Handbook of Nucleating Agents

George Wypych

• Publisher: ChemTec Publishing
• Year: 2016
• eBook ISBN: 9781927885123
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Handbook of Nucleating Agents gives engineers and materials scientists the information they need to increase the production rate, modify structure and morphology, and reduce haze of polymeric products with proper selection of nucleating agents and clarifying agents. Chemical origin and related properties of nucleating agents are analyzed in general terms to highlight the differences in their properties, including the essential theoretical knowledge required for correct selection and use of nucleating and clarifying agents. This includes methods of chemical modification of nucleating agents and their deposition on suitable substrates; methods and results of dispersion of nucleating agents; influence of their concentration and cooling rate on final result and rate of crystallization; nucleation efficiency of different products and the reasons behind it; and generally accepted mechanisms of nucleation. The book also covers application aspects in different formulations. Patent literature and research papers are extensively reviewed for different applications, and polymer processing methods which require use of nucleating agents are discussed, with an emphasis on the intricacies of use of nucleating agents in different polymers and products. - Enables engineers to use nucleating agents more effectively to increase production rate, modify structure and morphology, and reduce haze of polymer products - Provides a thorough theoretical grounding required for proper selection and use of nucleating and clarifying agents - Offers an extensive review of current applications of nucleating agents in different formulations - Includes analysis of the chemical origin and related properties of nucleating agents to highlight differences in their properties

1

INTRODUCTION

Nucleation is the initial process that occurs in the formation of a crystal from a solution, a liquid, or a vapor, in which a small number of ions, atoms, or molecules become arranged in a pattern characteristic of a crystalline solid, forming a site upon which additional particles are deposited as the crystal grows.¹

Phase transformation begins with formation of a new phase in the supersaturated old (mother) phase. The thermodynamic stability of the system requires continuity of the thermodynamic functions during the phase transformation, the change in the thermodynamic potential occurring close to the transition point is by nature very small.² Two possibilities exist: either an infinitely small amount of a new phase appears, having different properties than the old phase, or a new property appears.² The first case is known as the first-order phase transition because first derivatives of the thermodynamic potential are changed, whereas the second case is known as the second-order phase transition because second derivatives of the thermodynamic potential are changed.²

Nucleation is a step in the phase and state transitions, involved in such processes as condensation, evaporation, crystallization, or melting, which are all the first-order transitions. The first-order transition begins with a need to overcome a free-energy barrier to create nucleus of the new phase on which additional elements of the system are deposited to grow a crystalline phase.

Nucleation is either homogeneous or heterogeneous. Homogeneous nucleation is very rare since it requires specially designed experiments in system, which does not have any foreign elements. Although even in such cases, heterogeneous nucleation at container walls or free surface occurs (e.g., formation of bubbles in champagne poured into glass).³ In homogenous system, the formation of the new phase solely depends on fluctuations within the old phase. Assemblies of elements of the homogeneous system are formed in kinetic equilibrium with free liquid system and they are dissolved back into old phase. When temperature drops, more clusters are formed (metastable old phase becomes present) and finally stable nucleus is created on which other particles are deposited forming crystal. This means that the system needs to be brought into the metastable region to reduce the phase transition barrier until it becomes of the same order as the thermal energy, kT (where k is the Boltzmann constant and T is the absolute temperature).²

Heterogeneous nucleation occurs on the surface of impurities. These may exist in any system or special additives can be added to facilitate heterogeneous nucleation. Any interface with another material has potential importance for nucleation.³ Examples include a free surface, the wall of a container, embedded particle, an interphase boundary in a liquid or solid, and a grain or domain boundary in a solid.³ All such interfaces have positive free energies.³ Heterogeneous nucleation faces much smaller barrier towards phase transition. Rain, fog, ice and snow, salt crystallization by evaporation of sea water, and gas bubble formation in mineral water—in addition to polymer processing—begin with the nucleation of a new phase.

Polymeric materials during their production must undergo phase changes to be formed into shapes required by their product design. For this reason, nucleation processes are very essential for the production technology, economy of the production, and product characteristics.

This book discusses use of nucleating agents to increase the production rate, modify structure and morphology, and reduce haze of polymeric products with proper selection of nucleating agents (or the so-called clarifying agents). Handbook of Nucleating Agents brings analyses of important publications out of slightly less than 10,000 available today referring to various aspects of action of nucleating agents. Also many relevant patents are reviewed.

