is just below the liquid (Fig. 2.18). As the pressure is very slowly released the liquid rises in the dropper and the latter is lowered further into the liquid... 

---