NBR in Contact with Food, Potable Water ... - Plastverarbeiter

Perbunan Food grade application potable 

water application pharmaceutical 

application 

Inherent properties of elastomers such as 

elasticity which allows good sealing 

properties, low gas and water permeability, 

excellent oil resistance and a low 

level of migrating substances from rubber 

products are relevant for the application 

of NBR rubbers in food, water, 

pharmaceutical and cosmetic products. 

Stringent regulatory requirements are 

relevant for that field of application. The 

essential parts of the most important 

regulations like the US FDA CFR 21 parts 

177 –199, the German BgVV Recommendation 

XXI, the relevant French, 

British and Europeen regulations are reviewed. 

The important role that Perbunan has in 

the production of seals and gaskets for 

food containers, milking inflation (liners) 

and for the fast growing aerosol gasket 

industry is discussed in detail. 

NBR für Lebensmittel- und 

Trinkwasserkontakt sowie 

Artikel im Bereich Pharmazie 

und Kosmetik 

Perbunan Lebensmittelbedarfsgegenstände 

Trinkwasseranwendung 

Pharmazeutische Anwendungen 

Elastomereigenschaften wie Elastizität, 

die den Artikeln gute Dichtungseigenschaften 

verleiht, geringe Gasund 

Wasserpermeation, beste Úlbeständigkeit 

und eine geringe Menge 

von migrierbaren Chemikalien sind für 

die Verwendung von NBR-Elastomeren 

in Lebensmittelbedarfsgegenständen, 

Trinkwasseranwendungen 

und in den Bereichen Pharmazie und 

Kosmetik wesentlich. 

Das Anwendungsgebiet unterliegstengen, 

durch Verordnungen geregelten 

Anforderungen. Die wichtigsten 

wie die US FDA CFR 21 § 177 bis 

199, die deutsche BgVV Empfehlung 

XXI und die französischen, britischen 

und europäischen Vorschriften werden 

kurz besprochen. 

Die wichtige Rolle, die Perbunan bei 

Dichtungen für Lebensmittelbehälter, 

Zitzenbecher, Milchschläuche und für 

den wachsenden Markt der Aerosoldichtungen 

in der pharmazeutischen 

und kosmetischen Industrie darstellt, 

wird detailliert besprochen. 

ROHSTOFFE UND ANWENDUNGEN 

RAW MATERIALS AND APPLICATIONS 

NBR in Contact with Food, 

Potable Water, Pharmaceutical 

and Cosmetic Applications 

Rubber products are widely used in a variety 

of applications in contact with food or 

potable water and their use is growing fast 

in the pharmaceutical and cosmetic industries. 

The types of elastomers used in these very 

specific applications cover the whole range 

of available products, natural and synthetic. 

Acrylonitrile butadiene rubber (NBR), butyl 

rubber (IIR), ethylene propylene rubber 

(EPDM), and natural rubber (NR) are 

used in a variety of sealing elements or 

as packaging components in the abovementioned 

industries. The inherent properties 

of rubber, such as elasticity which allows 

good sealing and resealing properties, 

low gas and water permeability, excellent 

oil resistance, good physical and chemical 

properties, low level of migrating 

substances from the rubber products and 

compatibility with food, water, pharmaceutical 

and cosmetic products as well as 

compliance with stringent regulatory requirements 

are essential for this field of applications. 

This paper will be limited to a discussion of 

the role that Perbunan, an acrylonitrile butadiene 

rubber from Bayer AG, has in the 

production of seals and gaskets for food 

containers, potable water seals, milking inflations 

(liners) and, last but not least, in 

the fast growing aerosol gasket industry 

for the pharmaceutical and cosmetic industries. 

All of these products have to 

meet very severe and very different specific 

requirements, which will also be mentioned 

in this paper, set by each of the 

above-mentioned industries. 

Regulations applicable for rubber 

products in contact with food 

A prerequisite for polymers that are to be 

used in contact with food is compliance 

with food regulations. Many countries 

have a national positive list of materials 

permitted for contact with food. USA: title 

21 of the US Code of Federal Regulations, 

FDA (Food and Drug Administration), parts 

170 to 199. 

Germany: BgVV (German Federal Institute 

for Consumer Health and Veterinary Medicine) 

Recommendation XXI. 

France: issued by the Ministry for Health 

published in “Le Journal Officiel de la Republique 

Francaise” as “L’Arrêté du 9 Novembre 

1994”. 

Netherlands: “Verpakkingen en gebruiksartikelenbesluit” 

(Warenwet), Chapter III. 

United Kingdom: Statutory Instrument 

1987 No. 1523, “Materials and Articles 

in Contact with Foodstuffs”. This document 

requires only the use of materials 

safe for human consumption, but does 

not specify any positive list of ingredients 

which can be used. In the absence of a positive 

list, the US FDA and German BgVV 

XXI are often taken into account. 

Italy: “Gazetta Ufficialle della Repubblica 

Italiana” of 1994. 

