EFFECT OF ANTISTATIC AGENTS ON SOME PROPERTIES OF COMPOUNDED MATERIALS

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Effect of Antistatic Agents on Some Properties of Compounded Materials 12.1 MECHANICAL PROPERTIES Mária Omastová Polymer Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 842 36 Bratislava, Slovakia

Jürgen Pionteck Leibniz Institute of Polymer Research Dresden, Hohe Str. 6, D-01069 Dresden, Germany

Antistatic agents are classified by incorporation method as internal and external. Internal agents are usually compounded with polymer matrix at concentrations from 0.1 to 30 wt%. External agents are applied to the surface of processed polymeric product as water or alcohol based solution by spraying, dipping or wiping. They have an immediate effect, but their effect is not permanent. Both types of antistatic agents influence mechanical properties of final products. Considering the influence of additives on mechanical properties of polymers, strength (tensile and flexural), modulus (tensile and flexural), elongation, hardness, and impact resistance are tested and compared with unmodified materials. The effect of additives like antistatics on properties depends on the properties of the matrix and of the additive, its concentration and on the preparation and processing conditions. Some mechanical properties may be improved parallel to deterioration of other. Hard filler-like additives typically increase the moduli but decrease the toughness while soft, flexible or soluble additives may increase the toughness but reduce the strength. Antistatic coatings are used to hinder electrostatic charging. These coatings are often affecting also other properties of the surface like hardness, scratch resistance, haptic and optical properties, antibacterial properties, but the effect on intrinsic mechanical properties of the base material is rather small since the coated

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layer is typically thin compared to the coated polymer. Thin films or fibers, however, may be affected in respect of strength and stretching behavior. The ability of a material to resist breaking under tensile stress is one of the most important and widely measured properties of materials used in structural applications. The force per unit area required to break a material in such a manner is the ultimate tensile strength or tensile strength at break. Modulus is the ability of a sample of a material to resist deformation. Modulus is usually expressed as the ratio of stress exerted on the sample to the amount of deformation. For example, the tensile modulus is the ratio of stress applied to the elongation which results from the stress. Elongation is usually expressed as the length increased after stretching divided by the original length. Toughness is the ability of a sample to absorb mechanical energy without breaking. The external antistatic agent in the form of a film of free-standing tetraselenotetracene chloride, (TSeT)2Cl, in a polycarbonate matrix was prepared by Bleier et al.1 in a continuous casting process on a pilot-scale. Film cast from a solution of polycarbonate and tetraselenotetracene chloride in N-methyl-pyrrolidone with a loading of 1 wt% of (TSeT)2Cl related to the amount of polymer had bulk-conductivity of around 0.5 S cm-1 at a thickness of 28 µm. The stress at a lower elongation did not affect the electrical properties significantly. The needleshaped crystals are rather flexible. Therefore, bending and folding of the films of about 25 μm thickness does not affect the electrical properties. Bending a film 100 million times at bending diameters between three and ten millimeters resulted in an increase of resistance of only eight percent. The non-black antistatics have been used for a long time as additives in commodity plastics such as polypropylene, PP, polystyrene, PS, and also in engineering plastics such as acrylonitrile butadiene styrene copolymer, ABS, polyamide-6, PA-6, polycarbonate, PC, polyphenylene sulfide, PPS, and others, but their action depends on humidity. New generations of non-black antistatics also acting when humidity is as low as 15% are developed and marketed. Patent2 reports the use of block polymers for imparting the antistatic property to thermoplastic resins, especially polyolefins, comprising polyolefin blocks and hydrophilic polymer blocks having a volume resistivity of 105 to 1011 ohm-cm. The copolymer can be finely dispersed in the polymer matrix without the need of a compatibilizing agent. Molded polymer composites have permanent antistatic properties even when they were molded under shear-free conditions and even when the block polymer amount was small. The block copolymer was prepared by heating 85 parts of a low molecular weight polypropylene (Mn = 2500; density = 0.89 g cm-3) with 15 parts maleic anhydride at 200 °C for 20 h. It gave a maleated polypropylene 41 parts of which were combined with 59 parts of polyethylene glycol (Mn = 4,000) in the presence of Irganox 1010 (antioxidant) and Zr acetate at 230 °C and 1 mmHg for 3 h to give a block copolymer with Mn = 22,000. Blending 90 parts of polypropylene with 10 parts of the block copolymer and injection molding gave

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test pieces with mechanical strengths comparable with unmodified material and good antistatic properties and affinity to coating. Polyethyleneterephthalate, PET, fibers have a low moisture regain, which allows them to easily gather static charges, and many investigations have been carried out on this problem. Carboxy-terminated polyoxyethylenes, PEO-acid, with number-average molecular weights, Mn = 8,400, 3,300, and 1,000, were used for antistatic modification of PET. The blend of PET fibers containing 2.0 and 5.0 wt% of PEO-acids was melt-spun at 285°C with an extruder at 80°C.3 The processability of spinning and drawing were excellent at higher molecular weights of PEO-acid. The antistatic properties of the blend fibers were also improved with increasing molecular weight of PEO-acid. Since little ester interchange reaction took place between PET and PEO-acid during melt-spinning, the blend fibers retained almost the same mechanical properties as the original PET fiber. Block copoly(ester-ether)s containing different ionic units, i.e., sulfobetaine, S-betaine, carbobetaine, C-betaine, and ammonium tosylate, were prepared and evaluated as antistatic modifiers of PET fibers.4 The ionic units were derived from N,N-bis(2-hydroxyethyl)methylamine and co-condensed randomly with the polyester and PEO units. For the copolymers containing S-betaine units, a thick filament was melt-spun to evaluate their apparent electric resistivity. Depending on the unit compositions (25-75 wt% of PEO and 1-2 mol% of S-betaine), resistivities ranging from 108 to 1010 ohm-cm were obtained. Then, the three copolymertype modifiers were blended with PET by the blend-spinning technique. The blend PET fibers obtained showed not only good mechanical properties but also improved antistatic properties. Particularly, the fiber blended with the copolymer containing S-betaine units had the shortest half-life time of leakage of static charge, although the surface area resistivity, being in the order of 1013 ohm-cm was similar to that of the fibers blended with the copolymers containing C-betaine and ammonium tosylate units. These blend PET fibers were found to retain good antistatic properties even after dyeing and repeated washings, because both the hydrophilic and ionic groups are immobilized with the polyester chains. A series of poly(ethylene terephthalate-co-isophthalate), PEIT/poly(ethylene glycol), PEG, block copolymers were prepared by the incorporation of isophthalic acid, IPA, during esterification and PEG during condensation.5 PEG increased moisture affinity of PET, which, in turn, promoted the leakage of static charges. However, PET also then became easier to crystallize, even at room temperature, which led to decreased antistatic properties and increased manufacturing inconveniences. IPA was, therefore, used to reduce the crystallinity of the copolymers and, at the same time, make their crystalline structure looser for increased water absorption. Commonly, copolymerization can decrease a polymer fiber's tenacity. Both IPA and PEG decreased the fiber strength to some degree. Riches and Haward6 pointed out that the tensile properties of PEG block copolymers depend more on the number of hard and soft segments than on their lengths. So the

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mechanical properties correlate with the molar fraction of PEG rather than with its molecular weight. The higher the molar fraction of PEG, the lower the mechanical properties, so limiting the PEG content is necessary to preserve fiber mechanical strength. It was further found that the use of PEIT-PEG as an antistatic agent, blended with PET or PET modified with, for example, cationic dyes or disperse dyeable PET, could yield even better antistatic properties. Moreover, Li et al.5 claim that PEIT-PEG could be used with other antistatic agents to produce fibers with low volume resistances. Salts are effective antistatic agents when they can dissociate into their ions. Thus there is a strong humidity effect on the electrical properties, which can be diminished when polymers are used which are able to dissociate the salts permanently. Therefore, often polyethers like PEG are added reducing the sensitivity of the antistatic properties against moisture, but at the same time softening the material and reducing the mechanical strength.7 The introduction of ionic components like LiClO4 to a mixture of a polyether or polyester urethane (TPU) with PEO resulted in a solid polymer electrolyte (SPE) useful for introducing antistatic behavior to high impact polystyrene (HIPS).8 The electrical percolation was at about 5 wt% SPE, showing a drop in surface resistivity from 1016 ohm sq-1 to 1010 ohm sq-1, further reducing at higher SPE content especially in case of polyether based polyurethane due to ability of ether oxygen in polyether soft segments to dissociate LiClO4, effectively resulting in more free Li cations than in polyester TPU. At percolation concentration, continuous ion-conductive paths are formed. The surface resistivity is dependent on the SPE content, its composition (being more effective at higher PEO contents), and humidity. However, the ability of TPU and PEO itself to dissociate the Li salt results in antistatic behavior also at low relative humidity (RH). The tensile strength of HIPS/SPE (around 20 MPa at 80/20 composition by weight) is rather independent of SPE composition but the elongation at break increases with PEO content from 5% to 13% at a critical value of 4 or 8 phr (polyether or polyester TPU, respectively) and then it reduces again due to the reduction in TPU content. Overall the antistatic and mechanical properties make the material suitable for packaging applications. Ionic antistatic plasticizer (AP) can be prepared from different salts and plasticizers and used for different matrix polymers. For example, Che et al.9 prepared AP based on bis[2-(2-methoxyethoxy)ethyl]phthalate (BMEP) and sodium thiocyanate. When the blend does not contain additional 40 phr dibutyl phthalate (DBP) as a plasticizer, APs are softening the PVC/NBR (100/20, phr) blend already at a concentration of 5 phr effectively. The electrical percolation, i.e. the insulator/antistatic transition, occurs at 20 phr AP. In contrast, in plasticized PVC/ NBR blends containing 40 phr DBP, the electrical percolation concentration is about 5 phr AP and significant plasticization starts at 20 phr AP, detected as a strong increase in elongation at break in dependence on AP content. The tensile

