Atmospheric pressure plasma spraying of silane-based coatings targeting whey protein fouling and bacterial adhesion management

International audienc

Biomimetic nanostructured surfaces for antifouling in dairy processing

In dairy pasteurization equipment, fouling is an ongoing problem. Indeed, when heated, milk and its derivatives generate mineral and proteinaceous deposits on stainless steel walls. This heat-induced fouling impairs the process through the addition of an increasing thermal resistance to the system. Deposits are also a threat to food safety as they provide micro-organisms with good settlement opportunities. As a consequence, fouling mitigating strategies are needed. Biomimetic surfaces in particular, inspired from the surface morphology of lotus leaf could be considered for their self-cleaning abilities. Its dual-scale roughness (i.e. a micro roughness supporpsed by nanoscale roughness) allows for the composite Cassie-Baxter wetting state due to air remaining trapped between the liquid and the solid surface. As a result, those surfaces possess very high contact angles (typically higher than 150o) and very low contact angle hysteresis (typically less than 10°). However, a major limitation of this type of surface is the difficulty to maintain a stable Cassie-Baxter state over time: depending on the experimental conditions (pressure, vibration, evaporation, surface defect) the liquid penetrates sooner or later into the structures degrading their anti-biofouling properties. To overcome this limitation, it has been proposed to impregnate the textured surface by a liquid of low surface tension (usually an inert oil not miscible with water). This led to SLIPS surfaces (Slippery Liquid-Infused Porous Surfaces). Even if these surfaces present low contact angle, their hysteresis is also almost null whatever the experimental conditions leading to antifouling properties [1].   This work aims at designing Cassie-Baxter and SLIPS surfaces and test them in dairy processing conditions to assess their antifouling properties. To this end, 316L stainless steel surfaces were texturized via femtosecond laser irradiation to generate dual-scale (cauliflower-like) structures [2]. Some of the fabricated surfaces underwent further modifications: (i) silanization with perfluorodecyltrichloro-silane or (ii) silanization followed by impregnation with a fluorinated oil to create Slippery Liquid Infused Porous Surfaces (SLIPS) [3]. All surfaces were tested for their fouling properties in a pilot pasteurization equipement (UMET-PIHM, Institut National de la Recherche Agronomique, Villeneuve d'Ascq) [4] allowing to mimick industrial conditions of the pasteurization process. Thorough characterizations were performed on the surfaces before and after fouling, to (i) establish clearly their surface properties (wettability, surface energy, roughness) and (ii) to investigate the impact of the different surface properties on heat-induced dairy fouling compared to a native stainless steel as reference. A wide range of analytical tools such as Goniometry, cross-section Electron Probe Micro-Analysis X-ray mappings, and Scanning Electron Microscopy were implemented to this end. Outstanding results were obtained regarding antifouling properties of dual-scaled roughness surfaces in dairy processing conditions, with a reduction of fouling by more than 90% in weight. References [1] T.-S. Wong, S. H. Kang, S. K. Y. Tang, E. Smythe, B. D. Hatton, A. Grinthal, and J. Aizenberg, ?Bioinspired self-repairing slippery surfaces with pressure-stable omniphobicity,? Nature, vol. 477, pp. 443?447, 2011. [2] A.-M. Kietzig, S. G. Hatzikiriakos, and P. Englezos, ?Patterned Superhydrophobic Metallic Surfaces,? Langmuir, vol. 25, no. 8, pp. 4821?4827, 2009. [3] A. K. Epstein, T.-S. Wong, R. A. Belisle, E. M. Boggs, and J. Aizenberg, ?Liquid-infused structured surfaces with exceptional anti-biofouling performance,? PNAS, vol. 109, no. 33, pp. 13182?13187, 2012. [4] M. Jimenez, G. Delaplace, N. Nuns, S. Bellayer, D. Deresmes, G. Ronse, G. Alogaili, M. Collinet-Fressancourt, and M. Traisnel, ?Toward the understanding of the interfacial dairy fouling deposition and growth mechanisms at a stainless steel surface: A multiscale approach,? J. Colloid an interface Sci., vol. 404, pp. 192?200, 2013

Encrassement laitier sur acier inoxydable et design de surfaces anti-encrassantes

