Additives in Polymers

4 Additives in PolymersV. Ambrogi1, C. Carfagna2, P. Cerruti2 and V. Marturano2 1 2 University of Naples Federico II, Napoli, Italy; Institute for Polymers, Composites and Biomaterials (IPCB-CNR), Pozzuoli (NA), Italy 4.1 Introduction changed by adding whiteners, dyes, or pigments to the standard formulations (Bart, 2006). 4.1.1 Role of Polymer Additives Depending on its nature, an additive is able to modify in a more or less strong way the basic Pristine polymeric materials often show poor polymer characteristics, its performance, and durabil- properties and would result in a commercial failure. ity. Traditionally additives are added in powder form, Additives play a very important role both in the although this may cause hygiene and handling pro- processability of plastic materials and in their applica- blems. On the other side, only a few additives are tions (Gatcher and Muller, 1990). The incorporation added in the liquid form (e.g., Vitamin E). Additives of additives makes polymer materials suitable for in the ideal physical form have a spherical product multiple applications in the plastic market: automo- shape (500 1500 µm) ensuring at the same time the tive, design, packaging, constructions, electronics, same performance as the original powders, high telecommunication (Pritchard, 1998). Additivation of homogeneity, dispersibility, and mechanical resis- molecules or particles to the virgin polymer can tance. In recent years the market has experienced an improve its bulk and surface properties. For example, increase in additive masterbatches (concentrates con- polypropylene (PP) (and polyolefins in general) would taining high level of additives already dispersed in the not be one of the most widely employed commodity polymer), e.g., color masterbatch (Kutz, 2011). polymer without additives. It would, in fact, degrade Therefore, an effort is usually made in the compound- in weeks, because of its poor thermal oxidative stabil- ing techniques, because each complex material added ity (Bockhorn et al., 1999). According to the to the pristine polymer could result in different pro- European Community an additive is “a substance cessability characteristics. For example, handling of which is incorporated into plastics to achieve a techni- solid additives has been reviewed (Hubis, 2000). cal effect in the finished product, and is intended to be A key parameter to take into account for the design an essential part of the finished article.” This chapter of a compounding mechanism is the surface energy aims to give an insight on the most common additives involved in the polymer/filler interaction. High used in plastic in the last few decades; in particular it surface energies create dispersion issues, adversely will be focused on the following additives: antioxi- affecting mechanical properties in the final product. dants, light stabilizers, ultraviolet (UV) absorbers, Ideally, an additive needs to interact strongly with the flame retardants (FR), heat stabilizers, impact modi- polymer matrix, minimizing the surface energy. Some fiers, plasticizers, compatibilizers, coupling agents, of these dispersion problems can be overcome by add- colorants, pigments, whiteners. A brief description of ing dispersing agents to the polymer/additive formula- bio-based additives is also given. tion, typically fatty alcohols or phosphoric esters. For example, the addition of calcium carbonate, the most 4.1.2 Technological Aspects of used additive for plastics, rubbers, and paints, can be increased by up to 70% without significant mechani- Polymer Additives cal modifications. Different effects can be achieved, such as protec- Another concern is the aggregation of fillers, if tion from several external agents, and improvement added in particulate form. This is a particularly dan- of the material performances in mechanical, pro- gerous effect because it can lead to processing pro- cessability, and miscibility behavior. Additionally, blems, and can even damage the mixing machinery. the macroscopic appearance of material can be The basis of aggregation is to be found in the attractive Modification of Polymer Properties. DOI: http://dx.doi.org/10.1016/B978-0-323-44353-1.00004-X © 2017 Elsevier Inc. All rights reserved. 87 88 MODIFICATION OF POLYMER PROPERTIES forces that can occur between similar particles, in par- particularly the connection between aging and ticular adhesion forces (hydrogen bonding, acid/base oxygen absorption. Oxygen and sunlight are the interactions, other specific interactions). A way to hin- principal degrading agents for hydrocarbon poly- der these processes is to increase shear forces, which mers during outdoor weathering (Scott, 1965). instead lead to particle separation (Nardin and Papirer, Autoxidation plays an important role in the trans- 2006). formation of organic compounds in the atmosphere As all areas in polymer technology, health stan- (Crounse et al., 2013). In particular, hydrocarbon dards must be applied to regulate the use of addi- compounds react with molecular oxygen forming tives. The most sensitive problems involve the use oxidation products according to the autoxidation of halogen-containing FR, heavy metals (as used in scheme reported in Scheme 4.1. Free radicals form pigments and polyvinyl chloride (PVC) stabilizer and react in the presence of oxygen to generate per- systems), and plasticizers. Nowadays the main con- oxy radicals, which further react with organic mate- cerns of society regarding the polymer industry are rial leading to hydroperoxides (ROOH). The latter, focused on plastic recycling. So far, the most the primary products of autoxidation, are therefore exploited technology is incineration of plastics in the main initiators in both thermal and photo oxida- order to produce energy. Additivation of any partic- tion. Consequently, hydroperoxides and their ulate can affect the safety of the incineration pro- decomposition products are responsible for the cess, releasing dangerous combustion by-products changes in molecular structure and molar mass of into the atmosphere. Fortunately, toxicity and safety the polymer, which are manifested in practice by issues have led research and development teams to the loss of mechanical properties (e.g., impact, study more sustainable alternatives with applica- flexure, tensile, elongation) and by variation in tions in even wider areas than those originally the physical properties of the polymer surface envisaged. Therefore, the last section of this chap- (e.g., loss of gloss, reduced transparency, cracking, ter will be devoted to bio-based additives, which yellowing, etc.). could guarantee a valuable and more sustainable alternative to commercial additives. 4.2 Protective Additives Many factors affect the shelf life of polymers, so in the past they were considered very unsatisfactory materials if compared to most commonly used mate- rials, such as metals and ceramics. The main con- cerns regarding polymer stability and durability are now overcome with the use of polymer stabilizers, essential ingredients that can make the difference between the success and failure of plastic items. Under natural (weathering) conditions, several factors such as exposure to sunlight, day/night or seasonal temperature variation, humidity, and atmo- spheric contamination with highly corrosive elements affect polymer stability. Ultimately, these processes Scheme 4.1 Polymer degradation in presence of lead to mechanical failure, most commonly the forma- oxygen and mechanism of activity ascribed to antioxi- tion of a brittle surface layer (Rabek, 1996). dants. Adapted from Zweifel, H., 1998. Stabilization of Polymeric Materials. Springer, Berlin. 