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Crystallization and component properties of polyamide 12 at processing-relevant cooling conditions.

INTRODUCTION

For most conventional manufacturing technologies (e.g.. injection molding and extrusion), the material's cooling condition is the result of a variety of process parameters (e.g., mold temperature, chill roll temperature, material's melt temperature, component geometry, etc.). Regarding conventional injection molding, recent studies state cooling rates of about 1,000 K/s near the surface compared to significantly lower cooling rates of about 1 K/s in the core area, especially for thick-walled parts [1, 2], To assess resulting component properties qualitatively, the influence of different cooling rates on the formation of inner structures needs to be taken into account since the crystalline structures are the major influencing factor for the resulting global component properties.

The structure of semicrystalline thermoplastics comprises crystalline and amorphous fractions which typically arrange to spherulitic superstructures during the crystallization process at quiescent conditions [3], Besides pressure and shear, the temperature-time behavior of a semicrystalline thermoplastic during cooling is one major influencing factor of the formation of crystalline structures (e.g., spherulite size, degree of crystallization, and crystal modification), as the crystallization process with its nucleation and crystal growth phases takes place during cooling (4. 5], At low cooling rates, a distinct coarse spherulitic morphology develops. As a consequence of increased thermal nucleation and hindered crystal growth due to a higher number of nuclei, higher cooling rates result in a morphology which optically appears as a supposedly amorphous structure with high transparency [4-6]. Many researches have investigated the influence of the cooling rate on the resulting degree of crystallization (amount of the crystalline fraction) and isothermal as well as nonisothermal crystallization effects for semicrystalline thermoplastics [6-11]. Here, an increased cooling rate can lead to a decrease of the resulting degree of crystallization and, when exceeding a critical cooling rate, the melt can solidify amorphously. Furthermore, the great majority of semicrystalline thermoplastics can crystallize in different crystal modifications [9, 12-16] depending on. among other things, the cooling rate. Regarding PA 12, four crystal modifications (polymorphs) are reported in the literature and are denoted as [alpha], [alpha]', [gamma], and [gamma]'. As an even polyamide with more than seven carbon atoms. PA 12 crystallizes primarily in [gamma]-form at atmospheric pressure during moderate cooling conditions from the melt [17]. For quenching of PA 12, Hiramatsu et al. [18] (and for quenching followed by isothermal annealing at 60[degrees]C Li et al. |19]) reported the formation of primarily the [gamma]'-form. Both crystal modifications, [gamma] and [gamma]', have a hexagonal structure with only one main reflection regarding the WAXD patterns and, therefore, are difficult to distinguish from each other. The x-form can be obtained by crystallization from the melt at high pressures (>500 MPa), by drawing close to the melting point [18-21] as well as crystallization from solutions [22]. Furthermore. Ramesh [14] reported the crystal modification [alpha]' that can be observed for crystallization at high temperatures.

Regarding the influence of crystalline structures on resulting global component properties, it has to be considered that in most cases effects cannot be reduced to a single crystalline property since changing one crystalline property normally leads to a change of other crystalline properties as well. Keeping this in mind, researches could show that an increase of the degree of crystallization increases both stiffness and strength and decreases elongation at break [23]. Furthermore, a distinct fine spherulitic morphology can show higher strength and elongation al break than a coarse distinct spherulitic morphology [4, 24]. Regarding different crystal modifications, for example, for PA 6, Kolesov et al. [15] estimated the differences in storage modulus in chain direction from 300--310 to 50-140 GPa for [alpha] and [gamma], respectively.

EXPERIMENTAL

Material and Test Specimens

For this research, a commercial PA 12 grade (Grilamid L20G), supplied by EMS-GRIVORY, was used. Tensile bars for tensile tests were prepared from an extruded foil with the highest length of the tensile bars oriented in the direction of extrusion. Here, the geometry was derived from the Campus tensile bar according to DIN EN ISO 527-2B with a scaling of 1:4. For the dynamic-mechanical analyses, rectangular samples with a width of 1 mm and a length of 8 mm were prepared out of the extruded foil in the same way described before.

Fast Scanning Calorimetry (FSC)

The FSC measurements were carried out using a Flash DSC I of Mettler-Toledo. The test sample was prepared out of a 10 pm thin-cut using a scalpel and a microscope and placed on the sensor area of the FSC instrument. In this study, different cooling rates as well as idealized and measured temperature-time profiles were investigated by FSC.

