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Wacker presents novel low profile additive for room-temperature processes

News International-French

19 Mar 2013

Wacker has presented two new low profile additives (LPAs) for perfect surfaces and no shrinkage at the world’s leading composites tradeshow JEC Europe 2013

VINNAPAS® LL 8588 features a novel polymer architecture that makes it a compelling choice for the production of non-shrink composite parts in low-temperature processes. The product acts as an LPA even at room temperature, and so is highly conducive to high-efficiency, low-emission infusion processing. The other new product, VINNAPAS® LL 8251, scores points for its extremely low viscosity and thus its ready processability.
The LPA effectively keeps shrinkage in check in established high temperature processes while ensuring that the finished part has very high rigidity and good mechanical properties. Wacker has also exhibited pyrogenic silica for regulating the viscoelastic flow property of composite resins, silicone rubbers for the cost-effective, efficient production of fiber composite parts by the infusion and prepreg methods, and high-impact modifiers for epoxy resins.

Wacker's exhibits include two new products from its VINNAPAS® range of polyvinyl acetate (PVAc) solid resins for perfect non-shrink surfaces. Composite parts made from unsaturated polyester resins undergo substantial volumetric shrinkage unless a low profile additive is used. The consequences are often cracks, warped moldings, poor dimensional stability and optically flawed parts. The two new solid resins VINNAPAS® LL 8588 and VINNAPAS® LL 8251 can reduce this shrinkage to a value below 0.05 percent, and so create ex-tremely smooth, homogeneous surfaces (“Class A”).

What makes the new VINNAPAS® LL 8588 so special is its polymer architecture, which is composed of polyvinyl acetate and polystyrene segments. The resultant block polymer not only has a low viscosity in the liquid resin formulations and keeps shrinkage in check during curing, even at room temperature, but also ensures low water uptake by the finished part. The solid resin has been created specifically for semi-automated, low-emissions infusion processes. It promotes rapid resin infusion, and boosts production efficiency by eliminating the need for intermediate layers, while safeguarding a consistently high level of quality. The new VINNAPAS® LL 8588 is thus the perfect LPA for sophisti-cated composite parts for automotive applications, or boat and yacht building.

VINNAPAS® LL 8251, the second innovation is a copolymer of vinyl acetate and crotonic acid. Because its viscosity is similar to that of saturated polyesters, it is very easy to process, even at high fiber and filler contents. Formulations based on saturated polyesters have a tendency to yield end products of reduced rigidity and strength. VINNAPAS® LL 8251, however, offers effective shrinkage control combined with very high rigidity – in other words, a good mix of both properties. The very good mechanical properties lead to stable molded composite parts with extremely smooth Class A surfaces which, in addition to their flat structure, offer excellent gloss and consistently high product quality. Aside from typical applications in the automotive sector, composites could con-ceivably find use in the construction sector, e.g. for windows, doors, industrial profiles and railings.

Picture: Comparison of composite parts: If no additives are used, the composite parte shows noticeable fiber print-through (left side). VINNAPAS® LL 8588 compensates reaction shrinkage and thus enables absolutely smooth surfaces (right side).