Consequently, the objective of the present investigation is aimed at exploring the effect of functionalized

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1 FLAME RETARDANT POLYMERS CONTAINING NOVEL FUNCTIONALIZED NANO CLAYS S.Kenig (1) and O.Shepelev (1) Shenkar College of Engineering & Design Israel Plastics & Rubber Center Abstract Polymer resins enjoy a large increase in consumption due to their cost/properties combination. However, one of their main shortcomings originates from their flammability. To remedy the flammability of polymers relatively large amounts of flame retardant additives are used. This in turn decreases the mechanical properties of the resultant compound. With the development of nanoclay technology, new opportunities have emerged for imparting enhanced fire retardancy, mechanical and barrier properties to polymers. Consequently, the objective of the present investigation was aimed at exploring the effect of functionalized nanoclays using fire retardants chemicals, on the flammability retardation and mechanical properties of a variety of polymers among them polyolefins, styrenics and polyesters. Commercial as well as the novel functionalized nano clays were included in the study. Experimental results have shown that the burning mechanism of nano clay containing polymer compounds was completely changed due to formation of a char layer. Furthermore, small amounts of fire retardant functionalized nanoclays (<6%), reduced the required amount of conventional fire retardant additives by 5%, compared to the same polymers that did not contain nanoclays, to meet UL 94 V-2 and V- levels. The resulting fire retardant polymers compounds possessed higher modulus and strength while preserving, in most of the cases, the impact resistance compared with the neat resins. Introduction With the development of nanoclay technology, new opportunities have emerged for imparting enhanced fire retardance, mechanical and barrier properties to plastics. Significant improvements in rigidity, flame retardant characteristics (1-4) and barrier properties (5) could be realized by using a low content level of nanoclays (NCs). When properly intercalated and exfoliated in polymer matrices, the surface area of the resulting 1 nanometer thick (close to 1x1 micron area) NCs approach 7 square meters per gram. This unique feature gives rise to the properties enhancement realized in nanoclay polymer composites. Polypropylene resins and styrenics enjoy a large increase in consumption due to its cost/properties combination. However, one of its main shortcomings originates from its flammability. To improve the flame retardance of polypropylene and styrenics relatively large amounts of flame retardant (FR) additives have to be used. This in turn decreases the mechanical properties of the resultant compound. The commercial importance of polypropylene (PP) and styrenics: Polystyrene (PS), Styrene Acrylonitrile (SAN) and Acrylonitrile Butadiene Styrene (ABS) have been the main driving force for studying the effects of NCs on its properties (2.4). The main difficulties that are encountered during incorporation of NCs into polymer matrices stem from its basic structure where the single layers form stacks held by large ionic forces. To be useful the closed structure has to be delaminated. This is usually done by intercalation followed by exfoliation. The process of intercalation comprises an ion exchange of the binding ions with organic ions to form an organoclay. The expanded distance between the layers renders the partially opened layered structure to further exfoliate and disperse in the polymer matrix by applying mechanical stresses. The amount of bound organic modifier can reach 4% in commercial types of NCs. One of the most widely practiced methods of imparting fire retardant properties to polymers is by the use of brominated and or phosphated additives. The trend to cut down the content of halogenated compounds in polymer based compositions promoted extensive investigations aimed at developing of multifunctional systems using synergistic additives. Significant improvements in flammability properties of several polymeric nanocomposites have been reported (2,4,8-11). In most of the cases the improvement of flame retardancy was accompanied with a decrease in impact properties. Consequently, the objective of the present investigation is aimed at exploring the effect of functionalized nanoclays on the flammability retardation and mechanical properties of polypropylene and styrenics.

