In this study, high-density polyethylene (HDPE)/exfoliated graphite nanoplatelet (xGnP) composites reinforced with a 2 wt.% concentration of nano-magnesia (n-MgO) were fabricated using an injection moulding machine. The thermal properties and morphological structures of the composites were investigated. The XRD results showed the peaks of xGnP and n-MgO, where the intensity of the xGnP peaks became stronger with adding increasing amounts of xGnP into the polymermatrix. In terms of morphology, some agglomeration of particles was observed within the matrix, and the agglomeration decreased the thermal properties of the composites. The nanocomposites showed less thermal stability than the pristine polymer. The reduction in the onset temperature compared to that of neat HDPE was attributed to less adhesion between the fillers and the matrix. In addition, the crystallinity was reduced by the addition of fillers.
In the last era, the plastic industry had witnessed rapid growth in the production of synthetic polymers such as polyethylene (PE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), polyvinyl alcohol (PVA) and polyvinyl chloride (PVC). Accordingly, plastics have become inseparable and indispensable components of society. The use of plastics has significantly increased to meet the demands of society by enabling affordable manufacturing of numerous products for packaging, safety and protection, service, lightweight components in cars and aircraft, mobile phones, construction, medical devices, toys and other uses [
The thermal degradation of polymers has been studied in recent decades [
n-MgO and xGnP with a purity of 99.9% were used in this study as filler materials. The n-MgO and xGnP were purchased from Tritrust Industrial Co., China. The xGnP has a diameter of 10 μm and a thickness of 5 nm, whereas the MgO nanoparticles have a particle size of 10 nm. The HDPE matrix particles were supplied by SABIC, Kingdom of Saudi Arabia.
In this study, the different weight percentages of xGnP and n-MgO reinforcement used are shown in
The weighed powders were mixed using a mechanical disperser to obtain a homogeneous distribution of the filler materials in the HDPE matrix. Subsequently, the mixed powders were put into a Battenfeld HM 1000/750 injection moulding machine to produce the samples. Injection moulding was carried out using an L/D ratio of 22, screw diameter of 45 mm, a clamping force of 10 tons, barrel and nozzle temperatures of 230˚C, pressure of 3000 psi, and mould temperature of 20˚C. The different HDPE-xGnP/n-MgO composites shown in
XRD (Schimadzu 7000, Japan) was used to confirm the existing phases of the composites. Wide-angle X-ray diffraction (WAXD) patterns, which provide the characteristics of the nanoparticles, were obtained with an X-ray diffractometer equipped with CuKα radiation. The survey scan was run between 10˚ and 90˚ with a scanning speed of 2˚ per minute.
The samples were prepared by fracturing (cryo-fracturing) the samples into 1 cm long pieces at the neck portion of tensile samples and attaching each to a 12.5 mm diameter Al stub with sticky 12 mm diameter C tabs. The samples were Au-Pd sputter-coated for 1 - 2 minutes at a deposition current of 25 mA and a partial pressure of ~0.1 TorrAr. The samples were then transferred to be examined by SEM.
A spectrogram of the composite surface was collected using an FTIR 783 Perkin Elmer spectrometer. Each spectrum was obtained for 24 scans between 4000 and 400 cm−1 at intervals of 1 cm−1 with a resolution of 4 cm−1. An FTIR spectroscopic study was performed to assess the structural degradation of the immersed samples or changes in the chemical structure.
TGA was performed using a TGA Q500 instrument. The samples were placed in
n-MgO (wt.%) | xGnPs (wt.%) | HDPE (wt.%) | Sample |
---|---|---|---|
0 | 0 | 100 | Neat HDPE |
2 | 1 | 97 | HDPE-1G-2MgO |
2 | 2.5 | 95.5 | HDPE-2.5G-2MgO |
2 | 5 | 93 | HDPE-5G-2MgO |
a platinum crucible and heated in a nitrogen-filled environment with a heating rate of 20˚C/min from room temperature to 600˚C. The initial weights of the samples were approximately 22 mg. The data extracted from the test were used to plot both the weight loss as a function of temperature and the thermogravimetric analysis/derivative thermal gravimetry (TGA/DTG) relations.
Wide angle X-ray diffraction (WAXD) is a widely applied technique in the study of intercalation or exfoliation and has an advantage for composite characterization. X-ray diffraction (XRD) is used to explain the intercalation or exfoliation structures by utilizing methods for the inter-gallery spacing calculations, which are responsible for identification of the composite structures [
Samples | 2 Theta | d-spacing [Å] |
---|---|---|
100 wt. % HDPE | 21.48 | 4.13 |
HDPE/1xGnP/2n-MgO | 21.50 | 4.12 |
HDPE/2.5xGnP/2n-MgO | 21.53 | 4.12 |
HDPE/5xGnP/2n-MgO | 21.52 | 4.12 |
the distance between planes of atoms that gives rise to diffraction peaks. Each peak in a diffractogram results from a corresponding d-spacing. The planes of atoms can be referred to as a 3D coordinate system and can be described as a direction within the crystal. Therefore, the d-spacing, in addition to having a dimension, which is usually given in Ångstroms, can be labelled with a plane direction, hkl. With the development of nanotechnology, an increasing number of materials with d-spacings in the nanometre range have been made.
The TGA/DTG analysis of monolithic HDPE and HDPE/xGnP/n-MgO composites during heating from 20˚C to 600˚C/min are shown in
by increasing the composite loading, as shown in
These findings are in close agreement with those in the study by Wegrzyn et al. [
To investigate the surface morphology of the composites, SEM micrographs were taken for the monolithic HDPE and HDPE-xGnP/n-MgO composites, as shown in
Samples | Tm (˚C) | Tc (˚C) | Crystallinity (%) |
---|---|---|---|
100 wt.% HDPE | 131 | 117 | 62.83 |
HDPE/1xGnP/2n-MgO | 131.53 | 117.31 | 62.22 |
HDPE/2.5xGnP/2n-MgO | 130 | 118 | 61.6 |
HDPE/5xGnP/2n-MgO | 118.74 | 130 | 61.5 |
of aggregation. This is due to the high affinity between the particles and polymer during fabrication at the optimal injection conditions. Furthermore, less intercalation was obtained in the polymers with the addition of 5 wt.% xGnP, which could be associated with eitherparticle agglomeration or the possibility of losing the platelet morphology of xGnP, leading to the development of a rolled-up structure or folds during preparation and dispersion differences [
HDPE/xGnP/n-MgO composites were fabricated using an injection moulding machine. The present results show that the combination of xGnP and n-MgO filler provides varying degrees of reduction in the thermal properties of composites. Generally, all of the composite samples revealed lower thermal properties compared with the monolithic HDPE. This reduction can be attributed to the agglomeration of particles within the matrix as a consequence of inadequate matrix-reinforcement adhesion. Other preparation method such as in situ polymerization, can be utilised for investigating the intercalation level.
The author would like to thank SABIC for their assistantship and tremendous help and contribution in the preparation of the composites and their characterization.
The author declares no conflicts of interest regarding the publication of this paper.
Alateyah, A.I. (2019) High-Density Polyethylene Based on Exfoliated Graphite Nanoplatelets/Nano-Magnesium Oxide: An Investigation of Thermal Properties and Morphology. Materials Sciences and Applications, 10, 159-169. https://doi.org/10.4236/msa.2019.103013