A Binder Connects the World
Initial Attempts with Sunlight
But polymerization was still a challenge in those halcyon early years of plastics chemistry, when chemists lacked the processes that would enable targeted manufacturing of polymers. Since 1912, however, it had been known from the work of Fritz Klatte, a chemist from Frankfurt, that liquid vinyl acetate tends to spontaneously polymerize under the influence of light. That’s why, in the beginning, WACKER scientists had the monomer filled into ten-liter glass bottles, which were then exposed to the sun until solid polyvinyl acetate resin had formed in them. The bottles then had to be broken to get at their contents. One year later, in 1925, the discovery of peroxides provided a catalyst for accelerating the polymerization process. Shortly thereafter, the Consortium was granted a comprehensive utility patent for polyvinyl acetate-based binders and adhesives that are sold under the VINNAPAS® trademark. Following the breakthrough with the polymerization process that was patented in 1938, WACKER chemists rapidly developed the binder further. They mixed plasticizer additives into the VINNAPAS® homopolymer dispersions, for example, to create elastic bonds suitable for paper applications. The additive also enhanced the water resistance of distemper. By 1943, production of VINNAPAS® dispersions at Burghausen had reached 2,600 metric tons.
Emulsion Paint Becomes the Standard
After WWII, production was initially stopped and subsequently resumed in September 1945. The so-called plasticized VINNAPAS® dispersions – to which a plasticizer had been added – that had been developed at the end of the 1930s, became popular with the general public in the postwar years. It wasn’t long before polyvinyl acetate replaced glue as the binder and emulsion paint established itself as the standard product – all around the world today.
During the years of West Germany's economic miracle – the 1950s and 1960s – the new binders developed into a platform for ever more innovations. WACKER scientists experimented with the chemical structure of the polymer chains, inserted so-called copolymers and thus created new properties. In 1955, the 50/25 VL grade – in which vinyl laurate acted as the monomer, without plasticizing additives in the resulting copolymer – was launched on the market. This molecular building block rendered the dispersion film plastic; in addition, the plasticizer could now no longer evaporate. The advantage was that the dispersion film retained its high flexibility over the long term and did not become brittle over time. As a result, the product was ideal for wallpaper adhesives, for example, improving their wet-bonding and dry strength.
Terpolymer dispersions with vinyl chloride joined the product line in 1962, and in 1964 came the true quantum leap: VINNAPAS® EP1 – the first water-based copolymer dispersion based on vinyl acetate and ethylene – was launched on its road to success, initially in the adhesives market. Copolymerization with ethylene immediately expanded VINNAPAS® dispersions’ application range, because the ethylene component provided the polymer chain with greater flexibility and also made plasticizers redundant in later end-product formulations.
Several years earlier, VINNAPAS® had made another leap forward: polymer binders in the shape of so-called dispersible polymer powders. Here, a spray method was used to remove the water from special dispersions, which made it possible to store and transport the polymer binder. In the development of these powders, WACKER chemist Dr. Max Ivanovits was inspired by the concept of instant coffee – and so he built a miniature spray-drying test facility. His line of thinking was that if the Group could succeed in preparing its dispersions in the form of dispersible polymer powders, the market for polymeric binders would explode. Following the rapid success of Ivanovits' tests, industrial-scale production commenced at Burghausen on July 2, 1957, when the first 13.2 metric tons of free-flowing dispersible polymer powder emerged from a PVC dryer. The individual powder particles consist of a water-soluble protective-colloid matrix in which the water-insoluble polymer particles are embedded. The powder particles are prevented from sticking together by a so-called anti-blocking agent.
In the beginning, the production process required a lot of optimization, especially with regard to the spray drying. However, probably the biggest obstacle at that time was that, in the beginning, there was no market for dispersible polymer powder. That changed rapidly in the 1960s, as construction became increasingly industrialized and architects tried out new structures and building methods. The redesign of VINNAPAS® binders on the basis vinyl acetate-ethylene copolymers and the development of the spray-dryer process came at just the right time.
Since the 1970s oil crisis, energy conservation has been a particular challenge for the construction industry. And in 1977, the first regulation on energy-saving thermal insulation of buildings took effect in Germany requiring improvements such as double-glazing or similar in new buildings. This regulation has been amended many times, with ever more stringent provisions. As buildings were made fit in terms of energy efficiency and increasingly equipped with EIFS/ETICS since the late 1980s, higher-performance mortars became necessary. Chemists and applications engineers at WACKER POLYMERS were faced with the challenge of developing VINNAPAS® products for these systems. Polystyrene panels used to thermally insulate buildings’ facades have the disadvantage that they do not form stable bonds with pure cement mortars. However, even minor additions in the region of 4 percent of VINNAPAS® polymer powder to adhesive mortar are sufficient to form a stable, permanent bond between the polystyrene board and the mortar.