USA FDA 

The United States Food and Drug Administration 

(FDA) issues regulations for the 

manufacture of rubber articles used in contact 

with food. These include regulations 

as to which ingredients can be used in 

the production of rubber, in what proportions 

and what amount can be extracted in 

the media that are representative for food 

applications. FDA Title 21, Part 177.2600, 

Rubber Articles Intended for Repeated 

Use, is the only relevant section applicable 

to vulcanized rubber products. 

Part 177.2600 lists the chemicals which 

can be used in the manufacture of rubber 

N. De Coster, H. Magg, Leverkusen 

KGK Kautschuk Gummi Kunststoffe 56. Jahrgang, Nr. 7-8/2003 405

articles in contact with food. Parts 170 

through 199 of the same FDA Title 21 regulate 

these chemicals. In order to comply 

with FDA 177.2600, rubber manufacturers 

must use only those chemicals which are 

listed. 

What does this mean and what is a product 

in compliance with FDA? The manufacturer 

of the finished rubber products 

must verify that all ingredients in a rubber 

compound are used in concentrations as 

given in FDA 177.2600 and that migration 

limits are not exceeded. 

The manufacturer must carry out extraction 

tests according to the conditions described 

in FDA chapters 177–199 or provide 

test results from an independent laboratory. 

To obtain formal FDA approval, a submission 

to the FDA has to be made. This involves 

costs of several thousand US$ and 

requires several months for completion. 

The submission must contain details about 

composition and migration behavior to assess 

the toxicological risks that are associated 

with the intended use. Any change 

must be documented and re-approved by 

the FDA. 

The above procedure also applies for all 

rubber products used in pharmaceutical 

and cosmetic applications. 

European Regulations for Rubber 

Products in Contact with Food 

In Europe, the German BgVV approval procedure 

is similar. It must be noted that the 

German BgVV document is a recommendation. 

However, in the absence of an 

EEC official directive for rubber products, 

the BgVV Recommendations are widely accepted 

within Europe. 

Recommendation XXI of the BgVV provides 

a list of ingredients that may be 

used in rubber products in contact with 

food, as well as their quantities and migration 

limits. The BgVV also provides test procedures 

for extraction in media which are 

representative for food applications, water, 

alcohol, oil and acid. According to the 

BgVV, all rubber products are classified 

into 5 use categories as a function of 

time and temperature exposure to the 

food. 

Category 1 – includes all rubber products 

in contact with food over a long time (24 

hours to several months), such as storage 

containers, container linings, seals with 

very large surface area exposed to food, 

and seals for cans, glass vessels, bottles 

etc. The migration tests are carried out 

for 10 days at 40 8C in the food simulants 

such as distilled water, 10% v/v ethanol, 

3% w/w acetic acid. The global migration 

limit must not be exceeded. 

Category 2 – includes all rubber products 

that are in contact with food for not more 

than 24 hours, such as hoses for food 

transport, bottle stoppers and bottle 

caps, sealing rings for steam pressure cookers, 

coffee making machines, lock seals 

for milking cans. The migration tests for 

this category are carried out for 24 hours 

at 40 8C in the same food simulants as 

for Category 1 but the migration limits 

are different. 

Category 3 – includes rubber articles that 

come into contact with food for not more 

than 10 minutes, such as milking inflations 

(linings), milking machine tubes, seals in 

diary installations, membranes, diaphragms, 

roll covers, gloves and aprons 

which are worn during the handling of 

food. The migration tests are carried out 

for 10 minutes at 40 8C in the same 

food simulants as for Category 1. 

Category 4 – includes rubber products that 

come into contact with food for a very 

short time and therefore it is expected 

that no migration will take place. These 

products are conveyor belts, roll covers, 

suction and pressure hoses, seals for the 

pipelines, pumps, tap washers etc. No migration 

tests are specified for this category. 

Special category – includes all rubber products 

that can come into contact with the 

mouth, such as toys, balloons, baby teats, 

children’s dummies, nipple shields, teething 

rings, gum shields etc. The migration 

conditions for this category are carried out 

in distilled water for 24 hours at 40 8C. 

The BgVV continuously monitors the toxicological 

data of chemical substances and 

the decomposition products after, for example, 

the vulcanization process. As results, 

the lists have been updated in the 

form of circular letters. 

In Europe, all materials which are intended 

for contact with food must comply with 

EEC Directive 89/109/EEC which regulates 

the requirements for materials intended 

for food contact. There is also an EEC Directive 

(90/128/EEC) related to plastic materials 

intended to come into contact with 

food. Elastomers and rubber products are 

not covered by this directive. In practice, 

however, occasionally we find rubber products 

which carry a label of compliance 

with 90/128/EEC. 

To comply with 90/128/EEC, plastic materials 

should not transfer their constituents 

to foodstuff in quantities exceeding 

10 mg/dm 2 of surface area of material or 

article (overall migration limit). However, 

this limit is 60 mg of the constituents released 

per kilogram of foodstuff in the following 

cases: 

a) articles which are containers or are comparable 

to containers or which can be 

filled, with a capacity of not less than 

500 ml and not more than 10 l; 

b) articles which can be filled and for 

which it is impracticable to estimate 

the surface area contact with food stuff; 

c) caps, gaskets, stoppers or similar devices 

for sealing. 