4.2.1 Protection Against Weathering The phenomenon of oxidation has been investi- Photodegradation is a mechanism that involves gated since the late 1940s (Bolland, 1949), the activation of the polymeric chain by means of a 4: ADDITIVES IN POLYMERS 89 Table 4.1 Classification of Commercially Available Antioxidants Chemical Classification Composition Commercial Name (Supplier) Applications Primary Phenols ANOX 29 (Addivant), IRGANOX 1010 PVC, PA, PP, antioxidants (BASF), EVERNOX 10 (Everspring PE, cellulosic Chemical) polymers ADK STAB A040 (Adeka Corp), SONGNOX Cellulosic 1077 LQ (Songwon) polymers Amines AMINOX (Addivant), DUSANTOX 86 (Dulso), Natural rubbers ANTIOXIDANT DQ (Akrochem) Sipax DLTDP, BNX 2000 (Mayzo) PA, PE, PP Secondary Phosphites WESTON 705 (Addivant), ADK STAB 1500 Cellulosic antioxidants (Adeka Palmarole) polymers EVERFOS 168 (Everspring Chemical), ADK PVC, PS, PA, STAB PEP-36 (Adeka Palmarole), PP, PE, cellulosic ALKANOX 240 (Addivant) polymers Thioester Octolite 529 (Tiarco Chemical) Synthetic rubbers Songnox DSTDP (Songwon), Irganox PS800 PA, PE, PP, (BASF) PVC, PC light photon. Three main processes can be distin- groups, according to their protection mechanism guished (Lala and Rabek, 1980): (Rabek, 1990): • photoinitiated degradation where light is 1. Kinetic chain-breaking antioxidants (chain ter- absorbed by photoinitiators, that are then photo- minators, chain scavengers). They have the cleaved into free radicals, which can themselves capability to scavenge some or even all avail- initiate degradation on the polymeric able low molecular radicals (R•, RO•, ROO•, macromolecule; HO•, etc.) and polymeric radicals (P•, PO•, • photothermal degradation which occurs when POO•) by a process called chain-breaking elec- photodegradation and thermal degradation tron donor mechanism; enhance each other accelerating the process; 2. Peroxide decomposers, which decompose • photo-aging usually initiated by solar UV hydroperoxy groups (HOO ) present in a radiation, air, or other factors. polymer. Photooxidative degradation dominates at the Antioxidants cover different classes of com- surface, because the intensity of the UV fraction of pounds which can interfere with the oxidative sun radiation is maximum at the surface and has cycles to inhibit or retard the oxidative degradation low penetration efficiency, if compared to infrared of polymers (Al-Malaika and Sheena, 2005). Many radiation (Rabek, 1996). classes of additives have now been developed for the prevention or reduction of the oxidative degra- dation of PP. These additives seem to operate by 4.2.1.1 Antioxidants several mechanisms, some of which, in order of Antioxidants (AO) are chemical compounds increasing practical importance, are hydroperoxide which protect polymers and plastics against thermal decomposition and radical scavenging (Zweifel, and photooxidative processes that occur during 1998). A classification of commercially available natural aging. AO are generally classified into two antioxidants is reported in Table 4.1. 90 MODIFICATION OF POLYMER PROPERTIES 4.2.1.1.1 Primary Antioxidants Also available in an extensive range of molecu- Primary antioxidants inhibit oxidation via chain lar weights and product forms, aromatic amines are terminating reactions. They have reactive OH or often more active than hindered phenols, because NH groups (hindered phenols and secondary of less steric hindrance. Aromatic amines, however, aromatic amines). Inhibition occurs via a transfer of are more discoloring than hindered phenols, a proton to the free radical species. The resulting especially on exposure to light or combustion gases radical is stable and unable to abstract a proton (gas fade) and have limited FDA approval (Pocius, from the polymer chain. 2002). Hindered phenols are primary antioxidants that 4.2.1.1.2 Secondary Antioxidants act as hydrogen donors. They react with peroxy radicals to form hydroperoxides and prevent the Secondary antioxidants, frequently referred to as abstraction of hydrogen from the polymer backbone hydroperoxide decomposers, act to convert hydro- (Pospı́šil, 1993). Often used in combination with peroxides into nonradical, nonreactive, and secondary antioxidants, phenolic stabilizers are thermally stable products. They are often used in offered in an extensive range of molecular weights, combination with primary antioxidants to yield product forms, and functionalities. Sterically hin- synergistic stabilization effects. Hydroperoxide dered phenols are the most widely used stabilizers decomposers prevent the split of hydroperoxides of this type. They are effective during both proces- into extremely reactive alkoxy and hydroxy radicals. sing and long-term aging, and many have Food and Organophosphorus compounds and thiosynergists Drug Administration (FDA) approvals. ROO• antioxidants are widely used as hydroperoxide radicals are deactivated by hindered phenols via the decomposers (Shanina et al., 2002). reaction represented in Scheme 4.2 (Lutz and Phosphites, and in particular organophosphorus Grossman, 2001; Ingold and Pratt, 2014). compounds, are secondary antioxidants that decompose peroxides and hydroperoxides into stable, nonradical products, according to Scheme 4.4. They are extremely effective stabilizers during processing and are normally used in combination with a primary antioxidant. Trivalent phosphorus compounds are excellent hydroperoxide decompo- sers. Generally, phosphites (or phosphonites) are used and react according to the following general Scheme 4.2 Deactivation of ROO• radicals by hin- reaction, generating phosphates (Zweifel, 1998). dered phenols. The phenoxy radicals generated are very stable due to their ability to build numerous meso- meric forms. Scheme 4.4 Decomposition of hydroperoxides by Secondary aromatic amines act as primary means of organophosphorus compounds. antioxidants and are the most efficient hydrogen donors. The reaction of deactivation of peroxy radicals by secondary aromatic amines is reported Some of these compounds are sensitive to water in Scheme 4.3. and can hydrolyze, leading to formation of acidic Scheme 4.3 Deactivation of ROO• radicals by means of secondary aromatic amines. 4: ADDITIVES IN POLYMERS 91 species. The addition of an acid scavenger could Having several stabilizing functions combined in minimize the effect; however, the industry has the same molecule, multifunctional antioxidants generally turned directly to hydrolysis-resistant eliminate the need for costabilizers, such as compounds. phosphites and thioethers. This not only simplifies Thiosynergists. Among sulfur-based hydroperox- the formulation, but it also simplifies the storage, ide decomposers, thioethers and esters of 3,3-thio- handling, and use of the stabilizer. dipropionic acid play a very important role. Also known as thiosynergists, these compounds react according to the general reaction reported in 4.2.1.2 Photostabilizers Scheme 4.5. Hydroperoxide is typically reduced to Photodegradation is degradation of a photo- an alcohol and the thiosynergist is transformed into degradable molecule caused by the absorption a variety of oxidized sulfur products, including of photons, particularly those wavelengths sulfenic and sulfonic acid (Karian, 1999). found in sunlight, such as infrared radiation, visible light, and ultraviolet light (Yousif and Haddad, 2013). Photostabilization of polymers involves the inhi- bition or retardation of photochemical processes (mainly photooxidation) in polymers and plastics by a reduction in the rate of photoinitiation and/or a reduction in the kinetic chain length of the propa- gation stage of the photooxidation mechanism. Photostabilizers (UV, light stabilizers) are additives to plastics and polymeric materials, which prevent photochemical destructive processes and reactions Scheme 4.5 Decomposition of hydroperoxides by caused by UV radiation present in sunlight (Rabek, means of thiosynergists. 