Filler materials are particles added to resin or binders (plastics, composites, concrete) that can improve specific properties, make the product cheaper or a mixture of both. The two largest segments for filler material use is elastomers and plastics. Worldwide, more than 53 million tons of fillers (with a total sum of approximately $18 billion USD) are used every year in different application areas, such as paper, plastics, rubber, paints, coatings, adhesives and sealants. As such, fillers, produced by more than 700 companies, rank among the world's major raw materials and are contained in a variety of goods for daily consumer needs. The top filler materials used are ground calcium carbonate (GCC), precipitated calcium carbonate (PCC), kaolin, talc, and carbon black. Filler materials can affect the tensile strength, toughness, heat resistance, color, clarity etc. A good example of this is the addition of talc to polypropylene. Most of the filler materials used in plastics are mineral or glass based filler materials. There are two main subgroups of filler materials: particulates and fibers. Particulates are small particles of filler which are mixed in the matrix where size and aspect ratio are important. Fibers are small circular strands that can be very long and have very high aspect ratios.
- 1 Types
- 2 Mechanical Properties
- 3 Weldability of plastic fillers
- 4 Applications of filler in plastic industry
- 5 See also
- 6 References
Calcium carbonate (CaCO3)Edit
Referred to as "chalk" in the plastic industry, is derived from limestone and marble. It is used in many applications including PVC's and unsaturated polyesters. As much as 90% CaCO3 can be used to make a composite. These additions can improve molding productivity by decreasing cooling rate. They can also increase operating temperatures of materials and provide insulation for electrical wiring.
Calcium carbonate in filler masterbatch
CaCO3 is used in filler masterbatch as a base with large percentage in composition. Calcium carbonate powder accounts for 97% of composition will bring for white/opaque products more whiteness. So manufacturers can reduce the usage of white masterbatch. With smaller percent, calcium carbonate powder can be used for color products. In addition, it brings for final plastic products more bright and glossy surface.
Kaolin is derived from kaolinite and was discovered about 150 million years ago. If kaolinite is heated above 500 °C (932 °F) it changes into metakaolinite which can withstand temperature upwards of 960 °C (1760 °F). It is mainly used in plastics for its anti blocking characteristics as well as an infra red absorber in laser marking. It increases properties such as impact strength and heat resistance. Metakolinite is used in PVC to remove environmentally harmful ions from the matrix. Kaolin has also been shown to increase the abrasion resistance and can replace carbon black as a filler material and improve flow properties of glass reinforced substances.
Talc is most known for its use in babypowder and as a thickening agent. It is the softest mineral known and generally more expensive than calcium carbonate. It is derived from layering sheets of magnesium hydroxide with silica. In the plastic industry it is used for packaging and food application due to its long term thermal stability.
Wollastonite has an acicular crystal structure with a relatively high specific gravity and high hardness. Additions of this filler can improve moisture content, wear resistance, thermal stability and has a high dielectric strength. Wollastonite competes with platy filler substances like mica and talc and also can be used to replace glass fibers when creating thermoplastics and thermosets.
Glass filler materials come in a few different forms such as: glass beads, short glass fibers, long glass fibers. Even though there are many different fiber additions glass is the most used fiber in plastics by tonnage. Glass fibers are used to increase the mechanical properties of the thermoplastic or thermoset such as flexual modulus and tensile strength, There is normally not an economic benefit for adding glass as a filler material. Some disadvantages of having glass in the matrix is low surface quality, very viscous when melted, low weldability and warpage. The addition of glass beads will help with oil absorption and chemical resistance.
Nanofiller must have a particle size less than 100 nanometers. They have a high aspect ratio and are mainly used as scratch resistant and fire resistant fillers. Nanofillers can be broken out into 3 different groups nanoplates, nanofibers and nanoparticles. Nanoparticles are more widely used than nanoplates and nanofibers but nanoplates are starting be become more widely used. Nanoplates are like conventional platy fillers like talc and mica except the thickness is much smaller. Advantages of adding nanofillers include creating a gas barrier and their flame retardant properties.
