Introduction

Recently, the fabrication of polymer nanocomposites (PNCs) has become a key technology for both engineering and advanced composite materials. The attention to nano-size fillers is due to their extremely high surface area that facilitates strong filler-polymer interactions even at low nano-filler loading, leading to significant improvements in material properties [1]. Numerous studies have shown that addition of nano-size metals to polymers can lead to a significant enhancement of many properties, such as stiffness, strength and hardness [2, 3], thermal stability and fire retardancy [4, 5], magnetic, optical, and electrical properties [6, 7]. All these make metal reinforced PNCs potential candidates for a wide variety of engineering applications including catalysis [8], chemical sensing [9], biomedical applications [10], electronics, photonics and for fabrication of electromagnetic [11] and optical [12] devices.

Nanocrystalline Fe-Ni (nc Fe-Ni) alloys have been widely studied because of their high-saturation magnetization, low coercivity, good anticorrosion properties [13], low thermal expansion and excellent mechanical properties [14]. The studies focus on the synthesis of nc Fe-Ni alloys and the investigation of their magnetic and mechanical properties [13–15], without exploring the potential of using these alloys as nano-fillers in polymers.

Polyamide 6 (PA6) is a semicrystalline thermoplastic having a complicated polymorphic structure that exhibits two major crystal forms, namely α and γ. The α form crystals are more ordered, thermodynamically stable [16, 17] and stronger [18] than the metastable γ-form crystals. PA6 is extensively used in a number of consumer goods and industrial applications owing to its durability and high heat, wear and chemical resistance. Typical applications include fishing nets, brush bristles, fluid reservoirs and automotive components [19, 20].

The goal of this study is to explore the potential of using nc Fe40Ni60 as reinforcement for PA6 in order to provide new metal-PNC for engineering applications. This will be accomplished by developing Fe40Ni60/PA6 nanocomposites and characterizing their properties. Focus will be given on the alteration of PA6’s physical properties due to the presence of metallic nanofiller and the mechanical and thermomechanical properties of the nanocomposites. nc Fe-Ni alloy is a supermagnetic material, so the nanoparticles have a great tendency to agglomerate and proper compounding methods need to be employed to eliminate or minimize the agglomeration. The nc Fe40Ni60 fine particles were synthesized by chemical reduction in aqueous solution and the Fe40Ni60/PA6 nanocomposites were prepared by compounding, either via direct melt mixing (MM) or solution mixing (SM), followed by injection molding. MM is simple, economical and therefore has a great potential in the commercial production of PNCs. On the other hand, SM is more effective route for the preparation of PNCs with remarkable properties [21].

Experimental

Materials

The chemicals used for the synthesis of nc Fe40Ni60 alloy were nickel chloride hexahydrate (NiCl2.6H2O, 98 %) and ferrous chloride (FeCl2, 99 %) as sources of metal ions; hydrazine hydrate (N2H4.H2O, 99 %) as a reducing agent, sodium hydroxide (NaOH, 99 %) as a catalyst and distilled water as a solvent. NiCl2.6H2O and N2H4.H2O were purchased from Panreac Quimica, Spain. FeCl2 and NaOH were obtained from Spectrum Chemical MFG. CORP, USA and El Nasr Pharmaceutical, Egypt, respectively. The polymer used was PA6 pellets (BX3WQ662[X] (ISO)) kindly supplied in sealed packages by Custom Resins, Inc, USA. Formic acid (HCO2H, 98 %) and ethanol (C2H5OH, 96 %) used as a solvent and a precipitant for PA6, respectively, were purchased from VWR, USA.

Synthesis of nc Fe40Ni60 particles

The synthesis of the nc Fe40Ni60 particles was done according to the protocol reported in our previous work [13]. Briefly, FeCl2 and NiCl2.6H2O were dissolved in distilled water to form aqueous solution of 0.6 M with a [Fe2+]/[Ni2+] ratio of 4:6. The solution was vigorously stirred and heated to 80 °C. Then, a second solution of aqueous hydrazine, N2H4.H2O, (50 wt%), and aqueous NaOH (0.1 M) was added to it. Fine black particles were precipitated as a result of the reduction reaction. The resulting particles were separated magnetically, washed repeatedly with distilled water until neutral pH and dried in vacuum at 35 °C for 2 days.