1996). Photostabilizers can be classified into three main Although thiosynergists do not improve the melt classes: UV absorbers, Quenchers, and UV stability of polymers during polymer processing, screeners. they are very efficient for long-term thermal aging UV absorbers. The action of a UV absorber is applications. Sulfur-based hydroperoxide decompo- relatively simple, as it interacts with the first sers are mainly used in combination with hindered step of the photooxidation process by absorbing phenol antioxidants. The most common commer- the harmful UV radiation (300 400 nm) before cially available thiosynergists are based on either it reaches the photoactive chromophoric species lauric or stearic acid. in the polymer molecule. Therefore, the energy Multifunctional antioxidants (Scheme 4.6) have dissipates in a manner that does not lead to only recently become available. Due to their special photosensitization. A UV absorber must be light molecular design, they combine primary and stable, because otherwise it would be destroyed secondary antioxidant functions in one compound in stabilizing reactions (Yousif, 2012). A very (Collins et al., 2005). common process for energy dissipation is converting harmful UV radiation into harmless infrared radiation or heat that is dissipated through the polymer matrix. Carbon black (CB) is one of the most effective and commonly used light absorbers, as well as rutile titanium oxide which is effective in the 300 400 nm range but is not very useful in the very short wavelength UVB range below 315 nm. The activity of many hydroxyaromatic compounds as UV stabilizers Scheme 4.6 General structure of a multifunctional for several polymers has been reported. This is antioxidant molecule. due to their filtrating action which depends on 92 MODIFICATION OF POLYMER PROPERTIES their absorption characteristics (Ranby and The quenching reaction may be represented by a Rabek, 1975; Allen and McKellar, 1980). simple reaction, shown in Scheme 4.8, where Hydroxybenzophenone and hydroxyphenylbenzo- excited donor (D ) (an excited chromophoric group triazole are well-known aromatic UV stabilizers in a polymer, which can be responsible for the initi- that have the advantage of being suitable for ation of photodegradation) is deactivated by an neutral or transparent applications (Gugumus, acceptor (quencher) (A) molecule (Rabek, 1990): 1979). However, hydroxyphenylbenzotriazole is not very useful in thin parts below 100 microns. Other UV absorbers include oxanilides for polyamides, benzophenones for PVC, and benzotriazoles and hydroxyphenyltriazines for polycarbonate (Allen and Edge, 1992). Scheme 4.8 Schematization of the quenching Hydroxyaromatic compounds are often referred reaction. to as the classical absorbers because they were originally designed to absorb the ultraviolet The development of metal complexes, particu- portion of the sunlight spectrum in the range larly those based on nickel, resulted in compounds 290 400 nm, i.e., the region which is determi- with relatively low extinction coefficients in the nant to most polymer systems. For example, near UV region and yet are often found to be super- avobenzones dissipate absorbed energy by a ior in performance. Nickel chelates are very effec- mechanism that involves the reversible formation tive quenchers of the triplet state of carbonyl of a six membered hydrogen bonded ring. The groups in polyolefins. These chelates have been following two tautomeric forms in equilibrium tested for photostabilization of polyisobutylene, provide a facile pathway for deactivation of the polybutadiene (Lala and Rabek, 1980), as well as excited state induced by the absorption of light polystyrene (PS) (George, 1974). (Scheme 4.7): Scheme 4.7 Energy dissipation mechanism occurring in avobenzone based UV-absorbers. Quenchers. These compounds are able to deacti- Hindered amine light stabilizers (HALS) are vate excited states (singlet and/or triplet) of chro- long-term thermal stabilizers that act by trapping mophoric groups present in a polymer before bond free radicals formed during the photooxidation of a scission occurs (Wiles and Carlsson, 1980). In plastic material and thus limiting the photodegrada- contrast to absorbers, quenchers do not need to tion process. The ability of HALS to scavenge radi- have high absorption at the critical wavelength for cals created by UV absorption is explained by the polymer degradation. Quenching is a bimolecular formation of nitroxyl radicals through a process process characterized by a very fast kinetics. In known as the Denisov Cycle (Hodgson and Coote, other words, quenching is a diffusion controlled 2010). process and is effective in polymer protection only It has been generally accepted that during if the sensitizer triplets have a long half-life and if UV irradiation and in the presence of oxygen the quencher is freely diffusible (Heller, 1969). (air) and radicals (R•), hindered piperidine (e.g., 4: ADDITIVES IN POLYMERS 93 2,2,6,6-tetramethylpiperidine, which is the simplest Inorganic pigments are widely used for decorative model compound for HALS) produces hindered and color coding, but not for stabilization. In general piperidinoxy radicals according to Scheme 4.9 white pigments give a better reflectance in the (Yousif et al., 2011) 300 400 nm region than colored pigments. There is Scheme 4.9 Schematization of mechanism of radical scavenging of hindered piperidine. Although there are wide structural differences in not always a good synergy between polymer and pig- the HALS products commercially available, all share ment, so the match must be considered properly the 2,2,6,6-tetramethylpiperidine ring structure (Hihara et al., 2013; Bigger and Delatycki, 1989). For (Bottino et al., 2004). HALS are some of the most further information on pigments refer to Section 4.6. proficient UV stabilizers for a wide range of plastics. In Table 4.2 a classification of commercially For example, HALS have enabled the growth of PP available photostabilizers is shown. in the automotive industry. While HALS are very effective in polyolefins, polyethylene (PE), and poly- urethane, they are not useful in PVC. 4.2.2 Heat Stabilizers As most photostabilizers behave according to differ- Heat stabilizers are used to prevent degradation ent mechanisms, they are often combined into syner- of plastics by heat, especially during processing, gistic UV absorbing additives. For example, but also in applications. For example, they are benzotriazoles are often combined with HALS to pro- widely used in PVC compounds. Heat stabilizers tect pigmented systems from fading and color changes. act by stopping thermal oxidation or by attacking UV screeners. UV screeners are materials that can the decomposed products of oxidation (Murphy, reflect the damaging light from the surface of the poly- 1999). The autoxidation process has been reviewed mer. Some examples