Mineral Fillers Used in Plastics and Their Applications

Mineral fillers; according to DIN 55943 (EN-Colouring materials- Terms and definitions) standards, are powder-form substances that are insoluble in the environment where they are practically applied and are used to increase volume, obtain or enhance certain technical properties and/or modify optical properties. Filler materials are organic or inorganic substances added as solids to the plastic system and incompatible with the matrix resin. These substances can impart many properties to the system in which they are added, depending on whether they are active or inactive. If used consciously, filled systems gain not only cost advantages but also very significant benefits. Filler materials increase values such as specific gravity, E-modulus, compressive strength, bending resistance, hardness, and heat resistance in the mixture. Certain special additives provide the system with properties such as anti-static and flame retardancy, as well as advantages such as softness and lubricity that facilitate processing. The most important contribution of filler materials in plastics is preventing shrinkage of the material. The negative effects of fillers on plastic mixtures are not insignificant. The most important issue is the deterioration of tensile strength and impact resistance with fillers. Special additives are absolutely necessary to correct these effects. Exothermic heat in reactive resins can create many problems in the system. The majority of fillers reduce this exothermic peak, thereby reducing stresses created in the system. In this way, the final product shrinks less and surface waviness and crack formation are prevented. Thus, products with brighter, smoother surfaces and precise dimensions can be obtained, and the adhesion of plastic to other materials is also prevented with the addition of fillers. Fillers change the processing values of the entire system. This includes storage life and processing parameters.

The most important points to consider in selecting fillers can be listed as follows:

• Particle size,
• Distribution form,
• Dispersion property,
• Chemical composition,
• Surface structure and size,
• Abrasion risk,
• Surface hardness,
• Transport method,
• Price

Mineral Fillers Used in Plastics

The main mineral filler materials used in plastics are:

• Calcium carbonate (CaCO₃),
• Dolomite,
• Barite,
• Talc,
• Kaolin,
• Mica,
• Quartz sand,
• Wollastonite

The following section will discuss natural calcium carbonate, the most commonly used mineral filler.

1.1. Natural Calcium Carbonate (GCC)

Calcium carbonate is the most widely used filler material in the plastics sector. In thermoset plastics, it is most commonly used in SMC-BMC, and in thermoplastics, most commonly in PVC. Calcite, an inert material, provides cost savings while not causing negative changes in other properties of the resin.  

CaCO₃	98.5–99.5%
MgCO₃	0.5%
FeO	0.2%
Al Silicate	1.0%
Loss on Ignition	43.3–43.8%
Moisture	0.2%
Density	2.7
Mohs Hardness	3.0
Whiteness	85-95 El Repho green filter-MgO-100
pH Value	9.0–9.5
Oil Absorption	9-21 g/100 g powder
DOP Number-ASTM D 281-31	9-33 g/10 g powder
Specific Surface Area	1-15 m²/g

The most important applications of natural ground calcium carbonates (GCC) in the polymer industry are as follows: Plastic PVC: Depending on the application (cable, flooring, profile, film, etc.), uncoated or coated calcium carbonate of different fineness is used. PVC Plastisols: For applications such as leather garments, wallpaper, linoleum and floor covering, uncoated calcium carbonate with d₅₀ between 1.5-40 µm is applied. Rigid PVC: For pipes, window profiles, shutters, films and pipe fittings, very fine coated calcium carbonate with d₅₀ of -1.5 µm should be used. Polypropylene (PP): Natural calcium carbonates have many applications as follows: for wastewater pipes, trays for food and consumer goods packaging, BOPP films, technical components, garden furniture and domestic applications, d₅₀ should be between 1.4-3.5 µm. High whiteness is particularly preferred in surface coating. Polyethylene: Surface-coated calcium carbonate with d₅₀ less than 3 µm is used as a functional additive in films to increase elastic modulus. Additionally, calcium carbonate facilitates pigment dispersion. Polymer Resins: For SMC and BMC applications, calcium carbonates with d₅₀ between 1.5-10 µm are preferred. To increase packing density and reduce viscosity, relatively coarser particles can be added.

Desired Properties in Calcium Carbonate Mineral Fillers

• Non-toxic, odorless,
• High brightness, low refractive index,
• Soft,
• Dry, free of crystal water,
• Stable under normal plastic processing conditions,
• Low cost,
• Easy to disperse,
• Reduces thermal expansion coefficient,
• Increases thermal conductivity.

