Hybrid organic-inorganic POSS (polyhedral oligomeric silsesquioxane)/polypropylene nanocomposite filaments

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<ul><li><p>Fibers and Polymers 2010, Vol.11, No.8, 1137-1145</p><p>1137</p><p>Hybrid Organic-Inorganic POSS (Polyhedral Oligomeric silsesquioxane)/</p><p>Polypropylene Nanocomposite Filaments</p><p>B. S. Butola*, Mangala Joshi, and Sachin Kumar </p><p>Department of Textile Technology, Indian Institute of Technology, New Delhi 110016, India</p><p>(Received April 8, 2010; Revised August 5, 2010; Accepted August 9, 2010)</p><p>Abstract: Octamethyl-POSS and Octaphenyl-POSS reinforced polypropylene nanocomposite monofilaments were prepared</p><p>by melt blending route. It was observed that incorporation of Octamethyl-POSS and Octaphenyl-POSS in polypropylene</p><p>show improvement in mechanical as well as thermal properties. Octaphenyl POSS/PP nanocomposites show significant</p><p>increase in thermal stability even at very low concentration as compared to neat polymer matrix. An increase of 100 and</p><p>140</p><p>o</p><p>C was observed in thermal degradation temperature at 5 wt% loss and maximum degradation over neat PP filaments</p><p>respectively at low OP-POSS loadings (</p></li><li><p>1138 Fibers and Polymers 2010, Vol.11, No.8 B. S. Butola et al.</p><p>in PP was prepared in a DSM Twin screw extruder using</p><p>temperatures 180, 190, 200, and 210 in different zones for</p><p>4 min mixing time at 150 rpm. The master batch was used</p><p>for preparation of OP-POSS/PP nanocomposites monofilaments</p><p>by melt spinning.</p><p>Melt Spinning</p><p>The spinning of OM-POSS/PP and OP-POSS/PP nano-</p><p>composite monofilaments was carried out on a laboratory</p><p>single screw extruder (BETOL-1820) by varying POSS</p><p>concentration from 0.1 to 10 % by weight. The codes used</p><p>for describing nanocomposite fibres with various POSS</p><p>concentration are given in Table 1. </p><p>The diameter and the length of spinneret orifice were 0.5</p><p>and 2 mm respectively. Extruded POSS/PP monofilaments</p><p>were quenched in ice cooled water (82</p><p>o</p><p>C) to freeze the</p><p>structure in smectic phase (a phase possessing order</p><p>intermediate between the amorphous and crystalline state</p><p>can be obtained by quench cooling and is referred to as the</p><p>smetic phase. In the as Spun PP fibre the crystallites may</p><p>be in the paracrystallite Smectic form [17]. When drawn</p><p>and/or annealed they move towards the more stable form)</p><p>of PP. Spinning temperature of different heating zone was</p><p>190, 200, 210, and 220</p><p>o</p><p>C. Single screw extruder speed was</p><p>6 RPM and take up roller speed was 12 m/min.</p><p>Drawing </p><p>Two stage drawing of POSS/PP filaments was done on an</p><p>indigenously built drawing machine to improve the</p><p>molecular orientation and stabilization of the PP filament</p><p>structure to get better mechanical properties. The filaments</p><p>were drawn upto the maximum limit drawing just before</p><p>filament weakening due to void formation and stress</p><p>whitening started. The final diameter of the composite</p><p>filaments was approximately 0.2 mm, corresponding to a</p><p>linear density of 250 denier. The drawing parameters are</p><p>given in Table 2.</p><p>Characterization Techniques </p><p>X-ray Diffraction</p><p>The determination of volume fraction crystallinity and</p><p>orientation was carried out by Wide angle X-ray Diffraction</p><p>(WAXD) of the samples on a Philips X-ray diffractometer</p><p>(Model-XPERT PRO, Panalytical, Netherland) with Nickel-</p><p>filtered CuK (1.54 ) as the radiation source. The</p><p>diffractometer was operated at 40 kV and 30 mA in</p><p>reflection mode with angle 2 ranging from 5 to 35</p><p>o</p><p> at a</p><p>scanning rate of 2</p><p>o</p><p>/min. All the samples were prepared by</p><p>cutting the drawn monfilaments into fine powder form. The</p><p>degree of crystallinity of various samples was evaluated</p><p>from the X-ray diffraction pattern by separating the</p><p>crystalline and amorphous portions under the diffraction</p><p>pattern using the following expression.</p><p>Degree of crystallinity (%)={A</p><p>cr</p><p>/(A</p><p>cr</p><p>+A</p><p>am</p><p>)}100</p><p>Where, A</p><p>cr</p><p> is the area under crystalline peak and A</p><p>am</p><p> is the</p><p>area under amorphous halo.