2 Experimental The base polypropylene (PP) used in the investigation was a homopolymer having a melt flow index of 12. The styrenics included: HIPS, SAN and ABS. The commercial NCs used were: Cloisite 25A (treated with dimethyl-hydrogenated tallow, 2-ethylhexyl ammonium sulfate, from Southern Clay Products) and Cloisite 3B containing hydroxyl groups. For functionalization of Cloisite Na+, incorporated with PP, Ethyltriphenyl phosphonium bromide (ETPP-Br from Dishman Holland BV) and Tetrabromobisphenol A dibromopropyl ether (TBBPA) FR 72 from Dead Sea Bromine Works were used. The conventional FR used was also TBBPA and as a synergist Antimony Trioxide (AO) Blue Star grade was added. For functionalization of NC, incorporated with styrenics, phosphates, epoxy and phosphonium were used. The strategy of the current investigation was to perform modification and functionalization of the pristine NCs using FR agents like: ETPP-Br and TBBPA, phosphates and epoxy. Functionalization of the Na nano clays was accomplished by swelling of nano-clay particles in solutions of the FR chemicals using high-shear mixing, evaporation of solvent and final drying of powder were employed. FTIR (Fourier Transform Infra Red) was used to verify the chemical composition of the NCs following modification. XRD (X Ray Diffraction) was employed to examine the intercalation process as a result of the chemical modifications. TGA (Thermal gravimetrical Analysis) was carried out to study the level of thermal stability of the modified NCs. TEM (Transmission Electron Microscopy) was used to evaluate the exfoliation of the modified NCs in the polymer Matric. In all cases the NCs were compounded as master batches (2% organoclays) in a carrier materials system. The high loaded master-batch was diluted to the desired concentration in the matrix resins: PP, HIPS, SAN and ABS, respectively. Testing specimens were prepared by injection molding under optimized conditions. Mechanical properties of injection molded specimens were tested in accordance with appropriate ASTM methods. FR properties were examined in burning test of UL 94 Standard both for horizontal as well as vertical configurations. Furthermore, the tensile properties (modulus, strength, elongation and impact) of the molded specimens were evaluated. Results and Discussion To ensure optimal FR properties the nanoplatelets have to be delaminated, homogeneously dispersed in the polymer matrix and preferably parallel to the surface. Both chemical as well as physical means have to be applied to ensure these characteristics. In the first stage of the investigation the modified NCs were analyzed by FTIR to evaluate the effectiveness of the respective chemical modifications. FTIR spectra of the modified NCs identified the functional groups characteristic respectively of the hydroxyl, bromine, phosphonium and epoxy moieties and its associated compounds. Following the spectroscopy study XRD was used to follow the intercalation process. Figure 1 depicts some of the data, indicating that intercalation took place and that the gallery gap increased due to the ion exchange and /or the chemical reactions. Subsequently, the thermal stability of the various organoclays was studied using TGA at a heating rate of 1 o C/min. in air. As can be seen in Figure 2 the organic content of the commercial Cloisite 25A is 34%, that of the phosphonium/tbbpa 25% and of the TBBPA 75%. Furthermore, the thermal stability of the quaternary treated commercial NC is the lowest one. Degradation starts at less than 2 o C. The NCs with the TBBPA exhibited a higher thermal stability compared with the ETPP-Br modified NCs. In the former case decomposition started at 28 o C compared with the latter case at 22 o C. This difference is significant for PP and ABS based compositions since the temperature region of burning is between o C. Interesting phenomenon is observed in the case of TBBPA treated NCs. Two distinct regions of decomposition were identified. After intensive decomposition in the temperatures interval of o C, which could be attributed to decomposition of free TBBPA, a second region was identified where slower weight changes from 6% to about 3% were observed. This may be due to the high stable compounds formed as a result of chemical interactions, during intercalation, between the bromine and the NCs side OH groups and the Na + active sites inside the NC galleries. TEM indicated that a variety of exfoliation levels were achieved. Good exfoliation was observed in the case of ABS, while partial exfoliation was obtained in the case of PP.

