5-2011

English EditionInternational Journal for Applied Science

• Personal Care • Detergents • Specialties

W. Siegert

Preservative Trends in Wet Wipes

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sisting of good raw material quality,good production hygiene and a vali-dated preservative system (1). The influ-ence of the non-woven, the productionprocess, the choice of preservatives,preservative efficacy testing, responsiblecare and hygiene measures have to betaken into consideration.The Guidelines for Good ManufacturingPractice of Cosmetic Products (GMPC)from the Council of Europe are recom-mendations for the guidance of cosmet-ic manufacturers. The microbiologicalquality management (MQM) is a part ofGMPC.

� The Need of Preservation

Microorganisms can grow on almostevery substance existing in nature andare often able to attack or even decom-

W. Siegert*

Preservative Trends in Wet Wipes

� Introduction

The wet tissues market is a growing busi-ness. Besides cleansing tissues like wettoilet paper, baby wipes or hard surfacewipes other products such as sun pro-tection lotion or deodorants are offeredas wipes. The wet tissue liquids are mostly aque-ous, the cellulose is a good nutrient, thenon-woven is always moderately conta-minated with microorganisms and the

storage temperature is nearly optimalfor microbial growth. All factors for mi-crobial attack (Fig. 1) are fulfilled. To produce microbiological faultless wettissues, an integrated microbiologicalquality management is necessary, con-

The topic of preservation is al-ways of importance to formu-lators and finished goods

marketers. Formulators are awareof the necessity to adequatelypreserve their products in order toensure product safety and be incompliance with legislation. Thistask is made much more difficultwhen marketing requirements areadded to the factors influencingthe preservative choice. Demandssuch as global approval, softpreservation, »free of…«, etc. havelimited the number of acceptableactives.

Abstract

-Fig. 1 Factors for microbial attack

GrowthOrganisms

Nutrient

TemperatureMoisture

-Fig. 2 Microbial degradation of ethanol

pose them. The biological degradationhas to be stopped for a certain period. Apreservative must be added, but for en-vironmental reasons the preservativeshould be biodegradable, too. This is noconflict; for example a concentration ofethanol between 50 and 90 % it is a gooddisinfectant, between 13 and 50 % itacts as preservative, but below 13 %ethanol will be biologically degraded toacetic acid (Fig. 2).For wet wipes the need for preservationcan be summarised as follows:

• Wet tissues are an excellent environ-ment for the growth of bacteria, yeastsand moulds.

• The demand for flushable wipes andthe increased use of natural fibresmake mould growth with its easilyvisible staining more likely.

• Environmental requirements (e.g. fromthe EU Detergent Directive) to use on-ly biodegradable detergents increasethe susceptibility of the wet tissues tomicrobial growth.

• The demands for flushable wipes andthe increased use of natural fibresmake mould growth with its easilyvisible staining more likely.

• To ensure product and consumer safe-ty, the addition of preservatives isnecessary.

� Parameters which Influence thePerformance of the Preservation

The performances of the preservativesare mainly influenced by:

• Formulation of the wet tissue liquid

• Type of nonwoven

• Quality of raw materials

• Quality of nonwoven

• Type of preservative

• Amount of liquid per tissue

• Production process

• Distribution of the wet wipe liquidonto the wipe

� Trends within Preservatives inWipes

In a study from Biocide Information Lim-ited about biocides in wipes the mostsought after properties of preservativesin wipes are:

• Broad spectrum of activity (bacteria &fungi)

• Effective over a wide pH range

• Easy to use and handle

• Compatible in raw material and for-mulation

• Cost effective at low concentrations

• Practically free from odour and colour

• Extremely low toxicity to humans

• Environmentally acceptable

• Approved for use by many regulatorybodies world-wide

� Selection of Preservation

When selecting preservatives for wet tis-sues a number of factors have to be con-sidered. Legislation is an essential issue (Fig. 3).

