Introduction

MC nylon 6 is a widely used semi-crystalline engineering plastic for many industrial applications due to its low polymerization temperature, simple preparation process, high molecular weight, high mechanical strength, and excellent self-lubrication performance. However, it suffers from inferior properties, such as high water absorption due to strong polarity, poor toughness at low temperature, poor dimensional stability, and inferior heat resistance, when used as a high-temperature engineering plastic [1]. The main approaches to overcome these problems are to modify MC nylon 6by filling, reinforcing, copolymerization, blending, compounding, and other methods [2, 3]. In this context, some studies have been done on exploring the properties of blends comprising MC nylon 6 prepared through in-situ dispersion polymerization. Zhang et al. performed a comprehensive study on the influence of different pretreatment methods and the addition amount of cellulose nanocrystalline (CNC) on the properties of MC nylon 6 in-situ composites. They concluded that with the increase of the amount of CNC, the crystallinity showed an upward trend, with higher crystallization temperature and narrower half peak width. The tensile strength, flexural strength and flexural elastic modulus of MCPA6/CNC in-situ composite were higher than those of pure MCPA6, respectively [1]. Yang et al. studied the structure, thermal properties, mechanical properties and morphologies of the composites, and they concluded that the thermal properties of MC nylon 6 components in the composites were similar to those of commercial nylon 6, and the CF was uniformly distributed in the matrix and fully impregnated by MC nylon 6 [4]. Taki and coworkers investigated the effect of thermal annealing on the crystallinity and mechanical properties of PA6, textile glass fiber-reinforced PA6 (GF-PA6), and carbon fiber-reinforced PA6 (CF-PA6) (40% by vol). They showed that the crystallinity, tensile modulus, and strength of PA6 were improved by thermal annealing. The crystallinity of GF-PA6 was not improved, but the tensile modulus and strength were slightly improved. The crystallinity of CF-PA6 decreased, but the tensile modulus and strength improved [5].

Poly(phthalazinone ether sulfone) (PPES) containing phthalazinone structure as a variety of engineering thermoplastic polymers has been extensively applied in electronics, biomedical and automotive fields due to its excellent heat resistance (its glass transition temperature is up to 305℃), chemical corrosion resistance, dielectric properties, and mechanical properties [6]. Therefore, it has a broad prospect in the application of high-performance resin matrix composites. Liu et al. prepared carbon fiber-reinforced poly(CF/PPEK) and carbon fiber-reinforced poly(CF/PPES) unidirectional composites using the pre-impregnated hot compression molding process. They studied the properties and changing law of the holding ratio of the strength and modulus of the high-performance thermoplastic composites under high temperature. They found that the retention of extension strength and bending strength and their modulus were above 60% below 250 °C, which had a super high loading capacity [7]. Zhang [8] studied the high and low temperature mechanics performance and interface of high-performance thermoplastic resin–PPEK, PPES and their composites. He showed that PPEK, PPES and their composites also had good bend performance under high and low temperatures, and the discrimination between them was minor. Zhang prepared PPES-b-MCPA6 block copolymer and used it as a compatibilizer for PPES/PA6 systems. He founded that in PPES/PA6 systems, when they joined the block copolymer, the dispersion of PPES phase in the matrix PA6 increased, and at the same time the cohesive force between the PPES and PA6 interface increased, as well as the mechanical properties could increase 18–22%. The thermal decomposition temperature was improved by addition of copolymerization [9].

In this context, several efforts will be made to improve the comprehensive performance of MC nylon 6 by inclusion of PPES, especially the inferior heat resistance of MC nylon 6. Therefore, a series of PPES/MC nylon 6 in-situ composites with different contents were first prepared by anionic in-situ polymerization.

A review of the literature shows that there are no reports on the crystallization behavior of PPES/MC nylon 6 in-situ composites. On the other hand, MC nylon 6 as a semi-crystalline polymer exhibits highly sensitive crystallization kinetic toward inclusion of additives. PPES may change the degree of crystallinity of MC nylon 6 as well, which may in turn affect its properties. Considering that non-isothermal crystallization is consistent with practical industrial processing techniques, such as extrusion and injection molding, the corresponding research has more practical significance than isothermal crystallization studies. The main purpose of this work is to evaluate the influence of PPES inclusion on the crystallization kinetic of MC nylon 6. Using Jeziorny and Mo models, the non-isothermal crystallization kinetics of the developed in-situ composite systems were explored. The crystallization activation energies were also calculated. It is suggested that the results can provide a theoretical foundation to direct the molding process and regulate the performance of PPES/MC nylon 6 in-situ composites.