3 The properties of various PP, HIPS, SAN and ABS compositions are summarized in Tables 1,2,3 and 4. As can be seen, NCs modified with combination of ETPP-Br/TBBPA ensured V- flammability level at concentration of 4% NCs in PP compounds containing only 8.1% of TBBPA while material without NCs addition showed a V-2 UL-94 rating. AO synergist addition was obligatory FR rating of composition without AO turned to V-2 inspite higher NC content. NCs functionalized with TBBPA alone-demonstrated V- flammability rating at 2.5% NCs and the same low loading of conventional FR agent. Mechanical properties like elongation at break and impact strength were improved, however the modulus slightly decreased as a result of plasticizing effect of the TBBPA. PP based material of the same composition prepared with commercial type of Cloisite 25A (based on quaternary ammonium) demonstrated V-2 flammability rating. The material had a dark brown color after compounding and almost black color after injection molding, apparently due to the TBBPA decomposition under the effect of the ammonia salt used for NCs intercalation. The thermal stability of PP compositions was investigated by TGA. As can be seen in Fig.2 enhanced thermal stability was achieved as a result of small amounts of FR modified nano-clays compared with the neat PP and PP compound containing FR/AO combinations without NCs. The current study is concerned with the FR properties of injection molded articles, containing nano-clay alumino-silicate based platelets. Table 2 summarizes the mechanical and the FR properties of SAN/nanoclay composites. As can be seen when SAN is used without nanoclay additive it melts and burns completely in horizontal burning according to UL 94. When commercial (Cloisite 25A-hydrophobic, Cloisite 3B-hydrophilic) 5% nanoclays were added, the horizontal burning behavior changed, resulting in char formation. When the advanced nanoclays treatments (phosphate and epoxy) were practiced a profound change in the burning mechanism took place self extinguishing was obtained. The different FR behavior is attributed to the advanced thermally stable nanoclay treatments (phosphate and epoxy) compared to the commercially ammonium-organo ones, which degrades at temperatures above 19 C. It should be noticed that modulus and impact strength improved or ed unchanged while the tensile strength was some what reduced. When the same approach was taken in the case of HIPS no improvement was demonstrated in its FR characteristics. As can be seen in Table 3, when no clay was incorporated or when commercial nanoclay was added (25A) the injection molded samples burned completely. Only when a compatibilizer was introduced a profound change in the burning mechanism was observed resulting in char formation. Though, the tensile strength at yield or break was preserved in the char forming formulations, the elongation to break and the Izod impact were reduced by 3 to 6 %. In the case of ABS another strategy was followed, emanating from the high concentartion of the flammable toughener (butadiene). Table 4 summarizes the results obtained when the nano clays were treated with both phosphonium and phosphate FR. As can be noticed, nano clay free formulation did not exhibit any FR characteristics in both horizontal and vertical burning tests. Only when advanced treatment of the nano clays was used in addition to conventional phosphate FR char formation was obtained in horizontal as well as vertical burning tests. It should be noticed that in this case V2 rating was achieved. The tensile modulus and strength were enhanced compared to the no clay containing formulation. However, the Izod impact strength was significantly reduced. Morphology analysis and examination of the burning mechanism suggest that due to exfoliation and alignment of the nanoclay platelets on the specimen surface, a barrier is formed which inhibits oxygen permeation into the material and release of the burning products. These result in char formation and slowing down the spread of flames. Conclusions Modification and functionalization of NCs with conventional FR agents provided the possibility to formulate PP and styrenics based compounds that meet UL94 V- requirements using half of the amount of conventional FR generally needed for this purpose. In the case of PP best results were obtained with 2.5% of bromine functionalized nanoclay to meet V- rating according to UL 94. Furthermore, compositions without AO meet the V-2 rating. Whenever FR functionalized NCs and the conventional FR (TBBPA) were used impact properties were preserved. In the case of styrenics addition of 5% functionalized nano clays to optimally molded SAN resulted in char formation,change of the burning mechanism and self extinguishing. In the case of HIPS best results were obtained when a compatibilizer was added to the HIPS/Nano clay composite. ABS based formulations were

4 found to be of UL 94 V2 rating when both functionalized nanoclays and conventional FR were used. The impact properties of HIPS and ABS were decreased when nano clays were added. Additional studies are underway related to imparting improved impact characteristics to nano clay/styrenic composites as well as FR properties to a variety of additional polymer systems. References 1. Vaia R.A.,Ishii H., Giannelis E.P., Chem. Mater., 5, (1993). 2. Kenig S. and Shepelev O.,Preprints of Euro-Fillers 23, Alicante-Spain, Sept Manias E.,Touny A., Wu L., et oth. Chem.Mater., 13, (21). 4. Kenig S. and Shepelev O., Antec 25, 5. Strawhecker K., Manias E., Chem. Mater., 12, (2). 6. Kato M., Usuki A., Okada A., J. Appl. Polym. Sci, 66, (1997). 7. Gopakumar T.G. and Page D.J.Y.S., Antec 24, Gilman I.V., Jackson C.L., Morgan A.B. et oth., Chem.Mater., 12, (2). 9. Manias E., in Advances in Fire Retardant Chemicals, (22). 1. Fire Retardant Materials, CRC Press, Woodhesd Publishing Ltd, (21). 11.Giannelis E.P., Antec 1996, Table 1. Polypropylene based FR nanocompositions Materials / Properties COMPOSITION ( parts by weight) PP Homopolymer, MFI MB NC (ETPP-Br+TBBPA) MB NC (TBBPA) MB Cloisite 25A FR TBBPA AO Content, % NC (mineral) FR TBBPA ETPP-Br MECHANICAL PROPERTIES E-Modulus, (MPa) Tensile Strength, (MPa) Elongation at break (%) Izod Impact (J/m) FR PROPERTIES. Tested as UL-94 Vertical Burning Test. Thickness 3.2 mm NR V- V-2 V- V-2 V-2 V- Total flaming time, sec completely after 1-st Drip, no cotton Cotton after 1-st flame application Drip, no cotton Drip. Cotton after 2-nd flame application Drip. Cotton after 1-st flame application Drip. No cotton