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strength reduces rather linearly already at small amounts of added AP in both DBP plasticized and DBP free blends. The surface resistivity is only slightly dependent on RH due to the coordination of the sodium cations with the oxygen groups of AP. Ionic liquids (ILs) are another alternative for antistatic modification of polymers. Typically, miscible ILs act as plasticizer reducing the glass transition temperature and softening the matrix polymer. The addition of the IL 1-butyl-3methylimidazolium hexafluorophosphate to poly(vinylidene fluoride) (PVDF), however, modifies its crystallization/melting behavior changing the crystallinity and crystal structure.10 The tensile modulus reduces continuously with IL addition from 1045 MPa for pure PVDF to 389 MPa when 20 g IL are added to 100 g PVDF. Also, the yield strength reduces (from 56 to 41 MPa) but the elongation at break and the strength at break increase with IL addition from 254 to 693% and from 46.2 to 82.7 MPa, respectively. Only 2 g IL per 100 g PVDF are effective in providing antistatic behavior with a volume resistivity of 2 10-10 ohm-cm, which rises to 1.5 10-7 ohm-cm at 100 g PVDF/20 g IL composition. There is a lot of research concerning intrinsically conductive polymers, ICP, such as polyaniline, polypyrrole, polythiophene, and others for use as antistatic additives, but their commercialization is difficult because of costs, mechanical properties, and aging resistance. Rather high amounts of ICP are normally needed when melt mixing ICP with thermoplastic matrices. However, also reports are given where only a few wt% ICP resulted in a reduction of resistivity in the order of few magnitudes. Wu11 observed a reduction of surface resistance from 1016 to 108 ohm sq-1 when adding 3 wt% PANI to PBT by melt mixing. The surface resistance continuously decreases with the further addition of PANI to values near to that of pure PANI at 15 wt% PANI content. Reactive coupling of PANI to the matrix by means of a reactive compatibilizer is reducing the surface resistivity by ca. 1 order of magnitude in all compositions and at the same time very helpful in increasing the mechanical strength. Without the compatibilizer, the strength at break increases continuously from 55 to 60 MPa, with added compatibilizer from 50 to 85 MPa. Further PANI addition reduces the strength again but the values are always higher than these of pure PBT with up to 15 wt% PANI. One option to overcome the need of high amounts of ICP of theoretically 16 vol% for reaching antistatic properties is their use just as thin coatings or to use them as conductive coatings on hard fillers of different morphology and nature. Thus filler dominates the resulting mechanical properties of the composite and the thin ICP coating on the filler provides the antistatic and electrical conductivity. Technical viscose and lyocell textiles with intrinsically conductive properties were prepared by pyrrole polymerization on the fiber’s surface.12 The conductivity of prepared material is directly related to polypyrrole amount, oxidant to dopant ratio, and fiber structure with significant differences between viscose and lyocell. Polymerization occurs uniformly inside the fiber bulk, by producing a

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coherent composite polypyrrole/cellulose. FTIR and DSC analysis show that a significant modification of the cellulose occurs by effect of the polymerization, and a chemical bond with polypyrrole takes place. The mechanical and physical properties of cellulose fibers were not significantly modified and the best washing and light fastness also were observed. A monomer concentration over 0.5 g/l, causing monolayer overlapping, has a bad influence on the PPy adhesion to the textile substrate. The atmospheric oxidation produces a loss of the electrical properties in some weeks, but significant improvements can be obtained by application of protective coatings. Conductive fillers are widely used to modify the electrical and mechanical properties of thermoplastics, thermosets, coatings, or adhesives. Krupa and Novak13 compared the use of CB, different graphites, different basalt particles, and silver coated basalt fibers on the electrical and mechanical properties of thermoplastics (LDPE and HDPE) as well of thermosets (PUR and epoxide). All systems exhibited electrical percolation but the correlation to mechanical properties is much different, showing that any technical interesting combination has to be evaluated individually. Carbon black, CB, is the most widely-used antistatic additive, making the final polymeric compound conductive, but also black. Carbon black containing polymer composites can be used in a wide variety of applications, such as for electrostatic discharging or electromagnetic interference shielding. Some of these applications rely on the enhancement of conductivity that carbon black filler imparts to the polymer matrix. The percolation effect is observed in the dependence of composite conductivity versus filler content and manifests itself as a dramatic increase in conductivity by several orders of magnitude in a rather narrow concentration range of the filler around the so-called percolation threshold. In general, the percolation effect is a well-known phenomenon observed in fillermatrix systems as the abrupt extreme change of certain physical properties within a rather narrow concentration range of conductive filler. The effect is explained by the formation of conductive pathways through the matrix in such a way that the conductive particles are in close contact at a filler concentration corresponding to the percolation threshold. An increase in the Young's modulus values is observed with increasing CB content in PP matrix. A decrease of the tensile strength with increasing filler content was found for injection-molded and also for compressionmolded samples. The trend can be explained by a diminishing of and later vanishing of the orientational strengthening due to the lower deformability of the material with increasing filler content. The composites with higher CB content break before they are able to achieve a significant degree of orientational reinforcing due to drawing during the tensile tests.14 The analysis of experimental data on conductive composites consisting of a thermoplastic matrix and carbon black also indicated that the formation of an internal network leads to a dramatic decrease in elongation at break of the composites. It was shown that the steepest decrease in

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Figure 12.1 (left) Conductivity and elongation at break, eb, of PP/CB composites prepared by injection molding as a function of the CB content, (right) Conductivity and elongation at break, eb, of PP/ CB composites prepared by compression molding as a function of the CB content. [Adapted by permission from Chodák, I.; Omastová, M.; Pionteck, J., J. Appl. Pol. Sci., 82, 1903, 2001.]

elongation at break corresponded to the steepest increase in electrical conductivity at comparable filler contents.14-16 The critical crack formation and unstable crack growth in such a system are expected to be much easier and faster than in the virgin polymer matrix. The differences between injection- and compression-molded materials regarding both conductivity and deformation dependencies on the filler content are shown in Figure 12.1. In the compression molded samples, the CB is less perfectly distributed in the PP matrix. This leads to the formation of conducting CB “channels” already at lower concentrations, which leads to a higher conductivity, but also to the formation of more frequent failure sites. The effect is explained in terms of formation of a continuous network consisting of CB particles, which has a positive influence on the electrical but a negative one on the deformational behavior of the material. In general, the principle of segregated conductive polymer composites (sCPC) is very suitable to achieve very low electrical percolation concentrations of even less than 0.1 vol% when using different fillers like graphite nanosheets (GNS), CB, CNT, ICP, metal particles, or mixtures of them.17 The strength of the sCPC may be much reduced compared to the composites containing the same amount of modifier in the fine dispersion. Such composites, however, exhibit much worse conductivity values and need higher filler contents for reaching percolation. For example, compression molding of PP particles coated with polypyrrole (PPy) results in low electrical percolation but insufficient mechanical strength while injection molding destroys the original PPy morphology, allowing good intermixing of the PP matrix but giving only low electrical conductivity.18 The resulting morphology after compression molding or injection molding of coated particles is depicted in Figure 12.2. When instead of pure PPy-coated PP a mixture of these particles with PPy-coated clay is used, the deteriorative effect of shear forces on the percolating paths is reduced and a good balance of electrical conductivity and mechanical strength can be reached by injection molding.19

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Figure 12.2. Schematic presentation of (left) a segregated conductive polymer composites (sCPC) and (right) dispersed filler distribution, both obtained from coated particles either by compression molding or processing under shear, respectively. [Adapted, by permission, from Mravcáková, M., Omastová, M.,. Pötschke, P., Pozsgay, A., Pukánszky, B., Pionteck, J., Polym. Adv. Technol., 17, 715, 2006.]

The modification of the structure and surface functionality of a high structure carbon black by gasification with carbon dioxide was performed.20 Partial gasification of the carbon black decreased the room temperature volume resistivity, at the same concentration of carbon black in the composite, and decreased the magnitude of the positive temperature coefficient effect. M100 modulus was measured for the high structure carbon black/HDPE composites mixed at different concentrations in HDPE and then radiation crosslinked. The M100 modulus is the modulus measured at 100% strain. As the concentration of the high structure carbon black was increased there was an increase in the M100 modulus because the carbon black reinforces the polymer composite. After the high structure carbon black was treated with carbon dioxide and the M100 modulus for the corresponding radiation crosslinked composite measured, there was an increase in the M100 modulus as the reaction time increased. This increase in the M100 modulus with the extent of gasification supports the hypothesis that the corresponding decrease in the volume resistivity results from the selective gasification of carbon black primary particles within a carbon black aggregate by the development of porosity within the carbon black. The electrical resistivity, mechanical properties, outgassing, ion contamination and particle-shedding characteristics of new electrostatic dissipative, ESD, injection moldable thermoplastic composites containing carbon black and glass fibers, GF, were studied by Narkis et al.21 The results for polypropylene, polybutyleneterephthalate and polycarbonate-based compounds were compared to typical carbon black and carbon fiber filled materials. Injection moldable composites