Experimental

Materials

Industrial grade poly(phthalazinone ether sulfone) (PPES) was prepared from Jida High-tech Materials Co., Ltd. (China) and dried in a vacuum drying oven at 100 °C for 24 h before use. Polymerization grade caprolactam and sodium hydroxide (AR) were obtained from Yueyang Petrochemical Plant (China) and Shanghai No.3 Chemical Reagent Factory (China), respectively. 2,4-Toluene diisocyanate (2,4-TDI) (CP), reserved by vacuum distillation, was acquired from Shanghai No.3 Chemical Reagent Factory (China).

Sample preparation

Caprolactam monomer (250 g) was added into a glass test tube and heated up to 150℃ in an oil bath. After melting, sodium hydroxide was added as a catalyst and vacuumed under reduced pressure for 30 min to ensure as much water removal as possible. After stopping the vacuum pump, PPES particles were dispersed evenly in molten caprolactam by magnetic stirring after drying in vacuum, and then pumped into the vacuum so that the system would not bubble. The magnetic stirring was then stopped and the 2,4-toluene diisocyanate cocatalyst was added and stirred rapidly and uniformly. The temperature was kept constant at 150 °C for 60 min, and by removing the system it was cooled naturally to room temperature. Finally, PPES/MC nylon 6 in-situ composites were prepared by anion ring-opening polymerization. The samples of pure MC nylon 6 (S0) and PPES with the mass percentage of 2.0% (S1), 4.0% (S2), 6.0% (S3), and 8.0% (S4) were selected for the study. The schematic diagram of molecular structure and reaction process is shown in Fig. 1.

Fig. 1
figure 1

Schematic diagram of the molecular structure and reaction process

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Testing and characterization

The non-isothermal crystallization behavior and crystallization kinetics were studied with the assistance of a differential scanning calorimeter (TA-2910, USA). The samples with a mass of 3–4 mg were rapidly heated from the ambient temperature to 250 °C, and maintained at 250 °C for 5 min to remove the previous thermal history, under nitrogen atmosphere. Subsequently, all the samples were cooled down from the melting temperature to the ambient temperature at varying cooling rates (2.5, 5, 10, 15 and 20 °C/min), and the changes in enthalpy value of the samples with temperature during crystallization were measured. The DSC instrument was calibrated with indium at each cooling rate used herein.

The FTIR spectra were obtained using a Nicolet Company NexusTM IR spectrophotometer with KBr pellets with 32 scans.

The phase morphology of MC nylon 6 and PPES/MC nylon 6 in-situ composites was analyzed by a Hitachi S-3500N scanning electron microscope (SEM). For this purpose, the samples were fractured in liquid nitrogen, and the fractured sections were etched with chloroform, followed by a gold sputtering process.

Results and discussion

Fourier transform infrared spectroscopy (FTIR)

FTIR experiments were performed to detect the chemical structure of the PPES, MC nylon 6 and PPES/MC nylon 6 in-situ composites. As shown in Fig. 2a, the absorption at 3068.25 cm−1 in the PPES FTIR spectrum is due to the C–H stretching vibration of the benzene ring, the two distinctive absorption peaks at 1327.97 and 1310.47 cm−1 are related to the O=S=O asymmetric stretching vibration absorption (usually split into two peaks), the peak at 1151.53 cm−1 belongs to the symmetric stretching vibration of O=S=O, the peaks at 1240.28 and 1166.37 cm−1 are ascribed to the asymmetric and symmetric stretching vibrations of aryl ether, respectively, the peak at 1585.95 cm−1 is due to the C=C double bond stretching vibration of the benzene ring, and the peaks at 1201.90, 1086.93 and 1013.66 cm−1are attributed to the in-plane bending vibration of the benzene ring. The characteristic peaks in the PPES infrared spectrum show that they are consistent with the PPES molecular structure. As can be seen from Fig. 2b, compared with the infrared spectrum of MC nylon 6 (S0), there are characteristic peaks representing PPES molecular structure in PPES/MC nylon 6 in-situ composites, which are located at 1327.97, 1151.53, 1104.36, 1013.45, 973.99, 873.07 and 560.68 cm−1, respectively. With the increase of PPES content, the peak strength gradually increases. From the results of FTIR it indicates that PPES/MC nylon 6 in-situ composites have been successfully synthesized.