Les traitements thermiques des produits laitiers induisent des phénomènes d’encrassement des échangeurs thermiques, et donc des nettoyages réguliers, qui alourdissent les coûts de production ainsi que l’impact environnemental des procédés. Il est donc important de comprendre ces phénomènes d’encrassement et de développer des stratégies pour les limiter. Cette thèse vise à étudier l’impact des variations des propriétés de surface sur l’encrassement laitier, mettre au point des surfaces anti-encrassantes bioinspirées innovantes et comprendre le mode d’action de ces surfaces. . Il a été démontré que les propriétés de surface d’un substrat sont cruciales pour contrôler l’encrassement : la diminution conjointe de la rugosité et de l’énergie de surface sont favorables à la réduction de l’encrassement. Suivant ce constat, d’excellentes propriétés encrassantes ont été obtenues suite à la mise au point de trois surfaces bioinspirées (surfaces lubrifiées « SLIPS », revêtements par plasma atmosphérique et revêtements amphiphiles). Les revêtements amphiphiles ont obtenu sans conteste les meilleurs résultats. Ils préviennent non seulement totalement l’encrassement mais également l’adhésion de bactéries pathogènes. Ce type de revêtement pourrait donc permettre de réaliser des économies non négligeables, non seulement en termes de coût de nettoyage des installations industrielles, mais également en termes d’impact environnemental des procédés. Afin de quantifier l’impact de la modification de surface sur l’empreinte environnementale de la pasteurisation, une étude d’Analyse du Cycle de Vie a été menée et a permis d’établir que l’utilisation d’un revêtement anti-encrassant permettrait de réduire l’impact environnemental d’un procédé de pasteurisation de plus de 70%.Fouling is an ongoing issue which burdens the cost of dairy thermal processes as well as their environmental impact. Understanding the fouling phenomena and finding mitigation solutions is therefore of high interest. Consequently, this works aims at: (i) studying the impact of surface properties variation on dairy fouling and (ii) designing and characterizing the mechanisms of action of novel biomimetic antifouling surfaces. It was demonstrated that surface properties were crucial for fouling mitigation, low roughness and low surface energy being the most favorable conditions for fouling reduction. In a second time, three types of biomimetic surfaces, namely slippery liquid infused surfaces (SLIPS), nano-rough atmospheric plasma coatings and amphiphilic environment-responsive coatings were proven efficient against isothermal dairy fouling. The amphiphilic coatings unquestionably presented the best antifouling performances as they totally prevented fouling development as well as pathogenic bacteria adhesion. Such surfaces should allow for significant savings in cleaning costs and environmental impact through the adaptation of the cleaning procedures. In order to assess the real effect of the antifouling coatings on the footprint of the pasteurization process, a Life Cycle Assessment study was carried out. It was demonstrated that the use of such an antifouling coating could lead to the reduction of the environmental impact of a pasteurization process by more than 70%

Investigating the Effect of an Antifouling Surface Modification on the Environmental Impact of a Pasteurization Process: An LCA Study

International audienc

Graphite-based composites for whey protein fouling and bacterial adhesion management

International audienceDairy industries are burdened by fouling phenomena that increase costs and environmental impacts of thermal processes. One remedial solution could be to replace stainless-steel equipment by other materials less prone to fouling. This work studied the fouling behaviour and hygienic features of two hydrophobic and non-polar commercial graphite-based composites (Graphilor (R) XC and XTH) that were exposed to isothermal whey protein fouling in an industrial pasteurisation unit and to foodborne pathogenic bacterial strains, namely Staphylococcus aureus, Listeria monocytogenes and Salmonella enterica. Both composites exhibited impressive fouling-release properties: a simple 20 min water rinse was enough to remove all dairy deposit after 1.5 h of pasteurisation, as opposed to usual heavy clean-in-place procedures. The composites also showed a significant effect on bacterial adhesion, exhibiting lower cell counts than stainless-steel surfaces. These results suggest that graphite-based materials might successfully replace stainless steel as equipment material to reduce fouling in dairy fouling industries

Antifouling amphiphilic silicone coatings for dairy fouling mitigation on stainless steel

International audiencePasteurization of dairy products is plagued by fouling, which induces significant economic, environmental and microbiological safety concerns. Herein, an amphiphilic silicone coating was evaluated for its efficacy against fouling by a model dairy fluid in a pilot pasteurizer and against foodborne bacterial adhesion. The coating was formed by modifying an RTV silicone with a PEO-silane amphiphile comprised of a PEO segment and flexible siloxane tether ([(EtO)(3)Si-(CH2)(2)-oligodimethylsiloxane(m)-block-(OCH2CH2)(n)-OCH3]). Contact angle analysis of the coating revealed that the PEO segments were able to migrate to the aqueous interface. The PEO-modified silicone coating applied to pretreated stainless steel was exceptionally resistant to fouling. After five cycles of pasteurization, these coated substrata were subjected to a standard clean-in-place process and exhibited a minor reduction in fouling resistance in subsequent tests. However, the lack of fouling prior to cleaning indicates that harsh cleaning is not necessary. PEO-modified silicone coatings also showed exceptional resistance to adhesion by foodborne pathogenic bacteria

Surface engineering of stainless steel for dairy fouling management

International audienc

Antifouling biomimetic liquid-infused stainless steel: application to rairy industrial processing

International audienceFouling is a widespread and costly issue, faced by all food-processing industries. Particularly, in the dairy sector, where thermal treatments are mandatory to ensure product safety, heat-induced fouling represents up to 80% of the total production costs. Significant environmental impacts, due the massive consumption of water and energy, are also to deplore. Fouling control solutions are thus desperately needed, as they would lead to substantial financial gains as well as tremendous progress toward eco-responsible processes. This work aims at presenting a novel and very promising dairy fouling-mitigation strategy, inspired by nature, and to test its antifouling performances in real industrial conditions. Slippery liquid-infused surfaces were successfully designed directly on food grade stainless steel, via femtosecond laser ablation, followed by fluorosilanization and impregnation with an inert perfluorinated oil. Resulting hydrophobic surfaces (water contact angle of 112 degrees) exhibited an extremely slippery nature (contact angle hysteresis of 0.6 degrees). Outstanding fouling-release performances were obtained for these liquid-infused surfaces as absolutely no trace of dairy deposit was found after 90 min of pasteurization test in pilot-scale equipment followed by a short water rinse

Surface engineering of stainless steel for dairy fouling management

International audienceThis oral presentation sums up different approaches explored during the past years to manage dairy fouling over stainless steel substrates