Applications of Redispersible Powders

The building/construction industry is the main industry for redispersible powders. Over the years the usage of dry mortar technology has been developed dramatically and modernized the way mortars are being used on a job-site. The invention of redispersible powders enabled the industry for the first time to produce pre-packed, polymer modified building materials that needed only the addition of water before application. These materials, known as dry mortar mixes guarantee defined and consistent performance of construction materials. 

In the past up until to the 1950s mortars were exclusively used and apphed as job-site mixed mortars, where the mineral binder (mostly cement) and the aggregates (mostly silica sand) were transported separately to the job-site. The aggregates and the mineral binders were then mixed together by hand in the appropriate ratio and were gauged with water in order to obtain the fresh mortar ready to apply. 

The job-site mix mortar technology is not able to meet adequately all these requirements. As a practical consequence, the development of the modern construction and building chemical industry in the countries of the West from the 1960s onwards was influenced mainly by two important trends, which can be seen nowadays in the whole world. First there was a replacement of the job-site mixed mortars by premixed and pre-packed dry mix mortars, which are more and more applied with machines. Secondly mortars started to be modified with polymer binders in order to improve the product quality and to meet the requirements of the modem building industry. As a consequence the two-pack systems (mortar + dispersion) as well as 

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Lutz, H. and Hahner, C. (2002) Applications of redispersible powders. In D. Urban and K. Takamura (eds). Polymer Dispersions and Their Industrial Applications. WUey-VCH, Weinheim. 

The area of self-leveling underiayments (SLU) is out of a technical perspective probably the most complex one if it comes to applications of redispersible powders. On a given uneven substrate (i.e. screed or surface to be refurbished), self-leveling mortars have to provide a suitable, smooth and solid substrate in order to apply all kind of flooring materials Kke carpets, wood parquet, PVC, tiles etc. Self-levebng underiayments should be applicable in an easy and efficient manner, even for large areas. 

Standard ceramic tQe adhesives of good quality need approximately 1.5 to 3 % of redispersible powder on total dry mix. They meet the new European Norm for tile adhesives (mostly only Cl level) and pass also the ANSI specification 118.4and 118.11. Larger formatted tiles can be apphed with these materials over porous or less porous, dimensionally stable substrates. They are suitable for interior as well as exterior application. For standard apphcations these modified mortars provide higher quality security and a certain long-term stabihty, very much depending on the factors like climate conditions, weight traffic etc. 

Because of the use of redispersible powders, the application of E.I.F.S. has reached such a high level of reliability and quality consistency that manufacturers in Germany normally allow a 30-year warranty for their systems. So far this level of warranty is not yet achieved in the US. 

Of the several types of the polymer-modified mortars and concretes used for various construction applications, latex-modified mortar and concrete are by far the most widely used materials. Latex-modified mortar and concrete are prepared by mixing a latex, either in a dispersed liquid or as a redispersible powder form with fresh cement mortar and concrete mixtures. The polymers are usually added to the mixing water just as other chemical admixtures, at a dosage of 5-20% by weight of cement. Polymer latexes are stable dispersions of very small (0.05-5 pm in diameter) polymer particles in water and are produced by emulsion polymerization. Natural rubber latex and epoxy latex are exceptions in that the former is tapped from rubber trees and the latter is produced by emulsifying an epoxy resin in water by the use of surfactants [87]. 

Table 5.1 outlines useful properties, products and application areas of acrylic systems. Key market segments are coatings based on methacrylates as well as emulsions and water-based sealants. Acrylic emulsions and redispersible powders as cement modifiers offer many useful products for several end-uses. However, the high cost of acrylic has limited their use as cement modifiers. The use of water-based acrylic systems is increasing because of their non-toxic and environmentally friendly nature. 

Rapid shift of two-packaged systems to one-packaged systems (dry premix mortar or dry mix mortar systems) by use of high-grade redispersible pol5mier powders in the applications of polymer-modified mortar [62]... 

The main markets for the dispersions are paints and coatings (26%), paper coating (23%), adhesives (22%), and carpet backing (11%) [2], They are also used in such niche applications as diagnosis, drug delivery, and treatment [3], The main dry products are styrene-butadiene rubber for tires, nitrile rubber, about 10% of the PVC production, acrylonitrile butadiene styrene (ABS), and redispersable powders for construction materials. 

To guarantee the performance of a redispersible powder in its final application a protective colloid is added to the emulsion before the spraying process. The colloid protects the polymer particles from film forming during the spray drying process... 

Manufacturers, contractors, apphcators and end-users ( Do it yourselP market) all benefit significantly from dry mix mortars modified with redispersible powders. That technology almost exclusively makes machine applications, which become more and more popular with all kinds of constraction materials, possible. 

After hardening, UF-resins consist of insoluble, more or less three-dimensional networks and cannot be melted or thermoformed again. At their application stage, UF-resins are still soluble or dispersed in water or are spray dried powders, which in most cases are redissolved and redispersed in water for application. 

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