Preparation of Fe40Ni60/PA6 nanocomposites

The composites were made in a two step process: First the alloy particles were compounded with PA6 pellets either via MM or SM. The compounding was then followed by injection molding and standard Izod bars (ASTM D256) with nano-filler loading up to 5 wt% were fabricated. Before compounding, PA6 pellets were dried in a vacuum oven at 80 °C for 48 h. After molding, the specimens were sealed and placed in a desiccator for a minimum of 24 h prior to testing. The detailed sample codes are shown in Table 1.

Table 1 Sample codes
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A DSM Xplore 15 cc micro-compounder (vertical, co-rotating twin-screw extruder) and 10 cc micro-injection molding machine were used for the compounding and fabrication of MM nanocomposites, respectively. The conditions used were: 240 °C as Tbarrel in the compounder and injection molding machine, screw speed of 150 rpm, Tmold of 70 °C and injection pressure of 0.76 MPa.

The solution mixed nanocomposites were prepared as follows. PA6 pellets were dissolved in formic acid at ambient temperature using magnetic stirring. The polymer concentration in the solution was 10 wt%. The Fe40Ni60 particles were then added to the polymer solution and the mixture was vigorously stirred for 30 min. Addition of ethanol, with the ethanol/formic acid ratio being 2:1 vol/vol, initiated the precipitation of PA6 after 30 min and led to formation of the composite powder which was completed within 20 min. The composite powder was separated from mixed solvent through filtration and dried in vacuum oven at 80 °C for 48 h. The whole process was carried out under hood. Finally, the dried composite powder was fabricated into standard Izod bars via injection molding under the same conditions followed in the fabrication of MM nanocomposites.

Characterization of nc Fe40Ni60 particles

X-ray diffraction (XRD) was employed to characterize the crystallographic texture and crystal size of the synthesized Fe-Ni alloy. XRD measurements were carried out on a Shimadzu XRD-7000 diffractometer (30 kV, 30 mA; Cu Kα + Ni-filtered radiation, λ = 0.15406 nm). The 2θ range was 30–110°, at a scanning rate of 4°/min and a scanning step of 0.018°. Chemical composition was estimated by an area analysis using energy dispersive X-ray spectroscopy (EDS) equipped with the scanning electron microscope (SEM, JEOL, Model JSM 6360 LA). The morphology and particle size were analyzed by a field emission scanning electron microscope (Zeiss Ultra-60 FE-SEM), operating at 5 kV. The SEM samples were prepared by dropping a diluted dispersion of Fe−Ni particles onto a silicon wafer and letting the solvent to evaporate.

Characterization of Fe40Ni60/PA6 nanocomposites

Flexural test was performed using a MTS 810 testing machine (MTS Systems Corporation), according to ASTM-D790. Notched Izod impact strength was determined using a CS-137-083 impact tester (Custom Scientific Instruments, INC), according to ASTM-D256. All the tests were conducted at ambient temperature and the reported results reflect an average of three measurements. Thermomechanical properties, including storage modulus and loss tangent (tan δ), were characterized using dynamic-mechanical analyzer (DMA Q800, TA instruments). The properties were characterized as a function of temperature using a single cantilever mode applying constant strain. The strain amplitude was 0.15 %, the frequency 1 Hz and the heating rate was 3 °C/min. Measurements were performed in the temperature interval 25–180 °C. The presented data are the average of three measurements.

The degree of agglomeration and distribution of nc Fe40Ni60 particles in PA6 matrix were assessed through SEM examination of the impact fracture surface using Zeiss Ultra-60 FE-SEM operating at accelerating voltage of 5 kV. The specimens were gold coated using a Desk IV Sputter/Etch Unit (DENTON Vacuum, LLC).