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with desired surface resistivities in the static dissipative range (106 to 109 ohm/ square) for conveying in production lines, storage, shipment, and for clean room applications can be prepared by combining a number of polymeric materials with glass fibers and less than 2 wt% carbon black. The mechanical properties data showed that the PP/CB/GF composites containing less than 2 wt% carbon black are significantly stiffer and stronger than the PP/CB compounds, which results in lower particle shedding and better dimensional stability. With the goal to obtain flexible elastic antistatic materials Saleem et al.22 prepared silicon rubbers with different conductive fillers. Carbon fibers (CF) have been most effective in increasing conductivity compared to CB, nickel coated graphite or copper fibers. Depending on the curing conditions the hardness and flexibility of the rubber could be controlled and lowest electrical percolation threshold of less ca. 0.5 wt% was obtained with the more flexible rubber. For both rubbers, the tensile modulus is strongly increased with the addition of CF, but the flexibility and tensile strength remains rather stable or increases even in the case of harder rubber formulation. In the soft silicon rubber near electrical percolation (0.5 wt% CF), the drop in elongation at break is only from 300% to 270% and the tensile strength of 1.9 MPa is reduced by only 2%. At concentrations above percolation (up to 1.5 wt% CF) the silicon rubber is still flexible with an elongation at break of ca. 150% and also the harder silicon rubber is flexible with elongations at break of 50% at 4 wt% CF content. Multi-walled or single-walled carbon nanotubes (CNT) are very modern fillers for producing antistatic and conductive composites with improved mechanical properties. An overview about the electrical and mechanical properties of polymer-CNT composites, their preparation and application is given elsewhere.23 REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.

Bleier, H.; Finter, J.; Hilt, B.; Hofherr, W.; Mayer, C. W.; Minder, E.; Hediger, H.; Ansermet, J. P., Synth. Met., 57, 3605-3610, 1993. Higuchi, S; Shoichi, E., WO Patent 2,000,047,652. Zhao, Y. M.; Chen, J. W.; Sano, Y.; Kimura, Y., Angew. Makromol. Chem., 217, 129, 1994. Sano, Y.; Lee, C. W.; Kimura, Y.; Saegusa, T., Angew. Makromol. Chem., 242, 171, 1996. Li, X.; Liu, R. T.; Zhong, L. L.; Gu, L. X., J. Appl. Polym. Sci., 89, 1696, 2003. Riches, K. M.; Haward, R. N., Polymer, 9, 103, 1968. Li, C., Che, R., Xiang, J., Lei, J., Zhou, C., J. Appl. Polym. Sci., 131, 39921, 2014. Yang, W., Wang, J., Lei, J., Polym. Eng. Sci., 50, 739, 2010. Che, R., Yang, W., Wang, J., Lei, J., J. Appl. Polym. Sci., 116, 1718, 2010. Xing, C., Zhao, M., Zhao, L., You, Y., Cao, X., Li, Y., Polym. Chem., 4, 5726, 2013. Wu, C. S., eXPRESS Polym. Lett., 6, 465, 2012. Dall'Acqua, L.; Tonin, C.; Peila, R.; Ferrero, F.; Catellani, M., Synth. Met., 46, 213, 2004. Krupa, I., Novak, I., Electro-conductive composites and adhesives and their electrical, mechanical and adhesive properties, in: Polymeric Materials: New research, Caruta, B. M. (ed.), Nova Science Publishers, New York, 2005, Chapter 3, pp. 57-84. Chodák, I.; Omastová, M.; Pionteck, J., J. Appl. Polym. Sci., 82, 1903, 2001. Chodák, I.; Krupa, I., J. Mat. Sci. Lett., 18, 1457, 1999. Novák, I.; Krupa, I.; Chodák, I., Synth. Met., 131, 93, 2002. Pang, H., Xu, L., Yan, D.-X., Li, Z.-M., Prog. Polym. Sci., 39, 1908, 2014.

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18. Pionteck, J., Omastová, M., Pötschke, P., Simon, F., Chodák, I., J. Macromol. Sci. - Physics B, 38, 737, 1999. 19. Mravcáková, M., Omastová, M.,. Pötschke, P., Pozsgay, A., Pukánszky, B., Pionteck, J., Polym. Adv. Technol., 17, 715, 2006. 20. Mather, P. J.; Thomas, K. M., J. Mat. Sci., 32, 401, 1997. 21. Narkis, M.; Lidor, G.; Vaxman, A.; Zuri, L., J. Electrostat., 47, 201, 1999. 22. Saleem, A., Frormann, L., Soever, A., Polymers, 2, 200, 2010. 23. Byrne, M. T., Gun'ko, Y. K., Adv. Mater., 22, 1672, 2010.

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12.2 OPTICAL PROPERTIES Mária Omastová Polymer Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 842 36 Bratislava, Slovakia

Jürgen Pionteck Leibniz Institute of Polymer Research Dresden, Hohe Str. 6, D-01069 Dresden, Germany

Plastics differ in their ability to transmit light. Some plastics are transparent, exhibiting optical properties similar to glass. Other plastics are opaque; in this case, very little light is transmitted through plastic film or layer. Translucent plastics allow a significant fraction of the incident light to be transmitted through the object. Optical properties of plastics are evaluated by measuring light transmission, haze, or index of refraction. By definition, light transmission is the percentage of incident light that passes through the film. The polymer crystallinity of the plastic plays a major role in determining the optical properties of plastic, because polymer crystals are approximately of the same size as the wavelength of visible light, causing the light to scatter. Amorphous polymers, such as acrylates, polycarbonate, and polystyrene do not form crystals; they are naturally transparent. In general, transparent polymers are noncrystalline and translucent polymers are crystalline. This is not the case of crystalline PET, which is transparent because the crystal size is not visible within the light's wavelength. Fillers, additives such as antistatics, or coating of the plastic surfaces by antistatic substances, will usually decrease the light transmission of a material. Haze is the percentage of transmitted light which, when passing through a specimen, deviates from the incident beam by forward scattering. Lower haze values imply greater transparency. The refractive index for any substance is the ratio of the velocity of light in a vacuum to its velocity in the substance. If the object has an index of refraction near that of air, the object is transparent. Glass, polycarbonate, and polystyrene have indices of refraction close to air. If there is a need to design plastic goods or sheets which have to stay transparent, both common approaches for the preparation of antistatic plastic materials, e.g., coating of plastic surface by antistatic layer or mixing antistatic additives with polymer matrix can be used. Multilayer, biaxially-oriented film comprising a base layer which is optionally transparent and of at least one transparent cover layer, was developed.1 The cover layer(s) contain(s) at least one (co)polymer, which is made from lactic acid, and 2 to 10% glycerol fatty acid ester. A typical coextruded three-layer film comprised a polylactic acid base layer and two polylactic top layers containing 2% glycerol monostearate.

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The esters, e.g., triethanolamine distearate, are used as antistatics for thermoplastics, especially in transparent polyvinylchloride and polyolefins, e.g., low and high-density polyethylene compounds.2 Among the most important materials for transparent conducting coating are n-type oxide semiconductors such as indium tin oxide, In2O3:Sn, ITO,3,4 or antimony tin oxide, SnO2:Sb, ATO.5 Stable hybrid pastes and sols allowing the deposition of conducting, antistatic and antiglare-antistatic coatings fully processable at low temperature (T < 130°C) have been developed.3 They were obtained by modifying an ethanol suspension of redispersed crystalline ITO nanoparticles with a hydrolyzed silane acting as a binder. Single layers with a thickness of about 570 nm can be obtained by spin or dip coating processes on polymer (polymethylmethacrylate, PMMA, or polycarbonate, PC) and glass substrates. The curing process involves UV irradiation followed by a heat treatment at T = 130°C for 15 h and then a reducing treatment in forming gas. 570 nm thick coatings on 3 mm thick PC and PMMA substrate exhibited a high transparency ( T ≈ 87% ) and a stable sheet resistance as low as 1.6 kohm/square (resistivity  = 9×10-2 ohm-cm). Antistatic coatings combined with excellent transparency have been obtained by preparing a self-emulsified matrix material containing very low amounts of ATO particles of 8 to 10 nm diameter.6 The self-emulsified matrix was prepared by mixing hydroxypropyl acrylate with a water solution of a urethane acrylate oligomer and adding a photo initiator and the desired amount of ATO to this solution. Coating this solution on 2 mm thick PMMA resulted, after drying and UV curing, in a 2 µm thick antistatic layer. The resistivity strongly decreases already at low ATO contents with an insulator/conductor transition at 0.2 vol% ATO, having a resistivity of 106 ohm-cm. Above percolation, the haze is increased by less than 0.1% and the total luminous transmittance reduction is smaller 0.5%. The very low percolation concentration is caused by the formation of segregated conductive pathways consisting of single-stranded chain-like aggregated ATO particles, separated by ATO-depleted areas in the dimension of 200 to 400 nm. Self-aggregation of ATO particles was also observed when applying it in the form of a dispersion in a UV curable acrylic resin solution.7 The solution was applied to PMMA sheets as film and during drying and curing this film, the ATO particles formed clusters and were enriched at the surface, thus forming conductive pathways at about 0.4 vol% in the coating. Even if this method is less effective with regard to resistivity and transparency compared to the method described just above,6 it is a very practical way to obtain coatings, combining transparency and antistatic behavior in a good balance at low ATO contents. Highly transparent and antistatic ITO nanorod films, grown on a glass surface by sputter deposition, are superhydrophilic or superhydrophobic, depending on post-treatment.8 If this approach is suitable also for polymer matrices has to be tested.