are coatings (with paint or by in Section 4.2. Because of its structure, PVC is par- metallization) of the surface or incorporation of a pig- ticularly sensitive to heat. The largest use of heat ment with high UV reflectance (Rabek, 1990). Since stabilizers is indeed in the PVC industry, and PVC pigments act as highly absorbing additives, photooxi- has by far the most need for heat stabilizers. dative phenomena are limited mainly to the surface of Another important field of application for heat samples (Yousif, 2012). Pigments can be divided into stabilizers includes recycled materials, where they two classes: play the double role of inhibiting degradation and restabilizing post-use plastic waste. Three groups a. inorganic pigments: titanium dioxide (TiO2), zinc of materials can be classified for use as heat oxide, iron oxide (red), chromium oxide, etc.; stabilizers, and many commercially available heat b. organic pigments: phthalocyanine blues and stabilizers are classified in Table 4.3. greens, quinacridone reds, carbazole violet, Metallic salts, most commonly based on barium, ultramarine blue. cadmium, lead, or zinc, are often used together to 94 MODIFICATION OF POLYMER PROPERTIES Table 4.2 Classification of Commercially Available Photostabilizers Chemical Commercial Name Classification Composition (Supplier) Applications UV absorbers Benzophenones LOWLITE 20 (Addivant), Adhesives (polyolefins, MAXGARD 1000 (Lycus polyesters, acrylics, PVC) Ltd) Benzotriazoles TINUVIN 1130 (BASF), Adhesives (natural rubbers, SUNSORB 5411 polyurethanes, polyamides, (Everspringchem), polyvinyl alcohols, epoxies, MILESTAB 1130 (MPI polyolefins), sealants Chemie) Quenchers HALS LOWLITE 19 (Addivant) PVC, polyurethanes, PA, PET, PBT, PMMA ADK STAB LA-402AF PE, PP (Adeka) HALS GW 622 (Bejing PA, PE, PP, polyester, cellulosic Additives Institute) polymers Metal KRITILEN UV 17 (Plastika PE (agriculture, greenhouse) complexes Kritis), Vibatan PE UV MASTER 02566 (Viba Group) Table 4.3 Classification of Commercially Available Heat Stabilizers Chemical Classification Composition Commercial Name Applications Metallic salts Barium-Zinc ADK STAB 666 (Adeka) PVC Calcium-Zinc ADK STAB 36 (Adeka), PVC, PS, PE INTERLITE ZP9604 (Akcros Chemicals), ZINC STEARATE SP (Baerlocher) Organometallic Organotin ADK STB 129 (Adeka), Baeropan M26 SF PVC compounds (Baerlocher) Nonmetallic Bisphenol type ADK CIZER EP-13 (Adeka) PBT, other organic epoxy resin thermoplastics stabilizers Hydrolyzed Elvanol 51-05 (DuPont) PS polyvinyl alcohol obtain a synergistic effect. The mixed metal salts and groups covalently bonded directly to the tin atom. soaps are generally prepared by a reaction of com- Many of the alkyl tin stabilizers are considered safe mercially available metal oxides or hydroxides with to use in almost every conceivable end use for PVC the desired C8 C18 carboxylic acids. Zinc (and cad- (Figge, 1990). mium) salts react with defect sites on PVC to displace Nonmetallic organic stabilizers. Since the early the labile chloride atoms (Mesch, 1994). 1990s there has been a significant effort to reduce or Organometallic compounds, mainly based on tin. eliminate most metals, particularly lead, from PVC These compounds are all derivatives of tetravalent heat stabilizers. This crusade was launched in the tin, Sn(IV), and all have either one or two alkyl name of improving both human health and 4: ADDITIVES IN POLYMERS 95 environmental effects from metals that leach from 2. Phosphorus-based FR incorporate phosphorus PVC products. They are typically based on phos- into their structure, and the structure can vary phites, improving optical characteristics such as greatly from inorganic to organic forms, and transparency, initial color, and light fastness. between oxidation states (0, 13, 15) (Levchik Development in recent years has centered on and Weil, 2006). These FRs are also known as technical improvements, increases in processabil- char formers, because during the burning ity, handling, and dispersion (developing pellet- process they produce phosphoric acids, that ized and liquid systems) and studies on react with the substrate producing a char that toxicological properties for food contact and medi- acts as a protection of the substrate itself. cal applications. For applications in contact with 3. Metal hydrate FR. This class of FRs include food, FDA regulations recommend liquid antioxi- typically aluminum trihydroxide (Al(OH)3) dants based on natural compounds such as and magnesium hydroxide (Mg2(OH)4). These Vitamin E. products provide FR protection by releasing water upon heat decomposition, impacting the 4.2.3 Flame Retardants combustion process (Horn and Clever, 1996). All carbon-based materials, from wood to plas- tics, can be combusted as long as heat and oxygen are present, and because oxygen is plentifully 4.3 Plasticizers available, combustion is a constant force of nature on our planet. The energy is absorbed until the Plasticizers are organic substances of low volatil- C C, C O, C N bond in the backbone is broken ity that are added to plastic compounds to improve and low molecular weight volatile gases are their flexibility, extensibility, and processability. released in the atmosphere together with poten- They increase flow and thermoplasticity of plastic tially harmful elements such as nitrogen, oxygen, materials by decreasing the viscosity of polymer sulfur, fluorine, and chlorine (Morgan and Gilman, melts, the glass transition temperature (Tg), the 2013). The role of flame retardant is to make the melting temperature (Tm), and the elastic modulus polymer formulation less flammable by interfering of finished products (Chanda and Roy, 2006). with the chemistry and/or physics of the combus- Plasticizers are particularly used for polymers that tion process (Innes and Innes, 2003). FR can be are in a glassy state at room temperature. These classified into three types depending on their tech- rigid polymers become flexible due to strong inter- nology. A list of commercially available FR is actions between plasticizer molecules and chain reported in Table 4.4. units, which lower their brittle tough transition and extend the temperature range for their rubbery 1. Halogen-based FR. Halogen FRs, like their or viscoelastic state behavior (Štěpek and Daoust, name suggests, are molecules that incorporate 1983). One of the most important practical factors elements from group VII of the periodic to take into account is the mutual miscibility table—F, Cl, Br, and I. They can vary widely between plasticizers and polymers. If a polymer is in chemical structure, from aliphatic to soluble in a plasticizer at a high concentration of aromatic carbon substrates that have been the polymer, the plasticizer is called primary. per-halogenated (all hydrogens replaced with Primary plasticizers should gel the polymer rapidly halogen atoms) or can come in inorganic in the normal processing temperature range and form. The organo-halogen compounds find should not exude from the plasticized material. the most effectiveness as flame retardant Secondary plasticizers, on the other hand, have additives for polymers (Grand and Wilkie, lower gelation capacity and limited compatibility 2000). These work in the vapor or gas state with the polymer. In this case, two phases are interfering with the chemical radical mecha- present after plasticization process: one in which nism of the combustion process. However, the polymer is only partly plasticized, and another some FR belonging to this