- Email: [email protected]
polyamide nanocomposites prepared by melt processing with a PP-g-MAH compatibilizer
Materials and Design 34 (2012) 313–318
Contents lists available at SciVerse ScienceDirect
Materials and Design journal homepage: www.elsevier.com/locate/matdes
Short Communication
Properties of polypropylene/polyamide nanocomposites prepared by melt processing with a PP-g-MAH compatibilizer Benalia Kouini ⇑, Aicha Serier Laboratory of Coatings, Materials and Environment, M’Hamed Bougara University, Boumerdes 35000, Algeria
a r t i c l e
i n f o
Article history: Received 22 June 2011 Accepted 15 August 2011 Available online 19 August 2011
a b s t r a c t This article presents the mechanical properties, fire retardancy behavior and the morphology of polypropylene/polyamide66 blends compatibilized with PP-g-MAH and modified with nanoclays. All PP/PA66 formulations modified with untreated and treated nanoclays were prepared by using internal mixer and single screw extruder followed by injection molding. Maleic anhydride polypropylene (MAH-g-PP) was used as the compatibilizer and the nanoclays content was varied between 0 and 8 wt.%. The mechanical and flammability properties of PP/PA66 nanocomposites were examined. Also the structure of PP/PA66 nanocomposites has been characterized by the Scanning electron microscopy (SEM) and the X-ray diffraction (XRD). The obtained results indicate that the incorporation of nanoclay has a significant effect on the strength of PP/PA66 nanocomposites. Furthermore, it was found that SEM and XRD results revealed the intercalation, exfoliation of nanaclays of nanocomposites and the flame retardancy properties were improved significantly. In addition a good balance of impact strength and flame retardancy was obtained for PP/PA66 nanocomposites in the presence of PP-g-MA compatibilizer. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction Polymer/nanoclays nanocomposites and nanoblends present unique properties that are not observed in conventional composites. The achievement of compatibilization, even by addition a compatibilizer or by in situ chemical reaction between blends components (reactive blending), has played an important role in the development of polymer blends and provides a good solution for needs of industry [1]. Engineering polymers are used in a wide number of applications [2]. The aims of the incorporation of small amounts of nanoclay (<10 wt.%) into polymer matrices may improve dimension stability, mechanical, thermal, optical, electrical, gas barrier properties, and decrease the flammability of polymer–polymer blends [1,3]. It is known that blends of PP and PA66 are immiscible throughout the whole range of composition, and thus exhibit poor properties [4]. Unfavourable interactions at the molecular level lead to high interfacial tension and make the melt mixing of the components difficult. This also leads to unstable morphology and poor interfacial adhesion, which are the main cause’s poor mechanical properties of the blends [5]. In order to prevent the incompatibility problem, a suitable compatibilizer is synthesised by grafting maleic anhydride MAH onto PP (PP-g-MAH) because it has anhydride and carboxyl groups that interact with functional groups of the PA66. ⇑ Corresponding author. Tel./fax: +213 024 91 15 05. E-mail addresses: [email protected], [email protected] (B. Kouini). 0261-3069/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2011.08.025
Numerous researchers described polymer–clay nanocomposites based on single polymer matrix. Polymer-layered silicate nanocomposites are currently prepared in four ways: in situ polymerization, intercalation from a polymer solution, direct intercalation by molten polymer and sol–gel technology. Direct polymer melt intercalation is the most attractive because of its low cost, high productivity and compatibility with current polymer processing techniques [6]. However, thermoplastic nanocomposites based on blends of two or more polymeric materials, i.e. binary or ternary blends; seem to be a new approach in the nanocomposites studies. Polypropylene and polyamide blending has been attempted to achieve improvement in mechanical properties, paintability and barrier properties, where polyamide contribute mechanical and thermal properties, while PP ensures good processing and insensitivity to moisture. The presented work in this paper focuses on the study of thermoplastic nanocomposites based on blends of PP and PA66 modified by nanoclay (treated and untreated). The aim of this work was to evaluate the effect of nanoclay loading from 2 to 8 wt.% on the rheological, mechanical, morphological and thermal properties of PP-PPgMAH-PA66 nanocomposites.
2. Exprimental work 2.1. Material used Table 1 summarizes the materials used in this work as well as the specific characteristics and the suppliers.
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Table 1 Materials. Materials (trade name)
Characteristics
Supplier
Isotactic polypropylene (MOPLEN) Polyamide 66 (technylÒA216)
– semi-crystalline polymer – MFI = 28 (g/10 min), (2190 g at 230 °C) Was used as the dispersed (minor) phase in the blend
HIMONT company
Dicumyl peroxide (DCP)
– Was used for PP degradation as well as for the creation of reactive sites in order to prepare a compatibilizer for the blends – Mw = 324 (g/mole) – Purity greater than 99% – Half life time (t1/2) = 1 h at T° = 135 155 °C Was used to stabilize polypropylene against thermal oxidation especially when mixed with polyamide 66 Chemical formulae:C4H2O3
Stabilizer (irganox 1010) Maleic anhydride (MAH) Untreated nanoclays (DELLITE LVF) Treated nanclays (DELLITE 67G)
Rhone poulenc company Merck company
Nanoclay deriving from a naturally occurring especially purified montmorillonite
CIBA-GIEGY company Fluka chemical company Laviosa company
Treated with a high content of quaternary ammonium salt (dimethyl dehydrogenated tallow ammonium)
Laviosa company
2.2. Specimen preparation 2.2.1. Polypropylene grafted MAH (PP-g-MAH) The polypropylene was mixed with dicumyl peroxide DCP and maleic anhydride MAH at 200 °C for 6 min and at a speed of 70 rpm with a Rheocard Haake internal mixer to obtain the PP-g-MA compatibilizer [7,8]. The synthesized PP-g-MA compatibilizer was used to compatibilize the PP/PA66 formulations. The amount of PP-g-MAH was kept constant for all the composites.