Disadvantages

• High density,
• Increased plastic viscosity,
• More abrasive than polymer,
• Increases thermal conductivity (unwanted condition in window and door frames),
• Soluble in acid,
• Reduces compressive strength. PVC is the polymer system where the most mineral filler (especially CaCO₃) is used. It absorbs and neutralizes HCl gas released during plastic heat processing, thereby serving as a low-cost stabilizer. Very fine GCC particles provide the best stabilization. Due to its low cost and abundance, calcium carbonate (CaCO₃) is the most widely used mineral filler material. 1.2. Synthetic (Precipitated) Calcium Carbonate (PCC) The superior qualities of precipitated calcium carbonate are its fine particle structure, purity, and aragonite form. If subjected to surface treatment (surface coating), its dispersion in the matrix resin becomes very easy. This provides the following advantages:
  • Impact resistance increases,
  • Surface gloss increases in the final product,
  • Increased flexibility reduces cracking and tearing problems
  • E-modulus increases.
  Despite all these advantages, it also brings disadvantages. The primary among these is its high cost. Additionally, since viscosity increase is faster, less filler is used, and there is a risk of adsorption of other valuable additives due to surface activity. Precipitated calcium carbonate (PCC) has a d₅₀ between 0.07-2 µm and specific surface area of 10-40 m²/g. Its basic applications are plastisols used in the automotive industry (PVC and plasticizer mixture).

  2. Properties of Filled Plastics

  • • The most important difference between filled plastics and reinforced plastics is that tensile strength increases only in reinforced plastics. In contrast, E-modulus and hardness also increase with filler materials. Heat resistance does not increase as much with spherical fillers as with fiber-shaped reinforcement materials. In contrast, the addition of talc and mica, which have a flat particle structure, can be much more effective in heat resistance. It can be said that filler materials cause the following changes in plastics.
    • Density increase,
      • Increase in E-modulus, compression and bending values,
      • Improvement in surface hardness and quality,
      • Reduction in the effect of mechanical values on heat,
      • Cost is reduced significantly.

      In this way, the following changes are observed in plastics:

      • Deterioration in mechanical values is observed,
      • Compression and forming times are shortened,
      • A harder product is obtained,
      • It becomes more heat resistant,
      • It is possible to maintain dimensions, shrinkage is reduced
       
      • Friction problems are eliminated,
      • The tendency to relax under load is reduced,
      • Bending and impact values are also better. 3. Filler Applications in Plastics
      There are certain important issues to consider when adding filler materials to plastics. If the work is not done consciously, not only are the desired advantages not achieved, but major problems may also arise.

      Issues requiring attention can be listed as follows:

      • Particle size distribution should be appropriate,
      • The catalytic effect of the filler surface should be considered,
      • An optimum mixture and good compatibility with the matrix should be ensured,
      • It should be noted that many fillers can abrade processing equipment,
      • The properties of the composition should be known precisely,
      • Environmental problems should not be allowed during processing,
      • Cost reduction should be monitored. If all these issues are carefully examined, filler addition can provide the opportunity to obtain a composition and final product with desired superior qualities and economic benefits.

        4. Economic Importance of Plastic Filler Materials

        The use of filled reinforced plastics is increasing rapidly. Although increases are seen in some special fillers, 50% of filled plastics still prefer calcite. In addition to calcite, the largest increase is seen in talc, which has a plate structure and provides toughness to the material and surface smoothness. The excessive increase in oil prices causes plastics derived from petroleum to become more expensive, and the cost savings provided by filler materials become even more important. New R&D studies examine filler types and their compatibility with plastics, seeking solutions with higher filler rates. These research efforts target both cost reduction and superior quality with new fillers, new resins and easier mixing methods. Table 2. Unit cost of calcite-filled (40%) plastics

        Plastic and Mineral Filler	Density, g/cm³	Cost, $/ton
        Polypropylene, PP	0.89	880
        CaCO₃ᵃ	2.69	90
        60% PP, 40% CaCO₃	1.22	570
        PVC	1.39	830
        CaCO₃ᵇ	2.69	140
        60% PVC, 40% CaCO₃	1.73	550

        ᵃ Dry ground, 3 µm uncoated ᵇ Dry ground, 1 µm coated
       
     

Prof. Dr. Öner Yusuf Toraman Niğde Ömer Halisdemir University Faculty of Engineering Department of Mining Engineering     Associate Prof. Dr. Serkan Çayırlı Niğde Ömer Halisdemir University Faculty of Engineering Department of Mining Engineering

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, March/April 2012, Year:5 Issue:27, p.58-62. [4] Ö.Y. TORAMAN, Boya ve Plastikte Kullanılan Mineral Dolgu Maddeler, BoyaTürk, April/May 2014, p.34-36. [5] S.KOLTKA, E. SABAH, Boya Sektörü ve Sentetik (Çöktürülmüş) Kalsiyum Karbonat (PCC), 8th International Industrial Raw Materials Symposium, Proceedings Book, p. 47-56, 29-30 November 2012, Istanbul. [6] http://www.plastik-ambalaj.com/tr/plastik-ambalaj-makale/1053-plastik-dolgu-maddeleri