The migration tests are carried out in food 

simulants such as water, olive oil, alcohol 

solutions and acid solutions. 

Some food manufacturers in Europe are requesting 

that rubbers products should 

comply with this EEC Directive, ignoring 

the fact that rubber is very different from 

plastic materials. The vulcanization process 

associated with rubber products changes 

the chemicals used as components in the 

rubber formulation and they can migrate 

under the extraction conditions set for 

plastic materials. 

Perbunan in food applications 

Perbunan and Krynac are the trade names 

for acrylonitrile butadiene rubber (NBR) 

from Bayer AG. Standard grades have an 

acrylonitrile content of between 18 and 

50 %. Bayer also produces a range of special 

NBR grades, such as pre-crosslinked 

grades (XL), carboxylated (XNBR) and powder 

grades. 

Perbunan grades are used in a variety of 

rubber products that come into direct contact 

with food, such as oil and fat resistant 

seals and gasket for glass and metal food 

containers, roll coverings, milk hoses, linings 

and inflations, gloves, closures etc. 

Vulcanizates based on Perbunan meet 

the requirements of all existing regulations 

as far as migration limits, nitrosamine level 

and toxicological evaluation are concerned. 

During the production of Perbunan by 

emulsion polymerization, only materials 

listed in the FDA and BgVV positive lists 

are used. The level of nitrosamines, which 

under German law may not exceed 1 lg/ 

dm 2 , is also monitored and, with the exception 

of some specialty grades, Perbunan 

grades do not exceed this limit. The 

406 KGK Kautschuk Gummi Kunststoffe 56. Jahrgang, Nr. 7-8/2003

Table 1. Residual ACN Level in Perbunan 

Application Methanol 

extraction (%) 

level of residual monomers, acrylonitrile 

and butadiene, is also monitored and 

most Perbunan grades do not exceed 

the limits set by the current regulations. 

Recent results are presented in Table 1. 

According to the German BgVV, the level 

of free acrylonitrile monomer in finished articles 

must not exceed 1 mg/kg. 

According to the US FDA, the migration of 

acrylonitrile monomer from NBR vulcanizates 

may not exceed 0.03 mg/inch 2 

“when extracted at a time equivalent to initial 

batch usage utilizing food simulating 

solvents and temperature appropriate for 

the intended use”. The free ACN is measured 

using gas chromatography. 

Vulcanizates based on Perbunan also meet 

the requirements of the USFDA 180.22 

which limits the extraction of acrylonitrile 

monomer as a function of volume to surface 

area. The monomer extraction is monitored 

using the food simulants, distilled 

water, 50 % ethanol, 3 % acetic acid 

and either n-heptane or an appropriate 

oil or fat. 

Because of the recent problems related to 

BSE, the manufacturer using materials of 

animal origin must declare the origin of 

the animals, and only BSE-free materials 

are allowed to be used in polymers intended 

for contact with food and in pharmaceutical 

and medical applications. 

All Bayer Perbunan grades are made using 

BSE-free raw materials as specified in the 

following EEC documents: 

EEC Directive 96/239/EC of March 1996 

EEC Directive 96/362/EC of June 1996 

Amendment of EEC Directive 75/318/EC in 

1997 

EEC Directive 97/538 of July 1997 applicable 

as of January 1998. 

The origin of the fatty acid and other components 

of emulsifier systems used in the 

production of Perbunan is being monitored 

and is proven to be BSE-free. 

In addition to the polymer analysis, all finished 

rubber products must be checked for 

extractive materials according to the conditions 

specified by the above-mentioned 

regulations. Sometimes the end users apply 

their own extraction conditions if it is 

necessary to raise the temperature or exposure 

time of rubber to food simulants, 

or e.g., sterilization conditions. 

Criteria for the Selection of other 

Compounding Ingredients for 

Food, Potable Water and Pharmaceutical 

Applications 

To achieve the required level of physical 

properties and to ensure good processing 

properties, the polymer is mixed with fillers 

and plasticizers. 

Fillers 

Nitrosamine 

level (lg/kg) 

Residual 

acrylonitrile 

(mg/kg) 

Perbunan NT 3431 VP Injection molding 1,04 –1,52 2,5/1,4 

Perbunan NT 3445 VP General Purpose 1,41 0,6/0,6 

Perbunan NT 3945 VP Good oil resistance 

and low permeability 

0,98 2,9/2,5 



1,45 –1,52 < 20 0,4/0,5 



0,89 2,0/1,9 

Carbon black is the predominantly used filler 

in the compounding of NBR compounds 

that come into contact with 

food or potable water and for seals for 

the pharmaceutical and cosmetic industries. 

