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About this book

This book extensively reviews Polypropylene (PP), the second most widely produced thermoplastic material, having been produced for over 60 years. Its synthesis, processing and application are still accompanied by vigorous R&D developments because the properties of PP are at the borderline between those of commodity and engineering thermoplastics.
Readers are introduced to various tacticities and polymorphs of PP, and their effects on structural properties. Further, the book addresses the control of optical properties using nucleants, provides strategies for overcoming the limited cold/impact resistance of PP, examines in detail the effects of recycling, and presents guidelines for the property modification of PPs through foaming, filling and reinforcing with respect to target applications. Special attention is paid to descriptions and models of properties as a function of morphological variables. Last but not least, the book suggests potential practical applications of PP-based systems, especially in the packaging, appliances, building/construction, textile and automotive sectors.
Each chapter, written by internationally respected scientists, reflects the current state-of-art in the respective field and offers a vital source of information for students, researchers and engineers interested in the morphology, properties, testing and modeling of PP and PP-based systems. The content is indispensable to the appropriate application of PPs and related composites.

Table of Contents


Chapter 1. Tacticity, Regio and Stereoregularity

This chapter focus on the polypropylene tacticity. The stereoregularity and regioregularity of the processes catalyzed by heterogeneous and homogeneous Ziegler-Natta catalysts are discussed. The amazing variety of molecular architectures available for polypropylene-based materials are summarized together with the catalytic mechanisms for tacticity control. The main techniques applied for the determination of PP tacticity are reported as well as the outstanding development of new catalyst systems able to achieve unprecedented PP microstructures.
Giovanni Talarico, Claudio De Rosa, Finizia Auriemma

Chapter 2. Solid State Polymorphism of Isotactic and Syndiotactic Polypropylene

The crystal structure and polymorphism of isotactic (iPP) and syndioactic polypropylene (sPP) are illustrated, highlighting the rich variety of phase behavior of these polymers, the conditions of obtainment of the different polymorphs and the disorder phenomena occurring in the crystals. After description of the concepts of packing and conformational polymorphism occurring in the case of iPP and sPP respectively, the crystal structure of the different polymorphs of iPP and sPP are described. In particular, the main structural features relative to the monoclinc α-, the trigonal β- and the orthorhombic γ-forms, of iPP including the mesomorphic form, and the trigonal form which develops in random isotactic copolymers of propylene with pentene or hexene units, are described at first, the chain conformation in all these polymorphs being the 3/1 helix. Then, the complex polymorphism of sPP and the crystal structure of the orthorhombic helical form I and II, the orthorhombic trans-planar form III, the monoclininc form IV, and the trans-planar and helical mesophases are illustrated. The implications of the crystal structure with the final properties are outlined for these polymers, the great fortune of which was the almost simultaneous discovery of the polymerization catalyst systems and the structural elucidation.
Finizia Auriemma, Claudio De Rosa, Anna Malafronte, Miriam Scoti, Rocco Di Girolamo

Chapter 3. Polypropylene Nucleation

This chapter aims to summarize the most important details of nucleation in polypropylene. The details of crystallization as well as the most important ways of targeted manipulation of crystalline structure in polypropylene are also discussed. The basic techniques like calorimetry (DSC), thermo-optical and scanning electron microscopy (TOM and SEM) and wide angle X-ray scattering (WAXS) are introduced together with some rarely used technique—like rheology for example—for characterization of nucleating effect. The nucleating agents are classified into two main groups. The first group is the “conventional” heterogeneous nucleating agents and the second class is the “soluble” nucleating agents. The structure that develops in the presence of both nucleating agent groups is presented in details. Moreover, the correlation between the crystalline structure and the properties is also demonstrated. An empirical equation is also described, which links the crystalline structure to the tensile stiffness quantitatively. The most important structural parameters, which influence the optical properties of the polymer are also introduced, but the quantitative correlation cannot be provided.
Flóra Horváth, János Molnár, Alfréd Menyhárd

Chapter 4. Crystallization of Polypropylene

Various aspects of polypropylene (PP) crystallization are discussed. The methods of studying the crystallization process and formed crystalline structure are presented. The polymorphism of crystals of polypropylene is presented and discussed. The general aspects of crystal nucleation and growth are recalled and typical structures crystallizing in polypropylene are characterized: single crystals, spherulites, shish-kebabs. The main elements of the nucleation theory are presented and the formation of spherulitic structure is discussed in more details. The crystallization of PP under special conditions has been reviewed. Nucleants for crystallization of polypropylene are briefly revoked. The melting of polypropylene is described.
Andrzej Pawlak, Andrzej Galeski

