The synergetic effect of calcium carbonate (CC)-fly ash (FA) hybrid filler particles on the mechanical and physical properties of low density polyethylene (LDPE) has been investigated. Low density polyethylene is filled with varying weight percentages of FA and CC using melt casting. Composites are characterized for mechanical, thermal, microstructural and physical properties. Results show that the flexural strength increases with increases in FA content of the hybrid filler. It is evident from the study that to achieve optimum density a certain combination of both fillers need to be used. The optimum combination of CC and FA for a higher density (1.78 g/cm3) is found to be at 20 wt% FA and 30 wt% CC. An increase of 7.27% in micro-hardness over virgin polyethylene is obtained in composites with 10 wt% FA and 40 wt% CC. The presence of higher amount of CC is seen to be detrimental to the crystallinity of composites. X-ray, FTIR and DSC results show that composite with 45 wt% CC and 5 wt% FA exhibits a typical triclinic polyethylene structure indicating that the composite is amorphous in nature. There was the synergy between FA and CC fillers on flexural strength and crystallinity of composite. However, the fillers show the antagonistic effect on energy at peak and micro-hardness.
Low density polyethylene resins are among the most versatile polymers, but their uses are limited due to several drawbacks, namely low strength, stiffness and poor heat resistance. To overcome these drawbacks and to prepare material with improved properties, fillers are incorporated into the matrix [
Coal is a fossil fuel that has been largely utilized for electricity generation in some countries of the world including the United Kingdom and South Africa. In Nigeria, there is an estimated deposit of 4.0 billion tonnes of coal yet untapped [
Calcium carbonate (CC) is an inorganic, low cost and non-toxic substance that has been widely used as filler in polymer composite for improved properties. In our previous publications, the significant improvement in the mechanical properties of flexible polyurethane foam [
Atikler et al. [
Calcium carbonate (CC) (20 µm) and fly-ash particles (FA) (60 µm) are obtained from the Federal Institute of Industrial Research, Oshodi (FIIRO), Lagos, Nigeria.
LDPE (50 wt%) is blended with FA and CC at varying proportion of two fillers while keeping the amount of the
. Composition of fillers
Filler | % composition | ||||||
---|---|---|---|---|---|---|---|
SiO2 | Al2O3 | Fe2O3 | CaCO3 | CaO | Al | LOI | |
FA | 50 | 20 | 15 | - | 10 | - | 5 |
CC | 8 | - | - | 88 | 1 | 3 | - |
hybrid filler constant at 50 wt%. The blend is heated to 145˚C in aluminium pot using an electric stove under atmospheric pressure. The melt is cast into a metallic mould and allowed to cool to room temperature before removal. Cast samples are further prepared for various characterizations.
Densities of all samples are determined by first weighing the samples and dividing the known weights by their respective volumes using Equation (1).
To determine the rate of water absorption of the samples, samples are initially dried in an oven at 50˚C, weighed and suspended in a beaker of distilled water and reweighed at an interval of 24 hours for seven days. Water absorption rate is determined according to Equation (2).
where W1 = initial weight of specimen (dry weight);
W2 = final weight of specimen.
The rate of melt flow in (g/10min) is measured with the aid of a manually constructed melt flow indexer (see
Also
where w = the mass of material in grams flowing out;
t = constant time for all samples in seconds. The time used in this case was 45 seconds.
The flexural properties of all the samples are determined using a Testometric M500 universal tester according to ASTM D7264 at a cross-head speed of 40 mm/min, maintaining a span of 30 mm.
ALeco LM700AT Vicker’s hardness tester with a pyramidic diamond indenter and 1 kgf load is used to investigate the micro-hardness of all samples.