To evaluate the crystallization behavior during cooling, different cooling rates in the range of 5-2,000 K/s are analyzed. Here, the sample was first heated up to 265[degrees]C with a heating rate of 1,000 K/s and then held isothermally for 1 s. For the different measurements, the sample was cooled down to 10[degrees]C with the respective cooling rate. Afterward, the sample was heated up in a second heating step with a heating rate of 1,000 K/s.

Next to the effect of cooling rate, an idealized temperature-time profile during cooling, derived from the conventional manufacturing cooling step, was analyzed, compare Fig. 1. Starting from melt temperature Tm the sample was cooled with a constant cooling rate [greater than or equal to] 1,000 K/s to 60[degrees]C, respectively, I35[degrees]C. These temperatures represent the high mold temperature at the dynamic tempered injection molding process, respectively, the chill roll temperature at extrusion. Afterward, the temperature was kept constant for a defined isothermal holding time in the range of 0.0 and 180.7 s and then cooled with a constant cooling rate of 30 K/s (according to maximum achievable cooling rates of modern dynamic tempered injection molds [25, 26|) to 10[degrees]C. The analyzed temperature-time profiles are shown in Table 1. Again, a second heating with 1,000 K/s was conducted afterward.

Next to the idealized temperature-time profiles, measured temperature-time profiles were investigated. Here, the temperature-time behavior, measured during the foil extrusion (Fig. 2), was evaluated.

Processing

PA 12 foils were fabricated by flat film extrusion using chillroll casting using a single screw extruder, Collin E30M, with a 30 mm screw diameter and length/thickness-ratio of 25 and a coathanger die of 250 mm width in combination with a chill-roll, Collin CR136/350. The die temperature was set to 250[degrees]C. Foils have been produced at chill role temperatures of 60[degrees]C as well as 130[degrees]C to primarily generate [gamma]' or [gamma] forms, respectively. The isothermal holding time was set to 20 s (longest isothermal holding time possible for the used extruder) for the foil produced at 60[degrees]C and 10 s for the foil produced at 135[degrees]C chill roll temperature, since there should be an alignment of the resulting degrees of crystallization for the different crystal forms. The foil thickness was set to approximately 80 pm. During the manufacturing process, the foil temperatures were measured at all relevant positions during the production line with an IR-camera considering the respective emission coefficients. The aim was to obtain the temperature-time profile during the manufacturing process in order to transfer the values into the FSC experimental plan. These derived temperature-time profiles are shown in Fig. 2.

Investigation Methods

Morphology. The cross section's morphology of the extruded foils was investigated by linearly polarized light microscopy with an Axio Imager.M2 by Zeiss at 10-pm thin cuts at 45[degrees]. The cuts were taken from the middle of the foil along the direction of extrusion.

Degree of Crystallization. The degree of crystallization has been determined by WAXS measurements with a Seifert ID 3000 X-ray diffractometer using a voltage of 40 kV and a current of 30 mA. The radiation was realized with nickel-filtered Cu K[alpha] with 1.54 [Angstrom]. For evaluating the degree of crystallization, an angle from 10[degrees] to 40[degrees] has been chosen. Furthermore, the measurements were repeated 2 times.

Mechanical Parameters. To determine the storage modulus, dynamic-mechanical analyses (DMA) according to ISO 6721-4 have been carried out using a RSA-G2 by TA Instruments. For the tensile tests, a 5948 MicroTester by Instron was used. The tensile tests have been performed according to DIN EN ISO 527-1 and -3 at 23[degrees]C and 50% humidity. As parameters, the secant modulus and the tensile strength were determined. For both investigation methods (DMA and tensile tests), the samples have been conditioned at 23[degrees]C and 50% humidity. The samples were not tested in the dry state in order to avoid an influence on the inner component structures caused by the relatively high drying temperature (70[degrees]C). The measurements were repeated a minimum of 5 times. The tensile direction was chosen perpendicular to the extrusion direction.

