Polyoxymethylene is a material which has excellent mechanical properties similar to Nylon-6 filled with 30% GF. 75% POM and 25% glass fibre (POMGF) were blended with nanoclay to increase the tensile and flexural properties. Samples were extruded in twin screw extruder to blend POMGF and (1%, 3%, and 5%) Cloisite 25A nanoclay and specimens were prepared by injection moulding process. The tensile properties, flexural properties, impact strength, and hardness were investigated for the nanocomposites. The fibre pull-outs, fibre matrix adhesion, and cracks in composites were investigated by using scanning electron microscopy. 1% POMGF nanocomposite has low water absorption property. Addition of nanoclay improves the mechanical properties and thermal properties marginally. Improper blending of glass fibre and nanoclay gives low tensile strength and impact strength. SEM image shows the mixing of glass fibre and nanoclay among which 1% POMGF nanocomposite shows better properties compared to others. The thermal stability decreased marginally only with the addition of nanoclay.
POM composites composed of abacus and cellulose fibres were studied in which the tensile strength of abacus fibre was improved by the addition of natural fibre without increasing its density [
The field of clay-based polymer nanocomposites has attracted many researchers for the last three decades for their tremendous improvement in properties resulting from the long range interactions between polymer and surface of the clay. Blending different polymers has been a very convenient and attractive method for the production of materials with specific end-use applications. However, general immiscibility of the polymers associated with inherent thermodynamic incompatibility results in the formation of immiscible polymer blends in most of the cases and, thus, leads to the formation of phase separated blend with matrix-droplet morphology, in which the major constituent forms the matrix phase and the minor component acts as the dispersed phase [
Polyoxymethylene (POM) is an engineering thermoplastic used in precision parts that require high stiffness, low friction, excellent dimensional stability, high heat resistance, and good dielectric property. Because of its 70% crystallinity level and formation of spherulites (spherical semicrystalline regions) [
In this work, POM was mixed with the glass fibre and Cloisite 25A and reinforced and toughened POMGF nanocomposites were prepared. The effect of glass fibre and nanoclay addition on the mechanical properties and crystallization behaviour and the reinforcing mechanism of POM were investigated. The composites presented wide applications as construction material, such as fixtures, pump and fan propellers, gears, bearing liners, and rings.
The POM used in this work is a commercial grade without any additives supplied by DuPont, USA, in the form of pellets with melt flow index 10 g/10 min and a density of 910 kg/m3. Cloisite 25A (a montmorillonite modified with methyl) was supplied by Southern Clay Products, Inc., USA. Hereafter Cloisite 25A is referred to as nanoclay. Chopped E-GF (glass fibre) surface was treated with silane and having a density of 2550 kg/m3, average diameter of 14
Compositions were physically premixed and then compounded using the Brabender, KETSE 20/40 (Germany) twin screw extruder. The materials extruded from both formulations were pelletized into length of about 6 mm. In order to produce POM/GF/NC composites, the different ratios of the POM/NC and GF were physically mixed and recompounded in a twin screw extruder, using the same temperature profile and screw speed of 100 rpm. The dumbbell-shaped tensile and impact tests specimens, according to ASTM standard D63814 and ASTM standard E 23, respectively, were then injection-moulded using a Boy 55 M (Germany), with a 55-ton clamping force injection moulding machine. The processing temperature was set between 175°C and 185°C and the mould temperature was set at 25°C. The screw speed was maintained at 30–50 rpm.
Tensile and flexural tests were performed at a test speed of 2 mm/min according to EN ISO 527 and EN ISO 178 using a Zwick UPM 1446 machine. All tests were performed at room temperature (23°C) and at a relative humidity of 50%. Instrumented notched Charpy impact test was carried out using 10 notched samples according to EN ISO 179 using Zwick Charpy impact machine. Impact tests were carried out using a low velocity falling weight impact tester at room temperature in penetration mode according to EN ISO 6603-2. The impactor’s mass was 3.65 kg and the impact velocity was 4.4 m/s.
Hardness is tested by Rockwell hardness apparatus and Shore D.
Water absorption test for POM nanocomposites was performed as per ASTM D570. The specimens were immersed in distilled water at room temperature for 24 hours. The percentage increase in weight of the specimen after the immersion was calculated by the following formula:
Cloisite 25A has good mechanical properties and low water absorption.
The thermogravimetric analysis was done under nitrogen atmosphere in Perkin Elmer instrument, Pyris 7 software at scanning rate of about 10 to 200°C/min.
DSC experiments were performed with a Perkin Elmer Diamond DSC (USA). Each sample was subjected to heating and cooling cycles at a scanning rate of 10°C/min under nitrogen atmosphere with the nitrogen flow rate of 20 mL/min, in order to prevent oxidation. The test sample of between 5 and 10 mg was crimped in an aluminum pan and tested over a temperature range of 0°C–190°C.
X-ray diffraction (XRD) patterns of clay-polymer mixtures and the resulting coatings were studied using analytical (model Philips PW 1840) X-ray diffractometer.
The morphology of fibre reinforced POMGF nanocomposites was investigated using the scanning electron microscope (SEM) MV2300, by Cam Scan Electron Optics. Flexural samples were fractured after being submerged in liquid nitrogen and test specimens were prepared sputter-coated with gold.
