Particulate filled polypropylene composites

Particulate filled polypropylene (PP) is widely used in many fields of application. The major advantage of the introduction of fillers into PP is the higher stiffness of the composites, which is especially important in applications at higher temperatures. Increased stiffness is usually accompanied by decreased impact resistance, which is not always acceptable. The selection of an appropriate PP copolymer or the incorporation of additional elastomer may lead to the often desired simultaneous enhancement of stiffness and toughness. Incorporation of a filler into the polymer changes all properties at the same time, therefore an optimization of properties is required during development. The major benefits of modified PP are versatility and an exceptional price/volume/ performance ratio. 

Numerous devices are mentioned in connection with the preparation of particulate filled PP composites, i.e. two-roll mills, internal mixers. 

The properties of particulate filled polymers are determined by the characteristics of the components, composition, interaction and structure. All four factors can be varied in a wide range thus making possible the design of tailor-made composites. 

The most important properties of the matrix polymer are its chemical composition and melt viscosity. Copolymers have lower stiffness and higher impact strength than the homopolymer, which are transferred also to the composites. Products with Mgher modulus are usually prepared from homopolymers, while those subjected to dynamic loads during application are made from copolymers. Also the sequence distribution of the ethylene and propylene units is of importance, as 

The most important filler characteristics determining the properties of PP composites are particle size, particle size distribution, specific surface area and shape. None of these influence stiffness very much the reinforcing effect is a result of the orientation of the anisotropic particles. All other properties are considerably affected by these filler characteristics. Yield stress and strength usually increase with decreasing particle size and increasing surface area, while deformability and impact resistance change in the opposite direction. 

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Pukanszky B (1999) Particulate filled polypropylene composites. In Karger-Kocsis J (ed) Polypropylene An A-Z reference. Chapman Hall, London... 

The objective of this section is to provide a basis for predicting the limits of fracture toughness and impact strength of particulate-filled polypropylene by using the combined concepts of LEFM and small-scale yielding. To describe a concentration dependence of the composite yield strength, a microscopic model based on concepts of localized yielding and percolation theory is used (81). 

B Pukanszky. Particulate-filled polypropylene structure and properties. In J Karger-Kocsis, ed. Polypropylene Structure, Blends and Composites, Vol. 3, Composites. 1st ed. London Chapman and HaU, 1995, pp 21-35. 

In addition to the nature of particulate platelet orientation induced during injection moulding, the associated consequences on molecular orientation and crystalline order of the host thermoplastic matrix have also been reported with particular regard to various flake-filled polypropylenes [174], together with an attempt to interrelate these higher order structural parameters with physical properties of the composites [175]. 

Experimental data for standard Charpy impact suength was analyzed for array of particulate-filled and rubber-modified polypropylene composites (90). Table 6.1 summarizes interphase design characteristics. 

Particulate-filled composites are widely used in many fields of application. The filler used in largest quantity is CaCOs, which is added mainly to poly(vinyl chloride), but significant amounts are used also in polypropylene, polyethylene and other polymers. Typical products prepared from CaCOs-filled composites are sewer and drainage pipes, garden furniture and breathable films [1]. The properties of particulate-filled polymers are determined by several factors, of which interfacial interactions are extremely important [2, 3]. Particle-particle and... 

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