For food applications, most furnace blacks 

are considered safe. According to existing 

food regulations, the type and the amount 

of carbon black is limited. According to 

FDA 177.2600, the amount of carbon 

black may not exceed 50 % by weight 

of the rubber product. In rubber products 

intended for use in contact with milk or edible 

oils, the total carbon black amount 

may not exceed 10 %. 

According to German BgVV Recommendation 

XXI, the only carbon blacks that 

are allowed are those that fulfil the criteria 

for cleanliness according to German BGesundBL 

15,268 (1972). The amount of carbon 

black is limited to 30 % by weight of 

rubber products for all applications belonging 

to categories 2 and 3. Carbon 

black is not allowed in rubber products 

covered by the special category of the 

BgVV. 

All other fillers used in rubber products 

must comply with the BgVV Recommendation 

for fillers listed in LII of the BgVV. 

In potable water applications, results show 

that all pure carbon blacks do not support 

microbiological growth. Some very recent 

results related to German standard W 

270 suggest that only very pure carbon 

black gives satisfactory results. Very pure 

carbon blacks are furnace blacks and 

have very low toluene extraction. Such 

blacks are now available from some carbon 

black suppliers. 

Other fillers which are used are used alone 

or in blends with the carbon blacks are 

clays, calcined clays, silica fillers, talcs etc. 

As far as rubber products in contact with 

potable water are concerned, mineral fillers 

often show higher microbial growth 

than carbon black. 

For rubber products in contact with water 

or water-based solutions, silica fillers 

should be avoided because of their high 

water absorption. 

Plasticizers 

Most of the plasticizers used to facilitate 

the processing of rubber compounds are 

undesirable in food, potable water, and 

pharmaceutical applications. Because of 

their low molecular weight in comparison 

with the polymer, they can be easily extracted 

in contact with food and also during 

the process of sterilization and extraction 

tests. For example, a frequently used 

plasticizer, DOP, is easily extracted by alcohol 

and therefore cannot be recommended 

for alcohol-containing beverages 

and food. Plasticizers should be avoided in 

these compounds or limited to the lowest 

amount necessary for processing. 

The following factors have to be considered 

when selecting plasticizers: 

– compliance with the food regulations 

– compatibility with the base polymer 

– cleanliness 

– effect on specific properties of the final 

articles 

– extractability in water or other liquids. 

Perbunan is compatible with most of the 

ester- and ether-based plasticizers. However, 

these are easily extracted. 

Antioxidants 

Perbunan is protected with an appropriate 

antioxidant for standard storage conditions. 

However, for additional resistance against 

aging, antioxidants have to be added to 


the rubber compound. In most food applications, 

with the exception of some potable 

water applications, antioxidants do not 

present major problems when used in recommended 

concentrations. According 

to test results for microbial growth according 

the BSEN-681, antioxidants have been 

found to support microbial growth. Because 

of the difference in test procedures, 

no such effect has been reported in tests 

according to other test procedures used 

for the assessment of rubber products in 

contact with water, namely the German 

KTW and French standard. 

Vulcanization Agents 

The choice of the vulcanization system depends 

on the application of the final product. 

In rubber products intended for contact 

with food and milk, sulfur and sulfurdonor 

vulcanization systems are usually 

used, while for pharmaceutical applications 

and potable water both peroxideand 

sulfur-based systems are used. Post 

cure of the final products in all the 

above-mentioned applications has a beneficial 

effect in reducing the amount of the 

potentially extractable residuals. It is very 

difficult to discuss the effect of the curing 

system and to recommend the optimum 

one because of the variety of the vulcanization 

systems vulcanization processes 

used. It has to be underlined that because 

of a very complex vulcanization process the 

accelerators may remain in unreacted form 

or may form by-products, some of which 

may migrate into food and may be dangerous 

for human health. 

Processing Aids 

Table 2. Global migration of NBR-based compounds, 10 days/40 8C 

Sample designation Distilled water 

mg/dm 2 

Most of the low cost release agents or processing 

aids are not compatible with Perbunan 

and great attention has to be 

paid when selecting a suitable material. 

These additives are usually based on fatty 

acids and may migrate to the surface of the 

rubber compound and cause two phenomena 

observed during the molding process, 

exudation and mold fouling. In all 

food-related applications, processing aids 

are undesirable and should be avoided 

as much as possible. 

Some Examples of Compounds 

for Food Applications based on 

Perbunan 

Perbunan is used in many sealing rings for 

food containers. Because of its excellent 

resistance to oils and fats, Perbunan is 

used in sealing rings for the packaging 

of fat and oily food. 

Recent tests carried out on rubber seals for 

food containers with different Perbunan 

grades showed very low migration levels 

[1]. The global migration data are presented 

in Table 2. The extraction test was 

carried out according to the BgVV test procedure 

for category 1 (10 days/40 8C) in 

distilled water, 10 % ethanol and 3 % 

acetic acid. 

Rubber formulations used in this study are 

given in Table 3. 

