Heat Exchanger Fouling and Cleaning – 2011 June , 2011 Influence of soluble polysaccharides on the adherence of particulate soils Y. Touré, P.G. Rouxhet, C.C. Dupont-Gillain and M. Sindic

II- Experimental procedures Presentation outline III- Results and discussion I- Introduction IV- Conclusion

I- Introduction Who is concerned ? Particulate soils Microorganisms Why ? The cleaning efficiency influences: final quality of the products, absence of cross-contaminations, batch integrity. Background

Understanding the interactions in order to : reduce equipment fouling, reduce interruptions of production process for cleaning, improve the efficiency of cleaning and disinfection, develop easy-to-clean surfaces. I- Introduction Background

Study of soluble macromolecules associated with a suspension of particles: may give practical information on the interaction of surface nature and particle surface properties may give an insight into the physico-chemical mechanisms involved may clarify the role of the soluble macromolecules involved in particles adherence may open the way to designing and evaluating easy-to-clean surfaces I- Introduction Background

Assess the influence of soluble polysaccharides on particulate soils adhesion Improve: understanding of mechanisms affecting soiling cleanability I- Introduction Objectives

II- Experimental procedures

Material Model of soluble polysaccharide: dextran from Leuconostoc mesenteroides; PM: Da Model of surfaces : glass (hydrophilic), polystyrene (hydrophobic) Model of particulate soils : quartz (10-30µm)

Surfaces PolystyreneGlass Immersion dextran 80mg/l, 1h Immersion (RBS50 2% à 50°C), 10 min Sonication, 10min + MQ rinse Washing, alcohol + immersion, 30 min + MQ rinse Immersion, piranha mixture 10min + MQ rinse Fouling Drying, nitrogen Redrying, nitrogen Conditioned ? No Yes Substrate pretreatment

Yes Quartz particles (10-30µm) Suspension à 15% without dextran) Suspension (15%) with dextran (80 mg/l) 3 cycles, washing-decantation (MQ) – supernatant elimination surfaces pretreated fouling Suspension (15%) reconstitution Gentle agitation Storage, 72 h, 4°C Dextran present ? Yes or no Suspension (15%) with dextran and washed Soil preparation and treatment

Pretreated surfaces Soiling Particulate soils Soiling procedure

FLOW Radial-flow cell (90 ; 190 ; 390 ml/min) Drying, 30 min in dark, 19 ± 5°C, 39% H Picture I Cleaning method

r

Excel Drying after cleaning Pretreated surfaces Drying, 30 min in dark, 19 ± 5°C, 39% H OK ? Soiling LUCIA Result Particulate soils Yes No Radial-flow cell (90 ; 190 ; 390 ml/min) Picture II MATLAB picture I Data processing

r Critical detachment radius

Methods of characterization Contact angle Scanning electron microscopy (SEM) Individual size measurements Size measurements on a large population

III- Results and discussion

Wetting properties Contact angles on the substrates in the indicated state Glass ≠ Polystyrene, whatever substrate treatment

Glass Polystyrene Size and shape of adhering aggregates

Histograms (% in number) of the lateral size of the soiling entities formed on glass and polystyrene (equivalent diameter of the contour) Height of the soiling entities formed on glass and polystyrene plotted as a function of their lateral dimension (equivalent diameter of the contour) Height and lateral size, larger on polystyrene than glass No distinction between samples involving the same substrate NB: Larger population, density glass: 51±4 drops/mm 2, polystyrene: 33±4 drops/mm 2 D50% were: 30µm on glass, 55µm on polystyrene

Adhering much more firmly on glass compared to polystyrene Substrate influence: polystyrene with dextran increased slightly the adherence, while the opposite was observed with glass Influence of particles conditioning: no effect on adherence, whatever substrate and particles are conditioned or not with dextran. Critical detachment radius Bare surfacessurfaces with dextran Quartz without dexran Quartz with dextran Quartz with dextran and whased

IV- Conclusion Surface hydrophobicity influences aggregates morphology and adherence. study of wider range of concentrations is in progress Presence of dextrane (80mg/L) : - Conditioning polystyrene substrate: slightly increases the adherence - Conditioning glass substrate: slightly decreases - Conditioning powder…presence in the suspension: no effect

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