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The formation of composite structures with one transparent and one conducting phase is a well-established method for obtaining transparent electrically conductive materials. To assure transparency, the volume fraction of the lightabsorbing conducting species has to be sufficiently low. Bleier et al.9 published the preparation of transparent, electrically conductive materials by the crystallization of conducting charge transfer complexes in a polycarbonate matrix. A freestanding tetraselenotetracene chloride ((TSeT)2Cl) film was produced in a polycarbonate matrix in a continuous casting process on a pilot-scale. Film cast from a solution of polycarbonate and tetraselenotetracene chloride in N-methyl-pyrrolidone with a loading of 1 wt% (TSeT)2Cl related to the amount of polymer had the bulk-conductivity around 0.5 S cm-1 at a thickness of 28 µm and its optical transmittance varied between 60% and 75% in the spectral range from 400 to 800 nm. Robust optical transparent antistatic composites can be prepared by largescale extrusion of PC under addition of the room temperature ionic liquid (IL) bis(trifluoromethane)sulfonylimide.10 The good compatibility and softening effect of the IL to PC at low loading is reflected by reduced glass transition and increased elongation at break of the composites compared to pure PC. Fitting the chemical structure of the IL to the structure of the matrix polymer even at loadings of 20 g (please note that 2 g are sufficient for good antistatic properties) of the IL 1-butyl-3-methylimidazolium hexafluorophosphate to 100 g poly(vinylidene fluoride) (PVDF) resulted in a composite with >85% transparency at 300 µm thickness.11 The miscibility between PVDF and IL originates from the specific interaction between imidazolium ions with CF2 segments of PVDF and results not only in high transparency but also in softening the polymer. An amphiphilic graft copolymer having both segments compatible with matrix polymers and ionic segments has been synthesized by radical copolymerization of isopropenylphenyl-terminated poly(beta-methyl-delta-valerolactone) macromer and methacryloxyethyltrimethylammonium chloride.12 Solvent-cast blend films prepared from the graft copolymer and matrix polymers such as PMMA and polyvinylchloride, PVC, were highly transparent, having a surface resistance as low as 108 ohm/sq, and volume resistivity close to 109 ohm-cm. Xray microanalysis and the storage modulus of the film suggested that the low volume resistivity is attributable to the pseudo-crosslinking structure, i.e., networks consisting of the graft copolymer aggregates, and that the networks formed inside the film might act as an ion-conducting channel. UV curable, hard, and transparent organic-inorganic hybrid coatings with covalent links between the inorganic and the organic networks were prepared by the sol-gel method.13 These hybrid coating materials were synthesized using an acrylate end-capped polyurethane oligomeric resin, hexanedioldiacrylate, HDDA, as a reactive solvent, 3-(trimethoxysilyl) propoxymethacrylate, MPTMS, as a coupling agent between the organic and inorganic phase, and a metal alkoxide, tetraethylorthosilicate, TEOS. The materials were applied onto polycarbonate sheets

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and UV cured, followed by a thermal treatment to give a transparent coating with a good adhesion and abrasion resistance. The high transmission and the thermogravimetric behavior indicate the presence of a nano-scale hybrid composition. For obtaining antistatic coatings, an intrinsically conductive polymer, composed of poly(3,4Figure 12.3. Transparency at a wavelength of 633 ethylene dioxythiophene), PEDOT, stanm of the ICP-containing hybrid coatings on bilized by polystyrene sulfonate, PSS, polycarbonate. [Adapted, by permission, from was added to the optimized coating forWouters, M. E. L.; Wolfs, D. P.; van der Linde, mulation. The thickness of the coatings M.C.; Hovens, J. H. P; Tinnemans, A. H. A., Prog. Org. Coat., 51, 312, 2004]. was found to be between 50 and 100 μm. It was shown that the surface resistivity of the organic-inorganic hybrid coating can be reduced from 1016 to 106 ohm/sq at a high concentration of conductive polymer in the coating formulation. The transparency of the coatings was determined using a laser with a wavelength of 633 nm. From UV absorption investigation PEDOT stabilized by PSS absorbed some of the light with this wavelength, due to the slight blue tone of the coating, depending on concentration. All PEDOT stabilized by PSS-containing coatings are transparent, at higher PEDOT concentration the samples lost some transparency, as shown in Figure 12.3, because of the absorption at 633 nm by PEDOT. The use of modern organic conductors, contrary to the use of more traditional carbon black or salts, as fillers for the production of antistatic polymers is advantageous, especially for the formation of films. Conducting polymers have been intensively studied for more than 40 years and can be prepared by chemical or electrochemical polymerization. In the chemical polymerization process, monomers are oxidized by oxidizing agents to produce conducting polymers. The advantage of chemical synthesis is that it offers mass production at reasonable cost. Conducting polymers exhibit extraordinary electrical properties and a wide variation in color due to their conjugated double-bond chain structure, which derives from both their conducting or neutral (non-conducting) forms. However, in the doped forms their color is dark, almost black. Jonas and Schrader14 in 1991 reported conductive modifications of polymers with polypyrrole, PPy, and 3,4-polyalkylenedioxythiophenes. The coated films, independent of relative humidity, were permanently antistatic and had a surface resistance of 102 to 105 ohm/sq. Polymeric films coated with 3,4-polyalkylenedioxythiophene showed a higher conductivity and possessed greater environmental stability than PPy coated films. They are transparent, heat sealable, and vacuum moldable. Later on, industrial applications of the antistatic and transparent coating of polymers using 3,4-polyethylenedioxythiophene were also tested.15

12.2 Optical properties

163

Transparent (90%) antistatic polymer films were prepared from conducting core-shell lattices by heating the latex far above the glass transition temperature, Tg, of the core material polybutylmethacrylate, PBMA, covered by PPy thin shell.16,17 The amount of PPy was varied between 1 and 4 wt%, giving a PPy shell thickness between 1.2 and 4.6 nm on PBMA core particles Figure 12.4. Comparison of the development of about 700 nm in diameter. The influthe transparency at 120°C of lattices with difference of the PPy shell thickness on the ent PPy content. [Adapted by permission from latex film formation process was studHuijs, F. M.; Lang, J.; Kalicharan, D.; Vercauteren, F. F.; van der Want, J. J. L.; ied by transparency measurements. The Hadziioannou, G., J. Appl. Polym. Sci., 79, 900, development of the transparency 2001]. strongly depends on the thickness of the polypyrrole shell. Although the thickness of the shell is very small compared to the diameter of the core, it is the determining factor for the development of the transparency. The final transparency of the films containing 1, 2, and 4 wt% PPy was studied and results are shown in Figure 12.4. This suggests that the absorption of light by polypyrrole is not the determining factor. The voids between the particles have disappeared or, at least, they were reduced in size considerably. The initial film resistance containing 1 wt% PPy was below 1 Mohm/sq, but after two days of annealing the composite at 120°C in air, the film resistance increased strongly. It is possible to find only a few applications of conductive polymers as antistatic agents for polyethyleneterephthalate, PET, films for packaging, since they lack formability and transparency. A new antistatic film has been developed by coating 500 μm PET films with an alcohol-water solution containing a water soluble conductive polymer, sulfonated polyaniline, SPANI, and a water-soluble or water-dispersible polymer, which acts as a binder. The thickness of coating layer was from 0.05 to 0.5 μm. It was found that this combination gave excellent antistatic properties.18 The SPANI antistatic polymer, ASP, composite PET films have special characteristics, such as good transparency, excellent antistatic properties (surface resistivity, Rs = 106 to 1010 ohm) at low humidity (15% RH), and good resistance to heat, water, and ammonia. Nanofillers such as carbon nanotubes (CNT) have generated tremendous interest for the preparation of nanocomposites with polymeric matrix, because of their unique combination of electronic, mechanical, chemical, and thermal properties. CNT show a strong tendency to agglomerate due to intrinsic van der Waals attraction among tubes in combination with their high surface area and high aspect ratio. However, different methods and strategies have been developed to create

164

Effect of Antistatic Agents on Some Properties of Compounded Materials

homogenous dispersion of CNT in a wide variety of polymeric matrices, thus creating composites with excellent property combinations. Park et al.19 achieved an efficient dispersion of singlewall carbon nanotubes, SWCNTs, bundles in a polyimide matrix using in situ polymerization of monomer with SWCNTs. The predispersed SWCNTs dispersion remained stable throughout the reaction under sonication, producing a reasonably transparent, electrically conductive nanocomposite. SWCNTs/polyimide nanocomposite exhibited volume conductivity of about 10-8 S cm-1 at a very low SWCNTs loading (0.1 vol%) without significantly sacrificing optical transmission, which was 85% for polyimide and 68% for the composite of the same thickness of about 35 μm. Mechanical properties as well as thermal stability were also improved by the incorporation of the SWCNTs. SWCNTs/polyimide nanocomposites are potentially useful in a variety of aerospace and terrestrial applications, due to their combination of electrical conductivity and high optical transmission. The above described cases present a set of steady properties required to support certain applications. The higher level of technology is required in various optical devices in which properties should be controlled to prevent polarization losses such as is the case micro-electromechanical systems, MEMS, used in telecommunication.20 In these coatings it is important that light is not polarized at different angles of incidents. At the same time, electrostatically controlled mirrors must be shielded from external electrical fields.20 Deposition processes in these multilayer coatings affect their optical properties and they required sensitive methods of control, such as transmittance photometry and ellipsometry.21 Conductive polymers offer optical features which can be controlled by chemical structure changes.22 For example, poly(thieno[3,4-b]thiophene) has redox switching capability by chronocoulometry and chronoabsorptometry between reduced and p-doped states. Multiple changes between oxidized and reduced states do not affect the structure, which is stable when exposed to such electrical and optical changes.23 Poly(3,4-ethylenedioxythiophene) was found to have metallic state behavior in respect to ordinary index of refraction and dielectric behavior in extraordinary index of refraction.24 Combination of conductive polymer such as polyaniline with non-conductive copolyamide display liquid crystalline properties in a certain range of compositions.24 Optical effects in combination with antistatic or conductive surface properties can be realized by means of metallic effect pigments coated onto several types of material surfaces. Copper pigments carrying a silver coating were very effective compared to other effect pigments in preparing electrically conductive textiles suitable for EMI shielding application and exhibiting significant antibacterial properties.25 Controlling the size of silver particles deposited on merino wool, its color could be varied from yellow/brown to red/brown and to brown black, exploiting

12.2 Optical properties

165

the surface plasmon resonance effect of the silver particles.26 In addition the silver particles provide antistatic and antibacterial behavior to the wool. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26.