2.2.2. PP/PA66 nanocomposite Melt compounding of the PP/PA66 (70/30) blends and nanocomposites were done by a high shear internal mixer and single screw extruder. The extrusion zone temperature ranged from 220 to 230 °C. Prior to extrusion, PA66 pellets and nanoclay were dehumidified by using a vacuum oven at 80 8C for 8 h. The extrudates were pelletized with the Haake pelletizer. The pellets were injection molded into standard tensile bar using a Battenfeld injection molding machine. Injection molding temperature ranged from 240 to 265 °C. Prior to injection molding, all pellets were dehumidified in vacuum oven (85 °C for 12 h) [6]. The tensile test specimen was molded according to ASTM D 638 standard.1
2.3. Testing 2.3.1. Infrared spectroscopic analysis Fourier-transform infrared spectroscopy (FTIR) was used to obtain some qualitative information about the functional groups and chemical characteristics of the PP-g-MAH as a compatibilizer.
2.3.4. Morphological characterization 2.3.4.1. X-ray diffraction (XRD) analysis. Wide-angle X-ray spectra were recorded with a D 500 diffractometer (Philips PW 1710, France) in step scan mode using Ni-filtered CuKa radiation (1.5406 Å). Powder samples (clay) were scanned in reflection, whereas the injection-molded compounds were scanned in transmission in the interval 2° and 30°: The interlayer spacing of the nanoclay was derived from the peak position (d001-reflection) in the XRD diffractograms according to the Bragg’s equation. 2.3.4.2. Scanning electron microscopy analysis. Notched fractured surfaces of the different nanoblend formulations were examined under a scanning electron microscopy operating at 10–15 KV. Before scanning, a conductive coating layer was spread on the surface of the sample. 2.3.5. The fire retardancy properties The flammability test (UL94HB) was conducted using the flammability tester 6151/000 that consists of a test chamber, laboratory burner, wire gauge, ring stand and metal support fixture. First the test specimens of 63 mm in width and 3.17 mm in thickness were cut from the impact test specimen. Each specimen was marked at 2 cm from one end then fixed horizontally in the support fixture. After that, the flame of the burner was adjusted to have 6 mm height of its blue portion and the burner was inclined about 45° and moved to reach the specimen edge. Finally the time needed for the flame to spread till the 2 cm mark was recorded. The results were analyzed in terms of the flammability time as a function of the nanoclays content. 3. Results and discussion
2.3.2. Melt flow index (MFI) and density measurement Melt flow index and density of various formulations were measured by using Melt Flow Indexer (at 230 °C, load 2.16 kg) and density balance (model METTLER TOLEDO).
2.3.3. Mechanical properties The impact specimens were prepared according to ASTM D 256 standard2 using a Battenfeld injection molding machine. PP, as well as, PP-PPgMAH-PA66 nanoblends was injection molded under the same conditions: the nozzle temperature was set to be 265 °C, the injection pressure was fixed at 75 bar while the screw speed is set to 70 rpm. 1 2
The tensile test specimen was molded according to ASTM D 638 standard. The impact specimens were prepared according to ASTM D 256 standard.
3.1. FTIR analysis Fig. 1 shows FTIR spectra of PP and PP-g-MAH. It illustrates the presence of two new intense overlapping absorption bands at 1785 cm 1, 1712 cm 1 and a low absorption bands around 1855 cm 1 corresponding respectively to: symmetric, asymmetric stretching and carboxylic acid. This is an indication of the grafting of Maleic anhydride MAH onto PP molecular chain. These results have been reported elsewhere [8]. 3.2. Melt flow index (MFI) 3.2.1. PP-g-MAH compatibilizer It can be shown from Table 2 an important reduction of MFI of modified PP with the constant amounts of DCP and MAH versus
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Fig. 1. FTIR spectra of PP and modified PP.
Table 2 MFI values of PP and PP-g-MAH.
Table 3 Designation, composition, and MFI and density values of samples.
Designation
PP
PP-g-MAH
MFI (g/10 min), T = 180 °C MFI (g/10 min), T = 190 °C
28 32
19 22
neat PP. This is mainly due to the grafting reaction of MAH onto PP. This may be attributed to the higher reactivity of MAH resulting in the formation of a graft copolymer, viz. PP-g-PA66 in the blends. The intermolecular bonding in the copolymer may restrict the movement of the polymeric chains in the PP/PA66 nanoblends, thus affecting the melt viscosity. When MAH-g-PP was added to PP/PA66 nanoblends, the anhydride group of MAH would react with the terminal amino group of PA66 during melt mixing to form PP-g-PA66 copolymer [9].
Sample designation
Composition
Parts (Phr)
MFI (g/ 10 min)
Density q (g/ cm3)
F0 F2
PP/PA66/PP-g-MAH PP/PA66/PP-g-MAH/ untreated nanoclay PP/PA66/PP-g-MAH/ untreated nanoclay PP/PA66/PP-g-MAH/ untreated nanoclay PP/PA66/PP-g-MAH/ untreated nanoclay PP/PA66/PP-g-MAH/ untreated nanoclay PP/PA66/PP-g-MAH/ treated nanoclay PP/PA66/PP-g-MAH/ treated nanoclay PP/PA66/PP-g-MAH/ treated nanoclay PP/PA66/PP-g-MAH/ treated nanoclay PP/PA66/PP-g-MAH/ treated nanoclay
70/30/5 70/30/5/2
76.76 67.5
0.933 0.919
70/30/5/4
43.15
0.902
70/30/5/5
7.69
0.898
70/30/5/6
6.03
0.941
70/30/5/8
6.28
0.952
70/30/5/2
32.41
0.955
70/30/5/4
8.81
0.926
70/30/5/5
4.67
0.930
70/30/5/6
3.72
0.931
70/30/5/8
3.69
0.950
F4 F5 F6 F8 F22 F44 F55
3.2.2. PP/PA66 nanoblend Table 3 represents the variation of MFI versus clay content of both treated and untreated one. It is observed that the MFI values of PP/PA66 nanoblends decreased in the presence of PP-g-MAH and nanoclays. It can be shown that the effect of the treated nanoclay is more pronounced than the untreated one. A drastic reduction in MFI values is observed with a levelling of at 5 wt.%. This may be attributed to the interaction between the amine group of the intercalation the nanoclay and anhydride group of the MAH-g-PP because When MAH-g-PP was added to PA6/PP blends, the anhydride group of MAH would react with the terminal amino group of PA66 during melt mixing to form PP-g-PA66 [10]. Another possible interaction is between the nanoclay and PA66: the NH2 group in the octadecylamine is believed to be compatible with PA66 and is capable of forming hydrogen bonds [8]. These interactions reduce the chain mobility and yield lower MFI values. 3.3. Density measurement Table 3 represents the variation of densities versus nanoclays content. The addition of nanoclay has a minor effect on the density. Although the densities of the filled nanoblends with treated nanoclay are relatively superior to the untreated ones with a maximum density obtained at 2 wt.%. The treatment seems to lead to a more compact structure.