class, especially one where it is completely plasticized. For this brominated, are considered harmful for the reason these polymers do not deform homo- environment (De Wit, 2002). geneously when stressed, the deformation appears 96 MODIFICATION OF POLYMER PROPERTIES Table 4.4 Classification of Commercially Available Flame Retardants Chemical Commercial Name Classification composition (Supplier) Applications Halogen Brominated GREEN ARMOR PA, PE, PP, PS, cellulosic (Albermate) polymers BIOFR 245 (Bioray Chem) BE-51 (Chemtura) Chlorinates ARYAFIN A1/62 (Aditya PVC (flexible, rigid), cables, Birla Chem) hoses, pipes, etc. CHLOREZ 700 (Dover Other rubber ICC Institute) DECHLORANE plus 25 PA, PP, natural rubber, (Oxychem) cellulosic polymers Fluorinated BioFR KPBS (Bioray PC Chem) Phosphorus Ammonium BUDIT 380 (Budenheim) Other thermoset polyphosphates EXOLIT AP422 (Clariant) PP PE, PP, epoxy Other phosphorous BIOFR IPPP-35 (Bioray PVC, PE, PA, epoxy, PP based Chem) Other thermoplastics and EXOLIT OP 930 thermosets (Clariant) Metal hydrate Magnesium PERKALITE A100 (Akzo Natural rubber hydroxides Nobel) MAGNIFIN H-10C PVC (flexible/rigid) (Martinswerk) DUHOR C-02/s (Duslo) PP/PS Aluminum MARTINAL OL-104LEO PVC, PE, PP, other rubber trihydroxides (Albemarle) AC30 (Aluchem) Other rubber HALTEX 302 (TOR Minerals) only in the plasticizer-rich phase and the mechani- liquids, which can be added to PVC to obtain a cal properties of the systems are poor (Chanda and product with flexibility. Plasticizers for PVC can Roy, 2006). be divided into two main groups according to their PVC is the second largest selling pure polymer nonpolar part (Cadogan and Howick, 1996). The in Europe, after PE. However, PVC as a pure first group (Scheme 4.10A) consists of plastici- resin has very poor properties and requires the zers, such as phthalic acid esters, having polar use of additives to manufacture products of groups attached to aromatic rings. An important acceptable quality. The need for the use of PVC characteristic of these substances is the presence additives can be thought of in two ways: either of the polarizable aromatic ring. It has been sug- negatively, since such additives introduce gested that they behave like dipolar molecules and unwanted complexity and additional price, or posi- form a link between chlorine atoms belonging to tively, since the use of these additives gives the two polymer chains or two segments of the same additional ability to tailor the properties of the chain. The second group (Scheme 4.10B) consists final product. Plasticizers are typically organic of plasticizers having polar groups attached to 4: ADDITIVES IN POLYMERS 97 aliphatic chains and is called the polar aliphatic 4.4 Impact Modifiers group. Examples are aliphatic alcohols and acid or alkyl esters of phosphoric acid. Their polar groups The use of brittle polymers, such as PVC and PS, interact with polar sites on polymer molecules, but was limited prior to the development of rubber- since their aliphatic part is rather bulky and flexi- toughened polymers in the 1930s and 1940s. PVC ble other polar sites on the polymer chain may be has been toughened by the addition of small amounts screened by plasticizer molecules, reducing the of acrylonitrile rubber and other elastomeric materials extent of intermolecular interactions between (Seymour, 1987). The traditional purpose of impact neighboring polymer chains. modifiers is to absorb the impact energy by inducing Scheme 4.10 Effect of different types of plasticizers on PVC chains. From Chanda, M., Roy, S., 2006. Plastics Technology Handbook, fourth ed. CRC Press, Boca Raton, FL. Plasticizers can also be divided according to plastic deformation before crack initiation and propa- their chemical structures. In Table 4.5 commer- gation can happen. The general characteristics of cially available plasticizers are listed and they are such additives can be summarized as follows: divided into two main categories: phthalates and nonphthalates. The most widely used class of plas- • Low Tg; ticizers are indeed phthalates, and in particular • Effectiveness with minimum amount; phthalic acid esters. It is reported that phthalate exposure may pose health concerns. As the phthal- • Optimum particle size and particle size ate plasticizers are not chemically bound to PVC, distribution; they can leach, migrate, or evaporate into indoor air • Good adhesion to the thermoplastic matrix. and the atmosphere, foodstuff, other materials, etc. Consumer products containing phthalates can result There are basically two types of structures found in human exposure through direct contact and use, in impact resistant polymeric systems, which differ or indirectly through leaching into other products, in their fracture mechanism (Dufton, 1998): or general environmental contamination (Heudorf et al., 2007; Xu et al., 2010). In the general class of • Spherical elastomer particles (ABS [acryloni- nonphthalates are enclosed all other chemical com- trile-butadiene-styrene], MBS [methacrylate pounds, such as phosphoric acid esters, fatty acid butadiene styrene], acrylics); esters, etc. In Table 4.5, a list of commercially • Honeycomb, network-type dispersed elasto- available phthalates and nonphthalates plasticizers meric phase. is reported. 98 MODIFICATION OF POLYMER PROPERTIES Table 4.5 Classification of Commercially Available Plasticizers, Based on Their Chemical Structure Chemical Classification Composition Commercial Name Applications Phthalates Dioctyl EASTMAN DOP (Eastman PVC (flexible), pipes, hoses, phthalate Chemical Company) buildings, medical (DOP) PALATINOL DOP (BASF) PVC Diisononyl PALATINOL N (BASF) PVC phthalate LD-flex DINP (LG Chem) (DINP) Diisodecyl EMOLTENE 100 (Perstorp) PVC (flexible), phthalate KLJ-DIDP (KLJ Group) PVC (flexible, rigid), other (DIDP) rubbers, bioplastic, cellulosic polymers Di-n-buthyl PALATINOL C (BASF) PVC (flexible, rigid), other phthalate KLJ-DBP (KLJ Group) rubbers, bioplastic, cellulosic (DBP) polymers Nonphthalates Adipates ADIMOLL BO (Rhein Natural rubbers, PS, PVC, Chemie Additives) (calendaring, extrusion, injection) PALAMOLL 632 (BASF) PVC (flexible, rigid) Benzoates BENZOFLEX 2088 PVC (Eastman Chemical Company) K-FLEX 500 (Emerald performance materials) Phosphates DISFLAMOLL 51036 PVC (Rhein Chemie Additives) PVC (flexible, rigid), cellulosic KLJ-TCP-100 (KLJ Group) polymers Polyesters ADK CIZER HPN-3130 PVC (rigid)—wiring, cables, (ADK chemicals) pipes, packaging, magnetic tapes UPC Group-UN610 (UPC Cellulosic polymers, PS Group) Trimellitates EASTMAN TOTM PVC (flexible)—wiring, cables, (Eastman Chemical packaging, medical, automotive Company) MEXICHEM TOTM PVC—wiring, cables (Mexichem) Butadiene-based graft copolymers constitute one styrene and acrylonitrile in the presence of polybu- of the most used families of impact modifiers. Their tadiene to form a graft terpolymer. Each component success in the market is due to their low Tg (280°C). contributes to the effectiveness of these materials However, the presence of double bonds in diene as impact modifiers: the butadiene provides the soft polymers can induce thermal and oxidative degrada- rubbery phase, while styrene and acrylonitrile tion at fabrication temperatures and under UV and provide the polarity necessary for interfacial oxygen exposure. Therefore, these effects must be compatibility with the polymer in which they are minimized by the use of suitable antioxidants (Paul used. Other side features are also important: the and Newman, 1978). butadiene