Tribological Parameters. The wear coefficient [k.sub.r] was determined using the pin-on-disc test (schematic setup, see Fig. 3). As test specimen, a square-shaped section (4 mm X 4 mm) is prepared out of the foil and attached to a sample carrier. This so called pin is pressed against a rotating steel disc with a defined Rz value of 3.0 [micro]m. The rotational speed, respectively, the sliding speed v, between the interface and the pin is set to 0.5 m/s and the pressure p is set to 4 N/[mm.sup.2]. The ambient temperature T is held constant at 23[degrees]C. The tribological contact is technically dry. Measurements were performed at specimens that have been conditioned at 23[degrees]C and 50% humidity. The wear coefficient has been determined in the quasi-stationary phase at a depth of approximately 10-40 [micro]m. Furthermore, for the evaluation of the wear coefficient, the measurements have been repeated 3 limes with different samples.

RESULTS AND DISCUSSION

FSC--Crystallization at Different Cooling Rates

Figure 4 shows the measured heat flows during cooling and second heating for the examined cooling rates of 2,000 to 100 K/s. Regarding the results for 2,000 K/s, no significant exothermal peak can be measured during cooling indicating that the melt has presumably solidified primarily in the glassy state. For the second heating, a strong exothermal cold crystallization peak in the range between 50 and 90[degrees]C is measured that shows the crystallization process of amorphously solidified phases during heating. Generally, regarding the results for cooling, with decreasing cooling rate an exothermal peak does increasingly develop increasing and shifting toward higher temperatures while the cold crystallization enthalpy during second heating decreases. For the cooling rates of less than 200 K/s, no clear cold crystallization can be measured. Regarding the temperature range between 90 and 120[degrees]C at second heating, a weak exothermal peak is measured for all depicted cooling rates. At higher temperature an endothermal phase change takes place in the temperature interval 120-170[degrees]C. Here, no significant differences in enthalpy can be measured. It is known from the literature that PA 12 crystallizes in [gamma]'-form when quenched from melt [17]. Therefore, it is assumed that with decreasing cooling rate the fraction of amorphously solidified phases decreases and the share of the [gamma]'-form fraction increases. The behavior becomes apparent in the increasing exothermal peak during cooling in the temperature range from 30 to 70[degrees]C and the decreasing exothermal cold crystallization peak during second heating. Since there is no significant cold crystallization peak at second heating for cooling rates less than 200 K/s, it is assumed that the majority of polymer chain segments could crystallize during cooling in [gamma]'-form. Regarding the weak exothermal peak between 90 and 120[degrees]C at second heating, a recrystallization of the [gamma]'-form in the more stable [gamma]'-form is assumed to take place. Therefore, since for all measurements the y-form is built during heating at the same heating rate (1,000 K/s), no differences in the melting enthalpy are measured.

In Fig. 5, the results for the cooling rates 100 to 50 K/s are shown. Regarding the heat flows measured during cooling, with decreasing cooling rate the occurrence of a second peak at higher temperatures and, therefore, before the assumed [gamma]'-form is being built, can be measured. It can be assumed that this exothermal peak represents the [gamma]-form. With decreasing cooling rate, the enthalpy of the [gamma]-form increases while the enthalpy of the [gamma]'-form decreases. Furthermore, a shift of the respective peak temperature toward higher temperatures can be detected with decreasing cooling rate. For the second heating, it can be seen that the weak exothermal peak that represents the assumed [gamma]' to [gamma] transformation during heating decreases with decreasing cooling rate in the previous cooling step. This also may indicate that the fraction of the [gamma]'-form is lower for the lower cooling rates since the polymer chains have already crystallized in the [gamma]-form. Again, no change in the melting enthalpy in the range between 120 and 170[degrees]C can be measured.

Figure 6 shows the measured heat flows for the examined cooling rates from 50 to 5 K/s during cooling and second heating. Regarding the measured heat flows during cooling, no significant second peak at lower temperatures ([gamma]'-form) is measured for cooling rates below 40 K/s. Furthermore, the measured peak temperatures (assumed [gamma]-form) shift toward higher temperatures with decreasing cooling rate. For the second heating, an increase of the melting enthalpy can be detected for a reduced cooling rate in the previous cooling step. This may indicate that the crystal segments that were crystallized in y-form can order more perfectly.

At least. Fig. 7 sums up the measured crystallization peak temperatures during cooling with respect to the investigated cooling rates.