F66 F88
3.4. Mechanical properties 3.4.1. Impact test Fig. 2 represents the notch impact strength of nanoblends versus treated and untreated nanoclays content. About 50% increase in impact strength is reached by incorporation of 4 wt.% of treated nanoclays. Note that the additions of both nanoclays and PP-gMAH in the PP/PA66 nanoblends have affected the impact strength but he incorporation of untreated clay has a minor effect on this property. The nannoclay is able to act as reinforcing filler due to its high aspect ratio and platelet structure. The enhancement in the impact strength of PP/PP-g-MAH/PA66 nanocomposites became more significant with the incorporation of 4 wt.% treated clay in the presence of the PP-g-MAH compatibilizer. This is believed to be associated with the functionality of the nanoclay which promotes the interaction between the nanoclay and PP/PA66 matrix. When the concentration of nanoclay is above the saturation level, only a part of the molecules locates in the interfacial area, and the excess is dispersed in the matrix affecting its homogeneity and consequently the mechanical properties of the composites [10].
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(1) Untreated Clay (2) Treated Clay
110
σ (KJ/m2)
100
(2)
90 80 70
(1)
60 50 40 0
2
4
6
8
Nanoclay Content (%) Fig. 2. Impact strength versus nanoclay content.
However, in the presence of 4 wt.% treated clay, the impact strength of the PP/PP-g-MAH/PA66 nanocomposites was well improved. This improvement may be attributed to the platelet structure and related anisotropy when the layers of organoclay are delaminated. Delamination (i.e. intercalation and exfoliation) of the layered silicate could also affect the crystallinity and polymorphism in both PA6 and PP. Delamination of the layered organoclay is favored by the shear forces during extrusion compounding and injection molding [10]. Fig. 2 demonstrates the effect of treated nanoclays on the impact strength of the compounds. The results indicate that with increasing concentration of treated nanoclays (more than 4 wt.%) the impact strength of the PP/PA66 compound slightly decreased. Ide and Hasegawa had reported that two possible chemical interactions between PP, PA66, PP-g-MAH and nanoclays might have resulted [8]. The first is when PP-g-MAH is added to PP/ PA66 compounds, the anhydride group of MAH reacts with the terminal amino group of PA66 during melt mixing resulting in the formation of PP-g-PA66 copolymer. The second chemical reaction describes the proposed interaction between nanoclay and the PPg-PA66 copolymer formed in the presence of PP-g-MAH in the PP/PA66 nanoblends. It is believed that hydrogen bonding could form between the amide group of the PP-g-PA66 copolymer and the octadecylamine group of the intercalated nanoclay. Note that this amide–amine reaction could happen when the nanoclay was exfoliated in the PP/PA66 matrix; subsequently the octadecylamine (intercalated) is capable to form a chemical linkage with PP-g-PA66 copolymer.
3.4.2. Morphological characterization 3.4.2.1. X-ray diffraction (XRD) analysis. Fig. 3A and B shows the XRD patterns in the range of 2h = 2–30° for nanoclays and unmodified and modified PP/PA66 nanocomposites nanoclays respectively. The neat and treated MMT exhibit a single peak at the low 2h region at around 2h = 7.2° and 2h = 5.9° respectively. It can be observed also that the d001 peak shift to lower angles, corresponding to an increase on the basal spacing of the clays by exchange of interlayer spacing with coniums captions. This indicates that the ammonium ions intercalate into silicate layers and expand the basal spacing [10]. In fact, the basal spacing increases from 12.18 nm of the untreated clay to 15.07 nm of the treated one. Similar observations have been reported by Xie and Gao [11]. The XRD spectra of formulations containing neat clay do not show a characteristic basal reflection of the nanoclay. This means that the clay acts as simple filler. However, the modified formulations with treated clay show the disappearance of the characteristic peak of the clay except for formulations F55 and F88. The appearance of two diffuse peaks located close to each other for F55 is explained by partial intercalation. Similar results also reported by Garcia-Lopez et al. [12]. The appearance of the peaks of the formulation F88 could be attributed to the aggregation of small portion clay layers when the clay amount is high (8 wt.%). Similar observations have been reported in literature [13]. For the remaining formulations, the characteristic peak has been disappeared, i.e. that the gallery distance of the clay in the nanocomposites might be below the resolution of the equipment used in this study [12]. These results indicate also that the PP, PA66 molecular chains may intercalate into the clay galleries and destroy the layer structure of the clay [14]. This is a clear hint that a portion of the nanoclay is partially intercalated. The absence of the characteristic clay intense peak in the nanocomposites indicates the exfoliation of the clay platelets in the PP matrix. Tang and Hu [15] attributed the absence of diffraction peaks to the delaminating of the clay. It has been also reported elsewhere that the disappearance or decrease of intensity of diffraction peaks could be attributed to the fact that the silicates are partially or completely exfoliated [16].
