Chapter One
Search before Research Introduction
1.1 Additives 2 1.1.1 Additive functionality 3 1.2 Plastics formulations 5 1.2.1 Supply forms 7 1.2.2 Additive delivery 9 1.3 Economic impact of polymer additives 9 1.4 Analysis of plastics 11 1.4.1 Regulations and standardisation 15 1.4.2 Prior art 17 1.4.3 Databases 19 1.4.4 Scope 20 1.4.5 Chapter overview 22 1.5 Bibliography 23 1.5.1 Plastics additives 23 1.5.2 Processing technologies 23 1.5.3 Instrumental analysis 23 1.5.4 Polymer analysis 24 1.5.5 Polymer/additive analysis 24 1.6 References 24
The successful use of plastic materials in many applications, such as in the automotive industry, the electronics sector, the packaging and manufacturing of consumer goods, is substantially attributable to the incorporation of additives into virgin (and recycled) resins. Polymer industry is impossible without additives. Additives in plastics provide the means whereby processing problems, property performance limitations and restricted environmental stability are overcome. In the continuous quest for easier processing, enhanced physical properties, better long-term performance and the need to respond to new environmental health regulations, additive packages continue to evolve and diversify.
Additives can mean ingredients for plastics but they play a crucial role also in other materials, such as coatings, lacquers and paints, printing inks, photographic films and papers, and their processing. In this respect there is a considerable overlap between the plastics industry and the textiles, rubber, adhesives and food technology industries. For example, pigments can be used outside the plastics industry in synthetic fibres, inks, coatings, and rubbers, while plasticisers are used in energetic materials formulations (polymeric composite explosives and propellants). Additives for plastics are therefore to be seen in the larger context of specialty chemicals. 'Specialties' are considered to be chemicals with specific properties tailored to niche markets, special segments or even individual companies. Customers purchase these chemicals to achieve a desired performance.
Polymer and coatings additives are ideal specialty chemicals: very specific in their application and very effective in their performance, usually with a good deal of price inelasticity. The corresponding business is associated with considerable innovation and technical application knowledge. Research and development are essential and global operation is vital in this area. Plastics additives now constitute a highly successful and essential sector of the chemical industry. Polymer additives are a growing sector of the specialty chemical industry. Some materials that have been sold for over 20 years are regarded today as commodity chemicals, particularly when patents covering their use have expired. Others, however, have a shorter life or have even disappeared almost without trace, e.g. when the production process cannot be made suitably economic, when unforeseen toxicity problems occur or when a new generation of additive renders them technically obsolete.
1.1 ADDITIVES
It is useful at this point to consider the definition of an additive as given by the EC: an additive is a substance which is incorporated into plastics to achieve a technical effect in the finished product, and is intended to be an essential part of the finished article. Some examples of additives are antioxidants, antistatic agents, antifogging agents, emulsifiers, fillers, impact modifiers, lubricants, plasticisers, release agents, solvents, stabilisers, thickeners and UV absorbers. Additives may be either organic (e.g. alkyl phenols, hydroxybenzophenones), inorganic (e.g. oxides, salts, fillers) or organometallic (e.g. metallocarboxylates, Ni complexes, Zn accelerators). Classes of commercial plastic, rubber and coatings additives and their functionalities are given in Appendices II and III.
Since the very early stages of the development of the polymer industry it was realised that useful materials could only be obtained if certain additives were incorporated into the polymer matrix, in a process normally known as 'compounding'. Additives confer on plastics significant extensions of properties in one or more directions, such as general durability, stiffness and strength, impact resistance, thermal resistance, resistance to flexure and wear, acoustic isolation, etc. The steady increase in demand for plastic products by industry and consumers shows that plastic materials are becoming more performing and are capturing the classical fields of other materials. This evolution is also reflected in higher service temperature, dynamic and mechanical strength, stronger resistance against chemicals or radiation, and odourless formulations. Consequently, a modern plastic part often represents a high technology product of material science with the material's properties being not in the least part attributable to additives. Additives (and fillers), in the broadest sense, are essential ingredients of a manufactured polymeric material. An additive can be a primary ingredient that forms an integral part of the end product's basic characteristics, or a secondary ingredient which functions to improve performance and/or durability. Polypropylene is an outstanding example showing how polymer additives can change a vulnerable and unstable macromolecular material into a high-volume market product. The expansion of polyolefin applications into various areas of industrial and every-day use was in most cases achieved due to the employment of such speciality chemicals.
