Article pubs.acs.org/IECR
Unsaturated Polyester Resin Composites Containing Bentonites Modified with Silsesquioxanes Mariusz Oleksy* and Henryk Galina Faculty of Chemistry, Rzeszow University of Technology, 35-959 Rzeszow, Al. Powstańców Warszawy 6, Poland ABSTRACT: Unsaturated polyester (UP) resins were filled with up to 3 wt % of bentonites modified with silsesquioxanes (POSS). The effects on mechanical properties and flammability changes of the composites obtained therefrom are presented. The mechanical properties of cured resins were improved; the tensile strength and Charpy impact strength increased by up to 44% and 59%, respectively, compared to unmodified resins. The cured resins had a typical clay nanocomposite structure with layer-like morphology, as observed in scanning electron microscopy (SEM) photomicrographs of brittle fractures, an absence of X-ray diffraction pattern (because of the smectic structure of clays), and exfoliated structure, as evidenced by transmission electron microscopy (TEM) examination. The presence of POSS-modified bentonites in cured UP resins improved their flame resistance, as exemplified by the increase in the limiting oxygen index, from 17.2 for unfilled resin to 25.2 for the resin containing 3 wt % of Wyoming bentonite modified with POSS.
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INTRODUCTION The progress in organic composite materials involves application of better and better modifiers that, even when used in small quantities, provide materials with unique properties including improved flame resistance and thermal stability. Some attention as potential flame retardants attracted polyhedral oligomeric silsequioxanes (POSS).1 Their specificity is the structure consisting of a polyhedral (most often cubic) inorganic silicon−oxygen core with organic substituents in the vertices. The core size is ∼0.5 nm, and the size of the entire molecule seldom exceeds 1−3 nm. The most important limitation of a wide use of these compounds is their still rather large price. If, however, POSS derivatives containing quaternary ammonium groups are used as modifiers of layered aluminosilicates and the latter are then used as polymer fillers,2,3 the price starts to have a less-important role.4 The main advantage of aluminosilicates themselves, as well as those modified with silsesquioxane salts, is their relatively high thermal stability, with the temperature of the start of decomposition often exceeding 300 °C. Recently, a series of papers have been published,4−11 where POSS were used for the modification of clays. The thus-modified aluminosilicates were then used as nanofillers for several types of polymers, including polylactide,7 polyamide 12,8,9 poly(butylene terephthalate),10 epoxy resins,11,12 polystyrene,8,13−16 and polyurethanes.17 Our previous experience on nanocomposites with synthetic resins as matrices18−21 made us to try to prepare bentonites modified with quaternary ammonium salt containing POSS and used them as fillers of a commercial unsaturated polyester resin. Here, we report on the results.
(the formulas and names are presented in Table 1); (iii) commercial unsaturated polyester resin Polimal 109 (UP109); (iv) cobalt(II) naphtenate (2% styrene solution); and (v) Luperox K-1 (solution of methylethylketone hydroperoxide in dibutyl phthalate). Items (iii), (iv), and (v) were kindly provided by Chemical Plants, “Organika-Sarzyna-Ciech”, in Nowa Sarzyna, Poland. Modification of Bentonites with POSS Ammonium Salts. Modification of smectic clays with POSS ammonium salts was carried out using the following procedure.21 First, the bentonite was mixed with water to obtain a suspension containing 8−10 wt % of clay. Then, POSS1 or POSS2 in the form of 50% solution in ethanol was introduced dropwise to the clay suspension preheated to 70 °C. The amount of introduced POSS1 or POSS2 per 100 g of air-dry bentonite was 35 or 40 g, respectively. The suspension containing POSS then was vigorously stirred for 3 h, while slowly increasing the temperature to 80 °C. In the second stage of modification, the temperature was further increased to 90 °C and the suspension stirred for another 3 h. The mixture then was cooled to room temperature within 1 h with continuous stirring. The precipitate was freed from water excess by evaporating (POSS1) or by filtering under vacuum on a Buchner funnel (POSS2), rinsing it several times with distilled water. The resulting wet solid was dried at 100−120 °C in an oven with forced air circulation, until its humidity fell below 0.5 wt %. Dried modified bentonite was grinded in an impact and then in a ball mill and sieved through a sieve with the mesh size of 0.065 mm. The grain size distribution was measured using a Master Sizer Hydro MU2000 (Malvern) at 20 °C. Prior to measurement, the particles were ultrasonifically dispersed in isopropanol.