chain is susceptible to UV degradation ABS modifiers. Daly (1948) produced ABS and requires protection, while the acrylonitrile compositions in 1952 by the polymerization of brings hardness and chemical resistance. In this 4: ADDITIVES IN POLYMERS 99 Table 4.6 Classification of Commercially Available Impact Modifiers Classification Commercial Name (Supplier) Applications ABS-based ELIX TM 150 IG (Elix Polymers) PVC, rigid flexible, cellulosic polymers BLENDEX 101 (Galata chemicals) PVC rigid, cellulosic polymers Baymod A 52 (Lanxess) PVC (rigid) MBS, MABS-based CLEARSTRENGHT E950 (Archema) PC, PVC, PBT, polyesters PARALOID BTA-702S (Dow Chemical) PVC rigid Kane ace B382 (Kaneka) PVC (rigid), pipes, packaging, films Acrylic-based ADD-AIM-100 (Add chem) PVC flexible DURASTRENGHT (Archema) PVC rigid Paraloid EXL-2314 (Dow Chemical) PC, PA, PBT framework, ABS polymers are engineering thermo- methacrylate ethylhexyl acrylate styrene. Apart plastics exhibiting good processability, excellent from the improved light stability these materials toughness, and sufficient thermal stability. They also offer high impact strength, good heat resis- have found applications in many fields, such as tance, and good thermal stability (Platzer, 1972). appliances, buildings and constructions, automotive A list of commercially available impact modifiers electronic, and many others. is reported in Table 4.6. MBS modifiers. The MBS impact modifiers are similar to their ABS counterparts and are typically produced either by copolymerization of styrene and 4.5 Compatibilizers methyl methacrylate in the presence of polybutadi- ene or by polymerization of methyl methacrylate in Polymer blending is a convenient route for the the presence of a styrene butadiene rubber. Also in development of new polymeric materials, which this case the presence of butadiene makes these combine the excellent properties of more than one materials susceptible to UV degradation and limits existing polymer. This strategy is usually cheaper their use to indoor applications. The absence of and less time-consuming than the development of acrylonitrile enhances the clarity of the products new monomers and/or new polymerization routes, but reduces the chemical resistance. MBS modifiers as the basis for entirely new polymeric materials. provide the required toughness to obtain polymers, Polymer blending usually takes place in processing such as PVC, suitable for both transparent and machines, such as twin-screw extruders (Koning opaque packaging applications (impact resistant et al., 1998). However, polymers with different bottles, packaging films and sheets, electrical trunk- structures are not always thermodynamically misci- ing, etc.) (Titow, 1986). MBS impact modifiers ble and therefore cannot form homogeneous blends. demonstrated a significant impact-modifying effect The polymer in higher concentration will form a at low temperatures. However, in many cases the continuous phase and the polymer with a low addition of a large amount of the MBS impact concentration will be dispersed in the continuous modifiers is required to enhance impact strength matrix. However, the intermolecular adhesion (Tseng and Lee, 2000). between the continuous and the dispersed phase is Acrylic modifiers are probably the most widely very weak, resulting in poor mechanical perfor- used class of impact modifiers as they overcome mances of the blend. the problems associated with the limited weather Compatibilizers are macromolecular species resistance typical of ABS and MBS. This class of exhibiting interfacial activities in heterogeneous modifiers are typically graft terpolymers of methyl polymer blends. Usually the chains of a compatibi- methacrylate butyl acrylate styrene or methyl lizer have a blocky structure, with one constitutive 100 MODIFICATION OF POLYMER PROPERTIES block miscible with one blend component and a is a high loading of colorant carried in a base-resin. second block miscible with the other blend With regard to their solubility, colorants fall into component (Paul and Newman, 1978). The compa- two classes, i.e., dyes or pigments (Allen, 1971). tibilization methods can be divided into two catego- The key distinction is that dyes are soluble in water ries (Utracki, 2002): and/or an organic solvent, while pigments are insoluble in both types of liquid media. Table 4.8 1. Addition of (i) a small quantity of a compo- lists a number of commercially available dyes and nent which is miscible with both phases, (ii) pigments. a small quantity of copolymer whose one part is miscible with one phase and another with another phase, (iii) a large amount of a core- shell, multipurpose compatibilizer-impact 4.6.1 Dyes modifier; Organic dyes are often brighter and stronger than 2. Reactive compatibilization, which uses such inorganic colorants. Dyes are the best choice for a strategies as (i) trans-reactions, (ii) reactive totally transparent product. Even though some dyes formation of graft, block, or lightly cross- have poor thermal and light stability, they still linked copolymer, (iii) formation of ionically appear on the market in thousands of different bonded structures, (iv) mechanochemical formulations (Richardson and Lokensgard, 1996). blending that may lead to chain breaks and Azo dyes are numerically the most important recombination, thus generating copolymers. class of dyes, since more than 50% of all dyes listed in the Color Index are azo dyes. Covering all Strong environmental pressures are pushing shades of color, azo dyes are used for dyeing tex- industries to deal with the recycling of waste tiles, paper, leather, rubber, or even foodstuffs polymers, particularly those used in packaging (Fleischmann et al., 2015). Unlike most organic applications. PE in all its commercially available compounds, dyes possess color because they forms (high density polyethylene (HDPE), low den- (Abrahart, 1977): sity polyethylene (LDPE), linear low density polyethylene (LLDPE)) currently represents more 1. absorb light in the visible spectrum than 50% of the polymer recycling market. Along (400 700 nm); with PP, PS, PVC, and polyethylene terephthalate 2. have at least one chromophore (color-bearing (PET), PE forms the major postconsumer waste group); products concerning polymeric materials (La 3. have a conjugated system, i.e., a structure Mantia, 1993). According to the desired polymeric with alternating double and single bonds; blend, different types of compatibilizers are commercially available (Table 4.7). 4. exhibit resonance of electrons, which is a stabilizing force in organic compounds. One of their main disadvantages is their high 4.6 Dyes and Pigments solubility in plastics, for which reason they are very prone to move or migrate often resulting in Plastics can possess a wide range of colors and color macroscopically changing. Synthetic plastics designers have exploited this particular dyes cannot be commercialized unless they pose property. In fact, some uses of plastics rely little health risk under end-use conditions. For this completely on the availability of a multitude of reason, the raw materials employed in the manu- colors. When making a colored product, dry color, facture of synthetic dyes should not involve liquid color, or color concentrates may be used. compounds known to pose health risks. This Precolor is a material that has already been would include a large group of aromatic amines compounded to a desired color. Dry color is a (Ahlström et al., 2005) that are either cancer- powdered colorant, which is often difficult to suspect agents or established mutagens in the handle and leads to dust problems. Liquid color is a standard Salmonella mutagenicity assay (Prival color in a liquid base, and finally color concentrate et al., 1984). 