Polypropylene (PP)/montmorillonite (MMT) nanocomposites micro samples was produced
by micro injection molding at concentrations 2, 6 and 10% of Nanomax. The dispersion of the nanoclay particles
in polypropylene was characterized using optical microscopy in polarized light, X-ray diffraction (XRD)
and Scanning Electron Microscopy (SEM) and the mechanical characterisation was performed using the tensile
test.
The results of x-ray diffraction indicated the formation of nanocomposites with partially exfoliated or intercalated
structures, depending on the concentration of clay, with a maximum basal spacing of 6.217 nm. The micrographs
obtained by scanning electron microscopy of fractured nanocomposite showed good dispersion of
clay in polymer matrix without the presence of clusters. The tensile strength of PP/MMT is not much improved
compared with pure PP but deformation increased significantly

Cunha, A. C.

Pontes, A. J.

Universidade do Minho: RepositoriUM

1 INTRODUCTION The miniaturization of components and systems has clearly become a global trend of the most ad-vanced technological sectors with the rapid devel-opment of micro-engineering technologies. The de-velopment of new micro devices is highly dependent on manufacturing systems that can reliably and eco-nomically produce micro parts in large quantities. [1, 2] In this context, micro-injection molding of poly-mer materials is one of the most common manufac-turing processes of micro in microsystems’ technol-ogy, mainly for thermoplastic materials, because of the short cycle time, the high degree of automation, the high accuracy and consistency, low production cost, mass production capability, applicability for many materials and good tolerance, etc. [3- 5] The injection molding is one of the most econom-ically relevant methods of processing plastics seeing as almost all thermoplastic materials can be injected, with or without charges and / or reinforcements. Of all the different polymeric materials, nanocompo-sites have been deemed very interesting for applica-tions that require high performance. This is due to the good properties that these materials present, such as mechanical properties (strength and stiffness), de-creased permeability to water and gas, thermal sta-bility, chemical resistance, surface appearance and reduced gas emissions. For this reason, nanocompo-sites are ideally suited for the microinjection mold-ing process, mainly for applications where the mi-cro-components are required to provide high module and high impact resistance. An example of this are the micro-components used in the electronics and automobile [6]. The development of new nanostructured materials has been a very hot and stimulating topic in the sphere of Science and Engineering of Materials in the past few decades. Within the area of nanomateri-als, the nanocomposites stand out to be among the most promising of this emerging "nanoEra". The nanocomposites go far beyond the performance of the conventional composites, clearing the way into into new applications and  improving the mechanical and physical properties of the polymer. These prop-erties result from the individual contributions of each component as well as from the synergistic in-teractions between the components that happen al-most at the molecular level. [7] In recent years polymer/layered silicate (PLS) nanocomposites have attracted great interest, both in industry and in academia, because they often exhibit remarkable improvement in materials properties when compared with virgin polymer or conventional microand macro-composites. These improvements can include high moduli, increased strength and heat MicroInjection of Polipropylene with Nanoclays A. C. Cunha Dept. of Polymer Engineering, University of Minho, Guimarães, Portugal  A. J. Pontes IPC – Institute for Polymer and Composites, University of Minho, Guimarães, Portugal       ABSTRACT: Polypropylene (PP)/montmorillonite (MMT) nanocomposites micro samples was produced by micro injection molding at concentrations 2, 6 and 10% of Nanomax. The dispersion of the nanoclay parti-cles in polypropylene was characterized using optical microscopy in polarized light, X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) and the mechanical characterisation was performed using the ten-sile test. The results of x-ray diffraction indicated the formation of nanocomposites with partially exfoliated or interca-lated structures, depending on the concentration of clay, with a maximum basal spacing of 6.217 nm. The mi-crographs obtained by scanning electron microscopy of fractured nanocomposite showed good dispersion of clay in polymer matrix without the presence of clusters. The tensile strength of PP/MMT is not much im-proved compared with pure PP but deformation increaresistance, decreased gas permeability and flamma-bility, and increased biodegradability of biodegrada-ble polymers. [8-10] The main reason for these marked improvements stem from the large aspect ratio of layered silicate, for example, montmorillonite (MMT). Each individ-ual layer of MMT has a thickness on the order of 1 nm with lengths ranging from 100 to 300 nm. [9, 10] The properties of the nanocomposites are strongly influenced by how the clay is dispersed in the poly-mer. Polymer-clay nanocomposites can be classified morphologically into (a) separated, (b) intercalated, and (c) exfoliated (delaminated) states, as shown in Figure 1.   Figure 1 - Schematic showing polymer-clay nanocomposite classifications. The most desirable morphological state for the polymer-clay nanocomposites is exfoliation, fol-lowed by intercalation. [10-12]   2 EXPERIMENTAL 2.1 Micro parts The micro parts produced for this work are two (Figure 22), and their dimensions have been adapted to the process of microinjection.    