Stearic acid-coated fillers

Coating is increasingly used to enhance the properties of fillers. One of the most widely used materials is stearic acid. Metal stearates are particularly effective as coatings for reactive particulate fillers, such as magnesium hydroxide (MH), producing polypropylene compounds with better impact resistance than those containing uncoated, or stearic acid-coated fillers. 

Fillers. Fillers are used to improve strength and stiffness, to lower cost, and to control gloss. The most common filler is calcium carbonate, which ranges in size from 0.07 to well over 50 m. Some forms are treated with a stearic acid coating. Clay fillers, such as calcined clay, improve electrical properties. Glass fibers, talc, and mica improve tensile strength and stiffness, but at a loss in ductility. 

Particle size is important and, for some applications requiring good weathering and impact performance (window profile), the ultrafine milled, high whiteness, natural version is normally used. To ease dispersion, the filler is usually coated with stearic acid. Coated ultrafine and precipitated calcium carbonates are claimed also to have a positive effect on impact properties in impact modified formulations (52, 294, 462). The abrasive wear of calcium carbonate, on melt processing equipment, is not significant but increases with increasing levels (177). 

Papirer and co-workers have also used IGC to study stearic acid coated calcium carbonates [17]. In their work, a high surface area precipitated filler was used, and coating was from toluene solution. They also prepared fractional coating levels based on solution adsorption isotherms. Stearic acid treatment was again found to decrease both the dispersive and polar contributions of surface energy to values typical of a hydrocarbon. Both acidic and basic probes were used in this work and interestingly, the uncoated filler was found to contain sites capable of interaction with both. 

In elastomers the effects of stearic acid coating of fillers appear mnch more dramatic in solution polymerised polymers than in emnlsion ones. As shown by Rothon, this is dne to the presence of large amounts of residnal snrfactants in the emulsion polymerised polymer [29]. These probably adsorb on the filler snrface, prodncing effects similar to stearic acid. In the absence of these competing effects, stearic acid reduces viscosity but also reduces the filler polymer interaction, resnlting in decreased bound rubber and... 

Stearic acid coated calciuirt carbonates are commercially available, and are widely used. Stearic acid coating of magnesium hydroxide has been studied in some detail, and fatty acids could be used for coating other hydroxide and carbonate containing fillers. 

Maleinized polybutadiene has demonstrated particularly favourable effects for filled elastomers, improving the tensile strength, tear strength and modulus of a sulphur cured EPDM (ethylene propylene diene monomer rubber) containing 100 phr filler, while a stearic acid coating actually caused all these properties to deteriorate significantly. 

Normally, addition of filler reduces impact resistance, sometimes dramatically so. Even low levels of well-dispersed, stearic acid-coated calcium carbonate can lead to drastic reductions in impact resistance of ABS and to a lesser extent in HIPS. ABS and HIPS are impact modified using rubber particles whereby... 

One way of improving the adhesion between polymer and filler is to improve the level of wetting of the filler by the polymer. One approach, which has been used for many years, is to coat the filler with an additive that may be considered to have two active parts. One part is compatible with the filler, the other with the polymer. Probably the best known example is the coating of calcium carbonate with stearic acid. Such coated or activated whitings have been used particularly with hydrocarbon rubbers. It is generally believed that the polar end attaches itself to the filler particle whilst the aliphatic hydrocarbon end is compatible with the rubbery matrix. In a similar manner clays have been treated with amines. 

Calcium carbonate is the most commonly used extender. It is widely available and low in cost, and it provides for improvements in certain performance properties. The material is a mineral that is mined throughout the world. Common forms of calcium carbonate include limestone, marble, calcite, chalk, and dolomite. It is manufactured by precipitation processes and is commercially available from a number of sources. Calcium carbonate is available in many different particle sizes and in various grades. To improve dispersion in certain resins, the filler is often coated with calcium stearate or stearic acid. 

Monoalkoxy titanate Chelate titanate Quat titanate Neoalkoxy titanate Cycloheteroatom titanate Stearic acid functionality aids in dispersion of mineral fillers in polyolefins Greater stability in wet environments Water-soluble, aids adhesion of water-soluble coatings and adhesives Eliminates pretreatment associated with fillers, can be used as a concentrated solid additive Ultrahigh thermal properties for specialty applications... 

Calcium carbonate treated with stearic acid gave improved performance to poly(vinyl acetate) composites but only if the filler particles were sufficiently small. Smaller particles tend to agglomerate if they are not coated. Coating prevents agglomeration and improves their interaction with the matrix. Large particles do not interact with the matrix but form defects in the composite. All three examples show that... 

Fillers improve mechanical properties of films. Calcium carbonate coated with stearic acid improved the impact strength of polyethylene bag films. Production output was increased and printability of the film was improved. ... 

Use of fine particle size precipitated carbonate filler provides good reinforcing properties and also increases viscosity. Some fine particle size precipitated carbonates are coated with stearic acid to improve wetting. These fillers are desirable where a high pH is required in a compound. Fine particle size coated precipitated carbonates improve thixotropy of a compound. 

Chem. Descrip. Calcium carbonate, coated with < 2% stearic acid Chem. Analysis CaCOj (97.6%), MgCOs (1.5%), moisture (0.2% max.) Uses Coated pigment, filler, reinforcement with easy dispersion in plastic compds., e.g., polyolefins, rigid and flexible PVC, nat. and syn. rubbers and latexes for wire and cable insulation compds., water sealant compds., improved impact props, in PP hardens and stiffens stocks filler, pigment, reinforcing agent in paper, paints, caulks Features Flydrophobic disperses readily Regulatory NSF compliance... 

Both the ground and precipitated calcium carbonates can by treated with stearic acid to control water absorption, improve dispersabUity, and promote better wetting of the flUer by rubber. Silane treatment of these fillers is not effective. However, there is an ultra-fine grade coated with carboxylated polybutadiene, which reactively links to the particle surfaces. Such treated ultra-fine products can give reinforcement of about the same level of the semireinforcing thermal carbon blacks. 

Stearic Acid. This is frequently used to coat filler particles. In calcium carbonate, it is the preferred coupling agent Presumably the -CO2H group orients toward the filler particle, and probably reacts with iL while the -Cj7ll35 chain penetrates into the polymer matrix. 

Stearic acid. The effect of coating on crystallization depends on the number of layers deposited on the filler surface. Figure 7.2 shows the effect of excessive coating of filler surface. The nucleation of the PP lamellae is accomplished by the deposition of the first stem of lamellae on a smooth surface of the monolayer coating. The nucleation efficiency is diminished if there is an excess amount of stearic acid (absence of the smooth surface). It should be also noted that agglomeration of particles will diminish the nmnber of nuclei. Agglomeration can be caused by the lack of coating or the excessive amoimt of coated filler in formulation. 

Stearic acid will react to produce stearates, while stearates melt and form coatings. In some cases stearic acid or products of the intermediate melting temperature are produced later in the process, presumably by hydrolysis. Stearic acid produces the best coverage on calcium carbonate, but the poorest on MH. Of the metal stearates, the best filler coverage is produced when zinc stearate is used. 

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