Additives may be monomeric, oligomeric or high polymeric (typically: impact modifiers and processing aids). They may be liquid-like or high-melting and therefore show very different viscosity compared to the polymer melt in which they are to be dispersed.
Selection of additives is critical and often a proprietary knowledge. Computer-aided design is used for organic compounds as active additives for polymeric compositions. An advantage of virtual additives is that they do not require any additive analysis!
Additives are normally present in plastics formulations intentionally for a variety of purposes. There may also be unintentional additives, such as water, contaminants, caprolactam monomer in recycled nylon, stearic acid in calcium stearate, compounding process aids, etc. Strictly speaking, substances which just provide a suitable medium in which polymerisation occurs or directly influence polymer synthesis are not additives and are called polymerisation aids. Some examples are accelerators, catalysts, catalyst supports, catalyst modifiers, chain stoppers, cross-linking agents, initiators and promoters, polymerisation inhibitors, etc. From an analytical point of view it is not relevant for which purpose substances were added to a polymer (intentionally or not). Therefore, for the scope of this book an extended definition of 'additive' will be used, namely anything in a polymeric material that is not the polymer itself. This therefore includes catalyst residues, contaminants, solvents, low molecular components (monomers, oligomers), degradation and interaction products, etc. At most, it is of interest to estimate on beforehand whether the original substance added is intended to be transformed (as most polymerisation aids).
Additives are needed not only to make resins processable and to improve the properties of the moulded product during use. As the scope of plastics has increased, so has the range of additives: for better mechanical properties, resistance to heat, light and weathering, flame retardancy, electrical conductivity, etc. The demands of packaging have produced additive systems to aid the efficient production of film, and have developed the general need for additives which are safe for use in packaging and other applications where there is direct contact with food or drink.
The number of additives in use today runs to many thousands, their chemistry is often extremely complex and the choice of materials can be bewildering. Most commercial additives are single compounds, but some are oligomeric or technical mixtures. Examples of polymer additives containing various components are Irgafos P-EPQ, Anchor DNPD, technical grade glyceryl-monostearate and various HAS oligomers. Polymeric hindered amine light stabilisers are very important constituents of many industrial formulations. In these formulations, it is often not just one component that is of interest. Rather, the overall identity, as determined by the presence and distribution of the individual components, is critical. The processing stabiliser Irgafos P-EPQ consists of a mixture of seven compounds and the antistatic agent N,N-bis-(2-hydroxyethyl) alkylamine contains five components. Similarly, the antistat Atmos 150 is composed of glycerol mono- and distearate. Ethoxylated alcohols consist of polydisperse mixtures. 'Nonyl phenol' is a mixture of monoalkyl phenols with branched side-chains and an average molecular weight of 215. Commercial calcium stearate is composed of 70% stearate and 30% palmitate. Also dialkylphthalates are technical materials as well as the high-molecular weight (MW) release agent pentaerythritoltetrastearate (PETS). Flame retardants are often also mixtures, such as polybromodiphenyl ethers (PBDEs) or brominated epoxy oligomers (BEO). Surfactants rarely occur as pure compounds.
It is also to be realised that many additives are commercialised under a variety of product names. Appendix III shows some examples for a selection of stabilisers, namely a phenolic antioxidant (2,2'-methylene-bis-(6-tert-butyl-4-methylphenol)), an aromatic amine (N-1,3-dimethyl-butyl-N'-phenyl-paraphenylene-diamine), a phosphite (trisnonylphenylphosphite), a thiosynergist (dilaurylthiodipropionate), a UVabsorber (2-hydroxy-4-n-octoxybenzophenone), a nickel-quencher ((2,2-thio-bis-(4-tert-octylphenolato)-nbutylamine)-nickel), a low-MW hindered amine light stabiliser or HALS (di-(2,2,6,6-tetramethyl-4-piperidinyl)-sebacate) and a polymeric HALS compound (Tinuvin 622). Various commercial additive products are binary or ternary blends. Examples are Irganox B225 (Irganox 1010/Irgafos 168, 1:1), Ultranox 2840 (Ultranox 276/Weston 619, 3:2), and Tinuvin B75 (Irganox 1135/Tinuvin 765/Tinuvin 571, 1:2:2).
It may be seen from Appendix II that the tertiary literature about polymer additives is vast. Books on the subject fall into one of two categories. Some provide commercial information, in the form of data about the multitude of additive grades, or about changes in the market. Others are more concerned with accounts of the scientific and technical principles underlying current practice. This book gives higher priority to promoting understanding of the principles of polymer/additive deformulation than to just conveying factual information.