FSC--Crystallization at Idealized Temperature-Time Profiles

In addition to the investigated crystallization effects of PA 12 at different cooling rates, the idealized cooling conditions, derived from a conventional manufacturing process (Fig. 1), were analyzed. The results of the second heating are shown in Fig. 8. For the measurements with an isothermal holding step at 60[degrees]C, two endothermal peaks can be detected. While an increased isothermal holding time leads to a higher enthalpy of the peak at lower temperatures (peak 1) and the measured peak temperatures are shifting toward higher temperatures, the peaks at higher temperature (peak 2) show no influence for different isothermal holding conditions during the prior cooling step. It is known from the literature that, if quenched and then annealed at a temperature range of 60[degrees]C, PA 12 crystallizes in [gamma]'-form. Therefore, it is assumed that peak 1 shows the melting of the crystallized [gamma]'-form. Here, a longer isothermal holding time causes an increase of the degree of crystallization since the enthalpy is increasing with increasing isothermal holding time. It is assumed that peak 2 shows the melting of the [gamma]-form which has been built during recrystallization of [gamma]'-form during heating with 1.000 K/s. This recrystallization is measured between 90 and 120[degrees]C. As a consequence, it is assumed that a fast cooling to 60[degrees]C and a following isothermal holding step mainly leads to the formation of the [gamma]'-form. Nevertheless, to prove this hypothesis this matter requires further investigation involving varying heating rates.

For the measurements with an isothermal holding step at 135[degrees]C, two endothermal peaks are measured whereas (except for 5.7 s) only one of both peaks is being formed out depending on the isothermal holding time. For isothermal holding times of less than 5.7 s, the resulting peak is located at lower temperatures (peak 1). For isothermal holding times larger than 5.7 s, the peak (peak 2) is located at higher temperatures. Since peak 1 is identical with the melting peak (regarding the second heating) of a PA 12 sample cooled with 30 K/s, it is assumed that peak 1 represents the melting of crystalline fractions which were built during cooling with 30 K/s and. therefore, not within the isothermal holding time. Consequently, at 135[degrees]C, an isothermal holding time of up to 2.7 s is not sufficient for significant isothermal crystallization. Peak 2 is assumed to show the melting of crystalline fractions that were built primarily during isothermal holding time. Therefore, an isothermal holding time larger than 5.7 s leads to isothermal crystallization. At 5.7 s, the crystalline fractions appear to have been built during isothermal conditions as well as cooling conditions, since two overlaid peaks are measured. In contrast to the isothermal holding step at 60[degrees]C, for 135[degrees]C it is assumed that the main crystal form is the [gamma]-form.

FSC--Crystallization at Measured Temperature-Time Profiles

To evaluate, whether the extruded foils have passed the appropriate cooling conditions to form out primarily [gamma]-form, respectively, [gamma]'-form, the temperature-time profiles measured during the manufacturing process (compare Fig. 2) have been analyzed by FSC. Figure 9 shows the measured heat flows during second heating for the temperature-time profiles of the foils produced with an isothermal holding step at 60 and 130[degrees]C. Regarding the foils produced at 60[degrees]C, two endothermal melting peaks can be detected whereas the peak at lower temperature again is assumed to be built isothermally and the peak at higher temperature is occurring due to reorganization effects (compare idealized results from the idealized temperature-time profiles). Comparing the enthalpies of the [gamma]'- and the [gamma]-form, the latter shows a significantly higher value what may indicate a higher degree of crystallization.

Foil Characterization--Morphology

Figure 10 shows the morphologies across the extruded foil's cross section. For the foil produced at 60[degrees]C, a fine distinct crystalline structure can be detected over the entire cross section, whereas the morphology of the parts produced al 130[degrees]C shows coarse structures. Furthermore, at 130[degrees]C the surface which is in direct contact with the chill roll shows transcrystalline structures (grown crystalline structures that can develop if the polymer melt gets in direct contact with the mold at quiescent conditions due to the high amount of nuclei at the mold). The differences in the developed morphology regarding the structure size can be explained with differences in the amounts of thermally induced nuclei. Here, a high supercooling of the melt at 60[degrees]C causes high thermal nucleation during cooling which results in the finer structures. Furthermore, for example for PA 6 it is known that nodular structures form out at higher cooling rates [15] instead of sphcrulitic structures which may also be a reason for the apparently finer crystalline structure for PA 12. Nevertheless, for PA 12 this needs to be analyzed in further examinations by correlating morphologies al different cooling rates with their morphological appearance by AFM analysis. The small differences in morphology across the cross section can be explained by the small foil thickness of less than 100 pm. Here, it can be estimated that the cooling conditions are nearly the same over the entire cross section what also is proven by prior calculations for the estimation of the cross section cooling.