Ethanol 10 % 

mg/dm 2 

Acetic acid 3 % 

mg/dm 2 

A 158/1, Perbunan NT 4351 VP 14/13/13 66/61/49 62/66/63 

A 158/2, Krynac 3345 F 17/20/20 39/39/38 89/54/64 

A 158/3 PErbunan NT 3446 VP 17/21/18 27/25/25 23/14/16 

A 158/6 Perbunan NT 3431 19/21/18 33/32 * 34/34/34 

Global migration limit 50 mg/dm 2 50 mg/dm 2 150 mg/dm 2 

Table 3. Compound Formulations for Glass Containers for Fatty Food 

1289 A 158/1 158/2 158/3 158/6 

Perbunan NT 4351 VP 100,0 – – – 

Krynac 3445 F – 100,0 – – 

Perbunan NT 3446 – – 100,0 – 

Perbunan NT 3431 – – – 100,0 

Sulfur 90/95 0,4 0,4 0,4 0,4 

Stearic acid 1,0 1,0 1,0 1,0 

Polestar 200R 50,0 50,0 50,0 50,0 

Vulkasil S/G 10,0 10,0 10,0 10,0 

Diethylene glycol (DEG) 2,0 2,0 2,0 2,0 

Rhenocure S/G 1,5 1,5 1,5 1,5 

Vulkacit Thiuram/C 2,0 2,0 2,0 2,0 

Compounds for Potable Water 

based on Perbunan 

Compounds based on Perbunan are used 

in a variety of applications in contact with 

water, such as seals and membranes for 

plumbing, jointing material for water 

pipes, and for lining of water reservoirs. 

Many formulations have been developed 

[2] which offer the manufacturer the possibility 

of meeting the requirements for 

physical and aging properties imposed 

by a variety of national standards. 

Although it is not difficult to meet the physical 

properties requirements, the specific 

requirements for microbiological resistance 

are hard to meet. To prevent use 

of poor quality jointing and fitting parts, 

the United Kingdom, Germany, France 

and the USA introduced compulsory tests 

for microbiological resistance of all rubber 

materials used in contact with water. 

Standards and regulations for rubber products 

in contact with water encompass 

physical properties, immersion properties, 

aging properties and specific requirements 

for potable and waste waters (odor, taste, 

toxicity, cytotoxicity and the ability of the 

rubber material to support the growth of 

microorganisms). 

The above-mentioned requirements and 

the limits are summarized in the European 

standard EN 681. Although member states 

of the European Union have agreed on a 

common standard for physical and aged 

properties, they failed to a agree a common 

standard procedure for the evaluation 

of microbiological resistance. Over the 

years, some tests have been eliminated because 

of the poor reproducibility of the 

tests, such as exposure to Pseudomonas 

Aeruginosa from BS 2494 and BS EN 

681. On the other hand, a new requirement 

has been introduced in Germany 

by the water and gas controlling authorities 

in the specification W 270 which 

was added to the already very restrictive 

KTW 1.3.13 recommendation. 

This unfortunate situation has left the rubber 

manufacturers to continue the struggle 

to meet very stringent and very different 

national requirements of unproved reproducibility. 

Because of the great difference 

in requirements for microbiological 

resistance, it is very difficult to offer one 

compound formulation that can cover all 

available standard requirements and 

meet the positive list restrictions, such as 

KTW in Germany or FDA in the USA. Contrary 

to other countries, the water autho- 


ities in the UK do not require compliance 

with any of the existing positive lists for 

rubber products. 

The choice of polymer is primarily based on 

the ability of the polymer to withstand the 

growth of microorganisms. 

Most synthetic elastomers do not support 

biological attack which can occur for any 

of the following reasons: 

1. The elastomer may be a source of food 

2. The elastomer may be a barrier to be penetrated 

in the search for food 

3. The elastomer may not be resistant to 

by-products produced by various microorganisms 

4. The elastomer may provide a shelter or 

attachment during the life of an organism 

although there may not be any direct 

degradation involved in the attachment. 

The chemical structure of synthetic polymers, 

including Perbunan, inhibits attack 

and resistance is increased by their hardness, 

surface smoothness and low water 

absorption. This inertness applies only to 

pure polymers which, in practice, are not 

usually used alone. To achieve a specified 

level of physical properties, the polymer is 

mixed with fillers, plasticizers, stabilizers, 

vulcanization agents, processing aids etc. 

Except for polyisoprene, most synthetic 

elastomers, if properly compounded, do 

not support microbiological growth. Recommended 

elastomers are nitrile butadiene 

rubber (NBR), ethylene propylene 

diene rubber (EPDM), butyl rubber (IIR) 

and halogenated butyl rubber (HIIR). Polymers 

resistant to oxidation, such as EPDM, 

IIR, HIIR, CR and NBR are more resistant to 

microbiological growth than natural rubber 

(NR) or styrene butadiene rubber (SBR). 

