Blends and composites

1. The importance of polymer blends and composites, fields of application, trends and directions in development. Types: polymer blends, particulate filled polymers, and fiber reinforced composites. Products and grades within the main groups, property ranges and possible applications. General rules and aspects valid for all three groups. Contents of the course, main goals and questions.

2. Particulate filled polymers. Polymers and fillers applied in practice. Main filler characteristics and their effect on composite properties. The effect of fillers on the crystalline structure of the polymer and on the properties of the composites.

3. Interfacial interactions. The size of the interface, the strength of interfacial interactions, the thickness and properties of the interphase. Wetting, thermodynamic and kinetic conditions. Prediction of properties: viscosity, modulus, yield stress and strain, strength, fracture and impact resistance. Surface modification. Non-reactive coating, surfactants. Surface coverage, efficiency and optimum amount of coating. Reactive treatment, conditions of coupling, the formation covalent bonds. Application of functionalized polymers, interdiffusion, entanglements.

4.  The structure of particulate filled polymers. Aggregation. Dependence of the extent of aggregation on filler characteristics, surface tension, particle size. Determination of the extent of aggregation. Effect of aggregation on composite properties, fracture initiation. Effect of processing conditions, improvement of homogeneity. Segregation, attrition. Orientation and orientation distribution of anisotropic fillers. Dependence of orientation on processing technology. Effect of orientation on composite properties. Combined effect of several factors, case analysis.

5.  Nanocomposites. Types and preparation techniques. Expectations and reality. Composites containing reinforcements having one, two, or three dimensions in the nanometer range. Layered silicate nanocomposites. Surface modification, interfacial interactions. Dispersion and exfoliation. Hierarchical structure: particle, tactoid, platelets, and silicate network. Structure-property correlations. Comparison of micro- and nanocomposites. Possibilities for further development, possible application areas.

6.Miscibility of polymers, phase diagrams. Factors determining miscibility, entropy and enthalpy, interactions. Miscibility models. Measurements used for the estimation of miscibility: glass transition temperature, microscopy, scattering techniques and other methods. Blends of immiscible polymers, compatibility. Possible and most frequent morphologies, phase inversion.

7. Correlation between miscibility, structure and blend properties. Models describing the composition dependence of blend properties: viscosity, modulus, yield properties, strength and impact resistance. Characteristic dimension of the dispersed phase, dependence of this dimension on miscibility. Effect of processing on the characteristic dimension of the dispersed phase. Dependence of properties on the characteristic dimension, contact surface, interaction.

8. Compatibilization by physical and chemical methods, blending agents, modified polymers. Specific groups and reactions. Effect of blending agents on the structure and properties of the blend. Copolymers, effect of molecular weight and chain structure, critical micelle concentration, effect of shear. Compounding, general aspects, capillary number. Internal mixer, single and twin screw extrusion.

9. Components of fiber reinforced composites. Thermoplastic and thermoset matrices, comparison. Fibers: glass, carbon and organic fibers. Interfacial interactions, coupling, the structure of the interphase. Methods used for the determination of interfacial adhesion.

10. The use of natural fibers in composites. Advantages and drawbacks. Water absorption, biological effects, interaction. Modification of interaction, processability and processing. Modification of the fibers, non-reactive and reactive interaction, impregnation, chemical modification. Wood flour reinforced composites, microcrystalline cellulose.

11.  Structure of fiber reinforced composites, long and short fiber reinforcement. Cavities. Micromechanical deformation processes: debonding, fiber pull out, matrix fracture, buckling. Factors determining composite properties, stiffness, strength. Failure, design criteria: maximum stress or deformation, maximum work, interaction of stress components. Application of composites.

12. Stress concentration, thermal stresses, adhesion. Type of micromechanical deformations: shear yielding, crazing, debonding, cavitation. Criteria of the initiation of micromechanical deformation processes, competitive processes. Relation of micromechanical deformations and macroscopic properties.