Fillers for polypropylene

The most important information about the most important particulate fillers of PP are listed in the following paragraphs. For more detailed information refer to handbooks [1] and monographs [2]. 

Calcium carbonate exists in three crystalline modifications (calcite, aragonite, vaterite), but only calcite has practical importance. It can be found in large quantities all over the world, but fillers mined at different locations differ considerably in purity, size of the crystals and origin, which all influence their use as fillers. In nature, it can be found in three different forms limestone, chalk and marble. Limestone is a consolidated sedimentary rock formed by the deposition of shells and skeletons of marine organisms, chalk is soft-textured limestone laid down in the cretaceous period and consists of nanofossils marble is metamorphic limestone formed under high pressures and temperatures. CaCOj occupies second place in usage behind talc in PP. 

This reinforcement is used in two forms in PP. Glass mat reinforced PP (GMT-PP) is produced in small quantities for the automotive industry. Composites containing short GF are also used in this area, mostly for under-hood apphcations. The properties of GF reinforced PP are in the 

Filler Composition Density (glcm ) Mohs hardness Shape 

Kaolin is used only in small quantities in PR The anisotropic particle geometry of wollastonite and mica reinforces the pol)uner. The latter is applied more extensively in USA and Canada due to the closer location of mining facilities. Barite-filled PP has excellent vibration damping properties due to the high density of this filler. Wood flour filled PP is occasionally applied in the automotive industry for the preparation of door panels. Water absorption of this filler creates problems in processing and application. The most important characteristics of mineral fillers are collected in Table 2. 

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If higher stiffness is required, short glass reinforcement can be added. The use of a coupling agent can dramatically improve the properties of glass filled PP. Other fillers for polypropylene inclnde calcium carbonate and talc, which can also improve the stiffness of... 

The multiple functions of mica have been outlined in Chapter 1 of this book, along with an example of its role in the search of multifunctional fillers for polypropylene compounds for automotive applications. Mica-reinforced thermoplastics such as polypropylene, polyethylene, nylon, and polyesters are now established in a variety of automotive applications and consumer products where mica supplements or replaces glass fibers and other mineral fillers. The wider use of mica in many applications has been limited by low impact strength and low weld-line strength in certain plastics. These issues are the focus of continuing R D efforts by materials suppliers and compounders/molders. 

Sulfur free lignin, derived from the methanol based organosolve pulping of spruce wood as well as from beech wood prehydrolysis, has been proposed as a filler for polypropylene films [177]. 

Olefin Polymers. The flame resistance of polyethylene can be increased by the addition of either a halogen synergist system or hydrated fillers. Similar flame-retarder packages are used for polypropylene (see Olefin polymers). Typical formulations of the halogen synergist type are shown in Table 15 the fiUer-type formulations are in Table 16. 

It has been found that, for a fixed mineral filler content, the viscosity of PMF-based composites increases when the coat is made of polyethylene [164, 209, 293], poly(vinyl chloride) [316] and polypropylene [326, 327], The picture was different, however, for composites based on the ethylene/vinyl acetate copolymer to which kaolin with grafted poly (vinyl acetate) was added [336]. Addition of PMF with a minimum quantity of grafted polymer results in a sharp drop of flowability (rise of viscosity), in comparison to addition of unmodified filler but with a further increase of the quantity of grafted polymer the flow gradually increases and, depending on the kaolin content and quantity of grafted polymer, may even become higher than in specimens with unmodified filler, for equal concentrations. 

One outlet for polypropylene, polyethylene, and polyvinyl chloride waste is plastic lumber. These materials, often containing more than one polymer and a wide variety of additives, provide superior weather resistance in humid environments when compared to natural wood. To manufacture these materials, the compound incorporates compatibilizers, which allow dissimilar polymers to mix evenly, Additionally, they assist in the incorporation of fillers and additives, such as wood flour, calcium carbonate, and pigments. 

M. LeBras., Mineral fillers in intumescent fire retardant formulations - Criteria for the choice of a natural clay filler for the ammonium polyphosphate/pentaeythritol/polypropylene system, Fire and Materials, vol. 20, pp. 39-49,1996. 

Table 3.5 shows some examples of the property effect ratios for mineral filler-reinforced polypropylene. The effect ratio is the performance of the reinforced polymer divided by the performance of the neat polymer. Properties of low-level glass fibre reinforced polypropylene are given for comparison. 

Bulk storage of 70% acid or greater may be in mild steel semi ebonite lined (without silica filler). Polyethylene, polypropylene, and PVDF are commonly used for construction of other major components. 

In 75% of the cases, wood fibres are the preferred filler for thermoplastic matrices. Their high availability may account for this. The resulting composite material is internationally known as WPC, which stands for wood plastic composite. They have been produced industrially since 1980 and the market has gradually increased in the last 10 years, especially in the United States, reaching 700 000 metric tons with an 11% increase rate per annum. In Europe, the WPC market is considered to be emerging. At the best estimations, it reached only 100 000 metric tons in 2005 (Anonymous, 2006) and in lapan the market is even smaller. In America, more than 50% of the WPC is used for parquets and decking made with polyethylene. In Europe, it is the automobile sector that is preponderant with polypropylene-based composites. 