Fig. 2
figure 2

FTIR spectra of PPES, MC nylon 6 and PPES/MC nylon 6 in-situ composites: a overall view; and b partial enlarged figure

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Morphology of the PEES/MC nylon 6 composites

SEM analysis was used to investigate the phase morphology of PPES/MC nylon 6 in-situ composites. The effect of blending ratio on the blend morphology can be inferred from the comparison of Fig. 3, which reveals the blend morphology of PPES/MC nylon 6 in-situ composites. All samples exhibit refined and uniform biphasic morphology in which PPES particles are well dispersed, at micron levels, in the MC nylon 6 matrix. The good compatibility of these two polymers is due to the presence of a certain hydrogen bond interaction between PPES and molten caprolactam, which was analyzed in our previous study [10]. As expected, an increase in PPES content of the composite from 2 to 8% (by weight) increases the size of PPES particles due to coalescence phenomenon.

Fig. 3
figure 3

SEM photographs of PPES/MC nylon 6 in-situ composites etched by chloroform: a S1 × 2000; b S2 × 2000; c S3 × 2000; and d S4 × 2000

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Non-isothermal crystallization behavior

The DSC exotherms of MC nylon 6 and its in-situ composites obtained at different cooling rates are presented in Fig. 4, whereas the DSC data for all the studied samples are tabulated in Table 1. From the figure, generally it is seen that with increasing the cooling rate, the crystallization peaks shift toward lower temperatures and the peak shapes become wider due to the increased test speed, showing that when the cooling rate becomes slower, the molecular chains have enough time to arrange regularly and form more perfect and uniform crystals [11,12,13]. The in-situ blending of PEES with MC nylon6 and increasing the PPES content of the composites result in an increase of the Tini (initial crystallization temperature) and a small reduction of the Tc (crystallization peak temperature) of the MC nylon 6. This is mainly due to the fact that the presence of PPES particles being at solid state at the crystallization temperature of MC nylon 6, can act as a nucleating agent at the beginning of crystallization of MC nylon 6. In addition, there are present a certain hydrogen bond interaction between PPES and molten MC nylon 6, analyzed in our previous study [10], which can hamper the mobility of the MC nylon 6 chains. With increasing PPES content, large numbers, small size imperfect crystals were formed. This finding is consistent with that of Alvaredo et al., who characterized the effect of graphene nanosheets content on the melt crystallization of PEEK composites using differential scanning calorimetry. The DSC data revealed a dual action of graphene: one was that the nucleation effect caused crystallization to start at a higher temperature; the other was that the reduction of the mobility of the polymer segments made the overall crystallization time longer [14].

Fig. 4
figure 4

DSC cooling curves at different cooling rates: a S0; b S1; c S2; d S3; and e S4

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Table 1 Non-isothermal crystallization parameters of MC nylon 6 and PPES/MC nylon 6 in-situ composites at different cooling rates
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The degree of crystallinity (Xc) of the composites can be obtained from Eq. 1:

$$ X_{c} = \left\{ {\Delta H_{c} /\left[ {(1 - \varphi )\Delta H_{{\text{m}}}^{0} } \right]} \right\} \times 100\% , $$
(1)

where \(\Delta H_{{\text{c}}}\) is the crystallization heat of the sample, \(\Delta H_{{\text{m}}}^{0}\) is the melting enthalpy of complete crystallization of MC nylon 6 (230 J/g [15]) and φ is the mass percentage of PPES.

From Table 1, it is also seen that the Xc values for most of the studied samples decrease slightly with an increase in the cooling rate. While the increases in the PPES content increase the Xc value of MC nylon 6 slightly. ΔW values (half height–weight of crystallization peak) increase with an increase in the cooling rate, while they first decrease and then increase with the increase in PPES content.

Several important parameters can be extracted from the DSC thermograms to further shed light on the crystallization kinetics of the developed systems. One of these parameters is the relative degree of crystallinity at a certain temperature denoted as X(T). This parameter is obtained based on the following equation:

$$ X(T) = \frac{{\int_{{T_{0} }}^{T} {\frac{{{\text{d}}H_{{\text{c}}} (T)}}{dT}{\text{d}}t} }}{{\int_{{T_{0} }}^{{T_{{\text{f}}} }} {\frac{{{\text{d}}H_{{\text{c}}} (T)}}{{{\text{d}}T}}{\text{d}}T} }} = \frac{{A_{{\text{T}}} }}{{A_{{tot{\text{al}}}} }}, $$
(2)

where T0 and Tf are the initial and final temperatures of the crystallization process, respectively, obtained from the DSC crystallization peaks. Based on Eq. 2 and using experimental data, the variations of the relative crystallinity (X(T)) against temperature for the neat MC nylon 6 and PPES/MC nylon6 in-situ composites at different cooling rates were calculated, and the results are depicted in Fig. 5, respectively:

$$ t = \left( {T_{0} - T} \right)/\phi . $$
(3)
Fig. 5
figure 5

Relative degree of crystallinity (X(T)) versus temperature at different cooling rates: a S0, b S1, c S2, d S3, and e S4