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EXPERIMENTAL SECTION Materials. The following materials were used: (i) Wyoming bentonite (BW) and Ukrainian bentonite (BU), both supplied by CETCO-Poland; (ii) selected quaternary ammonium derivatives of octasilsesquioxanes (POSS1 and POSS2) provided by the group of Professor Marciniec from University of Poznan, Poland © 2013 American Chemical Society
Received: Revised: Accepted: Published: 6713
December 13, 2012 April 3, 2013 April 22, 2013 April 22, 2013 dx.doi.org/10.1021/ie303433v | Ind. Eng. Chem. Res. 2013, 52, 6713−6721
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Table 1. Silsesquioxanes Used for Bentonite Modification
Thermal Studies by Differential Scanning Microcalorimetry (DSC). The DSC measurements were made on a 822e apparatus (Mettler Toledo), in the temperature range of 50−500 °C at a heating rate of 10 °C/min in a nitrogen atmosphere. Preparation of Compositions Containing Unsaturated Polyester (UP) Resin and Bentonites Modified with POSS. A general-use commercial unsaturated polyester (UP) resin, Polimal 109 (Sarzyna, Poland), was used. The resin was mixed with 1.0, 2.0, or 3.0 wt % of bentonite BW or BU modified with POSS1 or POSS2. The compositions were premixed using a mechanical stirrer at the rate of 500 min−1, placed in hermetic glass jars, and further homogenized in an ultrasonic mixer for 15 min at 50 °C. The compositions then were mixed at the same temperature (50 °C) in a high-speed homogenizer equipped with a turbine-like mixing blade 50 mm in diameter. The time of mixing was 30 min at a rate of 8000 rpm. Finally, the compositions were homogenized for 10 min, using a highspeed shear grinder rotating at the rate of ca. 1000 s−1. This complex procedure (temperature and duration of homogenization stages) was adopted after years of experience in order to provide the best possible homogenization of bentonites, while reducing styrene evaporation and preserving integrity of bentonite platelets. The platelet sizes were estimated from wide-angle X-ray scattering (WAXS) diffractograms, using the Scherer equation. The thus-prepared compositions were kept in a refrigerator (4 °C) until further use.
Specimen for Mechanical Testing. The UP compositions containing modified bentonite were cured using Luperox K-1 (2 wt %) (commercial solution of methylethylketone hydroperoxide in dibutyl phthalate) and cobalt accelerator (0.4 wt %), as recommended by the resin producer. The compositions then were degassed and cast into silicone molds prepared, according to ISO Standard 527-1:1998 in a laboratory vacuum oven (VAKUUM UHG 400, Schuechl, Germany). The samples were kept at room temperature for 24 h and post-cured at 80 °C for 2 h. Two days later, the samples were mechanically tested, using the procedures described in the respective standards. Morphology and structure of Modified Bentonites and Composites. The morphology of bentonites, both plain and those modified with POSS, as well as that of brittle fractures of cured composites were analyzed by scanning electron microscopy (SEM) (Model Jeol 234a, JEOL, Japan). The fractures were obtained after impact breaking the samples cooled in dry ice. The morphology of composites was also examined using a transmission microscope (Tesla Model BS 500, accelerating voltage of 90 kV). Ultrathin specimens were cut using a Tesla microtome equipped with freshly shaped glass knifes. They were collected on acetone/water solution and placed on the standard copper micromesh. The chemical structure of the composites was also analyzed using a Fourier transform infrared (FT-IR) microscope (Nicolet iN10 MX) in order to check the uniformity of distribution of the 6714