A Panalytical X’Pert Pro MPD model diffractometer equipped with an X’celerator detector and GAADS software are used to observe the diffraction pattern of the composite. The diffraction patterns are collected by using small mass of the polymer composite placed on a rectangular flat glass 45 cm by 3.6 cm to ~1 mm thic over a rectangular space of 1.5 cm by 2 cm at a scan range of 5˚ - 78˚ (2θ) in step size of 0.0334, using a Ni filter. The diffraction patterns are generated for 7 - 8 min with the X-ray beam set to 40 kV and 40 mA at 29˚C (inner tem-
Melt flow indexer
perature), 25˚C (outside temperature). The glass spatula and the rectangular flat glass are cleaned with a tissue paper soaked in methanol before and after each sample test.
A Hitachi S-4700 model variable pressure Scanning Electron Microscope (SEM) fitted with an EDAX head is used to observe the longitudinal features of the polymer composite. The samples to be observed under the SEM are mounted on conductive adhesive tape prepared by placing the samples on circular disclined with carbon and coated with Au for 5 minutes to enable it conduct electricity using an E-1010 HITACHI model machine.
The DSC curves of polymer composites are recorded on a DSC Q200 machine with a temperature minimum of 40˚C and heating rates of 5˚C/min, 10˚C/min, 15˚C/min and 20˚C/min. The samples are heated to 200˚C, cooled to the minimum temperature and heated to 200˚C.
FTIR spectra are obtained by means of a Nicolet 6700 M spectrometer in transmission mode. Finely divided 10mg samples of the material surface are ground and dispersed in a matrix of KBr (500 mg), followed by compression at 22 - 30 MPa to form pellets. The transmittance measurements are carried out in the range of 400 - 4000 cm−1 at a resolution of 4 cm−1.
Flexural strength responses of polyethylene-CC/FA composite
The variation of energy at break of composites with filler content is shown in
Flexural modulus responses of polyethylene-CC/FA composite
Energy to peak responses of polyethylene-CC/FA composite
The variation of composite micro-hardness with filler content is shown in
The variation of density of composite with filler content is shown in
Hardness responses of polyethylene-CC/FA composite
Density of polyethylene-CC/FA composite
Melt flow index (MFI) reflects the ease of flow of a molten polymer and is usually employed in conjunction with melt flow rate (MFR) to define different grades of polyolefins [
Water absorption of polyethylene-CC/FA composite
Melt flow rate of polyethylene-CC/FA composite
the study of Şirin et al. [
The X-ray diffraction pattern (45 wt% CC and 5 wt% FA composite) in
XRD of polyethylene-CC/FA composite
FTIR spectrum polyethylene-CaCO3/fly ash composite
Absorbance polyethylene-CC/FA composite
. Thermal properties of modified polyethylene
Scan rate | Peak temperature |
---|---|
5 degree/min | 96.9˚C |
10 degree/min | 100.8˚C |
15 degree/min | 102.0˚C |
20 degree/min | 102.8˚C |
DSC scans polyethylene-CC/FA composite at different scanning rate
SEM polyethylene-CC/FA composite at different magnifications
The following findings can be summarized from the study;
1) Composite with 45/5 wt% FA/CC had the maximum flexural strength of 1.7995 MPa. The presence of 10 wt% FA and 40 wt% CC lead to over 100% decrease in flexural modulus but a higher percentage of FA led to increase in flexural modulus.
2) The peak energy at break (0.0651 J) is shown by the composite with 45 wt% FA and 5 wt% CC whereas the lowest energy (0.0288 J) is shown by neat polyethylene.
3) An increase of 7.27% HV over neat polyethylene is obtained in composites with 10 wt% FA and 40 wt% CC.
4) Optimum composition of composites for higher density is at 20 wt% FA and 30 wt% CC content.
The study on the effect of addition of calcium carbonate-fly ash hybrid filler on the mechanical, physical and chemical properties of LDPE has been done. Composites are found to possess higher melt flow index at higher amount of CC but lower melt flow index at higher amount of FA. Composite with 45 wt% and 5 wt% exhibits a typical triclinic polyethylene structure indicating that the composite is amorphous in nature. The hybrid of FA and CC fillers exhibits the synergetic effect on flexural strength and crystallinity of the composite. However, they show the parallel effect on energy at peak and micro-hardness.