In the case of Perbunan, the presence of 

the acrylonitrile group may confer some 

Table 4. Perbunan Compounds for Potable 

Water in Compliance with BS EN 681 

Compound B5V 68 (phr) 

Perbunan NT 3431 100 

Zinc oxide 5 

Stearic acid 0.5 

MC-Sulfur 0.4 

Vulkanox BKF 1.5 

SRF-N762 black 55 

Santicizer 148 12 

Vulkacit Thiuram/C 3.0 

Organoleptic properties 

Microbiological growth test 

Pass 

Coliform bacteria (per 100 ml) < 1 

Mean dissolved oxygen 2.1 

difference (mg/l) 

Toxic metals none 

Cytotoxicity screening test pass 

Table 5. KTW Requirements 

Category Total organic carbon 

migration into water 

(mg TOC m 2 day 1 ) 

protection against the growth of fungi. 

Although any Perbunan grade can be 

used in this application, most of the rubber 

compounds are based on Perbunan grades 

with medium (34 %) ACN content which 

are available with various Mooney viscosity 

levels. The microbiological properties of 

the rubber compounds in accordance 

with BS EN 681 are presented below. 

The representative rubber formulations for 

potable water applications are given in Table 

4. 

In Germany, the quality requirements for 

vulcanizates in contact with potable water 

are described in DIN EN 681-1, while specific 

properties, such as the effects on odor 

and taste of water, migration from rubber 

products, and microbiological resistance, 

are the subject of a separate document 

(KTW Recommendation) for non-metallic 

material in contact with potable water. 

The KTW Recommendation also provides 

a list of materials permitted for use in rubber 

compounds with their permitted concentrations. 

The KTW requirements can be summarized 

as follows: 

– the rubber surface in contact with potable 

water should not affect the water 

quality, 

– migration of organic substances from 

the rubber product and chlorine absorp- 

Chlorine absorption 

(mg Cl m 2 day 1 ) 

A Hoses, tubes 2.5 2 1:1 

B Containers (linings) 10 6 1:4 

C Accessories 15 12 1:6 

D1 Membranes 60 75 1:25 

D2 Seals, Gaskets 125 150 1:50 

Table 6. Compounds based on Perbunan in 

Accordance with German KTW 1.3.13 Recommendation 

phr 

Perbunan NT 3446 100 

Stearic acid 1 

Zinkoxyd aktiv 5 

Carbon black N 550 60 

Calcined clay 30 

Mesamoll 10 

Antilux L 2 

Vulkanox 4020 2 

Rhenofit DDA-70 1,5 

Sulfur 0,3 

Vulkacit CZ 2,0 

Vulkacit Thiuram 2,5 

Odor limits, cm 2 ml 1 

(surface volume ratio) 

tion by the rubber product from test 

water must not exceed the limits given 

in the KTW Recommendation for each 

category, 

– the materials used must be on the positive 

list of allowed substances. 

According to KTW 1.3.13, all rubber products 

coming into contact with water 

are classified in 5 categories. The specific 

requirements of the KTW are listed in Table 

5. 

Rubber compounds based on Perbunan do 

not meet the requirements of categories A, 

B and C because of the very low limits for 

chlorine absorption. Most compounds 

based on Perbunan are used for rubber 

seals which are covered under categories 

D1and D2. Based on studies carried out 

[3], emulsion-polymerized elastomers, as 

is the case with Perbunan, usually give 

higher chlorine absorption in comparison 

with solution elastomers. High chlorine absorption 

in NBR-based compounds is also 

caused by the presence of ester-type plasticizers, 

vulcanization systems and aminetype 

antioxidants. 

Rubber Compounds for Milking 

Inflations 

Milking inflations or liners are rubber parts 

based on acrylonitrile butadiene rubber 

which are used on milking machines. 

The requirements for the rubber parts 

are set by the machine suppliers. The rubber 

parts are fitted on the machines and 

exposed to the continuous milking process 

which lasts from 30 – 60 minutes followed 

by washing in acid (pH 1–2) and alkaline 

(pH 12) solutions for about 10 minutes. 