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silicon-containing components on the sample surface. The diagnostic band was that at 1045 cm−1. The distance between platelets in bentonites before and after modification and in the composites was evaluated by WAXS, according to Braggs’ law. A Dron 234 diffractometer (made in the former Soviet Union) with a molybdenum lamp (Kα at λ = 0.7124 Å) was used. The samples had a form of round plates 25 mm in diameter and 2 mm thick. Mechanical Testing. The tensile strength was measured using a testing machine (Instron, Model 5967) with an elongation rate of 2 mm/min, according to ISO Standard 5271:1998. The Rockwell hardness was measured using a different testing machine (Zwick, Model 3106) according to EN Standard 10109-1 standard. The penetrator load was 358 N. An average from at least 10 measurements was taken as the result. Charpy impact resistance was determined using a hammer of impact energy of 1 J, according to PN-EN ISO Standard 148-1:2010. Flammability of Composites. The limiting oxygen index (LOI) was measured, according to EN ISO Standard 4589-3 at 25 °C, using a device from Fire Testing Technology, Ltd. (England) to determine the LOI. The flammability of composites was measured according to Polish Standard PN82/C-89023. A sample in the form of a beam was weighed and its dimensions measured. A line perpendicular to its long axis was drawn 80 mm from the end to be ignited. The sample was then clamped horizontally at the other end and the free end was exposed to a flame from a gas burner for 60 s. After the burner was removed, the time until the flame died out or reached the marked line was measured. The remaining part of the beam was weighed, and the length of the remaining unburned part was measured. The measurements were made for at least 5 samples of each composition. The results were the averages of the length of burned sample and the time of burning.
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RESULTS AND DISCUSSION Modification Process. In order to assess the effectiveness of clay modification procedure, thermal (DSC) and X-ray analyses were made. The DSC curves of unmodified Wyoming (BW) and Ukrainian (BU) bentonites and those for bentonites modified with POSS1 and POSS2 are shown in Figure 1. In the thermograms, clear endothermic peaks can be seen in temperature ranges of 250−300 °C and 400−430 °C, and 225−260 °C and 380−440 °C, respectively. The effects are related to thermal decomposition of the modifiers. No peaks in these temperature ranges are present in the thermograms of unmodified bentonites. The only endotherms on the thermogram of plain bentonites, at 80−130 °C, are related to water release from the aluminosilicates. The same effect occurs also for the modified bentonites, but at slightly lower temperature (60−100 °C). The final verification of the bentonite modification was provided by WAXS analysis. The samples had the form of powdered filler and disks cast using UP composites containing the filler. The distances between platelets were calculated using the Bragg equation. Figures 2 and 3 present diffractograms of unmodified and modified BW and BU bentonites, respectively. The distance between platelets in Wyoming bentonite increased from 12.4 Å for unmodified to ca. 18.4 Å and 16.4 Å for the same clay modified with POSS1 and POSS2, respectively. For Ukrainian bentonite, the distances increased from 13.1 Å to 17.9 and 18.1 Å, for POSS1 and POSS2, respectively. The relatively large separation of platelets in the modified bentonites results in organophilization, in addition to facilitating
Figure 1. DSC curves for (a) unmodified BW and (b) BU, as well as for those modified with POSS1 (BWPOSS1, BUPOSS1) and POSS2 (BWPOSS2, BUPOSS2).
Figure 2. WAXS curves for unmodified Wyoming bentonite (BW) and those for bentonite modified with silsesquioxanes (BWPOSS1 and BWPOSS2).
penetration of the polymer chains or the growth of (macro)radicals between platelets. This, on the other hand, provides excellent distribution of filler particles in the resin. The grain size distribution for the modified bentonite powders was measured. The results are shown in Figure 4 and collected in Table 2. 6715
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Figure 3. WAXS curves for unmodified Ukrainian bentonite (BU) and those for bentonite modified with silsesquioxanes (BUPOSS1 and BUPOSS2).