Chapter 5. Morphology Development and Control

When referred to polymers, the word morphology is adopted to indicate: crystallinity, which is the relative volume occupied by each of the crystalline phases, including mesophases; dimensions, shape, distribution, and orientation of the crystallites. In this chapter, we describe the morphology of isotactic polypropylene in function of the main variables: temperature, pressure, and flow. This description is carried out not only under the phenomenological point of view but also considering the models which describe the effects of these variables. The chapter describes then the morphology development during injection molding, which is taken as an example of a complex process in which fast cooling rates, high pressures and strong flow fields are involved. A case study in which the simulation of the behavior of polypropylene during injection molding tests is eventually reported.
Roberto Pantani, Felice De Santis, Vito Speranza

Chapter 6. Polypropylene Copolymers

The wide variety of copolymers of polypropylene (PP) is one of the key reasons for the technical and commercial success of this polymer. While historically compounds with elastomers came before reactor-based compositions, the latter now dominate the market. This is the result of developments on both the catalyst and the process side of production. Two main classes are distinguished, homogeneous random copolymer with either ethylene or higher α-olefins (like butene or hexene, both of which can also be combined with ethylene to give terpolymers), and heterophasic copolymers. While the former are single-phase materials, even in case of bimodality in molecular weight and/or comonomer distribution, the latter feature a complex multi-phase structure. Design variations are possible for both the crystalline matrix and the elastomeric inclusions here, allowing a wide variety of property combinations. Applications of PP copolymers are defined by their respective properties and range from advanced packaging solutions through pipe and medical applications to components for the automotive industry.
Markus Gahleitner, Cornelia Tranninger, Petar Doshev

Chapter 7. Particulate Filled Polypropylene: Structure and Properties

The characteristics of all heterogeneous polymer systems including composites containing either micro or nano fillers are determined by four factors: component properties, composition, structure and interfacial interactions. The most important filler characteristics are particle size, size distribution, specific surface area and particle shape, while the main matrix property is stiffness. Segregation, aggregation and the orientation of anisotropic particles determine structure. Interfacial interactions lead to the formation of a stiff interphase considerably influencing properties. Interactions are changed by surface modification, which must be always system specific and selected according to its goal. Under the effect of external load inhomogeneous stress distribution develops around heterogeneities, which initiate local deformation processes determining the macroscopic properties of the composites. In filled polymers, the dominating deformation mechanism is usually debonding. Particulate filled polypropylene is used in many areas, but development never stops. Natural fiber and wood reinforced polymers, layered silicate nanocomposites and hybrid composites are in the focus of attention in recent times.
János Móczó, Béla Pukánszky

Chapter 8. Polypropylene Blends: Properties Control by Design

This chapter focused on the structure-property-processing relationship of polypropylene blends (PP binary and ternary blends). The topics covers PP/thermoplastic, PP/elastomer, PP/thermoset, PP/recycled polymer and all-PP blends. The toughening, crystallization and compatibilization strategies for PP blends are summarized. The processing techniques and properties (e.g. rheology, foamability, dyeability, etc.) of PP blends are discussed. Some of the ways of properties optimization, modeling of flow behavior and molecular simulation are documented. This chapter ends with a future trend and prospective of the PP blends based materials.
Wen Shyang Chow

Chapter 9. Composites

The current chapter is dedicated to polypropylene (PP) based composites. The material grouping and presentation in the chapter follows the logic of the reinforcement length gain and covers the areas from nano- to macro-composites. Thus, separate sections are devoted to PP-nanocomposites, discontinuous fiber-reinforced, mat-reinforced, fabric-reinforced and aligned fiber-reinforced composites. Each section describes the aspects of manufacturing techniques, structure development, properties characterization as well as processing and application of the related composites. As PP matrix belongs to the family of fairly unexpensive high-volume thermoplastics and related composites are feasible for semi-structural and structural applications, the chapter is mostly concentrated in PP-composites for automotive application.
Tatyana Ageyeva, Tamás Bárány, József Karger-Kocsis

Chapter 10. Foams

This chapter deals with polypropylene foams and consist out of 3 parts. Firstly—for a better understanding—the basics of foaming are described. This includes the fundamental physical processes of diffusion, nucleation and cell growth. Furthermore, material properties which are relevant for foaming are explained and typical blowing agents (physical and chemical) are introduced. Secondly, the foaming processes for polypropylene are summarized, beginning with the so-called batch foaming which is mostly relevant for scientific research. More industrial relevant processes for foaming PP are foam extrusion, foam injection molding (FIM) and bead foaming. With FIM light-weight parts with good mechanical properties can be produced. This can be achieved with physical and chemical blowing agents and with different methods. Bead foams possess a very low density and can be directly brought into relative complex shapes. Therefore, expanded Polypropylene (EPP) is maybe the most important PP foam at all. Both methods for bead foam production (discontinuous with autoclave and continuous with extrusion process) are described as well as the fusion processe (steam chest molding). The last part of this chapter is designated to the many additives that are used in PP foams (i.e. talc, clay etc.) and their influence on properties like expansion behavior and foam morphology.
Tobias Standau, Volker Altstädt
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