Applied Polymer ARTICLE sheet allowed the adhesion between fibers, which were under Tensile Testing. Tensile testing of the NFRUP and EGMRUP adapted temperature conditions. For this reason, the sheet was composites was carried out with a Lloyds Dynamometer univer- deposited in an air oven at a temperature of 120C, and the sal testing machine as per NF T 57-301 at a crosshead speed of sheet was passed through. The PET-PE fibers were submitted to 5 mm/min and a gripping length of 100 mm(Ksar Hellal in an increase in temperature. The binding was accomplished by a Tunisia). The specimen was cut out in the direction of ombination of heating, flowing, and cooling. Indeed, the initial nonwoven production. All of the results were calculated as the calorific energy weakened the outer surface of the thermobinder average of 10 samples for each test. which increased the contact surface with the other fibers, and Dielectric Analysis. Dielectric measurements were conducted then, the supplementary energy turned the outer binder into a with an Alpha dielectric-impedance analyzer(Novocontrol,Sfax fluid, whichin turn, molded the natural fibers with the ther- in Tunisia), with the measurements of the studied samples taken mobinder ones. After this consolidation. the nonwoven fibers over the temperature range from the ambient to 150C and in a were calendered at 120oC in an industry of developing nonwo. frequency interval from 10- to 10 Hz. A circular gold elec- ven materials to decrease the thickness of the sheet. The E-glass trode (2 cm in diameter)was sputtered on both surfaces of the fibers are supplied from a Tunisian company named(STIA: sample to ensure good electrical contact with the gold-plated Societe tunisienne de industrie automobile. Sousse in Tuni- measuring electrodes. A sinusoidal voltage was applied to create sia). They were presented in a sheet in which the fibers, whose an alternating electric field that produced polarization in the average length was about 50 mm, were randomly oriented. field but had a phase angle shift(8). This p a voltage with the ngle shift was measured by the comparison of the applied The composites(NFRUP, EGMRUP)were manufactured with the measured current, which was divided into capacitive and con- classical contact mold method. In fact, the fibers were deposited ductive components. With the following equations, the dielec- on the mold and impregnated with the liquid resin mixed with tric parameters were calculated suitable proportions of methyl ethyl ketone peroxide and cobalt ctanone as hardener and catalyst, respectively. The saturated materials were then pressed by a roller to remove bubbles. After the hardness of the resin was measured, the composites were withdrawn from the mold. The obtained NFrUP and EGMRUP composites had 5.2 and 5.5% fiber volume fractions, respectively (3) Measurements SEM. The morphologies of the composite surfaces were where()=-1; e and &"are the real and imaginary parts of the observed at room temperature by a Philips XL30 SEM instru- complex permittivity (e*);tan8(=g/e)is the dissipation factor; ment. A gold coating of a few nanometers in thickness was A and d are the area and thickness, respectively, of the sample; C formed on the surfaces of the samples to prevent charging, and is the capacitance; G is the conductance; and Eo is the permittivity the surfaces were examined at an accelerating voltage of 20 kV. of the free space and is equal to 8.854 x 10F/m These observations were conducted on the upper surface and Two kinds of dielectric experiments were carried out. One of he cross-sectional surface of the composite so that the longitu- them was an isochronal run with fixed frequencies and various dinal and cross-sectional aspects of the fibers, respectively, could be observed For this reason, the sample was cut with a saw at temperatures from ambient to 150C with a heating rate of room temperature in the direction of the composite cross-sec- 2C/min in a nitrogen atmosphere. The second was an isother- tional surface and perpendicular to the fiber axis. mal run with fixed temperatures and scanning frequencies from DSC. DSC was used to evaluate the glass-transition tempera cure(Ty)of the matrix and its NFRUP and EGMRUP compo- RESULTS AND DISCUSSION sites. Samples weighing between 10 and 15 mg were placed in a SEM Observation hermetic pan and sealed. A Jade DSC instrument(Perkin Elmer) SEM observation was made to explore the fiber-matrix interface was operated in the temperature interval-50 to 150.C in a in the NFRUP and EGMRUP composites. The SEM micro- nitrogen environment purged at 20 mw and according to a graphs of the composites are displayed in Figures 1(a-d)and heating-cooling-heating cycle. In the first heating step, the sam- 2(a-d). Figure 1(a, b) shows the micrographs of the longitudinal ples were heated from-50 to 150C at a heating rate of 5C/ fiber aspects for the NFRUP composite. These micrographs min. Then they were cooled from 150 to -50C at a cooling illustrate that the fibers were randomly dispersed in the matrix rate of 5%C/min. In the second heating step, the samples were and that the individual separation of the fibers were not in the heated from -50 to 150C at a heating rate of 5 C/min. The form of single fibers. Figure 1(c, d)shows the micrographs of thermograms were analyzed to estimate the Te values of the the longitudinal fiber aspects for the EGMRUP composite. This esin and its composites. The Ts value of each sample was deter- figure shows that the glass fibers were identical and were in the mined from the midpoint value of the jump in heat flow in the form of single fibers because they were synthetic. The analysis second heating run. The construction of the lines was done by of Figure 1(b, d)illustrated some physical contacts between the Pyris software, Perkin Elmer from Courtaboeuf, France. fibers and the matrix. Figure 2(a-d) depicts the micrographs of M Www. MaterialSviewS. cOm WILEYONLINELIBRARY. COM/APP J APPL POLYM. SCL 2013, DOl: 10.1002/APP. 38499 489sheet allowed the adhesion between fibers, which were under adapted temperature conditions. For this reason, the sheet was deposited in an air oven at a temperature of 120
