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III Synthetic Particulate Fillers

Carbon Black as a Polymer Filler

14

Michael E. Spahr and Roger Rothon

Contents

Definitions....................................................................................... 262

Introduction...................................................................................... 263

Carbon Black Manufacturing................................................................... 265

Principles of the Carbon Black Formation.................................................. 265

The Furnace Black Process.................................................................. 266

Dual-Phase Blacks........................................................................... 267

Surface-Modified Blacks.................................................................... 269

Unconventional Sources..................................................................... 269

Carbon Black Properties........................................................................ 269

Terminology of the Morphological Properties.............................................. 269

Carbon Black Microstructure................................................................ 270

Primary Particle Size and Porosity.......................................................... 271

Aggregate Size and Shape and Carbon Black Structure.................................... 273

Surface Properties............................................................................ 277

Solid Contaminants.......................................................................... 278

Electrical and Thermal Conductivity........................................................ 278

Typical Properties of Filler-Grade Carbon Blacks.......................................... 278

Carbon Black in Polymers...................................................................... 278

Reinforcement of Elastomers................................................................ 279

Carbon Black for Pigmentation............................................................. 288

Carbon Black for UV Protection............................................................ 288

Future Directions................................................................................ 290

Cross-References................................................................................ 290

References....................................................................................... 290

M.E. Spahr (*)

IMERYS Graphite and Carbon Ltd., Bodio, Ticino, Switzerland e-mail: This email address is being protected from spam bots, you need Javascript enabled to view it

R. Rothon

Rothon Consultants and Manchester Metropolitan University, Guilden Sutton, Chester, UK e-mail: This email address is being protected from spam bots, you need Javascript enabled to view it

© Springer International Publishing Switzerland 2017

R. Rothon (ed.), Fillers for Polymer Applications, Polymers and Polymeric Composites: A Reference Series, DOI 10.1007/978-3-319-28117-9_36

Abstract

Carbon black is the generic name for a family of small-size, mostly amorphous, or paracrystalline carbon particles grown together to form aggregates of different sizes and shapes. Carbon black is formed in the gas phase by the thermal decomposition of hydrocarbons in the absence or presence of oxygen in substoichiometric quantities and is industrially manufactured in the form of hundreds of defined commercial grades that vary in their primary particle size, aggregate size and shape, porosity, surface area, and chemistry.

Carbon blacks are mainly used as reinforcing fillers in tires and other rubber products. The reinforcement effect is influenced by the interaction between the elastomer molecules, between the carbon black particles themselves, and between the carbon black particles and the elastomer matrix. For elastomer reinforcement, the primary particle size (specific BET surface area) and surface activity of the carbon black types are important as well as their carbon black structure. In addition, the degree of carbon black dispersion achieved and the carbon black loading used in the elastomer composite play a role. The type of carbon black can significantly influence the properties of the resulting rubber compounds. This explains the existence of many different standardized industrial carbon black grades being used in rubber compounds for the body and tread of tires.

Carbon blacks are expected to continue to dominate the rubber market for the foreseeable future, but they are coming under considerable pressure from precipitated silica in some important tire applications. This is because the silica offers lower rolling resistance properties and hence improved fuel economy and lower emissions. This trend is expected to continue to grow.

Specialty carbon black grades are used as black color pigments in plastics, paints, and inks, as ultraviolet (UV) stabilizers in polymers to avoid their degradation under the influence of visible and UV light, and as fillers to impart electrical conductivity to polymers for electrostatic dissipative and conductive applications.

Keywords

Carbon black • Furnace black • Dual-phase black • Reinforcement • Color pigment • UV stabilizer • Elastomer • Thermoplastics • Carbon black production

Definitions

Carbon black is the generic name for a family of small-size, mostly amorphous, or paracrystalline carbon particles grown together to aggregates of different sizes and shapes and is a modification of carbon with high surface area-to-volume ratio. Carbon black is formed in the gas phase by the thermal decomposition of hydrocarbons from various sources and in that way is industrially manufactured in the form of hundreds of defined commercial grades that vary in their primary particle size, aggregate size and shape, porosity, as well as surface area and chemistry. The properties can be precisely controlled by varying the process type and process conditions. This distinguishes carbon black from other forms of soot being the term for mostly undesired, sometimes hazardous solid carbon by-products from the uncontrolled combustion of carbonaceous material. Carbon black is mainly used as a reinforcing filler in tires and other rubber products. Specialty grades are used as black color pigments in plastics, paints, and inks as well as fillers to impart electrical conductivity to polymers for electrostatic dissipative and conductive applications.