Foil Characterization--Degree of Crystallization

Figure 11 shows the X-ray patterns of the WAXD measurements that were performed to evaluate the degree of crystallization for the foils produced at 60 and 130[degrees]C. Regarding the calculated degree of crystallization, foils produced at 60[degrees]C reach a degree of crystallization of 45.2 [+ or -] 1.8% while foils produced at 130[degrees]C reach 46.9 [+ or -] 1.4%. Therefore, no significant differences in the resulting degree of crystallization are measured for the different foils. Since there are no clear differences in the measured X-ray patterns and only one main deflection is measured, it is assumed that only the [gamma]- and the [gamma]'-form, respectively, have formed. Since it is known from the literature [18] that these two crystal modifications cannot be clearly distinguished by WAXD measurements no further conclusions next to the degree of crystallization can be made at this point.

Foil Characterization--Mechanical Properties

Figure 12 shows a stress-strain diagram of an exemplary tensile test for each foil produced for different isothermal holding temperatures. The measured secant modulus and tensile strengths for the different isothermal holding temperatures are shown in Fig. 13. For both parameters, a clear increase can be measured for foils produced at higher temperature. Therefore, regarding the average values of the secant modulus and tensile strength an increase of 29%, respectively 18%, was measured. The increase in secant modulus and tensile strength could be explained by an interaction of the more distinct morphology as well as the different polymorphs.

The measured storage modulus with respect to increasing testing temperature is shown in Fig. 14. For all testing temperatures except for 170[degrees]C, foils produced at 60[degrees]C reach a lower storage module than foils produced at 130[degrees]C. Quantitatively, the storage modulus of foils produced at 130[degrees]C is approximately 45% higher than the one of foils produced at 60[degrees]C regarding temperatures lower than the glass transition temperature. For temperatures higher than the glass transition temperature, the difference equals about 70%. Only at 170[degrees]C both differently manufactured foils reach the same value since here, both foils start to melt. Again, a possible reason for the differences in the storage modulus is the different crystalline structures and, therefore, an interaction between the more distinct morphology and the different polymorphs.

Foil Characterization--Tribological Properties

In contrary to the clear effects regarding the mechanical properties, no clear influence regarding the wear coefficient are measured. Foils produced at 130[degrees]C (21.1 [+ or -] 2.5 X [10.sup.6] [mm.sup.3]/ Nm) show a trend toward less wear than foils produced at 60[degrees]C (23.4 [+ or -] 1.3 x [10.sup.-6] [mm.sup.3]/Nm). The lack of clear differences in the degree of crystallization might explain the minor effects in wear. Here, further researches in which the isothermal holding time is varied at different isothermal holding temperatures should be performed for a clear statement.

CONCLUSIONS

In this paper, the crystallization behavior of PA 12 during cooling has been investigated by varying the temperature-time behavior. Tests have been carried out analytically using the FSC and experimentally by manufacturing foils at two different isothermal holding temperatures via extrusion. Considering the examined cooling rates, results may indicate that two crystal modifications develop which are assumed to be the [gamma]'- and the [gamma]-form, respectively. Therefore, with decreasing the cooling rate from 2,000 to 100 K/s, the amount of amorphously solidified chain segments decreases and the amount of the [gamma]'-form increases. With further decreasing the cooling rate the amount of [gamma]'-form decreases and the main crystal modification, which is described to be the [gamma]-form, increases. Regarding the heat flow during cooling, at cooling rates less than 40 K/s, no significant formation of the [gamma]'-form can be detected and, during second heating, the melting enthalpy increases. Results of the idealized temperature-time behavior, derived from the conventional manufacturing cooling step, indicate the building of [gamma]'-form at 60[degrees]C as well as the building of [gamma]-form at 135[degrees]C. Comparing the results of these idealized measurements with the results of the measured temperature-time profiles of the extruded foils, the building of both crystal modifications is estimated. For the resulting crystalline structures of the produced foils, differences in the resulting morphology were shown. Here, due to the high supercooling of the melt and, therefore, a high thermal nucleation, at an isothermal holding temperature of 60[degrees]C the crystalline superstructures appear more finely distinct in comparison to the foils produced at 130[degrees]C. Furthermore, the degree of crystallization of foils produced at 60[degrees]C seems to equal the degree of crystallization for foils produced at 130[degrees]C. Due to the differences in crystalline structures, differences in the mechanical parameters are measured. Here, the foil produced at 60[degrees]C reaches less storage modulus, tensile strength as well as segment modulus than the foil produced at 130[degrees]C. Nevertheless, the differences in the resulting wear coefficient only show a trend toward less wear for the foil produced at higher temperature. Here, it is assumed that the small differences in degree of crystallization could explain the small differences regarding the wear.

