Fillers are insoluble additives which, when added to the base material (the matrix ) in a high content , u. a. change the mechanical, electrical or processing properties of materials significantly, and at the same time significantly reduce the proportion of the typically more expensive matrix in the finished product. In contrast, additives are usually dissolved in the matrix and have contents of less than a few percent.
Worldwide, over 53 million tons of fillers with a total value of around 16 billion euros are used for such diverse fields of application as paper, plastics , paints and pharmaceuticals. This makes fillers one of the most important raw materials of all and is contained in a large number of everyday items.
Cork , wheat chaff or wood flour.
Silicates ( clay , loam , talc , mica , kaolin , Neuburg Siliceous Earth ), carbonates / sulfates ( chalk , dolomite , barite ) and oxides / hydroxides (quartz flour, crystalline silica, aluminum / magnesium hydroxides and magnesium, zinc or calcium oxides).
Silicates, oxides and hydroxides, produced either by precipitation processes (silica, chalk, aluminum and magnesium hydroxide) or in thermal processes ( pyrogenic silicon dioxide , carbon black , metal oxides ); Glass fibers, glass spheres and broken glass.
In composite materials that are used in technical applications, the particle size, particle shape , particle structure, grain size distribution , size of the specific surface and surface activity of a filler are decisive factors for the properties of the mixture, its further processing and the properties of the final material. By changing the fillers, completely different results can be achieved, for example after curing paints and plastics or after vulcanizing elastomers.
In food , food additives are used as fillers, which form part of the volume of the food without making a significant contribution to its content of usable energy. This reduces the actual energy content per volume or per mass of the food.
Fillers are used here to reduce the physiological calorific value of a food (e.g. with light products ) and / or to increase the volume of a food (e.g. chewing gum ). Some also act as fiber . The most important fillers include above all water and air (which, however, are not food additives within the meaning of the relevant regulation), as well as:
In addition to the active substance and auxiliary substances, tablets also contain fillers, usually lactose , glucose , sucrose , starch , calcium sulfate or microcrystalline cellulose, depending on the recipe .
Plastics and elastomers
In plastics technology , fillers are used to optimize the property profile of plastics. The incorporation takes place through compounding . The focus of compounding with fillers is often the optimization and increase of rigidity , reduction of shrinkage and improvement of the surface appearance. A targeted increase in thermal or electrical conductivity is also possible.
The finished product of the compounding is divided into two groups, the plastic compound and the additive or color masterbatch. The use of such products is more accurate and cleaner for the processor of plastics.
A plastic compound is a ready-to-use mixture that can usually be processed without additives. Additive batches are those products that are filled with chemical substances in order to change the properties of the plastic, for example with lubricants or antiblock, both products that are used in the film industry.
Color masterbatches are justified in the fact that it is cleaner to use an already finished batch as an additive instead of raw pigments. Before use, the pigment is incorporated into a carrier material that is compatible with the plastic to be colored. The filling level of such color batches can reach up to 85% depending on the nature of the pigments. A combination batch is used when several properties are to be achieved with one batch (slip / antiblock batch).
To illustrate the confusing picture of compound, additive and color masterbatch with a comparison: Compounds can be equated with ready-made baking mixes that can be processed directly without further additives. Additives take on the role of yeast or baking powder, colors can be the chocolate or cocoa that are added to a cake mix. Batches are only part of the compound in the sense of the finished mixture.
Important fillers of thermoplastic polymers are:
- Glass fibers , glass spheres and broken glass
- mineral fillers such as calcium carbonate and talc
- Carbon fibers (short fibers)
Fillers are also often used in thermosetting plastics . In this area, they are often the cause of increased demands on the potting systems used for processing , due to the increasing viscosity , the segregation (demixing) of the phases and the abrasive effect of the fillers.
Carbon black and inorganic fillers are used in elastomers . The focus here is on the mechanical parameters.
In papermaking mainly silicates, mostly kaolin , a white china clay, are used as fillers. Kaolin makes the paper opaque ( opaque ), white and increases the density. The filler also gives the paper a smoother surface because it fills the voids between the fibers. Depending on the type, paper can contain up to 30% filler.
Carbonates are often used as fillers, mostly chalk , but also sulfates such as gypsum or oxides, for example titanium dioxide . Barium sulfate can be used as a filler for the production of baryta paper , which is therefore remarkably heavy.
With the exception of titanium dioxide, fillers are cheaper than the pulp used. The use of fillers can therefore reduce the production costs of a paper. The addition of fillers has hardly any significant effects on some of the mechanical properties of paper. In particular, the tensile strength is not noticeably reduced, since with modern paper formulations a strong bond between pulp and filler is achieved through optimized auxiliaries and sizing agents. However, the fillers serve to increase the whiteness , to influence the weight per unit area and to shape the paper absorbency, which is of great importance for the print quality.
In colorants , fillers are used to increase the volume and to change technical and optical properties. Also pigments may be used as filler; Whether a coloring, insoluble substance is to be regarded as a filler or a pigment depends on its application.
Coating materials such as paints are first applied to objects in liquid or powder form and then harden. Fillers are used here to influence the processing, the technical properties, the visual appearance and sometimes the haptics of a surface. As with plastics, mineral fillers such as calcium carbonate and talc , but also barium sulfate and aluminum hydroxide are preferred in the paint industry .
Heavy-duty detergent contains up to 50% sodium sulfate (Glauber's salt), which is counted as a setting agent . It hardly influences the effect, but serves good flowability, dosability, solubility and shelf life. But sodium sulphate leads to salinisation of the waters.
Building materials and coating materials
In the case of building materials and related materials, the fillers are summarized under the term aggregate .
- Market study fillers by Ceresana Research ( Memento of the original from July 9, 2009 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. .
- Neuburg Siliceous Earth. Extraction, refinement, applications as a functional filler . The library of technology, Bd. 308. Munich: Süddeutscher Verlag onpact, 2008. ISBN 978-3-937889-77-1 . Pp. 7-12.
- Otto-Albrecht Neumüller (Ed.): Römpps Chemie-Lexikon. Volume 4: M-Pk. 8th revised and expanded edition. Franckh'sche Verlagshandlung, Stuttgart 1985, ISBN 3-440-04514-5 , pp. 2981-2986.
- DIN 55943 . In: German Institute for Standardization e. V. (Ed.): Colorants 1 . 7th edition. DIN-Taschenbuch 49.Berlin, Vienna, Zurich 2012, ISBN 978-3-410-23202-5 , pp. 510 .