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-Fig. 3 Different regulations for cosmetic wipes

-Fig. 4 CIR Database

Cosmetic wipes marketed in the Euro-pean Union have to be in compliancewith the Cosmetics Directive 76/768/EEChttp://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CONSLEG:1976L0768:20090225:EN:PDF and the New CosmeticProducts Regulation 1223/2009 http://eur-lex.europa.eu/ LexUriServ/LexUriServ.do?uri=OJ:L:2009: 342:0059:0209:EN:PDF,which applies latest from 11 July 2013.The EU regulation is similar adoptedfrom many countries as e.g. the ASEANCosmetics Directive. Beside this, themost important regulation is related tothe USA. Most producers of a cosmeticproduct follow the CIR recommenda-tions (Fig. 4).Wet tissues that are claimed for cleans-ing of hard surfaces have to be preservedaccording to the Biocidal Product Direc-tive (BPD) http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CONSLEG:2003R2032:20070104:EN:PDF. The scope ofthe BPD is very wide and covers disin-fectants for home and industrial use aswell as preservatives for manufacturedand natural products.

� Difference in Regulations onthe Example of IPBC

Fig. 5 shows the different evaluations inthe EU compared to the CIR recommen-dation.The lowest use concentrations in the dif-ferent regulations are the recommendedones for international formulations.Fig. 6 shows an example of an acid basedpreservative.

� Preservative Actives in Focus

Most preservative actives are in a certainpublic discussion. In most cases scientif-ic assessment of the suspected risks is notcompleted yet. Typical examples are:

Formaldehyde/Formaldehyde-donorsDMDMH, imidazolidinyl urea, diazolidinyl urea• suspected of carcinogenic potential

Organic Halogen CompoundsIsothiazolinones, methyldibromo glutaronitrile, IPBC

• sensitisation potential

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-Fig. 5 Different evaluations in the EU compared to the CIR recommendation

-Fig. 6 Observance of different regulations

Bronopol• avoid nitrosamine formation

ParabensMethyl-, propyl-, ethyl-, butyl-,isobutylparabens suspected of• pseudo-oestrogenic and androgenic

potential• association with breast-cancer• association with skin aging

(methylparaben)

Benzyl Alcohol• listed on Annex III CPD as perfume

»allergen«

Phenoxyethanol• glycol ether discussion in France

� Possibilities for Future Developments

Most new developments are based onfollowing actives and preservative en-hancer:

Organic acids• sorbic acid• benzoic acid• dehydroacetic acid

Alcohols• benzyl alcohol• phenoxyethanol

Cationics• polyaminopropyl biguanide

Multifunctional additives• ethylhexylglycerin• glycol (butylene glycol, pentylene

glycol, etc.)

Chelating agents• EDTA• tetrasodium glutamate diacetate

� Synergistic Mixtures

To minimise the amount of preservativeactives, synergistic mixtures have beendeveloped (2-6):

• Combinations of preservative actives

• Addition of multifunctional actives toboost the antimicrobial effect

• Addition of chelating agents

• Combination of multifunctional ac-tives to achieve self-preserving sys-tems

� Synergistic Combinations ofPreservative Actives

The efficacy of a simple acid / alcoholmixture (Product A) was compared witheuxyl® K 702 (Product B) using the syn-ergistic effect described in the patentsDE4026756 and US5670160 with fol-lowing compositions:

The testing was performed using a ser-ial dilution test to compare the minimalinhibition concentrations (MIC values),a germ count reduction test to comparethe biocidal effect and also a repeatedchallenge test to evaluate the efficacyas preservative under practical condi-tions.Determination of the minimum in-hibitory concentration in serial dilutiontests produced the following values atpH 5.5:

Dilutions of product A and Product Bare prepared with sterile tap water andadjusted with sodium hydroxide to pH5.5. 50 ml portions of the end solu-tions are inoculated with 0.5 ml mi-croorganism suspension (initial micro-organism count approx. 108 cfu/ml) andstirred.

The solutions are streaked out onto tryp-tone soya agar or sabouraud-dextrose4% agar after 3, 6, 24, 48, 72 and 168hours, depending on the test organism.

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Product A Product B

Phenoxyethanol 74% 74%Benzoic acid 12% 12%Dehydroacetic acid 7% 7%Aqua 7% 4%Ethylhexylglycerin 2%Polyaminopropyl biguanide 1%

Test organisms ATCC N°

Pseudomonas aeruginosa 15442Escherichia coli 11229Candida albicans 10231Aspergillus niger 6275

Product A Product B

Species ATCC N° MIC value [%]

Gram-negative:Burkholderia cepacia 17759 0.50 0.25Enterobacter gergoviae 33028 0.75 0.06Escherichia coli 11229 0.25 0.06Klebsiella pneumoniae 4352 0.50 0.12Pseudomonas aeruginosa 15442 0.50 0.25Pseudomonas fluorescens 17397 0.25 0.06Pseudomonas putida 12633 0.50 0.12