Milan, S., WO Patent, 2,002,087,877. Arai, S.; Watabe, T., WO Patent, 2,000,044,824. Al-Dahoudi, N.; Aegerter, M. A., J. Sol-Gel Sci. Technol., 26, 693, 2003. Al-Dahoudi, N.; Aegerter, M. A., Mol. Cryst. Liq. Cryst., 374, 91, 2002. Goebbert, C.; Bisht, H.; Al-Dahoudi, N.; Nonninger, R.; Aegerter, M. A.; Schmidt, H. J., Sol-Gel Sci. Technol., 19, 201, 2000. Wakabayashi, A., Sasakawa, Y., Dobashi, T., Yamamoto, T., Langmuir, 23, 7990, 2007. Wakabayashi, A., Sasakawa, Y., Dobashi, T., Yamamoto, T., Langmuir, 22, 9263, 2006. Park, H. K., Yoon, S. W., Chung, W. W., Min, B. K., Do, Y. R., J. Mater. Chem. A, 1, 5860, 2013. Bleier, H.; Finter, J.; Hilt, B.; Hofherr, W.; Mayer, C. W.; Minder, E.; Hediger, H.; Ansermet, J. P., Synth. Met., 57, 3605-3610, 1993. Xing, C., Zheng, X., Xu, L., Jia, J., Ren, J., Li, Y., Ind. Eng. Chem. Res., 53, 4304, 2014. Xing, C., Zhao, M., Zhao, L., You, Y., Cao, X., Li, Y., Polym. Chem., 4, 5726, 2013. Ohta, T.; Sano, S.; Goto, J.; Kasai, A., New Polym. Mat., 4, 235, 1995. Wouters, M. E. L.; Wolfs, D. P.; van der Linde, M. C.; Hovens, J. H. P.; Tinnemans, A. H. A., Prog. Org. Coat., 51, 312, 2004. Jonas, F.; Schrader, L., Synth. Met., 41, 831, 1991. Lerch, K.; Jonas, F.; Linke, M., J. Chim. Phys. Physico-Chim. Biol., 95, 1506, 1998. Huijs, F. M.; Vercauteren, F. F.; Hadziioannou, G., Synth. Met., 125, 395, 2001. Huijs, F. M.; Lang, J.; Kalicharan, D.; Vercauteren, F. F.; van der Want, J. J. L.; Hadziioannou, G., J. Appl. Polym. Sci., 79, 900, 2001. Konagaya, S.; Abe, K.; Ishihara, H., Plast. Rubber Compos., 31, 201, 2002. Park, C.; Ounaies, Z.; Watson, K. A.; Crooks, R. E.; Smith, J.; Lowther, S. E.; Connell, J. W.; Siochi, E. J.; Harrison, J. S.; Clair, T. L. S.; Chem. Phys. Lett., 364, 303, 2002. Dobrowolski, J. A.; Ford, J. E.; Sullivan, B. T.; Lu, L.; Osborne, N. R., Optics Express, 12, 25, 6258-6269, 2004. Sittinger, V.; Pflug, A.; Werner, W.; Rickers, C.; Vergoehl, M.; Kaiser, A.; Szyszka, B., Thin Solid Films, 502, 2, 175-180, 2006. Lee, K.; Sotzing, G. A., Polym. Prep., 43, 2, 610-611, 2002. Pettersson, L. A. A.; Carlsson, F.; Inganas, O.; Arwin, H., Thin Solid Films, 313-314, 356-361, 1998. Bi, X.; Xue, Z., Polym. Intern., 26, 3, 151-5, 1991. Topp, K., Haase, H., Degen, C., Illing, G., Mahltig, B., J. Coat. Technol. Res., 11, 943, 2014. Kelly, F. M., Johnston, J. H., ACS Appl. Mater. & Interfaces, 3, 1083, 2011.

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Effect of Antistatic Agents on Some Properties of Compounded Materials

12.3 SPECTRAL PROPERTIES Some data on principal absorption bands in FTIR spectra can be found in literature. These data are useful in identification and they are given in Table 12.1. Table 12.1 Principal absorption bands in FTIR spectra of antistatics Antistatic compound

Polyaniline

1

Polypyrrole2

ZnO

1

Poly(thiophene-3acetic acid)

Absorption band, cm-1

Assignment

1650-1400

aromatic ring breathing mode, N-H deformation and C-N stretching

1581

nitrogen quinoid

1490

benzenoid ring

1141

charge delocalization in polymer backbone due to doping

819

para linkage of rings in polymer chain

1558, 1326

ν ring

1326

ν ring pulsation

1048

δ(C – H) + δ(N – H )

969

δ ( C – N ), – C=H, out of plane

928

δ(C – H)

797,682

γ(C – H)

3000-3600

hydroxyl group present on the surface

3405

ν O – H in acetic acid

2947

ν C – H in acetic acid

1716

ν C = O in acetic acid

1601

ν C = C in thiophene ring

839

ν C – H, out of plane in thiophene ring

720

C – H in position 2 of thiophene ring after polymerization

Some UV absorption studies have also been conducted. The characteristic absorption of some antistatics is given in Table 12.2. Table 12.2 UV/visible absorption by some antistatics Antistatic compound

Polyaniline

1

Absorption, nm

Assignment

320,620

undoped in N-methyl pyrrolidone

332,439,815

doped with p-toluene sulfonic acid

351,432,734

doped with dodecylbenzene sulfonic acid

12.3 Spectral properties

167

Table 12.2 UV/visible absorption by some antistatics Antistatic compound

Polyaniline

6

Absorption, nm

Assignment

620

undoped in reflectance spectrum

422,774

doped and grafted on glass fabric

420,820

doped on conducting substrate (Pt)

X-ray photoelectron spectroscopy, XPS or ESCA, studies were used to analyze surface layers of polypyrrole/polymethylmethacrylate,3 polyimide/polythiophene,4 and polyurethane/grafted polyvinyl acetate5 conductive blends for qualitative and quantitative determination of surface properties. REFERENCES 1. 2. 3. 4. 5. 6.

Dhawan, S. K.; Singh, N.; Rodrigues, D., Sci. Techn. Advanced Mater., 4, 2, 105-113, 2003. Ma, C.-C. M.; Chen, Y.-J.; Kuan, H.-C., J. Appl. Polym. Sci., 98, 5, 2266-2273, 2005. Omastova, M.; Pavlinec, J.; Pionteck, J.; Simon, F.; Kosina, S., Polymer, 39, 25, 6559-6566, 1998. Zhang, F.; Srinivasan, M. P., Thin Solid Films, 479, 2, 95-102, 2005. Zhou, X.; Liu, P., J. Appl. Polym. Sci., 90, 13, 3617-3624, 2003. Trivedi, D. C.; Dhawan, S. K., J. Mater. Chem., 2, 10, 1091-6, 1992.

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Effect of Antistatic Agents on Some Properties of Compounded Materials

12.4 RHEOLOGICAL PROPERTIES Petra Pötschke Leibniz Institute of Polymer Research Dresden, Hohe Str. 6, D-01069 Dresden, Germany

12.4.1 EFFECT OF LOW MOLECULAR WEIGHT ORGANIC ADDITIVES Low molecular weight organic additives normally lead to a reduction in melt viscosity of the matrix polymer melt. They act as plasticizers. Typically, the amounts of additives are in the range of 0.1 to 10 wt%. Whereas the low amounts will not influence the rheology significantly, higher amounts of low molecular weight additives may have significant activity as plasticizers. Such additives may also lower polymer glass transition temperature and/or melting temperatures, thus enabling processing at lower temperatures. In most cases, reduction in melt viscosity can be regarded as a positive effect, since better-flowing materials provide advantages in processing, such as reduced pressures during extrusion, lower polymer degradation because of lower stresses, higher variability in using processing equipment, reduced mixing time with other fillers, etc. In injection molding, form filling can be easier achieved and injection of thin wall applications can be enabled. 12.4.2 EFFECT OF CONDUCTIVE INORGANIC MATERIALS Solid conductive inorganic materials normally lead to an increase in melt viscosity of the matrix polymer melt.1-7 The melt flow index (volume flow index) is typically reduced. The effect strongly depends on the concentration of the filler, especially whether the amount added is below or above the electrical percolation threshold. Since the amount of conductive filler needed for antistatic dissipative material Figure 12.5. Steady state viscosity as a function behavior is near or above the percolaof shear rate for polystyrene filled with carbon tion threshold composition of the solid black at 170°C. [Adapted, by permission, from filler in the matrix, rheological effects Lobe, V. M.; White, J. L., Polym. Eng. Sci., 19, 617, 1979.] have to be considered. In general, the shear viscosity is enhanced, especially at low shear rates. When using linear viscoelastic shear oscillatory measurements, rotational tests, or capillary measurements, typically the Newtonian behavior at low shear rates of unfilled polymers changes into a