3.4.2.2. Scanning electron microscope analysis. Fig. 4 illustrates the morphology of the impact fractured surfaces of unmodified
Fig. 3. XRD spectra for the neat (A) and modified (B) nanoblends formulations.
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(1) Untreated Nanoclay (2)
52
Treated Nanoclay
50
(2)
5µm (a) Gr.x4000
Time (Sec)
48 46 44
(1)
42 40 38 0
2
4
6
8
Nanoclay Content (%) Fig. 5. The flammability time versus nanoclay content.
10µm (b) Gr.x2000
in the flammability time. In addition, the treatment seems to have a more pronounced effect. A 23% increase is observed only when 4 wt.% nanoclay is added and a longer flammability time is noticed with treated clay. This may be attributed to the stacking of nanoclay which creates a physical protective barrier on the surface of the material. Similar behavior has been reported by Kocsis and Apostolov [19]. 4. Conclusion
(b) Gr.x2000
20µm (c) Gr.x1000 Fig. 4. SEM micrographs of impact fractured surfaces of formulations: (a): Unmodified nanoblend F0. (b): Modified nanoblend with 5 wt.% untreated nanoclay F5. (c): Modified nanoblend with 5 wt.% treated nanoclay F55.
nanocomposites (F0) and modified ones containing 5 wt.% untreated (F5) and treated nanoclay (F55). Micrograph (a) shows a classical alloy where the particles of dispersed phase (PA66) are well anchored the matrix (PP) and a good interaction between PP and PA66. Similar observations have been reported elsewhere [10]. Micrographs (b) and (c) represent the effect of the clay treatment. A drastic change in morphology is clearly observed. Flow induced morphology has been introduced for the treated clay. Well aligned molecular chains are observed. This stacking behavior is due to the lamellar shape of the clay, the enhanced clay treatment surface and the intercalation phenomena [17]. The realised morphology shows exfoliated silicate layers distributed in the PP phase. However, there are also some layered silicate agglomerates which coexist with the exfoliated and intercalated ones in the PP phase. It also indicates the interaction between the amine groups of octadecylamine intercalate of the exfoliated nanoclay and amide groups of the PA66 and PP-g-PA66 [18]. 3.5. The fire retardancy properties Fig. 5 represents the flammability time versus nanoclay content. It can be observed that the presence of the clay leads to an increase
Based on the results of the present study, the following conclusions can be drawn: The preparation of PP-g-MAH as a compatibilizer for PP/PA66 nanocomposites was successful. The incorporation of PP-g-MA compatibilizer enhanced the impact strength and flame retardancy properties of PP/ PA66 nanocomposites. Addition of treated and untreated nanoclays led to processable nanocomposites .i.e., MFI results evidence the effect of clay treatment. The impact properties of the modified nanocomposites were improved significantly in the presence of treated nanoclays. XRD results revealed the formation of nanocomposites as the nanoclay was intercalated and exfoliated. SEM analysis showed the development of a lamellar morphology by the clay treatment of nanoclays especially by incorporation of 5 wt.% of treated nanoclay in the F55 formulations. A very important increase in the flammability time of the nanocomposites was obtained with the treated clay. References [1] Araujo EM, Araujo KD, Paz RA, Gouveia TR, Barbosa R, Ito EN. Polyamide 66/ brazilian clay nanocomposites. J Nanomater 2009;2009:5. [2] Ravi Kumar BN, Suresha B, Venkataramareddy M. Effect of particulate fillers on mechanical and abrasive wear behaviour of polyamide 66/polypropylene nanocomposites. Mater Des 2009;30:3852–8. [3] Utraki LA. History of commercial polymer alloys and blends (from a perspective of the patent literature). Polym Eng Sci 1995;35:2–17. [4] Yu ZZ, Yan C, Yang M, Mai YW. Mechanical and dynamic mechanical properties of nylon 66/montmorillonite nanocomposites fabricated by melt compounding. Polym Int 2004;53:1093–8. [5] Heino M, Kirjava J, Heitaoja P, Seppala J. Compatibilization of polyethylene terephthalate/polypropylene blends with styrene–ethylene/butylene–styrene (sebs) block copolymers. J Appl Polym Sci 1997;65:241–9. [6] Vocke C, Anttila U, Heino M, Hietaoja P, Seppälä J. Use of oxazoline functionalized polyolefins and elastomers as compatibilizers for thermoplastic blends. J Appl Polym Sci 1998;70:1923–30. [7] Kouini B. Synthesis and characterization of PP-PPgMAH-PA66 alloys filled with nanoclays. Master Thesis, Polymer Engineering Department IAP/SH; 2006. [8] Ide F, Hasegawa A. Studies on polymer blends of nylon 6 and polypropylene or nylon 6 and polystyrene using the reaction of polymer. J Appl Polym Sci 1974;18:963. [9] Huang XY, Lewis S, Brittain WJ, Vaia RA. Synthesis of polycarbonate layered silicate nanocomposites via cyclic oligomers. Macromolecules 2000;33.
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[10] Chow WS, Mohd Ishak ZA, Karger-Kocsis J, Apostolov AA, Ishiaku US. Compatibilizing effect of maleated polypropylene on the mechanical properties and morphology of injection molded polyamide 6/polypropylene/ organoclay nanocomposites. Polymer 2003;44:7427–40. [11] Xie Wei, Gao Zongming, Pan Wei-Ping, Hunter Doug, Singh Anant, Vaia Richard. Thermal characterization of organically modified montmorillonite. Thermochim Acta J 2001;367–368:339–50. [12] Garcia-Lopez D et al. Eur Polym J 2003;39:945–50. [13] Vaia RA, Jandt KD, Kramer EJ, Giannelies EP. Kinetics of polymer melt intercalation. Macromolecules 1995;28(24):8080–5. [14] MA J, Qi Z-N, HU Y. Synthesis and characterization of polypropylene/clay nanocomposites. J Appl Polym Sci 2001;82:3611–7. [15] Tang Yong, Hu Yuan. Preparation of polypropylene/layered nanocomposite by melt intercalation from pristine montmorillonite. Polym Adv Technol 2003;14:733–7.
