Measurement of Water Contract Angle on Ceramic Tiles Treated with Silicone Emulsions. Audrey Wipret Dow Corning S.A.

Transcription

1 Measurement of Water Contract Angle on Ceramic Tiles Treated with Silicone Emulsions Audrey Wipret Dow Corning S.A. Seneffe, Belgium

2 Because today s consumers have less time to clean their homes, they look for cleaning products that combine convenience with performance. Countertops are the surface consumers feel pressed to clean most frequently, followed closely by floors and sinks.1 Bathtubs,toilets and appliances also have surfaces that demand regular care. To meet consumers purchasing demands, the household care market is turning toward stain protection for hard surfaces, especially in bath and toilet care applications. In addition to the initial cleaning process, one way to prevent soil deposition and stainsonthese ceramic surfaces and keep them cleaner longer is to modify their wettability by making them hydrophobic. A hydrophobic material causes water to bead on its surface, and the most common method of quantifying the water beading ability of a solid surface is by contact angle measurements. In this paper, the contact angle of distilled water on silicone-treated ceramic tile was measured for a variety of silicone materials, and results show a range of hydrophobicity. These evaluations may serve as an initial screening tool for product formulators, helping them shorten development time while also targeting optimal properties for specific hard surface care products. Why Silicones? Silicones are used in a variety of coatings and surface treatments throughout industry to aid spreading and wetting and to provide water resistance or barrier properties. Variations on these applications suggest that creative formulators might transfer useful surface modification techniques to household hard surface care. In the textile industry, for example, the wetting and spreading properties of silicones can be used to advantage in coatings that are resistant to soil, stains or water. Surface-active agents such as silicones reduce the surface energy of a formulation. Compared to solvent-based systems, water-based coatings have much higher surface tension, which results from water having a surface tension of 7.4 mn/m. For this reason, water-based coatings have poor substrate wetting capabilities compared to solvent-based systems. Most cleaning products are water-based systems, in part to maintain reasonable costs for the consumer. They also are easier to formulate and reflect the general trend away from solventbased systems for environmental and health reasons. By incorporating the appropriate additive, the surface tension of a cleaning product can be modified to improve substrate wetting. Additives of this type lower surface tension, allowing the cleaner to wet out over the substrate. Cleaning products not only need to uniformly wet the surface to be cleaned, but in some cases are called upon to modify the surface for example, to make it hydrophobic against soil. Silicones often act as multifunctional additives in product formulations. In addition to making a surface hydrophobic to give it water resistance or even barrier properties, silicone additives can modify surfaces in other ways. Some, like Dow Corning IE-6683 Water Repellent Emulsion, are useful for making porous surfaces hydrophobic. Originally developed for the construction industry, this silicone material may also have surface modification applications for household products. For example, even sealed grout can be susceptible to soil and staining, and a cleaning product that would impart renewed hydrophobicity with each cleaning could significantly aid its appearance. This material can be used as supplied, diluted with water or incorporated into other formulations. Because silicones have many useful properties in cleaning applications, this study focused on identifying materials that might be used as additives to modify surfaces and improve the performance of hard surface care formulations.

3 Measuring Contact Angles Contact angle (Ø) is defined as the angle between the baseline of a drop (solid surface) and the tangent to its surface at the point of contact of the two (Figure 1). Various techniques are used for measuring contact angle, the most common being sessile drop measurement. This approach involves direct measurement of contact angle from a drop of liquid resting on a flat surface of the solid with a goniometer scale, or from a photograph of the drop profile. Evaluating Silicone Emulsions Water-based household cleaning formulations can contain anionic, nonionic and/or cationic surfactants. Because of the inherent incompatibility of silicone with water, silicone emulsions rather than neat silicones were selected to facilitate their incorporation into the product. In addition, to avoid silicone emulsion instability in the final product formulation, nonionic silicone emulsions were preferably screened. The silicone functionalities evaluated for their potential hydrophobic benefits on ceramic tiles include: Linear polydimethylsiloxane H 3 C Si O Si O Si CH n 3 Figure 1. Sessile drop method for contact angle measurement Table 1 shows the water beading ability of a surface depending on contact angle. The higher the contact angle, the poorer the wetting and the more hydrophobic the surface. Table 1. Wetting and Hydrophobicity Based on Contact Angle Contact Angle Wetting Hydrophobicity θ = 180º No Outstanding 180º> θ > 90º Poor Good θ = 90º Moderate Moderate 90º > θ > 0º Good Poor θ = 0 Spontaneous None Amino-functional polydimethylsiloxane R' Si O Si O x Si O Si R' y R R = -(CH ) 3 NH or -CH CH( )CH NH(CH ) NH R' = - or -OH Amido-functional polydimethylsiloxane R' Si O Si O x Si O Si R' y R R = -CH CH( )CH NH(CH ) NHC(O)(CH ) 3 OH R' = -