12.4 Rheological properties

169

Figure 12.6. Linear viscoelastic shear oscillatory measurements of polycarbonate-multiwalled carbon nanotube composites at 260°C, left: complex viscosity, right storage modulus, G'. [Adapted, by permission, from Pötschke, P.; Fornes, T. D.; Paul, D. R., Polymer, 43, 3247, 2002.]

shear thinning behavior after filler addition. This is shown in Figure 12.5 for an example of polystyrene filled with carbon black.1 The extent of this behavior depends on the quality of filler dispersion and the interactions between filler and matrix. The amount of filler at which these changes appear depends on the parameters leading to filler percolation, as discussed in Section 6.2.2, even if electrical and rheological percolation do not necessarily occur at the same loadings.8 The effects start at lower filler content for filler with high aspect ratio, e.g., carbon nanotubes or graphene nanoplates as compared to the lower aspect ratio fillers like low-structured carbon black. Combined with the effect seen in viscosity, an increase in the storage modulus, G', is observable when performing viscoelastic shear oscillatory measurements. The storage modulus develops a plateau and finally gets independent on oscillation frequency. This is shown in Figure 12.6 for multiwalled carbon nanotube filled polycarbonate which begun to get conductive at 2 wt% nanofiller addition.5 Elastic behavior develops because of the network-like structure of filler particles connected by polymer chains.8,9 The development of a combined elastic network of filler and polymer chains becomes especially obvious when filler and polymer chain dimensions become of the same order as in nanocomposites. Such networks may exhibit a yield stress which must be exceeded to initiate flow of the filled material. Yield stress was reported for highly filled composites with microscaled 2-4,10,11 and for low contents of nanoscaled fillers.5 At higher shear rates, the viscosity near the electrical percolation threshold is normally not changed significantly; sometimes even a decreased shear viscosity is observed which can result from orientation effects of anisotropic fillers in the matrix during shear flow. However, at filler contents well above the electrical percolation, the high shear rate viscosity also may be enhanced, as seen in Figures 12.5 and 12.6. Thus, in antistatic materials containing fillers at concentrations

170

Effect of Antistatic Agents on Some Properties of Compounded Materials

Figure 12.7. Extrudate swell, B, for polystyrene filled with carbon black at 170°C. [Adapted, by permission, from Lobe, V. M.; White, J. L., Polym. Eng. Sci., 19, 617, 1979.]

Figure 12.8. The change in elongational viscosity with elongation rate for carbon black filled polystyrene at 180°C. The elongational viscosity increases with filler loading (0, 10, 20, 30 vol%). [Adapted, by permission, from Tanaka, H.; White, J. L., Polym. Eng. Sci., 20, 949, 1980.]

around the electrical percolation composition, processing such as injection molding should be not severely influenced by addition of conductive fillers. Extrudate swell, also known as die swell, is a normal phenomenon for viscoelastic materials after leaving a die. It was reported that die swell is dramatically reduced when adding conductive fillers, as shown for polystyrene filled with carbon black in Figure 12.7.1 A significant suppression of die swell was also reported for multiwalled carbon nanotube filled polypropylene at 2.5 vol% filler which is above the electrical percolation composition.6 For this system, negative normal stresses also were measured. Another flow regime of interest is extensional (elongational) flow. This deformation is important in many polymer processing operations such as fiber spinning, foam production, and film blowing. Elongational viscosity was also found to increase with the amount of conductive fillers, as illustrated in Figure 12.8 for carbon black filled polystyrene.12 Again, the effect is more dominant at low elongational rates. Elongational melt strength was found to be increased significantly after addition of carbon nanofibers into polyetheretherketone, PEEK, which enabled formation of high quality PEEK foams.13 In the case of polycarbonate filled with 2 wt% multiwalled carbon nanotube, which is above the percolation threshold of the unstretched material, no significant influence on elongational viscosity of the polycarbonate was observed at different elongation rates.14 However, significant changes were found in the strain recovery behavior. The recovered stretch was

12.4 Rheological properties

171

much smaller in the composite as compared to the pure polycarbonate, which is discussed in context of the yield stress in this composite. These changed properties after adding conductive fillers provide good conditions for materials with enhanced melt strength and enhanced strain hardening which are favorable for melt spinning at higher speeds, film blowing, and the production of finer and stabler foams. In some cases, the conductive fillers may also lead to some polymer degradation effects which reduce melt viscosity slightly. This was observed for multiwalled carbon nanotubes in polycarbonate15 and can be attributed to remaining metallic catalyst particles within the nanotube material which acts hydrolytically during melt processing.16 REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

11. 12. 13. 14. 15. 16.

Lobe, V. M.; White, J. L., Polym. Eng. Sci., 19, 617, 1979. Hornsby, P. R., Rheology, Compounding and Processing of Filled Thermoplastics, in: Adv. Polym. Sci., 139, 1999, pp. 155-217. Mutel, A. T.; Kamal, M. R., Rheological Properties of Fiber-Reinforced Polymer Melts, in: Two Phase Polymer Systems, Utracki, L. A. (ed.), Carl Hanser Verlag, Munich, Vienna, New York, Barcelona, 1991, Chapter 12, pp. 305-331. Shenoy, A. V., Rheology of Filled Polymer Systems, Kluwer Academic Publishers, Dordrecht, Boston, London, 1999. Pötschke, P.; Fornes, T. D.; Paul, D. R., Polymer, 43, 3247, 2002. Kharchenko, S. B.; Douglas, J. F.; Obrzut, J.; Grulke, E. A.; Migler, K. B, Nature Mat., 3, 564, 2004. Pötschke, P.; Abdel-Goad, M.; Pegel, S.; Jehnichen, D.; Mark, J. E.; Zhou, D.; Heinrich, G., J. Macromol. Sci. A: Pure Appl. Chem., 47, 12, 2010. Pötschke, P.; Abdel-Goad, M.; Alig, I.; Dudkin, S.; Lellinger, L. Polymer, 24, 8863, 2004. Kim, H.; Macosko, C.W., Polymer, 50, 3797, 2009. Utracki, L. A., Rheology and Processing of Multiphase Systems, in: Current Topics in Polymer Science, Vol. II. Rheology and Polymer Processing/Multiphase Systems, Ottenbrite, R. M; Utracki, L. A.; Inoue, S. (eds.), Carl Hanser Verlag, Munich, Vienna, New York, 1987, pp. 7-59. Dealy, M; Wissbrun, K. F., Melt Rheology and its Role in Plastic Processing Theory and Application, Kluwer Academic Publishers, Dordrecht, Boston, London, 1999. Tanaka, H.; White, J. L., Polym. Eng. Sci., 20, 949, 1980. Werner, P.; Verdejo, R.; Wöllecke, F.; Altstädt, V.; Sandler, J. K. W.; Shaffer, M S. P., Adv. Mater., 17, 2864, 2005. Handge, U A.; Pötschke, P., Rheol. Acta, 46, 889, 2007. Pötschke, P.; Bhattacharyya, A. R.; Janke, A.; Goering, H., Composite Interfaces, 10, 389, 2003. Kashiwagi, T.; Grulke, E.; Hilding, J.; Harris, R.; Awad, W.; Douglas, J., Macromol. Rapid Commun., 23, 761, 2002.

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Effect of Antistatic Agents on Some Properties of Compounded Materials

12.5 ELECTRICAL PROPERTIES This entire book contains information on electrical properties of materials containing antistatics. In this section, we will summarize the major influences. Figure 12.9 shows that four different antistatics used in the same concentration have a different impact on volume resistivity.1 Because three well-performing antistatics are fibers, it is safe to assume that less fiber is required to reduce resistivity as compared with particulate antistatics. Various studies indicate that in most cases the volume resistivity does Figure 12.9. Volume resistivity of PC/ABS resin not form a linear relationship with confilled with 10 wt% of different fillers: 1  nickelcoated fiber, 2  stainless steel fiber, 3  carbon ductive filler concentration but a comfiber, 4  conductive carbon black. [Adapted, by plex relationship described by permission, from Amarasekera, J.; Burnell, A.; percolation threshold curve. Many such Lietzau, C.; Balfour, K., Polym. Prep., 42, 2, 3637, 2001.] curves are available in this book (see, for example, Figures 9.11, 9.12, 9.17, 9.18, and 13.10). Usually, resistivity changes very little if concentration is increased far from the percolation threshold, but very rapid changes are observed close to percolation threshold. The addition of conductive material above the percolation threshold again becomes less effective. This is explained by the need of formation of an internal network able to conduct electric currents. Unlike in the case of the so-called permanent antistatic, the surface-acting compounds do not follow percolation threshold behavior. Their performance also depends on the amount incorporated but rather in terms of durability of antistatic finish than short-term performance. On the other hand, their performance depends on humidity, as illustrated by Figures 11.5 and 11.6.2 The performance of both types of antistatics is affected by temperature but this effect is fundamentally different. In the case of migrating antistatics, the rate of diffusion increases with increasing temperature, therefore, more antistatic is present on the surface (good short-term but decreasing long-term performance). With antistatics operating in bulk, their performance depends on the distance between conducting particles and their mobility. Below the glass transition temperature, conductive particles are immobilized within the matrix and their influence decreases with temperature until it reaches a minimum at around the glass transition temperature (the so-called positive temperature coefficient). This happens because distances between conducting particles increase due to thermal

12.5 Electrical properties

173

expansion of polymer matrix. Above the glass transition temperature, all components of the mixture become more mobile and this causes resistivity to decrease with increasing temperature.3,4 Many other parameters of antistatics and processing are relevant to electric properties of composites and they are discussed in various sections of this book and specialized publications.5 REFERENCES 1. 2. 3. 4. 5.