Gram-positive:Staphylococcus aureus 6538 0.50 0.12Staphylococcus epidermidis 12228 0.50 0.06

Mould fungi:Aspergillus niger 6275 0.25 0.12Penicillium funiculosum 36839 0.25 0.12

Yeasts:Candida albicans 10231 0.25 0.12

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-Fig. 7 Reduction of microorganism for produt B in comparison to product A

The cultures are incubated for 48 hoursat 37 °C, except in the case of Aspergillusniger, which is incubated for 72 hours at25 – 27 °C. The evaluation is made on thebasis of a semi-quantitative assessmentof the microbial growth of the streaks.In Fig. 7, the microorganism reductionachieved for product B in comparison toproduct A at pH 5.5 as a function of thecontact time and use-concentration ispresented for the various test organisms. Product B has a more efficient germ re-duction, as evidenced by the greater killrate at earlier time readings. This is es-pecially useful for pre-contaminatedraw materials, such as the productionwater or the non-woven, as they may bemore easily sanitised with product B.

� The Importance of pH Control

The pH value is a critical control point forthe efficacy of preservatives based onorganic acids. The pH value has not onlybe checked in the wet tissue liquid, butin a liquid squeezed from the tissue. Astypical example a wet tissue liquid pre-served with 1% phenoxyethanol, benzylalcohol, potassium sorbate mixture(euxyl® K 700) is demonstrated in Table 1.Particularly Airlaid showed a severe in-fluence of the pH.Phenoxyethanol is a familiar and wellaccepted cosmetic preservative. The ad-dition of ethylhexylglycerin enhancesthe efficacy of phenoxyethanol (euxyl®

PE 9010). The innovative, multifunction-al additive affects the interfacial tensionat the cell membrane of microorganisms,improving the preservative activity of

phenoxyethanol. Due to its water solu-bility it can be used in clear solutions,which is often a problem with parabenbased preservatives. Several hundred ef-

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Wet wipe liquid itself Wet wipe liquid squeezed from the tissue

Immediately after After one month Immediately after After one monthproduction storage production storagepH 5.1 pH 5.1 pH 5.5 pH 5.5

Table 1 Influence of the nonwoven on the pH value

Phase INCI Name Function % w/w

A Water (Aqua) 43.00B Hydroxyethylacrylate (and) sodium Thickener, emulsifier 0.60

acryloyldimethyl taurate copolymer (and) squalane (and) polysorbate 60Isopropyl palmitate Binder, emollient, solvent 5.00Mineral oil 5.00

C Water (Aqua) q.s.D Sodium palmitoyl proline (and) Lipo-amino soothing 0.50

nymphaea alba flower extract agentTocopheryl acetate Antioxidant 0.10Fragrance Fragrance 0.10Phenoxyethanol/ethylhexyl- Preservative 1.00glycerin (9:1)

100.00250% of solution based on the dry weight of the wipe for the substrate SPUNLACE viscose/polyester65/35 55 g/m2

Table 2 Example of a wet wipe formulation passing challenge testing

-Fig. 8 Effect of EDTA on combination phenoxyethanol/ethylhexylglycerin

ficacy tests in different leave-on-formu-lations proved the mixture of phenoxy-ethanol / ethylhexylglycerin to be farmore effective than phenoxyethanolalone and to be comparable with tradi-tional phenoxyethanol / paraben mix-tures (5). Table 2 shows an example fora wipe formulation.

� Addition of Chelating Agents

Chelating agents can enhance the effi-cacy of »soft preservatives«. Fig. 8 showsthe effect of EDTA on the combinationphenoxyethanol / ethylhexylglycerin inthe before described germ count reduc-tion test.Glutamic acid, N,N-diacetic acid, tetra-sodium salt (GLDA) (Dissolvine® GL) →INCI Tetrasodium Dicarboxymethyl Glu-tamate, a readily biodegradable chelat-ing agent, that can be used as alterna-tive for EDTA. Especially when used to-gether with citric acid GLDA shows abetter effect as EDTA (Fig. 9).