Figure 2 - Micro samples a) Traction b) Impact 2.2 Material The polypropylene (PP) Domolen 1100N was used as the matrix and the nano clay montmorillonite as the reinforcement; this is presented in the form of masterbatch (Nanomax), provided by the company Nanocor. The nanocomposites contained 2, 6 and 10% of masterbatch.  2.3 MicoInjection Moulding The microinjection machine used to produce nanocomposites was BOY 12A, equipped with a plasticization screw of 14mm diameter. The condi-tions were set in the typical values used in this type of processing for these materials and in the technical specifications. In order to achieve the best processing conditions for this material we began to inject some parts until we had stabilized the process and in this way obtain-ing the ideal conditions for the production of the samples, which resulted in the following conditions:  Table 1 - Processing Conditions for micro samples with PP Processing Conditions PP + Nanoclay Barrel Temperature (ºC) 140 160 185 215 230 Injection pressure (bar) 120 Mold temperature (ºC) 80 Injection Speed (mm/s) 240 Cushion (mm) 2  2.4 Characterization 2.4.1 Optical microscopy of polarized light The optical microscopy analyses was been used in some studies as a preliminary method of observation of the microstructure to observe the existence of clusters. In this work, we used an optical microscope, polar-ized light, Olympus model B; the observations were performed using a 3.3 x ocular and an objective magnification of 4, 10 and 20 x.  2.4.2 Scanning electron microscopy The technique of the scanning electron microsco-py is used to analyze the microstructure of the sam-ples, it allows to characterize the morphology of the particles of clay. The samples were fractured and coated with gold-palladium alloy and later observed in a scanning electron microscope of ultra high reso-lution (New Nanos 200) in the Materials Characteri-a) b) zation’s Services’ Laboratory at the University of Minho (SEMAT / A)  2.4.3 X-ray diffraction The materials were characterized according to type of structure obtained by the diffraction of the X-rays, the equipment used was the Bruker AXS NanoStar, from the Materials Characterization’s Services’ Laboratory, University of Minho (SEMAT / A). This equipment used a potential difference in the tube 40KV, an electrical current of 35mA and CuKα radiation (λ = 1.5406 Å). The scan was used in the range of 2θ from 1 to 24 degrees.  2.4.4 Tensile Test The tensile tests were performed in Microtester, a homemade machine, specially designed to character-ize the mechanical behavior of micro-components. The tests were performed at room temperature and at a constant speed of 1 mm / minute with a load cell of 500N.  3 RESULTS AND DISCUSSION 3.1 Morphology of nanocomposites Optical microscopy of polarized light Through the optical microscope, in bright field, we could verify the existence of clusters in some of the sam-ples. In the impact and tensile samples, with 2% of nanoclays, there wasn’t any cluster visible this is due to the reduced amounts of nanoclays and to the high shear rate. The same happened with the 6 and 10% nanoclays tensile samples, where there wasn’t any visible agglom-erate due to the samples’ geometry being thin when compared to the impact samples’, so promoting higher shear rate and, thus, better dispersion. Moreover, the im-pact samples with 6 and 10% of nanoclays present, in certain areas of the sample, the existence of agglomerate. This is due to the thickness of the sample, which being higher than the tensile’s test-piece results in that the ma-terial isn’t subject to higher shear rate, and this in turn results in the presence of aglomerates.   Figure 3 - Longitudinal section of tensile samples with 6% nanoclays a)polarized light b)bright field (magnification 20x3.3)   Figure 4 - Longitudinal section of impact samples with 10% of nanoclays a)polarized light b)bright field (Magnification 4x3.3)   3.2 Scanning Electron Microscopy The images of the fracture surfaces of the nano-composites with different compositions, obtained by SEM, showed that there is a good distribution and dispersion of reinforcement in the matrix. When analyzing the tensile and impact samples with lower magnification it is noticeable that these present a good distribution/dispersion of nanoclays, however, when the magnification is increased it ap-pears that the distribution is not 100% homogeneous, only this is due to the fact that it is a very small sam-ple area that is being analyzed. This observation is well illustrated by the cross sections micrographs of the nanocomposites prepared with different compo-sitions (2, 6 and 10% masterbatch), obtained by SEM and represented in Figure 5. Figure 6 a) shows that the layers of nanoclays have lengths and thickness in the range of nanome-ters. In Figure 6 b) can be verified that nanoclays’ layers seems to have a good adhesion between the polymer and the nanofiller, which will be of signifi-cant importance to improve the mechanical proper-ties. Good adhesion, good distribution and a disper-sion of the layers of nanoclays contributes to a significant increase in properties in relation to the pure polymer.                