Figure 4. Diagram of the grain size distribution for BWPOSS1.
Table 2. Grain Size Distribution of Unmodified and Modified Bentonites Distribution of Grain Sizes (%) bentonite
0.5−1 μm
1−5 μm
5−10 μm
10−50 μm
50−100 μm
BW BWPOSS1 BWPOSS2 BU BUPOSS1 BUPOSS2
4.1 3.5 2.6 3.2 3.0 2.1
13.4 10.6 9.3 13.6 10.1 8.8
20.4 18.3 17.4 20.6 18.0 16.9
30.6 33.2 31.8 31.4 34.1 30.6
31.5 34.4 38.9 31.2 34.8 41.6
As can be seen in Table 2, the grain-size distributions of unmodified and modified bentonites are quite different. The fraction of grains >10 μm in size increases in modified bentonites, particularly for those containing POSS2, relative to the size of unmodified aluminosilicates. One should bear in mind, however, that, before use, the bentonite fillers have micrometer-sized grains. The grains disintegrate into nanosized platelets or their small aggregates only after dispersion in UP resin by using the multistage homogenization procedure and after curing. Morphology of Modified Bentonites. The morphology of bentonite grains after modification with POSS were studied by SEM. Some results are presented in Figure 5. In Figure 5a, one can observe a lamellar structure consisting of thin layers ordered in regular packets. After modification with POSS1 the structure changes and a thin opaque layer appears on the surface of lamellae. In the case of BW modified with POSS2, agglomerates of broken platelets glued together with the modifier seem to
Figure 5. SEM photomicrograph of (a) unmodified Wyoming bentonite (BW), (b) BW modified with POSS1, and (c) BW modified with POSS2.
prevail. This latter structure does not seem to facilitate homogenization of the filler within the resin. A similar image of bonded small disintegrated platelets was observed for the other bentonite (BU). To summarize the observations on the bentonite modification, one may state that replacing POSS1 by POSS2 rather negatively affects the surface of grains, thermal stability, and the interlamellar distances between platelets in modified bentonites, at least in the case of BW bentonite. Compositions of UP Containing Fillers. The compositions of unsaturated polyester resin with Wyoming and 6716
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Figure 6. SEM photomicrographs of (a) unfilled cured UP resin, (b) cured UP resin filled with 3 wt % BWPOSS1, and (c, d) cured UP resin filled with 3 wt % BWPOSS2.
Ukrainian bentonites modified with POSS1 and POSS2 were found to be easy to homogenize and the filler formed very stable dispersion in the resin (practically no sedimentation). Our earlier experience with the methods of dispersing bentonite filler within polymer matrices19 have let us select proper homogenizing procedures consisting of several stages. Consequently, more uniform compositions were obtained than those previously prepared; the compositions were more transparent than those described previously. We found the homogenization temperature (50 °C) to be an optimal one to reduce viscosity of the compositions and, hence provide better homogenization of the systems. This temperature was still safe from the point of view of reactivity and shelf stability of the resin. Morphology and Structure of Nanocomposites. The SEM photomicrographs of UP composites containing BWPOSS1 and BWPOSS2 fillers indicate that their brittle fractures have shattered surfaces with flat fragments of resin that are difficult to distinguish from bentonite platelets. This morphology suggests a good compatibility of organophilized bentonite with the resin. The structure of UP composite containing 3 wt % of BWPOSS1 (Figure 6b) is characteristic for a nanocomposite. Unfortunately, in the case of the other composite UP + BWPOSS2 (Figures 6c and 6d), one can notice the evident presence of filler agglomerates. This suggests that microcomposites rather than nanocomposites are formed, at least in