Sufficient understanding for proper use of nucleation technology requires analyses of many aspect related to this subject. The book is divided into 14 chapters each of which concentrates on the essential performance of nucleating agents. Chemical origin and related properties of nucleating agents are analyzed in the general terms to highlight the differences in their properties and thus mode of their action. The specific agents are discussed in Databook of Nucleating Agents which is published as a separate book to help in selection of products available in the commercial markets and to analyze properties of different products.

Many theoretical principles help in proper application of nucleating agents. One of the important aspects is their effect on the rate and the degree of crystallization of polymeric matrices into which they have been introduced. Critical processes occur here during crystallization process. Decrease of temperature alone already causes crystallization of polymers, usually with formation of α-crystals. Addition of nucleating agent contributes to formation of β-crystals which drive equilibrium of properties towards faster solidification (possibility of speeding process of removal of parts from forms) or to better organization of internal structure which translates to improved mechanical performance. Also, addition of well selected nucleating agents helps to produce sufficiently small spherulites that they do not interfere with light transmission thus help to produce materials having high clarity.

Quality of contact between the nucleating agent and the matrix polymer affects efficiency of its action. This will depend on properties of a pair polymer-agent and distribution of agent in the polymer matrix. Good wetting and absorption may lead to a complete removal of barrier to nucleation between both phases.

Effect of concentration of nucleating agent and cooling rate are part of well designed system, which is able to produce expected results, and able to increase nucleation efficiency. Knowledge of the mechanisms of nucleation is also important aspect of selection of nucleating agents for particular tasks.

Large segment of the book discusses use and selection of nucleating agents for different processing methods, different polymers and specific products. These sections contain practical know-how on use of nucleating additives in different environments.

This part is followed by chapters discussing effect of nucleating agents on mechanical and physical properties of materials, important analytical methods used in their studies, and health and safety information in the relationship to application of nucleating agents.

Chemical origins of nucleating agents are discussed in the next chapter. There are 20 chemical groups of nucleating agents which are either currently used as commercially available additives or tried in experimental formulations. Each group is characterized by range of properties characteristic for representatives of the group.

REFERENCES

1. Encyclopedia Britannica.

2. Nanev, C. The Theory of Nucleation, Handbook of Crystal Growth, 2nd Ed., Elsevier; 2015:315–358.

3. Kelton, K F, Greer, A L. Heterogeneous nucleation, Nucleation in Condensed Matter; Vol. 15. Elsevier, 2010:165–226.

2

CHEMICAL ORIGIN OF NUCLEATING AGENTS

Twenty chemical groups of inorganic and organic chemical are involved in production of nucleating agents. They include:

• acids

• amides

• carbon nanotubes

• graphene derivatives

• hydrazides

• inorganic materials

boron nitride

calcium carbonate

hydroxides

silica

talc

others

• masterbatches

• phosphate salts

• polymeric materials

• proprietary formulations

• salts of carboxylic acids

• sorbitol derivatives

• xylan esters

• others

Each group is discussed in a separate section below. The main output includes a table containing properties of nucleating agents which belong to the particular group. The data come from 300 gener...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Chapter 1: INTRODUCTION
• Chapter 2: CHEMICAL ORIGIN OF NUCLEATING AGENTS
• Chapter 3: POLYMER CRYSTALLIZATION WITH AND WITHOUT NUCLEATING AGENTS
• Chapter 4: PARAMETERS OF CRYSTALLIZATION
• Chapter 5: WHAT INFLUENCES NUCLEATION?
• Chapter 6: NUCLEATION EFFICIENCY MEASURES
• Chapter 7: MECHANISMS OF CRYSTALLIZATION
• Chapter 8: DISPERSION OF NUCLEATING AGENTS
• Chapter 9: NUCLEATING AGENTS IN DIFFERENT PROCESSING METHODS
• Chapter 10: APPLICATION OF NUCLEATING AGENTS IN SPECIFIC POLYMERS
• Chapter 11: NUCLEATING AGENTS IN VARIOUS PRODUCTS
• Chapter 12: EFFECT OF NUCLEATING AGENTS ON PHYSICAL-MECHANICAL PROPERTIES
• Chapter 13: IMPORTANT ANALYTICAL METHODS USED IN THE STUDIES OF NUCLEATING AGENTS
• Chapter 14: HEALTH AND SAFETY WITH NUCLEATING AGENTS
• INDEX