1.1.1 Additive Functionality
Additives used in plastics materials are normally classified according to their intended performance, rather than on a chemical basis (cf. Appendix II). For ease of survey it is convenient to classify them into groups with similar functions. The main functions of polymer additives are given in Table 1.1.
Generally, polymer modification by additives provides a cost-effective and flexible means to alter polymer properties. Traditionally, however, the use of an additive is very property-specific in nature, with usually one or two material enhancements being sought. An additive capable of enhancing one property often does so at the cost of a separate trait. Today many additives are multifunctional and combine different additive functionalities such as melt and light stabilisation (e.g. in Nylostab[R] S-EED) or metal deactivation and antioxidation (e.g. in Lowinox[R] MD24) (cf. Table 10.14). Dimethyl methyl phosphonate (DMMP) is a multifunctional molecular additive acting as an antiplasticiser, processing aid and flame retardant in cross-linked epoxies. In a variety on the theme, some multifunctional antioxidants, such as the high-MW Chimassorb 944, combine multiple functions in one molecule. Adhikari et al. have presented a critical analysis of seven categories of multifunctional rubber additives having various combinations of antidegradant, activator, processing aid, accelerator, antioxidant, retarder, curing agent, dispersant, and mould release agent functions.
In analogy to plastics additives, paper coating additives are distinguished in as many as twenty-one functional property categories (for dispersion, foam and air entrainment control, viscosity modification, levelling and evening, water retention, lubricity, spoilage control, optical brightness improvement, dry pick improvement, dry nub improvement and abrasion resistance, wet pick improvement, wet rub improvement, gloss-ink hold-out, grease and oil resistance, water resistance, plasticity, fold endurance, electroconductivity, gloss improvement, organic solvent coating additives, colouring), even excluding those materials whose primary function is as a binder, pigment or vehicle.
Typical technology questions raised by plastic producers and manufacturers and directed at the additive supplier are given in Table 1.2, as exemplified in the application of injection moulding of polyamides. These problems may be tackled with appropriate addition of chain extenders and cross-linking agents, nucleating agents and lubricants, release agents, reinforcements, etc.
There are now far more categories of additives than a few decades ago. The corresponding changes in additive technology are driven partly by the desire to produce plastics which are ever more closely specified for particular purposes. The benefits of plastics additives are not marginal. As outlined before, they are not simply optional extras but essential ingredients, which make all the difference between success and failure in plastics technology. Typically, PVC is a material whose utility is greatly determined by plasticisers and other additives. The bottom line on the use of any additive is a desired level of performance. The additive package formulation needs to achieve cost effectively the performance required for a given application. In this respect we recall that early plastics were often unsatisfactory, partly because of inadequate additive packages. In the past, complaints about plastics articles were common. Use of additives brings along also some potential disadvantages. Many people have been influenced by a widespread public suspicion of chemicals in general (and additives in particular, whether in foods or plastics). Technological actions must take place within an increasingly (and understandably) strict environment which regulates the potential hazards of chemicals in the workplace, the use of plastics materials in contact with foodstuffs, the possible side-effects of additives as well as the long-term influence of the additives on the environment when the product is recycled or otherwise comes to final disposal.
Concerns are expressed by legislation and regulations, such as:
General Health & Fitness for purpose (food/water Safety contact materials, toys, medical)
Montreal Protocol Blowing agents for foams
EU Directives Food contact
Landfill Directives Disposal, recycling
Life Cycle Analysis Realistic evaluation of product use (flame retardants, volatiles, etc.).
All additives are subject to some form of regulatory control through general health and safety at work legislation. From an environmental and legislative point of view three additive types in particular experience pressures, namely halogen-containing flame retardants (actions pending), heavy metals (as used in pigments and PVC stabiliser systems), and plasticisers. The trend towards the incineration of plastics, which recovers considerable energy for further use, leads to concern and thought about the effects of any additives on the emissions produced. Environmental issues often have beneficial consequences. The toxicity of certain pigments, both in plastics and in paints, has been a driving force for the development of new, safer pigments with applications in wider areas than those originally envisaged. Where food contacts are the issue, the additives used must be rigorously tested to avoid any tainting of the contents of the packaging. On the whole, the benefits of additives far outweigh the disadvantages.
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Excerpted from Additives in Polymersby Jan Bart Copyright © 2005 by John Wiley & Sons, Ltd. Excerpted by permission.
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