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Based on Eq. 3, the crystallization temperature can switch to the crystallization time [16]. Where ϕ and T0 are the cooling rate and the initial temperature of the crystallization process, respectively. T is the instant temperature at time t within the crystallization zone.

By combining Eqs. 2 and 3, one can calculate the relative degree of crystallinity at any given time, that is, X(t) can be obtained from Eq. 4 [17]. Accordingly, the variations of X(t) against time for a neat MC nylon 6 and PPES/MC nylon 6 in-situ composites at different cooling rates were calculated and the results are depicted in Fig. 6. Based on the results presented in Figs. 5 and 6, using different existing models, detailed crystallization kinetic analyses were performed, and the results are presented in the subsequent sections:

$$ X(t) = \frac{{X_{{\text{c}}} (t)}}{{X_{{\text{c}}} (t = \infty )}} = \frac{{\int_{0}^{t} {\frac{{{\text{d}}H_{{\text{c}}} (t)}}{{{\text{d}}(t)}}{\text{d}}t} }}{{\int_{0}^{t = \infty } {\frac{{{\text{d}}H_{{\text{c}}} (t)}}{{{\text{d}}t}}{\text{d}}t} }} = 1 - \exp \left( { - Zt^{n} } \right). $$
(4)
Fig. 6
figure 6

Relative degree of crystallinity (X(t)) versus time at different cooling rates: a S0, b S1, c S2, d S3, and e S4

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Non-isothermal crystallization kinetics

Many works have reported on the study of non-isothermal crystallization kinetics of polymer systems by DSC method [18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33]. Starting from the Avrami equation for treating isothermal crystallization and considering the characteristics of non-isothermal crystallization, some methods for treating non-isothermal crystallization kinetics have been obtained by modifying the Avrami equation. In this paper, Jeziorny model [19] and Mo model [20, 21, 34, 35] were used to analyze, independently.

Jeziorny model

Crystallization kinetics is often investigated and analyzed by Avrami model according to the following equations [36, 37]:

$$ 1 - X(t) = \exp \left( { - Zt^{n} } \right) $$
(5)
$$ \log \left[ { - \ln (\left( {1 - X(t)} \right)} \right] = \log Z + n\log (t). $$
(6)

The values of the Avrami exponent (n) and the rate parameter (Z) can be determined from the slope and intercept of the plot of log[− ln(1 − X(t))] versus log(t). The Avrami exponent indicates the mechanism of nucleation and crystal growth dimensions, whereas Z determines the crystallization rate. In a non-isothermal condition, these parameters have different physical concepts, because temperatures are constantly changing. Considering the effect of cooling rate, the crystallization rate constant (Z) can be modified by the following equation [19, 38]:

$$ \log Z_{{\text{c}}} = \left( {\log Z} \right)/\phi . $$
(7)

In Eq. 7, Zc is the modified crystallization rate constant, and the semi-crystallization time, \(t_{1/2} = (\ln 2/Z_{{\text{c}}} )^{1/n}\), is further calculated [39]. The larger the value t1/2 is, the slower the crystallization rate is.

The modified Avrami equation (Jeziorny model) can be applied to experimental data to obtain the corresponding crystallization kinetic parameters. The results of Jeziorny model for MC nylon 6 and PPES/MC nylon 6 in-situ composites are presented in Fig. 7. As seen, the crystallization behavior exhibits two regimes of primary and secondary crystallizations. In the primary crystallization, it has a good linear relationship between log[− ln(1 − X(t))] and log(t) (its linear fitting results are shown in Fig. 8). While in the secondary crystallization, the free growth of crystals is restricted due to the collision between the crystals, which makes the curve deviate obviously [40]. The obtained model parameters are presented in Table 2.