Amarasekera, J.; Burnell, A.; Lietzau, C.; Balfour, K., Polym. Prep., 42, 2, 36-37, 2001. Colburn, Peter D., Annual Techn. Conf., SPE, 3105-3109, 2005. Klason, C.; McQueen, D. H.; Kubat, J., Macromol. Symp., 108, Eurofillers 95, 247-260, 1996. Bandara, A. J.,; Curley, J., New electrically conducting polymeric fillers, Addcon Asia '97, Rapra Technology, Shawbury, 1997. Van Bellingen, C.; Probst, N.; Grivei, E., Specific conductive carbon blacks in plastics applications, Addcon World 2001, Rapra Technology, Shawbury, 2001.

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Effect of Antistatic Agents on Some Properties of Compounded Materials

Figure 12.10. Glass transition temperature of soft segment of waterborne polyurethane composite vs. concentration of multiwall carbon nanotubes. [Data from Kwon, J.; Kim, H., J. Polym. Sci., Part A: Polym. Chem., 43, 17, 3973-3985, 2005.]

Figure 12.11. Glass transition temperature of hard segment of waterborne polyurethane composite vs. concentration of multiwall carbon nanotubes. [Data from Kwon, J.; Kim, H., J. Polym. Sci., Part A: Polym. Chem., 43, 17, 3973-3985, 2005.]

12.6 GLASS TRANSITION TEMPERATURE Metal acrylic acid complexes were grafted, in the presence of dicumyl peroxide used as a free radical initiator, onto polypropylene. The glass transition temperature, Tg, and the melting temperature, Tm, were affected by the metal used.1 Only copper causes a decrease of Tg by 3oC. Other metals (Co, Ni, Mn, and Zn) all increased Tg by 2 to 8oC. Melting point remained largely unaffected with exception of Mn and Co which decreased Tm by ~10oC.5 The increases of Tg were explained by the presence of ionic “crosslinks” (interactions) which Figure 12.12. Glass transition temperature of reduce segmental mobility. polyvinylalcohol composite vs. concentration of Figures 12.10 and 12.11 show the CdS. [Data from El-Tantawy, F.; Abdel-Kader, K. effect of addition of multiwall carbon M.; Kaneko, F.; Sung, Y. K., Eur. Polym. J., 40, 2, 415-430, 2003.] nanotubes to waterborne polyurethane

12.6 Glass transition temperature

175

on Tg of soft and hard segments in polyurethanes, respectively.2 In both cases (soft and hard segments), glass transition temperature increases meaning that there is an interaction between carbon nanotubes and polyurethane matrix. The interaction with the hard segment is more pronounced. The antistatic multilayer graphene filled poly(vinyl chloride) higher glass transition temperature than neat PVC, which is closely associated with crumpled morphology of the graphene and good compatibility between components of the composite.6 Figure 12.12 shows the effect of CdS on polyvinylalcohol glass transition temperature.3 All these relationships come as a surprise because it is generally expected that addition of filler particles to polymeric systems causes a decrease in segmental mobility of polymer forming the matrix and this results in an increase of the glass transition temperature. The same is the case of the addition of ZnO nanopowders to polystyrene.4 Regardless of the composition of coupling agent used together with nanopowder, glass transition temperature increases with increasing concentration of nanopowder.4 REFERENCES 1. 2. 3. 4. 5. 6

Allan, J. R.; McCloy, B.; Gardner, A. R., Thermochimica Acta, 214, 2, 249-53, 1993. Kwon, J.; Kim, H., J. Polym. Sci., Part A: Polym. Chem., 43, 17, 3973-3985, 2005. El-Tantawy, F.; Abdel-Kader, K. M.; Kaneko, F.; Sung, Y. K., Eur. Polym. J., 40, 2, 415-430, 2003. Ma, C.-C. M.; Chen, Y.-J.; Kuan, H.-C., J. Appl. Polym. Sci., 100, 1, 508-515, 2006. Lerch, K.; Jonas, F.; Linke, M., J. Chim. Phys. Physico-Chim. Biol., 95, 1506, 1998. Wang, H; Xie, G; Fang, M; Ying, Z; Tong, Y, Zeng, Y, Composites Part B: Eng., 79, 444-50, 2015.

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Effect of Antistatic Agents on Some Properties of Compounded Materials

Figure 12.13. Decomposition maximum temperature of polymethylmethacrylate/polypyrrole blends vs. concentration of polypyrrole in the blends. [Data from Omastova, M.; Pavlinec, J.; Pionteck, J.; Simon, F.; Kosina, S., Polymer, 39, 25, 6559-6566, 1998.]

Figure 12.14. Temperature of 10% weight loss by polypropylene/polypyrrole blends vs. polypyrrole content. [Data from Omastova, M.; Kosina, S.; Pionteck, J.; Janke, A.; Pavlinec, J., Synthetic Metals, 81, 1, 49-57, 1996.

12.7 THERMAL STABILITY Thermal stability of material containing antistatics is one of the main requirements and here we will review whether this requirement is likely fulfilled. Some conductive polymers are involved in blends with insulating polymers and, for some, we know their influence on thermal stability of their blends.1,2,5-7,9 Polymethylmethacrylate/polypyrrole blend’s thermal stability is well characterized by the maximum decomposition temperature (Figure 12.13). It is very likely that polypyrrole does not decrease the thermal stability of polymethylmethacrylate but the improvement of thermal stability is slightly disappointing, considering that polypyrrole has a decomposition temperature of 695oC.1 Figure 12.14 shows that polypyrrole increases the thermal stability of its blends with polypropylene. Here polypyrrole has a more noticeable stabilizing influence.5 The effect of temperature on antistatic properties of these blends is negligible.5,6 In polyimide-polythiophene studies the thermal stability of blends was between the stability of both components. ABS thermal stability was increased when up to 10% polyaniline was incorporated.9 The same effect resulted from sulfonated polyaniline on polyethyleneterephthalate film.10 Grafting copolymers based on polyethyleneoxide did not affect ABS thermal stability.14 It can be summarized that available data indicate that blends of conductive and insulative components have good thermal stability. Their less thermally stable component (most likely insulative polymer) is improved by the presence of a conductive component.

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Decomposition kinetic energy of polyvinylalcohol/CdS composite increases with increased content of inorganic antistatic compound (Figure 12.15).3 The presence of inorganic antistatic increases the thermodynamical stability of matrix polymer because of interaction.3 Another study shows that nanoscale ZnO increases the stability of composite with polystyrene.4 Glycerin ester derivative, metal powder, and metal oxide did not show an effect on the discoloration of plasticized PVC, and aging of antistatic PVC compounds containing these antistatics Figure 12.15. Decomposition kinetic energy of for 3 weeks at 80oC did not affect their polyvinylalcohol/CdS composite vs. CdS content. [Data from El-Tantawy, F.; Abdel-Kader, K. M.; antistatic performance. Kaneko, F.; Sung, Y. K., Eur. Polym. J., 40, 2, Surface coating by sulfonated 10 415-430, 2003.] and spraying with quaternary ammonium compounds11 did not influence the thermal stability of substrates such as polyethyleneterephthalate10 and polyetherimide and polyetheretherketone.11 Dihydrogen phosphate of -aminocaproic acid was found to be a very good multipurpose additive (including acting as an antistatic compound) to isoprene rubber compounds. It did not affect thermal stability of rubber.12 The polyaniline/sulfonated polystyrene composites are more thermally stable than pure polyaniline.15 Based on the review of available literature, it can be concluded that antistatic agents do not affect or improve the thermal stability of materials into which they were incorporated. REFERENCES 1.

Omastova, M.; Pavlinec, J.; Pionteck, J.; Simon, F.; Kosina, S., Polymer, 39, 25, 6559-6566, 1998. 2. Zhang, F.; Srinivasan, M. P., Thin Solid Films, 479, 2, 95-102, 2005. 3. Omastova, M.; Pavlinec, J.; Pionteck, J.; Simon, F., Polym. Intern., 43, 2, 109-116, 1997. 4. Ramamurthy, P. C.; Tewary, A.; Hardaker, S. S.; Gregory, R. V., Polym. Prep., 43, 2, 1242-1243, 2002. 5. Omastova, M.; Kosina, S.; Pionteck, J.; Janke, A.; Pavlinec, J., Synthetic Metals, 81, 1, 49-57, 1996. 6. Omastova, M.; Pavlinec, J.; Pionteck, J.; Simon, F., Polym. Intern., 43, 2, 109-116, 1997. 7. Ramamurthy, P. C.; Tewary, A.; Hardaker, S. S.; Gregory, R. V., Polym. Prep., 43, 2, 1242-1243, 2002. 8. Jando, T.; Stelczer, T.; Farkas, F., J. Electrostatics, 23, 117-125, 1989. 9. Koul, S.; Chandra, R., Annual Techn. Conf., SPE, 3039-3044, 2004. 10. Konagaya, S.; Abe, K.; Ishihara, H., Plastics, Rubber Composites, 31, 5, 201-204, 2002. 11. McGinnis, A. J.; Raghavan, S.; Lindstrom, T.; Leal, J.; Martin, D. R., Advances in Coatings

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Technologies for Corrosion and Wear Resistant Coatings, Proc. Symposium, Las Vegas, Nev., Feb. 12-16, 1995, 127-40, 1995. Vladkova, T. G., Polym. Intern., 53, 7, 844-849, 2004. Ward, J.; Simmons, R.; Chatham, P., Annual Techn. Conf., SPE, Vol. 2, 1782-1786, 1998. Tsai, Y.; Li, K.-C.; Lee, J.-S.; Cheng, L.-Y.; Chang, R.-K.; Wu, F.-M., Annual Techn. Conf., SPE, 1997. Moussa, M A; Rehim, M H A; Khairy, S A; Soliman, M A; Ghoneim, A M; Turky, G M, Synth. Met., 209, 34-40, 2015.