The objective of the washing is to get rid 

of milk stone, calcium salts, proteins and 

fats. During the milking process, the inflations 

are exposed to about 15 % extension 

and, depending on the geographical position 

of the farm, to oxygen, ozone, and 

also to milk fat. Perbunan has been used 

successfully in this application alone or in 

blends with other elastomers, mainly 


Table 7. Compound Formulations for Milking Inflations 

1289 A 931 932 933 934 935 936 

Perbunan NT 3480 70,0 – – – – – 

Perbunan NT 2865 – 100,0 100,0 85,0 80,0 70,0 

Krylene 1500 30,0 – – 15,0 20,0 30,0 

Sulfur 95/C 1,3 1,5 1,5 1,5 1,5 1,5 

Stearic acid 1,0 0,5 0,5 0,5 0,5 0,5 

Zinkoxyd aktiv 2,5 2,5 2,5 2,5 2,5 2,5 

Carbon black N 772 25,0 25,0 35,0 35,0 35,0 35,0 

Carbon black N 660 20,0 29,0 20,0 29,0 29,0 29,0 

Vulkanox 4020/LG 1,5 1,3 1,3 1,3 1,3 1,3 

Antilux L 2,0 2,0 2,0 2,0 2,0 2,0 

DOP (Vestinol AH) 20,0 10,0 10,0 10,0 10,0 10,0 

Mesamoll 16,5 15,0 15,0 15,0 15,0 15,0 

Vulkacit DM/MG 1,2 1,2 1,2 1,2 1,2 1,2 

Rhenogran TMTM 80 0,375 0,625 0,625 0,625 0,625 0,625 

Total 191,400 188,625 189,625 198,625 198,625 198,625 

SBR. A selection of compounding ingredients 

is based on BgVV Recommendation 

XXI. The compounding principles had to 

be changed in 1995 when the BgVV introduced 

very low limits of 20 lg/kg of food 

for primary aromatic amines which can be 

extracted from the rubber compounds. Primary 

aromatic amines are decomposition 

products generated from the antioxidant 

Figure 1. Ozone 

Resistance of Vulcanizates 

based on 

Perbunan 

6 PPD (N-(1,3,-dimethylbutyl)-N’phenyl-pphenylenediamine 

which is used as a fatigue 

and ozone protective agent in the 

NBR-based milking inflations. Antioxidant 

6 PPD provides the best resistance against 

ozone cracking of NBR-based vulcanizates 

[4] and it is approved for use in rubber products 

in contact with food. The current 

specification for milking inflations requires 

Table 8. HNBR Compounds for Milking Inflations 

1289 A 971 972 973 974 975 976 977 978 

Therban C 3446 70,0 – 100,0 – – – – – 

Therban C 3467 – 70,0 – 100,0 – – – – 

Therban A 3907 – – – – 100,0 – 100,0 – 

Therban A 4307 – – – – – 100,0 – 100,0 

Krylene 1500 30,0 30,0 – – – – – – 

Carbon black N 

550 (FEF) 

40,0 40,0 40,0 40,0 40,0 40,0 – – 

Carbon black N 

990 (Thermax) 

40,0 40,0 40,0 40,0 40,0 40,0 50,0 50,0 

DOP (Vestinol AH) 20,0 20,0 20,0 20,0 20,0 20,0 10,0 10,0 

Mesamoll 16,5 16,5 16,5 16,5 16,5 16,5 10,0 10,0 

Zinkoxyd activ 2,5 2,5 2,5 2,5 – – – – 

Antilux 2,0 2,0 – – – – – – 

Sulfur 95/C 1,5 1,5 1,5 1,5 – – – – 

Rhenocure Thiuram 

MS/EG C 

0,5 0,5 0,5 0,5 – – – – 

Vulkacit DM/C 1,2 1,2 1,2 1,2 – – – – 

Perkadox 14-40/B – – – – 6,0 6,0 6,0 6,0 

MgO (Maglite DE) – – – – 2,0 2,0 2,0 2,0 

Total 224,2 224,2 222,2 222,2 224,5 224,5 178,0 178,0 

no ozone cracks on the specially designed 

dumbbells exposed to 40 % elongation as 

well good flex resistance. To meet these 

stringent specification requirements, a 

minimum amount of 2–2,5 phr of 6 PPD 

has to be used. Since the introduction of 

the limits for primary aromatic amines, 

the amount of 6 PPD has had to be reduced 

to the levels which will not produce 

more than 20 lg/kg of food. 

A series of compounds based on Perbunan 

that perform well was developed from the 

results of development work [5] carried out 

in our laboratories. These compounds are 

based on various grades and are given in 

Table 7. 

All the above-mentioned compounds 

meet all requirements for physical and 

aging properties as well as ozone resistance. 

The results for ozone resistance 

are shown in Figure 1. 

An alternative to 6 PPD-stabilized NBR vulcanizates 

might be the use of an ozone-resistant 

polymer, for example, fully hydrogenated 

nitrile rubber (HNBR)-based compounds 

[6] such as given in Table 8. 

Some Therban grades comply with FDA 

177.2600. At present, none of the Therban 

grades comply with the BgVV Recommendation. 

Bayer AG has filed a petition 

with the BgVV for inclusion of Therban 

in the positive list. 

Perbunan Compounds for Pharmaceutical 

and Cosmetic Applications 

Perbunan grades are successfully used in 

seals for aerosol devices in the pharmaceutical 

and cosmetic industries. One of the 

most important applications of rubber 

seals based on Perbunan is in asthma inhalers. 

The use of NBR has grown over last 

years because of the increase of asthma 

sufferers around the world and the necessity 

for treatment with inhalers which today 

are made to supply the exact amount 

of medication via respiratory airways – the 

fastest and the most efficient way of treating 

asthma and asthma attacks. The shelf 

life of the pharmaceutical product is influenced 

by the permeability of the propellant 

(an HCFC type) and compatibility with the 

pharmaceutical preparation. 

As shown in [7], the NBR Perbunan has low 

permeability against the new CFC-free refrigerants. 