Figure 5 - Fracture surface of tensile samples containing 6% nanoclays with a magnification of a) 10 000x b) 50 000x    Figure 6 - Detail of the size of the layers of nanoclays. a)magnification 5000x b)magnification 150000x  3.3 X-rays Diffraction The Figure 7 shows the XRD results obtained for the masterbatch and nanocomposites. The diffraction peaks of interest in the characterization of the nano-composites are those that appear in the regions be-tween the 1º and 3º; these peaks are related to the ba-sal spacing of clay. To complete this analysis, the ideal would be to analyze the XRD also for nanoclay natural (montmorillonite), but due to the absence of this material it wasn’t possible to make the diffrac-tion of X-rays. However, according to the literature [11, 13, 14, 15, 16], the montmorillonite has diffrac-tion peaks between 3 (d = 2.8 nm) and 5 (d = 1.7 nm), and its peak appears primarily at 2θ = 4 (d = 2.1 nm). After analyzing the results obtained, it can be said that the masterbatch already has an interleaved struc-ture, because the montmorillonite presents a peak at the 4 ° with a basal spacing of 2.1 nm, while the masterbatch’s peak of clay has a displacement of 1.57 and the basal’s spacing was increased to 5.623 nm, showing that there is an intercalation of the PP between the layers of clay. Thus, as the masterbatch   Figure 7 – XRD graphics of masterbatch and PP nanocompo-sites (samples Traction) already has a structure intercalated, the nanocompo-sites will possibly also present an exfoliated or inter-calated structure. This is something that was predict-b) a) a) b) ed by the analysis in the SEM, which shows a struc-ture with good distribution / dispersion. For the tensile nanocomposites, all the composi-tions show an intercalated structure. Not only the masterbatch has a basal spacing greater than the montmorillonite, but also the compositions with 2, 6 and 10% of masterbatch have a slightly higher basal spacing than the masterbatch as can be seen from the Table 2. Table 2 – basal spacing of the  nanocomposites Sample 2θ Basal spacing (nm) Masterbatch 1,57 5,623 PP + 2% Tensile 1,50 5,885 PP + 6% Tensile 1,42 6,217 PP + 10% Tensile 1,45 6,088 PP + 2% Impact 1,51 5,846 PP + 6% Impact 1,52 5,808 PP + 10% Impact 1,60 5,518  The structure presented in the impact samples is also interspersed, while, for tensile samples, the val-ues for the diffraction peaks are very similar to the masterbatch. As shown in the Table 2, the basal spacing for these nanocomposites did not vary much and are slightly lower than the tensile test-piece. However, excluding the sample with 10%, these spacings are greater than in the masterbatch. Some studies [17] showed that from a certain percentage of nanoclay up the basal spacing of the nanoclay in the PP and in other polymers decreased with the increase of the percentage of the nanoclay. This is because high amounts of clay can lead to a non-uniform dispersion, hindering the penetration of the polymer into the layers of the nanoclay.  3.4 Tensile test The results of the tensile tests for the PP nano-composites are summarized in Table 3. The values of maximum stress were very similar for both the pure PP and nanocomposites. However, the nanocomposites with only 2% of masterbatch (49.11 MPa) have a higher maximum stress than the pure PP (38.67 MPa) and the other compositions. As the concentration of nanoclays increases, the Stress at rupture decreases, and there is a greater de-crease in the compositions of 6 and 10% compared to the pure PP and the PP with 2% masterbatch; the stress in the compositions of 2 and 6% of mas-terbatch reduces from 22.4 MPa to 1.75 MPa. The fact that the stress at rupture is less in the compositions with a higher quantity of nanoclays is due to the greater quantity of nanoclays layers dis-persed in the matrix. The good adhesion between the nanoclays and the polypropylene, promotes the slid-ing of the nanoclays when subjected to the tensile forces. Contrary to what is presented in the literature [9, 11, 18], where the results show that the defor-mation at rupture decreases with increase of the per-centage of nanoclays in the matrix, the results ob-tained in this study show the opposite, ie, the deformation at the rupture increases with the in-crease of nanoclays. This observation is due to the fact that we have used a lower test speed (1mm/min) and masterbatch. When is used a masterbatch that al-ready contains the clay modified to be compatible with the polymer, promotes good adhesion and in-teraction between the matrix and nanoclay, creating strong links between them, and consequently an in-crease in deformation [19]. A good distribution and dispersion of clay layers in the matrix leads to the improvement tensile strength, which can be attributed to the tenacity of the layers of nanoclay that contribute to the for-mation of immobilized or partially immobilized pol-ymeric phases. It is also possible that the orientation of the layers of clay as well as the molecular orienta-tion contribute to the observed reinforcement effects [11].   Table 3 - Summary of mechanical properties of nanocomposites Properties PP 0% PP 2% PP 6% PP 10% Maximum Stress (MPa) 38,67 ±4,533 39,11 ±2,636 37,616 ±1,571 37,265 ±0,786 Stress at rupture (MPa) 29,882 ±5,56 22,411 ±11,244 1,757 ±0 1,757 ±0 Deformation at rupture (%) 155,803 ±43,011 164,7 ±56,798 286,958 ±80,9 367,146 ±87,890         4 CONCLUSIONS The methodology used in the preparation of the nanocomposites resulted in materials with inter-spersed structures in all the compositions. The larg-est basal spacing (6.217 nm) was observed in the tensile samples, in the composition with 6% of nanoclays. The images of the microstructure of the nano-composites revealed homogeneity, which indicates that there was a good dispersion of the clay layers in the matrix of polypropylene. 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Microinjection of polipropylene with nanoclays

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Universidade do Minho: RepositoriUM