Department of Mining Engineering
Mineral fillers, according to DIN 55943 (EN-Coloring materials-Terms and definitions) are insoluble materials in which they are in powder form used to increase volume, obtain or increase certain technical properties and/or alter optical properties.Fillers are materials of organic or inorganic origin,which are added to the system as a solid in plastics and are incompatible with matrix resin.
These materials may give many features to the system in which they are added, depending on whether they are active or inactive. If it is used consciously, filled systems will gain significant advantages as well as cheapness.The fillers increase values such as specific gravity,
Emodulus,compressive strength, bending resistance,hardness, heat resistance in the mixture. Some special additives give the system anti static and non-flammable properties as well as softness and slippery which provide ease of processing.
The most important contribution of fillers in plastics is that it prevents the material from shrinking. There is no negative effect of fillers on plastic mixtures. The most important issue is the deterioration of tensile strength and impact resistance with filler.
Special additives are absolutely necessary to correct this effect.Exothermic heat in reactive resins can cause many problems in the system. The majority of the filler slower this exothermic peak and reduce stresses in the system. This result in less shrinkage of the final product and prevents surface fluctuations and cracks.
In this way, it is possible to obtain products with glossy and smooth surface and full dimensions. Adhesion of plastic to other materials is prevented by the addition of filler. The fillers alter the processing value of the whole system. This includes storage life and processing parameters.
The most important issues to be considered in the selection of fillers can be listed as follows:
• Particle size,
• Distribution type,
• Dispersion features,
• Chemical structure,
• Surface structure and size,
• Risk of abrasion,
• Surface hardness,
• Transport type,
• Price.
1. Mineral Fillers Used in Plastic
The major mineral fillers used in plastics are:
• Calcium carbonate,
• Dolomite,
• Barite,
• Talc,
• Kaolin,
• Mica,
• Quartz sand,
• Wollastonite.
In this section, the most commonly used calcium carbonate as mineral filler will be mentioned.
1.1. Natural Calcium Carbonate Calcium carbonate is the most common filler in the plastic industry. In thermoset plastics, it is used the most in SMC-BMC and in thermoplastic PVC, it is used the most in PVC. Calcite, which is an inert material,does not cause any negative change in other properties of the resin while providing cheap price.
The most important applications of natural grounded calcium carbonate (GCC) in the polymer industry are as follows:
Plastic PVC: Depending on the application (cable,flooring, profile, film, etc.), uncoated or coated calcium carbonate with different fineness is used.
PVC Plastisols:
For application such as leather clothing’s,wallpaper, tarpaulin and floor covering, uncoatedcalcium carbonate is applied between d50=1.5-40μm.
Rigid PVC: For pipes, window profiles, shutters, filmsand pipe fittings, a very fine coated calcium carbonateof d50= -1.5 μm should be used.
Polyprophylene (PP):
Many applications of naturalcalcium carbonates are wastewater pipes, trays forpackaging food and consumer goods, BOPP films,technical components, for household applicationssuch as garden furniture should be between d50=1.4-3.5 μm. Particularly high whiteness is preferred for surfacecoating.
Polyethylene:
Used as a functional additive in films toincrease the surface-coated calcium carbonate elasticmodulus of d50 less than 3 μm. In addition, calciumcarbonate provides the dispersion of pigments.
Polymer Resins:
For SMC and BMC applications, calciumcarbonates with a d50 of 1.5-10 μm are preferred.In order to increase the packaging density and to reducethe viscosity, finer grains can be added to therelatively coarse grains.
Desired Properties of Calcium Carbonate Mineral Fillers
• Non-toxic, odorless,
• High brightness, low refractive index,
• Soft,
• Dry, crystal-water-free,
• Stable under normal plastic processing conditions,
• Lower costs,
• Easy to disperse,
• Reduces thermal expansion coefficient,
• Increases thermal conductivity.
Disadvantages
• High density,
• Increases plastic viscosity,
• More abrasive than polymer,
• Increases thermal conductivity (unwanted situation
in window and door frames),
• Acid soluble,
• Reduces compressive strength.
PVC is the polymer system where the most mineral fillers(especially CaCO3) are used. It absorbs and neutralizesHCl gas released in the heat treatment of theplastic and thus acts as a low-cost stabilizer.
Ultra-fineGCC particles give the best stabilization. Due to its low cost and abundance, calcium carbonate(CaCO3) is the most widely used in mineral filler.