[16] Nam PH, Maiti P, Okamato M, Kotaka T, Hasegawa N, Usuki A. A hierarchical structure and properties of intercalated polypropylene/clay nanocomposites. Polymer 2001;42(23):9633–40. [17] Kusmono, Mohd Ishak ZA, Chow WS, Takeichi T, Rochmadi. Enhancement of properties of PA6/PP nanocomposites via organic modification and compatibilization. Express Polym Lett 2008;2(9):655–64. [18] Pegoretti A, Dorigato A, Penati A. Tensile mechanical response of polyethylene – clay nanocomposites. Express Polym Lett 2007;1:123–31. [19] Kocsis J, Apostolov AA. The effect of organoclay on the mechanical properties and morphology of injection-molded polyamide 6/poypropylene nanocomposites. J Appl Polym Sci 2004;91:175–89.
Contents lists available at SciVerse ScienceDirect
Materials and Design journal homepage: www.elsevier.com/locate/matdes
Short Communication
Properties of polypropylene/polyamide nanocomposites prepared by melt processing with a PP-g-MAH compatibilizer Benalia Kouini ⇑, Aicha Serier Laboratory of Coatings, Materials and Environment, M’Hamed Bougara University, Boumerdes 35000, Algeria
a r t i c l e
i n f o
Article history: Received 22 June 2011 Accepted 15 August 2011 Available online 19 August 2011
a b s t r a c t This article presents the mechanical properties, fire retardancy behavior and the morphology of polypropylene/polyamide66 blends compatibilized with PP-g-MAH and modified with nanoclays. All PP/PA66 formulations modified with untreated and treated nanoclays were prepared by using internal mixer and single screw extruder followed by injection molding. Maleic anhydride polypropylene (MAH-g-PP) was used as the compatibilizer and the nanoclays content was varied between 0 and 8 wt.%. The mechanical and flammability properties of PP/PA66 nanocomposites were examined. Also the structure of PP/PA66 nanocomposites has been characterized by the Scanning electron microscopy (SEM) and the X-ray diffraction (XRD). The obtained results indicate that the incorporation of nanoclay has a significant effect on the strength of PP/PA66 nanocomposites. Furthermore, it was found that SEM and XRD results revealed the intercalation, exfoliation of nanaclays of nanocomposites and the flame retardancy properties were improved significantly. In addition a good balance of impact strength and flame retardancy was obtained for PP/PA66 nanocomposites in the presence of PP-g-MA compatibilizer. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction Polymer/nanoclays nanocomposites and nanoblends present unique properties that are not observed in conventional composites. The achievement of compatibilization, even by addition a compatibilizer or by in situ chemical reaction between blends components (reactive blending), has played an important role in the development of polymer blends and provides a good solution for needs of industry [1]. Engineering polymers are used in a wide number of applications [2]. The aims of the incorporation of small amounts of nanoclay (<10 wt.%) into polymer matrices may improve dimension stability, mechanical, thermal, optical, electrical, gas barrier properties, and decrease the flammability of polymer–polymer blends [1,3]. It is known that blends of PP and PA66 are immiscible throughout the whole range of composition, and thus exhibit poor properties [4]. Unfavourable interactions at the molecular level lead to high interfacial tension and make the melt mixing of the components difficult. This also leads to unstable morphology and poor interfacial adhesion, which are the main cause’s poor mechanical properties of the blends [5]. In order to prevent the incompatibility problem, a suitable compatibilizer is synthesised by grafting maleic anhydride MAH onto PP (PP-g-MAH) because it has anhydride and carboxyl groups that interact with functional groups of the PA66. ⇑ Corresponding author. Tel./fax: +213 024 91 15 05. E-mail addresses: [email protected], [email protected] (B. Kouini). 0261-3069/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2011.08.025
Numerous researchers described polymer–clay nanocomposites based on single polymer matrix. Polymer-layered silicate nanocomposites are currently prepared in four ways: in situ polymerization, intercalation from a polymer solution, direct intercalation by molten polymer and sol–gel technology. Direct polymer melt intercalation is the most attractive because of its low cost, high productivity and compatibility with current polymer processing techniques [6]. However, thermoplastic nanocomposites based on blends of two or more polymeric materials, i.e. binary or ternary blends; seem to be a new approach in the nanocomposites studies. Polypropylene and polyamide blending has been attempted to achieve improvement in mechanical properties, paintability and barrier properties, where polyamide contribute mechanical and thermal properties, while PP ensures good processing and insensitivity to moisture. The presented work in this paper focuses on the study of thermoplastic nanocomposites based on blends of PP and PA66 modified by nanoclay (treated and untreated). The aim of this work was to evaluate the effect of nanoclay loading from 2 to 8 wt.% on the rheological, mechanical, morphological and thermal properties of PP-PPgMAH-PA66 nanocomposites.
2. Exprimental work 2.1. Material used Table 1 summarizes the materials used in this work as well as the specific characteristics and the suppliers.