Modulated differential scanning calorimeter (MDSC Q200, TA instruments) was used to determine the degree of crystallinity and analyze the melting and crystallization behaviors of neat PA6 and PA6 phase in the nanocomposites. The samples of 7 mg were heated from ambient temperature to 270 °C, held at this temperature for 3 min to erase the thermal history and then cooled to 25 °C. All MDSC runs were conducted under nitrogen atmosphere with heating/cooling rates of 5 °C/min. The degree of crystallinity, XC, was calculated from the enthalpy evolved during melting based on the heating scans, using the following formula [21]:

$$ {{\mathrm{X}}_{\mathrm{C}}}=\frac{{\varDelta {{\mathrm{H}}_{\mathrm{m}}}}}{{\left( {1-\emptyset } \right)\varDelta {{\mathrm{H}}^0}_{\mathrm{m}}}}\times 100 $$
(1)

Where ΔHm is the apparent enthalpy of melting of sample, ΔH0 m is the extrapolated value of the enthalpy corresponding to the melting of 100 % crystalline pure PA6, which is taken as 190 J/g [22], and ∅ is weight fraction of nc Fe40Ni60 in the composites.

XRD was employed to determine the relative fraction of α and γ crystalline phases in neat PA6 and PA6 phase within the nanocomposites. XRD patterns were obtained using X’Pert PRO MPD diffractometer in reflection mode (45 kV, 40 mA; Cu Kα + Ni-filtered radiation, λ = 0.154 nm). The analysis was performed on the injection molded Izod bars, at ambient temperature with a 2θ range between 8 and 80°, at a scanning rate of 4°/min and a scanning step of 0.016°. Samples were then heated gradually to 60, 90, 120, 150 and 180 °C and held at each temperature for 5 min before commencing the data collection. The range of 2θ measurement was 8–30° at the same scanning rate and step.

XRD traces were de-convolved to diffraction peaks corresponding to amorphous phase and crystalline phase which is composed of α and γ crystal forms, using MDI Jad9 software. The percentage of γ-phase with respect to the total crystalline phase was calculated by:

$$ \gamma \left( \% \right)=\frac{{{{\mathrm{A}}_{\gamma }}}}{{{{\mathrm{A}}_{\alpha }}+{{\mathrm{A}}_{\gamma }}}}\times 100 $$
(2)

Where Aα is the area under α diffraction peaks and Aγ is the area under γ diffraction peaks [23]. In order to check the influence of high temperature processing on the nanostructure of nc Fe40Ni60 alloy, crystallite sizes of nc Fe40Ni60 particles in the nanocomposites were also determined.

Results and discussion

Characteristics of nc Fe40Ni60 particles

Figure 1 shows the XRD pattern of the chemically synthesized particles. The four characteristic peaks for the disordered FCC γ-Fe-Ni taenite phase (2θ = 44.05°, 51.3°, 75.6° and 91.5°), marked by Miller indices ((111), (200), (220) and (311)) are observed [13, 24]. This reveals that the synthesized particles are pure Fe-Ni alloy. The average crystallite size of the synthesized alloy, based on the full width at half maximum of the (111) peak using Scherrer formula [25], is 11 nm. According to EDS quantitative analysis the alloy composition is 36 at.% Fe and 64 at.% Ni, excluding the other elements like carbon in the supporting film and oxygen in the oxide layer formed on the particle surface. Additionally, the oxygen content is only 6 at.%, indicating that the oxide layer formed on particle surface is very thin. The SEM image, presented in Fig. 2, shows that the produced Fe40Ni60 alloy is composed of spherical particles with a mean diameter of about 150 nm. This suggests that each spherical particle is nanostructured, i.e. it is composed of several nanocrystallites, as previously reported [13, 24]. Based on XRD, EDS and FE-SEM results, it is concluded that the chemically synthesized black particles are nc Fe40Ni60 submicron sized particles.