The mechanical properties of the POMGF nanocomposites such as tensile strength, flexural strength, and impact strength have been evaluated and presented in Table
Mechanical properties.
Material | Tensile strength (MPa) | Flexural strength (MPa) | Impact strength (Charpy test) (Kg/m2) | Impact strength (Izod test) (Kg/m2) |
---|---|---|---|---|
POM | 60.27 | 86.57 | 10.823 | 7.191 |
POMGF | 70.34 | 96.37 | 6.352 | 4.967 |
1% POMGF | 66.15 | 102.10 | 6.303 | 4.042 |
3% POMGF | 57.83 | 89.76 | 4.625 | 4.082 |
5% POMGF | 55.21 | 78.74 | 6.460 | 3.859 |
Addition of nanoclay resulted in the decrease in tensile strength with increase in nanoclay content. The decrease in the tensile properties could be due to the immiscibility of the polymer blends with the nanoclay due to weak interfacial interaction between nanoclay and polymer. These observations suggested that the composition of clay has a strong influence on the structural properties of POMGF nanocomposites.
Considering the composition analysis, 1% nanoclay addition showed better tensile strength compared to other concentration ratios and was found to be the optimum composition.
The flexural strength test results of POMGF nanocomposites at different nanoclay compositions are given in Table
The impact strength results of POMGF composites with and without nanoclay are listed in Table
Hardness is an important property among mechanical properties. Addition of nanoclay increases the hardness of the materials. 1% POMGF nanocomposite shows increase in hardness of 84. It shows the strong glass fibre filler added in the composition.
In case of MFI, the addition of glass fibre decreases the MFI from 10.58 to 4.54 g/min. The decrease in melt flow is due to the high viscous nature of glass fibre. The decrease of MFI from 10.58 to 5.73 g/10 min is due to the high viscous nature of nanoclay which resists the flow of melt. Table
Hardness, MFI, and water absorption.
Material | Hardness | MFI |
Water absorption |
---|---|---|---|
POM | 82.25 | 10.58 | 0.051 |
POMGF | 83.5 | 4.54 | 0.037 |
1% POMGF | 84 | 9.97 | 0.02 |
3% POMGF | 75.4 | 7.23 | 0.051 |
5% POMGF | 70.8 | 5.73 | 0.078 |
Thermogravimetric data of composites.
Material | Onset temperature ( |
Peak temperature ( |
Weight loss (%) at peak second temperature |
---|---|---|---|
POM | 301.73 | 323.16 | 99.753 |
POMGF | 305.99 | 340.66 | 99.601 |
1% POMGF | 294.46 | 320.53 | 100.016 |
3% POMGF | 281.42 | 318.27 | 99.462 |
5% POMGF | 276.15 | 293.75 | 99.084 |
From the water absorption values found in Table
Thermal stability of polymeric composites was shown to be strongly dependent on the degree of nanoclay concentration. At relatively low concentration of nanoclay, the initial thermal stability increased reaching maximum of 1% and decreased when the nanoclay concentration was more than 1%. Thus optimal thermal stabilization was observed at 1% nanoclay concentration. This may be due to internal thermal stability of the clay layers. The shift towards higher temperature was found to be due to the formation of a high performance carbonaceous silicate char residue on the surface of the insulates, the underlying material, and slow escape of volatile products generated during decomposition. Table
TGA of virgin POM, POMGF, and POMGF nanocomposites.
The melting and crystallization behavior of virgin POM, POMGF, and their nanocomposites were investigated using DSC and are listed in Table
Melting and crystallization behavior.
Sample number | Material | Melting point °C |
|
|
% of crystallinity |
---|---|---|---|---|---|
1 | POM | 170.6 | 102.5 | −109.3 | 3.99 |
2 | POMGF | 174 | 155.2 | 157 | 1.03 |
3 | 1% POMGF | 168.3 | 80.16 | 90.8 | 6.32 |
4 | 3% POMGF | 165.4 | 95.53 | 97.6 | 1.25 |
5 | 5% POMGF | 157.1 | 155.2 | 157 | 1.03 |
DSC heating curve.
The degree of crystallinity (
The degree of crystallinity is an important parameter to define chemical and physical properties of polymeric material. The changes in the interlayer distance of clay can generally be elucidated using XRD. A shift to lower angles in the peak represents the formation of an intercalated structure, whereas the disappearance of the peak signals the potential existence of an exfoliated structure. Figure
XRD of POM, POMGF, and nanocomposites.
X-ray diffraction patterns of POM, POMGF, and nanocomposites are illustrated in Figure
The morphology of prepared composite has been investigated using scanning electron microscopy (SEM). SEM images of fractured surface of impact specimen as shown in Figures
SEM of 1% POMGF.
SEM of 3% POMGF.
SEM of 5% POMGF.
Glass fibre reinforced POM nanocomposites were prepared at various weights of nanoclay. 25% glass fibre and 75% POM (POMGF) were optimized for blending composition. Mechanical properties slightly decreased on addition of glass fibre due to the immiscibility of nanoclay. Tensile strength of nanocomposites decreases due to the improper blending of glass fibre and nanoclay. Flexural strength increases for 1% POMGF nanocomposite. But it has good hardness and low water absorption properties. The thermal stability decreased marginally with the addition of nanoclay.
The authors declare that there is no conflict of interests regarding the publication of this paper.