C, and the sheet was passed through. The PET–PE fibers were submitted to an increase in temperature. The binding was accomplished by a combination of heating, flowing, and cooling. Indeed, the initial calorific energy weakened the outer surface of the thermobinder fibers (PE fibers with a low melting temperature of 110
C), which increased the contact surface with the other fibers, and then, the supplementary energy turned the outer binder into a fluid, which, in turn, molded the natural fibers with the ther￾mobinder ones. After this consolidation, the nonwoven fibers were calendered at 120
C in an industry of developing nonwo￾ven materials to decrease the thickness of the sheet. The E-glass fibers are supplied from a Tunisian company named (STIA: Soci
et
e Tunisienne de l’Industrie Automobile, Sousse in Tuni￾sia). They were presented in a sheet in which the fibers, whose average length was about 50 mm, were randomly oriented. Composite Processing The composites (NFRUP, EGMRUP) were manufactured with the classical contact mold method.21 In fact, the fibers were deposited on the mold and impregnated with the liquid resin mixed with suitable proportions of methyl ethyl ketone peroxide and cobalt octanone as hardener and catalyst, respectively. The saturated materials were then pressed by a roller to remove bubbles. After the hardness of the resin was measured, the composites were withdrawn from the mold. The obtained NFRUP and EGMRUP composites had 5.2 and 5.5% fiber volume fractions, respectively. Measurements SEM. The morphologies of the composite surfaces were observed at room temperature by a Philips XL30 SEM instru￾ment. A gold coating of a few nanometers in thickness was formed on the surfaces of the samples to prevent charging, and the surfaces were examined at an accelerating voltage of 20 kV. These observations were conducted on the upper surface and the cross-sectional surface of the composite so that the longitu￾dinal and cross-sectional aspects of the fibers, respectively, could be observed. For this reason, the sample was cut with a saw at room temperature in the direction of the composite cross-sec￾tional surface and perpendicular to the fiber axis. DSC. DSC was used to evaluate the glass-transition tempera￾ture (Tg) of the matrix and its NFRUP and EGMRUP compo￾sites. Samples weighing between 10 and 15 mg were placed in a hermetic pan and sealed. A Jade DSC instrument (PerkinElmer) was operated in the temperature interval 50 to 150
C in a nitrogen environment purged at 20 mW and according to a heating–cooling–heating cycle. In the first heating step, the sam￾ples were heated from 50 to 150
C at a heating rate of 5
C/ min. Then they were cooled from 150 to 50
C at a cooling rate of 5
C/min. In the second heating step, the samples were heated from 50 to 150
C at a heating rate of 5
C/min. The thermograms were analyzed to estimate the Tg values of the resin and its composites. The Tg value of each sample was deter￾mined from the midpoint value of the jump in heat flow in the second heating run. The construction of the lines was done by Pyris software, Perkin Elmer from Courtaboeuf, France. Tensile Testing. Tensile testing of the NFRUP and EGMRUP composites was carried out with a Lloyds Dynamometer univer￾sal testing machine as per NF T 57-301 at a crosshead speed of 5 mm/min and a gripping length of 100 mm (Ksar Hellal in Tunisia).22 The specimen was cut out in the direction of nonwoven production. All of the results were calculated as the average of 10 samples for each test. Dielectric Analysis. Dielectric measurements were conducted with an Alpha dielectric–impedance analyzer (Novocontrol, Sfax in Tunisia), with the measurements of the studied samples taken over the temperature range from the ambient to 150
C and in a frequency interval from 101 to 106 Hz. A circular gold elec￾trode (2 cm in diameter) was sputtered on both surfaces of the sample to ensure good electrical contact with the gold-plated measuring electrodes. A sinusoidal voltage was applied to create an alternating electric field that produced polarization in the sample, which oscillated at the same frequency as the electric field but had a phase angle shift (d). This phase angle shift was measured by the comparison of the applied voltage with the measured current, which was divided into capacitive and con￾ductive components. With the following equations,23 the dielec￾tric parameters were calculated: e ¼ e 0 je 00 (1) e 0 ¼ cpðsampleÞd e0A (2) e 00 ¼ GðsampleÞd xe0A (3) where (j)2 ¼ 1; e0 and e00 are the real and imaginary parts of the complex permittivity (e*); tan d (¼e00/e0 ) is the dissipation factor; A and d are the area and thickness, respectively, of the sample; Cp is the capacitance; G is the conductance; and e0 is the permittivity of the free space and is equal to 8.854  1012 F/m. Two kinds of dielectric experiments were carried out. One of them was an isochronal run with fixed frequencies and various temperatures from ambient to 150
C with a heating rate of 2
C/min in a nitrogen atmosphere. The second was an isother￾mal run with fixed temperatures and scanning frequencies from 101 to 106 Hz. RESULTS AND DISCUSSION SEM Observation SEM observation was made to explore the fiber–matrix interface in the NFRUP and EGMRUP composites. The SEM micro￾graphs of the composites are displayed in Figures 1(a-d) and 2(a-d). Figure 1(a,b) shows the micrographs of the longitudinal fiber aspects for the NFRUP composite. These micrographs illustrate that the fibers were randomly dispersed in the matrix and that the individual separation of the fibers were not in the form of single fibers. Figure 1(c,d) shows the micrographs of the longitudinal fiber aspects for the EGMRUP composite. This figure shows that the glass fibers were identical and were in the form of single fibers because they were synthetic. The analysis of Figure 1(b,d) illustrated some physical contacts between the fibers and the matrix. Figure 2(a–d) depicts the micrographs of WWW.MATERIALSVIEWS.COM WILEYONLINELIBRARY.COM/APP J. APPL. POLYM. SCI. 2013, DOI: 10.1002/APP.38499 489 ARTICLE