</p><p>Crystallite Thickness</p><p>The average lateral crystalline thickness is estimated from</p><p>the broadening observed in the WAXD pattern recorded for</p><p>Table 1. Codes used for describing nanocomposite monofilaments</p><p>S. No. Code % POSS concentration</p><p>1 P0 0</p><p>2 P01 0.1</p><p>3 P02 0.25</p><p>4 P05 0.5</p><p>5 P1 1.0</p><p>6 P2 2.0</p><p>7 P5 5.0</p><p>8 P7 7.0</p><p>9 P10 10.0</p><p>Table 2. Drawing process conditions during drawing</p><p>Drawing roller speed (RPM) Temperature of heater (</p><p>o</p><p>C)</p><p>First roller 2 First heating zone 605</p><p>Second roller 8 Second heating zone 1305</p><p>Third roller 20</p><p>Figure 1. Molecular structure of octamethyl POSS.</p><p>Figure 2. Molecular structure of octaphenyl POSS.</p></li><li><p>Hybrid POSS/Polypropylene Nanocomposite Filaments Fibers and Polymers 2010, Vol.11, No.8 1139</p><p>2 range of 10-35</p><p>o</p><p>, at a scanning rate of 2</p><p>o</p><p>/min. The</p><p>integral breadth of the diffraction intensity arising from the</p><p>imperfection of crystallites is measured in terms of </p><p>1/2 </p><p>(hkl).</p><p>Higher the value of </p><p>1/2 </p><p>(hkl), lower is the crystalline</p><p>perfection.</p><p>Apparent crystalline size was determined according to</p><p>Scherrers equation:</p><p>Where, is the half width of the diffraction peak in radian,</p><p>K is equal to 0.9, is the Bragg angle and is the wave</p><p>length of the X-rays. The values of D</p><p>(hkl)</p><p> for (110) reflection</p><p>were calculated.</p><p>Differential Scanning Calorimetry</p><p>DSC studies were carried out to study the melting</p><p>behaviour, crystallinity level and crystallization behaviour of</p><p>the nanocomposites. The instrument used was Perkin Elmer</p><p>Pyris-1 Differential Scanning Calorimeter in flowing nitrogen</p><p>atmosphere. The scans were obtained from 50-180</p><p>o</p><p>C at a</p><p>heating rate of 10</p><p>o</p><p>C/min with sample weight around 5 mg.</p><p>The onset, end and peak melting temperatures, as well as</p><p>heat of fusion (H) were calculated from the scans using an</p><p>inbuilt software. The crystallinity of the samples was</p><p>calculated using the following relationship:</p><p>X</p><p>dsc</p><p>=H</p><p>sample</p><p>/ 209 </p><p>Where X</p><p>dsc</p><p>=DSC crystallinity of the sample, H</p><p>sample</p><p>=</p><p>heat of fusion of the sample and 209 kJ/kg [18] is the heat of</p><p>fusion of 100 % crystalline PP.</p><p>Scanning Electron Microscopy (SEM)</p><p>The surface and cross-section of the filaments of selected</p><p>nanocomposites were studied on a scanning electron</p><p>microscope (SEM), ZEISS (EVO-50) manufactured by K.E</p><p>Developers Ltd., Cambridge, England. Samples were coated</p><p>with a thin layer of silver. The basic aim of the study was to</p><p>look at the coarse level of POSS aggregation and any</p><p>possible change in the morphology caused by presence of</p><p>POSS in PP matrix.</p><p>Thermogravimetric Analysis</p><p>Thermogravimetric Analysis was carried out on a Perkin</p><p>Elmer TGA-7 instrument under nitrogen atmosphere.</p><p>Samples were heated at a heating rate of 20</p><p>o</p><p>C/minute from</p><p>50 to 900</p><p>o</p><p>C. The percentage weight loss of the samples as a</p><p>function of temperature was recorded.</p><p>Tensile Properties</p><p>Tensile testing of the sample filaments was carried out on</p><p>Instron 4301 tester (ASTM-D5035-90). Test settings used</p><p>for nanocomposite filaments were as follows: load cell:</p><p>1 kg, gauge length: 250 mm, strain rate: 300 mm/min. </p><p>Sonic Modulus</p><p>The sonic modulus is a dynamic modulus (Youngs</p><p>modulus) measured by the velocity of train of the sound</p><p>pulses through the fibre. The sonic modulus for a long thin</p><p>fibre is given by </p><p>E=C</p><p>2</p><p>Where E is the sonic modulus, is the density and C is the</p><p>sonic velocity. The velocity of wave depends upon the</p><p>degree of crystallinity and orientation of sample. </p><p>The dynamic modulus tester PPM-SR (H. M. Morgan Co.