Chemistry & Life Sciences

Novel Materials and More Efficient Processes for New Applications

05.02.2014 -

Industry Constantly Evolves - The plastics industry requires continuous innovation because of the assimilation to the market's demands. For more than 50 years, SKZ has observed this evolution and provided solutions for the industry to expand realizable applications.

This occurs because of the development of high-performance materials as well as novel and more efficient processing technologies. The results are applications that were unimaginable until now. The benefits are for both costumers and manufacturers: The standing of the plastics industry is strengthened, and end users get components with new functionalities or more sustainable products for lower costs.

Value-Added Materials

Plastics offer a wide range of applications thanks to their modification opportunities. Plastic compounding is the most suitable and efficient way to adjust their properties. Antimicrobial materials are a trend because of society's increasing health requirements (see figure 1). Examples are light switches or doorknobs, particularly in public places. A substantial drawback of using conventional additives such as silver is its environmental effect. This metal accumulates in waters and therefore in aquatic animals. It keeps its antimicrobial effect in such surroundings, where it can be undesirable or even harmful.

A novel method is the use of naturally occurring titanium dioxide with a special crystal structure. In interaction with ultraviolet radiation, for example, from daylight, the photocatalytic effect destroys organic compounds. Germs and bacteria get killed. This can be a benefit compared with silver because the effect occurs only in combination with ultraviolet light. The challenge is the accurate processing and recipe formulation since the degradative reaction affects the polymer matrix itself. But SKZ has promising solutions to avoid this.

Ceramics Meet Plastics

Ceramics are also an upcoming class of material. Despite their excellent low-wear and high-temperature properties, the design and shape possibilities are limited. However, the use of plastics offers economical processing methods as well as a wide variety of shaping potentials. What could be more obvious than the combination of these material classes?

SKZ realized this intention in an innovative patent pending process. The base material is a special modified wood plastic composite (WPC). It consists of a very high amount of carbon, which is necessary for the further processing and is melt processable with all advantages concerning design opportunities or economy of scale. Treatment by pyrolysis follows shaping (see figure 2). Here, the plastic blank changes in a pure carbon template under high temperatures and inert atmosphere. In the subsequent siliconizing process, the shaped carbon skeleton reacts to silicon carbide ceramics (SiC). Therefore plastics and ceramics were married and a new opportunity was born: a method to produce SiC ceramic parts economically with all possibilities of plastics shaping on the base of renewable material-filled polymers.

The formulations and processes for extruded products are already well-developed, for example, heat exchangers or furnace spacers. The next step is the transfer to discrete shaping processes such as injection molding.

Rubberlike but Thermoplastic and Flame-Protected

Thermoplastic elastomers (TPE) are very interesting polymeric materials. They combine the elastic properties of conventional rubbers with the melt and multi-component processability with resulting shorter cycle times and wider spectra of shapes.  One challenge for TPE is their poor flame retardant property. Usually, the need for very high contents of flame retardants will downgrade the mechanical behavior significantly. Suitable additives with needs for lower contents are halogenated and therefore unwanted.

The solution is a smart combination of different flame retardants with synergists. For that purpose the mechanism of actions for each ingredient as well as the interactions between the flame retardants and synergists have to be investigated. One goal is the minimization of the additive's content to reduce the adverse influence on the mechanical properties (see figure 3). Very promising results are already available for styrenic block copolymers.

Reinforced Direct from Endless Fiber to Shaped Part

Direct processing has been in mind for several years. Besides the cost reduction due to avoiding the step between compounding and injection molding, the big advantage is the gentle material processing. But this demands also a proper knowledge about the material formulations and the compounding processes even for the previous injection molder. Longer resulting fiber length in the final parts allows even commodities such as polyolefins the operation in applications that had been reserved for engineering plastics such as polyamides.

However, SKZ wants to push the achievable maximum fiber length. Two basic concepts are available: an injection molding machine with modified screw and metering unit (see figure 4) as well as an injection molding compounder (IMC). To obtain the goal of longer final fibers, SKZ breaks new ground. Instead of glass-fiber bundles or pultruded pellets, the endless fiber is fed directly to the processing machine. This requires a special fiber guidance, adapted chopping unit, screw design and suited control systems. Only the perfect interaction between each component enables mean fiber length up to 3.4 mm and contents of more than 15% with fiber length greater than 2 mm in the final part.

Price and Quality Through Soft Sensors

The high demands are forcing processors to implement continuous quality assurance measures. Soft or virtual sensors offer new opportunities that are not yet well-known in the plastics industry. They are not sensors in the conventional sense but rather software solutions, which use the input data that are usually supplied by existing simple hardware sensors. These data are evaluated by mathematical models, which allow the generation of characteristic quality values in real-time. Therefore, the process can be immediately modified to achieve the desired quality.

A simple but promising method is the use of artificial neural networks, which have improved greatly in recent years. A main advantage is the suitability for highly nonlinear relationships, which are common in plastics processing. The generated comprehensive process models give a deeper insight into the process. It can be linked to economic data, such as throughput or manufacturing costs, with genetic algorithms to provide further optimization, for example in product price or use of resources for a given quality (see figure 5). This increases productivity as well as permitting faster development cycles and process optimizations. SKZ works with Atlan-tec Systems GmbH to tap this potential. Various plastics processing procedures can benefit from the possibilities of soft sensors. In the medium term, this technology can become much more widespread in the plastics industry.