Perbunan with medium and high acrylonitrile 

levels, 34–39 %, have been successfully 

used as seals by the leading pharma- 


ceutical companies. A very low extraction 

level from Perbunan has been recognized 

as the important factor for selection of the 

base polymer for the rubber seal compounds. 

For quality assessment, prior to 

Figure 2. Ozone concentration 

50 pphm, 

23 8C. 55 % rel. humidity 

Figure 3. Relative 

Permeability of 134a 

through Elastomers 

at 80 8C 

Table 9. ....... 

1289 A 1011 1012 1013 1014 1015 1016 1017 

Therban A 3406 100,0 100,0 100,0 – – – – 

Therban A 3407 – – – 100,0 100,0 – – 

Therban VP.KA 8798 – – – – – 100,0 100,0 

Carbon black N 550 (FEF) 40,0 – – – – – – 

Carbon black 990 (Thermax) 

16,0 – – – – – – 

Carbon black N 772 – 35,0 28,0 35,0 25,0 35,0 25,0 

Carbon black N 660 – 20,0 30,0 20,0 29,0 20,0 29,0 

DOP (Vestinol AH) 20,0 20,0 20,0 20,0 10,0 20,0 10,0 

Mesamoll 16,5 16,5 16,5 16,5 15,0 16,5 15,0 

Perkadox 14-40/B 6,0 6,0 6,0 6,0 6,0 6,0 6,0 

MgO (Maglite DE) 2,0 2,0 2,0 2,0 2,0 2,0 2,0 

Total 200,5 199,5 202,5 199,5 187,0 199,5 187,0 

Table 10. Rubber Compounds for Aerosol Pump Seals 

1289 A 179/1 179/3 179/4 179/5 180/2 180/4 

Perbunan NT 3430 100,0 – – – – – 

Perbunan NT 3431 VP – 100,0 – – – – 

Krynac 3330F – – 100,0 – – – 

Perbunan NT 3445 – – – 100,0 – – 

Perbunan NT 3945 VP – – – 100,0 – 

Perbunan NT 3945 – – – – – 100,0 

Carbon black N 550 50,0 50,0 50,0 50,0 50,0 50,0 

Vulkanox HS/LG 1,0 1,0 1,0 1,0 1,0 1,0 

Perkadox BC 40B 4,0 4,0 4,0 4,0 4,0 4,0 

use, the polymers are extracted in methanol 

and examined by gas chromatography. 

Once the amount of total extraction has 

been agreed, it must be kept unchanged, 

as must the composition of the polymer. 

For these applications, every change carried 

out on the polymer must be documented 

and registered at the US FDA. Each 

rubber seal producer has its own Drug 

Master File at the FDA where all formulations 

used for medical devices must be registered 

as well as all changes carried out 

on the rubber formulation, for whatever 

reason. The same applies to the producers 

of the drug that is contained in the inhaler. 

The above procedure often causes a problem 

for polymer suppliers, rubber seals 

producers and the end user because of 

the lengthy and expensive process. 

Similar approval procedures apply for cosmetic 

products, although they are not as 

severe as for the pharmaceutical applications. 

The polymer suppliers for the above applications 

are obliged to monitor the quality 

of all ingredients used in the production, 

the production processes and final product. 

The compounding principles used for 

these products are similar to those for all 

other pharmaceutical applications. Perbunan 

is mixed with carbon black, a predominately 

used filler, very little or no plasticizer 

and the curing system which is usually a 

peroxide cure system. A typical rubber formulation 

is given in Table 9. 

References 

[1] N. Harmsworth, TN 1301, Bayer internal report, 

2001-04-11. 

[2] N. Harmsworth, Bayer TIB – Rubber Compounds in 

Contact with Water, KA-FK-0496e/02/10.00. 

[3] D. Gross, Elastomere in Trinkwasserkontakt I, II, III, 

Kautschuk, Gummi, Kunststoffe 33 (1980), 997, 

Teil II ibid 34 (1981) 464, Teil III ibid 35 (1982). 

[4] N. Harmsworth, G. Abts and C.A. Moakes, Improvement 

in the Ozone Resistance of Elastomers 

with Non Staining Antioxidants, KGK 9/96, p. 

597 – 606. 

[5] N. Harmsworth, TN 1138 Optimisation of Rubber 

Compounds for Milking Inflations, Bayer AG internal 

report, 1998-12-04. 

[6] N. Harmsworth, TN 1151 – Assessment of HNBR in 

Rubber Compounds for Milking Inflations, Bayer 

AG internal report, 1998-12-01. 

[7] N. Harmsworth, Rubber for Air Conditioning 

Hoses, 154 Meeting of the ACS, Rubber Division, 

Nashville, Tennessee, USA, 1998. 

Corresponding author 

Dr. H. Magg 

Bayer AG 

KA – Forschung und Entwicklung/ 

Spezialelastomere 

51368 Leverkusen

NBR in Contact with Food, Potable Water ... - Plastverarbeiter

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