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B. Kouini, A. Serier / Materials and Design 34 (2012) 313–318
Table 1 Materials. Materials (trade name)
Characteristics
Supplier
Isotactic polypropylene (MOPLEN) Polyamide 66 (technylÒA216)
– semi-crystalline polymer – MFI = 28 (g/10 min), (2190 g at 230 °C) Was used as the dispersed (minor) phase in the blend
HIMONT company
Dicumyl peroxide (DCP)
– Was used for PP degradation as well as for the creation of reactive sites in order to prepare a compatibilizer for the blends – Mw = 324 (g/mole) – Purity greater than 99% – Half life time (t1/2) = 1 h at T° = 135 155 °C Was used to stabilize polypropylene against thermal oxidation especially when mixed with polyamide 66 Chemical formulae:C4H2O3
Stabilizer (irganox 1010) Maleic anhydride (MAH) Untreated nanoclays (DELLITE LVF) Treated nanclays (DELLITE 67G)
Rhone poulenc company Merck company
Nanoclay deriving from a naturally occurring especially purified montmorillonite
CIBA-GIEGY company Fluka chemical company Laviosa company
Treated with a high content of quaternary ammonium salt (dimethyl dehydrogenated tallow ammonium)
Laviosa company
2.2. Specimen preparation 2.2.1. Polypropylene grafted MAH (PP-g-MAH) The polypropylene was mixed with dicumyl peroxide DCP and maleic anhydride MAH at 200 °C for 6 min and at a speed of 70 rpm with a Rheocard Haake internal mixer to obtain the PP-g-MA compatibilizer [7,8]. The synthesized PP-g-MA compatibilizer was used to compatibilize the PP/PA66 formulations. The amount of PP-g-MAH was kept constant for all the composites.
2.2.2. PP/PA66 nanocomposite Melt compounding of the PP/PA66 (70/30) blends and nanocomposites were done by a high shear internal mixer and single screw extruder. The extrusion zone temperature ranged from 220 to 230 °C. Prior to extrusion, PA66 pellets and nanoclay were dehumidified by using a vacuum oven at 80 8C for 8 h. The extrudates were pelletized with the Haake pelletizer. The pellets were injection molded into standard tensile bar using a Battenfeld injection molding machine. Injection molding temperature ranged from 240 to 265 °C. Prior to injection molding, all pellets were dehumidified in vacuum oven (85 °C for 12 h) [6]. The tensile test specimen was molded according to ASTM D 638 standard.1
2.3. Testing 2.3.1. Infrared spectroscopic analysis Fourier-transform infrared spectroscopy (FTIR) was used to obtain some qualitative information about the functional groups and chemical characteristics of the PP-g-MAH as a compatibilizer.
2.3.4. Morphological characterization 2.3.4.1. X-ray diffraction (XRD) analysis. Wide-angle X-ray spectra were recorded with a D 500 diffractometer (Philips PW 1710, France) in step scan mode using Ni-filtered CuKa radiation (1.5406 Å). Powder samples (clay) were scanned in reflection, whereas the injection-molded compounds were scanned in transmission in the interval 2° and 30°: The interlayer spacing of the nanoclay was derived from the peak position (d001-reflection) in the XRD diffractograms according to the Bragg’s equation. 2.3.4.2. Scanning electron microscopy analysis. Notched fractured surfaces of the different nanoblend formulations were examined under a scanning electron microscopy operating at 10–15 KV. Before scanning, a conductive coating layer was spread on the surface of the sample. 2.3.5. The fire retardancy properties The flammability test (UL94HB) was conducted using the flammability tester 6151/000 that consists of a test chamber, laboratory burner, wire gauge, ring stand and metal support fixture. First the test specimens of 63 mm in width and 3.17 mm in thickness were cut from the impact test specimen. Each specimen was marked at 2 cm from one end then fixed horizontally in the support fixture. After that, the flame of the burner was adjusted to have 6 mm height of its blue portion and the burner was inclined about 45° and moved to reach the specimen edge. Finally the time needed for the flame to spread till the 2 cm mark was recorded. The results were analyzed in terms of the flammability time as a function of the nanoclays content. 3. Results and discussion
2.3.2. Melt flow index (MFI) and density measurement Melt flow index and density of various formulations were measured by using Melt Flow Indexer (at 230 °C, load 2.16 kg) and density balance (model METTLER TOLEDO).
2.3.3. Mechanical properties The impact specimens were prepared according to ASTM D 256 standard2 using a Battenfeld injection molding machine. PP, as well as, PP-PPgMAH-PA66 nanoblends was injection molded under the same conditions: the nozzle temperature was set to be 265 °C, the injection pressure was fixed at 75 bar while the screw speed is set to 70 rpm. 1 2
The tensile test specimen was molded according to ASTM D 638 standard. The impact specimens were prepared according to ASTM D 256 standard.
3.1. FTIR analysis Fig. 1 shows FTIR spectra of PP and PP-g-MAH. It illustrates the presence of two new intense overlapping absorption bands at 1785 cm 1, 1712 cm 1 and a low absorption bands around 1855 cm 1 corresponding respectively to: symmetric, asymmetric stretching and carboxylic acid. This is an indication of the grafting of Maleic anhydride MAH onto PP molecular chain. These results have been reported elsewhere [8]. 3.2. Melt flow index (MFI) 3.2.1. PP-g-MAH compatibilizer It can be shown from Table 2 an important reduction of MFI of modified PP with the constant amounts of DCP and MAH versus
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Fig. 1. FTIR spectra of PP and modified PP.
Table 2 MFI values of PP and PP-g-MAH.
Table 3 Designation, composition, and MFI and density values of samples.
Designation
PP
PP-g-MAH
MFI (g/10 min), T = 180 °C MFI (g/10 min), T = 190 °C
28 32
19 22
neat PP. This is mainly due to the grafting reaction of MAH onto PP. This may be attributed to the higher reactivity of MAH resulting in the formation of a graft copolymer, viz. PP-g-PA66 in the blends. The intermolecular bonding in the copolymer may restrict the movement of the polymeric chains in the PP/PA66 nanoblends, thus affecting the melt viscosity. When MAH-g-PP was added to PP/PA66 nanoblends, the anhydride group of MAH would react with the terminal amino group of PA66 during melt mixing to form PP-g-PA66 copolymer [9].