FIGURE 7.3 Temperature profiles for polypropylene compounds containing increasing loadings of magnesium oxide filler. (From Hornsby, P.R. and Watson, C.L., Plast. Rubber Process. Appl., 11, 45, 1989. With permission.)... 

Bertelli, G., Goberti, P., Marchini, R., Camino, G., and Luda, M.P., Combined melamine/mineral fillers as fire retardants for polypropylene, Proceedings from 6th European Meeting on Fire Retardancy of Polymeric Materials (FRPM 97), Lille, France, 1997, p. 34. 

For some plastics, surface treatments were necessary—for example, chromic acid treatment for polypropylene. When fillers were present in the plastics the results with cyanoacrylates often were better (this was apparent in particular with polyethylene). 

In addition to familiar phenomena such as these, new phenomena arise because of the synergism between the properties of the polymer and those of the particle filler. One such synergistic effect is enhanced shear thinning, which occurs because the shear rate experienced by the polymer confined between two particles can be much larger than the overall imposed shear rate (Khan and Prud homme 1987). Another general observation is that the filled melt is often effectively less elastic than the polymer alone, evidently because the filler enhances the viscosity more than it does the first normal stress difference Ni (Han 1981 Han et al. 1981). Thus, Fig, 6-38 shows that at fixed shear stress the first normal stress difference Nj for polypropylene decreases upon addition of CaC03 particles. ... 

Attempts to improve flexural strength by surface treatment of fillers have not, to date, been successful. A variety of silanes, titanates, and fatty acids and their derivatives have been used to coat magnesium hydroxide for use as a filler in polypropylene. " Almost all composites had inferior flexural properties. In the few cases where some improvement was seen, it was 10% more then the unfilled material. 

Figure 10.1 shows the effect of the addition of fillers to polypropylene on its crystallinity. This study was conducted under the same conditions for all specimens tested. There is a difference in the effect of CaCO-, and talc. Calcium carbonate lacks surface functional groups so it tends to have a very small influence on crystallinity and the crystallization behavior. Talc has interacting functional groups on its surface which cause the increase in crystallinity along with the concentration increase. 

The last example of macroheterogeneous lamellar solids concerns talcs that are common fillers for polyolefinic matrices because their crystalline structure induces the crystallization of, say, the polypropylene matrix. Of course, talcs are natural products whose superficial properties depend on the location of the mine. Their characteristics are reported in Table 3. 

Most composite decking manufacturers utilize high-density polyethylene, (HDPE), polypropylene, or polyvinylchloride (PVC) as polymer matrix, and wood flour or rice hulls as the principal filler for their products. Some manufacturers also add mineral fillers, such as talc. These and other changes in compositions make composite materials to vary in their appearance, shape, strength, deflection, moisture absorption, fade resistance, microbial resistance, slip resistance, flammability, and other properties, which will be discussed later in this book. 

Talc is hydrated magnesium silicate, a nonmetallic mineral, white-colored, chemically inert. Unlike many other minerals, its particles have a distinct platy shape. It has a natural affinity to oil and, therefore, serves as a good filler for hydrophobic plastics, such as polyethylenes and polypropylene. Platy particles of talc are structurally not uniform they have a layered composition, in which a brucite (magnesium-based, tetrahedron-cell atomic structure) sheet is sandwiched between two silica (octahedron-cell atomic structure) sheets. The elementary sheet is of ik (0.7 nm) thick. 

Impact resistance typically suffers progressively with an increased content of a mineral filler. For example, 40% of talc in polypropylene decreases unnotched impact... 

Mica is not in nse—so far—as a mineral filler for WPCs. However, it was rather extensively stndied in model WPC systems. Generally, it behaves similarly with calcinm carbonate in some systems—decreases flexnral modnlns of 60-mesh pine wood flonr (16.7% and 25% w/w)-filled oriented polypropylene from 10 to 20 to 30% loading level of mica (overall from 390,000-420,000 psi with no mica to 320,000 psi with 20 and 30% w/w of mica), and also decreases flex strength in the same system from 6500 psi (control) to 4000-5000 psi. As the anthor of the stndy [9] has noticed, comparisons with other phyllosilicates show mica to have the least benehts. 

Stark N, Berger MJ. Effect of species and particle size on properties of wood-tlour-filled polypropylene composites. Proceedings of the Functional fillers for thermoplastics thermosets 1997 Madison, WI. Wisconsin USDA Forest Service. Forest Products Laboratory 1997. p 1. 

Nakamura ct al. [68] have used the instrumented Charpy test to examine the effect of silica fillers on epoxy resins, while Wang ct al. [69] have used the same technique for examining RIM parts. An examination of fillers in polypropylene has been reported by Jancar and DiBcncdetto [70]. Trantina and Ochler [71] discuss the application of Charpy (and Izod) tests to the prediction of impact resistance for use in design calculations. Sharpe... 

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