</p><p>Inc., Norwood, Mass, USA) was used for testing sonic</p><p>modulus of neat PP as well POSS/PP nanocomposite</p><p>filaments. The filament was clamped at one end, passed over</p><p>a pulley, kept taut by a reasonable weight to the other end</p><p>(for slight tension). The fibre scanner had two transducers</p><p>mounted on the instrument. The fixed transducer containing</p><p>a propagation meter supplied sound pulses of longitudinal</p><p>waves at a frequency of 5 KHz. The other transducer</p><p>(receiver transducer) was driven by a synchronized motor</p><p>and moved along the sample at a constant speed (2.5 inch/</p><p>min). The transit time was monitored directly as a function</p><p>of the distance between probes on an attached recorder. The</p><p>sonic velocity can be calculated from the reciprocal of the</p><p>slope (1/C) of the line plotted by the instrument.</p><p>Results and Discussion</p><p>XRD Analysis of OM-POSS and OP-POSS/PP Nano-</p><p>composites</p><p>Figure 3 shows the diffraction pattern for PP and OM-</p><p>POSS/PP nanocomposite filaments and it is observed from</p><p>the shape of diffraction patterns that presence of POSS does</p><p>not interfere with the crystal pattern of PP. It can also be seen</p><p>that a peak corresponding to the dominant OM-POSS peak</p><p>just appears at 0.25 wt% POSS. Though upto 1 wt%</p><p>concentration of OM-POSS, the peak height increases</p><p>progressively, it is not pronounced. However, beyond 1 wt%</p><p>D hkl( )</p><p>K</p><p>cos</p><p>--------------</p><p>=</p><p>Figure 3. XRD of different OM-POSS/PP nanocomposite filaments.</p></li><li><p>1140 Fibers and Polymers 2010, Vol.11, No.8 B. S. Butola et al.</p><p>content, the peaks becomes well defined, pronounced, rather</p><p>sharp and grow progressively with increase in the content of</p><p>OM-POSS in PP. This means that OM-POSS molecules</p><p>exist as crystals in PP matrix at OM-POSS concentrations</p><p>just over 0.25 wt%. Zheng et al. [19] reported that POSS is</p><p>able to crystallize in nanocomposites even when it is a part</p><p>of the polymeric chain and there are restrictions on its</p><p>movement. Hence, it is obvious that POSS is able to</p><p>crystallize when it is dispersed physically in PP matrix and</p><p>there are no chemical linkages to restrict its movement. It</p><p>means upto 0.25 wt%, POSS is almost completely dispersible</p><p>in PP matrix and at higher concentrations POSS starts</p><p>agglomerating and crystallizing. Another observation that</p><p>can be made from the diffractograms is that the peaks are not</p><p>as sharp as neat POSS peaks. This means that the dispersed</p><p>OM-POSS crystals are not as perfect as neat OM-POSS</p><p>crystals. It can be inferred that, these crystallites are formed</p><p>from the dispersed OM-POSS particles and although the</p><p>process of melt mixing is able to disperse the OM-POSS at</p><p>nano/molecular level in PP matrix, eventually POSS manages</p><p>to crystallize when concentration levels increase beyond</p><p>0.25 wt%. </p><p>The size of the OM-POSS crystals was determined using</p><p>Scherrers equation and given in Table 3. It is clear from the</p><p>results that crystals from dispersed OM-POSS in nanocom-</p><p>posites are smaller than the neat OM-POSS crystals.</p><p>The corresponding X-ray diffraction patterns for OP-</p><p>POSS and OP-POSS/PP nanocomposite filaments are shown</p><p>in Figure 4. Here also the presence of OP-POSS does not</p><p>seem to affect the crystal pattern of PP matrix. Appearance</p><p>of characteristic peaks of OP-POSS in nanocomposite</p><p>filaments means OP-POSS too crystallizes in PP matrix.</p><p>However, it is quite clear that the tendency to crystallize for</p><p>OP-POSS in PP matrix is more subdued than the OM-POSS.</p><p>Not only the dominant peak heights are lower, these appear</p><p>at higher OP-POSS (2.0 wt%) concentration as compared to</p><p>OM-POSS/PP nanocomposites. This is to be expected since</p><p>the bulky phenyl groups attached to the POSS skeleton</p><p>hinder its mobility and hence the tendency to crystallize.</p><p>Differential Scanning Calorimetry of OP-POSS/PP</p><p>Nanocomposite</p><p>DSC is another investigative tool to obtain useful</p><p>information about the thermal transitions of polymers. The</p><p>Original DSC thermograms for OM-POSS/PP and OP-</p><p>POSS/PP composites are shown in Figure 5 and 6. The</p><p>values of melting temperatures for different POSS/PP</p><p>nanocomposites are given in Table 4. The values indicate</p><p>that there is no significant effect of OM-POSS and OP-</p><p>POSS molecules on the melting temperature of PP polymer</p><p>upto 5 wt%.