Sample designation
Composition
Parts (Phr)
MFI (g/ 10 min)
Density q (g/ cm3)
F0 F2
PP/PA66/PP-g-MAH PP/PA66/PP-g-MAH/ untreated nanoclay PP/PA66/PP-g-MAH/ untreated nanoclay PP/PA66/PP-g-MAH/ untreated nanoclay PP/PA66/PP-g-MAH/ untreated nanoclay PP/PA66/PP-g-MAH/ untreated nanoclay PP/PA66/PP-g-MAH/ treated nanoclay PP/PA66/PP-g-MAH/ treated nanoclay PP/PA66/PP-g-MAH/ treated nanoclay PP/PA66/PP-g-MAH/ treated nanoclay PP/PA66/PP-g-MAH/ treated nanoclay
70/30/5 70/30/5/2
76.76 67.5
0.933 0.919
70/30/5/4
43.15
0.902
70/30/5/5
7.69
0.898
70/30/5/6
6.03
0.941
70/30/5/8
6.28
0.952
70/30/5/2
32.41
0.955
70/30/5/4
8.81
0.926
70/30/5/5
4.67
0.930
70/30/5/6
3.72
0.931
70/30/5/8
3.69
0.950
F4 F5 F6 F8 F22 F44 F55
3.2.2. PP/PA66 nanoblend Table 3 represents the variation of MFI versus clay content of both treated and untreated one. It is observed that the MFI values of PP/PA66 nanoblends decreased in the presence of PP-g-MAH and nanoclays. It can be shown that the effect of the treated nanoclay is more pronounced than the untreated one. A drastic reduction in MFI values is observed with a levelling of at 5 wt.%. This may be attributed to the interaction between the amine group of the intercalation the nanoclay and anhydride group of the MAH-g-PP because When MAH-g-PP was added to PA6/PP blends, the anhydride group of MAH would react with the terminal amino group of PA66 during melt mixing to form PP-g-PA66 [10]. Another possible interaction is between the nanoclay and PA66: the NH2 group in the octadecylamine is believed to be compatible with PA66 and is capable of forming hydrogen bonds [8]. These interactions reduce the chain mobility and yield lower MFI values. 3.3. Density measurement Table 3 represents the variation of densities versus nanoclays content. The addition of nanoclay has a minor effect on the density. Although the densities of the filled nanoblends with treated nanoclay are relatively superior to the untreated ones with a maximum density obtained at 2 wt.%. The treatment seems to lead to a more compact structure.
F66 F88
3.4. Mechanical properties 3.4.1. Impact test Fig. 2 represents the notch impact strength of nanoblends versus treated and untreated nanoclays content. About 50% increase in impact strength is reached by incorporation of 4 wt.% of treated nanoclays. Note that the additions of both nanoclays and PP-gMAH in the PP/PA66 nanoblends have affected the impact strength but he incorporation of untreated clay has a minor effect on this property. The nannoclay is able to act as reinforcing filler due to its high aspect ratio and platelet structure. The enhancement in the impact strength of PP/PP-g-MAH/PA66 nanocomposites became more significant with the incorporation of 4 wt.% treated clay in the presence of the PP-g-MAH compatibilizer. This is believed to be associated with the functionality of the nanoclay which promotes the interaction between the nanoclay and PP/PA66 matrix. When the concentration of nanoclay is above the saturation level, only a part of the molecules locates in the interfacial area, and the excess is dispersed in the matrix affecting its homogeneity and consequently the mechanical properties of the composites [10].
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(1) Untreated Clay (2) Treated Clay
110
σ (KJ/m2)
100
(2)
90 80 70
(1)
60 50 40 0
2
4
6
8
Nanoclay Content (%) Fig. 2. Impact strength versus nanoclay content.
However, in the presence of 4 wt.% treated clay, the impact strength of the PP/PP-g-MAH/PA66 nanocomposites was well improved. This improvement may be attributed to the platelet structure and related anisotropy when the layers of organoclay are delaminated. Delamination (i.e. intercalation and exfoliation) of the layered silicate could also affect the crystallinity and polymorphism in both PA6 and PP. Delamination of the layered organoclay is favored by the shear forces during extrusion compounding and injection molding [10]. Fig. 2 demonstrates the effect of treated nanoclays on the impact strength of the compounds. The results indicate that with increasing concentration of treated nanoclays (more than 4 wt.%) the impact strength of the PP/PA66 compound slightly decreased. Ide and Hasegawa had reported that two possible chemical interactions between PP, PA66, PP-g-MAH and nanoclays might have resulted [8]. The first is when PP-g-MAH is added to PP/ PA66 compounds, the anhydride group of MAH reacts with the terminal amino group of PA66 during melt mixing resulting in the formation of PP-g-PA66 copolymer. The second chemical reaction describes the proposed interaction between nanoclay and the PPg-PA66 copolymer formed in the presence of PP-g-MAH in the PP/PA66 nanoblends. It is believed that hydrogen bonding could form between the amide group of the PP-g-PA66 copolymer and the octadecylamine group of the intercalated nanoclay. Note that this amide–amine reaction could happen when the nanoclay was exfoliated in the PP/PA66 matrix; subsequently the octadecylamine (intercalated) is capable to form a chemical linkage with PP-g-PA66 copolymer.
3.4.2. Morphological characterization 3.4.2.1. X-ray diffraction (XRD) analysis. Fig. 3A and B shows the XRD patterns in the range of 2h = 2–30° for nanoclays and unmodified and modified PP/PA66 nanocomposites nanoclays respectively. The neat and treated MMT exhibit a single peak at the low 2h region at around 2h = 7.2° and 2h = 5.9° respectively. It can be observed also that the d001 peak shift to lower angles, corresponding to an increase on the basal spacing of the clays by exchange of interlayer spacing with coniums captions. This indicates that the ammonium ions intercalate into silicate layers and expand the basal spacing [10]. In fact, the basal spacing increases from 12.18 nm of the untreated clay to 15.07 nm of the treated one. Similar observations have been reported by Xie and Gao [11]. The XRD spectra of formulations containing neat clay do not show a characteristic basal reflection of the nanoclay. This means that the clay acts as simple filler. However, the modified formulations with treated clay show the disappearance of the characteristic peak of the clay except for formulations F55 and F88. The appearance of two diffuse peaks located close to each other for F55 is explained by partial intercalation. Similar results also reported by Garcia-Lopez et al. [12]. The appearance of the peaks of the formulation F88 could be attributed to the aggregation of small portion clay layers when the clay amount is high (8 wt.%). Similar observations have been reported in literature [13]. For the remaining formulations, the characteristic peak has been disappeared, i.e. that the gallery distance of the clay in the nanocomposites might be below the resolution of the equipment used in this study [12]. These results indicate also that the PP, PA66 molecular chains may intercalate into the clay galleries and destroy the layer structure of the clay [14]. This is a clear hint that a portion of the nanoclay is partially intercalated. The absence of the characteristic clay intense peak in the nanocomposites indicates the exfoliation of the clay platelets in the PP matrix. Tang and Hu [15] attributed the absence of diffraction peaks to the delaminating of the clay. It has been also reported elsewhere that the disappearance or decrease of intensity of diffraction peaks could be attributed to the fact that the silicates are partially or completely exfoliated [16].