Fig. 1
figure 1

XRD pattern of the chemically synthesized black particles

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Fig. 2
figure 2

SEM image of the nc Fe40Ni60 alloy particles

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Mechanical and thermomechanical properties of Fe40Ni60/PA6 nanocomposites

Figure 3 shows the flexural modulus and strength of MM and SM composites as a function of nc Fe40Ni60 content. Regardless of the nanofiller content, SM composites acquire much higher modulus and strength than the corresponding MM composites. This can be attributed to the intensive mixing applied during solution mixing which broke up particle agglomerates and improved the distribution of alloy particles within the polymer matrix as indicated also by SEM. Improved distribution of particles or particle agglomerates and smaller agglomerates result in stronger filler-matrix interactions and thus more efficient stress transfer between the two phases. Figure 3 also indicates that addition of nc Fe40Ni60 particles to PA6 significantly enhances the modulus and strength in case of SM composites especially for low nano-filler content. The maximum improvement observed is 35 % (modulus) and 26 % (strength), at 3 wt% nc Fe40Ni60.

Fig. 3
figure 3

Flexural properties of Fe40Ni60/PA6 nanocomposites as a function of particle content

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It is worth mentioning that although melt mixing usually results in polymer nanocomposites with reasonable mechanical performance [26], in this study the MM composites except MM1, which has comparable modulus and strength to neat PA6, exhibit lower modulus and strength compared to those of neat PA6. This implies that the interfacial adhesion between filler agglomerates and PA6 matrix is very poor and overrides the reinforcing action of the nanofiller, leading to mechanical property deterioration. This is mainly because the supermagnetic Fe-Ni alloy has a strong agglomeration tendency, which couldn’t be overcome by the week forces, applied in MM process.

The impact strength of Fe40Ni60/PA6 nanocomposites as a function of the nanofiller loading and compounding method is presented in Fig. 4. Again the SM composites possess much higher impact strength than the corresponding MM composites do. However, both composites exhibit lower impact strength compared to that of the neat PA6. The decrease in impact strength becomes more pronounced at higher particle loading. This may be because i) addition of nc Fe40Ni60 particles to PA6 boosts its hardness and stiffness which, in turn, reduces toughness or/and ii) the increased particle agglomeration and agglomerate size at higher filler content, as confirmed by SEM, act as crack nucleation sites [27].

Fig. 4
figure 4

Impact strength of Fe40Ni60/PA6 nanocomposites as a function of particle content

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The storage modulus and tan-δ of MM and SM composites as a function of temperature at various nanofiller loadings are shown in Fig. 5a and b, respectively. As indicated the SM composites have higher storage modulus than the MM composites throughout the tested temperature range and both composite systems exhibit higher modulus compared to that of the neat PA6. In addition, the tan-δ of SM composites is significantly lower than that of MM composites in the low 25 °C to 55 °C temperature range, indicating that SM composites are more elastic and can store more energy than the MM composites. It is also noted that the storage modulus is enhanced as the nanofiller content increases in SM composites. Thus, SM5 shows the maximum improvement in storage modulus, 23 %, at ambient temperature. On the other hand, the SM composites have significantly lower tan-δ than neat PA6 (SM0) in the low temperature range from 25 °C to 45 °C. This indicates that as the nanofiller content increases, the load bearing capacity is significantly improved while the dissipated energy is decreased during dynamic deformation of nanocomposites.

