additives for plastics handbook || an overview of additives
TRANSCRIPT
CHAPTER 1
An Overview of Additives
From the very beginnings of the plastics industry, it has been necessary to add materials to a basic polymer resin in order, at least, to make it processable. It has also been clear that additive materials are necessary to modify a resin, to improve properties that are desirable, and to eliminate or mitigate properties that are undesirable. In developing additive systems, the plastics industry has learnt much from the earlier experience of the rubber industry, but the pace of development responding to market needs has produced research in completely new fields, developing additive systems using new chemistry.
While the plastics industry is a major user of additives, it is not the only one. Additives overall can be classified as follows:
Table 1.1 Types and uses of additives
Type Main applications
Additives
Antimicrobials
Coatings
Colours
Fine chemicals
Heat and light stabilizers
Optical brighteners
Products, normally used in small quantities, which enhance the value of materials such as plastics, paints, colour prints, and lubricants, by improving their processability, performance, and appearance during manufacture and in use.
Substances that prevent the growth of microbes and give consumer products such as soaps and toothpastes a medicated property.
The broad term for paints, inks, and lacquers. While often associated with decoration, coatings also protect surfaces from corrosion and damage.
Can be soluble dyes for textiles, leather, paper, or insoluble pigments for plastics, coatings, and printing inks.
Highly complex functional intermediates or ingredients for 'high-tech' applications; for example, in the pharmaceutical, agrochemical, and electronic industries.
Additives that prevent the degradation of plastics and coatings under the effects of heat, oxygen, and light.
Chemicals which impart whiteness to textiles, detergents, paper, fibres, and plastics.
2 An Additives for Plastics Handbook
Type Main applications
Photo/repro additives
Pigments
UV curing
Water treatments
Additives that, when irradiated with light, promote the hardening of printing inks, coatings, and adhesives, and chemically fix images used in electronic or graphic materials.
Colorants that remain undissolved before, during, and after application: they are used to colour plastics, inks, paints, and synthetic fibres.
Hardening of coatings and adhesives by means of ultraviolet light.
Help purify water for industrial and domestic applications. They also modify water as an agent for the processing of minerals and oils, and have a variety of properties to process water (for example, flocculants separate water from solid particles).
Source: Ciba Specialty Chemicals
For plastics, the range of additives is very large, involving the improvement of many properties:
Table 1.2 The main effect of additives on the properties of a compound
Physical properties Thermal conductivity Heat deflection temperature Abrasion resistance Impact strength Tensile strength Flexural strength Compressive strength Dielectric constant
Processing Exotherm Thixotropy Machinability Cost reduction
Calcium carbonate, calcium silicate. powdered aluminium. or copper
++ ++
= ----++
-= ++
-
Alumina, flint powder. carborundum. silica, molybdenum disulphide
++ ++
+ +
-= = = + +
----
Chopped glass
++ ++
+ + ++ ++ + + + + ++
---=
Mica, silica. powdered or flaked glass
++ ++
+ +
----++
-= --
Metallic fillers or alumina
++ ++
-++
= = = ++
-= ++
-
Colloidal silica, bentonite clay
-=
-= = = -=
-++ + + + +
Key: - decreases; ++ increases; = essentially no effect.
An Overview of Additives 3
Table 1.3 Main types of additive for plastics^ and their functions
Type Examples Functions
Calcium carbonate, talc, mica Fillers and mineral reinforcements
Fibre reinforcements Aramid, carbon, glass, natural fibres
Colorants
Black and white pigments
Heat resistance
UV resistance
Flame retardants
Antistatics, conductives
Curing systems for thermosets
Cross-linking, coupling, compatibilizing
Plasticizers
Process modifiers, processing aids
Blowing agents
Lubricants
Other types
RecycUng additives
Pigments, liquid colours, colour pastes, dyestuffs, special effects
Carbon black, titanium dioxide
Antioxidants and stabilizers
UV stabilizers
Reactive, additive, other systems
Antistatic/conductive additives
Accelerators, curing agents, and catalysts
Forming cross-links between suitable polymer and other molecules
Mainly phthalates, but many systems are used
Lubricants and plasticizers, nucleating agents
Inert gas or gas-forming chemicals injected or mixed into a compound to react during processing
Lubricants, mould release agents, slip and anti-block
Barrier properties, shrinkage, acoustics, surfactants, antimicrobials
Impact modifiers, stabilizers
Adding bulk to a compound: increasingly used to improve stiffness, surface hardness
Mechanical strength: used as short fibre, long fibre, spheres
Virtually unlimited, added as powders or liquids: easier mixing, replacement of heavy metals
Also for improved UV resistance and (carbon black) electrical conductivity
Act to delay/prevent oxidation of polymer under heat, during processing or application
Delay/prevent oxidation of end-product under prolonged exposure to sunlight
Prevent ignition of polymer, promote extinguishing: types not producing smoke or fumes
Increase electrical conductivity, to prevent electrostatic discharge, sticking/clinging (e.g. films)
Initiate and control the cure of thermosetting resins
Cross-linking agents for thermoplastics; coupling agents, compatibilizers to promote bonds between polymers and additives
Improvement in processability, flexibility: used mainly in PVC, but limited use in other plastics
Improvement of mixing/blending; control of viscosity
Production of foams and expanded plastics; replacement of chlorofluorocarbons (CFCs)
Improvement in processing; release properties; reduced slippage and blocking with films
Giving specific properties
Used to improve/protect properties of waste plastics during mechanical recycling