Further researches should extend the experimental setup by producing foils at different isothermal holding temperatures for a closer examination of the resulting inner and global component properties. The FSC measurements should be performed by varying the sample mass to verify the quantitative results as well as by varying heating rate. Furthermore, next to PA 12, other semicrystalline materials should be investigated. Finally, it is the aim to transfer the gained knowledge to the injection molding process by considering further influences on the crystallization such as pressure and shear. Here, the possibility to investigate the first heating of an injection molded sample section with the FSC could give an indication of local cooling conditions during the injection molding process and should be investigated.

ACKNOWLEDGMENTS

The authors thank the German Research Foundation (DFG) for funding this work within the project JU 2944/1-1 "Mikrostrukturierte Formteile auf Basis thermoplastischer Folien." The authors are also grateful to the company EMSChemie HOLDING AG for providing the material as well as the department of Polymer Engineering at the University of Bayreuth for performing the WAXD measurements.

REFERENCES

[1.] P.K. Kennedy and R. Zheng, Flow Analysis of Injection Molds, Carl Hanser Verlag, Munich (2013).

[2.] A.M. Rhoades, J.L. Williams, and R. Androsch, Thermochim. Acta, 603, 85 (2015).

[3.] G. Menges, E. Haberstroh, W. Michaeli, and E. Schmachtenberg, Werkstoffkunde Kunststoffe, Carl Hanser Verlag, Munich (2011).

[4.] G. W. Ehrenstein, Polymer-Werkstoffe: Struktur-Eigenschaften-Anwendungen, Carl Hanser Verlag, Munich (2011).

[5.] E. Piorkowska and G.C. Rutledge, Handbook of Polymer Crystallization. Wiley, New Jersey, NY (2013).

[6.] A. Jungmeier, G.W. Ehrenstein, and D. Drummer, Plast. Rubber Compos., 39, 308 (2010).

[7.] A. Jungmeier, I. Kuhnert, G. W. Ehrenstein and T. A. Osswald, "Process-Induced Properties of Micro Injection Molded Parts--New Aspects." in SPE Proceedings ANTEC, Chicago, USA, 1328 (2009).

[8.] B. G. Millar, P. Douglas, W. R. Murphy and G. M. Mc Nally, "The Effect of Cooling Regime on the Thermal, Mechanical and Morphological Properties of Polyolefins," in SPE Proceedings ANTEC, Boston, USA, 2258 (2005).

[9.] I. Kolesov, D. Mileva, R. Androsch, and C. Schick, Polymer, 52, 1107 (2011).

[10.] A. Toda, R. Androsch, and C. Schick, Polymer, 91, 239 (2016).

[11.] A. Mollova, R. Androsch, D. Mileva, C. Schick, and A. Benhamida, Macromolecules, 46, 828 (2013).

[12.] M. Drongelen, T. Meijer-Vissers, D. Cavallo, G. Portale, G.V. Poel, and R. Androsch, Thermochim. Acta. 563, 33 (2013).

[13.] M. Ito, K. Mizuochi, and T. Kanamoto, Polymer, 39, 4593 (1998).

[14.] C. Ramesh, Macromolecules, 32, 3721 (1999).

[15.] I. Kolesov, D. Mileva, and R. Androsch, Polym. Bull., 71, 581 (2014).

[16.] J.E.K. Schawe, Thermochim. Acta, 603, 128 (2015).

[17.] M.I. Kohan, Nylon Plastics Handbook, Carl Hanser Verlag, Munich (1995).

[18.] N. Hiramatsu, K. Haraguchi, and S. Hirakawa, Jpn. J. Appl. Phys., 22, 335 (1983).

[19.] L. Li, M.H.J. Koch, and W.H. Jeu, Macromolecules, 36, 529 (2003).

[20.] S. M. Aharoni, n-Nylons: Their Synthesis. Structure and Properties. John Wiley & Sons Ltd., West Sussex, England (1997).

[21.] T. Ishikawa, S. Nagai, and N. Kasai, Die Makromol. Chem., 182, 977 (1981).