Fig. 5
figure 5

Thermomechanical properties of Fe40Ni60/PA6 nanocomposites as a function of temperature at various nc Fe40Ni60 content. a Storage modulus, (b) tan-δ

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The maximum of tan δ is associated with the α-transition (glass transition) of PA6. For SM samples, the temperature of α-peak (glass transition temperature, Tg) increases from 60.5 to 66.2 °C with increasing the particle content from 0 to 5 wt%. As reported in [28], an increase in the Tg of polymer upon addition of a reinforcing nano-filler is an evidence for the good distribution of filler within polymer matrix. This suggests that nc Fe40Ni60 particles exhibit good distribution in PA6 matrix, causing severe constraint on the polymer segmental motion, so that, the transition from glassy state to rubbery state occurs at higher temperature. In case of MM composites the Tg of PA6 is slightly shifted to higher temperature upon addition of 1 wt% nc Fe40Ni60 particles. Whereas, further increase of particle loading causes Tg to decrease again, which reveals that nanofiller does not affect polymer chain mobility. This may be due to the presence of agglomerates and poor distribution within polymer matrix which decrease the nc Fe40Ni60-particles/polymer contact area and interactions.

Restriction of polymer chain mobility that is evidenced by increased Tg of PA6 matrix in SM composites, contributes to the enhancement of storage modulus, flexural modulus and strength and the decreased impact strength of these nanocomposites compared to the properties of neat PA6.

Morphology of Fe40Ni60/PA6 nanocomposites

SEM micrographs of MM and SM composites are presented in Fig. 6. It is referred to some of nc Fe40Ni60 particles, appeared in the micrographs, by arrows in order to clearly indicate them. For MM composites, it is obvious that nanoparticle agglomeration is predominant, the degree of agglomeration is more pronounced and the agglomerate size increases at larger filler content. Furthermore, the agglomerates are not uniformly distributed within the PA6 matrix. Such morphology limits the filler-matrix contact area which, in turn, results in poor interfacial interactions and therefore insufficient stress transfer between the two phases, leading to poor mechanical and thermomechanical properties. Unlike MM composites, SEM micrographs of SM composites reveal fewer nc Fe40Ni60 agglomerates that are better distributed within the PA6 matrix. As expected, the degree of agglomeration increases with the particle content as shown in the micrograph of SM5. This observation is in agreement with the trend found for the flexural properties of the SM composites.

Fig. 6
figure 6

SEM micrographs of Fe40Ni60/PA6 nanocomposites

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The number average particle sizes (PS) of nc Fe40Ni60 particles in MM and SM composites have been calculated by individual measurement of about 50 particles from SEM micrographs of each composite, using SmartTiff software. In addition the particle-size distribution histograms have been produced using Matlab®, to provide quantitative assessment of the degree of agglomeration of alloy particles within composites. The PS data reveal that the particle size is much greater for MM samples. Moreover, representative particle-size distribution histograms for MM1, Fig. 7a, and SM1, Fig. 7b, clearly show that the number of small nanoparticles is higher in the SM1 composite whereas the MM1 composite contains larger number of agglomerates and exhibits a broader size distribution. Obviously, the average particle sizes of nc Fe40Ni60 particles within SM composites are significantly smaller than that estimated from the SEM image of the chemically synthesized alloy powder, Fig. 2. This confirms that the intensive mixing applied during solution mixing broke up the submicron supermagnetic agglomerates into smaller nanoparticles.

Fig. 7
figure 7

Particle-size distributions histogram of nc Fe40Ni60 particles in (a) MM1 and (b) SM1

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Crystalline structure of Fe40Ni60/PA6 nanocomposites

Figure 8 illustrates the MDSC heating scans for MM, SM composites and the corresponding PA6 controls. Upon heating from 40 to 270 °C, a small exothermic peak, around 189 °C for MM composites and 195 °C for SM composites, followed by a sharp endothermic peak around 222 °C were observed for all samples. This endothermic peak is mainly associated with the melting of α-form crystals of PA6 [29]. However, the presence of a long tail at the beginning of peak reveals that there is a fraction of γ-form crystals which usually melt around 210 °C [30]. The sub-Tm exotherm in nylons is attributed to the release of strain energy absorbed during processing [31].