Fig. 7
figure 7

Plots of log[− ln(1-X(t))] versus log(t) based on Jeziorny model: a S0, b S1, c S2, d S3, and e S4

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Fig. 8
figure 8

Curves of linear fitting of primary crystallization using Jeziorny model: a S0, b S1, c S2, d S3, and e S4

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Table 2 Non-isothermal kinetic parameters of MC nylon6 and PPES/MC nylon 6 in-situ composites
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Based on the data obtained from Jeziorny model, MC nylon 6 has a slow crystallization rate with Zc values changing from 0.052 to 1.048 and n values of about four, which demonstrate a 3D spherulitic growth mechanism for MC nylon 6 crystallization. By adding PPES to MC nylon 6, the mechanism of nucleation and crystal growth dimensions change slightly as the n values have not changed significantly while distinctively for the composite containing 8% PPES [17, 41, 42]. In addition, with the increase of cooling rate, the Zc of MC nylon 6 and its in-situ composites gradually increase, and their semi-crystallization times t1/2 decrease.

From the data reported in Table 2, the lower values of Zc for the in-situ composites as compared to those of the neat MC nylon 6 indicate that MC nylon 6 crystallization process becomes slower in the presence of PPES. We explain from the following viewpoints. Cheng et al. [43] believed that the adsorption of macromolecular chains on the heterogeneous surface would reduce the mobility of the chain segments and hinder the transport of macromolecules from the melt to the crystalline region, thus reducing the crystallization rate. From the perspective of thermodynamics, Ebengou [44] believed that when macromolecular chains are adsorbed on the pre-existing heterogeneous surface, the conformational entropy of the chains decreases, which reduces the free energy of the nucleation process and increases the crystallization rate. Combined with Cheng's viewpoint, Ebengou believed that the adsorption of macromolecular chains on the heterogeneous surfaces can reduce the activity of the chain segments and hinder the crystallization. On the other hand, it can reduce the conformational entropy of the chain and promote crystallization, so the final result depends on the synergistic effect of the two factors. In this work, PPES acts as a nucleating agent in the nucleation stage and restricts the movement of chain segments for MC nylon 6 during crystal growth. These findings are in line with the non-isothermal crystallization behavior results.

Mo model

Mo Zhishen et al. combined Ozawa and Avrami equations and proposed a new dynamic model [45, 46]:

$$ \log (\phi ) = \log F(T) - a\log (t). $$
(8)

In Eq. 8, F(T) = [P(T) − Z]1/m is the ratio of the cooling rate to Z, and a = n/m is the ratio of the Avrami to Jeziorny exponents. Based on this relationship at each cooling rate, the changes in the degree of crystallinity are determined. By fitting this relationship on the experimental data, the parameters F(T) and a can be obtained from the intercept and the slope of the lines, respectively. The parameter F(T) has a definite physical and practical meaning and is the value of cooling rate, which has to be chosen at a specific crystallization time to reach a certain degree of crystallinity. A lower F(T) value implies that the system needs a shorter time to develop a certain degree of crystallinity, and it has a higher rate of crystallization. Figure 9 exhibits the lines obtained from fitting the Mo model on the experimental data.

Fig. 9
figure 9

Plots of log(ϕ) versus log(t) based on Mo model: a S0, b S1, c S2, d S3, and e S4

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As it is seen from the data presented in Table 3, the a values remain close to unity, indicating that the ratio of the Avrami–Ozawa exponents remains almost unchanged, which confirms that both the models propose the same mechanism for crystal growth. While the F(T) values of the composites are generally higher as compared to the pure MC nylon 6. This implies that PPES/MC nylon 6 in-situ composites need a longer time to develop a certain degree of crystallinity, and therefore, they have a lower rate of crystallization as compared to the MC nylon 6. This finding corroborates the previous results regarding the role of PPES in acting as a nucleating agent in the nucleation stage and restricting the movement of chain segments for MC nylon 6 during crystal growth.

Table 3 Crystallization kinetic parameters obtained based on Mo model at different relative degrees of crystallinity
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Activation energy of non-isothermal crystallization

The activation energy for a non-isothermal crystallization process can be calculated based on several methods presented by Augis and Bennett [47], Kissinger [48], Friedman [49], and Takhor [50].