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12.8 EFFECT OF UV AND IONIZED RADIATION ON MATERIALS CONTAINING ANTISTATICS Some antistatics cover the surface, others are in intimate contact with matrix polymers, therefore their effect on weathering and protection against different forms of radiation is important in many commercial applications. Many studies were devoted to carbon black because it is an important stabilizer of many products such as those manufactured from rubber, but also for many synthetic polymers. A complete review of the effect of carbon black and other fillers on weathering and interaction with ionized radiation can be found in appropriate monographs.1,2 The understanding of the performance of migrating additives is very limited3,4 and recent studies cannot be found. Two commercial additives (bis-(2hydroxyethyl)amide of lauric acid and bis-(2-hydroxyethyl)-octadecylamine) were studied for the effect of UV radiation. It was found that both were degraded forming carbonyl compounds after dissociation of C−N bond. The amide was more vulnerable than an amine.3 The presence of UV stabilizers prevented degradation. Incorporation of antistatics in polyethylene influenced its oxidative stability.4 REFERENCES 1. 2. 3. 4.

Wypych, G., Handbook of Materials Weathering, 5th Ed., ChemTec Publishing, Toronto, 2013. Wypych, G., Handbook of Fillers, 4th Ed., ChemTec Publishing, Toronto, 2016. Porubska, M.; Zahradnickova, A.; Sedlar, J. Polym. Deg. Stab., 21, 1, 29-41, 1988. Porubska, M.; Krb, R.; Welnitz, L., Polym. Deg. Stab., 21, 3, 191-204, 1988.

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12.9 MORPHOLOGY, CRYSTALLIZATION, STRUCTURE, AND ORIENTATION OF MACROMOLECULES Three aspects are briefly discussed in literature, including: • antistatic distribution and orientation • effect of antistatics on morphology and crystalline properties of the matrix • influence on the technology of incorporation on morphological defects. The known information is summarized below. Different surface coatings were used to prepare carbon fiber for interaction with a polymer matrix composed of PBT/PET/PC blend.1 There was a noticeable difference between surface coatings in terms of their wetting properties. When the same treated fibers were incorporated into polyamide-6,6, both types of surface finish on carbon fibers gave good wetting properties. At the same time, good wetting and compatibility between fiber and matrix resulted in increasing resistivity and EMI shielding effectiveness.1 Polyvinylalcohol filled with CdS does not show a characteristic crystalline peak but a new phase is formed at a different absorption angle.2 The change of zeta potential with increasing concentration of CdS from negative to positive sign suggests an effect of very strong interface adhesion and chemical interaction between the matrix and the surface of the conductive filler.2 Indium tin oxide particles are very well dispersed in the coating solution.3 Their average particle size is 15 to 20 nm and high-resolution transmission electron microscopy, HR-TEM, and X-ray measurements do not show any traces of agglomeration. When the coating is cured by different methods such as UV and heat treatment, some agglomeration occurs (more extensive in hot air curing; globular particles having 40 to 80 nm size are found). This agglomeration causes the increase in interparticle distances and decreases conductivity, which is lower for heat-cured samples.3 Silane coupling agents were found to be beneficial in ZnO particle dispersion in polystyrene nanocomposites.4,5 Particle sizes of nanofiller were kept substantially smaller, glass transition temperature was increased (better interaction), resistance was reduced (smaller gaps between neighboring particles), and mechanical properties were improved (reinforcement).4,5 Kinetics of nucleation in films from polycarbonate containing needle-like tetraselenotetracene chloride was affected by processing conditions, such as the type of solvent, concentration of conductive filler, temperature, and viscosity.6 The number and width of crystals can be increased by increasing the nucleation rate. This can be simply done by spraying and selection of solvent.6 Polyaniline blend with poly(p-phenylene/diphenyl ether-terephthalmide) has fiber-like morphology and orientation. Cross-sectional morphology shows that polyaniline fibers are homogeneously distributed in the matrix.7 Polyaniline blend

12.9 Morphology, crystallization, structure, and orientation of macromolecules 181

with styrene-butadiene-styrene copolymer was extruded.8 Elongated structures were formed parallel to the extrusion direction. Compression molding of polypropylene/polypyrrole blend was found to preserve the original network of polypyrrole and material had good conductivity, but it was brittle. Injection molding was damaging the morphological structure of the blend, reducing conductivity but producing a material having better mechanical properties.9 Polyethyleneoxide is a conductive polymer. With several polymers such as ABS, polycarbonate, polystyrene and polyolefins, it can form alloys without greatly changing the mechanical properties of the host polymers. Conductivity depends on the preservation of properties of the interpenetrating network.10 The performance of migrating antistatics, such as, for example, glycerol monostearate, can be influenced by nucleation of the polymer. Controlled nucleation increases crystallinity because of formation of smaller, more numerous spherulites. Increased crystallinity causes a decrease of the antistatic’s solubility and increase of its migration rate.11 Morphological studies were helpful in evaluation of rubbing effect on performance of external antistatics deposited on the surface of textiles,12 void formations during electrostatic powder coating,13 and antistatics were found to prevent surface degradation of fibers observed in a scanning electron microscope.14 REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.

Patel, N., Annual Techn. Conf., SPE, 1918-1921, 2000. El-Tantawy, F.; Abdel-Kader, K. M.; Kaneko, F.; Sung, Y. K., Eur. Polym. J., 40, 2, 415-430, 2003. Al-Dahoudi, N.; Bisht, H.; Gobbert, C.; Krajewski, T.; Aegerter, M. A., Thin Solid Films, 392, 2, 299-304, 2001. Ma, C.-C. M.; Chen, Y.-J.; Kuan, H.-C., J. Appl. Polym. Sci., 98, 5, 2266-2273, 2005. Ma, C.-C. M.; Chen, Y.-J.; Kuan, H.-C., J. Appl. Polym. Sci., 100, 1, 508-515, 2006. Bleier, H.; Finter, J.; Hilt, B.; Hofherr, W.; Mayer, C. W.; Minder, E.; Hediger, H.; Ansermet, J. P., Synth. Met., 57, 3605-3610, 1993. Bi, X.; Xue, Z., Polym. Intern., 26, 3, 151-5, 1991. Cruz-Estrada, R. H., Annual Techn. Conf., SPE, 2390-2394, 2003. Pionteck, J.; Omastova, M.; Potschke, P.; Simon, F.; Chodak, I., J. Macromol. Sci., Phys., B38, 5-6, 737-748, 1999. Rosner, R. B., Electrical Overstress/Electrostatic Discharge Symp. Proc., Anaheim, CA, US, Sept. 26-28, 2000, 121-131, 2000. Dieckmann, D., Polyolefins X, International Conference, Houston, Feb. 23-26, 571-583, 1997. Dietzel, Y.; Przyborowski, W.; Nocke, G.; Offermann, P.; Hollstein, F.; Meinhardt, J., Surface Coatings Techn., 135, 1, 75-81, 2000. McGinnis, A. J.; Raghavan, S.; Lindstrom, T.; Leal, J.; Martin, D. R., Advances in Coatings Technologies for Corrosion and Wear Resistant Coatings, Proc. Symposium, Las Vegas, Nev., Feb. 12-16, 1995, 127-40, 1995. Ladizesky, N. H.; Pang, M. K. M., Scanning Microscopy, 5, 3, 665-77, 1991.

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12.10 HYDROPHILIC PROPERTIES, SURFACE FREE ENERGY Hydrophilic surfaces reduce electrostatic charge accumulation.1 The surface character can be changed by photochemical, chemical, or grafting processes. Waterswellable (poly-2-hydroxyethylmethacrylate) and water soluble (polyacrylamide) polymers were grafted on polypropylene by a vapor phase photochemical process.1 On water immersion, the surface hydrogel is formed, which reduces contact angle and improves antistatic properties of grafted material.1 Corona discharge surface treatment of polyethylene increased its surface free energy.2 During storage at normal conditions, the surface free energy decreases, due to the migration of process additives.2 Sodium n-dodecyl benzenesulfonate, an anionic surfactant, can almost quantitatively bind to the cationic moiety (e.g., antistatic additive) existing in the product.3 This affects the antistatic performance of the additive. Tosaf has developed an antistatic masterbatch for use in polypropylene packaging and moldings.4 ST7505HP is effective in conditions of very low atmospheric humidity, allowing rapid decay of static electrical charge.4 The decay time of <10 s after 3-7 months at 12% relative humidity has been determined.4 REFERENCES 1. 2. 3. 4

Morra, M.; Occhiello, F.; Garbassi, F., J. Colloid Interface Sci., 149, 1, 290-4, 1992. Novak, I.; Florian, S., Macromol. Mater. Eng., 289, 3, 269-274, 2004. Piao, D. S.; Ikada, Y., Colloid Polym. Sci., 272, 3, 244-50, 1994. Addit. Polym., 2016, 2, 2, 2016.