</p><p>In the earlier section on analysis of X-ray diffraction</p><p>patterns for OM and OP-POSS/PP nanocomposites, it was</p><p>concluded that presence of either type of POSS does not</p><p>cause significant change either in the crystal structure or</p><p>crystal volume fraction of PP matrix. As the crystal pattern</p><p>remains largely unaffected, melting temperatures too are not</p><p>affected significantly. </p><p>Figure 4. XRD of different OP-POSS/PP nanocomposite filaments.</p><p>Figure 5. DSC thermograms of selected OM-POSS/PP</p><p>nanocomposites.</p><p>Table 3. Crystal size of POSS in free and dispersed state (using</p><p>Scherrers equation)</p><p>Material Crystal size (nm)</p><p>Neat POSS 40</p><p>P10 17</p><p>P7 14</p><p>P5 14</p><p>P2 17</p><p>P1 18</p></li><li><p>Hybrid POSS/Polypropylene Nanocomposite Filaments Fibers and Polymers 2010, Vol.11, No.8 1141</p><p>Mechanical Properties of POSS/PP Nanocomposites</p><p>Tensile Properties</p><p>The raw stress strain curves of POSS/PP nanocomposite</p><p>monofilament are plotted in Figure 7 and 8. From the results</p><p>it can be observed that increase in the concentration of OM-</p><p>POSS and OP-POSS upto 0.5 and 1 wt% respectively results</p><p>in gradual increase of the tenacity of nanocomposite</p><p>monofilaments. Beyond these limits of concentrations,</p><p>tenacity starts to fall down. It is proposed that due to cage</p><p>like structure, POSS acts as a lubricant when it is dispersed</p><p>at molecular/nanolevel, thus helping in improving the</p><p>drawablity of filaments [20,21]. But above 0.5-1.0 wt%</p><p>POSS concentration, aggregation tendency of POSS molecules</p><p>(confirmed from X-ray diffraction) increases which results</p><p>in decrease in tenacity as well as drawablity of polymer. At</p><p>low concentrations, it reduces the viscosity during melt</p><p>spinning of polymer and thus improves the processablity of</p><p>polymers as reported by authors [21] in an earlier study on</p><p>Figure 6. DSC thermograms of selected OP-POSS/PP</p><p>nanocomposites.</p><p>Figure 7. Stress strain curves of OM-POSS/PP nanocomposites.</p><p>Figure 8. Stress strain curves of OP-POSS/PP nanocomposites.</p><p>Figure 9. Effect of POSS concentration on modulus of POSS/PP</p><p>nanocomposite monofilament.</p><p>Table 4. Melting temperature for POSS/PP nanocomposites from</p><p>DSC studies</p><p>POSS conc. </p><p>in PP (%)</p><p>Melting temperature</p><p>OM-POSS/PP OP-POSS/PP</p><p>0 165.0 165.0</p><p>0.1 165.5 165.2</p><p>0.25 165.1 165.9</p><p>0.5 164.5 165.6</p><p>1 164.8 165.6</p><p>2 164.8 165.9</p><p>5 164.8 166.1</p><p>7 165.0 167.8</p><p>10 165.8 165.0</p></li><li><p>1142 Fibers and Polymers 2010, Vol.11, No.8 B. S. Butola et al.</p><p>HDPE-OM POSS system.</p><p>The effect of incorporation of POSS molecules on the</p><p>modulus of nanocomposite filaments is shown in Figure 9.</p><p>Again it is apparent that as in case of tensile strength,</p><p>Youngs modulus too shows a gradual increase with increase</p><p>in POSS content upto 0.5 to 1.0 wt%, for both nanocomposites,</p><p>and decreases at higher concentrations.</p><p>Sonic Modulus</p><p>The sonic modulus values of OM-POSS nanocomposite</p><p>monofilaments are shown in Figure 10. The results show that</p><p>sonic modulus values increase as OM-POSS concentration in</p><p>PP matrix increases upto 0.5 wt%, which means better</p><p>orientation due to better drawability. Beyond 0.5 wt%</p><p>concentration, the modulus values start to fall. The same</p><p>trend is shown in case of OP-POSS also but upto a value of</p><p>1 wt%.</p><p>These findings are consistent with the results of tensile</p><p>properties of nanocomposite monofilaments. In case of</p><p>tensile strength, it was observed that tenacity values of</p><p>nanocomposite monofilaments increase upto a concentration</p><p>of 0.5 wt% in case of OM-POSS and 1 wt% in case of OP-</p><p>POSS. Sonic waves travel faster in crystalline and oriented</p><p>structures as compared to amorphous and randomly oriented</p><p>structures. </p><p>Thermogravimetric Analysis</p><p>The results of thermogravimetric analysis of different</p><p>POSS/PP nanocomposites in terms of Temperature of</p><p>degradation for 5...</p></li></ul>


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