Fig. 8
figure 8

MDSC heating traces of Fe40Ni60/PA6 nanocomposites

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The degree of crystallinity, melting and crystallization temperatures of PA6 matrix in MM and SM composites are listed in Table 2. For MM composites, it is evident that the degree of crystallinity, melting and crystallization temperatures of PA6 are insensitive to the presence of nc Fe40Ni60 particles, at all nanofiller loadings used in the study. On contrary all SM composites have significantly higher degree of crystallinity and crystallization temperature than neat PA6. The increased crystallization temperatures of PA6 phases in such composites indicate that the nc Fe40Ni60 particles act as effective nucleating agent, thus allowing the crystallization of PA6 molecules to start earlier and inducing the rate of crystallization that eventually leads to increased degree of crystallinity. Conversely, the increased restriction of PA6 chain mobility with the increase of nanofiller content, as revealed from Tg values, hinders the crystallization of PA6 molecules and as a consequence lowers the degree of crystallinity. These counteracting effects of nc Fe40Ni60 particles interpret why the increase in the degree of crystallinity of PA6 phase over that of neat PA6, exhibits maximum at 1 wt% nc Fe40Ni60 then decreases as the nanofiller content increases within SM composites. Unlike the degree of crystallinity and crystallization temperature, no significant change in the melting temperature with the nanofiller content is observed, revealing that the size and perfection of PA6 crystals appear unaffected by the increase of nanofiller content in SM composites.

Table 2 DSC data for MM and SM composites
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XRD patterns for MM, SM composites and the corresponding PA6 controls are presented in Fig. 9. The peaks around 2θ ≈ 20° and 23° are assigned to α1 and α2 crystal planes of PA6, respectively. While the peaks around 2θ ≈ 10°, that appears only in the XRD scan of SM5, and 21° are assigned to γ1 and γ2 crystal planes of PA6, respectively [29]. The observed peaks around (2θ = 44°, 51°, 75°) are attributed to the disordered FCC γ-Fe-Ni taenite phase, as mentioned before. γ-phase (%) and crystallite sizes of nc Fe40Ni60 in MM, SM composites and the corresponding neat PA6 controls are listed in Table 3. Clearly, the α-form is predominant in both neat PA6 controls and MM composites. Presence of nc Fe40Ni60 particles has a negligible effect on the polymorphic crystalline structure of PA6 in MM composites (the γ-phase (%) in MM3 and MM5 is slightly higher than that in MM0), which is in agreement with DSC results. This reveals that the crystallization of PA6 phase is insensitive to the presence of nc Fe40Ni60 particles in MM composites, owing to large particle agglomeration and poor distribution which minimize the filler-matrix interactions. Conversely, the relative fraction of γ-form to α-form crystals significantly increases as the nanofiller content increases in SM composites and γ-form becomes predominant in SM3 and SM5. Based on the discussion reported in previous researches which studied the crystallization of clay/PA6 [23] and MWNTs/PA6 nanocomposites [17], it is speculated that the possible reasons of this phenomenon are: a) nc Fe40Ni60 particles constrain the mobility of PA6 molecules, and as a result, chain packing into well ordered crystals becomes more difficult than in neat PA6. Therefore, the less ordered γ-crystal form is favored in the presence of nc Fe40Ni60 particles; b) as the size of the good distributed nc Fe40Ni60 particles within PA6 phase is somewhat large, the filler particles disturb the PA6 crystals while being formed during the crystallization process, leading to the profusion of less ordered γ-phase crystals in SM composites as compared to neat PA6. The significant effect of nc Fe40Ni60 particles on the crystallization of PA6, as revealed from DSC and XRD analyses, can be considered as evidence for the good interfacial interaction between nc Fe40Ni60 particles and PA6 in SM composites.

Fig. 9
figure 9

XRD patterns of Fe40Ni60/PA6 nanocomposites

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Table 3 XRD data for MM and SM composites
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XRD traces at high temperatures indicate that the relative fraction of γ-form to α-form crystals in neat PA6 control and SM composites increases by increasing temperature up to 120 °C. Further increase in temperature, however, results in reconversion of γ-form crystals to α-form crystals and α-phase become predominant at 180 °C. This explains why melting peak in the DSC thermograms is mainly associated to α-form crystals, although, γ phase is predominant in SM composites at ambient temperature.