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6 Table 2. SAN based nanocompositions. MATERIALS / PROPERTIES COMPOSITION (Parts by weight) SAN + Antioxidant Cloisite 25A Cloisite 3B NC (Phosphate modified) NC (Epoxy modified) MECHANICAL PROPERTIES Modulus (MPa) Strength, (MPa), break Elongation, (%), break Izod impact, notched, (J/m) HDT, oc (1.8 MPa) FR PROPERTIES. UL-94, HORIZONTAL BURNING. 3.2 mm thick. Flame spread, mm / min 26.5 No drip, smoke 27.7 No drip, smoke Self-extinguished 13.8 completely Table 3. HIPS FR nanocompositions. MATERIALS / PROPERTIES COMPOSITION (Parts by weight) HIPS Phosphate FR Compatibilizer MB HIPS / Compatibilizer MB PS / Cloisite 25A MB PS /Compatibilizer/ 25A MB HIPS/Compatibilizer/ 25A MECHANICAL PROPERTIES Modulus, (MPa) Strength, (MPa), yield / break 3 / / / 3 4 / / / 26 Elongation at break, (%) Izod impact, notched, (J / m) FR PROPERTIES. UL-94 HORIZONTAL BURNING TEST. 3.2 mm thick. Flame spread, mm / min 35.6 complete 33.2 complete 34.3 part of skeleton 28.3 skeleton 29.3 skeleton 28.2 skeleton

7 Table 4. ABS FR nanocompositions. MATERIALS / PROPERTIES COMPOSITION (Parts by weight) ABS B.D. Rubber MB ABS/NC (Phosphonium 1) MB ABS/NC (Phosphonium 2) MB ABS/NC (Phosphonium 3) FR Phosphate MECHANICAL PROPERTIES Modulus, (MPa) Strength, (MPa), yield/break 38 / / / / / / 27 Elongation, (%), yield / break 3.8 / / / / / 6 2 / 6 Izod impact, notched, (J/m) FR PROPERTIES UL-94 HB, 3.2 mm thick Flame spread, mm / min 27 complete drip, smoke UL-94, Vertical. 3.2 mm thick Total Flaming time, sec. complete in first in sec. Flaming drip % by weight V2 173 big parts ed % by weight V2 186 Slow drops, char. Remain 58% % by weight V2 193 Slow drip Remain 56% Moderate char, 34% by weight V2 177 Char. Remain 64% % by weight V2 161 slow drip Remain 64%

8 3 FIGURE Figure 1 2 XRD of Modified XRD Nanoclays data 25 2 Intensity, counts Theta Cloisite Na, MMT not modified 11 Phosphonium modified MMT 18.5 MMT modified with Phosphonium / Brominated FR combination 18 MMT modified with TBBPA 13 Epoxy modified MMT 13.5

9 FIGURE 2 TGA of Modified Nanoclays Figure 3 Thermal stability of treated NCs Weight, % Temperature, oc Cloisite 25A Cloisite 3B Modification with ETPP-Br Modification with ETPP-Br / TBBPA combination Modification with TBBPA Modification with Epoxy Modification with Phosphate Figure 2 Thermal stability of PP compositions containing functionalized NCs 1 8

10 FIGURE 3 TGA of PP Nanocomposites Containing Modified Nanoclays