Friedman method

According to the Friedman method:

$$ \ln \left( {\frac{{{\text{d}}X}}{{{\text{d}}t}}} \right)_{X,j} = {\text{const}} - \frac{{\Delta E_{X} }}{{RT_{x,j} }}, $$
(9)

where dX/dt is the ratio of changes in the relative degree of crystallinity with time, and ΔEX is the crystallization activation energy at a certain degree of crystallinity. To obtain ΔEX, one needs to determine dX/dt. The dX/dt values for all the studied samples were determined. According to Eq. 9, from the plots of ln(dX/dt) versus 1/RTx, the activation energies can be obtained from the slopes of the straight lines fitted on the experimental data. Therefore, for each value of the relative degree of crystallinity, the Friedman equation was fitted on the data and the obtained Friedman lines for MC nylon6 and PPES/MC nylon 6 in-situ composites are presented in Fig. 10. Accordingly, the variations of activation energy against the relative degree of crystallinity and average temperature for all the studied samples are shown in Fig. 11. It is found that the values of ΔEX are negative as expected. From these figures, it can be inferred that the presence of PPES in the MC nylon 6 matrix has reduced the crystallization activation energy, which can be attributed to PPES in the MC nylon 6 matrix that can act as heterogeneous nucleating agent, and can promote the formation of MC nylon 6 crystal nucleus. In addition, with the increase of crystallinity, all the absolute values of ΔEX of MC nylon6 and PPES/MC nylon 6 in-situ composites decrease. In addition, with the increase of temperature, all the absolute values of ΔEX of MC nylon 6 and PPES/MC nylon 6 in-situ composites increase. The activation energy sign indicates that crystallization gradually becomes easy with the decreasing crystallization temperature.

Fig. 10
figure 10

Friedman plots of ln(dX/dt) versus 1/RTx at different relative degrees of crystallinity: a S0, b S1, c S2, d S3, and e S4

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Fig. 11
figure 11

a Dependency of activation energy on degree of crystallization conversion by the Friedman method, and b plots of the effective activation energy as function of the average temperature for MC nylon6 and PPES/MC nylon 6 in-situ composites

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Kissinger method

Also, the activation energy of non-isothermal crystallization is usually analyzed by Kissinger method [26, 51,52,53,54], and the formula is as follows:

$$ \ln \left( {\phi /T_{{\text{c}}}^{2} } \right) = \frac{ - \Delta E}{R}\left( {1/T_{{\text{c}}} } \right). $$
(10)

In Eq. 10, ϕ is the cooling rate, Tc is the corresponding crystallization peak temperature at a specific cooling rate, ΔE is the activation energy of non-isothermal crystallization (kJ/mol), and R is the gas constant. The activation energy data of non-isothermal crystallization can be obtained by the slope of the plots of Tc−1 versus ln(ϕ/Tc2). The plots and data obtained are shown in Fig. 12 and Table 4.

Fig. 12
figure 12

Plots of Tc−1 versus ln(ϕ/Tc2) by Kissinger equation

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Table 4 Activation energy of crystallization obtained based on Kissinger method
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Accordingly, it is observed that the crystallization activation energy of MC nylon 6 is 266.94 kJ/mol. As the amount of PPES increases, the absolute values of crystallization activation energy of PPES/MC nylon 6 in-situ composites gradually decrease. Due to the heterogeneous nucleation of PPES and reducing the crystallization barrier energy, it can promote the formation of MC nylon 6 crystal nucleus.

In summary, analysis of crystallization kinetics of the developed systems by various models quantitatively confirmed that inclusion of PPES to MC nylon 6increased the crystallinity, while the crystallization rate was reduced. Analysis of data based on theoretical models revealed that PPES acted as a nucleating agent in the nucleation stage and restricted the movement of chain segments for MC nylon 6 during crystal growth. Furthermore, the in-situ composites had lower crystallization activation energy compared to MC nylon 6 due to the nucleation effect of PPES.

Conclusions

The hypothesis regarding the sensitivity of crystallization kinetic of MC nylon 6 toward different PPES contents was examined and quantitatively analyzed by various models. Morphological study using SEM revealed PPES particles were well dispersed, at micron levels, in the MC nylon 6 matrix. It was found that inclusion of PPES to MC nylon 6 increased the crystallinity, while the crystallization rate was reduced. Crystallization kinetic studied by Jeziorny model revealed two levels of primary and secondary crystallization mechanisms for all samples. The lower values of Zc for the in-situ composites as compared to those of MC nylon 6 indicated that MC nylon 6 crystallization process becomes slower in the presence of PPES. The F(T) values of the composites are generally higher as compared to those of pure MC nylon 6, indicating that the interaction between PPES and MC nylon 6 matrix was stronger and the mobility of the polymer molecular chain was difficult. Moreover, the activation energies of crystallization of the in-situ composites were lower than that of MC nylon 6. Analysis of data based on theoretical models revealed that PPES acts as a nucleating agent in the nucleation stage and restricts the movement of chain segments for MC nylon 6 during crystal growth.