4 Silane R'O OR' Si OR' R R, R : alkyl groups R O groups: trans-esterify or hydrolyze in the presence of ROH or water; permit control of stability, adhesion to inorganic media R groups: stable to trans-esterification or hydrolysis; choice of R permits reaction with a wide range of organic systems Epoxy-functional silicone H 3 C Si O Si O x Si O Si CH y 3 R R, R : alkyl groups Emulsions of silicones with differing molecular weights were chosen according to the theory that greater molecular weight might improve deposition on the surface. Molecular weight influences rate of migration to the interface with the substrate. Increased molecular weight typically leads to increased viscosity, but may also give greater substantivity to surfaces and improved shine. Emulsions containing aminofunctional and amido-functional silicones also were tested because these functionalities are known to improve deposition on some surfaces. One silane was included in the study. These monomeric silicon compounds have four substituent groups attached to the silicon atom. The substituent groups can be almost any combination of nonreactive, inorganically reactive, or organically reactive groups. In the case of alkyl silanes, the organo-reactive groups (CH3OH) improve silicone adhesion to surfaces, whereas alkyl groups impart water repellency. An epoxy-functional silicone polymer also was evaluated. These polymers could be very O R' reactive in the presence of adequate reactant. The epoxide cleavage occurs under mild conditions; alcohol groups are formed and can further undergo dehydration when combined with the hydroxyl groups available in some surface materials. Microemulsions (particles <100 nm in diameter) as well as macroemulsions (particles >100 nm in diameter) were tested. In general, microemulsions would be expected to deposit more easily on surfaces, but the degree of deposition ultimately depends on the formulation of the final product. Microemulsions have another advantage: because of their small particle size, many can be used to formulate clear products, which consumers may perceive as being more natural. Table summarizes the characteristics of the silicone emulsions evaluated in this study. Experimental Procedure Ceramic tile treatment. Ceramic tiles were prepared according to the following guidelines. 1. Prewash This step was performed to remove dirt from the tiles. The tiles were manually cleaned with Dreft liquid laundry detergent and water. They were dried with paper towels and wiped with paper soaked with isopropyl alcohol.. Treatment Solutions of % and % active of silicone were prepared by diluting the silicone emulsion. The ceramic tiles were dipped into the treatment solution and left for 30 minutes, after which they were dried at room temperature for one hour. The soaking period was intended to represent typical cleaning conditions in which the product is left on surface to maximize cleaning before rinsing. Dreft is a product of Procter & Gamble, Cincinnati, OH

5 Table. Silicone Emulsions Evaluated Material Emulsion Type Surfactant Type a Internal Polymer b Silicone Content (%) XIAMETER MEM-186 Emulsion Micro A PDMS; low MW XIAMETER MEM-1473 Emulsion Macro N PDMS; 30 cst 0 Dow Corning HMW 00 Nonionic Emulsion Macro N PDMS; > 10,000,000 cst 60 XIAMETER MEM-8663 Emulsion Micro N Amino; low MW 1 XIAMETER MEM-803 Emulsion Micro N Amino; low MW 18 XIAMETER MEM-8177 Emulsion Micro N Amino; 1,000 cst 14 Dow Corning IE-6683 Water Repellent Emulsion Macro N Silane 40 XIAMETER MEM-871 Emulsion Macro N Epoxy 40 a A = anionic, N = nonionic b PDMS = polydimethylsiloxane Contact angle measures. Contact angle measurements can range from low to high and can be interpreted differently depending on specific applications. For example, some may indicate a more hydrophilic surface, which when considering cleaning, is important to thorough wetting. In contrast, at the other end of the spectrum is hydrophobicity, the property that helps keep stains from depositing on thesurface. A volume drop tensiometer (Tracker; I.T. Concept, France) was used to measure contact angles. Distilled water was used to form the drops, and drop volume was approximately 0.1 ml. The contact angle measurement was taken 30 seconds after the drop deposition on the ceramic tile. To determine if the silicone deposition was homogeneous, contact angle measurements were taken on five regions of the ceramic tile, and the average value was calculated. To check the repeatability of the results, for the same level of determined silicone emulsion, the test was repeated at least twice. The first time, on the first ceramic tile, contact angle measurements were taken on five regions of the tile. On the second ceramic tile, contact angle measurements were also taken on five regions. Results. Table 3 shows the average contact angle values obtained on ceramic tiles treated with the silicone emulsions. The more hydrophobic the surface, the higher the contact angle. A contact angle between 0 and 90º indicates poor hydrophobicity. If greater than 90º, hydrophobicity will be moderate to good, indicating the silicone has a hydrophobic effect on the surface.