some regions. This explains the somewhat-worse properties of the composites filled with BWPOSS2. In the composite containing 3 wt % BWPOSS1, the peak at 2θ ≅ 5° is no longer present in WAXS diffractograms, compared to that in the WAXS diffractogram of the pure filler (Figure 7a). This confirms the presence of an exfoliated structure (i.e., a structure with bentonite platelets dispersed in a polymer matrix). In the WAXS curves of composites containing 3 wt % BWPOSS2 (Figure 7b), the peak corresponding to 2θ is located close to that of the filler (i.e., BWPOSS2). This means that the distance between platelets in the bentonite has not changed. Hence, no exfoliation took place and only microcomposites were formed, as already concluded from SEM photomicrographs. The microphotographs of ultrathin slices of UP composite containing BWPOSS1 filler observed in transmission microscope seem to confirm that exfoliated nanocomposites23 were obtained. In Figure 8a, one can observe platelets of modified bentonite 0.5−2 nm thick, each of which is well-separated from the others. On the other hand, in Figure 8b, a microphograph of a slice of composite UP + 3% BWPOSS2 is shown with evidently no exfoliated structure of bentonite. The surface of cast specimens of UP composites was examined using infrared (IR) microscopy in order to assess the distribution uniformity of modified aluminosilicates within composites. The apparatus was set to the 1045 cm−1 band characteristic vibrations of Si−O−Si bonds. For the UP + 3% BWPOSS2 composites, 6717
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of the clay galleries by polymer chains. As a result, the bentonite grains preserve their initial sizes (of the order of micrometers). To summarize, the results of structure examinations by using SEM, TEM, WAXS, and IR spectroscopy indicate that it was possible to obtain a nancomposite for the system consisting of commercial unsaturated polyester resin with 3 wt % of BWPOSS1 filler. In the case of the other filler, BWPOSS2, which also was used in the amount of 3 wt %, microcomposites rather than nanocomposites were obtained. Mechanical Properties of Composites. The results of mechanical testing of the UP composites are collected in Table 3. Static Tensile Strength. The presence of BWPOSS1, BWPOSS2, BUPOSS1, or BUPOSS2 fillers in cured commercial UP resin Polimal 109 clearly improved the toughness of the material. Both the tensile strength and Young modulus increased. For the composite with UP matrix containing 3 wt % of BWPOSS1 filler the tensile strength and Young modulus increased by as much as 44% and 33%, respectively (see Table 3). Somewhat worse improvement of the tensile properties was recorded for composites containing BWPOSS2 filler. No improvement was observed by increasing the amount of filler (Table 3). This result was probably related to the tendency of the filler to agglomerate and form a microcomposite (as shown also by WAXS, SEM, TEM, and IR mapping measurements). With the Ukrainian bentonites, the improvements of the static mechanical properties were by 6%−34.5% and 3.8%−26.5% for tensile strength and Young modulus, respectively, for UP composites containing BWPOSS1. For BWPOSS2, the respective improvements were 2%−21% for tensile strength and 3.8%−12.6% for Young modulus. The values increased as the amount of filler increased (see Table 3). Rockwell Hardness. The results shown in Table 2 indicate that the hardness of composites was dependent on all the factors that have been varied in this work, i.e., the type and amount of filler. Generally, the hardness of UP composites filled with both bentonites modified with POSS1 and POSS2 was slightly reduced, compared to that of the unfilled UP. The most significant effect was observed for the composites modified with POSS1 (the Rockwell hardness decreased by 1.4%−6.5%). Hence, the resin containing modified bentonite slightly softened, compared to unmodified cured UP resin. The smallest hardness
Figure 7. WAXS curves recorded for cured composites: (a) UP + 3% BWPOSS1 and (b) UP + 3% BWPOSS2.
silicate agglomerates approximately several dozen micrometers in size can be seen in the photomicrographs (see Figure 9c). On the surface of composites containing BWPOSS1 (Figure 9b), the areas of high IR adsorption are much smaller (10−20 μm). This seems to be more evidence of the poor miscibility of BWPOSS2 with a UP resin and, hence, insufficient intercalation
Figure 8. TEM photomicrographs of ultrathin slices of UP composite containing 3 wt % of (a) BWPOSS1 and (b) BWPOSS2. 6718
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Figure 9. Surface maps of UP composites showing the intensity of IR adsorption at the band of 1045 cm−1, characteristic for Si−O−Si vibrations: (a) IR spectrum of bentonite, (b) surface adsorption map for UP + BWPOSS1 composites, and (c) surface adsorption map for UP + BWPOSS2 composites.