|Mohs Hardness||Mean Size
|Calcium Carbonate||2.7||3-4||0.02-30||1-3 Blocky|
|Silica (Precipitated)||1.9-2.1||5.5||0.005-0.1||~1 Round|
|Carbon Black||1.7-1.9||2-3||0.014-0.25||~1 Round|
|Barium Sulfate||4.0-4.5||3-3.5||0.1-30||~1 Round|
|ATH Al(OH)3||2.42||2.5-3||5-80||1-10 Plate|
|MDH Mg(OH)2||2.4||2.5-3||0.5-8||1-10 Plate|
|Diatomaceous earth||2-2.5||5.5-6||4-30||2-10 Disc|
|Zinc Oxide||5.6||4.5||0.05-10||1 Round|
|Titanium Dioxide||4.23||6||0.1-10||1 Round|
Tensile strength is the most used method to evaluate filler materials. The tensile strength of the composite can be calculated using the equation
σc= σp(1-aΦbf +cΦfd)
σc - tensile strength of composite
σb - tensile strength of polymer matrix
Φf - volume fraction of filler
a, b, c, d are constants depending of the type of filler. "a" relates to stress concentration and is based on adhesion characteristics of the filler material. "b" is normally 0.67. c and d are constants that are inversely related to particle size.
E = E0 (1 + 2.5Φ + 14.1Φ2)
E0= Modulus of unfilled resin or binder
Φ = Filler concentration
Polymers with smaller additions of filler follow this equation closely. If there is a very high filler content the equation above will become less accurate. In general addition of filler materials will increase the modulus. The additions of calcium carbonate and talc will increase the elastic modulus, while addition of an elastic filler materials can reduce the value slightly. Filler materials increase the modulus due to the ridged particles and good adhesion.
In general fillers will increase impact resistance. The contributing factors that improve impact resistance is particle size, particle shape and particle rigidity. Fibers improve impact resistance the most due to their large aspect ratio. Low hardness fillers will decrease impact strength. Particle size, within a specific range can increase the impact strengths based on the filler material.
The wear volume for plastic materials can be calculated using the equation below.
Ws= Wear Volume
K = Proportionality constant
P = force
E = Modulus
D = Sliding distance
W = load
Is= Interlaminar shear strength
Matrix and filler both contribute to wear resistance. In general you want to choose a filler material that will decrease the friction coefficient of the material. Particle size and shape also can affect the wear resistance. Smaller particle size will increase wear resistance because they cause less debris. silica, alumina, molybdenum disulfide and graphite powder are common fillers that improve wear resistance.
Filler can have a negative or positive effect on fatigue resistance depending on the filler type and shape. In general fillers create small discontinuities in the matrix. This can contribute to crack initiation point. If the filler is brittle fatigue resistance will be low, where as if the filler is very ductile the composite will be fatigue resistant. Adhesion is also a important factor influencing fatigue resistance. If stress is higher than the particles adhesion a crack will form/propagate. Fiber ends are areas where cracks initiate most often due to the high stress on fiber ends with lower adhesion. Talc is a filler that can be used to increase fatigue resistance.
Filler materials have a large influence on thermal deformation in crystalline polymers. Amorphous polymers are negligibly affect by filler material. Glass fiber additions are used the most to deflect the most heat. Carbon fibers have been shown to do better than glass in some base materials. In general fibrous materials are better at deflecting heat than particle fillers.
εc(t)/εm(t) = Em/Ec
εc(t) = is strain of filled polymer
εm(t) = is strain of matrix or unfilled polymer
Em = is Young's Modulus of matrix
Ec =is the Young's Modulus of filled polymer
The better the filler bonds with the matrix the better creep resistance will be. Lots of interactions will have a positive influence. Glass beads and fibers both have been shown to improve creep resistance in some materials. Aluminum oxide also has a positive effect on creep resistance. Water absorption will decrease the creep resistance of a filled material.
Weldability of plastic fillersEdit
Additions of filler materials can drastically effect the weldability of the plastic. This also depends on the type of welding process used. For ultrasonic welding, fillers like calcium carbonate and kaolin can increase the resins ability to transmit ultrasonic waves. For electromagnetic welding and hot plate welding additions of talc and glass will reduce the weld strength by as much as 32%. The strength of the plastic after welding would decrease with increasing amount of fillers in the matrix compared to the bulk material. Use of abrasive fillers can have an effect on the tool used for welding. Abrasive fillers will degrade the welding tools faster, for example, the surface of the ultrasonic horn in contact with the plastic. The best way to test the weldability of a filler material is to compare weld strength to resin strength. This can be hard to do since many filler materials contain different level of additives that change the mechanical behavior.
Applications of filler in plastic industryEdit
Filler is a widely used material in the production process of plastic products. Filler is used to change the properties of the original plastic. By using plastic filler, manufacturers can save production costs as well as raw materials.
Undeniably the importance of filler masterbatch in improving the physical properties of plastics, especially minimizing cost and production efficiency. With the advantage of price and stability, plastic filler supports the production of:
- Blown film & lamination
- Non woven fabric
- Blow molding
- Injection Molding
- Extrusion (pipe, sheet)
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