6 Table 3. Hydrophobicity Based on Treatment Type Test Material Treatment Type a Active (%) Ave Contact Angle Hydrophobicity None (Control) 4º Poor XIAMETER MEM-186 Emulsion PDMS; low MW < 0º Poor XIAMETER MEM-1473 Emulsion PDMS; medium MW < 0º Poor Dow Corning HMW 00 Nonionic Emulsion PDMS; very high MW < 0º < 0º Poor XIAMETER MEM-8663 Emulsion Amino 9º 99º Moderate to good XIAMETER MEM-8177 Emulsion Amino 101º 104º Good XIAMETER MEM-803 Emulsion Amido 96º 96º Good Dow Corning IE-6683 Water Repellent Emulsion Silane 110º 10º Good XIAMETER MEM-871 Emulsion Epoxy < 0º Poor a PDMS = polydimethylsiloxane Nonionic emulsions based on volatile and linear polydimethylsiloxane did not provide hydrophobicity to the ceramic tiles, even if the molecular weight was increased. The epoxyfunctional nonionic emulsion did not appear to impart water beading to the ceramic tile. Amino-functional and amido-functional polydimethylsiloxane nonionic emulsions provided moderate to good hydrophobicity to the ceramic tiles. This was due to the amino andamido groups, which are known to improve adhesion on the surface. A level of % silicone active appeared to be sufficient to treat the surface; increasing the active level to % did not appear to improve its hydrophobic properties. Nonetheless, some decrease of gloss was observed on some regions of the ceramic tiles after the silicone treatment. The silane emulsion imparted the best hydrophobic properties to the ceramic tiles. A level of % silicone active resulted in a contact angle of 10. Figure shows a side view of water beading on an untreated ceramic tile (left) and a tile treated with the silane emulsion (right).

7 also simplifies manufacturing processes, which require only cold processing via simple pouring and mixing. Figure. Side view of untreated tile (left) and tile treated with silane emulsion (right). Figure 3 shows the same tiles from above, with the untreated tile on the left and the silanetreated tile on the right. Conclusions The silicone emulsions described in this paper are versatile in their functionality, offering a flexible starting point for screening materials and later fine tuning of systems for specific formulations. While the contact angle results of this study focus on specific silicone emulsions, results can be expected to differ in fully-formulated products based on specific ingredients and use levels. By incorporating appropriate silicone additives, cleaning products may be formulated to modify surfaces, resulting in overall improved cleaning performance and stain resistance. Figure 3. Overhead view of untreated tile (left) and silane-treated tile (right). However, it is possible that use levels as low as 0. to 1% active silicone may provide the necessary hydrophobicity, based on the use of these materials in other applications such as textile treatments. Even so, a % use level indicates cost effectiveness of the material and potential for competitive advantage in an effective formulation. Because the silicone materials described in this paper are delivered in emulsion form, they are compatible with a variety of materials used in household cleaning products. Their emulsion form

8 Two brands to serve you Whether you need industry-leading innovation or greater cost efficiency, Dow Corning can help. Dow Corning brand solutions are dedicated to meeting your needs for specialty materials, collaborative problem-solving and innovation support. Learn how we can help you at dowcorning.com. HANDLING PRECAUTIONS PRODUCT SAFETY INFORMATION REQUIRED FOR SAFE USE IS NOT INCLUDED IN THIS DOCUMENT. BEFORE HANDLING, READ PRODUCT AND MATERIAL SAFETY DATA SHEETS AND CONTAINER LABELS FOR SAFE USE, PHYSICAL AND HEALTH HAZARD INFORMATION. THE MATERIAL SAFETY DATA SHEET IS AVAILABLE ON THE DOW CORNING WEBSITE AT DOWCORNING.COM, OR FROM YOUR DOW CORNING SALES APPLICATION ENGINEER, OR DISTRIBUTOR, OR BY CALLING DOW CORNING CUSTOMER SERVICE. LIMITED WARRANTY INFORMATION PLEASE READ CAREFULLY The information contained herein is offered in good faith and is believed to be accurate. However, because conditions and methods of use of our products are beyond our control, this information should not be used in substitution for customer s tests to ensure that our products are safe, effective, and fully satisfactory for the intended end use. Suggestions of use shall not be taken as inducements to infringe any patent. Dow Corning s sole warranty is that our products will meet the sales specifications in effect at the time of shipment. Your exclusive remedy for breach of such warranty is limited to refund of purchase price or replacement of any product shown to be other than as warranted. DOW CORNING SPECIFICALLY DISCLAIMS ANY OTHER EXPRESS OR IMPLIED WAR- RANTY OF FITNESS FOR A PARTICULAR PURPOSE OR MERCHANTABILITY. DOW CORNING DISCLAIMS LIABILITY FOR ANY INCIDENTAL OR CONSEQUENTIAL DAMAGES. Dow Corning is a registered trademark of Dow Corning Corporation. XIAMETER is a registered trademark of Dow Corning Corporation. We help you invent the future is a trademark of Dow Corning Corporation Dow Corning Corporation. All rights reserved. Printed in USA Form No.7-18A-01