The increased degree of crystallinity of PA6 phase in SM composites is a possible reinforcing mechanism that contributes to the increased storage modulus, flexural modulus and strength but lower impact strength of such composites as compared to neat PA6. Damping in the increased degree of crystallinity and increase of the relative fraction of γ-form to α-form crystals, however, lead to the reduced rate at which the storage modulus, flexural modulus and strength are enhanced with the increase of the nanofiller content in SM nanocomposites. The later factor is also responsible for the significantly higher impact strength of SM composites compared to that of the corresponding MM ones.

On the other hand, Table 3 shows that crystallite sizes of nc Fe40Ni60 particles in both MM and SM composites are slightly larger than that of the as synthesized alloy powder. This indicates that there is small Fe40Ni60 crystal growth due to the thermal energy applied during composites processing. The phenomenon is more obvious in SM composites where the composite powder tends to sinter when subjected to heat during feeding into extruder, forming large aggregates. Feeding of these composite aggregates into extruder was very difficult and slow, leading to more crystal growth and little extent of oxidation of nc Fe40Ni60 particles. Oxidation of small portion of nc Fe40Ni60 particles is evidenced from the very weak magnetite peak (2θ = 35.6°) [13], that appears in XRD traces of SM3 and SM5.

Finally, the relative mechanical and thermomechanical properties of SM composites are compared with those of previously investigated clay, carbon nanotubes (CNT’s) and silica reinforced PA6 nanocomposites for evaluating the novel Fe-Ni alloy/PA6 nanocomposite among the currently existing PA6 nanocomposites. The data are illustrated in Table 4. The preparation method of composites and whether the reinforcing nanofiller is pristine (p-) or functionalized with polar molecules, are indicated. This is because; these two parameters significantly affect the morphology, crystalline structure and therefore the overall performance of PA6 nanocomposites. Clearly, that the performance of p-Fe40Ni60/PA6 nanocomposites made by SM is in general good as well as those of other PA6 nanocomposites, indicating that this new nanocomposite is promising. The performance can be further significantly improved by minimizing particle agglomeration and improving the interfacial adhesion between metallic nanofiller and PA6 matrix through functionalization of alloy particles with polar molecules, utilizing ultrasound power during nanocomposite preparation or preparation of nanocomposite by in-situ method. Thereby, Fe40Ni60/PA6 nanocomposite will be potential candidate material for engineering applications.

Table 4 Relative mechanical and thermomechanical properties of Fe40Ni60/PA6 nanocomposites made by SM and previously studied PA6 nanocomposites
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Conclusions

Fe40Ni60/PA6 nanocomposites were fabricated using two different compounding processes and their properties were characterized as a function of the compounding method and nanofiller content. Structural analyses including SEM, DSC and XRD reveal that there is good interfacial interaction between nanofiller particles and PA6 in SM composits but not in MM ones. Thus, the improved distribution of particles, presence of fewer and smaller particle agglomerates, increased crystallinity and Tg counteract the growth of γ-crystal form and the net result is significant enhancement of storage modulus, flexural modulus and strength of SM composites over neat PA6 and MM composites. However, larger particle size, worse distribution of particles, damping in the increased degree of crystallinity and growth of the relative fraction of γ-form to α-form crystals interpret the reduced rate of enhancement of such properties with the increase of nanofiller content in SM composites. The impact strength of SM composites is remarkably higher than MM composites but, unlike other properties, is less than that of neat PA6 because increased crystallinity and Tg diminish the toughness.

Considering the mechanical and thermomechanical properties, it is concluded that 3 wt% nc Fe40Ni60/PA6 composite made by SM is the composite with the optimum overall performance. Thus, compared to the previously investigated PA6 nanocomposites reinforced with other fillers, SM3 can be a good candidate material for engineering applications.