Polyurethane Elastomers: From Morphology to Mechanical Aspects

ISBN-13: 9783709105139 / Angielski / Twarda / 2011 / 255 str.

Cristina Prisacariu

Opis

A comprehensive account of the physical / mechanical behaviour of polyurethanes (PUs) elastomers, films and blends of variable crystallinity. Aspects covered include the elasticity and inelasticity of amorphous to crystalline PUs, in relation to their sensitivity to chemical and physical structure. A study is made of how aspects of the constitutive responses of PUs vary with composition: the polyaddition procedure, the hard segment, soft segment and chain extender (diols and diamines) are varied systematically in a large number of systems of model and novel crosslinked andthermoplastic PUs. Results will be related to: microstructural changes, on the basis of evidence from x-ray scattering (SAXS and WAXS), and also dynamic mechanical analyses (DMA), differential scanning calorimetry (DSC) and IR dichroism. Inelastic effects will be investigated also by including quantitative correlations between the magnitude of the Mullins effect and the fractional energy dissipation by hysteresis under cyclic straining, giving common relations approached by all the materials studied. A major structural feature explored is the relationship between the nature of the hard segment (crystallising or not) and that of the soft segments. Crystallinity has been sometimes observed in the commercial PUs hard phase but this is usually limited to only a few percent for most hard segment structures when solidified from the melt. One particular diisocyanate, 4,4'-dibenzyl diisocyanate (DBDI) that, in the presence of suitable chain extenders ( diols or diamines), gives rise to significant degrees of crystallinity i-iii] and this is included in the present work. Understanding the reaction pathways involved, in resolving the subtle morphological evolution at the nanometre level, and capturing mathematically the complex, large-deformation nonlinear viscoelastic mechanical behaviour are assumed to bring new important insights in the world basic research in polyurethanes and towards applied industrial research in this area.

Recenzje

Jiri G. Drobny, President
Drobny Polymer Associates
Merrimack, NH USA

The book is written by a true expert on the subject. It is not only a review of the state of the art but also a collection of new contributions in some specialized areas. The size of the publication is only 250 pages but it is amazing how much it covers: chemistry, structural studies, thermal behavior, mechanical aspects, morphology, new developments, and perspectives. The treatment of the subject is thorough and systematic, yet the text is clearly written and the style is readable. Given that, the book will be a very useful resource for a wide range of readers, from advanced students to university educators and scientists working in the field of polyurethane elastomers.

Spis treści

 Introduction.

The past and the present of polyurethanes (PUs).

Chapter 1

Chemistry of PUs

1.1.Macrodiols

1.2.Chain Extenders (diols and diamines)

1.3.Diisocyanates

1.3.1Conventional model rigid diisocyanates

1.3.1.1.Diisocyanates reactivity with alcohols

1.3.1..2.Diisocyanates reactivity with diols

1.3.1.3. Secondary reactions of diisocyanates group during polyurethane formation

1.3.1.4. Methods to investigate the mechanism of polymer crystallization

1.3.2. 4ovel flexible diisocyanates: their versatility to polyaddition processes

1.4. PUs preparation methods. The effect of reaction conditions on structure heterogeneity

Chapter 2

Hydrogen bonding in polyurethanes

2.1. Hydrogen bond influence on polyurethane formation

2.2. Effect of hydrogen bonding on phase separation

2.3. Effect of the hard segment nature (crystallizing or not) on hydrogen bonding

2.4. Effect of hydrogen bonding on mechanical properties

Chapter 3

PUs morphology and thermal behaviour. Crystallinity and phase segregation as revealed by:

3.1. Structural studies (WAXS, SAXS, SANS)

3.2. Thermal methods (DCS, DMA, TGA, thermal creep)

3.3. Morphology (IR dichroism; SEM)

3.4.IR spectroscopy

3.4. A comparison between conventional PUs based on rigid, hard segments (not crystallizing) and novel

PUs derived from the flexible DBDI giving hard segments of constitutional mobility (crystallizing or not).

Chapter 4

PUs Mechanical Properties

4.1.General considerations

4.1.1. Influence of Hydrogen bonding on the mechanical properties. (A comparison between PUs with

hydrogen bonding and analogous structures but achieved without hydrogen bonding)

4.1.1.1. Hydrogen substitution with Deuterium. Deuterated PUs.

4.1.1.1.1 Deuterated PUs achieved with deuterated chain extenders.

4.1.1.1.2.Deuterated PUs achieved with deuterated macrodiols.

4.1.1.2. Hydrogen substitution with inert (-CH3) groups

4.1.1.2.1. Partial Hydrogen substitution.

4.1.1.2.2. Total Hydrogen substitution

4.1.1.Influence of the type of soft segment macrodiol

4.1.2. Influence of hard segment nature (crystallizing or not)

4.1.3. Influence of the type chain extender.

4.1.4. Influence of the polyaddition procedure.

4.2. Elasticity and inelasticity. Inelasticity measures.

4.2.1 Tensile Modulus.

4.2.2 Hysteresis: work input and unrecovered strain.

4.2.3.Mullins effect

4.3. Creep and Stress Relaxation

Chapter 5.

Sensitivity of elasticity to PUs chemical and physical structure

5.1. Variation of cyclic tensile responses with PUs degree of crystallinity

5.2. Variation of cyclic tensile responses with PUs degree of phase separation.

Chapter 6.

PUs strain induced orientation and crystallization

6.1. Orientation of structure under tensile deformation as revealed by WAXS and SAXS

measurements

6.2. Orientation and crystallization of PU microstructure as revealed by dichroic measurements

Conclusions

Perspectives