Table 3. Effect of the Amount of Filler on the Tensile Strength, Young Modulus, Charpy Impact Resistance, and Rockwell Hardness of Cured Commercial Unsaturated Polyester Resin (UP) Filled with (a) BWPOSS1 and BWPOSS2 or (b) BUPOSS1 and BUPOSS2a (a) UP Composites Containing BW Bentonite Modified with POSS UP property tensile strength [MPa] Young modulus [MPa] Charpy’s impact resistance [kJ/m2] Rockwell hardness [MPa]
0.0 wt %
BWPOSS1 1.0 wt %
BWPOSS2 3.0 wt %
1.0 wt %
60.4 ± 4.7 67.1 ± 3.8 74.2 ± 2.6 86.9 ± 4.3 64.6 ± 4.2 3960 ± 25 4256 ± 31 4932 ± 19 5267 ± 26 4187 ± 23 5.6 ± 0.9 6.7 ± 0.8 7.8 ± 0.6 8.9 ± 0.2 6.2 ± 0.3 49.3 ± 4.7 48.6 ± 1.9 47.4 ± 2.5 46.3 ± 4.2 48.8 ± 2.1 (b) UP Composites Containing BU Bentonite Modified with POSS UP
a
2.0 wt %
BUPOSS1
2.0 wt %
3.0 wt %
69.3 ± 3.8 4325 ± 27 6.9 ± 0.8 47.9 ± 0.4
74.3 ± 5.6 4600 ± 18 7.3 ± 0.7 47.2 ± 0.9
BUPOSS2
property
0.0 wt %
1.0 wt %
2.0 wt %
3.0 wt %
1.0 wt %
2.0 wt %
3.0 wt %
tensile strength [MPa] Young modulus [MPa] Charpy’s impact resistance [kJ/m2] Rockwell hardness [MPa]
60.4 ± 4.7 3960 ± 25 5.6 ± 0.9 49.3 ± 4.7
63.9 ± 2.5 4112 ± 19 6.3 ± 0.6 48.9 ± 2.3
72.5 ± 3.3 4798 ± 31 7.3 ± 0.4 48.1 ± 1.2
81.3 ± 3.1 5009 ± 26 8.0 ± 0.5 47.4 ± 3.1
61.2 ± 4.2 4110 ± 18 6.0 ± 0.2 49.1 ± 1.3
68.4 ± 3.3 4231 ± 22 6.7 ± 0.5 48.6 ± 1.2
72.9 ± 3.7 4460 ± 21 7.0 ± 0.3 47.9 ± 0.5
The standard deviation for each value also is shown.
reduction (0.4%−2.9%) was noticed for the composites filled with BUPOSS2. Charpy Impact Resistance. As follows from the values collected in Table 3, the presence of all types of fillers studied in this work was advantageous from the point of view of impact resistance. Again, the most spectacular changes were observed for
UP composites containing BWPOSS1. The important factor is the amount of filler. The greatest increase of the unnotched Charpy’s impact resistance, by as much as 59%, was observed for the cured polyester resin filled with 3 wt % of BWPOSS1. A somewhat-worse effect was observed for the other bentonite (BU) that was also modified with POSS1 (3 wt %). In this case, 6719
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the increase of impact resistance was 43%, with respect to that of unmodified polyester resin. As expected, the weakest effect of brittleness improvement was observed for the composites containing bentonites (BW or BU) modified with POSS2. To summarize the results of static mechanical testing, one can state that much better properties than those of the native polyester resins had the composites filled with up to 3 wt % bentonites modified with silsesquioxane quaternary ammonium derivative POSS1 (recall Table 1). Replacement of the modifier with POSS2 made the composites less mechanically improved. From among the two bentonites studied, clearly the better effects were obtained for Wyoming bentonite, compared to those for Ukrainian bentonite. All the results are presented in Table 3. The Effect of Bentonites Modified with POSS on the Flammability of UP Composites. The limiting oxygen number measurements for the cured UP composites indicated a generally advantageous effect of POSS modified bentonites on the reduction of flammability of these materials. As can be seen in Figure 10, in all cases, the limiting oxygen index (LOI) of the
Figure 11. Relative change of burned part of the sample in flammability test, versus the amount of bentonite in UP composites.