4: ADDITIVES IN POLYMERS 101 Table 4.7 Commercially Available Compatibilizers for Targeted Blends Commercial Name Supplier Target Resins Ken-React CAPS L 12/L Kenrich HDPE/PP blends, post-consumer recycle, comm./eng. (20% active pellet) Petrochemicals, thermoplastics Inc. Ken-React CAPOW L 12/ Kenrich HDPE/PP blends, post-consumer recycle, comm./eng. H (65% active powder) Petrochemicals, thermoplastics Inc. Ken-React LICA 12 Kenrich HDPE/PP blends, post-consumer recycle, comm./eng. (100% active liquid) Petrochemicals, thermoplastics Inc. Vistamaxx propylene- Exxon Polyisobutylene (PIB), styrene isoprene styrene (SIS), based elastomer polyvinyl chloride (PVC) Exxelor polymer resins Exxon “Most commonly used polar polymers and polyolefins” Fusabond M603 DuPont PE/PA, PE/EVOH, PA/EVOH/PE Fusabond E226 DuPont PE/PA, EVOH or PA Bynel 41E710 DuPont PE/EVOH or PA/EVOH/PE Fusabond P353 DuPont PP/PA or PP/EVOH/PP Elvaloy PTW DuPont (Recycle stream) polyesters/PE Arkema Arkema Polyamide/polyolefin Styrennics Kraton Polymers Polypropylene/polystyrene or PPE, nylon/polyethylene or nylon/polypropylene, nylon/polystyrene or PPE, polypropylene/polyethylene 4.6.2 Pigments 4.6.2.2 Inorganic Pigments Pigments can be used to color any polymeric sub- Most inorganic pigments are based on metals, e.g., strate but by a mechanism quite different from that oxides and sulfides of heavy metals such as titanium, of dyes, in that surface only coloration is involved zinc, iron, cadmium, and chromium. The easiest way unless the pigment is mixed with the polymer before to classify the inorganic pigments is to divide them in fiber or molded article formation (Zollinger, 1987). three classes: white pigments (mostly based on TiO2), black pigment (CBs), and colored pigments (Huckle and Lalor, 1955). The migration of organic pigments 4.6.2.1 Organic Pigments does not occur easily unless the plastic material is Unlike dyes, which are present in polymeric degraded by weathering or chemical attack. substrates as either single molecules or small clus- However, the recycling process of the artifacts con- ters, pigments are applied in the form of discrete taining such additives represents a major concern crystalline particles well dispersed in the medium considering that the heavy metals may leach out of (Hao and Iqbal, 1997). Therefore, they must be the plastic artifact, and end up in groundwater, posing mixed and evenly dispersed within the resin. a health hazard. For this reason the use of some of the Organic pigments provide the most brilliant opaque listed metals is restricted (Järup, 2003). colors available. However, the translucent and transparent colors achieved with organic pigments 4.6.2.2.1 Titanium Dioxide (TiO2) are not as brilliant as those produced with dyes. Classified as a hiding pigment, as a result of its Organic pigments can be hard to disperse, they tend high refractive index, it owes its dominant position to form clumps of pigment particles, which behave to its ability to provide a high degree of opacity as agglomerates causing spots and specks in the and whiteness (maximum light scattering with max- product (Herbst and Hunger, 1997). imum light absorption) and to its excellent 102 MODIFICATION OF POLYMER PROPERTIES Table 4.8 Classification of Commercially Available Dyes and Pigments for Polymer Coloring Chemical Classification Composition Commercial Name (Supplier) Applications Soluble dyes Antraquinone Oil green 5602, Plast Blue 8514 (Arimoto PMMA, PS, PC, Chemical) cellulosic Solvent blue 63 (Ningbo precise color), polymers, PA, Plastone GS blue GP (Wuxi Ming Hui Int. nylon Trading) Azo Oil Red 5330 (Arimoto Chemical), PS, other rubbers Solvent Red 2BS(SRI95) (Hangzhow Dimacolor), Keyplast Scarlet BLZ (Keystone) Inorganic Iron oxide Eupolen PE Brown 29-1505 (BASF) PP, PE, pigments polyolefins Molybdated lead Lufilen Orange 30.2505 C6 (BASF) PP, PE (fibers, chromate yarns) Carbon Blacks Black Masterbatch 045 black (Changzhou PE, LDPE Plastic Modification) (packaging, agriculture) JE-BLACK JE2100 (China synthetic PVC, other rubber rubber) QualiBlack M13 (Ngai Hing Hong Coltec) HDPE, LDPE, LLDPE, food contact Titanium dioxide Polywhite 8000 (A. Shulman) PE, PP, food contact Tronox R-FK-2 (Tronox) PVC, other thermoplast Organic Benzimidazolone Akafast Carmine HF3C (Akafast), PMMA, PS, PC, Pigments Benzimidazolone Red HF2B (Haining cellulosic Light Industry) polymers, PA, nylon Quinacridone CINQUASIA Red B RT-790-D (BASF) PVC, PE, PP, PS, cellulosic polymers Mono Azo Sinfast Yellow 2008-001 (Corporation) PS, PUR, PVC BENZIDINE YELLOW RN (Hangzhou Dimachema) durability and nontoxicity. The pigment can be 4.6.2.2.2 Carbon Black (CB) produced in two polymorphic forms: rutile and CB is widely used as a reinforcing filler to anatase. The rutile form with its higher refractive improve dimensional stability, as a conductive index and better weathering properties is much filler, ultraviolet light stabilizer, antioxidant to more important than the anatase form. However, prolong the lifetime of rubber, and a pigment or the anatase form exhibits lower absorption in the colorant (Huang, 2002). CB is by far the most blue-violet region of visible light below 420 nm important black pigment, and is the second most and is frequently used, often in conjunction with used in terms of volume of all pigments employed fluorescent brightening agents (Diebold, 2003). by the plastic industry, ranking behind only TiO2. 4: ADDITIVES IN POLYMERS 103 In applications where their role is to provide a scattered at edges and corners of the particles black color, CB pigments exhibit high tinctorial increases. Larger particles are better reflectors lead- strength and an outstanding range of fastness ing to higher brilliance and brightness. The metallic property at a relatively low cost. However, CB can appearance depends also on the orientation of the adopt a number of other important functions when metal flakes in the application system, the particle incorporated into polymers. The pigments excel shape, the transparency of the binder matrix, and in their ability to protect polymers against weather- the presence of other colorants. The required parti- ing, as a result of a combination of UV absorption cle size of the pigments depends on the intended and their capability to function at the particle use and can vary from a few micrometers (offset surfaces as traps for radicals formed in the printing) to medium grades (10 45 µm, automotive photodecomposition. coatings, gravure, and flexographic printing) and coarser grades (corrosion-inhibiting systems, 4.6.2.3 Special Effect Pigments plastics). The thickness of the flakes can vary from smaller than 0.1 1 µm. Bronze pigments are intro- Special effect pigments may be organic or inor- duced in plastics to reproduce a gold or copper ganic compounds. Colored glass is used in a fine effect (Maile et al., 2005). powder form and it is a heat and light stable pigment for plastic, and highly effective in exterior uses because of its color stability and chemical resistance. 