3.4.2.2. Scanning electron microscope analysis. Fig. 4 illustrates the morphology of the impact fractured surfaces of unmodified
Fig. 3. XRD spectra for the neat (A) and modified (B) nanoblends formulations.
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(1) Untreated Nanoclay (2)
52
Treated Nanoclay
50
(2)
5µm (a) Gr.x4000
Time (Sec)
48 46 44
(1)
42 40 38 0
2
4
6
8
Nanoclay Content (%) Fig. 5. The flammability time versus nanoclay content.
10µm (b) Gr.x2000
in the flammability time. In addition, the treatment seems to have a more pronounced effect. A 23% increase is observed only when 4 wt.% nanoclay is added and a longer flammability time is noticed with treated clay. This may be attributed to the stacking of nanoclay which creates a physical protective barrier on the surface of the material. Similar behavior has been reported by Kocsis and Apostolov [19]. 4. Conclusion
(b) Gr.x2000
20µm (c) Gr.x1000 Fig. 4. SEM micrographs of impact fractured surfaces of formulations: (a): Unmodified nanoblend F0. (b): Modified nanoblend with 5 wt.% untreated nanoclay F5. (c): Modified nanoblend with 5 wt.% treated nanoclay F55.
nanocomposites (F0) and modified ones containing 5 wt.% untreated (F5) and treated nanoclay (F55). Micrograph (a) shows a classical alloy where the particles of dispersed phase (PA66) are well anchored the matrix (PP) and a good interaction between PP and PA66. Similar observations have been reported elsewhere [10]. Micrographs (b) and (c) represent the effect of the clay treatment. A drastic change in morphology is clearly observed. Flow induced morphology has been introduced for the treated clay. Well aligned molecular chains are observed. This stacking behavior is due to the lamellar shape of the clay, the enhanced clay treatment surface and the intercalation phenomena [17]. The realised morphology shows exfoliated silicate layers distributed in the PP phase. However, there are also some layered silicate agglomerates which coexist with the exfoliated and intercalated ones in the PP phase. It also indicates the interaction between the amine groups of octadecylamine intercalate of the exfoliated nanoclay and amide groups of the PA66 and PP-g-PA66 [18]. 3.5. The fire retardancy properties Fig. 5 represents the flammability time versus nanoclay content. It can be observed that the presence of the clay leads to an increase
Based on the results of the present study, the following conclusions can be drawn: The preparation of PP-g-MAH as a compatibilizer for PP/PA66 nanocomposites was successful. The incorporation of PP-g-MA compatibilizer enhanced the impact strength and flame retardancy properties of PP/ PA66 nanocomposites. Addition of treated and untreated nanoclays led to processable nanocomposites .i.e., MFI results evidence the effect of clay treatment. The impact properties of the modified nanocomposites were improved significantly in the presence of treated nanoclays. XRD results revealed the formation of nanocomposites as the nanoclay was intercalated and exfoliated. SEM analysis showed the development of a lamellar morphology by the clay treatment of nanoclays especially by incorporation of 5 wt.% of treated nanoclay in the F55 formulations. A very important increase in the flammability time of the nanocomposites was obtained with the treated clay. References [1] Araujo EM, Araujo KD, Paz RA, Gouveia TR, Barbosa R, Ito EN. Polyamide 66/ brazilian clay nanocomposites. J Nanomater 2009;2009:5. [2] Ravi Kumar BN, Suresha B, Venkataramareddy M. Effect of particulate fillers on mechanical and abrasive wear behaviour of polyamide 66/polypropylene nanocomposites. Mater Des 2009;30:3852–8. [3] Utraki LA. History of commercial polymer alloys and blends (from a perspective of the patent literature). Polym Eng Sci 1995;35:2–17. [4] Yu ZZ, Yan C, Yang M, Mai YW. Mechanical and dynamic mechanical properties of nylon 66/montmorillonite nanocomposites fabricated by melt compounding. Polym Int 2004;53:1093–8. [5] Heino M, Kirjava J, Heitaoja P, Seppala J. Compatibilization of polyethylene terephthalate/polypropylene blends with styrene–ethylene/butylene–styrene (sebs) block copolymers. J Appl Polym Sci 1997;65:241–9. [6] Vocke C, Anttila U, Heino M, Hietaoja P, Seppälä J. Use of oxazoline functionalized polyolefins and elastomers as compatibilizers for thermoplastic blends. J Appl Polym Sci 1998;70:1923–30. [7] Kouini B. Synthesis and characterization of PP-PPgMAH-PA66 alloys filled with nanoclays. Master Thesis, Polymer Engineering Department IAP/SH; 2006. [8] Ide F, Hasegawa A. Studies on polymer blends of nylon 6 and polypropylene or nylon 6 and polystyrene using the reaction of polymer. J Appl Polym Sci 1974;18:963. [9] Huang XY, Lewis S, Brittain WJ, Vaia RA. Synthesis of polycarbonate layered silicate nanocomposites via cyclic oligomers. Macromolecules 2000;33.
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