Introduction

The use of carbon black as black pigment for paints and inks goes back to the early civilizations of mankind. With the invention of the book printing in the fifteenth century, which developed to be the most important way of communicating information until recently, the demand for strong black pigment has increased steadily. The traditional carbon black initially used for these coloring purposes was lampblack. In the first manufacturing processes of lampblack, wood was burnt smoldering under low air supply, and the smoke passed into a cone-like soot chamber where the carbon black settled on the walls of metal, linen, or wool. The charred wood was sold as charcoal. In the early 1900s, the lampblack producer Binney & Smith, later well known for their crayon products, began selling their carbon black chemicals to Goodrich Tire Company, initially as a coloring agent to change the white rubber tires into black. By this coincidence, it was found that the use of carbon black in rubber manufacturing significantly increased certain desirable qualities for rubber meant to be turned into tires. It was in 1904 in England when Sidney Charles Mote and a team of experimenters discovered the reinforcing effect that carbon black imparts to rubber, and some years later, this beneficial effect became common knowledge and general practice in tire tread compounding. In addition to the reinforcement, the resistance of carbon black to ultraviolet (UV) radiation and its function as ozone scavenger stabilizes the tire rubber toward UV light as well as oxidation and prevents the rubber tire from fissuring and cracking. Adding carbon black avoids electrostatic charging and also helps to conduct heat away from certain hot spots on the tire, specifically, in the tread and belt areas, which can get particularly hot at times while driving. This reduces thermal damage on the tire, which further extends its lifespan. The first larger industrial manufacturing plants for tire blacks were channel black processes using at a very low carbon black yield the natural gas which occurred in oil production as a by-product.

The introduction of synthetic rubbers, particularly of styrene-butadiene rubber (SBR), during World War II again stimulated large development activities for carbon black fillers as the strength of SBR as pure gum vulcanizate was too low to be used for tires. It was found that these synthetic rubbers with the newly developed oil furnace black fillers made tire treads of greater abrasion resistance than natural rubber with the traditional channel black boosting the demand for these grades.

Table 1 Global markets for carbon black (CY 2013)

Application/market

Quantity

[ktons]

Main use

Total global carbon black consumption

11,360

Rubber for tire applications

8,320

Reinforcing agent

Rubber for nontire applications

2,240

Reinforcing agent

Plastics

350

Pigment, UV stabilizer

Plastics, rubber

105

Conductive additive

Surface coatings

190

Pigment

Inks

150

Pigment

Others

5

The two fundamental properties of carbon black are closely linked to the two main polymer application areas: its reinforcing effect in natural and synthetic rubber and its color, which makes it the most widely used black pigment in plastics, paints, and inks. Moreover, within special applications, its thermal and electrical conductivity and its resistance to UV radiation and antioxidation effect play a role. In 2013, a total amount of about 11.4 Mio. tons of carbon black were consumed globally (Ita 2013). As shown in the market overview in Table 1, about 73% of this carbon black went into rubber compounds used for tires and about 20% into rubber compounds for nontire applications. Today, these rubber black grades are almost exclusively manufactured by variants of the modern furnace black process. The remaining 7% was consumed in specialty applications like color pigments, antioxidants, light stabilizers, and fillers for electrically and thermally conducting plastics or elastomer composites.

Depending on the application, carbon black has special property profiles that are specifically defined by the nature of the industrial production process and by varying the process parameters. This aspect distinguishes carbon black from soot which is the term used for mostly undesired carbon by-products from incomplete combustion of carbonaceous materials in heating systems, engines, and furnaces. The incomplete combustion also creates oily residues that may be found in the soot as well as polyaromatic hydrocarbons (PAH) absorbed at the soot surface and being potentially carcinogenic. The polluting and harmful effects have brought soot to the attention of public authorities such that the formation and emission of soot are increasingly restricted by legislation. Nevertheless, the increasing public environmental concerns and stricter regulations for pollution and energy and fuel consumption as well as for emission of climate-changing gases have also triggered the improvement of carbon black manufacturing technology. In this regard, more efficient manufacturing processes with an improved combustion and higher yield as well as the recovery of heat and chemical energy created as by-product of the carbon black production have become the objective of recent process development activities.

 
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