4.7 Bio-Based Additives and 4.6.2.3.1 Fluorescent Pigments Formulations The striking brilliance of a fluorescent color results when a molecule absorbs visible radiation For more than 50 years, plastic polymers have and reemits an intense narrow band of visible light been the most practical and economical solution for at somewhat higher wavelengths, reinforcing the several applications, such as packaging, personal color already present due to normal visible light care, etc., replacing more traditional materials such absorption. Fluorescent pigments are formed using as paper, glass, and metals in many packaging solid solutions at low concentrations of fluorescent applications, due to their low cost, low density, dyes in finely ground transparent resin. The main resistance to corrosion, ready availability, and out- use in plastics is visual impact in toys, packages of standing physical properties. In fact, packaging safety applications (Christie, 1994). accounts for approximately 40% of all plastic consumption. However, nowadays the biggest envi- 4.6.2.3.2 Pearlescent Pigments ronmental problem around plastics is their low The additivation of these pigments to plastics recycling percentage. Whereas 35% of metal, 30% give rise to a white pearl effect and a colored iri- of paper, and 18% of glass is recycled, only 3 4% descence. The most important pearlescent pigments of plastic is currently recycled. In the case of are thin platelets of mica coated with TiO2, which plastics the other options are energy recovery and both reflect and transmit incident light. The sense landfill disposal, and in the specific case of Europe of depth is given by the simultaneous light reflec- it can be said that around 50% of plastic is not tion from many layers of oriented platelets. recycled, hence not valorized. Therefore, bio-based, Modulating the platelets thickness colors can be biodegradable polymer formulations are increas- produced by interference phenomena (Pfaff, 2008). ingly studied, and a large number of biodegradable 4.6.2.3.3 Metallic Pigments polymers are already commercially available The most important effect pigments without a (Malinconico et al., 2014). In this regard, substitu- layer structure are by far the metal effect pigments. tion of oil-based, synthetic additives with natural They consist of flakes or lamellae of aluminum compounds acting as processing aids (Ambrogi (aluminum bronzes), copper and copper-zinc alloys et al., 2011), plasticizers (Battegazzore et al., (gold bronzes), zinc, or other metals. The metallic 2014), stabilizers (Bridson et al., 2015), or antibac- effect is caused by the reflection of light at the sur- terials (Arrieta et al., 2014) is also attracting face of the pigment particles. The observed luster interest with the aim of manufacturing bio-based effect is decreased when the part of the light and biodegradable polymer formulations. 104 MODIFICATION OF POLYMER PROPERTIES In Table 4.9, a list of commercially available (oil, protein, meal) are now being used in a wide bio-based alternative to traditional polymer addi- variety of products, such as plastics and elastomers, tives is provided. As we can notice, a good percent- paint and coatings, lubricants, adhesives, and age of products are based on vegetable oil solvents, in addition to the well-established use of derivatives (soy, palm, linseed, jatropha). The use soy oil to make biodiesel. The United Soybean of soy in industrial products has a long history: Board maintains a current listing of commercial soap, drying oils in wood finishes, adhesives, and products utilizing soy as a raw material or ingredi- paper sizing (Schmitz et al., 2008). Soy products ent (Soy Products Guide). Table 4.9 Commercially Available Bio-Based Additives Chemical Commercial Name Classification Composition (Supplier) Applications Light stabilizers/UV Mixed metal AKEROSTAB LT- PVC (flexible): fibers, textiles absorbers epoxidized 4803 (Akros soybean oil blend Chemicals) Epoxidized Vikoflex Epoxidized Chlorinated rubbers, PVC soybean oil vegetable oil (flexible, rigid): automotive, (Archema) fibers, textiles, packaging Epoxidized Vikoflex 7190 PVC (rigid, flexible) linseed oil Epoxidized vegetable oil (Archema) 8(2,2,6,6- CAPLIG 770 PE, PP tetramethyl-4- (Nanjing Capatue) piperidyl) sebacate Heat stabilizers Epoxidized Baerostab LSA PVC (rigid) soybean oil (Baerlocher) Barium salt of a Ligastab BAL (Peter PVC technical lauric Greven) acid Flame retardants Polyhydric Charmor PM40 Care alcohol (Perstorp) Crestl diphenyl Kronitex COP (Great Natural rubber, PVC phosphate Lakes) Plasticizers Esther of di-fatty SYNCROFLEX 3019 PVC, other rubbers acid (Croda) Fatty acid ester DOMPLAST BIO Natural rubbers, chlorinated DEN (Domus rubber chemicals) Acetyl 2- CITOFOL AHII PVC: wiring cables, automotive ethylhexyl citrate (Jungbunzlauer) Inorganic TiO2 Polywhite 8100 ES PE, PP pigments titanium (A. Shulman) dioxide Organic pigments Advaitya Pigment Other rubbers Green 7 (Advaita Dye Chem) 4: ADDITIVES IN POLYMERS 105 As we mentioned in Section 4.3, plasticizers are Ambrogi, V., Cerruti, P., Carfagna, C., added to polymers to facilitate processing and improve Malinconico, M., Marturano, V., Perrotti, M., flexibility of otherwise rigid polymers, mainly PVC. et al., 2011. Natural antioxidants for polypropyl- Unfortunately, unmodified vegetable oils are largely ene stabilization. Polym. Degrad. Stab. 96, incompatible with PVC. A modified soybean oil, e.g., 2152 2158. epoxidized soybean oil (ESBO), is more compatible Arrieta, M.P., López, J., Hernández, A., Rayón, E., and provides an alternative to petroleum-based plasti- 2014. Ternary PLA PHB Limonene blends cizers with PVC resin (Benecke et al., 2004). Another intended for biodegradable food packaging appli- example is epoxidized methyl ester of soybean oil cations. Eur. Polym. J. 50, 255 270. (soy-eFAME), which can be used as the sole plasti- Bart, J.C.J. (Ed.), 2006. Additives in Polymers: cizer for PVC and other polymers or it can be blended Industrial Analysis and Applications. John Wiley with ESBO (Ghosh-Dastidar et al., 2013). Soy-based & Sons, New York. plasticizers can also be utilized in bioplastics such as Battegazzore, D., Bocchini, S., Alongi, J., Frache, poly(lactic acid) and polyhydroxyalkanoates A., 2014. Plasticizers, antioxidants and reinforce- (Mekonnen et al., 2013; Xu and Qu, 2009). ment fillers from hazelnut skin and cocoa by-pro- The new business development of bio-based ducts: extraction and use in PLA and PP. Polym. chemicals does have its risks and difficulties. Degrad. Stab. 108, 297 306. Differentiation is often focused on cost and environ- Benecke, H.P., Vijayendran, B.R., Elhard, J.D., mental profiles which can require a significant advan- 2004. Plasticizers derived from vegetable oils. tage to drive change, and the barrier to entry for U.S. Patent 6797753. substitutes may be low. However, chemicals with Bigger, S.W., Delatycki, O., 1989. The effects of new functionality targeting substitution of conven- pigments on the photostability of polyethylene. tional materials may have advantages of long-term J. Mater. Sci. 24, 1946 1952. low cost compared to petro-based materials, enabling Bockhorn, H., Hornung, A., Hornung, U., bio-based claims due to renewable feedstock sources, Schawaller, D., 1999. Kinetic study on the ther- and opportunities to change the end-of-life options mal degradation of polypropylene and polyethyl- for applications (Hatti-Kaul et al., 2007). ene. J. Anal. Appl. Pyrolysis 48, 93 109. Therefore, a dramatic increase in adoption of Bolland, J.L., 1949. Kinetics of olefin oxidation. bio-based additives is expected in the near future, Q. Rev. Chem. 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