ABSTRACT
I. Introduction ................................................................. 381 II. Techniques to Study Toughness Mechanisms........... 383
A. Materials and Sample Preparation................. 383 B. Study of Morphology ........................................ 383 C. Study of Micromechanical Properties ............. 383 D. Determination of Mechanical Properties........ 384
III. Mechanisms of Toughness Enhancement.................. 385 A. General Aspects and Overview ....................... 385 B. Rubber Particle Toughening ............................ 385 C. Rubber Network Toughening........................... 388 D. Inclusion Yielding ............................................. 391 E. Particle-Filled Polymers (Composites) ............ 392 F. Self-Reinforcement and Compaction............... 395 G. Phase Transformation...................................... 395 H. Thin Layer Yielding Mechanisms ................... 395
IV. Results and Discussion ............................................... 396 A. Amorphous Polymers Modified with
Core-Shell Particles .......................................... 396 1. Materials Used.................................... 396 2. Toughening Mechanism in
General ................................................ 396 3. Advantages of Core-Shell
Particles ............................................... 398 B. Low Temperature Toughness in
Semicrystalline Thermoplastics....................... 402 1. Materials Used.................................... 402 2. Deformation Mechanism .................... 403
C. Block Copolymers ............................................. 405 1. Materials Used and Sample
Preparation.......................................... 405 2. Deformation Mechanism and Effect
of Thin Layer Yielding........................ 405 3. Influence of Processing Conditions
and Deformation Temperature........... 411 4. Comparison with Other Lamellae-
Forming Polymers............................... 414 D. Block Copolymer-PS blends ............................ 415
1. Materials Used.................................... 415 2. Deformation Mechanisms................... 416
E. Multilayered Systems....................................... 419 1. Materials and Sample Preparation ... 419 2. Deformation Mechanisms................... 420
V. Conclusions/Outlook.................................................... 423 Acknowledgments................................................................. 427 References............................................................................. 427
I. INTRODUCTION
In nearly all applications of polymers, the mechanical behavior cannot be ignored. Important mechanical properties include stiffness, strength, elongation at break, and, as an average property, toughness or fracture toughness. Within this context, the term “toughness” denotes the absorption of mechanical energy during a deformation that ends up in fracture. The aim of improvement or modification of polymeric materials is often to develop a material with high toughness and a large plastic elongation of break, whilst retaining a high level of other desirable properties such as stiffness and strength. These are opposed demands, and the usual technique of manufacturing of high-impact polymers — the rubber toughening — has the disadvantage of a pronounced decrease in strength and stiffness due to the rubber content [1]. Additionally, in many applications of polymers, a good balance of the mechanical properties with other properties (e.g., transparency, electric properties, flame retardancy) and a good processability is demanded. With our present knowledge, a combination of such different properties is impossible to realize in a homogeneous polymer on the basis of new monomers but only in a heterogeneous one by modifying the polymer structure on a meso-, micro-and sub-micrometer scale. There is a large variety of macromolecular and supermolecular structures (the morphology), but not all of them are of equal importance for property improvements. Only certain details of the structure are decisive for the mechanical behavior, and these details are called
property-determining structures
[2]. Often, structural defects exist that are responsible for premature failure of materials. A better understanding of such important structures or defects and their role in influencing mechanical properties is a task of particular scientific and economic importance and a key to modify and to improve the properties of polymeric materials.