� Self-preserving Systems

Self-preserving technology is composedof six »hurdles«:

1. Good manufacturing practice (GMP)I. Cold or hot aseptic fillingII. Clean-room technology

2. Hygiene-compliant packaging

3. Emulsion form

4. Water activity

5. pH control

6. Multifunctional ingredients withbiostatic effect.

Fig. 10 shows antimicrobial ingredientsused in »self-preserving« skin care prod-ucts. Ethylhexylglycerin enhances the an-timicrobial efficacy of these ingredients.An optimised combination is 70% Oc-tane-1,2-diol with 30% 3[(2-Ethylhexyl)oxy]1,2-propandiol → INCI Caprylyl Gly-col / Ethylhexylglycerin (sensiva® SC 10),it is suitable to formulate wet wipeswithout classical preservatives.

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-Fig. 9 Effect of GLDA on a combination phenoxyethanol/ethylhexylglycerin

-Fig. 10 Example of antimicrobial ingredients used in »self-preserving« skin care products

� General Technical Aspects

Solution versus EmulsionThe change from solutions to emulsionsis changing various aspects:

• Solutions must be preserved withwater-soluble actives

• Good physical stability

• Easy to produce

• Only one interface ==> liquid / solid

• Emulsions can be preserved withpartly water soluble systems

• Stability must be checked carefully

• One more interface ==> oil / water

• Migration of preservatives into the oilphase might occur

• Special equipment necessary

• Single layer wetting is preferred.

The Influence of the Production ProcessThe main parameters influencing the mi-crobial stability are listed (7):

• Variation in weight of impregnated

wipes dependent on the method ofmanufacture.

• An impregnation of the nonwovenprior to conversion into the finishedstack of wipes provides a more uni-form product.

• Prevent a discharge of actives from animmersion bath – especially cationiccompounds are adsorbed on the non-woven.

• Stack impregnation leads to a lessuniform distribution of the wet wipeliquid.

• The ingredients of the wet tissue liq-uid can be separated on the tissue likein a thin layer chromatography.

• Depending on the dosing system youcan get a non-uniform impregnationleading to microbiological spoilage.

• Apply the wet wipe liquid uniformlywith a shower from the top.

The influence of using sustainable/ natural sourcesNatural raw materials lead to changes inthe demand for microbial protection:

• Biodegradable ingredients need better protection

e.g. sugar-based surfactants

• Flushable wipes need special attention

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• Natural fibres, like cotton or cellulos-es, are changing the typical product-spoiling microorganisms

e.g. Trichoderma viride is a typicalcellulose-degrading mould

• challenge testing has to be adapted

• Natural fibres might carry a highermicrobial load.

� Summary

Safety and care for consumer and prod-ucts are legally demanded. A cosmeticproduct should not damage humanhealth.The finished product has to be stabilisedagainst microbial growth.

Market Situation• Limited number of preservative ac-

tives

• Almost every active under public dis-cussion

New concepts in preservation required• Formulators are looking for new al-

ternatives to be free of molecules un-der discussion

• Preservation must be part of new for-mulation concepts, not an after-thought

• Focus on antimicrobial stabilisers

• substances not listed on any positivelist for preservatives (e.g. Europe,Japan)

• claims like »free of harsh preservative«,»paraben-free« are achievable

References

(1) Karl-Heinz Diehl, The key to microbiologicalquality assurance SÖFW-Journal, 03-1992

(2) K.Weber, J.Siebert: Organic acids, mild cosmet-ic preservatives, low sensitation potential,comparative tests, colour stability SÖFW-Jour-nal, 06-2003

(3) W. Siegert, The Benefit of Using SynergisticMixtures of Preservatives SÖFW-Journal, 12-2006

(4) W. Beilfuß, M. Leschke, K. Weber, A New Con-cept to Boost the Preservative Efficacy of Phe-noxyethanol, SÖFW-Journal, 11-2005

(5) M. Leschke, S. Wüstermann, A Reliable Alter-native for Traditional Preservative Systems,SÖFW-Journal, 04-2006

(6) W. Siegert, Can New Biodegradable Complex-ing Agents Replace Tetrasodium EDTA to BoostPreservatives? SÖFW-Journal, 1/2-2008

(7) W. Siegert, Microbiological quality manage-ment for the production of wet-wipes, House-hold and Personal Care Today, 2-2008

* Author’s address:Wolfgang Siegert

Schülke & Mayr GmbH22840 Norderstedt

GermanyEmail: Wolfgang.Siegert@schuelke.com