[22.] T. Ishikawa, S. Nagai, and N. Kasai, J. Polym. Sci.: Polym. Phys. Ed.. 18, 291 (1980).

[23.] F.R. Schwarzl, Polymermechanik: Struktur unci mechanisches Verhalten von Polymeren, Springer-Verlag, Berlin (1990).

[24.] R. Kunkel, "Auswahl und Optimierung von Kunststoffen fur tribologisch beanspruchte Systeme," Dissertation, Friedrich-Alexander-University Erlangen-Nuremberg (2005).

[25.] C. Fischer and D. Drummer, Adv. Mech. Eng., 2014, 10 (2014).

[26.] C. Fischer and D. Drummer, J. Plast. Technol., 11, 43 (2015).

Christopher Fischer, Andreas Seefried, Dietmar Drummer

Institute of Polymer Technology, Erlangen, Germany

Correspondence to: C. Fischer; e-mail: fischerc@lkt.uni-erlangen.de

DOI 10.1002/pen.24441

Published online in Wiley Online Library (wilcyonlinelibrary.com).

Caption: FIG. 1. Schematical lime-temperature behavior for analyzing the crystallization process for an idealized temperature-time behavior during cooling derived from the conventional manufacturing cooling step.

Caption: FIG. 2. Measured temperature-time profile for the extruded foils measured with an IR-camera and analyzed by FSC.

Caption: FIG. 3. Schematic setup of the pin-on-disc test (FR = friction force).

Caption: FIG. 4. Heal flow measured during cooling (left) and second healing (right) of PA 12 with respect to the examined cooling rates of 100-2.000 K/s.

Caption: FIG. 5. Heat How measured during cooling (left) and second heating (right) of PA 12 with respect to the examined cooling rates of 50-100 K/s.

Caption: FIG. 6. Heat How measured during cooling (left) and second healing (right) of PA 12 with respect to the examined cooling rates of 5-50 K/s.

Caption: FIG. 7. Crystallization peak temperatures with respect to the examined cooling rates derived from FSC measurements (glass transition temperature derived from internal DSC measurements during heating at 10 K/min).

Caption: FIG. 8. Heat How measured during second heating of an idealized temperature-time behavior, isothermal holding step al 60[degrees]C (left) and 135[degrees]C (right).

Caption: FIG. 9. Measured heat Hows during second healing for the measured temperature-lime profiles of the extruded foils.

Caption: FIG. 10. Morphology over the cross section of extruded foils manufactured al 60[degrees]C (isothermal holding time = 20 s) and 130[degrees]C (isothermal holding time = 10 s).

Caption: FIG. 11. Exemplary X-ray patterns of the manufactured foils produced al 60[degrees]C (isothermal holding time = 20 s) and 130[degrees]C (isothermal holding time = 10 s).

Caption: FIG. 12. Stress-strain diagram of an exemplary tensile test for a foil produced at 60[degrees]C (isothermal holding time = 20 s) and 130[degrees]C (isothermal holding time = 10 s).

Caption: FIG. 13. Secant modulus and tensile strength for the foils produced at 60[degrees]C (isothermal holding time = 20 s) and 130[degrees]C (isothermal holding time = 10 s).

Caption: FIG. 14. Storage modulus with respect to temperature for the foils produced at 60[degrees]C (isothermal holding time = 20 s) and 130[degrees]C (isothermal holding time = 10 s).
TABLE 1. Temperature-time profiles analyzed by FSC.

                                                Isothermal
  Melting           Cooling                      holding
temperature         velocity                   temperature
 [T.sub.m]     [v.sub.cooling.1]                [T.sub.h]
([degrees]C)         (K/s)                     ([degrees]C)

265                  2,050                          60
                     1,300                         135

  Melting
temperature                   Isothermal holding time
 [T.sub.m]                          [t.sub.h](s)
([degrees]C)

265                  0.0 0.7 1.7 5.7 10.7 20.7 40.7 70.7 180.7

  Melting
temperature     Cooling velocity    End temperature
 [T.sub.m]     [v.sub.vooling. 2]     [T.sub.end]
([degrees]C)         (K/s)           ([degrees]C)

265                    30                 10
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Author:Fischer, Christopher; Seefried, Andreas; Drummer, Dietmar
Publication:Polymer Engineering and Science
Article Type:Report
Date:Apr 1, 2017
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