Figure 12. Relative burning time of sample beams, versus the amount of BW and BU bentonites modified with POSS1 and POSS2. Figure 10. Limiting oxygen number (LOI) values measured for UP composites containing BW and BU bentonites modified with POSS fillers.
in the form of quaternary ammonium compounds can be considered as starting materials for hybrid composites of reduced flammability or self-extinguishing materials.
samples increased monotonically as the amount of filler increased. These results show that the lowest concentration of oxygen in a mixture with nitrogen necessary to support sample burning was higher than that for unmodified polyester resin. The best result (LOI = 22.7%) was obtained for the composite containing 3 wt % BWPOSS1. Flammability of UP Composites Containing Bentonites Modified with POSS Fillers. According to literature data,15 nanofillersin particular, modified bentonitesmay act as fire retardants for composites. Hence, one of the objectives of this work was to verify whether the preparation methods that we have used indeed lead to composites based on a polyester matrix of reduced flammability. Flammability tests showed that composites containing 3 wt % BWPOSS1 or BUPOSS1 were indeed less flammable than plain cured UP resins. The test involved weighing the unburned part of specimen beam. The results, in the form of relative weight loss of burned sample in reference to that of unmodified resin, are presented in Figure 11. Similar to that observed with the other physical properties, the best effect of flammability reduction was observed for bentonites modified with POSS1. A similar conclusion could be drawn from the time of burning measured in another standard flammability test (see Figure 12). Hence, the results indicate that the cured UP resins filled with well-distributed bentonites modified with POSS fillers
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CONCLUSIONS The following conclusions are reached from the research: • The organofilized fillers (BWPOSS1, BWPOSS2, BUPOSS1, and BUPOSS2) used for modification of a commercial unsaturated polyester (UP) resin mix well with the resin and had no tendency to sediment. • BWPOSS1 filler added to UP evidently improved the mechanical properties of cured resin. Tensile strength increased by 44%, Young modulus increased by 33%, and unnotched impact resistance increased by 59%. • All UP composites obtained in this work had improved flame resistance. The best reduction of flammability was obtained for unsaturated polyesters filled with BWPOSS1.
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AUTHOR INFORMATION
Corresponding Author
*Tel.: + 48 17865 1223. Fax: +48 17 854 3655. E-mail: molek@ prz.edu.pl. Notes
The authors declare no competing financial interest. 6720
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(21) Gołębiewski, J.; Rózȧ ński, A.; Gałęski, A. Study on the process of preparation of polypropylene nanocomposite with montmorillonite (in Pol.). Polimery (Warsaw, Pol.) 2006, 51, 374. (22) Need to add ref 22 or remove citation for ref 22 that appears shortly after the Figure 1 citation in the Results and Discussion section.
ACKNOWLEDGMENTS The study was carried out as a part of the project, “Silsesquioxanes as Nanofillers and Modifiers in Polymer Composites” (under Grant No. WND-POIG.01.03.01-30-173/ 09, co-financed by the European Union, within the European Fund for Regional Development).
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REFERENCES
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dx.doi.org/10.1021/ie303433v | Ind. Eng. Chem. Res. 2013, 52, 6713−6721