1.2. Synthetic (Precipitated) Calcium Carbonate
The superior properties of the precipitated calcium carbonate are the fine particle, purity and aragonite structure. If the surface is treated (surface coating), it is very easy to disperse in the matrix resin. This provides the following advantages:
• Impact resistance increases,
• Surface gloss increases in end products,
• İncreased flexibility reduces fracture and tear problems,
• E-module increases.
In addition to all these advantages, it brings negativity. One of them is expensiveness. Furthermore, since the viscosity increase is faster, less filler is used and there is a danger of adsorbing other valuable additives due to surface activity.
Precipited calcium carbonate (PCC) has a d50 of 0.07-2 μm and a specific surface area of 10-40 m2/g. Its main applications are plastisol’s used in automotive (mixture of PVC and plasticizer).
2. Properties of Filled Plastics
The most important difference between reinforced plastics in filled plastics is that the tensile strength increases only in reinforced plastics. In contrast, E-modulus and hardness increase with fillers. Heat resistance does not increase as much as with spherical fillers and fiber-shaped reinforcing materials.
Conversely, the addition of flat grain talc and mica can be much more effective in heat resistance. It can be said that fillers cause the following changes in plastics:
• Density increase,
• Increased printing and bending values with E module,
• Improvement of surface hardness and quality,
• Decrease in the heat effect of mechanical values,
• Cost reduction.
This allows the following changes in plastics:
• Ease of use of plastics,
• Printing and forming times are shortened,
• A harder product is obtained,
• More heat resistance,
• It is possible to meet the dimensions, the depressions are reduced,
• Creep problems are eliminated,
• Reduced tendency to release itself under load,
• Better bending and impact values.
3. Filler Applications in Plastic
There are some important issues to be considered when adding plastic fillers. If you don’t work consciously, the desired advantages cannot be provided, and it is possible to face big problems.
Issues that required attention can be listed as follow:
• Particle size distribution should be appropriate,
• Consider the catalytic effect of the filler surface,
• Optimal mixing and good compatibility with the
matrix,
• It should be noted that most of the fillings can
erode construction equipment,
• Know the properties of the composition,
• Environmental problems should not be allowed
during operation,
• Control cost reduction.
If all these issues are examined with care, the addition of fillers can provide and economical and end product with the desired superior qualities.
4. Economic Importance of Plastic Filler
The use of filled reinforced plastics are increasing rapidly. Although some special fillers also increase, 50% calcite is still preferred in filled plastics. The greatest increase in addition to calcite is observed in talc, which is in the structure of the plate, because it gives toughness and provides smoothness.
The excessive increase in oil prices causes the cost of plastic materials which are the source of petroleum and the cheapness provided with fillers becomes more important.
With the new research and development efforts, filler types and their compatibility with plastics are investigated and solutions are sought with higher fill rates. These researches aim at the both cheapness and superior quality with new fillers, new resins and easer mixing methods.
a Dry ground, 3 μm coated
b Dry ground, 1 μm coated
Prof. Dr. Öner Yusuf Toraman
University of Niğde Ömer Halisdemir
Engineering Faculty
Department of Mining Engineering
Doç. Dr. Serkan Çayırlı
University of Niğde Ömer Halisdemir
Engineering Faculty
References
[1] Paints, Coatings and Solvents, Edited by Dieter Stoye, VCH Publishers, Inc., NY (USA), 1993.
[2]Industrial Minerals and Their Uses- A Handbook and Formulary, Peter A. Ciullo, Noyes Publ., 1996.
[3] Ö.Y. TORAMAN, Plastik Endüstrisinde Kullanılan Doğal Mineral Katkı Maddeleri, Turkchem, Mart/Nisan 2012, Yıl:5 Sayı:27, s.58-62.
[4] Ö.Y. TORAMAN, Boya ve Plastikte Kullanılan Mineral Dolgu Maddeler, BoyaTürk, Nisan/Mayıs 2014, s.34-36.
[5]S.KOLTKA, E. SABAH, Boya Sektörü ve Sentetik (Çöktürülmüş) Kalsiyum Karbonat (PCC), 8.Uluslararası Endüstriyel Hammaddeler Sempozyumu,
Bildiriler Kitabı, s. 47-56, 29-30 Kasım 2012, İstanbul.
[6]http://www.plastik-ambalaj.com/tr/plastik-ambalaj-makale/1053-plastik-dolgu-maddeleri
